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RESUB 1-BLD2024-1018+Stormwater Site Plan-Iron Vista+9.6.2024_1.40.07_PM+4485345IEC INSIGHT ENGINEERING CO. BLD2022-0926 STORMWATER SITE PLAN For Iron Vista Road Prepared for The City of Edmonds 121 5th Ave N Edmonds, WA 98020 425-771-0220 Project Site Location: 9500 190th St SW 19128, 19126, 19124, and 19122 94th Ave W Edmonds, WA 98020 Applicant: Landsverk Quality Homes, Inc. 24113 56th Ave W Mountlake Terrace, WA 98043 RESUB Apr 25 2024 CITY OF EDMONDS DEVELOPMENT SERVICES DEPARTMENT Contact: IECO P.O. Box 1478 Everett, WA 98206 425-303-9363 Tax Id: 00434600006102, 00434600006104, 00434600006105, 00434600006106 IECO Project: 20-1094 Certified Erosion and Sedimentation Control Lead: To be named by contractor Stormwater Site Plan Prepared By: Nicole Neufeld, E.I.T. Stormwater Site Plan Preparation Date: May 9, 2022 Revision Date: November 10, 2022 Approximate Construction Date: May 1, 2023 P.O. Box 1478 *Everett, WA 98206• P: 425.303.9363 info@insightengineering.net 0411212024 COMPLIES WITH APPLICABLE CITY STORMWATER CODE 05/12/2024 TABLE OF CONTENTS 1.0 Executive Summary................................................................................................................3 1.1 Minimum Requirements Summary ..............................................................................................7 2.0 Existing Conditions.................................................................................................................9 3.0 Offsite Analysis.....................................................................................................................15 3.1 Upstream Analysis.....................................................................................................................15 3.2 Downstream Analysis................................................................................................................15 4.0 Developed Conditions..........................................................................................................18 5.0 Site Hydraulic Analysis.........................................................................................................20 5.1 Existing Basin Summary............................................................................................................20 5.2 Developed Basin Summary........................................................................................................20 5.3 Water Quality.............................................................................................................................21 6.0 Performance Standards.......................................................................................................22 7.0 Appendix...............................................................................................................................23 Figures Figure1 - Vicinity Map.................................................................................................................6 Figure2 - Soil Map......................................................................................................................10 Figure 3 - Downstream Analysis Map 1....................................................................................16 Figure 4 - Downstream Analysis Map 2....................................................................................17 Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -1- Acronyms and Abbreviations BLA Boundary Line Adjustment BMP Best Management Practices DOE Department of Ecology ECDC Edmonds Community Development Code EDDS Engineering Design and Development Standards ESC Erosion and Sediment Control IECO Insight Engineering Company MR Minimum Requirement SWPPP Stormwater Pollution Prevention Plan SWMMWW Stormwater Management Manual for Western Washington TESC Temporary Erosion and Sediment Control WWHM Western Washington Hydrology Model Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -2- 1.0 Executive Summary The proposed project Iron Vista Road is located at 9500 190th St SW and 19128, 19126, 19124, and 19122 941h Ave W, Edmonds, Washington. More generally, the site is in Section 13, Township 27 North, and Range 3 East of the Willamette Meridian in Snohomish County, Washington. Please refer to the Vicinity Map attached later in the section. This project is subject to the City of Edmonds' 2022 requirements and the requirements defined in DOE's 2019 SWMMWW. The site area is 1.23 Acres. The site is currently undeveloped and exists as lawn with a few trees. The site contains one drainage basin that slopes steeply to the west. Please refer to the downstream analysis map for more details. The site is located within a landslide hazard area and has moderate to severe erosion potential, according to the City of Edmonds GIS. According to the Geotechnical evaluation, the slopes on -site do not meet the criteria of landslide hazard area and can be safely graded for development. The soils also display no evidence of instability or erosion. Please refer to the Geotech Addendum in Appendix C. Per NRCS survey of Snohomish County, the project site contains Alderwood soils that have a hydrologic classification of Type "C". Please refer to the soils map and descriptions attached later in this report for more details. The proposal is to construct a drive aisle from 94th Ave W with associated utility stubs to the future development on parcels 00434600006102, 00434600006104, 00434600006105, and 00434600006106. Access to the site will be provided from 94th Ave W. The total new hard surface area will be 21,965 SF. Per Figure 3.1, (Flow Chart for Determining Requirements for Development) from the 2022 Edmonds Stormwater Addendum, Minimum requirements #1 through 9 shall apply for this project. See section 1.1 for Minimum Requirements Summary included later in this report. Flow Control requirements will be met by a 97'x16'x8' detention vault located under the proposed drive aisle. The vault will provide a total detention capacity of 10,759 cf. The detention vault has been Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -3- sized to detain the runoff from the impervious area in parcel numbers 00434600006102, 00434600006104, 00434600006105, and 00434600006106. Please refer to section 5.0 Site Hydraulic Conditions for more information. Water quality requirements will be met by a Contech Stormfilter located downstream of the detention vault. Per ECDC 18.30.060.D.5.b.iii, Minimum Requirement #5: On -site Stormwater Management, the following roof BMPs must be considered in the following order: Full Dispersion, Full Infiltration, Bioretention, Downspout Dispersion Systems, Perforated Stub -out Connections, and Detention Vaults or Pipes. Dispersion, Infiltration, Bioretention, Downspout Dispersion, and Perforated Stub -out Connections are infeasible due to the presence of steep slopes all around the site. The future roof drains will be connected to the proposed detention vault via catch basins. Please refer to Appendix A for tables detailing BMP feasibility. Per ECDC 18.30.060.D.5.b.iii, Minimum Requirement #5: On -site Stormwater Management, the BMPs for other hard surfaces must be considered in the following order: Full Dispersion, Permeable Pavement, Bioretention, Sheet Flow Dispersion, and Detention Vaults or Pipes. Dispersion, Infiltration, Bioretention, Downspout Dispersion, and Perforated Stub -out Connections are infeasible due to the presence of steep slopes all around the site. Runoff from other hard surfaces will be directed to the proposed detention vault via catch basins. Please refer to Appendix A for tables detailing BMP feasibility. Post -Construction Soil Quality and Depth BMP T.5.13 is proposed to provide onsite stormwater management for the pervious areas of the site. Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -4- Flow Chart for Determining Requirements for Development. Does the project result in 2,000 square feet, or greater, of nc%ti• plus replaced hard surface area? OR Does the land disturbing activity total 7,000 square feet or greater? Yes No Minimum Requirements No. I through 5 apply I Minimum Requirement No. 2 applies Next Question Does the project add 5,000 square feet or more of new plus replaced hard surfaces? OR Convert 0.75 acres or more of vegetation to lawn or landscaped areas? OR Convert 2.5 acres or more of native vegetation to pasture? No Yes Is this a road related project? All Minimum Requirements apply to the new and replaced hard surfaces and converted vegetation areas_ All Minimum Requirements apply to the new hard surfaces and converted vegetation areas. Yes Insight Engineering Co. - Stormwater Site Plan No Yes Does the project add 5,000 square feet or No more of new hard surfaces? Yes Do new hard surfaces add 50°0 or more to the existing hard surfaces within the project limits? No No additional requirements. 2/3/2022 -5- FIGURE 1. VICINITY MAP • v Alf j7 'iY 5�%Oetl id R � t• ��, i rt 1 �y "Op INSIGHT ENGINEERING CO. P.O. Box 1478, Everett, WA 98206 425-303-9363 Info@insightengineering.net Taken from Google Maps Figure 1 -Vicinity Map Iron Vista Road Edmonds, Washington SCALE: DATE: 3/15/24 JOB#: 20-1094 NTS FILE NAME: BY: NAM 20-1094/doc/Stormwater Site Plan Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -6- 1.1 Minimum Requirements Summary MR : Minimum Requirement SWPPP : Stormwater Pollution Prevention Plan MR #1 Stormwater Site Plan Narrative: The Stormwater Site Plan preparation follows the City of Edmonds 2022 requirements and in accordance with DOE's 2019 SWMMWW. Refer to the executive summary within Section 1.0. MR #2 SWPPP Narrative: A SWPPP has been included in the Appendix A under Section 6. MR #3 Water Pollution Source Control for New Development: Please refer to Appendix G for the Source Control Plan. MR #4 Preservation of Natural Drainage Systems and Outfalls: The runoff from the site will flow into the onsite drainage system and will be connected to the existing drainage system along 190th Pl SW to continue its natural drainage pathway. MR #5 Onsite Stormwater Management: Per ECDC 18.30.060.D.5.b.iii, Minimum Requirement #5: On -site Stormwater Management, the following roof BMPs must be considered in the following order: Full Dispersion, Full Infiltration, Bioretention, Downspout Dispersion Systems, Perforated Stub -out Connections, and Detention Vaults or Pipes. Dispersion, Infiltration, Bioretention, Downspout Dispersion, and Perforated Stub -out Connections are infeasible due to the presence of steep slopes all around the site. The future roof drains will be connected to the proposed detention vault via catch basins. Please refer to Appendix A for tables detailing BMP feasibility. Per ECDC 18.30.060.D.5.b.iii, Minimum Requirement #5: On -site Stormwater Management, the BMPs for other hard surfaces must be considered in the following order: Full Dispersion, Permeable Pavement, Bioretention, Sheet Flow Dispersion, and Detention Vaults or Pipes. Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -7- Dispersion, Infiltration, Bioretention, Downspout Dispersion, and Perforated Stub -out Connections are infeasible due to the presence of steep slopes all around the site. Runoff from other hard surfaces will be directed to the proposed detention vault via catch basins. Please refer to Appendix A for tables detailing BMP feasibility. Post -Construction Soil Quality and Depth BMP T.5.13 is proposed to provide onsite stormwater management for the pervious areas of the site. The total pervious area of the site after development is 33,783 SF. No impervious reduction credits will be claimed for this project. MR #6 Runoff Treatment: MR #6 water quality will be met by a Contech Stormfilter located downstream of the detention pipe. Runoff from all proposed impervious areas will be filtered. Please refer to the water quality flow rates shown in the WWHM report. MR #7 Flow Control: Per Figure 3.1, (Flow Chart for Determining Requirements for Development) from the 2022 Edmonds Stormwater Addendum, Minimum requirements # 1 through 9 shall apply for this project. See section 1.1 for Minimum Requirements Summary included later in this report. Flow Control requirements will be met by a 97'xl6'x8' detention vault located under the proposed drive aisle. The vault will provide a total detention capacity of 10,759 cf. The detention vault has been sized to detain the runoff from the impervious area in parcel numbers 00434600006102, 00434600006104, 00434600006105, and 00434600006106. Please refer to section 5.0 Site Hydraulic Conditions for more information. Water quality requirements will be met by a Contech Stormfilter located downstream of the detention vault. MR #8 Wetlands protection: There are no wetlands present on site and the site will not discharge to a wetland area. MR #9 Operation and Maintenance: An Operation and Maintenance Manual will be provided with the construction submittal. Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -8- 2.0 Existing Conditions The proposed project Iron Vista Road is located at 9500 190th St SW and 19128, 19126, 19124, and 19122 941h Ave W, Edmonds, Washington. More generally, the site is in Section 13, Township 27 North, and Range 3 East of the Willamette Meridian in Snohomish County, Washington. Please refer to the Vicinity Map attached later in the section. This project is subject to the City of Edmonds' 2022 requirements and the requirements defined in DOE's 2019 SWMMWW. The site area is 1.23 Acres. The site is currently undeveloped and exists as lawn with a few trees. The site contains one drainage basin that slopes steeply to the west. Please refer to the downstream analysis map for more details. The site is located within a landslide hazard area and has moderate to severe erosion potential, according to the City of Edmonds GIS. According to the Geotechnical evaluation, the slopes on -site do not meet the criteria of landslide hazard area and can be safely graded for development. The soils also display no evidence of instability or erosion. Please refer to the Geotech Addendum in Appendix C. Per NRCS survey of Snohomish County, the project site contains Alderwood soils that have a hydrologic classification of Type "C". Please refer to the soils map and descriptions attached later in this report for more details. Insight Engineering Co. - Stormwater Site Plan 2/3/2022 r. FIGURE Z SOIL MAP SOILS LEGEND 4- Alderwood-Everett gravelly sandy loams, 25 to 70 percent slopes 6- Alderwood Urban Land Complex, 8 to 15 percent slopes Figure 2 - Soil Map ME Iron Vista Road Edmonds, Washington INSIGHT ENGINEERING CO. SCALE: DATE: 3/15/24 JOB#: 20-1094 NONE P.O. Box 1478, Everett, WA 98206 FILE NAME: 42 9363 20-1094/ doc/Stormwater Site Plan Info@insigMenghtengineering.net BY: NAM Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -10- Snohomish County Area, Washington 4—Alderwood-Everett gravelly sandy loams, 25 to 70 percent slopes Map Unit Setting • National map unit symbol: 2hyy • Elevation: 50 to 800 feet • Mean annual precipitation: 25 to 60 inches • Mean annual air temperature: 48 to 52 degrees F • Frost -free period: 180 to 220 days • Farmland classification: Not prime farmland Map Unit Composition • Alderwood and similar soils: 60 percent • Everett and similar soils: 25 percent • Minor components: 15 percent • Estimates are based on observations, descriptions, and transects of the mapunit. Description of Alderwood Setti na • Landform: Till plains • Parent material: Basal till Typical profile • H1 - 0 to 7 inches: gravelly ashy sandy loam • H2 - 7 to 35 inches: very gravelly ashy sandy loam • H3 - 35 to 60 inches: gravelly sandy loam Properties and qualities • Slope: 25 to 70 percent • Depth to restrictive feature: 20 to 40 inches to densic material • Drainage class: Moderately well drained • Capacity of the most limiting layer to transmit water (Ksat): Very low to moderately low (0.00 to 0.06 in/hr) • Depth to water table: About 18 to 36 inches • Frequency of flooding: None • Frequency of ponding: None • Available water supply, 0 to 60 inches: Low (about 3.0 inches) Interpretive Groups • Land capability classification (irrigated): None specified • Land capability classification (nonirrigated): 7e • Hydrologic Soil Group: B • Ecological site: F002XA004WA - Puget Lowlands Forest • Hydric soil rating: No Description of Everett Setting • Landform: Plains, terraces • Parent material: Glacial outwash Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -11- Typical profile • HI - 0 to 6 inches: gravelly ashy sandy loam • H2 - 6 to 18 inches: very gravelly ashy sandy loam • H3 - 18 to 60 inches: extremely gravelly sand Properties and qualities • Slope: 25 to 70 percent • Depth to restrictive feature: 14 to 20 inches to strongly contrasting textural stratification • Drainage class: Somewhat excessively drained • Capacity of the most limiting layer to transmit water (Ksat): High (1.98 to 5.95 in/hr) • Depth to water table: More than 80 inches • Frequency of flooding: None • Frequency of ponding: None • Available water supply, 0 to 60 inches: Very low (about 2.1 inches) Interpretive groups • Land capability classification (irrigated): None specified • Land capability classification (nonirrigated): 7e • Hydrologic Soil Group: A • Ecological site: F002XA004WA - Puget Lowlands Forest • Hydric soil rating: No Minor Components Mckenna • Percent of map unit: 5 percent • Landform: Depressions • Other vegetative classification: Wet Soils (G002XN102WA) • Hydric soil rating: Yes Norma, undrained • Percent of map unit: 5 percent • Landform: Depressions • Other vegetative classification: Wet Soils (G002XN102WA) • Hydric soil rating: Yes Terric medisaprists, undrained • Percent of map unit: 5 percent • Landform: Depressions • Other vegetative classification: Wet Soils (G002XN102WA) • Hydric soil rating: Yes Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -12- Snohomish County Area, Washington 6—Alderwood-Urban land complex, 8 to 15 percent slopes Map Unit Setting • National map unit symbol: 2hzn • Elevation: 50 to 800 feet • Mean annual precipitation: 25 to 60 inches • Mean annual air temperature: 48 to 52 degrees F • Frost -free period: 180 to 220 days • Farmland classification: Not prime farmland Map Unit Composition • Alderwood and similar soils: 60 percent • Urban land: 25 percent • Minor components: 5 percent • Estimates are based on observations, descriptions, and transects of the mapunit. Description of Alderwood Setti na • Landform: Till plains • Parent material: Basal till Typical profile • H1 - 0 to 7 inches: gravelly ashy sandy loam • H2 - 7 to 35 inches: very gravelly ashy sandy loam • H3 - 35 to 60 inches: gravelly sandy loam Properties and qualities • Slope: 8 to 15 percent • Depth to restrictive feature: 20 to 40 inches to densic material • Drainage class: Moderately well drained • Capacity of the most limiting layer to transmit water (Ksat): Very low to moderately low (0.00 to 0.06 in/hr) • Depth to water table: About 18 to 36 inches • Frequency of flooding: None • Frequency of ponding: None • Available water supply, 0 to 60 inches: Low (about 3.0 inches) Interpretive Groups • Land capability classification (irrigated): None specified • Land capability classification (nonirrigated): 4s • Hydrologic Soil Group: B • Ecological site: F002XA004WA - Puget Lowlands Forest • Forage suitability group: Limited Depth Soils (G002XN302WA) • Other vegetative classification: Limited Depth Soils (G002XN302WA) • Hydric soil rating: No Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -13- Minor Components Norma, undrained • Percent of map unit: 5 percent • Landform: Drainageways • Other vegetative classification: Wet Soils (G002XN102WA) • Hydric soil rating: Yes Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -14- 3.0 Offsite Analysis A site reconnaissance was performed by Brian Kalab of Insight Engineering on January 21, 2021 to verify the downstream flow paths and observe any drainage problems downstream of the site. The sky was cloudy with a temperature of 48 degrees. The site area is 1.23 Acres. The site is currently undeveloped and exists as lawn with a few trees. The site contains one drainage basin that slopes steeply to the west. The site is located within a landslide hazard area and has moderate to severe erosion potential, according to the City of Edmonds GIS. According to the Geotechnical evaluation, the slopes on -site do not meet the criteria of landslide hazard area and can be safely graded for development. The soils also display no evidence of instability or erosion. Please refer to the Geotech Addendum in Appendix C. 3.1 Upstream Analysis Based on the site reconnaissance and the topographic survey of the site, the upstream flows appear to be minimal. 3.2 Downstream Analysis There is one drainage basin on site that slopes steeply to the west. The runoff sheet flows west for about 325 ft before entering the existing drainage system along Olympic View Drive. The runoff then heads north for about 170 ft through a series of 12" concrete pipe before turning west along Cherry St. It flows for about 1,200 ft through a series of 24" concrete pipe before turning northeast along Soundview PI for about 500 ft before entering Fruitdale Creek. The creek meanders northwest for about 470 ft before entering the Puget Sound. This is where the downstream analysis was concluded. There did not appear to be any restrictions or erosional problems downstream of the site. In the mitigated state, the runoff will drain into the proposed onsite drainage system and will be connected to the existing drainage system along 190th PI SW. The flows will then head west for about 300 ft before joining with the natural drainage pathway on Olympic View Drive. Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -15- FIGURE 3. DOWNSTREAM ANALYSIS MAP 1 v m3rc) INSIGHT ENGINEERING CO P.O. Box 1478, Everett, WA 98206 425-303-9363 Info@insightengineering.net Map taken from City of Edmonds GIs Figure 3 - Downstream Analysis Map Iron Vista Lot A Edmonds, Washington SCALE: DATE: 3/15/24 JOB #: 20-1094 NONE FILE NAME: BY: NAM 20-1094/doc/Stormwater Site Plan Insight Engineering Co. - Stormwater Site Plan 2/3/2022 9200 -16- FIGURE 4. DOWNSTREAM ANALYSIS MAP 2 Puget Sound m3rc) INSIGHT ENGINEERING CO P.O. Box 1478, Everett, WA 98206 425-303-9363 Info@insightengineering.net Map taken from City of Edmonds GIs Figure 4 - Downstream Analysis Map Iron Vista Lot A Edmonds, Washington ISC DATE: 3/15/24 JOB #: 20-1094 NONE I I I I FILE NAME: BY: NAM 20-1094/doc/Stormwater Site Plan Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -17- 4.0 Developed Conditions The proposed project Iron Vista Road is located at 9500 190th St SW and 19128, 19126, 19124, and 19122 94th Ave W, Edmonds, Washington. More generally, the site is in Section 13, Township 27 North, and Range 3 East of the Willamette Meridian in Snohomish County, Washington. The proposal is to construct a drive aisle from 94th Ave W with associated utility stubs to the future development on parcels 00434600006102, 00434600006104, 00434600006105, and 00434600006106. Access to the site will be provided from 94th Ave W. The total new hard surface area will be 21,965 SF. Per Figure 3.1, (Flow Chart for Determining Requirements for Development) from the 2022 Edmonds Stormwater Addendum, Minimum requirements #1 through 9 shall apply for this project. See section 1.1 for Minimum Requirements Summary included later in this report. Flow Control requirements will be met by a 97'xl6'x8' detention vault located under the proposed drive aisle. The vault will provide a total detention capacity of 10,759 cf. The detention vault has been sized to detain the runoff from the impervious area in parcel numbers 00434600006102, 00434600006104, 00434600006105, and 00434600006106. Please refer to section 5.0 Site Hydraulic Conditions for more information. Water quality requirements will be met by a Contech Stormfilter located downstream of the detention vault. Per ECDC 18.30.060.D.5.b.iii, Minimum Requirement #5: On -site Stormwater Management, the following roof BMPs must be considered in the following order: Full Dispersion, Full Infiltration, Bioretention, Downspout Dispersion Systems, Perforated Stub -out Connections, and Detention Vaults or Pipes. Dispersion, Infiltration, Bioretention, Downspout Dispersion, and Perforated Stub -out Connections are infeasible due to the presence of steep slopes all around the site. The future roof drains will be connected to the proposed detention vault via catch basins. Please refer to Appendix A for tables detailing BMP feasibility. Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -18- Per ECDC 18.30.060.D.5.b.iii, Minimum Requirement #5: On -site Stormwater Management, the BMPs for other hard surfaces must be considered in the following order: Full Dispersion, Permeable Pavement, Bioretention, Sheet Flow Dispersion, and Detention Vaults or Pipes. Dispersion, Infiltration, Bioretention, Downspout Dispersion, and Perforated Stub -out Connections are infeasible due to the presence of steep slopes all around the site. Runoff from other hard surfaces will be directed to the proposed detention vault via catch basins. Please refer to Appendix A for tables detailing BMP feasibility. Post -Construction Soil Quality and Depth BMP T.5.13 is proposed to provide onsite stormwater management for the pervious areas of the site. Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -19- 5.0 Site Hydraulic Conditions Per NRCS survey of Snohomish County, the project site contains Alderwood soils that have a hydrologic classification of Type "C". A ROW and clearing/grading permit will be required for the RS-12 zoned project. Site Area = 1.23 Acres (53,749 SF) Study Area = 1.23 Acres (53,749 SF) 5.1 Existing Basin Summary Site Area = 1.23 Acres Study Area =1.23 Acres There is no existing impervious area in the existing basin. There is no existing unmanaged hard surface area that will remain after project completion. The entire existing basin was modeled as forested area. 5.2 Developed Basin Summary Site Area = 1.23 Acres Study Area =1.23 Acres Impervious: Roof* Driveway* Sidewalk/patio*** Road**** Total Impervious = 0.27 Acres (11,820 SF) = 0.06 Acres ( 2,575 SF) = 0.04 Acres ( 1,906 SF) = 0.13 Acres ( 5.664 SF) Pervious Area = 1.23 Acres — 0.50 Acres = 0.73 Acres 0.50 Acres (21,965 SF) *The roof area includes 2,921 SF from Lot A, 2,933 SF from Lot B, 2,966 SF from Lot C and 3, 000 SF from Lot D. * *The driveway area includes 684 SF from Lot A, 690 SF from Lot B, 451 SF from Lot C, and 750 SF from Lot D. ***The sidewalk/patio area includes 569 SF from Lot A, 540 SF from Lot B, 597 SF from Lot C, and 200 SF from Lot D. ****The existing driveway area (1,400 SF) to 19210 and 19204 94`h Ave W will remain. This area of this driveway has been included in the sizing calculations in the event that the driveway must be repaved. The entire site will be cleared for the proposed project. 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B I � i ✓ / � � 5 20200�0176 C PROPERTY TINE AND 6 FlNLY ENCONPASSm B/ AFN-20200B201 JB I L0T I L. !!! lll... E. .. .. � FOW1D CASED IN CONa DDWN a9'. 1 I\ I I :• r� O 0.75W I O.TSN OF PRQIECIFD SOU1x LNE m LOT 82 SFANflI' /RAGS PFR SUMEY AFN 100811065002(RS) ! ( PoN:TO8.Q1 E. 1(A1.86 I Y 12 g { I ` • / '/ .• y Z0f6O800WP(Rf). NSllm 20. POSRION M A 2-2T- sO1RX LIfE L0182 SFA44W iRIC15 FOUND & a W/8lE0RbE CAP O.Y(W) 0.1'(S) OF CNiNER. 33 FENCE WR. 0.3•(N) ! I r------- ------- -- ------ T a4'm of carMx_ 1 N 89',su� N 84,1'2S• W W..81'(NX w 850.00' I) 84890 R) 81515 OF BFAl6NC I A9'1 00 1 / 5 I I I i��.A FOUND REHA4 W CAP STAWED� I 1r11 A f fo B11llm a at END EENa 0.05' gz9e9' af'(s) ! as(Wj m �PRmFR1Y I 1810E HER, AW W SS LdVE� i'M0 P I ASEMEfJ( � I J10-7EI I 19120 941x AW W 3 C fec Is• �HWI/ 0043460mlo1 IX F �.OQL2•(� I � p• F I ra1RRr REHNE w/cw FOUND -22 W/i 518D ✓ siAMMD R286B' 0.1'(A� BTAxPFD `12989' az'(x) E 12• CPP(x)=26 W LOrmE)D PROW m FM REFEMM W 12• CW(W)-262.J6 l �. N 00/BBW/GDaN N/AS-/E�.15 g• C i LIE AM p1Y UII116 (iWJ / ��D.Y4 \ I 11 9 C ') I I MG 2 E 12 CP26J.B4 ,2' L EP(S)=18A09 m I t� \ =LIE 10 l 8 7 F �lHOKM VM W OORIEI9 SCALE: 1'1 = 50' J .• .. A-81 1 _ �, S � ' �� '' %`•:ic r t�Ea.R C l Myra r�wB r� PoM.156.28\ \ \ ACCESS EISENENT 1 BN' 0.2'(I 39MM LIE (IIP.J O 2 ` C /, E. 10.28 OF A,k-191 I J JV ER EASED CON& NON. w/r 0. DISN e x DBBN O.a'. M,D FDR WMl? , NBI,FI♦ 2 2J Nl. N BY,B13 W .. DEVELOPED O * 19� a B;IiFR LE�•% EIY MY=T6J.IJ * AFN-1928BB2 -• I (!0 fANNTNN CONNMUS e192f0 E iACN LEAD A&CESS i0 W,92,D l,MT\M) a s�1 W/tY0.5MR BTANPED BASIN MAP 19210 84 AVE W ?2gW' 0.2'(N) mCdNFA) N-n . IE e• V(SE) UD(sI IE B' PW(N) IE B' PK;(N}-28f.M JB 1 y 5.3 Water Quality A Contech Stormfilter is proposed downstream of detention to provide basic water quality treatment. The filter has been sized according to a water quality flow rate of 0.014 cfs. Please see the following page for the sizing letter from Contech. Per item 104 on the City of Edmonds Checklist #2, the summation of volumes and the volume treated by the treatment system must meet or exceed at least 91 % of the total stormwater runoff profile. All of the proposed runoff from the site will be collected via the detention system and will be directed to the Stormfilter. Items 105-107 are addressed in the Conveyance Analysis in Appendix H. Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -21- C=:: NTECK ENGINEERED SOLUTIONS Prepared by Stephanie Jacobsen on October 23, 2023 Size and Cost Estimate Iron Vista — Stormwater Treatment System Edmonds, WA Information provided: • Water quality flow, Qwq = 0.014 cfs • Peak hydraulic flow rate, Qpeak = 0.11 CfS • Presiding agency = City of Edmonds, WA Assumptions: • Media = ZPG cartridges • Cartridge flow rate = 7.5 gpm • Drop required from inlet to outlet = 2.3' minimum Size and cost estimates: The StormFilter is a flow -based system and is therefore sized by calculating the peak water quality flow rate associated with the design storm. The water quality flow rate provided to Contech Engineered Solutions LLC for the purposes of developing this estimate. The StormFilter for this site was sized based on a water quality flow rate of 0.014 cfs. To accommodate this flow rate, Contech Engineered Solutions recommends using a 48" StormFilter manhole with 1 cartridge (see attached detail). The estimated cost of this system is $15,800, complete and delivered to the job site. This estimate assumes that the vault is 15 feet deep. The final system cost will depend on the actual depth of the units and whether extras like doors rather than castings are specified. The contractor is responsible for setting the 48" StormFilter Manhole and all external plumbing. Typically, the precast StormFilters have internal bypass capacities of 1 cfs. If the peak discharge off the site is expected to exceed this rate, we recommend placing a high -flow bypass upstream of the StormFilter system. Contech Engineered Solutions could provide our high -flow bypass, the StormGate, which provides a combination weir -orifice control structure to limit the flow to the StormFilter. The estimated cost of this structure is $4,000. The final cost would depend on the actual depth and size of the unit. Stephanie Jacobsen, P.E. Sr. Design Engineer- Stormwater I Team Lead SW Washington Stormwater Consultant Contech Engineered Solutions ©2012 Contech Engineered Solutions LLC 11835 NE Glenn Widing Dr., Portland OR 97220 www.conteches.com Toll-free:800.548.4667 Fax:800.561.1271 Page 1 of 1 TS-P027 6.0 Performance Standards Flow Control requirements will be met by a 97'x16'x8' detention vault located under the proposed drive aisle. The pipe will provide a total detention capacity of 10,759 cf. The detention pipe has been sized to detain the runoff from the impervious area in parcel numbers 00434600006102, 00434600006104, 00434600006105, and 00434600006106. The outlet structure from the detention system consists of a 12" riser pipe with a 0.5" wide bottom orifice, a 0.5" orifice at 241.84 elevation, and a 1" orifice at 245.61 elevation. The inlet and outlet elevation of the outlet structure is 238.61, giving the vault 0.5' of sediment storage. Please see the WWHM Report located in Appendix E for more details. Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -22- 7.0 Appendix A. Minimum Requirement #5 BMP Feasibility B. Stormwater Pollution Prevention Plan C. Geotech Report D. Operation & Maintenance Manual E. WWHM Report F. Project Site Map G. Source Control Plan H. Conveyance Analysis Insight Engineering Co. - Stormwater Site Plan 2/3/2022 - 23 - A. MINIMUM REQUIREMENT #5 BMP FEASIBILITY Roof BMPs Per ECDC 18.30.060.D.5.e Minimum Requirement #5 BMP Feasibility BMP Feasibility Conditions T5.30 Full Dispersion Infeasible Full Dispersion is infeasible because of the steep slopes present on the site. T5. I OA Downspout Infeasible Downspout Full Infiltration is infeasible because Full Infiltration of the steep slopes present on the site. Bioretention Infeasible Bioretention is infeasible because of the presence of steep slopes on the site. T5.1 OB Downspout Infeasible Downspout Dispersion is infeasible because of Dispersion the steep slopes present on the site. T5.1OC Perforated Infeasible Perforated Stub -out Connections are infeasible Stub -out Connections because of the steep slopes present on the site. Detention Vault or Pipe Feasible Other Hard Surface BMPs Per ECDC 18.30.060.D.5.e Minimum Requirement #5 BMP Feasibility BMP Feasibility Conditions T5.30 Full Dispersion Infeasible Full Dispersion is infeasible because of the steep slopes present on the site. T5.15 Permeable Infeasible Permeable Pavement is infeasible because of the Pavement steep slopes present on the site. Bioretention Infeasible Bioretention is infeasible because of the presence of steep slopes on the site. T5.12 Sheet Flow Infeasible Sheet Flow Dispersion and Concentrated Flow Dispersion or T5.13 Dispersion are infeasible because of the steep Concentrated Flow slopes present on the site. Dispersion Detention Vault or Pipe Feasible Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -24- B. STORMWATER POLLUTION PREVENTION PLAN Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -25- Construction Stormwater General Permit (CSWGP) Stormwater Pollution Prevention Plan (SWPPP) for Iron Vista Prepared for: The Washington State Department of Ecology Northwest Regional Office 3190 —160' Avenue SE Bellevue, WA 98008 Permittee / Owner Developer Operator / Contractor Landsverk Quality Homes, LLC TBD TBD 24113 56t" Ave W Moutnlake Terrace, WA 98043 9500 190" St SW 19128, 19126, 19124, and 19122 94th Ave W Edmonds, WA 98020 Certified Erosion and Sediment Control Lead (CESCL) Name Organization Contact Phone Number Brian Kalab, RE Insight Engineering 425-303-9363 SWPPP Prepared By Name Organization Contact Phone Number Nicole Neufeld, E.13 Insight Engineering 425-303-9363 SWPPP Preparation Date November 11, 2022 Project Construction Dates Activity / Phase Start Date End Date Construction MM / DD / YYYY MM / DD / YYYY Table of Contents 1 Project Information.................................................................................................................. 5 1.1 Existing Conditions.......................................................................................................... 5 1.2 Proposed Construction Activities..................................................................................... 6 2 Construction Stormwater Best Management Practices(BMPs).............................................. 7 2.1 The 13 Elements............................................................................................................... 7 2.1.1 Element 1: Preserve Vegetation / Mark Clearing Limits .......................................... 7 2.1.2 Element 2: Establish Construction Access............................................................... 8 2.1.3 Element 3: Control Flow Rates................................................................................. 9 2.1.4 Element 4: Install Sediment Controls..................................................................... 10 2.1.5 Element 5: Stabilize Soils....................................................................................... 11 2.1.6 Element 6: Protect Slopes....................................................................................... 14 2.1.7 Element 7: Protect Drain Inlets............................................................................... 15 2.1.8 Element 8: Stabilize Channels and Outlets............................................................. 16 2.1.9 Element 9: Control Pollutants................................................................................. 17 2.1.10 Element 10: Control Dewatering............................................................................ 21 2.1.11 Element 11: Maintain BMPs................................................................................... 22 2.1.12 Element 12: Manage the Project............................................................................. 23 2.1.13 Element 13: Protect Low Impact Development (LID) BMPs................................ 25 3 Pollution Prevention Team.................................................................................................... 26 4 Monitoring and Sampling Requirements............................................................................... 27 4.1 Site Inspection................................................................................................................ 33 4.2 Stormwater Quality Sampling........................................................................................ 33 4.2.1 Turbidity Sampling................................................................................................. 33 4.2.2 pH Sampling........................................................................................................... 35 5 Discharges to 303(d) or Total Maximum Daily Load (TMDL) Waterbodies ....................... 36 5.1 303(d) Listed Waterbodies............................................................................................. 36 5.2 TMDL Waterbodies....................................................................................................... 36 6 Reporting and Record Keeping............................................................................................. 38 6.1 Record Keeping.............................................................................................................. 38 6.1.1 Site Log Book......................................................................................................... 38 6.1.2 Records Retention................................................................................................... 38 6.1.3 Updating the SWPPP.............................................................................................. 38 6.2 Reporting........................................................................................................................39 6.2.1 Discharge Monitoring Reports................................................................................ 39 6.2.2 Notification of Noncompliance............................................................................... 39 List of Tables Table 1 — Summary of Site Pollutant Constituents......................................................................... 6 Table2 — Pollutants...................................................................................................................... 17 Table 3 — pH -Modifying Sources................................................................................................. 19 Table4 — Dewatering BMPs......................................................................................................... 21 Table5 — Management.................................................................................................................. 23 Table 6 — BMP Implementation Schedule.................................................................................... 24 Table 7 — Team Information......................................................................................................... 26 Table 8 — Turbidity Sampling Method.......................................................................................... 27 Table 9 — pH Sampling Method.................................................................................................... 29 List of Appendices Appendix/Glossary A. Site Map B. BMP Detail C. Correspondence D. Site Inspection Form E. Construction Stormwater General Permit (CSWGP) F. 303(d) List Waterbodies / TMDL Waterbodies Information G. Contaminated Site Information H. Engineering Calculations List of Acronyms and Abbreviations Acronym / Abbreviation Explanation 303(d) Section of the Clean Water Act pertaining to Impaired Waterbodies BFO Bellingham Field Office of the Department of Ecology BMP(s) Best Management Practice(s) CESCL Certified Erosion and Sediment Control Lead CO2 Carbon Dioxide CRO Central Regional Office of the Department of Ecology CSWGP Construction Stormwater General Permit CWA Clean Water Act DMR Discharge Monitoring Report DO Dissolved Oxygen Ecology Washington State Department of Ecology EPA United States Environmental Protection Agency ERO Eastern Regional Office of the Department of Ecology ERTS Environmental Report Tracking System ESC Erosion and Sediment Control GUILD General Use Level Designation NPDES National Pollutant Discharge Elimination System NTU Nephelometric Turbidity Units NWRO Northwest Regional Office of the Department of Ecology pH Power of Hydrogen RCW Revised Code of Washington SPCC Spill Prevention, Control, and Countermeasure sU Standard Units SWMMEW Stormwater Management Manual for Eastern Washington SWMMWW Stormwater Management Manual for Western Washington SWPPP Stormwater Pollution Prevention Plan TESC Temporary Erosion and Sediment Control SWRO Southwest Regional Office of the Department of Ecology TMDL Total Maximum Daily Load VFO Vancouver Field Office of the Department of Ecology WAC Washington Administrative Code WSDOT Washington Department of Transportation WWHM Western Washington Hydrology Model Project Information (1.0) Project/Site Name: Iron Vista Street/Location: 9500 190th St SW and 19128, 19126, 19124, and 19122 94th Ave W City: Edmonds State: WA Zip code: 98020 Subdivision: Receiving waterbody: Puget Sound Existing Conditions (1.1) Total acreage (including support activities such as off -site equipment staging yards, material storage areas, borrow areas). Total acreage: 1.23 Disturbed acreage: 1.23 Existing structures: 0 Landscape topography: 1.23 Drainage patterns: Sheet Flow Existing Vegetation: Native vegetation Critical Areas (wetlands, streams, high erosion risk, steep or difficult to stabilize slopes): Steep slopes, Landslide and erosion hazard List of known impairments for 303(d) listed or Total Maximum Daily Load (TMDL) for the receiving waterbody: Puget Sound Table 1 includes a list of suspected and/or known contaminants associated with the construction activity. Table 1 — Summary of Site Pollutant Constituents Constituent (Pollutant) Location Depth Concentration Bacteria -Fecal Coliform 303D-KSLU03 17.9 col/100 mL Bacterial-Enterococci WA614011 12.7 col/100 mL Proposed Construction Activities (1.2) Description of site development: The proposal is to construct a drive aisle from 94th Ave W with associated utility stubs to the future development on parcels 00434600006102, 00434600006104, 00434600006105, and 00434600006106. Access to the site will be provided from 94th Ave W. The total new hard surface area will be 21,965 SF. Description of construction activities (example: site preparation, demolition, excavation): The entire site will be cleared in preparation of site construction. TESC BMPs will be installed according to the approved construction plans and this SWPPP document. Description of site drainage including flow from and onto adjacent properties. Must be consistent with Site Map in Appendix A: Runoff from the site sheet flows to the west. Upstream flows entering the site come from the properties at 19110 and 19120 941h Ave W. Description of final stabilization (example: extent of revegetation, paving, landscaping): A total of 0.50 acres of the site will be hard surface area after development. Please refer to Section 5.0 of the drainage report for more details. The remaining 0.73 acres of the site to remain as pervious area will be revegetated as lawn area and will be amended per BMP T5.13 Post -construction Soil Quality and Depth. Contaminated Site Information: Proposed activities regarding contaminated soils or groundwater (example: on -site treatment system, authorized sanitary sewer discharge): A Contech Stormfilter is proposed downstream of the detention vault. Construction Stormwater Best Management Practices (BMPs) (2.0) The SWPPP is a living document reflecting current conditions and changes throughout the life of the project. These changes may be informal (i.e. hand-written notes and deletions). Update the SWPPP when the CESCL has noted a deficiency in BMPs or deviation from original design. The 12 Elements (2.1) Element 1: Preserve Vegetation / Mark Clearing Limits (2.1.1) To protect adjacent properties and to reduce the area of soil exposed to construction, the limits of construction will be clearly marked with high-vis fencing before land -disturbing activities begin. Trees that are to be preserved, as well as all sensitive areas and their buffers, shall be clearly delineated, both in the field and on the plans. In general, natural vegetation and native topsoil shall be retained in an undisturbed state to the maximum extent possible. A protective barrier shall be placed around the protected trees prior to land preparation or construction activities, and shall remain in place until all construction activity is terminated. No equipment, chemicals, soil deposits or construction materials shall be placed within the protective barriers. Any landscaping activities subsequent to the removal of the barriers shall be accomplished with light machinery or hand labor. List and describe BMPs: BMP C101 — Preserving Natural Vegetation BMP C103 — High -Visibility Fence Installation Schedules: Install orange barrier fencing along the clearing limits, according to the approved construction plans, prior to any construction activities. Maintain until all construction activities are completed. Inspection and Maintenance plan: Site inspections will be conducted at least once a week and within 24 hours following any rainfall event which causes a discharge of stormwater from the site. For sites with temporary stabilization measures, the site inspection frequency can be reduced to once every month. Responsible Staff: Permittee shall take immediate action(s) to: stop, contain, and clean up the unauthorized discharges, or otherwise stop the noncompliance; correct the problem(s); implement appropriate Best Management Practices (BMPs), and/or conduct maintenance of existing BMPs; and achieve compliance with all applicable standards and permit conditions. In addition, if the noncompliance causes a threat to human health or the environment, the Permittee shall comply with the Noncompliance Notification requirements in Special Condition S5.F of the permit. Element 2: Establish Construction Access (2.1.2) Construction access or activities occurring on unpaved areas shall be minimized, yet where necessary, access points shall be stabilized to minimize the tracking of sediment onto public roads, street sweeping, and street cleaning shall be employed to prevent sediment from entering state waters. List and describe BMPs: BMP C105 — Stabilized Construction Entrance Installation Schedules: Install the temporary construction entrance, according to the approved construction plans, prior to any clearing or grading activities. Inspection and Maintenance plan: Maintain until access road is constructed. Responsible Staff: Contractor Element 3: Control Flow Rates (2.1.3) In order to protect the properties and waterways downstream of the project site, stormwater discharges from the site will be controlled. In general, discharge rates of stormwater from the site will be controlled where increases in impervious area or soil compaction during construction could lead to downstream erosion, or where necessary to meet local agency stormwater discharge requirements. Wattles will be used perpendicular to the slope runoff direction on site to intercept stormwater runoff. Detention facilities will be constructed as one of the first steps in grading and will be fully functioning prior to construction of site improvements. Will you construct stormwater retention and/or detention facilities? Yes No Will you use permanent infiltration ponds or other low impact development (example: rain gardens, bio-retention, porous pavement) to control flow during construction? Yes No List and describe BMPs: BMP C235 — Wattles Installation Schedules: Install wattles according to the approved construction plans, prior to any clearing or grading activites. Inspection and Maintenance plan: Inspect after significant storms and repair any areas where wattles are not in contact with soil. Responsible Staff: Contractor. Element 4: Install Sediment Controls (2.1.4) Whenever possible, sediment laden water shall be discharged into onsite, relatively level, vegetated areas (BMP C240 paragraph 5, page 4-102). In some cases, sediment discharge in concentrated runoff can be controlled using permanent stormwater BMPs (e.g., infiltration swales, ponds, trenches). Sediment loads can limit the effectiveness of some permanent stormwater BMPs, such as those used for infiltration or bio- filtration; however, those BMPs designed to remove solids by settling (wet ponds or detention ponds) can be used during the construction phase. When permanent stormwater BMPs will be used to control sediment discharge during construction, the structure will be protected from excessive sedimentation with adequate erosion and sediment control BMPs. Any accumulated sediment shall be removed after construction is complete and the permanent stormwater BMP will be re -stabilized with vegetation per applicable design requirements once the remainder of the site has been stabilized. The following BMP will be implemented as end -of -pipe sediment controls as required to meet permitted turbidity limits in the site discharge(s). Prior to the implementation of these technologies, sediment sources and erosion control and soil stabilization BMP efforts will be maximized to reduce the need for end -of -pipe sedimentation controls. In addition, sediment will be removed from paved areas in and adjacent to construction work areas manually or using mechanical sweepers, as needed, to minimize tracking of sediments on vehicle tires away from the site and to minimize wash -off of sediments from adjacent streets in runoff. List and describe BMPs: BMP C233 — Silt Fence BMP C220 — Storm Drain Inlet Protection Installation Schedules: Install silt fencing, according to the approved plans, prior to any clearing or grading activities. Install catch basin filters, according to the approved construction plans, as catch basins are installed and become operable. Inspection and Maintenance plan: Repair any damage to silt fence immediately. Check uphill side of fence for clogging and channelization of flows. Replace the fence and remove trapped sediment in the event of channelization. Remove sediment deposits when it reaches 1/3 the height of the silt fence. Replace any fecing that has deteriorated due to ultraviolet breakdown. Inspect inlet protection after storm events. Clean and replace clogged filters. Maintain silt fence and inlet protection until all construction activities are completed. Responsible Staff: Contractor Element 5: Stabilize Soils (2.1.5) The project site is located west of the Cascade Mountain Crest. As such, no soils shall remain exposed and unworked for more than 7 days during the dry season (May 1 to September 30) and 2 days during the wet season (October 1 to April 30). Regardless of the time of year, all soils shall be stabilized at the end of the shift before a holiday or weekend if needed based on weather forecasts. In general, cut and fill slopes will be stabilized as soon as possible and soil stockpiles will be temporarily covered with plastic sheeting. All stockpiled soils shall be stabilized from erosion, protected with sediment trapping measures, and where possible, be located away from storm drain inlets, waterways, and drainage channels. Disturbance to steep slopes will be minimized by temporary and permanent seeding as well as mulching. Soil compaction on site will be minimized by limiting equipment access to the proposed road areas as much as possible. West of the Cascade Mountains Crest Season Dates Number of Days Soils Can be Left Exposed During the Dry Season May 1 — September 30 7 days During the Wet Season October 1 — April 30 2 days Soils must be stabilized at the end of the shift before a holiday or weekend if needed based on the weather forecast. Anticipated project dates: Start date: May 1, 2023 End date: April 1, 2024 Will you construct during the wet season? Yes No List and describe BMPs: BMP C120 — Temporary and Permanent Seeding BMP C121 — Mulching BMP C123 — Plastic Covering Installation Schedules: Seed and mulch all disturbed areas that are not vegetated at final site stabilization. Apply mulch until the ground is at least 95% covered. Mulch thickness should be increased is steep areas. Plastic covering should not be installed perpendicular to the slope. Provide a minimum of an 8" overlap at the seams of plastic covering. Inspection and Maintenance plan: Reseed any areas that do not establish at least 75% cover. Any areas that experience erosion should be re -mulched and/or protected with a net or blanket. Nets/blankets should maintain contact with the ground otherwise erosion will occur. Remove and replace torn plastic or plastic that has been broken down due to ultraviolet radiation. Responsible Staff: Contractor Element 6: Protect Slopes (2.1.6) All cut and fill slopes will be designed, constructed, and protected in a manner that minimizes erosion. Slopes will be graded to a maximum slope of 2:1 and will be protected with nets and blankets as well as plastic covering. Once the final grade is done, slopes will be protected with mulching and seeding. Will steep slopes be present at the site during construction? Yes No List and describe BMPs: BMP C120 — Temporary and Permanent Seeding BMP C121 — Mulching BMP C122 — Nets and Blankets BMP C123 — Plastic Covering Installation Schedules: Seed and mulch all disturbed areas that are not vegetated at final site stabilization. Apply mulch until the ground is at least 95% covered. Mulch thickness should be increased is steep areas. Plastic covering should not be installed perpendicular to the slope. Provide a minimum of an 8" overlap at the seams of plastic covering. Inspection and Maintenance plan: Reseed any areas that do not establish at least 75% cover. Any areas that experience erosion should be re -mulched and/or protected with a net or blanket. Nets/blankets should maintain contact with the ground otherwise erosion will occur. Remove and replace torn plastic or plastic that has been broken down due to ultraviolet radiation. Responsible Staff: Contractor Element 7: Protect Drain Inlets (2.1.7) All storm drain inlets and culverts made operable during construction shall be protected to prevent unfiltered or untreated water from entering the drainage conveyance system. However, the first priority is to keep all access roads clean of sediment and keep street wash water separate from entering storm drains until treatment can be provided. Storm Drain Inlet Protection (BMP C220) will be implemented for all existing drainage inlets and culverts that could potentially be impacted by sediment -laden runoff on and near the project site. List and describe BMPs: BMP C220 — Storm Drain Inlet Protection Installation Schedules: Install catch basin filters, according to the approved construction plans, as catch basins become operable. Inspection and Maintenance plan: Inspect inlet protection after storm events. Clean and replace clogged filters. Maintain until all construction activities are completed. Do not wash sediment into storm drains while cleaning. Responsible Staff: Contractor Element 8: Stabilize Channels and Outlets (2.1.8) No site runoff is to be conveyed into channels, or discharged to a stream or some other natural drainage point.— The onsite flowrates will be minimal therefore no BMP's are proposed Stabilize Channels and Outlets. If any BMP's are provideded, the project site is located west of the Cascade Mountain Crest. As such, all temporary on -site conveyance channels shall be designed, constructed, and stabilized to prevent erosion from the expected peak 10 minute velocity of flow from a Type IA, 10-year, 24- hour recurrence interval storm for the developed condition. Alternatively, the 10-year, 1-hour peak flow rate indicated by an approved continuous runoff simulation model, increased by a factor of 1.6, shall be used. Stabilization, including armoring material, adequate to prevent erosion of outlets, adjacent stream banks, slopes, and downstream reaches shall be provided at the outlets of all conveyance systems. Provide stabilization, including armoring material, adequate to prevent erosion of outlets, adjacent stream banks, slopes, and downstream reaches, will be installed at the outlets of all conveyance systems. Element 9: Control Pollutants (2.1.9) The following pollutants are anticipated to be present on -site: Table 2 — Pollutants Pollutant (and source, if applicable) Petroleum products Chemicals stored in the construction area Solid waste All pollutants, including waste materials and demolition debris, that occur onsite shall be handled and disposed of in a manner that does not cause contamination of stormwater. Good housekeeping and preventative measures will be taken to ensure that the site will be kept clean, well organized, and free of debris. If required, BMPs to be implemented to control specific sources of pollutants are discussed below. Vehicles, construction equipment, and/or petroleum product storage/dispensing: • All vehicles, equipment, and petroleum product storage/dispensing areas will be inspected regularly to detect any leaks or spills, and to identify maintenance needs to prevent leaks or spills. • On -site permanent fueling tanks and petroleum product storage containers shall include secondary containment. • Spill prevention measures, such as drip pans, will be used when conducting maintenance and repair of vehicles or equipment. • In order to perform emergency repairs on site, temporary plastic will be placed beneath and, if raining, over the vehicle. • Contaminated surfaces shall be cleaned immediately following any discharge or spill incident. Chemical storage: • Any chemicals stored in the construction areas will conform to the appropriate source control BMPs listed in Volume IV of the Ecology stormwater manual. In Western WA, all chemicals shall have cover, containment, and protection provided on site, per BMP C153 for Material Delivery, Storage and Containment in SWMMWW 2005 Excavation and tunneling spoils dewatering waste: • Dewatering BMPs and BMPs specific to the excavation and tunneling (including handling of contaminated soils) are discussed under Element 10. Demolition: • Dust released from demolished sidewalks, buildings, or structures will be controlled using Dust Control measures (BMP C140). • Storm drain inlets vulnerable to stormwater discharge carrying dust, soil, or debris will be protected using Storm Drain Inlet Protection (BMP C220 as described above for Element 7). • Process water and slurry resulting from saw -cutting and surfacing operations will be prevented from entering the waters of the State by implementing Saw -cutting and Surfacing Pollution Prevention measures (BMP C152). Concrete and grout: • Process water and slurry resulting from concrete work will be prevented from entering the waters of the State by implementing Concrete Handling measures (BMP C151). Sanitary wastewater: • Portable sanitation facilities will be firmly secured, regularly maintained, and emptied when necessary. Solid Waste: • Solid waste will be stored in secure, clearly marked containers. Other: • Other BMPs will be administered as necessary to address any additional pollutant sources on site. A SPCC plan is required for this site. As per the Federal regulations of the Clean Water Act (CWA) and according to Final Rule 40 CFR Part 112, as stated in the National Register, a Spill Prevention, Control, and Countermeasure (SPCC) Plan is required for construction activities. A SPCC Plan has been prepared to address an approach to prevent, respond to, and report spills or releases to the environment that could result from construction activities. This Plan must be well thought out in accordance with good engineering; List and describe BMPs: BMP C151 — Concrete Handling BMP C152 — Sawcutting and Surfaceing Pollution Prevention BMP C153 — Material Delivery, Storage, and Containment BMP C220 — Inlet Protection Installation Schedules: Wash concrete trucks only at approved off -site locations or in a designated concrete washout area only throughout the duration of the project. Vacuum slurry and cuttings during cutting and surfacing operations. Do not let slurry and cuttings remain on permanent concrete or asphalt pavement overnight. The materials storage area should be placed away from vehicular traffic, near the construction entrance, and away from storm drains. During the wet season, (Oct 1 — Apr 30), materials should be stored in a covered area. Inspection and Maintenance plan: All pollutants, including waste materials and demolition debris, that occur onsite shall be handled and disposed of in a manner that does not cause contamination of stormwater. Good housekeeping and preventative measures will be taken to ensure that the site will be kept clean, well organized, and free of debris. Responsible Staff: Contractor Will maintenance, fueling, and/or repair of heavy equipment and vehicles occur on -site? Yes No Will wheel wash or tire bath system BMPs be used during construction? Yes No Will pH -modifying sources be present on -site? Ye No Table 3 — pH -Modifying Sources None X Bulk cement X Cement kiln dust X Fly ash X Other cementitious materials X New concrete washing or curing waters Waste streams generated from concrete grinding and sawing Exposed aggregate processes X Dewatering concrete vaults Concrete pumping and mixer washout waters Recycled concrete Other (i.e. calcium lignosulfate) [please describe] List and describe BMPs: BMP C154 — Concrete Washout Area Installation Schedules: Install concrete washout area according to the approved plans prior to any concrete handling. Inspection and Maintenance plan: Hardened concrete shall be broken up and removed from the concrete washout area on a regular basis. The washout area should maintain a freeboard of at least 12 inches. Responsible Staff: Contractor. Stormwater runoff will be monitored for pH starting on the first day of any activity that includes more than 40 yards of poured or recycled concrete, or after the application of "Engineered Soils" such as, Portland cement treated base, cement kiln dust, or fly ash. This does not include fertilizers. For concrete work, pH monitoring will start the first day concrete is poured and continue until 3 weeks after the last pour. For engineered soils, the pH monitoring period begins when engineered soils are first exposed to precipitation and continue until the area is fully stabilized. Stormwater samples will be collected daily from all points of discharge from the site and measured for pH using a calibrated pH meter, pH test kit, or wide range pH indicator paper. If the measured pH is 8.5 or greater, the following steps will be conducted: 1. Prevent the high pH water from entering storm drains or surface water. 2. Adjust or neutralize the high pH water if necessary using appropriate technology such as CO2 sparging (liquid or dry ice). 3. Contact Ecology if chemical treatment other than CO2 sparging is planned. Concrete trucks must not be washed out onto the ground, or into storm drains, open ditches, streets, or streams. Excess concrete must not be dumped on -site, except in designated concrete washout areas with appropriate BMPs installed. Element 10: Control Dewatering (2.1.10) No dewatering is proposed for the development. If dewatering is needed, Transport. off -site in a vehicle (vacuum truck for legal disposal). Table 4 — Dewatering BMPs Infiltration X Transport off -site in a vehicle (vacuum truck for legal disposal) Ecology -approved on -site chemical treatment or other suitable treatment technologies Sanitary or combined sewer discharge with local sewer district approval (last resort) Use of sedimentation bag with discharge to ditch or swale (small volumes of localized dewatering) Element 11: Maintain BMPs (2.1.11) All temporary and permanent Erosion and Sediment Control (ESC) BMPs shall be maintained and repaired as needed to ensure continued performance of their intended function. Maintenance and repair shall be conducted in accordance with each particular BMP specification (see Volume 11 of the SWMMWW or Chapter 7 of the SWMMEW). Visual monitoring of all BMPs installed at the site will be conducted at least once every calendar week and within 24 hours of any stormwater or non-stormwater discharge from the site. If the site becomes inactive and is temporarily stabilized, the inspection frequency may be reduced to once every calendar month. All temporary ESC BMPs shall be removed within 30 days after final site stabilization is achieved or after the temporary BMPs are no longer needed. Trapped sediment shall be stabilized on -site or removed. Disturbed soil resulting from removal of either BMPs or vegetation shall be permanently stabilized. Additionally, protection must be provided for all BMPs installed for the permanent control of stormwater from sediment and compaction. BMPs that are to remain in place following completion of construction shall be examined and restored to full operating condition. If sediment enters these BMPs during construction, the sediment shall be removed and the facility shall be returned to conditions specified in the construction documents. Element 12: Manage the Project (2.1.12) The project will be managed based on the following principles: • Projects will be phased to the maximum extent practicable and seasonal work limitations will be taken into account. Inspection and monitoring: o Inspection, maintenance and repair of all BMPs will occur as needed to ensure performance of their intended function. o Site inspections and monitoring will be conducted in accordance with Special Condition S4 of the CSWGP. Sampling locations are indicated on the Site Map. Sampling station(s) are located in accordance with applicable requirements of the CSWGP. • Maintain an updated SWPPP. o The SWPPP will be updated, maintained, and implemented in accordance with Special Conditions S3, S4, and S9 of the CSWGP. As site work progresses the SWPPP will be modified routinely to reflect changing site conditions. The SWPPP will be reviewed monthly to ensure the content is current. Table 5 — Management X Design the project to fit the existing topography, soils, and drainage patterns X Emphasize erosion control rather than sediment control X Minimize the extent and duration of the area exposed X Keep runoff velocities low X Retain sediment on -site X Thoroughly monitor site and maintain all ESC measures X Schedule major earthwork during the dry season Other (please describe) Table 6 — BMP Implementation Schedule Phase of Construction Stormwater BMPs Date Wet/Dry Project Season Mark Clearing Limits High Visibility Plastic or Metal Fence 05/01/2023 Dry (BMP C103) Mobilize equipment on Construction Road/Parking area 05/01/2023 Dry site stabilization (BMP C107) Mobilize and store all ESC Silt Fence (BMP C233) 05/01/2023 Dry and soil stabilization Storm Drain Inlet Protection (BMP products C220) Plastic Covering (BMP C123) Surface roughening (BMP C130) Install ESC measures Silt Fence (BMP C233) 05/01/2023 Dry Storm Drain Inlet Protection (BMP C220) Install stabilized Stabilized Construction Entrance 05/01/2023 Dry construction entrance (BMP C105) Begin clearing and Dust Control (BMP C140) 05/15/2023 Dry grubbing Site grading begins Dust Control (BMP C140) 05/27/2023 Dry Grade road and stabilize Dust Control (BMP C140) 05/27/2023 Dry with gravel base Begin excavation for new 07/01/2023 Dry utilities and services Soil stabilization on Mulching (BMP C121) 08/05/2023 Dry excavated side slopes (in Dust Control (BMP C140) idle, no work areas) Plastic Covering (BMP C123) Nets and Blankets (BMP C122) Temporary erosion control Temporary Seeding (BMP C120) 09/01/2023 Dry measures (hydro -seeding) Site grading ends 09/15/2023 Dry Begin pouring concrete BMP C151 10/01/2023 Wet curbs & sidewalks and Concrete Handling (BMP C151) implement Sawcutting and Surfacing Pollution Prevention (BMP C152) Pave asphalt roads 11/05/2023 Wet Implement Element #12 Scheduling (BMP C162) 12/01/2023 Wet BMPs and manage site to CESC Lead (BMP C160) minimize soil disturbance during the wet season Final landscaping and 03/1/2024 Wet planting begins Permanent erosion control Permanent Seeding (BMP C120) 04/01/2024 Wet measures (hydro -seeding) Element 13: Protect Low Impact Development (LID) BMPs (2.1.13) On -site stormwater management BMPs used for runoff from roofs and other hard surfaces are not proposed for this project. Pollution Prevention Team (3.0) Table 7 — Team Information Title Names Phone Number Certified Erosion and Sediment Control Lead (CESCL) Brian Kalab 425-303-9363 Resident Engineer Brian Kalab/Insight Engineering 425-303-9363 Emergency Ecology Contact Tracy Walters 425-649-7000 Emergency Permittee/ Owner Contact Non -Emergency Owner Contact Monitoring Personnel TBD Ecology Regional Office Northwest Regional Office 425-649-7000 Monitoring and Sampling Requirements (4.0) Monitoring includes visual inspection, sampling for water quality parameters of concern, and documentation of the inspection and sampling findings in a site log book. A site log book will be maintained for all on -site construction activities and will include: • A record of the implementation of the SWPPP and other permit requirements • Site inspections • Stormwater sampling data The site log book must be maintained on -site within reasonable access to the site and be made available upon request to Ecology or the local jurisdiction. Numeric effluent limits may be required for certain discharges to 303(d) listed waterbodies. See CSWGP Special Condition S8 and Section 5 of this template. Complete the following paragraph for sites that discharge to impaired waterbodies for fine sediment, turbidity, phosphorus, or pH: The receiving waterbody, Puget Sound, is impaired for: Bacteria -Fecal Coliform and Bacteria- Enterococci. All stormwater and dewatering discharges from the site are subject to an effluent limit of 8.5 su for pH and/or 25 NTU for turbidity. Site Inspection (4.1) Site inspections will be conducted at least once every calendar week and within 24 hours following any discharge from the site. For sites that are temporarily stabilized and inactive, the required frequency is reduced to once per calendar month. The discharge point(s) are indicated on the Site Map (see Appendix A) and in accordance with the applicable requirements of the CSWGP. Stormwater Quality Sampling (4.2) Turbidity Sampling (4.2.1) Requirements include calibrated turbidity meter or transparency tube to sample site discharges for compliance with the CSWGP. Sampling will be conducted at all discharge points at least once per calendar week. Method for sampling turbidity: Table 8 — Turbidity Sampling Method X Turbidity Meter/Turbid imeter (required for disturbances 5 acres or greater in size) Transparency Tube (option for disturbances less than 1 acre and up to 5 acres in size) The benchmark for turbidity value is 25 nephelometric turbidity units (NTU) and a transparency less than 33 centimeters. If the discharge's turbidity is 26 to 249 NTU or the transparency is less than 33 cm but equal to or greater than 6 cm, the following steps will be conducted: 1. Review the SWPPP for compliance with Special Condition S9. Make appropriate revisions within 7 days of the date the discharge exceeded the benchmark. 2. Immediately begin the process to fully implement and maintain appropriate source control and/or treatment BMPs as soon as possible. Address the problems within 10 days of the date the discharge exceeded the benchmark. If installation of necessary treatment BMPs is not feasible within 10 days, Ecology may approve additional time when the Permittee requests an extension within the initial 10-day response period. 3. Document BMP implementation and maintenance in the site log book. If the turbidity exceeds 250 NTU or the transparency is 6 cm or less at any time, the following steps will be conducted: Telephone or submit an electronic report to the applicable Ecology Region's Environmental Report Tracking System (ERTS) within 24 hours. https://www.ecology.wa.gov/About-us/Get-involved/Report-an-environmental-issue • Central Region (Benton, Chelan, Douglas, Kittitas, Klickitat, Okanogan, Yakima): (509) 575-2490 Eastern Region (Adams, Asotin, Columbia, Ferry, Franklin, Garfield, Grant, Lincoln, Pend Oreille, Spokane, Stevens, Walla Walla, Whitman): (509) 329-3400 • Northwest Region (King, Kitsap, Island, San Juan, Skagit, Snohomish, Whatcom): (425) 649-7000 • Southwest Region (Clallam, Clark, Cowlitz, Grays Harbor, Jefferson, Lewis, Mason, Pacific, Pierce, Skamania, Thurston, Wahkiakum,): (360) 407-6300 2. Immediately begin the process to fully implement and maintain appropriate source control and/or treatment BMPs as soon as possible. Address the problems within 10 days of the date the discharge exceeded the benchmark. If installation of necessary treatment BMPs is not feasible within 10 days, Ecology may approve additional time when the Permittee requests an extension within the initial 10-day response period 3. Document BMP implementation and maintenance in the site log book. 4. Continue to sample discharges daily until one of the following is true: • Turbidity is 25 NTU (or lower). • Transparency is 33 cm (or greater). • Compliance with the water quality limit for turbidity is achieved. 0 1 - 5 NTU over background turbidity, if background is less than 50 NTU 0 1 % - 10% over background turbidity, if background is 50 NTU or greater • The discharge stops or is eliminated. pH Sampling (4.2.2) pH monitoring is required for "Significant concrete work" (i.e. greater than 1000 cubic yards poured concrete or recycled concrete over the life of the project).The use of engineered soils (soil amendments including but not limited to Portland cement -treated base [CTB], cement kiln dust [CKD] or fly ash) also requires pH monitoring. For significant concrete work, pH sampling will start the first day concrete is poured and continue until it is cured, typically three (3) weeks after the last pour. For engineered soils and recycled concrete, pH sampling begins when engineered soils or recycled concrete are first exposed to precipitation and continues until the area is fully stabilized. If the measured pH is 8.5 or greater, the following measures will be taken: 1. Prevent high pH water from entering storm sewer systems or surface water. 2. Adjust or neutralize the high pH water to the range of 6.5 to 8.5 su using appropriate technology such as carbon dioxide (CO2) sparging (liquid or dry ice). 3. Written approval will be obtained from Ecology prior to the use of chemical treatment other than CO2 sparging or dry ice. Method for sampling pH: Table 8 — pH Sampling Method X pH meter H test kit Wide range pH indicator paper Discharges to 303(d) or Total Maximum Daily Load (TMDL) Waterbodies (5.0) 303(d) Listed Waterbodies (5.1) Is the receiving water 303(d) (Category 5) listed for turbidity, fine sediment, phosphorus, or pH? Yes No List the impairment(s): LISTING ID WATERBODY PARAMETER CURRENT CATEGORY 40107 1 PUGET SOUND -CENTRAL I Bacteria -Fecal Coliform I Cateaory -5 61015 1 PUGET SOUND -CENTRAL I Bactiera-Enterococci I CateRory -5 TMDL Waterbodies (5.2) Discharges to TMDL receiving waterbodies will meet in -stream water quality criteria at the point of discharge. The Construction Stormwater General Permit Proposed New Discharge to an Impaired Water Body form is included in Appendix F. Reporting and Record Keeping (6.0) Record Keeping (6.1) Site Log Book (6.1.1) A site log book will be maintained for all on -site construction activities and will include: • A record of the implementation of the SWPPP and other permit requirements • Site inspections • Sample logs Records Retention (6.1.2) Records will be retained during the life of the project and for a minimum of three (3) years following the termination of permit coverage in accordance with Special Condition S5.0 of the CSWGP. Permit documentation to be retained on -site: • CSWGP • Permit Coverage Letter • SWPPP • Site Log Book Permit documentation will be provided within 14 days of receipt of a written request from Ecology. A copy of the SWPPP or access to the SWPPP will be provided to the public when requested in writing in accordance with Special Condition S5.G.2.b of the CSWGP. Updating the SWPPP (6.1.3) The SWPPP will be modified if: • Found ineffective in eliminating or significantly minimizing pollutants in stormwater discharges from the site. • There is a change in design, construction, operation, or maintenance at the construction site that has, or could have, a significant effect on the discharge of pollutants to waters of the State. The SWPPP will be modified within seven (7) days if inspection(s) or investigation(s) determine additional or modified BMPs are necessary for compliance. An updated timeline for BMP implementation will be prepared. Reporting (6.2) Discharge Monitoring Reports (6.2.1) Cumulative soil disturbance is one (1) acre or larger; therefore, Discharge Monitoring Reports (DMRs) will be submitted to Ecology monthly. If there was no discharge during a given monitoring period the DMR will be submitted as required, reporting "No Discharge". The DMR due date is fifteen (15) days following the end of each calendar month. DMRs will be reported online through Ecology's WQWebDMR System To sign up for WQWebDMR go to: https://www.ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Water-quality- permits-guidance/WQWeb Portal -guidance Notification of Noncompliance (6.2.2) If any of the terms and conditions of the permit is not met, and the resulting noncompliance may cause a threat to human health or the environment, the following actions will be taken: 1. Ecology will be notified within 24-hours of the failure to comply by calling the applicable Regional office ERTS phone number (Regional office numbers listed below). 2. Immediate action will be taken to prevent the discharge/pollution or otherwise stop or correct the noncompliance. If applicable, sampling and analysis of any noncompliance will be repeated immediately and the results submitted to Ecology within five (5) days of becoming aware of the violation. 3. A detailed written report describing the noncompliance will be submitted to Ecology within five (5) days, unless requested earlier by Ecology. Anytime turbidity sampling indicates turbidity is 250 NTUs or greater, or water transparency is 6 cm or less, the Ecology Regional office will be notified by phone within 24 hours of analysis as required by Special Condition S5.A of the CSWGP. • Central Region at (509) 575-2490 for Benton, Chelan, Douglas, Kittitas, Klickitat, Okanogan, or Yakima County Eastern Region at (509) 329-3400 for Adams, Asotin, Columbia, Ferry, Franklin, Garfield, Grant, Lincoln, Pend Oreille, Spokane, Stevens, Walla Walla, or Whitman County • Northwest Region at (425) 649-7000 for Island, King, Kitsap, San Juan, Skagit, Snohomish, or Whatcom County Southwest Region at (360) 407-6300 for Clallam, Clark, Cowlitz, Grays Harbor, Jefferson, Lewis, Mason, Pacific, Pierce, Skamania, Thurston, or Wahkiakum Include the following information: 1. Your name and / Phone number 2. Permit number 3. City / County of project 4. Sample results 5. Date / Time of call 6. Date / Time of sample 7. 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I ' I / i C / / / mvrcna, ro er mom�m ro wr o LOT D ITT LVIF 02 a IM �\II� _ y' /�e 'R �\ / I � IL�l l� \ \ Zy j / / / / I `P-] I CIKCWNA.SSCD 6Y A!N-10MD62101]6-A�/ \ ' - O.r(W)COA)ER. 133 1 nll / aq.) Or COPKR. I IlJ'YI I I Na,zW \ \ / / XIJI- B. BMP Detail BMP C101: Preserving Natural Vegetation Purpose The purpose of preserving natural vegetation is to reduce erosion wherever practicable. Limiting site disturbance is the single most effective method for reducing erosion. For example, conifers can hold up to about 50 percent of all rain that falls during a storm. Up to 20-30 percent of this rain may never reach the ground but is taken up by the tree or evaporates. Another benefit is that the rain held in the tree can be released slowly to the ground after the storm. Conditions of Use Natural vegetation should be preserved on steep slopes, near perennial and intermittent water- courses or swales, and on building sites in wooded areas. . As required by local governments. Phase construction to preserve natural vegetation on the project site for as long as possible during the construction period. Design and Installation Specifications Natural vegetation can be preserved in natural clumps or as individual trees, shrubs and vines. The preservation of individual plants is more difficult because heavy equipment is generally used to remove unwanted vegetation. The points to remember when attempting to save individual plants are: . Is the plant worth saving? Consider the location, species, size, age, vigor, and the work involved. Local governments may also have ordinances to save natural vegetation and trees. Fence or clearly mark areas around trees that are to be saved. It is preferable to keep ground disturbance away from the trees at least as far out as the dripline. Plants need protection from three kinds of injuries: Construction Equipment- This injury can be above or below the ground level. Damage results from scarring, cutting of roots, and compaction of the soil. Placing a fenced buffer zone around plants to be saved prior to construction can prevent construction equipment injuries. Grade Changes- Changing the natural ground level will alter grades, which affects the plant's ability to obtain the necessary air, water, and minerals. Minor fills usually do not cause prob- lems although sensitivity between species does vary and should be checked. Trees can typ- ically tolerate fill of 6 inches or less. For shrubs and other plants, the fill should be less. When there are major changes in grade, it may become necessary to supply air to the roots of plants. This can be done by placing a layer of gravel and a tile system over the roots before the fill is made. The tile system should be laid out on the original grade leading from a dry well 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 271 around the tree trunk. The system should then be covered with small stones to allow air to cir- culate over the root area. Lowering the natural ground level can seriously damage trees and shrubs. The highest per- centage of the plant roots are in the upper 12 inches of the soil and cuts of only 2-3 inches can cause serious injury. To protect the roots it may be necessary to terrace the immediate area around the plants to be saved. If roots are exposed, construction of retaining walls may be needed to keep the soil in place. Plants can also be preserved by leaving them on an undis- turbed, gently sloping mound. To increase the chances for survival, it is best to limit grade changes and other soil disturbances to areas outside the dripline of the plant. Excavations - Protect trees and other plants when excavating for drainfields, power, water, and sewer lines. Where possible, the trenches should be routed around trees and large shrubs. When this is not possible, it is best to tunnel under them. This can be done with hand tools or with power augers. If it is not possible to route the trench around plants to be saved, then the following should be observed: Cut as few roots as possible. When you have to cut, cut clean. Paint cut root ends with a wood dressing like asphalt base paint if roots will be exposed for more than 24-hours. Backfill the trench as soon as possible. Tunnel beneath root systems as close to the center of the main trunk to preserve most of the important feeder roots. Some problems that can be encountered with a few specific trees are: • Maple, Dogwood, Red alder, Western hemlock, Western red cedar, and Douglas fir do not readily adjust to changes in environment and special care should be taken to protect these trees. . The windthrow hazard of Pacific silver fir and madrona is high, while that of Western hemlock is moderate. The danger of windthrow increases where dense stands have been thinned. Other species (unless they are on shallow, wet soils less than 20 inches deep) have a low windthrow hazard. . Cottonwoods, maples, and willows have water -seeking roots. These can cause trouble in sewer lines and infiltration fields. On the other hand, they thrive in high moisture conditions that other trees would not. . Thinning operations in pure or mixed stands of Grand fir, Pacific silver fir, Noble fir, Sitka spruce, Western red cedar, Western hemlock, Pacific dogwood, and Red alder can cause ser- ious disease problems. Disease can become established through damaged limbs, trunks, roots, and freshly cut stumps. Diseased and weakened trees are also susceptible to insect attack. Maintenance Standards Inspect flagged and/or fenced areas regularly to make sure flagging or fencing has not been removed or damaged. If the flagging or fencing has been damaged or visibility reduced, it shall be repaired or replaced immediately and visibility restored. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 272 If tree roots have been exposed or injured, "prune" cleanly with an appropriate pruning saw or top- pers directly above the damaged roots and recover with native soils. Treatment of sap flowing trees (fir, hemlock, pine, soft maples) is not advised as sap forms a natural healing barrier. 2019 Stormwater Management Manual for Western Washington Volume ll - Chapter 3 - Page 273 BMP C103: High -Visibility Fence Purpose High -visibility fencing is intended to: • Restrict clearing to approved limits. • Prevent disturbance of sensitive areas, their buffers, and other areas required to be left undis- turbed. . Limit construction traffic to designated construction entrances, exits, or internal roads. • Protect areas where marking with survey tape may not provide adequate protection. Conditions of Use To establish clearing limits plastic, fabric, or metal fence may be used: . At the boundary of sensitive areas, their buffers, and other areas required to be left uncleared. . As necessary to control vehicle access to and on the site. Design and Installation Specifications High -visibility plastic fence shall be composed of a high -density polyethylene material and shall be at least four feet in height. Posts for the fencing shall be steel or wood and placed every 6 feet on center (maximum) or as needed to ensure rigidity. The fencing shall be fastened to the post every six inches with a polyethylene tie. On long continuous lengths of fencing, a tension wire or rope shall be used as a top stringer to prevent sagging between posts. The fence color shall be high -visibility orange. The fence tensile strength shall be 360 Ibs/ft using the ASTM D4595 testing method. If appropriate install fabric silt fence in accordance with BMP C233: Silt Fence to act as high -visibility fence. Silt fence shall be at least 3 feet high and must be highly visible to meet the requirements of this BMP. Metal fences shall be designed and installed according to the manufacturer's specifications. Metal fences shall be at least 3 feet high and must be highly visible. Fences shall not be wired or stapled to trees. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 274 Maintenance Standards If the fence has been damaged or visibility reduced, it shall be repaired or replaced immediately and visibility restored. BMP C105: Stabilized Construction Access Purpose Stabilized construction accesses are established to reduce the amount of sediment transported onto paved roads outside the project site by vehicles or equipment. This is done by constructing a sta- bilized pad of quarry spalls at entrances and exits for project sites. Conditions of Use Construction accesses shall be stabilized wherever traffic will be entering or leaving a construction site if paved roads or other paved areas are within 1,000 feet of the site. For residential subdivision construction sites, provide a stabilized construction access for each res- idence, rather than only at the main subdivision entrance. Stabilized surfaces shall be of sufficient length/width to provide vehicle access/parking, based on lot size and configuration. On large commercial, highway, and road projects, the designer should include enough extra mater- ials in the contract to allow for additional stabilized accesses not shown in the initial Construction SWPPP. It is difficult to determine exactly where access to these projects will take place; additional materials will enable the contractor to install them where needed. Design and Installation Specifications See Figure II-3.1: Stabilized Construction Access for details. Note: the 1 00'minimum length of the access shall be reduced to the maximum practicable size when the size or configuration of the site does not allow the full length (100'). Construct stabilized construction accesses with a 12-inch thick pad of 4-inch to 8-inch quarry spalls, a 4-inch course of asphalt treated base (ATB), or use existing pavement. Do not use crushed con- crete, cement, or calcium chloride for construction access stabilization because these products raise pH levels in stormwater and concrete discharge to waters of the State is prohibited. A separation geotextile shall be placed under the spalls to prevent fine sediment from pumping up into the rock pad. The geotextile shall meet the standards listed in Table 11-3.2: Stabilized Con- struction Access Geotextile Standards. Table 11-3.2: Stabilized Construction Access Geotextile Standards Geotextile Property I Required Value Grab Tensile Strength (ASTM D4751) 1 200 psi min. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 275 Table II-3.2: Stabilized Construction Access Geotextile Standards (continued) Geotextile Property Required Value Grab Tensile Elongation (ASTM D4632) 30% max. Mullen Burst Strength (ASTM D3786-80a) 400 psi min. AOS (ASTM D4751) 20-45 (U.S. standard sieve size) Consider early installation of the first lift of asphalt in areas that will be paved; this can be used as a stabilized access. Also consider the installation of excess concrete as a stabilized access. During large concrete pours, excess concrete is often available for this purpose. Fencing (see BMP C103: High -Visibility Fence) shall be installed as necessary to restrict traffic to the construction access. Whenever possible, the access shall be constructed on a firm, compacted subgrade. This can substantially increase the effectiveness of the pad and reduce the need for maintenance. Construction accesses should avoid crossing existing sidewalks and back of walk drains if at all possible. If a construction access must cross a sidewalk or back of walk drain, the full length of the sidewalk and back of walk drain must be covered and protected from sediment leaving the site. Alternative Material Specification WSDOT has raised safety concerns about the Quarry Spall rock specified above. WSDOT observes that the 4-inch to 8-inch rock sizes can become trapped between Dually truck tires, and then released off -site at highway speeds. WSDOT has chosen to use a modified specification for the rock while continuously verifying that the Stabilized Construction Access remains effective. To remain effective, the BMP must prevent sediment from migrating off site. To date, there has been no per- formance testing to verify operation of this new specification. Jurisdictions may use the alternative specification, but must perform increased off -site inspection if they use, or allow others to use, it. Stabilized Construction Accesses may use material that meets the requirements of WSDOT's Stand- ard Specifications for Road, Bridge, and Municipal Construction Section 9-03.9(1) (WSDOT, 2016) for ballast except for the following special requirements. The grading and quality requirements are listed in Table II-3.3: Stabilized Construction Access Alternative Material Requirements. Table II-3.3: Stabilized Construction Access Alternative Material Requirements Sieve Size Percent Passing 2'/2" 99-100 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 276 Table II-3.3: Stabilized Construction Access Alternative Material Requirements (continued) Sieve Size Percent Passing 2" 65-100 3/4" 40-80 No. 4 5 max. No. 100 0-2 % Fracture 75 min. . All percentages are by weight. . The sand equivalent value and dust ratio requirements do not apply. The fracture requirement shall be at least one fractured face and will apply the combined aggregate retained on the No. 4 sieve in accordance with FOP for AASHTO T 335. Maintenance Standards Quarry spalls shall be added if the pad is no longer in accordance with the specifications. . If the access is not preventing sediment from being tracked onto pavement, then alternative measures to keep the streets free of sediment shall be used. This may include replace- ment/cleaning of the existing quarry spalls, street sweeping, an increase in the dimensions of the access, or the installation of BMP C 106: Wheel Wash. Any sediment that is tracked onto pavement shall be removed by shoveling or street sweep- ing. The sediment collected by sweeping shall be removed or stabilized on site. The pavement shall not be cleaned by washing down the street, except when high efficiency sweeping is inef- fective and there is a threat to public safety. If it is necessary to wash the streets, the con- struction of a small sump to contain the wash water shall be considered. The sediment would then be washed into the sump where it can be controlled. Perform street sweeping by hand or with a high efficiency sweeper. Do not use a non -high effi- ciency mechanical sweeper because this creates dust and throws soils into storm systems or conveyance ditches. Any quarry spalls that are loosened from the pad, which end up on the roadway shall be removed immediately. . If vehicles are entering or exiting the site at points other than the construction access(es), BMP C103: High -Visibility Fence shall be installed to control traffic. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 277 Upon project completion and site stabilization, all construction accesses intended as per- manent access for maintenance shall be permanently stabilized. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 278 Figure II-3.1: Stabilized Construction Access cu roadsi Notes: 1. Driveway shall meet the requirements of the permitting agency. 2. It is recommended that the access be crowned so that runoff drains off the pad. DEPARTMENT OF ECOLOGY State of Washington 12" minimum thickness NOT TO SCALE n. 1 b' min. Provide full width of ingress/egress area Stabilized Construction Access Revised June 2018 Please see http://www.ecy.wa.gov/cop3aVht.htm1 for copyright notice including permissions, limitation of liability, and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 279 Approved as Functionally Equivalent Ecology has approved products as able to meet the requirements of this BMP. The products did not pass through the Technology Assessment Protocol — Ecology (TAPE) process. Local jurisdictions may choose not to accept these products, or may require additional testing prior to consideration for local use. Products that Ecology has approved as functionally equivalent are available for review on Ecology's website at: https:Hecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per- mittee-guidance-resources/Emerging-stormwater-treatment-technologies 2019 Stormwater Management Manual for Western Washington Volume // - Chapter 3 - Page 280 BMP C120: Temporary and Permanent Seeding Purpose Seeding reduces erosion by stabilizing exposed soils. A well -established vegetative cover is one of the most effective methods of reducing erosion. Conditions of Use Use seeding throughout the project on disturbed areas that have reached final grade or that will remain unworked for more than 30 days. The optimum seeding windows for western Washington are April 1 through June 30 and September 1 through October 1. Between July 1 and August 30 seeding requires irrigation until 75 percent grass cover is established. Between October 1 and March 30 seeding requires a cover of mulch or an erosion control blanket until 75 percent grass cover is established. Review all disturbed areas in late August to early September and complete all seeding by the end of September. Otherwise, vegetation will not establish itself enough to provide more than average pro- tection. Mulch is required at all times for seeding because it protects seeds from heat, moisture loss, and transport due to runoff. Mulch can be applied on top of the seed or simultaneously by hydroseeding See BMP C121: Mulching for specifications. Seed and mulch all disturbed areas not otherwise vegetated at final site stabilization. Final sta- bilization means the completion of all soil disturbing activities at the site and the establishment of a permanent vegetative cover, or equivalent permanent stabilization measures (such as pavement, riprap, gabions, or geotextiles) which will prevent erosion. See BMP T5.13: Post -Construction Soil Qualitv and Depth. Design and Installation Specifications General Install channels intended for vegetation before starting major earthwork and hydroseed with a Bonded Fiber Matrix. For vegetated channels that will have high flows, install erosion control blankets over the top of hydroseed. Before allowing water to flow in vegetated channels, establish 75 percent vegetation cover. If vegetated channels cannot be established by seed 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 284 before water flow; install sod in the channel bottom — over top of hydromulch and erosion con- trol blankets. • Confirm the installation of all required surface water control measures to prevent seed from washing away. • Hydroseed applications shall include a minimum of 1,500 pounds per acre of mulch with 3 per- cent tackifier. See BMP C121: Mulching for specifications. . Areas that will have seeding only and not landscaping may need compost or meal -based mulch included in the hydroseed in order to establish vegetation. Re -install native topsoil on the disturbed soil surface before application. See BMP T5.13: Post -Construction Soil Quality and Depth. • When installing seed via hydroseeding operations, only about 1/3 of the seed actually ends up in contact with the soil surface. This reduces the ability to establish a good stand of grass quickly. To overcome this, consider increasing seed quantities by up to 50 percent. • Enhance vegetation establishment by dividing the hydromulch operation into two phases: Phase 1- Install all seed and fertilizer with 25-30 percent mulch and tackifier onto soil in the first lift. Phase 2- Install the rest of the mulch and tackifier over the first lift. Or, enhance vegetation by: o Installing the mulch, seed, fertilizer, and tackifier in one lift. o Spread or blow straw over the top of the hydromulch at a rate of 800-1000 pounds per acre. Hold straw in place with a standard tackifier. Both of these approaches will increase cost moderately but will greatly improve and enhance vegetative establishment. The increased cost may be offset by the reduced need for: o Irrigation. Reapplication of mulch. Repair of failed slope surfaces. This technique works with standard hydromulch (1,500 pounds per acre minimum) and Bon- ded Fiber Matrix/ Mechanically Bonded Fiber Matrix (BFM/MBFMs) (3,000 pounds per acre minimum). . Seed may be installed by hand if: o Temporary and covered by straw, mulch, or topsoil. Permanent in small areas (usually less than 1 acre) and covered with mulch, topsoil, or erosion blankets. The seed mixes listed in Table II-3.4: Temporary and Permanent Seed Mixes include 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 285 recommended mixes for both temporary and permanent seeding. . Apply these mixes, with the exception of the wet area seed mix, at a rate of 120 pounds per acre. This rate can be reduced if soil amendments or slow -release fertilizers are used. Apply the wet area seed mix at a rate of 60 pounds per acre. Consult the local suppliers or the local conservation district for their recommendations. The appropriate mix depends on a variety of factors, including location, exposure, soil type, slope, and expected foot traffic. Alternative seed mixes approved by the local authority may be used, depending on the soil type and hydrology of the area. Table 11-3.4: Temporary and Permanent Seed Mixes Common Name Latin Name % Weight % Purity % Germination Temporary Erosion Control Seed Mix A standard mix for areas requiring a temporary vegetative cover. Chewings or Festuca rubra var. annual bluegrass commutata or Poa 40 98 90 anna Perennial rye Lolium perenne 50 98 90 Redtop or colonial Agrostis alba or 5 92 85 bentgrass Agrostis tenuis White dutch clover Trifolium repens 5 98 90 Landscaping Seed Mix A recommended mix for landscaping seed. Perennial rye blend Lolium perenne 70 98 90 Chewings and red Festuca rubra var. fescue blend commutata or Fes- 30 98 90 tuca rubra Low -Growing Turf Seed Mix A turf seed mix for dry situations where there is no need for watering. This mix requires very little main- tenance. Dwarf tall fescue Festuca arundin- 45 98 90 (several varieties) acea var. Dwarf perennial Lolium perenne 30 98 90 rye (Barclay) var. barclay Red fescue Festuca rubra 20 98 90 Colonial bentgrass Agrostis tenuis 5 98 90 Bioswale Seed Mix A seed mix for bioswales and other intermittently wet areas. Tall or meadow fes- Festuca arundin- 75-80 98 90 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 286 Table II-3.4: Temporary and Permanent Seed Mixes (continued) Common Name Latin Name % Weight % Purity % Germination acea or Festuca cue elatior Seaside/Creeping Agrostis palustris 10-15 92 85 bentgrass Redtop bentgrass Agrostis alba or 5-10 90 80 Agrostis gigantea Wet Area Seed Mix A low -growing, relatively non-invasive seed mix appropriate forvery wet areas that are not regulated wet- lands. Consult Hydraulic Permit Authority (HPA) for seed mixes if applicable. Tall or meadow fes- Festuca arundin- acea or Festuca 60-70 98 90 cue elatior Seaside/Creeping Agrostis palustris 10-15 98 85 bentgrass Meadow foxtail Alepocurus praten- 10-15 90 80 sis Alsike clover Trifolium hybridum 1-6 98 90 Redtop bentgrass Agrostis alba 1-6 92 85 Meadow Seed Mix A recommended meadow seed mix for infrequently maintained areas or non -maintained areas where col- onization by native plants is desirable. Likely applications include rural road and utility right-of-way. Seed- ing should take place in September or very early October in order to obtain adequate establishment prior to the winter months. Consider the appropriateness of clover, a fairly invasive species, in the mix. Amending the soil can reduce the need for clover. Redtop or Oregon Agrostis alba or bentgrass Agrostis ore- 20 92 85 gonensis Red fescue Festuca rubra 70 98 90 White dutch clover Trifolium repens 10 98 90 Roughening and Rototilling The seedbed should be firm and rough. Roughen all soil no matter what the slope. Track walk slopes before seeding if engineering purposes require compaction. Backblading or smoothing of slopes greater than 4H:1 V is not allowed if they are to be seeded. Restoration -based landscape practices require deeper incorporation than that provided by a simple single -pass rototilling treatment. Wherever practical, initially rip the subgrade to improve long-term permeability, infiltration, and water inflow qualities. At a minimum, 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 287 permanent areas shall use soil amendments to achieve organic matter and permeability per- formance defined in engineered soil/landscape systems. For systems that are deeper than 8 inches complete the rototilling process in multiple lifts, or prepare the engineered soil system per specifications and place to achieve the specified depth. Fertilizers • Conducting soil tests to determine the exact type and quantity of fertilizer is recommended. This will prevent the over -application of fertilizer. . Organic matter is the most appropriate form of fertilizer because it provides nutrients (includ- ing nitrogen, phosphorus, and potassium) in the least water-soluble form. . In general, use 10-4-6 N-P-K (nitrogen -phosphorus -potassium) fertilizer at a rate of 90 pounds per acre. Always use slow -release fertilizers because they are more efficient and have fewer environmental impacts. Do not add fertilizer to the hydromulch machine, or agit- ate, more than 20 minutes before use. Too much agitation destroys the slow -release coating. . There are numerous products available that take the place of chemical fertilizers. These include several with seaweed extracts that are beneficial to soil microbes and organisms. If 100 percent cottonseed meal is used as the mulch in hydroseed, chemical fertilizer may not be necessary. Cottonseed meal provides a good source of long-term, slow -release, available nitrogen. Bonded Fiber Matrix and Mechanically Bonded Fiber Matrix . On steep slopes use Bonded Fiber Matrix (BFM) or Mechanically Bonded Fiber Matrix (MBFM) products. Apply BFM/MBFM products at a minimum rate of 3,000 pounds per acre with approximately 10 percent tackifier. Achieve a minimum of 95 percent soil coverage during application. Numerous products are available commercially. Most products require 24-36 hours to cure before rainfall and cannot be installed on wet or saturated soils. Generally, products come in 40-50 pound bags and include all necessary ingredients except for seed and fertilizer. . Install products per manufacturer's instructions. • BFMs and MBFMs provide good alternatives to blankets in most areas requiring vegetation establishment. Advantages over blankets include: • BFM and MBFMs do not require surface preparation. • Helicopters can assist in installing BFM and MBFMs in remote areas. • On slopes steeper than 2.5H:1 V, blanket installers may require ropes and harnesses for safety. • Installing BFM and MBFMs can save at least $1,000 per acre compared to blankets. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 288 Maintenance Standards Reseed any seeded areas that fail to establish at least 75 percent cover (100 percent cover for areas that receive sheet or concentrated flows). If reseeding is ineffective, use an alternate method such as sodding, mulching, nets, or blankets. Reseed and protect by mulch any areas that experience erosion after achieving adequate cover. Reseed and protect by mulch any eroded area. Supply seeded areas with adequate moisture, but do not water to the extent that it causes run- off. Approved as Functionally Equivalent Ecology has approved products as able to meet the requirements of this BMP. The products did not pass through the Technology Assessment Protocol — Ecology (TAPE) process. Local jurisdictions may choose not to accept these products, or may require additional testing prior to consideration for local use. Products that Ecology has approved as functionally equivalent are available for review on Ecology's website at: https:Hecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per- mittee-guidance-resources/Emerging-stormwater-treatment-technologies BMP C121: Mulching Purpose Mulching soils provides immediate temporary protection from erosion. Mulch also enhances plant establishment by conserving moisture, holding fertilizer, seed, and topsoil in place, and moderating soil temperatures. There are a variety of mulches that can be used. This section discusses only the most common types of mulch. Conditions of Use As a temporary cover measure, mulch should be used: . For less than 30 days on disturbed areas that require cover. At all times for seeded areas, especially during the wet season and during the hot summer months. During the wet season on slopes steeper than 3H:1 V with more than 10 feet of vertical relief. Mulch may be applied at anytime of the year and must be refreshed periodically. For seeded areas, mulch may be made up of 100 percent: cottonseed meal; . fibers made of wood, recycled cellulose, hemp, or kenaf; 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 289 . compost; or blends of these. Tackifier shall be plant -based, such as guar or alpha plantago, or chemical -based such as poly- acrylamide or polymers. Generally, mulches come in 40-50 pound bags. Seed and fertilizer are added at time of application. Recycled cellulose may contain polychlorinated biphenyl (PCBs). Ecology recommends that products should be evaluated for PCBs prior to use. Refer to BMP C 126: Polyacrylamide (PAM) for Soil Erosion Protection for conditions of use. PAM shall not be directly applied to water or allowed to enter a water body. Any mulch or tackifier product used shall be installed per the manufacturer's instructions. Design and Installation Specifications For mulch materials, application rates, and specifications, see Table II-3.6: Mulch Standards and Guidelines. Consult with the local supplier or the local conservation district for their recom- mendations. Increase the application rate until the ground is 95% covered (i.e. not visible under the mulch layer). Note: Thickness may be increased for disturbed areas in or near sensitive areas or other areas highly susceptible to erosion. Where the option of "Compost" is selected, it should be a coarse compost that meets the size grad- ations listed in Table 11-3.5: Size Gradations of Compost as Mulch Material when tested in accord- ance with Test Method 02.02-13 found in Test Methods for the Examination of Composting and Compost (Thompson, 2001). Table 11-3.5: Size Gradations of Compost as Mulch Material Sieve Size Percent Passing 3" 100% 1" 90% -100% 3/4" 70% -100% 1/4" 40% - 100% Mulch used within the ordinary high-water mark of surface waters should be selected to minimize potential flotation of organic matter. Composted organic materials have higher specific gravities (densities) than straw, wood, or chipped material. Consult the Hydraulic Permit Authority (H PA) for mulch mixes if applicable. Maintenance Standards The thickness of the mulch cover must be maintained. Any areas that experience erosion shall be remulched and/or protected with a net or blanket. If the erosion problem is drainage related, then the problem shall be fixed and the eroded area remulched. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 290 Table II-3.6: Mulch Standards and Guidelines Mulch Mater- Guideline Description ial Quality Standards Air-dried; free from undesirable seed and coarse material. Application 2"-3" thick; 5 bales per 1,000 sf or 2-3 tons per acre Rates Cost-effective protection when applied with adequate thickness. Hand - application generally requires greater thickness than blown straw. The Straw thickness of straw may be reduced by half when used in conjunction with seeding. In windy areas straw must be held in place by crimping, using a tackifier, or covering with netting. Blown straw always has to be held in Remarks place with a tackifier as even light winds will blow it away. Straw, however, has several deficiencies that should be considered when selecting mulch materials. It often introduces and/or encourages the propagation of weed species and it has no significant long-term benefits It should also not be used within the ordinary high-water elevation of surface waters (due to flot- ation). Quality No growth inhibiting factors. Standards Application Approx. 35-45 Ibs per 1,000 sf or 1,500 -2,000 Ibs per acre Hydromulch Rates Shall be applied with hydromulcher. Shall not be used without seed and Remarks tackifier unless the application rate is at least doubled. Fibers longer than about 3/4 -1 inch clog hydromulch equipment. Fibers should be kept to less than 3/4 inch. Quality No visible water or dust during handling. Must be produced per WAC 173- Standards 350, Solid Waste Handling Standards, but may have up to 35% biosolids. Application 2 thick min.; approx. 100 tons per acre (approx. 750 Ibs per cubic yard) Rates More effective control can be obtained by increasing thickness to 3". Excel - Compost lent mulch for protecting final grades until landscaping because it can be dir- ectly seeded or tilled into soil as an amendment. Compost used for mulch Remarks has a coarser size gradation than compost used for BMP C 125: Topsoiling / Composting or BMP T5.13: Post -Construction Soil Quality and Depth. It is more stable and practical to use in wet areas and during rainy weather conditions. Do not use near wetlands or near phosphorous impaired water bodies. Quality Gradations from fines to 6 inches in length for texture, variation, and inter - Chipped Standards locking properties. Include a mix of various sizes so that the average size Site Veget- is between 2- and 4- inches. ation Application Rates 2" thick min.; 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 291 Table 11-3.6: Mulch Standards and Guidelines (continued) Mulch Mater- Guideline Description ial This is a cost-effective way to dispose of debris from clearing and grub- bing, and it eliminates the problems associated with burning. Generally, it should not be used on slopes above approx. 10% because of its tendency to be transported by runoff. It is not recommended within 200 feet of sur- Remarks face waters. If permanent seeding or planting is expected shortly after mulch, the decomposition of the chipped vegetation may tie up nutrients important to grass establishment. Note: thick application of this material over existing grass, herbaceous spe- cies, and some groundcovers could smother and kill vegetation. Quality No visible water or dust during handling. Must be purchased from a supplier Standards `^iith a Solid Waste Handling Permit or one exempt from solid waste reg- ulations. Application 2" thick min.; approx. 100 tons per acre (approx. 750 lbs. per cubic yard) Wood- Rates Based This material is often called "wood straw" or "hog fuel". The use of mulch Mulch ultimately improves the organic matter in the soil. Special caution is Remarks advised regarding the source and composition of wood -based mulches. Its preparation typically does not provide any weed seed control, so evidence of residual vegetation in its composition or known inclusion of weed plants or seeds should be monitored and prevented (or minimized). Quality A blend of loose, long, thin wood pieces derived from native conifer or Standards deciduous trees with high length -to -width ratio. Application 2" thick min. Rates Wood Cost-effective protection when applied with adequate thickness. A min - Strand imum of 95-percent of the wood strand shall have lengths between 2 and Mulch 10-inches, with a width and thickness between 1/16 and 1/2-inches. The Remarks mulch shall not contain resin, tannin, or other compounds in quantities that would be detrimental to plant life. Sawdust orwood shavings shall not be used as mulch. [Specification 9-14.4(4) from the Standard Specifications for Road, Bridge, and Municipal Construction (WSDOT, 2019 BMP C122: Nets and Blankets Purpose Erosion control nets and blankets are intended to prevent erosion and hold seed and mulch in place on steep slopes and in channels so that vegetation can become well established. In addition, some nets and blankets can be used to permanently reinforce turf to protect drainage ways during high flows. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 292 Nets (commonly called matting) are strands of material woven into an open, but high -tensile strength net (for example, coconut fiber matting). Blankets are strands of material that are not tightly woven, but instead form a layer of interlocking fibers, typically held together by a biodegradable or pho- todegradable netting (for example, excelsior or straw blankets). They generally have lower tensile strength than nets, but cover the ground more completely. Coir (coconut fiber) fabric comes as both nets and blankets. Conditions of Use Erosion control netting and blankets shall be made of natural plant fibers unaltered by synthetic materials. Erosion control nets and blankets should be used: . To aid permanent vegetated stabilization of slopes 2H:1 V or greater and with more than 10 feet of vertical relief. For drainage ditches and swales (highly recommended). The application of appropriate net- ting or blanket to drainage ditches and swales can protect bare soil from channelized runoff while vegetation is established. Nets and blankets also can capture a great deal of sediment due to their open, porous structure. Nets and blankets can be used to permanently stabilize channels and may provide a cost-effective, environmentally preferable alternative to riprap. Disadvantages of nets and blankets include: . Surface preparation is required. . On slopes steeper than 2.5H:1 V, net and blanket installers may need to be roped and har- nessed for safety. . They cost at least $4,000-6,000 per acre installed. Advantages of nets and blankets include: . Installation without mobilizing special equipment. . Installation by anyone with minimal training . Installation in stages or phases as the project progresses. . Installers can hand place seed and fertilizer as they progress down the slope. . Installation in any weather. . There are numerous types of nets and blankets that can be designed with various parameters in mind. Those parameters include: fiber blend, mesh strength, longevity, biodegradability, cost, and availability. An alternative to nets and blankets in some limited conditions is BMP C202: Riprap Channel Lining. Ensure that BMP C202: Riprap Channel Lining is appropriate before using it as a substitute for nets and blankets. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 293 Design and Installation Specifications See Figure II-3.3: Channel Installation (Clackamas County et al., 2008) and Figure II-3.4: Slope Installation for typical orientation and installation of nets and blankets used in channels and as slope protection. Note: these are typical only; all nets and blankets must be installed per manufacturer's installation instructions. . Installation is critical to the effectiveness of these products. If good ground contact is not achieved, runoff can concentrate under the product, resulting in significant erosion. . Installation of nets and blankets on slopes: 1. Complete final grade and track walk up and down the slope. 2. Install hydromulch with seed and fertilizer. 3. Dig a small trench, approximately 12 inches wide by 6 inches deep along the top of the slope. 4. Install the leading edge of the net/blanket into the small trench and staple approximately every 18 inches. NOTE: Staples are metal, "U"-shaped, and a minimum of 6 inches long. Longer staples are used in sandy soils. Biodegradable stakes are also available. 5. Roll the net/blanket slowly down the slope as the installer walks backward. NOTE: The net/blanket rests against the installer's legs. Staples are installed as the net/blanket is unrolled. It is critical that the proper staple pattern is used for the net/blanket being installed. The net/blanket is not to be allowed to roll down the slope on its own as this stretches the net/blanket, making it impossible to maintain soil contact. In addition, no one is allowed to walk on the net/blanket after it is in place. 6. If the net/blanket is not long enough to cover the entire slope length, the trailing edge of the upper net/blanket should overlap the leading edge of the lower net/blanket and be stapled. On steeper slopes, this overlap should be installed in a small trench, stapled, and covered with soil. • With the variety of products available, it is impossible to cover all the details of appropriate use and installation. Therefore, it is critical that the designer consult the manufacturer's inform- ation and that a site visit takes place in order to ensure that the product specified is appro- priate. Information is also available in WSDOT's Standard Specifications for Road, Bridge, and Municipal Construction Division 8-01 and Division 9-14 (WSDOT, 2016). • Usejute matting in conjunction with mulch (BMP C121: Mulching). Excelsior, woven straw blankets and coir (coconut fiber) blankets may be installed without mulch. There are many other types of erosion control nets and blankets on the market that may be appropriate in cer- tain circumstances. • In general, most nets (e.g., jute matting) require mulch in order to prevent erosion because they have a fairly open structure. Blankets typically do not require mulch because they usually provide complete protection of the surface. • Extremely steep, unstable, wet, or rocky slopes are often appropriate candidates for use of synthetic blankets, as are riverbanks, beaches and other high-energy environments. If 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 294 synthetic blankets are used, the soil should be hydromulched first. 100-percent biodegradable blankets are available for use in sensitive areas. These organic blankets are usually held together with a paper or fiber mesh and stitching which may last up to a year. Most netting used with blankets is photodegradable, meaning it breaks down under sunlight (not UV stabilized). However, this process can take months or years even under bright sun. Once vegetation is established, sunlight does not reach the mesh. It is not uncommon to finc non -degraded netting still in place several years after installation. This can be a problem if maintenance requires the use of mowers or ditch cleaning equipment. In addition, birds and small animals can become trapped in the netting. Maintenance Standards . Maintain good contact with the ground. Erosion must not occur beneath the net or blanket. Repair and staple any areas of the net or blanket that are damaged or not in close contact with the ground. . Fix and protect eroded areas if erosion occurs due to poorly controlled drainage. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 295 Figure 11-3.3: Channel Installation NOT TO SCALE LONGITUDINAL ANCHOR TRENCH TERMINAL SLOPE AND CHANNEL ANCHOR TRENCH TAKE AT X-5'P TER VAL5. CHECK SLOT AT 25' INTERVALS INITIAL CHANNEL ANCHOR TRENCH INTERMITTENT CHECK SLOT Notes: 1. Check slots to be constructed per manufacturers specifications. (Clackamas County et al., 2008) 2. Staking or stapling layout per manufacturers specifications. Channel Installation Revised July 2016 DEPARTMENT OF ECOLOGY Please see http.'1Avww.ecy.wa.gov/cop3aVht.html for copyright notice including permissions, State of Washington limitation of liability, and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume /I - Chapter 3 - Page 296 Figure II-3.4: Slope Installation Notes: 1. Slope surface shall be smooth before placement for proper soil contact. 2. Stapling pattern as per manufacturers recommendations. 3. Do not stretch blankets/mattings tight - allow the rolls to mold to any irregularities. 4. For slopes less than 3HAV, rolls may be placed in horizontal strips. 5. If there is a berm at the top of the slope, anchor upslope of the berm. 6. Lime, fertilize, and seed before installation. Planting of shrubs, trees, etc. should occur after installation. DEPARTMENT OF ECOLOGY State of Washington area, turn the end under 4" and staple at 12" intervals Slope Installation NOT TO SCALE Revised June 2016 Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, limitation of liability, and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 297 BMP C123: Plastic Covering Purpose Plastic covering provides immediate, short-term erosion protection to slopes and disturbed areas. Conditions of Use Plastic covering may be used on disturbed areas that require cover measures for less than 30 days, except as stated below. • Plastic is particularly useful for protecting cut and fill slopes and stockpiles. However, the rel- atively rapid breakdown of most polyethylene sheeting makes it unsuitable for applications greater than six months. • Due to rapid runoff caused by plastic covering, do not use this method upslope of areas that might be adversely impacted by concentrated runoff. Such areas include steep and/or unstable slopes. • Plastic sheeting may result in increased runoff volumes and velocities, requiring additional on - site measures to counteract the increases. Creating a trough with wattles or other material can convey clean water away from these areas. . To prevent undercutting, trench and backfill rolled plastic covering products. . Although the plastic material is inexpensive to purchase, the cost of installation, maintenance, removal, and disposal add to the total costs of this BMP. • Whenever plastic is used to protect slopes, install water collection measures at the base of the slope. These measures include plastic -covered berms, channels, and pipes used to convey clean rainwater away from bare soil and disturbed areas. Do not mix clean runoff from a plastic covered slope with dirty runoff from a project. . Other uses for plastic include: • Temporary ditch liner. • Pond liner in temporary sediment pond. • Liner for bermed temporary fuel storage area if plastic is not reactive to the type of fuel being stored. • Emergency slope protection during heavy rains. • Temporary drainpipe ("elephant trunk") used to direct water. Design and Installation Specifications Plastic slope cover must be installed as follows: 1. Run plastic up and down the slope, not across the slope. 2. Plastic maybe installed perpendicular to a slope if the slope length is less than 10 feet. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 298 3. Provide a minimum of 8-inch overlap at the seams. 4. On long or wide slopes, or slopes subject to wind, tape all seams. 5. Place plastic into a small (12-inch wide by 6-inch deep) slot trench at the top of the slope and backfill with soil to keep water from flowing underneath. 6. Place sand filled burlap or geotextile bags every 3 to 6 feet along seams and tie them together with twine to hold them in place. 7. Inspect plastic for rips, tears, and open seams regularly and repair immediately. This prevents high velocity runoff from contacting bare soil, which causes extreme erosion. 8. Sandbags may be lowered into place tied to ropes. However, all sandbags must be staked in place. • Plastic sheeting shall have a minimum thickness of 0.06 millimeters. . If erosion at the toe of a slope is likely, a gravel berm, riprap, or other suitable protection shall be installed at the toe of the slope in order to reduce the velocity of runoff. Maintenance Standards . Torn sheets must be replaced and open seams repaired. • Completely remove and replace the plastic if it begins to deteriorate due to ultraviolet radi- ation. • Completely remove plastic when no longer needed. • Dispose of old tires used to weight down plastic sheeting appropriately. Approved as Functionally Equivalent Ecology has approved products as able to meet the requirements of this BMP. The products did not pass through the Technology Assessment Protocol — Ecology (TAPE) process. Local jurisdictions may choose not to accept these products, or may require additional testing prior to consideration for local use. Products that Ecology has approved as functionally equivalent are available for review on Ecology's website at: https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per- mittee-guidance-resources/Emerging-stormwater-treatment-technologies 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 299 BMP C151: Concrete Handling Purpose Concrete work can generate process water and slurry that contain fine particles and high pH, both of which can violate water quality standards in the receiving water. Concrete spillage or concrete dis- charge to waters of the State is prohibited. Use this BMP to minimize and eliminate concrete, con- crete process water, and concrete slurry from entering waters of the State. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 315 Conditions of Use Any time concrete is used, utilize these management practices. Concrete construction project com- ponents include, but are not limited to: • Curbs . Sidewalks • Roads • Bridges • Foundations • Floors • Runways Disposal options for concrete, in order of preference are: 1. Off -site disposal 2. Concrete wash -out areas (see BMP C154: Concrete Washout Area) 3. De minimus washout to formed areas awaiting concrete Design and Installation Specifications Wash concrete truck drums at an approved off -site location or in designated concrete washout areas only. Do not wash out concrete trucks onto the ground (including formed areas awaiting concrete), or into storm drains, open ditches, streets, or streams. Refer to BMP_ C 154: Concrete Washout Area for information on concrete washout areas. Return unused concrete remaining in the truck and pump to the originating batch plant for recycling. Do not dump excess concrete on site, except in designated concrete washout areas as allowed in BMP C154: Concrete Washout Area. • Wash small concrete handling equipment (e.g. hand tools, screeds, shovels, rakes, floats, trowels, and wheelbarrows) into designated concrete washout areas or into formed areas awaiting concrete pour. . At no time shall concrete be washed off into the footprint of an area where an infiltration fea- ture will be installed. • Wash equipment difficult to move, such as concrete paving machines, in areas that do not dir- ectly drain to natural or constructed stormwater conveyance or potential infiltration areas. • Do not allow washwater from areas, such as concrete aggregate driveways, to drain directly (without detention or treatment) to natural or constructed stormwater conveyances. • Contain washwater and leftover product in a lined container when no designated concrete washout areas (or formed areas, allowed as described above) are available. Dispose of con- tained concrete and concrete washwater (process water) properly. 2019 Stormwater Management Manual for Western Washington Volume ll - Chapter 3 - Page 316 . Always use forms or solid barriers for concrete pours, such as pilings, within 15-feet of surface waters. Refer to BMP C252: Treating and Disposing of High pH Water for pH adjustment require- ments. Refer to the Construction Stormwater General Permit (CSWGP) for pH monitoring require- ments if the project involves one of the following activities: Significant concrete work (as defined in the CSWGP) The use of soils amended with (but not limited to) Portland cement -treated base, cement kiln dust or fly ash. Discharging stormwater to segments of water bodies on the 303(d) list (Category 5) for high pH. Maintenance Standards Check containers for holes in the liner daily during concrete pours and repair the same day. BMP C152: Sawcutting and Surfacing Pollution Prevention Purpose Sawcutting and surfacing operations generate slurry and process water that contains fine particles and high pH (concrete cutting), both of which can violate the water quality standards in the receiving water. Concrete spillage or concrete discharge to waters of the State is prohibited. Use this BMP to minimize and eliminate process water and slurry created through sawcutting or surfacing from enter- ing waters of the State. Conditions of Use Utilize these management practices anytime sawcutting or surfacing operations take place. Saw - cutting and surfacing operations include, but are not limited to: • Sawing • Coring • Grinding . Roughening • Hydro -demolition • Bridge and road surfacing 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 317 Design and Installation Specifications . Vacuum slurry and cuttings during cutting and surfacing operations. . Slurry and cuttings shall not remain on permanent concrete or asphalt pavement overnight. . Slurry and cuttings shall not drain to any natural or constructed drainage conveyance includ- ing stormwater systems. This may require temporarily blocking catch basins. • Dispose of collected slurry and cuttings in a manner that does not violate ground water or sur- face water quality standards. • Do not allow process water generated during hydro -demolition, surface roughening or similar operations to drain to any natural or constructed drainage conveyance including stormwater systems. Dispose of process water in a manner that does not violate ground water or surface water quality standards. • Handle and dispose of cleaning waste material and demolition debris in a manner that does not cause contamination of water. Dispose of sweeping material from a pick-up sweeper at an appropriate disposal site. Maintenance Standards Continually monitor operations to determine whether slurry, cuttings, or process water could enter waters of the state. If inspections show that a violation of water quality standards could occur, stop operations and immediately implement preventive measures such as berms, barriers, secondary containment, and/or vacuum trucks. BMP C153: Material Delivery, Storage, and Containment Purpose Prevent, reduce, or eliminate the discharge of pollutants to the stormwater system or watercourses from material delivery and storage. Minimize the storage of hazardous materials on -site, store mater- ials in a designated area, and install secondary containment. Conditions of Use Use at construction sites with delivery and storage of the following materials: • Petroleum products such as fuel, oil and grease • Soil stabilizers and binders (e.g., Polyacrylamide) • Fertilizers, pesticides and herbicides • Detergents . Asphalt and concrete compounds 2019 Stormwater Management Manual for Western Washington Volume // - Chapter 3 - Page 318 • Hazardous chemicals such as acids, lime, adhesives, paints, solvents, and curing compounds . Any other material that maybe detrimental if released to the environment Design and Installation Specifications . The temporary storage area should be located away from vehicular traffic, near the con- struction entrance(s), and away from waterways or storm drains. . Safety Data Sheets (SDS) should be supplied for all materials stored. Chemicals should be kept in their original labeled containers. • Hazardous material storage on -site should be minimized. • Hazardous materials should be handled as infrequently as possible. • During the wet weather season (Oct 1 — April 30), consider storing materials in a covered area. • Materials should be stored in secondary containments, such as an earthen dike, horse trough, or even a children's wading pool for non -reactive materials such as detergents, oil, grease, and paints. Small amounts of material may be secondarily contained in "bus boy" trays or con- crete mixing trays. • Do not store chemicals, drums, or bagged materials directly on the ground. Place these items on a pallet and, when possible, within secondary containment. . If drums must be kept uncovered, store them at a slight angle to reduce ponding of rainwater on the lids to reduce corrosion. Domed plastic covers are inexpensive and snap to the top of drums, preventing water from collecting. • Liquids, petroleum products, and substances listed in 40 CFR Parts 110, 117, or 302 shall be stored in approved containers and drums and shall not be overfilled. Containers and drums shall be stored in temporary secondary containment facilities. . Temporary secondary containment facilities shall provide for a spill containment volume able to contain 10% of the total enclosed container volume of all containers, or 110% of the capa- city of the largest container within its boundary, whichever is greater. • Secondary containment facilities shall be impervious to the materials stored therein for a min- imum contact time of 72 hours. • Sufficient separation should be provided between stored containers to allow for spill cleanup and emergency response access. • During the wet weather season (Oct 1 — April 30), each secondary containment facility shall be covered during non -working days, prior to and during rain events. . Keep material storage areas clean, organized and equipped with an ample supply of appro- priate spill clean-up material (spill kit). . The spill kit should include, at a minimum: 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 319 1-Water Resistant Nylon Bag 3-Oil Absorbent Socks Yx 4' 2-Oil Absorbent Socks 3" x 10' O 12-Oil Absorbent Pads 17"xl9" 1-Pair Splash Resistant Goggles o 3-Pair Nitrile Gloves 10-Disposable Bags with Ties Instructions Maintenance Standards • Secondary containment facilities shall be maintained free of accumulated rainwater and spills. In the event of spills or leaks, accumulated rainwater and spills shall be collected and placed into drums. These liquids shall be handled as hazardous waste unless testing determines them to be non -hazardous. • Re -stock spill kit materials as needed. BMP C154: Concrete Washout Area Purpose Prevent or reduce the discharge of pollutants from concrete waste to stormwater by conducting washout off -site, or performing on -site washout in a designated area. Conditions of Use Concrete washout areas are implemented on construction projects where: • Concrete is used as a construction material . It is not possible to dispose of all concrete wastewater and washout off -site (ready mix plant, etc.). • Concrete truck drums are washed on -site. Note that auxiliary concrete truck components (e.g. chutes and hoses) and small concrete handling equipment (e.g. hand tools, screeds, shovels, rakes, floats, trowels, and wheel- barrows) may be washed into formed areas awaiting concrete pour. At no time shall concrete be washed off into the footprint of an area where an infiltration feature will be installed. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 320 Design and Installation Specifications Implementation • Perform washout of concrete truck drums at an approved off -site location or in designated con- crete washout areas only. • Do not wash out concrete onto non -formed areas, or into storm drains, open ditches, streets, or streams. • Wash equipment difficult to move, such as concrete paving machines, in areas that do not dir- ectly drain to natural or constructed stormwater conveyance or potential infiltration areas. • Do not allow excess concrete to be dumped on -site, except in designated concrete washout areas as allowed above. • Concrete washout areas may be prefabricated concrete washout containers, or self -installed structures (above -grade or below -grade). • Prefabricated containers are most resistant to damage and protect against spills and leaks. Companies may offer delivery service and provide regular maintenance and disposal of solid and liquid waste. . If self -installed concrete washout areas are used, below -grade structures are preferred over above -grade structures because they are less prone to spills and leaks. . Self -installed above -grade structures should only be used if excavation is not practical. • Concrete washout areas shall be constructed and maintained in sufficient quantity and size to contain all liquid and concrete waste generated by washout operations. Education • Discuss the concrete management techniques described in this BMP with the ready -mix con- crete supplier before any deliveries are made. • Educate employees and subcontractors on the concrete waste management techniques described in this BMP. . Arrange for the contractor's superintendent or Certified Erosion and Sediment Control Lead (CESCL) to oversee and enforce concrete waste management procedures. . A sign should be installed adjacent to each concrete washout area to inform concrete equip- ment operators to utilize the proper facilities. Contracts Incorporate requirements for concrete waste management into concrete supplier and subcontractor agreements. 2019 Stormwater Management Manual for Western Washington Volume ll - Chapter 3 - Page 321 Location and Placement • Locate concrete washout areas at least 50 feet from sensitive areas such as storm drains, open ditches, water bodies, or wetlands. . Allow convenient access to the concrete washout area for concrete trucks, preferably near the area where the concrete is being poured. . If trucks need to leave a paved area to access the concrete washout area, prevent track -out with a pad of rock or quarry spalls (see BMP C105: Stabilized Construction Access). These areas should be far enough away from other construction traffic to reduce the likelihood of acci- dental damage and spills. . The number of concrete washout areas you install should depend on the expected demand for storage capacity. . On large sites with extensive concrete work, concrete washout areas should be placed in mul- tiple locations for ease of use by concrete truck drivers. Concrete Truck Washout Procedures Washout of concrete truck drums shall be performed in designated concrete washout areas only. Concrete washout from concrete pumper bins can be washed into concrete pumper trucks and discharged into designated concrete washout areas or properly disposed of off -site. Concrete Washout Area Installation • Concrete washout areas should be constructed as shown in the figures below, with a recom- mended minimum length and minimum width of 10 ft, but with sufficient quantity and volume to contain all liquid and concrete waste generated by washout operations. • Plastic lining material should be a minimum of 10 mil polyethylene sheeting and should be free of holes, tears, or other defects that compromise the impermeability of the material. • Lath and flagging should be commercial type. • Liner seams shall be installed in accordance with manufacturers' recommendations. • Soil base shall be prepared free of rocks or other debris that may cause tears or holes in the plastic lining material. Maintenance Standards Inspection and Maintenance . Inspect and verify that concrete washout areas are in place prior to the commencement of con- crete work. . Once concrete wastes are washed into the designated washout area and allowed to harden, 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 322 the concrete should be broken up, removed, and disposed of per applicable solid waste reg- ulations. Dispose of hardened concrete on a regular basis. • During periods of concrete work, inspect the concrete washout areas daily to verify continued performance. • Check overall condition and performance. • Check remaining capacity (% full). • If using self -installed concrete washout areas, verify plastic liners are intact and side - walls are not damaged. • If using prefabricated containers, check for leaks. • Maintain the concrete washout areas to provide adequate holding capacity with a minimum freeboard of 12 inches. • Concrete washout areas must be cleaned, or new concrete washout areas must be con- structed and ready for use once the concrete washout area is 75% full. If the concrete washout area is nearing capacity, vacuum and dispose of the waste material in an approved manner. • Do not discharge liquid or slurry to waterways, storm drains or directly onto ground. • Do not discharge to the sanitary sewer without local approval. • Place a secure, non -collapsing, non -water collecting cover over the concrete washout area prior to predicted wet weather to prevent accumulation and overflow of pre- cipitation. • Remove and dispose of hardened concrete and return the structure to a functional con- dition. Concrete may be reused on -site or hauled away for disposal or recycling. When you remove materials from a self -installed concrete washout area, build a new struc- ture; or, if the previous structure is still intact, inspect for signs of weakening or damage, and make any necessary repairs. Re -line the structure with new plastic after each cleaning. Removal of Concrete Washout Areas • When concrete washout areas are no longer required for the work, the hardened concrete, slurries and liquids shall be removed and properly disposed of. • Materials used to construct concrete washout areas shall be removed from the site of the work and disposed of or recycled. Holes, depressions or other ground disturbance caused by the removal of the concrete washout areas shall be backfilled, repaired, and stabilized to prevent erosion. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 323 Figure II-3.7: Concrete Washout Area with Wood Planks Plan Lath and flagging on 3 sides Sandbag 3erm Sandbag 10 mil plastic lining A 1m ,r %• '' Berm Section A -A Type "Below Grade" Notes: 1. Actual layout determined in the field. 2. A concrete washout sign shall be installed within 10 m of the temporary concrete washout facility. Wood frame B securely fastened around entire perimeter with two stakes 10 mil f plastic lining Stake (typ.) iil plastic lining 2x12 rough Plan wood frame Tvae "Above Grade" with Wood Planks NOT TO SCALE Concrete Washout Area with Wood Planks Revised June 2016 DEPARTMENT OF ECOLOGYplease see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, State of Washington limitation of liability, and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 324 Figure II-3.8: Concrete Washout Area with Straw Bales Straw bale astic lining Binding wire Staples material (2 per bale) L'ol) Wood or Plywood metal stakes 1200 mm x 610 mm Wood post (2 per bale) painted white (89 mm x 89 mm Lag screws x 2.4 m) Section B-B r. (12.5 mm) iCONCRETEi I Black letters WASHOUT , 1 l o 150 mm height 915 mm 1 3m Minimum Stake (typ) B� Varies ■ Straw bale J (typ•) DEPARTMENT OF ECOLOGY State of Washington Plan tIu u 915 mm Concrete Washout Sign Detail (or equivalent) �B 50 mm 200 mm �` 3.05 mm dia. steel wire Staple Detail 10 mil plastic lining Notes: 1. Actual layout determined in the field. 2. The concrete washout sign shall be installed within 10 m of the temporary concrete washout facility. Type "Above Grade" with Straw Bales NOT TO SCALE Concrete Washout Area with Straw Bales Revised June 2016 Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, limitation of liability, and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 325 Figure 11-3.9: Prefabricated Concrete Washout Container w/Ramp DEPARTMENT OF ECOLOGY State of Washington NOT TO SCALE Prefabricated Concrete Washout Container w/Ramp Revised June 2016 Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, limitation of liability, and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 326 BMP C220: Inlet Protection Purpose Inlet protection prevents coarse sediment from entering drainage systems prior to permanent sta- bilization of the disturbed area. Conditions of Use Use inlet protection at inlets that are operational before permanent stabilization of the disturbed areas that contribute runoff to the inlet. Provide protection for all storm drain inlets downslope and within 500 feet of a disturbed or construction area, unless those inlets are preceded by a sediment trapping BMP. Also consider inlet protection for lawn and yard drains on new home construction. These small and numerous drains coupled with lack of gutters can add significant amounts of sediment into the roof drain system. If possible, delay installing lawn and yard drains until just before landscaping, or cap these drains to prevent sediment from entering the system until completion of landscaping. Provide 18-inches of sod around each finished lawn and yard drain. Table II-3.10: Storm Drain Inlet Protection lists several options for inlet protection. All of the methods for inlet protection tend to plug and require a high frequency of maintenance. Limit contributing drain- age areas for an individual inlet to one acre or less. If possible, provide emergency overflows with additional end -of -pipe treatment where stormwater ponding would cause a hazard. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 356 Table 11-3.10: Storm Drain Inlet Protection Type of Inlet Pro- Emergency Applicable for tection Overflow Paved/ Earthen Sur- Conditions of Use faces Drop Inlet Protection Yes, temporary Applicable for heavy flows. Easy Excavated drop flooding may Earthen to maintain. Large area requirement: inlet protection occur 30'x30'/acre Block and gravel Applicable for heavy concentrated flows. drop inlet pro- Yes Paved or Earthen Will not pond. tection Gravel and wire Applicable for heavy concentrated flows. drop inlet pro- No Paved or Earthen Will pond. Can withstand traffic. tection Catch basin filters Yes Paved or Earthen Frequent maintenance required. Curb Inlet Protection Curb inlet pro- Small capacity Used for sturdy, more compact install- tection with overflow Paved ation. wooden weir Block and gravel curb inlet pro- Yes Paved Sturdy, but limited filtration. tection Culvert Inlet Protection Culvert inlet sed- N/A N/A 18 month expected life. iment trap Design and Installation Specifications Excavated Drop Inlet Protection Excavated drop inlet protection consists of an excavated impoundment around the storm drain inlet. Sediment settles out of the stormwater prior to entering the storm drain. Design and installation spe- cifications for excavated drop inlet protection include: . Provide a depth of 1-2 ft as measured from the crest of the inlet structure. . Slope sides of excavation should be no steeper than 2H:1 V. . Minimum volume of excavation is 35 cubic yards. Shape the excavation to fit the site, with the longest dimension oriented toward the longest inflow area. . Install provisions for draining to prevent standing water. . Clear the area of all debris. 2019 Stormwater Management Manual for Western Washington Volume 11- Chapter 3 - Page 357 • Grade the approach to the inlet uniformly. • Drill weep holes into the side of the inlet. • Protect weep holes with screen wire and washed aggregate. • Seal weep holes when removing structure and stabilizing area. • Build a temporary dike, if necessary, to the down slope side of the structure to prevent bypass flow. Block and Gravel Filter A block and gravel filter is a barrier formed around the inlet with standard concrete blocks and gravel. See Figure II-3.17: Block and Gravel Filter. Design and installation specifications for block gravel fil- ters include: • Provide a height of 1 to 2 feet above the inlet. • Recess the first row of blocks 2-inches into the ground for stability. • Support subsequent courses by placing a pressure treated wood 2x4 through the block open- ing. • Do not use mortar. • Lay some blocks in the bottom row on their side to allow for dewatering the pool. • Place hardware cloth or comparable wire mesh with'/2-inch openings over all block openings. • Place gravel to just below the top of blocks on slopes of 2H:1 V or flatter. . An alternative design is a gravel berm surrounding the inlet, as follows: • Provide a slope of 3H:1 V on the upstream side of the berm. • Provide a slope of 2H:1 V on the downstream side of the berm. • Provide a 1-foot wide level stone area between the gravel berm and the inlet. Use stones 3 inches in diameter or larger on the upstream slope of the berm. Use gravel'/2- to 3/4-inch at a minimum thickness of 1-foot on the downstream slope of the berm. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 358 Figure II-3.17: Block and Gravel Filter Drain grate a �595 CPC In, Plan View crete block Gravel backfill Concrete block Wire screen or filter fabric Gravel backfill Overflow waterer —I�� (�Ponding height on o9'� IIWaterl II I I I I n ^� fino Drop inlet Section A -A Notes: 1. Drop inlet sediment barriers are to be used for small, nearly level drainage areas. (less than 5%) 2. Excavate a basin of sufficient size adjacent to the drop inlet. 3. The top of the structure (ponding height) must be well below the ground elevation downslope to prevent runoff from bypassing the inlet. A temporary dike may be necessary on the downslope side of the structure. NOT TO SCALE Block and Gravel Filter Revised June 2016 DEPARTMENT OF ECOLOGYPlease see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, State of Washington limitation of liability, and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 359 Gravel and Wire Mesh Filter Gravel and wire mesh filters are gravel barriers placed over the top of the inlet. This method does not provide an overflow. Design and installation specifications for gravel and wire mesh filters include: • Use a hardware cloth or comparable wire mesh with'/2-inch openings. Place wire mesh over the drop inlet so that the wire extends a minimum of 1-foot bey- ond each side of the inlet structure. Overlap the strips if more than one strip of mesh is necessary. • Place coarse aggregate over the wire mesh. Provide at least a 12-inch depth of aggregate over the entire inlet opening and extend at least 18-inches on all sides. Catch Basin Filters Catch basin filters are designed by manufacturers for construction sites. The limited sediment stor- age capacity increases the amount of inspection and maintenance required, which may be daily for heavy sediment loads. To reduce maintenance requirements, combine a catch basin filter with another type of inlet protection. This type of inlet protection provides flow bypass without overflow and therefore may be a better method for inlets located along active rights -of -way. Design and install- ation specifications for catch basin filters include: • Provides 5 cubic feet of storage. • Requires dewatering provisions. • Provides a high -flow bypass that will not clog under normal use at a construction site. . Insert the catch basin filter in the catch basin just below the grating. Curb Inlet Protection with Wooden Weir Curb inlet protection with wooden weir is an option that consists of a barrier formed around a curb inlet with a wooden frame and gravel. Design and installation specifications for curb inlet protection with wooden weirs include: • Use wire mesh with'/2-inch openings. • Use extra strength filter cloth. • Construct a frame. . Attach the wire and filter fabric to the frame. • Pile coarse washed aggregate against the wire and fabric. • Place weight on the frame anchors. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 360 Block and Gravel Curb Inlet Protection Block and gravel curb inlet protection is a barrier formed around a curb inlet with concrete blocks and gravel. See Figure 11-3.18: Block and Gravel Curb Inlet Protection. Design and installation spe- cifications for block and gravel curb inlet protection include: • Use wire mesh with'/2-inch openings. • Place two concrete blocks on their sides abutting the curb at either side of the inlet opening. These are spacer blocks. • Place a 2A stud through the outer holes of each spacer block to align the front blocks. • Place blocks on their sides across the front of the inlet and abutting the spacer blocks. • Place wire mesh over the outside vertical face. • Pile coarse aggregate against the wire to the top of the barrier. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 361 Figure II-3.18: Block and Gravel Curb Inlet Protection n Back of sidewalk Back of curb Wire scre filter %a << . Drain gravel Plan View 3/4 inch (20 mm) Drain gravel Wire screen or filter fabric 2x4 Wood stud (100x50 Timber stud) Ponding height Overflow ANNow Catch basin Concrete block ud block Section A -A Notes: 1. Use block and gravel type sediment barrier when curb inlet is located in gently sloping street segment, where water can pond and allow sediment to separate from runoff. 2. Barrier shall allow for overflow from severe storm event. 3. Inspect barriers and remove sediment after each storm event. Sediment and gravel must be removed from the traveled way immediately. NOT TO SCALE Block and Gravel Curb Inlet Protection Revised June 2016 DEPARTMENT OF ECOLOGYPlease see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, State of Washington limitation of liability, and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 362 Curb and Gutter Sediment Barrier Curb and gutter sediment barrier is a sandbag or rock berm (riprap and aggregate) 3 feet high and 3 feet wide in a horseshoe shape. See Figure II-3.19: Curb and Gutter Barrier. Design and installation specifications for curb and gutter sediment barrier include: Construct a horseshoe shaped berm, faced with coarse aggregate if using riprap, 3 feet high and 3 feet wide, at least 2 feet from the inlet. . Construct a horseshoe shaped sedimentation trap on the upstream side of the berm. Size the trap to sediment trap standards for protecting a culvert inlet. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 363 Figure II-3.19: Curb and Gutter Barrier Back of sidewalk Burlap sacks to overlap onto curb Back of curb Runoff � " I��1-- Curb inlet Runoff Spillway Catch basin Plan View Gravel filled sandbags stacked tightly Notes: 1. Place curb type sediment barriers on gently sloping street segments, where water can pond and allow sediment to separate from runoff. 2. Sandbags of either burlap or woven 'geotextile' fabric, are filled with gravel, layered and packed tightly. 3. Leave a one sandbag gap in the top row to provide a spillway for overflow. 4. Inspect barriers and remove sediment after each storm event. Sediment and gravel must be removed from the traveled way immediately. NOT TO SCALE DEPARTMENT OF ECOLOGY State of Washington Curb and Gutter Barrier Revised June 2016 Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, limitation of liability, and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 364 Maintenance Standards Inspect all forms of inlet protection frequently, especially after storm events. Clean and replace clogged catch basin filters. For rock and gravel filters, pull away the rocks from the inlet and clean or replace. An alternative approach would be to use the clogged rock as fill and put fresh rock around the inlet. Do not wash sediment into storm drains while cleaning. Spread all excavated material evenly over the surrounding land area or stockpile and stabilize as appropriate. Approved as Functionally Equivalent Ecology has approved products as able to meet the requirements of this BMP. The products did not pass through the Technology Assessment Protocol — Ecology (TAPE) process. Local jurisdictions may choose not to accept these products, or may require additional testing prior to consideration for local use. Products that Ecology has approved as functionally equivalent are available for review on Ecology's website at: https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per- mittee-guidance-resources/Emerging-stormwater-treatment-technologies 2019 Stormwater Management Manual for Western Washington Volume // - Chapter 3 - Page 365 BMP C233: Silt Fence Purpose Silt fence reduces the transport of coarse sediment from a construction site by providing a temporary physical barrier to sediment and reducing the runoff velocities of overland flow. Conditions of Use Silt fence may be used downslope of all disturbed areas. Silt fence shall prevent sediment carried by runoff from going beneath, through, or over the top of the silt fence, but shall allow the water to pass through the fence. Silt fence is not intended to treat concentrated flows, nor is it intended to treat substantial amounts of overland flow. Convey any concentrated flows through the drainage system to a sediment trapping BMP. Do not construct silt fences in streams or use in V-shaped ditches. Silt fences do not provide an adequate method of silt control for anything deeper than sheet or overland flow. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 370 Figure 11-3.22: Silt Fence Joints in geotextile fabric shall be spliced at posts. Use staples, wire rings or equivalent to attach fabric to posts 2"x2" by 14 Ga. wire or equivalent, if standard strength fabric used —:\—\i\—�i1�\LLB%`\\/.��i�\/\\!`\ Minimum I I 6' max I I 4"x4" trench u Post spacing may be increased to 8' if wire backing is used 2"x2" wood posts, steel fence posts, or equivalent DEPARTMENT OF ECOLOGY State of Washington 2"x2" by 14 Ga. wire or equivalent, if standard strength fabric used Geotextile fabric 2' min Backfill trench with native soil or 4" - /\� 1.5" washed gravel �j12' min Minimum 47x4" trench 27x2" wood posts, steel fence posts, or equivalent Silt Fence NOT TO SCALE Revised July 2017 Please see http://www.ecy.wa.gov/cop3aVht.html for copyright notice including permissions, limitation of liability, and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 371 Design and Installation Specifications . Use in combination with other construction stormwater BMPs. Maximum slope steepness (perpendicular to the silt fence line) 1 H:1 V. Maximum sheet or overland flow path length to the silt fence of 100 feet. Do not allow flows greater than 0.5 cfs. Use geotextile fabric that meets the following standards. All geotextile properties listed below are minimum average roll values (i.e., the test result for any sampled roll in a lot shall meet or exceed the values shown in Table 11-3.11: Geotextile Fabric Standards for Silt Fence): Table II-3.11: Geotextile Fabric Standards for Silt Fence Geotextile Property Minimum Average Roll Value 0.60 mm maximum for slit film woven (#30 sieve). Polymeric Mesh AOS 0.30 mm maximum for all other geotextile types (#50 sieve). (ASTM D4751) 0.15 mm minimum for all fabric types (#100 sieve). Water Permittivity 0.02 sec-1 minimum (ASTM D4491) Grab Tensile Strength 180 lbs. Minimum for extra strength fabric. (ASTM D4632) 100 Ibs minimum for standard strength fabric. Grab Tensile Strength 30% maximum (ASTM D4632) Ultraviolet Resistance 70% minimum (ASTM D4355) Support standard strength geotextiles with wire mesh, chicken wire, 2-inch x 2-inch wire, safety fence, or jute mesh to increase the strength of the geotextile. Silt fence materials are available that have synthetic mesh backing attached. . Silt fence material shall contain ultraviolet ray inhibitors and stabilizers to provide a minimum of six months of expected usable construction life at a temperature range of 0°F to 120°F. One -hundred percent biodegradable silt fence is available that is strong, long lasting, and can be left in place after the project is completed, if permitted by the local jurisdiction. Refer to Figure 11-3.22: Silt Fence for standard silt fence details. Include the following Stand- ard Notes for silt fence on construction plans and specifications: The Contractor shall install and maintain temporary silt fences at the locations shown in the Plans. 2. Construct silt fences in areas of clearing, grading, or drainage prior to starting those activities. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 372 3. The silt fence shall have a 2-feet min. and a 2'/2-feet max. height above the original ground surface. 4. The geotextile fabric shall be sewn together at the point of manufacture to form fabric lengths as required. Locate all sewn seams at support posts. Alternatively, two sections of silt fence can be overlapped, provided that the overlap is long enough and that the adjacent silt fence sections are close enough together to prevent silt laden water from escaping through the fence at the overlap. 5. Attach the geotextile fabric on the up -slope side of the posts and secure with staples, wire, or in accordance with the manufacturer's recommendations. Attach the geotextile fabric to the posts in a manner that reduces the potential for tearing. 6. Support the geotextile fabric with wire or plastic mesh, dependent on the properties of the geotextile selected for use. If wire or plastic mesh is used, fasten the mesh securely to the up -slope side of the posts with the geotextile fabric up -slope of the mesh. 7. Mesh support, if used, shall consist of steel wire with a maximum mesh spacing of 2- inches, or a prefabricated polymeric mesh. The strength of the wire or polymeric mesh shall be equivalent to or greater than 180 lbs. grab tensile strength. The polymeric mesh must be as resistant to the same level of ultraviolet radiation as the geotextile fabric it supports. 8. Bury the bottom of the geotextile fabric 4-inches min. below the ground surface. Backfill and tamp soil in place over the buried portion of the geotextile fabric, so that no flow can pass beneath the silt fence and scouring cannot occur. When wire or polymeric back-up support mesh is used, the wire or polymeric mesh shall extend into the ground 3-inches min. 9. Drive or place the silt fence posts into the ground 18-inches min. A 12—inch min. depth is allowed if topsoil or other soft subgrade soil is not present and 18-inches cannot be reached. Increase fence post min. depths by 6 inches if the fence is located on slopes of 3H :1 V or steeper and the slope is perpendicular to the fence. If required post depths cannot be obtained, the posts shall be adequately secured by bracing or guying to pre- vent overturning of the fence due to sediment loading. 10. Use wood, steel or equivalent posts. The spacing of the support posts shall be a max- imum of 6-feet. Posts shall consist of either: • Wood with minimum dimensions of 2 inches by 2 inches by 3 feet. Wood shall be free of defects such as knots, splits, or gouges. . No. 6 steel rebar or larger. . ASTM A 120 steel pipe with a minimum diameter of 1-inch. • U, T, L, or C shape steel posts with a minimum weight of 1.35 lbs./ft. • Other steel posts having equivalent strength and bending resistance to the post sizes listed above. 11. Locate silt fences on contour as much as possible, except at the ends of the fence, 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 373 where the fence shall be turned uphill such that the silt fence captures the runoff water and prevents water from flowing around the end of the fence. 12. If the fence must cross contours, with the exception of the ends of the fence, place check dams perpendicular to the back of the fence to minimize concentrated flow and erosion. The slope of the fence line where contours must be crossed shall not be steeper than 3H:1 V. . Check dams shall be approximately 1-foot deep at the back of the fence. Check dams shall be continued perpendicular to the fence at the same elevation until the top of the check dam intercepts the ground surface behind the fence. . Check dams shall consist of crushed surfacing base course, gravel backfill for walls, or shoulder ballast. Check dams shall be located every 10 feet along the fence where the fence must cross contours. Refer to Figure II-3.23: Silt Fence Installation by Slicing Method for slicing method details. The following are specifications for silt fence installation using the slicing method: 1. The base of both end posts must be at least 2- to 4-inches above the top of the geo- textile fabric on the middle posts for ditch checks to drain properly. Use a hand level or string level, if necessary, to mark base points before installation. 2. Install posts 3- to 4-feet apart in critical retention areas and 6- to 7-feet apart in standard applications. 3. Install posts 24-inches deep on the downstream side of the silt fence, and as close as possible to the geotextile fabric, enabling posts to support the geotextile fabric from upstream water pressure. 4. Install posts with the nipples facing away from the geotextile fabric. 5. Attach the geotextile fabric to each post with three ties, all spaced within the top 8- inches of the fabric. Attach each tie diagonally 45 degrees through the fabric, with each puncture at least 1-inch vertically apart. Each tie should be positioned to hang on a post nipple when tightening to prevent sagging. 6. Wrap approximately 6-inches of the geotextile fabric around the end posts and secure with 3 ties. 7. No more than 24-inches of a 36-inch geotextile fabric is allowed above ground level. 8. Compact the soil immediately next to the geotextile fabric with the front wheel of the tractor, skid steer, or roller exerting at least 60 pounds per square inch. Compact the upstream side first and then each side twice for a total of four trips. Check and correct the silt fence installation for any deviation before compaction. Use a flat -bladed shovel to tuck the fabric deeper into the ground if necessary. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 374 Figure 11-3.23: Silt Fence Installation by Slicing Method Ponding height max. 24" Attach fabric to upstream side of post FLOW - Drive over each side of silt fence 2 to 4 times with device exerting 60 p.s.i. or greater POST SPACING: 7' max. on open runs 4' max. on pooling areas POST DEPTH: As much below ground as fabric above ground 100% compaction 11 1 100% com N No more than 24" of a 36" fabric is allowed above ground Operation Horizontal chisel point (76 mm width) Top of Fabric ` Belt I# topy 8" f Diagonal attachment doubles strength Attachment Details: • Gather fabric at posts, if needed. • Utilize three ties per post, all within top 8" of fabric. • Position each tie diagonally, puncturing holes vertically a minimum of 1" apart. • Hang each tie on a post nipple and tighten securely. Use cable ties (50 Ibs) or soft wire. Roll of silt fence Slicing blade (18 mm width) Vibratory plow is not acceptable because of horizontal compaction DEPARTMENT OF ECOLOGY State of Washington Fabric above ground 200 - 300mm F Post installed after compaction Silt Fence Completed Installation NOT TO SCALE Silt Fence Installation by Slicing Method Revised June 2016 Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, limitation of liability, and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 375 Maintenance Standards • Repair any damage immediately. . Intercept and convey all evident concentrated flows uphill of the silt fence to a sediment trap- ping BMP. . Check the uphill side of the silt fence for signs of the fence clogging and acting as a barrier to flow and then causing channelization of flows parallel to the fence. If this occurs, replace the fence and remove the trapped sediment. • Remove sediment deposits when the deposit reaches approximately one-third the height of the silt fence, or install a second silt fence. • Replace geotextile fabric that has deteriorated due to ultraviolet breakdown. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 376 BMP C235: Wattles Purpose Wattles are temporary erosion and sediment control barriers consisting of straw, compost, or other material that is wrapped in netting made of natural plant fiber or similar encasing material. They reduce the velocity and can spread the flow of rill and sheet runoff, and can capture and retain sed- iment. Conditions of Use Wattles shall consist of cylinders of plant material such as weed -free straw, coir, wood chips, excelsior, or wood fiber or shavings encased within netting made of natural plant fibers unaltered by synthetic materials. . Use wattles: In disturbed areas that require immediate erosion protection. On exposed soils during the period of short construction delays, or over winter months. o On slopes requiring stabilization until permanent vegetation can be established. The material used dictates the effectiveness period of the wattle. Generally, wattles are effect- ive for one to two seasons. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 377 Prevent rilling beneath wattles by entrenching and overlapping wattles to prevent water from passing between them. Design Criteria . See Figure 11-3.24: Wattles for typical construction details. • Wattles are typically 8 to 10 inches in diameter and 25 to 30 feet in length. . Install wattles perpendicular to the flow direction and parallel to the slope contour. • Place wattles in shallow trenches, staked along the contour of disturbed or newly constructed slopes. Dig narrow trenches across the slope (on contour) to a depth of 3- to 5-inches on clay soils and soils with gradual slopes. On loose soils, steep slopes, and areas with high rainfall, the trenches should be dug to a depth of 5- to 7- inches, or 1 /2 to 2/3 of the thickness of the wattle. . Start building trenches and installing wattles from the base of the slope and work up. Spread excavated material evenly along the uphill slope and compact it using hand tamping or other methods. . Construct trenches at intervals of 10- to 25-feet depending on the steepness of the slope, soil type, and rainfall. The steeper the slope the closer together the trenches. . Install the wattles snugly into the trenches and overlap the ends of adjacent wattles 12 inches behind one another. . Install stakes at each end of the wattle, and at 4-foot centers along entire length of wattle. . If required, install pilot holes for the stakes using a straight bar to drive holes through the wattle and into the soil. • Wooden stakes should be approximately 0.75 x 0.75 x 24 inches min. Willow cuttings or 3/8- inch rebar can also be used for stakes. • Stakes should be driven through the middle of the wattle, leaving 2 to 3 inches of the stake pro- truding above the wattle. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 378 Figure II-3.24: Wattles Straw rolls must be placed along slope contours 10' - 25' (3-8m) Spacing depends on soil type and slope steepness Live Stake 7— 3' - 4' � f (1.2m) /// Sediment, organic matter, and native seeds are captured behind the rolls. 3" - 5" (75-125mm) V x 1" Stake l/ (25 x 25mm) Overlap adjacent rolls 12" behind one another 8" - 10" Dia. (200-250mm) wt NOTE: r 1. Straw roll installation requires the placement and secure staking of the roll in a trench, 3" - 5" (75-125mm) deep, dug on contour. Runoff must not be allowed to run under or around roll. NOT TO SCALE Wattles Revised December 2016 DEPARTMENT OF ECOLOGYplease see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, State of Washington limitation of liability, and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 379 Maintenance Standards Wattles may require maintenance to ensure they are in contact with soil and thoroughly entrenched, especially after significant rainfall on steep sandy soils. . Inspect the slope after significant storms and repair any areas where wattles are not tightly abutted or water has scoured beneath the wattles. Approved as Functionally Equivalent Ecology has approved products as able to meet the requirements of this BMP. The products did not pass through the Technology Assessment Protocol — Ecology (TAPE) process. Local jurisdictions may choose not to accept these products, or may require additional testing prior to consideration for local use. Products that Ecology has approved as functionally equivalent are available for review on Ecology's website at: https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per- mittee-guidance-resources/Emerging-stormwater-treatment-technologies 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 380 C. Correspondence Ecology EPA Local Government D. Site Inspection Form Construction Stormwater Site Inspection Form Project Name Permit # Inspection Date Name of Certified Erosion Sediment Control Lead (CESCL) or qualified inspector if less than one acre Print Name: Approximate rainfall amount since the last inspection (in inches): Approximate rainfall amount in the last 24 hours (in inches): Current Weather Clear ❑ Cloudy ❑ Mist ❑ Rain ❑ Wind ❑ Fog ❑ A. Type of inspection: Weekly ❑ Post Storm Event ❑ Other ❑ B. Phase of Active Construction (check all that apply): Pre Construction/installation of erosion/sediment controls Concrete pours Offsite improvements C. Questions: Time Clearing/Demo/Grading Infrastructure/storm/roads Vertical Utilities Construction/buildings Site temporary stabilized Final stabilization 1. Were all areas of construction and discharge points inspected? Yes No 2. Did you observe the presence of suspended sediment, turbidity, discoloration, or oil sheen Yes No 3. Was a water quality sample taken during inspection? (refer to permit conditions 54 & 55) Yes No 4. Was there a turbid discharge 250 NTU or greater, or Transparency 6 cm or less?* Yes No 5. If yes to #4 was it reported to Ecology? Yes No 6. Is pH sampling required? pH range required is 6.5 to 8.5. Yes No If answering yes to a discharge, describe the event. Include when, where, and why it happened; what action was taken, and when. *If answering yes to # 4 record NTU/Transparency with continual sampling daily until turbidity is 25 NTU or less/ transparency is 33 cm or greater. Sampling Results: Date: Parameter Method (circle one) Result Other/Note NTU cm pH Turbidity tube, meter, laboratory pH Paper, kit, meter Page 1 Construction Stormwater Site Inspection Form D. Check the observed status of all items. Provide "Action Required "details and dates. Element # Inspection BMPs BMP needs BMP Action Inspected maintenance failed required (describe in yes no n/a section F) 1 Before beginning land disturbing Clearing activities are all clearing limits, Limits natural resource areas (streams, wetlands, buffers, trees) protected with barriers or similar BMPs? (high visibility recommended) 2 Construction access is stabilized Construction with quarry spalls or equivalent Access BMP to prevent sediment from being tracked onto roads? Sediment tracked onto the road way was cleaned thoroughly at the end of the day or more frequent as necessary. 3 Are flow control measures installed Control Flow to control stormwater volumes and Rates velocity during construction and do they protect downstream properties and waterways from erosion? If permanent infiltration ponds are used for flow control during construction, are they protected from siltation? 4 All perimeter sediment controls Sediment (e.g. silt fence, wattles, compost Controls socks, berms, etc.) installed, and maintained in accordance with the Stormwater Pollution Prevention Plan (SWPPP). Sediment control BMPs (sediment ponds, traps, filters etc.) have been constructed and functional as the first step of grading. Stormwater runoff from disturbed areas is directed to sediment removal BMP. 5 Have exposed un-worked soils Stabilize been stabilized with effective BMP Soils to prevent erosion and sediment deposition? Page 2 Construction Stormwater Site Inspection Form Element # Inspection BMPs BMP needs BMP Action Inspected maintenance failed required (describe in yes no n/a section F) 5 Are stockpiles stabilized from erosion, Stabilize Soils protected with sediment trapping Cont. measures and located away from drain inlet, waterways, and drainage channels? Have soils been stabilized at the end of the shift, before a holiday or weekend if needed based on the weather forecast? Has stormwater and ground water 6 been diverted away from slopes and Protect disturbed areas with interceptor dikes, Slopes pipes and or swales? Is off -site storm water managed separately from stormwater generated on the site? Is excavated material placed on uphill side of trenches consistent with safety and space considerations? Have check dams been placed at regular intervals within constructed channels that are cut down a slope? 7 Storm drain inlets made operable Drain Inlets during construction are protected. Are existing storm drains within the influence of the project protected? 8 Have all on -site conveyance channels Stabilize been designed, constructed and Channel and stabilized to prevent erosion from Outlets expected peak flows? Is stabilization, including armoring material, adequate to prevent erosion of outlets, adjacent stream banks, slopes and downstream conveyance systems? 9 Are waste materials and demolition Control debris handled and disposed of to Pollutants prevent contamination of stormwater? Has cover been provided for all chemicals, liquid products, petroleum products, and other material? Has secondary containment been provided capable of containing 110% of the volume? Were contaminated surfaces cleaned immediately after a spill incident? Were BMPs used to prevent contamination of stormwater by a pH modifying sources? Page 3 Construction Stormwater Site Inspection Form Element # Inspection BMPs BMP needs BMP Action Inspected maintenance failed required (describe in yes no n/a section F) 9 Wheel wash wastewater is handled Cont. and disposed of properly. 10 Concrete washout in designated areas. Control No washout or excess concrete on the Dewatering ground. Dewatering has been done to an approved source and in compliance with the SWPPP. Were there any clean non turbid dewatering discharges? 11 Are all temporary and permanent Maintain erosion and sediment control BMPs BMP maintained to perform as intended? 12 Has the project been phased to the Manage the maximum degree practicable? Project Has regular inspection, monitoring and maintenance been performed as required by the permit? Has the SWPPP been updated, implemented and records maintained? 13 Is all Bioretention and Rain Garden Protect LID Facilities protected from sedimentation with appropriate BMPs? Is the Bioretention and Rain Garden protected against over compaction of construction equipment and foot traffic to retain its infiltration capabilities? Permeable pavements are clean and free of sediment and sediment laden - water runoff. Muddy construction equipment has not been on the base material or pavement. Have soiled permeable pavements been cleaned of sediments and pass infiltration test as required by stormwater manual methodology? Heavy equipment has been kept off existing soils under LID facilities to retain infiltration rate. E. Check all areas that have been inspected. ✓ All in place BMPs All disturbed soils I I All concrete wash out area All material storage areas All discharge locations All equipment storage areas All construction entrances/exits ❑ Page 4 Construction Stormwater Site Inspection Form F. Elements checked "Action Required" (section D) describe corrective action to be taken. List the element number; be specific on location and work needed. Document, initial, and date when the corrective action has been completed and inspected. Element # Description and Location Action Required Completion Date Initials Attach additional page if needed Sign the following certification: "I certify that this report is true, accurate, and complete, to the best of my knowledge and belief" Inspected by: (print) Title/Qualification of Inspector: (Signature) Date: Page 5 E. Construction Stormwater General Permit (CSWGP) Download CSWGP: https://www.ecology.wa.gov/Regulations-Permits/Permits- certifications/Stormwater-general-permits/Construction-stormwater-permit F. 303(d) List Waterbodies / TMDL Waterbodies Information LISTING ID WATERBODY PARAMETER CURRENT CATEGORY 40107 PUGET SOUND -CENTRAL Bacteria -Fecal Coliform Category -5 61015 PUGET SOUND -CENTRAL Bactiera-Enterococci Category -5 G. Contaminated Site Information Please see the Geotechnical Report for soils information. H. Engineering Calculations C. GEOTECH REPORT Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -26- COBALT G E 0 S C I E N C E S Geotechnical Investigation Proposed Residential Development 191xx 941h Avenue West Edmonds, Washington September 17, 2020 GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON Table of Contents 1.o INTRODUCTION............................................................................................................. 1 2.0 PROJECT DESCRIPTION.............................................................................................. 1 3.0 SITE DESCRIPTION....................................................................................................... 1 4.o FIELD INVESTIGATION............................................................................................... 1 4.1.1 Site Investigation Program................................................................................... 1 5.0 SOIL AND GROUNDWATER CONDITIONS.............................................................. 1 5.1.1 Area Geology........................................................................................................ 2 5.1.2 Groundwater........................................................................................................ 2 6.o GEOLOGIC HAZARDS................................................................................................... 3 6.1 Erosion Hazard.................................................................................................... 3 6.2 Seismic Hazard.................................................................................................... 3 7.o DISCUSSION................................................................................................................... 4 7.1.1 General.................................................................................................................4 8.o RECOMMENDATIONS.................................................................................................. 4 8.1.1 Site Preparation................................................................................................... 4 8.1.2 Temporary Excavations........................................................................................ 4 8.1.3 Erosion and Sediment Control.............................................................................. 5 8.1.4 Foundation Design............................................................................................... 6 8.1.5 Reinforced Concrete Retaining Walls................................................................... 7 8.1.6 Slab-on-Grade...................................................................................................... 7 8.1.E Groundwater Influence on Construction.............................................................. 8 8.1.8 Utilities................................................................................................................ 8 8.1.9 Pavements............................................................................................................8 9.o CONSTRUCTION FIELD REVIEWS...........................................................................10 io.o CLOSURE...................................................................................................................10 LIST OF APPENDICES Appendix A — Statement of General Conditions Appendix B — Figures Appendix C — Test Pit Logs GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON September 17, 2020 1.o Introduction COBALT GEOSCIENCES In accordance with your authorization, Cobalt Geosciences, LLC (Cobalt) has completed a geotechnical investigation for the proposed residential development located at 191xx 94th Avenue West in Edmonds, Washington (Figure 1). The purpose of the geotechnical investigation was to identify subsurface conditions and to provide geotechnical recommendations for foundation design, stormwater management, earthwork, soil compaction, and suitability of the on -site soils for use as fill. The scope of work for the geotechnical evaluation consisted of a site investigation followed by engineering analyses to prepare this report. Recommendations presented herein pertain to various geotechnical aspects of the proposed development, including foundation support of the new buildings and pavement design. 2.0 Project Description The project includes construction of multiple single-family residences, driveways, and utility infrastructure. Stormwater will be infiltrated if determined to be feasible. Anticipated building loads are expected to be light to moderate and site grading will include cuts and fills on the order of 4 feet or less. We should be provided with the final plans when they become available. 3.0 Site Description The site is located at 191xx 94th Avenue West in Edmonds, Washington (Figure 1). The property consists of four adjoining parcels with a total area of about 1.11 acres. The property is undeveloped and vegetated with grasses, bushes/shrubs, blackberry vines, along with variable diameter evergreen and deciduous trees. The site slopes gently to moderately downward from east to west at magnitudes of 5 to about 35 percent and relief of about 75 feet. The site is bordered on all sides by residential properties. Access is near the southeast corner and 94tn Avenue West. 4.o Field Investigation 4.1.1 Site Investigation Program The geotechnical field investigation program was completed on August 27, 202o and included excavating and sampling six test pits within the property for subsurface analysis. The soils encountered were logged in the field and are described in accordance with the Unified Soil Classification System (USCS). PO Box 82243 Kenmore, WA 98028 cobaltgeoOgmail.com 2o6-331-1097 GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON September 17, 2020 COBALT GEOSCIENCES A Cobalt Geosciences field representative conducted the explorations, collected disturbed soil samples, classified the encountered soils, kept a detailed log of the explorations, and observed and recorded pertinent site features. The results of the sampling are presented on the exploration logs enclosed in Appendix C. 5.0 Soil and Groundwater Conditions 5.1.1 Area Geology The site lies within the Puget Lowland. The lowland is part of a regional north -south trending trough that extends from southwestern British Columbia to near Eugene, Oregon. North of Olympia, Washington, this lowland is glacially carved, with a depositional and erosional history including at least four separate glacial advances/retreats. The Puget Lowland is bounded to the west by the Olympic Mountains and to the east by the Cascade Range. The lowland is filled with glacial and non -glacial sediments consisting of interbedded gravel, sand, silt, till, and peat lenses. The Geologic Map of the Edmonds East and West Quadrangles, indicates that the site is underlain by Vashon Glacial Till. Vashon Glacial Till is typically characterized by an unsorted, non -stratified mixture of clay, silt, sand, gravel, cobbles and boulders in variable quantities. These materials are typically dense and relatively impermeable. The poor sorting reflects the mixing of the materials as these sediments were overridden and incorporated by the glacial ice. Explorations All of the test pits encountered 6 to 12 inches of topsoil and vegetation underlain by approximately 2.5 to 4.5 feet of loose to medium dense, silty -fine to fine grained sand with gravel (Weathered Glacial Till). These materials were underlain by dense to very dense, silty -fine to fine grained sand with gravel (Glacial Till), which continued to the termination depths of the test pits. 5.1.2 Groundwater Groundwater was not encountered during our exploration work. Mottled and cemented soils were encountered at shallow depths. It is likely that perched groundwater may be present at shallow depths during the wet season. Water table elevations often fluctuate over time. The groundwater level will depend on a variety of factors that may include seasonal precipitation, irrigation, land use, climatic conditions and soil permeability. Water levels at the time of the field investigation may be different from those encountered during the construction phase of the project. 2 PO Box 82243 Kenmore, WA 98028 cobaltgeoOgmail.com 2o6-331-1097 GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON September 17, 2020 6.o Geologic Hazards 6.1 Erosion Hazard COBALT GEOSCIENCES The Natural Resources Conservation Services (NRCS) maps for Snohomish County indicate that the site is underlain by Alderwood—Urban Land Complex (8 to 15 percent slopes) and Alderwood-Everett gravelly sandy loams (25 to 70 percent slopes). These soils would have a slight to severe erosion potential in a disturbed state, depending on the slope magnitude. It is our opinion that soil erosion potential at this project site can be reduced through landscaping and surface water runoff control. Typically erosion of exposed soils will be most noticeable during periods of rainfall and may be controlled by the use of normal temporary erosion control measures, such as silt fences, hay bales, mulching, control ditches and diversion trenches. The typical wet weather season, with regard to site grading, is from October 31st to April ist. Erosion control measures should be in place before the onset of wet weather. 6.2 Seismic Hazard The overall subsurface profile corresponds to a Site Class D as defined by Table 1613.5.2 of the 2015 International Building Code (2015 IBC). A Site Class D applies to an overall profile consisting of dense to very dense soils within the upper too feet. We referenced the U.S. Geological Survey (USGS) Earthquake Hazards Program Website to obtain values for Ss, S,, FQ, and F,,. The USGS website includes the most updated published data on seismic conditions. The site specific seismic design parameters and adjusted maximum spectral response acceleration parameters are as follows: PGA (Peak Ground Acceleration, in percent of g) Ss 129.6o% of g S, 45.8o% of g FA 1.2 Fv Null Additional seismic considerations include liquefaction potential and amplification of ground motions by soft/loose soil deposits. The liquefaction potential is highest for loose sand with a high groundwater table. The relatively dense soil deposits that underlie the site have a low liquefaction potential. 3 PO Box 82243 Kenmore, WA 98028 cobaltgeoOgmail.com 2o6-331-1097 GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON September 17, 2020 7.o DISCUSSION 7-m General COBALT GEOSCIENCES The site is underlain by weathered and unweathered glacial till. The proposed residential buildings may be supported on shallow foundation systems bearing on medium dense or firmer native soils and structural fill placed on suitable native soils. Local overexcavation of fill and/or loose soils may be necessary below proposed foundation elements. Fill depths are expected to vary with location. We recommend detention with overflow of stormwater devices into City stormwater infrastructure. Infiltration of runoff is not feasible in glacial till soils at this site. 8.o Recommendations 8.1.1 Site Preparation Trees, shrubs and other vegetation should be removed prior to stripping of surficial organic -rich soil and fill. Based on observations from the site investigation program, it is anticipated that the stripping depth will be 6 to 18 inches. Deeper excavations will be necessary below large trees and in any areas underlain by undocumented fill materials. The native soils consist of silty -sand with gravel and sandy silt with gravel. These soils may be used as structural fill provided they achieve compaction requirements and are within 3 percent of the optimum moisture. These soils may only be suitable for use as fill during the summer months, as they will be above the optimum moisture levels in their current state. These soils are variably moisture sensitive and may degrade during periods of wet weather and under equipment traffic. Imported structural fill should consist of a sand and gravel mixture with a maximum grain size of 3 inches and less than 5 percent fines (material passing the U.S. Standard No. 200 Sieve). Structural fill should be placed in maximum lift thicknesses of 12 inches and should be compacted to a minimum of 95 percent of the modified proctor maximum dry density, as determined by the ASTM D 1557 test method. 8.1.2 Temporary Excavations Based on our understanding of the project, we anticipate that the grading could include local cuts on the order of approximately 4 feet or less for foundation and utility placement. Any deeper excavations should be sloped no steeper than 1.5H:1V (Horizontal:Vertical) in loose native soils and 1H:1V in medium dense to dense native soils. Steeper excavations (3/4H:1V) are suitable in soils that are very dense. If an excavation is subject to heavy vibration or surcharge loads, we recommend that the excavations be sloped no steeper than 2H:1V, where room permits. Temporary cuts should be in accordance with the Washington Administrative Code (WAC) Part N, Excavation, Trenching, and Shoring. Temporary slopes should be visually inspected daily by a qualified person during construction activities and the inspections should be documented in daily reports. The contractor is responsible for maintaining the stability of the temporary cut slopes and reducing slope erosion during construction. 4 PO Box 82243 Kenmore, WA 98028 cobaltgeoOgmail.com 2o6-331-1097 GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON September 17, 2020 COBALT GEOSCIENCES Temporary cut slopes should be covered with visqueen to help reduce erosion during wet weather, and the slopes should be closely monitored until the permanent retaining systems or slope configurations are complete. Materials should not be stored or equipment operated within io feet of the top of any temporary cut slope. Soil conditions may not be completely known from the geotechnical investigation. In the case of temporary cuts, the existing soil conditions may not be completely revealed until the excavation work exposes the soil. Typically, as excavation work progresses the maximum inclination of temporary slopes will need to be re-evaluated by the geotechnical engineer so that supplemental recommendations can be made. Soil and groundwater conditions can be highly variable. Scheduling for soil work will need to be adjustable, to deal with unanticipated conditions, so that the project can proceed and required deadlines can be met. If any variations or undesirable conditions are encountered during construction, we should be notified so that supplemental recommendations can be made. If room constraints or groundwater conditions do not permit temporary slopes to be cut to the maximum angles allowed by the WAC, temporary shoring systems may be required. The contractor should be responsible for developing temporary shoring systems, if needed. We recommend that Cobalt Geosciences and the project structural engineer review temporary shoring designs prior to installation, to verify the suitability of the proposed systems. 8.1.3 Erosion and Sediment Control Erosion and sediment control (ESC) is used to reduce the transportation of eroded sediment to wetlands, streams, lakes, drainage systems, and adjacent properties. Erosion and sediment control measures should be implemented and these measures should be in general accordance with local regulations. At a minimum, the following basic recommendations should be incorporated into the design of the erosion and sediment control features for the site: • Schedule the soil, foundation, utility, and other work requiring excavation or the disturbance of the site soils, to take place during the dry season (generally May through September). However, provided precautions are taken using Best Management Practices (BMP's), grading activities can be completed during the wet season (generally October through April). All site work should be completed and stabilized as quickly as possible. • Additional perimeter erosion and sediment control features may be required to reduce the possibility of sediment entering the surface water. This may include additional silt fences, silt fences with a higher Apparent Opening Size (AOS), construction of a berm, or other filtration systems. • Any runoff generated by dewatering discharge should be treated through construction of a sediment trap if there is sufficient space. If space is limited other filtration methods will need to be incorporated. 5 PO Box 82243 Kenmore, WA 98028 cobaltgeoOgmail.com 2o6-331-1097 GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON September 17, 2020 8.1.4 Foundation Design COBALT GEOSCIENCES The proposed residential buildings and garages may be supported on shallow spread footing foundation systems bearing on undisturbed medium dense or firmer native soils or on properly compacted structural fill placed on the suitable native soils. If structural fill is used to support foundations, then the zone of structural fill should extend beyond the faces of the footing a lateral distance at least equal to the thickness of the structural fill. Depending on the location and finish floor elevations of new buildings, some overexcavation may be required. Fill is likely present near existing buildings and possibly in yard areas. Any fill will need to be removed below new footings and replaced with compacted structural fill as discussed above. For shallow foundation support, we recommend widths of at least 16 and 24 inches, respectively, for continuous wall and isolated column footings supporting the proposed structure. Provided that the footings are supported as recommended above, a net allowable bearing pressure of 2,000 pounds per square foot (psf) may be used for design. A 1/3 increase in the above value may be used for short duration loads, such as those imposed by wind and seismic events. Structural fill placed on bearing, native subgrade should be compacted to at least 95 percent of the maximum dry density based on ASTM Test Method D1557. Footing excavations should be inspected to verify that the foundations will bear on suitable material. Exterior footings should have a minimum depth of 18 inches below pad subgrade (soil grade) or adjacent exterior grade, whichever is lower. Interior footings should have a minimum depth of 12 inches below pad subgrade (soil grade) or adjacent exterior grade, whichever is lower. If constructed as recommended, the total foundation settlement is not expected to exceed 1 inch. Differential settlement, along a 25-foot exterior wall footing, or between adjoining column footings, should be less than 1/2 inch. This translates to an angular distortion of 0.002. Most settlement is expected to occur during construction, as the loads are applied. However, additional post -construction settlement may occur if the foundation soils are flooded or saturated. All footing excavations should be observed by a qualified geotechnical consultant. Resistance to lateral footing displacement can be determined using an allowable friction factor of 0.40 acting between the base of foundations and the supporting subgrades. Lateral resistance for footings can also be developed using an allowable equivalent fluid passive pressure of 225 pounds per cubic foot (pcf) acting against the appropriate vertical footing faces (neglect the upper 12 inches below grade in exterior areas). The allowable friction factor and allowable equivalent fluid passive pressure values include a factor of safety of 1.5. The frictional and passive resistance of the soil may be combined without reduction in determining the total lateral resistance. A 1/3 increase in the above values may be used for short duration transient loads. Care should be taken to prevent wetting or drying of the bearing materials during construction. Any extremely wet or dry materials, or any loose or disturbed materials at the bottom of the footing excavations, should be removed prior to placing concrete. The potential for wetting or drying of the bearing materials can be reduced by pouring concrete as soon as possible after completing the footing excavation and evaluating the bearing surface by the geotechnical engineer or his representative. 6 PO Box 82243 Kenmore, WA 98028 cobaltgeoOgmail.com 2o6-331-1097 GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON September 17, 2020 8.1.5 Stormwater Management COBALT GEOSCIENCES The site is underlain by glacial till which typically has a very low permeability. We encountered mottled soils above the unweathered glacial till. Additionally, the unweathered till was cemented. It is our opinion that infiltration is not feasible due to the soil and anticipated groundwater conditions during the wet season. Infiltrating runoff would migrate laterally along the weathered -unweathered glacial till contact and into adjacent properties. This migrating runoff could flow into any adjacent basements, utilities, or fill zones. We performed a small scale pilot infiltration test in TP-1 at a depth of 3 feet below grade. Following saturation, testing, and application of correction factors for site variability (o.8), influent control (o.9), and testing (0.5), the rate was o.1 inches per hour. We encountered ponded stormwater below the area after completion of the testing. We recommend utilizing dispersion trenches if there is adequate space. Other options include detention vaults with overflow to City infrastructure and possibly rain gardens and permeable pavements, depending on their location and elevations. We can provide additional input upon request and once a civil plan has been prepared. 8.1.6 Slab -on -Grade We recommend that the upper 12 inches of the existing fill and/or native soils within slab areas be re - compacted to at least 95 percent of the modified proctor (ASTM D1557 Test Method). Often, a vapor barrier is considered below concrete slab areas. However, the usage of a vapor barrier could result in curling of the concrete slab at joints. Floor covers sensitive to moisture typically requires the usage of a vapor barrier. A materials or structural engineer should be consulted regarding the detailing of the vapor barrier below concrete slabs. Exterior slabs typically do not utilize vapor barriers. The American Concrete Institutes ACI 36oR-o6 Design of Slabs on Grade and ACI 302.1R-04 Guide for Concrete Floor and Slab Construction are recommended references for vapor barrier selection and floor slab detailing. Slabs on grade may be designed using a coefficient of subgrade reaction of 18o pounds per cubic inch (pci) assuming the slab -on -grade base course is underlain by structural fill placed and compacted as outlined in Section 8.1. A 6 inch thick capillary break should be placed over the prepared subgrade. This should consist of 5/8 inch clean angular rock or pea gravel. A perimeter drainage system is recommended unless interior slab areas are elevated a minimum of 12 inches above adjacent exterior grades. If installed, a perimeter drainage system should consist of a 4 inch diameter perforated drain pipe surrounded by a minimum 6 inches of drain rock wrapped in a non -woven geosynthetic filter fabric to reduce migration of soil particles into the drainage system. The perimeter drainage system should discharge by gravity flow to a suitable stormwater system. Exterior grades surrounding buildings should be sloped at a minimum of one percent to facilitate surface water flow away from the building and preferably with a relatively impermeable surface cover immediately adjacent to the building. 7 PO Box 82243 Kenmore, WA 98028 cobaltgeoOgmail.com 2o6-331-1097 COBALT GEOTECHNICAL INVESTIGATION GEOSCIENCES EDMONDS, WASHINGTON September 17, 2020 8.1.7 Groundwater Influence on Construction Groundwater was not encountered during the test pit exploration work. We anticipate that perched groundwater could be present at shallow depths during the wet season. If groundwater is encountered, we anticipate that sump excavations and small diameter pumps systems will adequately de -water short-term excavations, if required. Any system should be designed by the contractor. We can provide additional recommendations upon request. 8.1.8 Utilities Utility trenches should be excavated according to accepted engineering practices following OSHA (Occupational Safety and Health Administration) standards, by a contractor experienced in such work. The contractor is responsible for the safety of open trenches. Traffic and vibration adjacent to trench walls should be reduced; cyclic wetting and drying of excavation side slopes should be avoided. Depending upon the location and depth of some utility trenches, groundwater flow into open excavations could be experienced, especially during or shortly following periods of precipitation. In general, silty and sandy soils were encountered at shallow depths in the explorations at this site. These soils have low cohesion and density and will have a tendency to cave or slough in excavations. Shoring or sloping back trench sidewalls is required within these soils in excavations greater than 4 feet deep. All utility trench backfill should consist of imported structural fill or suitable on site soils. Utility trench backfill placed in or adjacent to buildings and exterior slabs should be compacted to at least 95 percent of the maximum dry density based on ASTM Test Method D1557. The upper 5 feet of utility trench backfill placed in pavement areas should be compacted to at least 95 percent of the maximum dry density based on ASTM Test Method D1557. Below 5 feet, utility trench backfill in pavement areas should be compacted to at least 90 percent of the maximum dry density based on ASTM Test Method D1557. Pipe bedding should be in accordance with the pipe manufacturer's recommendations. The contractor is responsible for removing all water -sensitive soils from the trenches regardless of the backfill location and compaction requirements. Depending on the depth and location of the proposed utilities, we anticipate the need to re -compact existing fill soils below the utility structures and pipes. The contractor should use appropriate equipment and methods to avoid damage to the utilities and/or structures during fill placement and compaction procedures. 8.1.9 Pavement Recommendations The near surface subgrade soils generally consist of silty sand with gravel. These soils are rated as good for pavement subgrade material (depending on silt content and moisture conditions). We estimate that the subgrade will have a California Bearing Ratio (CBR) value of 10 and a modulus of subgrade reaction value of k = 200 pci, provided the subgrade is prepared in general accordance with our recommendations. We recommend that, at a minimum, 18 inches of the existing subgrade material be moisture conditioned (as necessary) and re -compacted to prepare for the construction of pavement sections. Deeper levels of recompaction or overexcavation and replacement may be necessary in areas where fill and/or very poor (soft/loose) soils are present. Any soils that cannot be compacted to required levels and soils that have more than 40 percent fines by weight should be removed and replaced with imported structural fill. 8 PO Box 82243 Kenmore, WA 98028 cobaltgeoOgmail.com 2o6-331-1097 GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON September 17, 2020 COBALT GEOSCIENCES The subgrade should be compacted to at least 95 percent of the maximum dry density as determined by ASTM Test Method D1557. In place density tests should be performed to verify proper moisture content and adequate compaction. The recommended flexible and rigid pavement sections are based on design CBR and modulus of subgrade reaction (k) values that are achieved, only following proper subgrade preparation. It should be noted that subgrade soils that have relatively high silt contents will likely be highly sensitive to moisture conditions. The subgrade strength and performance characteristics of a silty subgrade material may be dramatically reduced if this material becomes wet. Based on our knowledge of the proposed project, we expect the traffic to range from light duty (passenger automobiles) to heavy duty (delivery trucks). The following tables show the recommended pavement sections for light duty and heavy duty use. ASPHALTIC CONCRETE (FLEXIBLE) PAVEMENT LIGHT DUTY Asphaltic Concrete Aggregate Base* Compacted Subgrade* ** 2.5 in. 6.o in. 12.0 in. HEAVY DUTY Asphaltic Concrete Aggregate Base* Compacted Subgrade* ** 3.5 in. 6.o in. 12.0 in. PORTLAND CEMENT CONCRETE (RIGID) PAVEMENT Min. PCC Depth Aggregate Base* Compacted Subgrade* ** 6.o in. 6.o in. 12.0 in. * 95% compaction based on ASTM Test Method D1557 **A proof roll may be performed in lieu of in place density tests The asphaltic concrete depth in the flexible pavement tables should be a surface course type asphalt, such as Washington Department of Transportation (WSDOT) 1/2 inch HMA. The rigid pavement design is based on a Portland Cement Concrete (PCC) mix that has a 28 day compressive strength of 4,000 pounds per square inch (psi). The design is also based on a concrete flexural strength or modulus of rupture of 550 psi. 9 PO Box 82243 Kenmore, WA 98028 cobaltgeoogmail.com 2o6-331-1097 COBALT GEOTECHNICAL INVESTIGATION GEOSCIENCES EDMONDS, WASHINGTON September 17, 2020 9.o Construction Field Reviews Cobalt Geosciences should be retained to provide part time field review during construction in order to verify that the soil conditions encountered are consistent with our design assumptions and that the intent of our recommendations is being met. This will require field and engineering review to: ■ Monitor and test structural fill placement and soil compaction ■ Observe bearing capacity at foundation locations ■ Observe slab -on -grade preparation ■ Observe excavation stability Geotechnical design services should also be anticipated during the subsequent final design phase to support the structural design and address specific issues arising during this phase. Field and engineering review services will also be required during the construction phase in order to provide a Final Letter for the project. io.o Closure This report was prepared for the exclusive use of Landsverk Quality Homes, Inc. appointed consultants. Any use of this report or the material contained herein by third parties, or for other than the intended purpose, should first be approved in writing by Cobalt Geosciences, LLC. The recommendations contained in this report are based on assumed continuity of soils with those of our test holes, and assumed structural loads. Cobalt Geosciences should be provided with final architectural and civil drawings when they become available in order that we may review our design recommendations and advise of any revisions, if necessary. Use of this report is subject to the Statement of General Conditions provided in Appendix A. It is the responsibility of Landsverk Quality Homes, Inc. who is identified as "the Client" within the Statement of General Conditions, and its agents to review the conditions and to notify Cobalt Geosciences should any of these not be satisfied. 10 PO Box 82243 Kenmore, WA 98028 cobaltgeoOgmail.com 2o6-331-1097 GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON September 17, 2020 Respectfully submitted, Cobalt Geosciences, LLC Original signed by: HONrWA y9 a ✓ 'i yam. 54896 s CIST AONA1.�- 9/17/2020 Phil Haberman, PE, LG, LEG Principal PH/sc PO Box 82243 Kenmore, WA 98028 cobaltgeoogmail.com 2o6-331-1097 179 2513 ��• K d G e COBALT GEOSCIENCES 11 APPENDIX A Statement of General Conditions Statement of General Conditions USE OF THIS REPORT: This report has been prepared for the sole benefit of the Client or its agent and may not be used by any third party without the express written consent of Cobalt Geosciences and the Client. Any use which a third party makes of this report is the responsibility of such third party. BASIS OF THE REPORT: The information, opinions, and/or recommendations made in this report are in accordance with Cobalt Geosciences present understanding of the site specific project as described by the Client. The applicability of these is restricted to the site conditions encountered at the time of the investigation or study. If the proposed site specific project differs or is modified from what is described in this report or if the site conditions are altered, this report is no longer valid unless Cobalt Geosciences is requested by the Client to review and revise the report to reflect the differing or modified project specifics and/or the altered site conditions. STANDARD OF CARE: Preparation of this report, and all associated work, was carried out in accordance with the normally accepted standard of care in the state of execution for the specific professional service provided to the Client. No other warranty is made. INTERPRETATION OF SITE CONDITIONS: Soil, rock, or other material descriptions, and statements regarding their condition, made in this report are based on site conditions encountered by Cobalt Geosciences at the time of the work and at the specific testing and/or sampling locations. Classifications and statements of condition have been made in accordance with normally accepted practices which are judgmental in nature; no specific description should be considered exact, but rather reflective of the anticipated material behavior. Extrapolation of in situ conditions can only be made to some limited extent beyond the sampling or test points. The extent depends on variability of the soil, rock and groundwater conditions as influenced by geological processes, construction activity, and site use. VARYING OR UNEXPECTED CONDITIONS: Should any site or subsurface conditions be encountered that are different from those described in this report or encountered at the test locations, Cobalt Geosciences must be notified immediately to assess if the varying or unexpected conditions are substantial and if reassessments of the report conclusions or recommendations are required. Cobalt Geosciences will not be responsible to any parry for damages incurred as a result of failing to notify Cobalt Geosciences that differing site or sub -surface conditions are present upon becoming aware of such conditions. PLANNING, DESIGN, OR CONSTRUCTION: Development or design plans and specifications should be reviewed by Cobalt Geosciences, sufficiently ahead of initiating the next project stage (property acquisition, tender, construction, etc), to confirm that this report completely addresses the elaborated project specifics and that the contents of this report have been properly interpreted. Specialty quality assurance services (field observations and testing) during construction are a necessary part of the evaluation of sub -subsurface conditions and site preparation works. Site work relating to the recommendations included in this report should only be carried out in the presence of a qualified geotechnical engineer; Cobalt Geosciences cannot be responsible for site work carried out without being present. APPENDIX B Figures: Vicinity Map, Site Plan 10.2 PO Box 82243 Kenmore, WA 98028 cobaltgeoogmail.com 2o6-331-1097 1Z2"Yl.UUIJ' W 1L1 1U.DUU- W WGS84 122'19.000' W a ,1 WASHINGTON j ! ^ �• ii r r ° Edmonds r a /" ` - - .•" t5W Project 73 Location - - 1 j . lalb°tRdr t 1:74th. 476tii St SV11 -_ - - --- r �� 't°i • � 'a I� �' '° 178thStSW 418 fSW rNvrlN •180 z \ 81'st PI z o : • . ,-2f - _ - - �� ' '82nd St -SW P sw o o —> �, n /'^ _r 1. '_ a '. �_ � . � � • e al sw � � _ V n 106th it 514 3 � ash d •-`�� ro,Ql � �`� •s,.= '" •61 �`,� 1 1m • 1v n• d 1 ' t I • Oth 3 SW f7 i� °---I ,balk 92nd .192nd PI SVIf� • . •� pd� / , q _`\.,Q t^6..• O Ifl�� •Q :i m •II _ 3 '193r'a Way— e' .Y yiewla-n Wa' l� Ir • > a c ,I c3 T� > y--• i Z d.• a- 194th 1N t g -� z 200th St SW1 00 0 o o c. , z _6 z , ?ul n '.3ti: 3 § •r ::M 3a I. 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'r i' 122'23.000' W 122'22.000' W 122'21.000' W 122,20.000' W WG584 122'19.000' W 0 5 I TN MN NATIONAL 1000 0 1000 2000 30M 4000 M"`� 16° N GEOGRAPHIC 5 0 KItOMETfRS "`t IA 1000 0 METERS 1000 11/26/14 Cobalt Geosciences, LLC Proposed Res. Development VICINITY P.O. Box 82243 1 th Avenue West �P Kenmore, WA g8o28 COBALT 91XX 94 (206) 331-1097 Edmonds, Washington FIGURE i www.cobaltgeo.com cobaltgeo(&gmail.com TP-1 Approximate 9 Test Pit Location Proposed Res. Development 191xx 94th Avenue West Edmonds, Washington SITE PLAN FIGURE 2 N A Cobalt Geosciences, LLC P.O. Box 82243 Kenmore, WA 98028 (206) 331-1097 www.cobaltgeo.com cobaltgeopgmail.com APPENDIX C Exploration Logs Unified Soil Classification System (USCS) MAJOR DIVISIONS SYMBOL TYPICAL DESCRIPTION Clean Gravels GW Well -graded gravels, gravels, gravel -sand mixtures, little or no fines Gravels (more than 50% (less than 5% fines) GP Poorly graded gravels, gravel -sand mixtures, little or no fines COARSE GRAINED SOILS of coarse fraction retained on No. 4 sieve) Gravels with Fines (more than 12% fines) GM Silty gravels, gravel -sand -silt mixtures GC Clayey gravels, gravel -sand -clay mixtures (more than 50% retained on Clean Sands ;•; sw Well -graded sands, gravelly sands, little or no fines No. 200 sieve) Sands (50% or more of coarse fraction (less than 5% fines) sP Poorly graded sand, gravelly sands, little or no fines passes the No. 4 sieve) Sands with Fines sM Silty sands, sand -silt mixtures (more than 12% fines) sc Clayey sands, sand -clay mixtures ML Inorganic silts of low to medium plasticity, sandy silts, gravelly silts, FINE GRAINED (50% or more Silts and Clays (liquid limit less than 50) Inorganic cL or clayey silts with slight plasticity Inorganic clays of low to medium plasticity, gravelly clays, sandy clays silty clays, lean clays Organic rganic oL Organic silts and organic silty clays of low plasticity passes the MH Inorganic silts, micaceous or diatomaceous fine sands or silty soils, No. 200 sieve) Silts and Clays (liquid limit 50 or more) Inorganic elastic silt CH Inorganic clays of medium to high plasticity, sandy fat clay, or gravelly fat clay Organic OHOrganic clays of medium to high plasticity, organic silts HIGHLY ORGANIC SOILS Primarily organic matter, dark in color, and organic odor PT Peat, humus, swamp soils with high organic content (ASTM D4427) Classification of Soil Constituents MAJOR constituents compose more than 50 percent, by weight, of the soil. Major constituents are capitalized (i.e., SAND). Minor constituents compose 12 to 50 percent of the soil and precede the major constituents (i.e., silty SAND). Minor constituents preceded by "slightly" compose 5 to 12 percent of the soil (i.e., slightly silty SAND). Trace constituents compose o to 5 percent of the soil (i.e., slightly silty SAND, trace gravel). Relative Density (Coarse Grained Soils) Consistency (Fine Grained Soils) N, SPT, Relative N, SPT, Relative Blows/FT Density Blows/FT Consistency 0-4 Very loose Under 2 Very soft 4 -10 Loose 2-4 Soft 10 - 30 Medium dense 4-8 Medium stiff 30 - 50 Dense 8 -15 Stiff Over 50 Very dense 15 - 30 Very stiff Over 3o Hard Grain Size Definitions Description Sieve Number and/or Size Fines <#200 (o.o8 mm) Sand -Fine #200 to #40 (o.o8 to 0.4 mm) -Medium #40 to #10 (0.4 to 2 mm) -Coarse #10 to #4 (2 to 5 mm) Gravel -Fine #4 to 3/4 inch (5 to 19 mm) -Coarse 3/4 to 3 inches (19 to 76 mm) Cobbles 3 to 12 inches (75 to 305 mm) Boulders >12 inches (305 mm) 1 Moisture Content Definitions 1 Dry Absence of moisture, dusty, dry to the touch Moist Damp but no visible water Wet Visible free water, from below water table Cobalt Geosciences, LLC P.O. Box 82243 Kenmore, WA 98028 Soil Classification Chart Figure Ci (206) 331-1097 _ www.cobaltgeo.com cobaltgeo(&gmail.com Test Pit TP-1 Date: August 27, 2020 Depth: 7' Groundwater: None Contractor: Client Provided Elevation: Logged By: PH Checked By: SC 0 o Moisture Content (%) N Q Plastic I Liquid U N Limit Limit N Material Description o c ? o DCP Equivalent N-Value G 0 10 20 30 40 50 ------ ---- -- ToosoMYe__ Catn io-------------------------------- 1 SM/ Loose to medium dense, silty -fine to fine grained sand with gravel, 'I ML mottled yellowish brown to grayish brown, dry to moist. 2 (Weathered Glacial Till) ---- ---- -- --------------------------------------------- SM Dense to very dense, silty -fine to fine grained sand with gravel, 4 ML grayish brown, moist. (Glacial Till) 5 -Till is cemented 6 YZ End of Test Pit 7' 8 9 10 Date: August 27, 2020 Depth: 8' Groundwater: None Contractor: Client Provided Elevation: Logged By: PH Checked By: SC o Moisture Content (�) NPlastic 1 Liquid U E 3 Limit Limit N Material Description o ? o DCP Equivalent N-Value C 0 10 20 30 40 50 IIII Topsoil/Vegetation SM/ Loose to medium dense, silty -fine to fine grained sand with gravel, 2 ML mottled yellowish brown to grayish brown, dry to moist. (Weathered Glacial Till) 3 4 5 ----- ---- -- ------------------------------------------- 6 SM Dense to very dense, silty -fine to fine grained sand with gravel, ML grayish brown, moist. (Glacial Till) 7 Till is cemented End of Test Pit 8' 9 10 Cobalt Geosciences, LLC Proposed Development P.O. Box 82243 lxx th Avenue West Test Pit Kenmore, WA 98028 COBALT1 9 94 (2o6) 331-1097 • Edmonds, WA Logs www.cobaltgeo.com cobaltgeo(Rigmail.com Test Pit TP-3 Date: August 27, 2020 Depth: 7' Groundwater: None Contractor: Client Provided Elevation: Logged By: PH Checked By: SC 0 o Moisture Content (%) N Q Plastic I Liquid U N Limit Limit N Material Description o c ? o DCP Equivalent N-Value G 0 10 20 30 40 50 ------ ---- -- ToosoMYe__ Catn io-------------------------------- 1 SM/ Loose to medium dense, silty -fine to fine grained sand with gravel, 'I ML mottled yellowish brown to grayish brown, dry to moist. 2 (Weathered Glacial Till) ----- ---- -- --------------------------------------------- SM Dense to very dense, silty -fine to fine grained sand with gravel, 4 ML grayish brown, moist. (Glacial Till) 5 -Till is cemented 6 YZ End of Test Pit 7' 8 9 10 Date: August 27, 2020 Depth: 8' Groundwater: None Contractor: Client Provided Elevation: Logged By: PH Checked By: SC 0) o Moisture Content (�) N JO -0 Plastic Liquid U E 3 Limit Limit N Material Description o ? o DCP Equivalent N-Value C 0 10 20 30 40 50 IIII Topsoil/Vegetation SM/ Loose to medium dense, silty -fine to fine grained sand with gravel, 2 ML mottled yellowish brown to grayish brown, dry to moist. (Weathered Glacial Till) 3 �— --- —-------- SM/ Dense to very dense, silty -fine to fine grained sand with gravel, 5--- ML grayish brown, moist. (Glacial Till) i 7 1 14.1.111 1 1 Till is cemented End of Test Pit 8' 9 10 Cobalt Geosciences, LLC Proposed Development P.O. Box 82243 lxx th Avenue West Test Pit Kenmore, WA 98028 COBALT1 9 94 (2o6) 331-1097 • Edmonds, WA Logs www.cobaltgeo.com cobaltgeo(Rigmail.com Test Pit TP-5 Date: August 27, 2020 Depth: 7' Groundwater: None Contractor: Client Provided Elevation: Logged By: PH Checked By: SC 0 o Moisture Content (%) N Q Plastic I Liquid U N Limit Limit N Material Description o c ? o DCP Equivalent N-Value G 0 10 20 30 40 50 ------ ---- — -- ToosoMYe__ Cation -------------------------------- 1 SM/ Loose to medium dense, silty -fine to fine grained sand with gravel, ML mottled yellowish brown to grayish brown, dry to moist. 2 (Weathered Glacial Till) 3 ------- 4 -- SM/ --------------------------------------------- Dense to very dense, silty -fine to fine grained sand with gravel, ML grayish brown, moist. (Glacial Till) 5 -Till is cemented 6 YZ End of Test Pit 7' 8 9 10 Date: August 27, 2020 Depth: 8' Groundwater: None Contractor: Client Provided Elevation: Logged By: PH Checked By: SC 0) o Moisture Content (�) N JO -0 Plastic Liquid U E 3 Limit Limit N Material Description o ? o DCP Equivalent N-Value C 0 10 20 30 40 50 IIII Topsoil/Vegetation SM/ Loose to medium dense, silty -fine to fine grained sand with gravel, 2 ML mottled yellowish brown to grayish brown, dry to moist. (Weathered Glacial Till) 3 —A--- ---- - -- -------------------------------------------- SM/ Dense to very dense, silty -fine to fine grained sand with gravel, 5 ML grayish brown, moist. (Glacial Till) b 7 Till is cemented 9 10 End of Test Pit 8' Cobalt Geosciences, LLC Proposed Development P.O. Box 82243 • 1 lxx th Avenue West Test Pit Kenmore, WA 98028 • B9 94 (2o6) 331-1097 • Edmonds, WA Logs www.cobaltgeo.com cobaltgeo(Rigmail.com Test Pit TP-7 Date: August 27, 2020 Depth: 7' Groundwater: None Contractor: Client Provided Elevation: Logged By: PH Checked By: SC 0 o Moisture Content (%) N Q Plastic I Liquid u N Limit Limit N Material Description o c ? o DCP Equivalent N-Value G 0 10 20 30 40 50 ------ ---- — -- ToosoMYe__ Cation -------------------------------- 1 SM/ Loose to medium dense, silty -fine to fine grained sand with gravel, ML mottled yellowish brown to grayish brown, dry to moist. 2 (Weathered Glacial Till) 3 —4---------- -- --------------------------------------------- SM/ Dense to very dense, silty -fine to fine grained sand with gravel, 5 ML grayish brown, moist. (Glacial Till) b YZ -Till is cemented End of Test Pit 7' 8 9 10 Cobalt Geosciences, LLC Proposed Development P.O. Box 82243 \ • 1 lxx th Avenue West Test Pit Kenmore, WA 98028 • 9 94 (2o6) 331-1097 —•- • Edmonds WA Logs www.cobaltgeo.com cobaltgeo(Rigmail.com L�COBALT G E 0 S C I E N C E S November 28, 2022 Landsverk Quality Homes Attn: Mr. Joseph Rowett josephPlgh-inc.com RE: Geotechnical Addendum Proposed Development 950019oth Street SW Parcel No.'s 004346000006io2,104, 105, & 1o6 Edmonds, Washington Cobalt Geosciences, LLC P.O. Box 82243 Kenmore, Washington 98028 In accordance with your authorization, Cobalt Geosciences, LLC has prepared an addendum letter for the project. Steep Slope/Landslide Hazards There are local slopes near the property that have magnitudes of at least 40 percent and relief of more than 10 feet. Per the City of Edmonds GIS maps, areas that have magnitudes of 40 percent or more and relief of at least 10 feet are located near the north property line and elsewhere on properties to the northwest and northeast of the subject property (within 50 feet of the subject property). Areas within the property do not meet the criteria of steep slope or landslide hazards since their vertical relief is less than 10 feet. These areas can be safely benched and graded as part of site development. Overall, the steep slope areas on adjacent parcels appear stable at this time with no evidence of instability or erosion. Note that we observed these areas from the subject site and aerial photographs. The total relief is about 15 feet for slopes to the northwest of the site and relief of about 40 feet for slopes to the north and northeast of the site. While these areas consist of steep slope hazards, they do not exhibit evidence or characteristics of landslide hazard areas. Code Information 23.80.o6o Development standards — General requirements. A. Alterations of geologically hazardous areas or associated buffers may only occur for activities that: 1. Will not increase the threat of the geological hazard to adjacent properties beyond predevelopment conditions; 2. Will not adversely impact other critical areas; 3. Are designed so that the hazard to the project is eliminated or mitigated to a level equal to or less than predevelopment conditions; and 4. Are certified as safe as designed and under anticipated conditions by a qualified engineer or geologist, licensed in the state of Washington. www.cobaltgeo.com (2o6) 331-1097 November 28, 2022 Page 2 of 4 Geotechnical Addendum The project will include local grading and lot creation within moderately steep slope areas and for the north lot, near local steep slope hazard areas. It is our opinion that this work will not affect global or local stability provided work is monitored by the geotechnical engineer and erosion control measures are in place during construction. It will be necessary to bench and key anX existing slope areas with new structural fills (where proposed) and construction of properlX designed retaining walls where proposed and necessary. Similarly._ grading can be completed near the mapped steep slope hazard areas near the north propeM line provided any temporary excavations are protected from erosion and are created per our recommendations. These areas, if proposed to be graded, may be faced with retaining walls if necessarylproposed. The steep slope hazard areas appear to terminate at the north property line. The slope areas are cross gradient (do not slope toward the property) and it is our opinion that no buffer or setback is required from this area. However, we must review the final plans to verify that site grading and development in these areas do not require shoring or other design considerations, such as shoring. The proposed construction can be completed with no increase of the threat of geologic hazards on adjacent properties, will not impact other critical areas, and can be considered safe as designed under anticipated conditions. Again, we should be provided with the grading and development plans for this area to confirm suitability. 23.80.07o Development standards — Specific hazards. A. Erosion and Landslide Hazard Areas. Activities on sites containing erosion or landslide hazards shall meet the requirements of ECDC 23.80.o6o, Development standards — General requirements, and the specific following requirements: 1. Minimum Building Setback. The minimum setback shall be the distance required to ensure the proposed structure will not be at risk from landslides for the life of the structure, considered to be 120 years, and will not cause an increased risk of landslides taking place on or off the site. A setback shall be established from all edges of landslide hazard areas. The size of the setback shall be determined by the director consistent with recommendations provided in the geotechnical report to eliminate or minimize the risk of property damage, death, or injury resulting from landslides caused in whole or part by the development, based upon review of and concurrence with a critical areas report prepared by a qualified professional; No specific setback is required from steep slope areas. Properly designed walls or graded areas are generally suitable near the north property line and closest steep slope areas. 2. Buffer Requirements. A buffer may be established with specific requirements and limitations, including but not limited to, drainage, grading, irrigation, and vegetation. Buffer requirements shall be determined by the director consistent with recommendations provided in the geotechnical report to eliminate or minimize the risk of property damage, death, or injury resulting from landslides caused in whole or part by activities within the buffer area, based upon review of and concurrence with a critical areas report prepared by a qualified professional; No buffer is required from the localized steep slope hazard area near the north property line. We anticipate that new homes will be located at least.-, feet from the north property line and hazard areas. Proper erosion control, temporary cuts, and permanent walls or graded areas are anticipated and required. www.cobaltgeo.com (2o6) 331-1097 November 28, 2022 Page 3 of 4 Geotechnical Addendum 3. Alterations. Alterations of an erosion or landslide hazard area, minimum building setback and/or buffer may only occur for activities for which a hazards analysis is submitted and certifies that: a. The alteration will not increase surface water discharge or sedimentation to adjacent properties beyond predevelopment conditions; b. The alteration will not decrease slope stability on adjacent properties; and c. Such alterations will not adversely impact other critical areas; Provided earthwork activities are performed in accordance with the approved plans, all runoff is fully controlled, and periodic geotechnical oversight is performed, the development will not decrease slope stability on adjacent properties, will not increase surface water discharge or sedimentation beyond current levels, and will not impact other critical areas. Temporary and permanent erosion and sediment control devices should be in at all times during construction. The steep slope hazard areas themselves will not be disturbed or graded. 4. Design Standards within Erosion and Landslide Hazard Areas. Development within an erosion or landslide hazard area and/or buffer shall be designed to meet the following basic requirements unless it can be demonstrated that an alternative design that deviates from one or more of these standards provides greater long-term slope stability while meeting all other provisions of this title. The requirement for long-term slope stability shall exclude designs that require regular and periodic maintenance to maintain their level of function. The basic development design standards are: a. The proposed development shall not decrease the factor of safety for landslide occurrences below the limits of 1.5 for static conditions and 1.2 for dynamic conditions. If stability at the proposed development site is below these limits, the proposed development shall provide practicable approaches to reduce risk to human safety and improve the factor of safety for landsliding. In no case shall the existing factor of safety be reduced for the subject property or adjacent properties; b. Structures and improvements shall be clustered to avoid geologically hazardous areas and other critical areas; c. Structures and improvements shall minimize alterations to the natural contour of the slope, and foundations shall be tiered where possible to conform to existing topography; d. Structures and improvements shall be located to preserve the most critical portion of the site and its natural landforms and vegetation; e. The proposed development shall not result in greater risk or a need for increased buffers on neighboring properties; f. The use of retaining walls that allow the maintenance of existing natural slope area is preferred over graded artificial slopes; and g. Development shall be designed to minimize impervious lot coverage; The very limited project scope does not pose a risk to critical areas or the need to increase buffers on adjacent properties. Essentially, the current stability will not be affected by the proposed construction since the proposed grading and slope stability will be equal to what is currently present once completed (or more stable). Factors of safety against landslide movements are well above minimum values based on the soil types, topography, and locations of the development. www.cobaltgeo.com (2o6) 331-1097 November 28, 2022 Page 4 of 4 Geotechnical Addendum 5. Vegetation Retention. Unless otherwise provided or as part of an approved alteration, removal of vegetation from an erosion or landslide hazard area or related buffer shall be prohibited; 6. Seasonal Restriction. Clearing shall be allowed only from May 1st to October 1st of each year; provided, that the director may extend or shorten the dry season on a case -by -case basis depending on actual weather conditions, except that timber harvest, not including brush clearing or stump removal, may be allowed pursuant to an approved forest practice permit issued by the city of Edmonds or the Washington State Department of Natural Resources; 7. Point Discharges. Point discharges from surface water facilities and roof drains onto or upstream from an erosion or landslide hazard area shall be prohibited except as follows: a. Conveyed via continuous storm pipe downslope to a point where there are no erosion hazard areas downstream from the discharge; b. Discharged at flow durations matching predeveloped conditions, with adequate energy dissipation, into existing channels that previously conveyed storm water runoff in the predeveloped state; or c. Dispersed discharge upslope of the steep slope onto a low -gradient, undisturbed buffer demonstrated to be adequate to infiltrate all surface and storm water runoff, and where it can be demonstrated that such discharge will not increase the saturation of the slope; and We concur with the above code items and have no additional comments at this time. We should be on site to verify aspects of the construction. These include but are not limited to soil bearing for footings, vault excavation and backfill placement, footing drainage, fill compaction, slab on grade and road preparation, temporary excavations, erosion control, and drainage systems. Sincerely, Cobalt Geosciences, LLC HONry9 W Asyy 06 r •1 y`. �� 54896 ��FssCISTER��\�� ZONAL�- 11/28/2022 Phil Haberman, PE, LG, LEG Principal www.cobaltgeo.com (2o6) 331-1097 D. OPERATION & MAINTENANCE MANUAL Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -27- Table V-4.5.2(3) Maintenance Standards - Closed Detention Systems (Tanks/Vaults) Results Expec Maintenance Defect Conditions When Maintenance is ted When Component Needed Maintenance is Performed Plugged Air One-half of the cross section of a vent Vents open and Vents is blocked at any point or the vent is functioning. damaged. Accumulated sediment depth exceeds 10% of the diameter of the storage area for 1/2 length of storage vault or any All sediment Debris and Sed- point depth exceeds 15% of diameter. and debris iment (Example: 72-inch storage tank would removed from require cleaning when sediment storage area. reaches depth of 7 inches for more than 1/2 length of tank.) Any openings or voids allowing mater- All joint Joints Between ial to be transported into facility. between Storage Area Tank/Pipe Sec- tank/pipe sec- tion (Will require engineering analysis to tions are determine structural stability). sealed. Any part of tank/pipe is bent out of Tank/pipe Tank Pipe Bent shape more than 10% of its design repaired or Out of Shape shape. (Review required by engineer to replaced to determine structural stability). design. Cracks wider than 1/2-inch and any Vault replaced evidence of soil particles entering the or repaired to Vault Structure structure through the cracks, or main- g design spe- cifications and Includes Cracks tenance/inspection personnel determ- is structurally in Wall, Bottom, ines that the vault is not structurally sound. Damage to sound. Frame and/or Cracks wider than 1/2-inch at the joint No cracks more Top Slab of any inlet/outlet pipe or any evidence than 1/4-inch of soil particles entering the vault wide at the joint through the walls. of the inlet/out- let pipe. Manhole Cover Not in Cover is missing or only partially in Manhole is Place place. Any open manhole requires closed. maintenance. 2014 Stormwater Management Manual for Western Washington Volume V - Chapter 4 - Page 835 Table V-4.5.2(3) Maintenance Standards - Closed Detention Systems (Tanks/Vaults) (continued) Results Expec Maintenance Defect Conditions When Maintenance is ted When Component Needed Maintenance is Performed Mechanism cannot be opened by one Locking Mech- maintenance person with proper tools. Mechanism anism Not Work- Bolts into frame have less than 1/2 inch opens with ing of thread (may not apply to self-locking proper tools. lids). Cover can be One maintenance person cannot removed and Cover Difficult to remove lid after applying normal lifting reinstalled by Remove pressure. Intent is to keep cover from one main - sealing off access to maintenance. tenance per- son. Ladder meets Ladder is unsafe due to missing rungs design stand - Ladder Rungs misalignment, not securely attached to ards. Allows Unsafe maintenance structure wall, rust, or cracks. person safe access. Catch Basins See "Catch Bas- See "Catch Basins" (No. 5). See "Catch ins" (No. 5) Basins" (No. 5). Table V-4.5.2(4) Maintenance Standards - Control Structure/Flow Restrictor Maintenance Component Defect Condition When Main- tenance is Needed Results Expected When Maintenance is Performed Trash and Material exceeds 25% of Control structure orifice is not Debris sump depth or 1 foot below blocked. All trash and debris (Includes orifice plate. removed. Sediment) General Structure is not securely Structure securely attached to attached to manhole wall. wall and outlet pipe. Structural Structure is not in upright Structure in correct position. Damage position (allow up to 10% Connections to outlet pipe are from plumb). watertight; structure repaired Connections to outlet pipe or replaced and works as 2014 Stormwater Management Manual for Western Washington Volume V - Chapter 4 - Page 836 Table V-4.5.2(4) Maintenance Standards - Control Structure/Flow Restrictor (continued) Maintenance Defect Condition When Main- Results Expected When Component tenance is Needed Maintenance is Performed are not watertight and show signs of rust. designed. Any holes - other than Structure has no holes other designed holes - in the than designed holes. structure. Cleanout gate is not water- Gate is watertight and works tight or is missing. as designed. Gate cannot be moved up Gate moves up and down eas- Cleanout Damaged or and down by one main- tenance person. it and is watertight. y g Gate Missing Chain is in place and works as Chain/rod leading to gate is designed. missing or damaged. Gate is rusted over 50% of Gate is repaired or replaced to its surface area. meet design standards. Control device is not work - Damaged or ing properly due to missing, Plate is in place and works as Orifice Plate Missing out of place, or bent orifice designed. plate. Any trash, debris, sediment, Plate is free of all obstructions Obstructions or vegetation blocking the and works as designed. plate. Overflow Any trash or debris blocking Pipe is free of all obstructions Pipe Obstructions (or having the potential of and works as designed. blocking) the overflow pipe. See "Closed Manhole Detention See "Closed Detention Sys -See "Closed Detention Sys - Systems" tems" (No. 3). tems" (No. 3). (No. 3). See "Catch Catch Basin Basins" (No. See "Catch Basins" (No. 5). See "Catch Basins" (No. 5). 5). 2014 Stormwater Management Manual for Western Washington Volume V - Chapter 4 - Page 837 Table V-4.5.2(5) Maintenance Standards - Catch Basins Results Maintenance Conditions When Maintenance is Expected Defect When Main- Component Needed tenance is performed No Trash or debris loc- Trash or debris which is located imme- ated imme- diately in front of the catch basin opening or diately in is blocking inletting capacity of the basin by front of catch more than 10%. basin or on Trash or debris (in the basin) that exceeds grate open- 60 percent of the sump depth as measured ing. from the bottom of basin to invert of the low- No trash or est pipe into or out of the basin, but in no debris in the Trash & case less than a minimum of six inches catch basin. Debris clearance from the debris surface to the invert of the lowest pipe. Inlet and out- let pipes free Trash or debris in any inlet or outlet pipe of trash or blocking more than 1/3 of its height. debris. General Dead animals or vegetation that could gen- No dead erate odors that could cause complaints or animals or dangerous gases (e.g., methane). vegetation present within the catch basin. Sediment (in the basin) that exceeds 60 per- cent of the sump depth as measured from the bottom of basin to invert of the lowest pipe into or out of the basin, but in no case No sediment Sediment less than a minimum of 6 inches clearance in the catch from the sediment surface to the invert of the basin lowest pipe. Structure Top slab has holes larger than 2 square Top slab is Damage to inches or cracks wider than 1 /4 inch. (Intent free of holes Frame and/or is to make sure no material is running into and cracks. Top Slab basin). Frame is sit- 2014 Stormwater Management Manual for Western Washington Volume V - Chapter 4 - Page 838 Table V-4.5.2(5) Maintenance Standards - Catch Basins (continued) Results Maintenance Conditions When Maintenance is Expected Component Defect Needed When Main- tenance is performed Frame not sitting flush on top slab, i.e., sep- ting flush on aration of more than 3/4 inch of the frame the riser rings from the top slab. Frame not securely or top slab attached and firmly attached. Basin Maintenance person judges that structure is replaced or unsound. repaired to Fractures or design stand - Cracks in Grout fillet has separated or cracked wider ards. Basin Walls/ than 1/2 inch and longer than 1 foot at the g Bottom joint of any inlet/outlet pipe or any evidence Pipe is of soil particles entering catch basin through regrouted cracks. and secure at basin wall. Basin Settlement/ If failure of basin has created a safety, func- replaced or Misalignment tion, or design problem. repaired to design stand- ards. No veget- Vegetation growing across and blocking ation block - more than 10% of the basin opening. ing opening to basin. Vegetation Vegetation growing in inlet/outlet pipe joints No that is more than six inches tall and less veget- than six inches apart. ation or root growth present. Contamination See "Detention Ponds" (No. 1). No pollution and Pollution present. Cover Not in Cover is missing or only partially in place. Catch basin Catch Basin Place Any open catch basin requires main- cover is tenance. closed Cover Locking Mech- Mechanism cannot be opened by one main- Mechanism anism Not tenance person with proper tools. Bolts into opens with 2014 Stormwater Management Manual for Western Washington Volume V - Chapter 4 - Page 839 Table V-4.5.2(5) Maintenance Standards - Catch Basins (continued) Results Maintenance Conditions When Maintenance is Expected Component Defect Needed When Main- tenance is performed Working frame have less than 1/2 inch of thread. proper tools. One maintenance person cannot remove lid Cover can be Cover Difficult after applying normal lifting pressure. removed by to Remove (Intent is keep cover from sealing off access one main - tenance per - to maintenance.) son. Ladder meets design stand Ladder Rungs Ladder is unsafe due to missing rungs, not ards and Ladder Unsafe securely attached to basin wall, mis- allows main - alignment, rust, cracks, or sharp edges. tenance per- son safe access. Grate open - Grate opening Grate with opening wider than 7/8 inch. ing meets Unsafe design stand- ards. Metal Grates Trash and Trash and debris that is blocking more than Grate free of (If Applic- Debris 20% of grate surface inletting capacity. trash and able) debris. Grate is in Damaged or Grate missing or broken member(s) of the place and Missing. grate. meets design standards. 2014 Stormwater Management Manual for Western Washington Volume V - Chapter 4 - Page 840 Table V-4.5.2(15) Maintenance Standards - Manufactured Media Filters Maintenance Condition When Maintenance is Results Expected Component Defect Needed When Maintenance is Performed Below Sediment Accu- Sediment depth exceeds 0.25- No sediment depos- Ground Vault i inches. its which would mulation on impede permeability Media. of the compost media. Sediment Accu-Sediment depth exceeds 6-inches No sediment depos- mulation in in first chamber. its in vault bottom of Vault first chamber. Trash/Debris Trash and debris accumulated on Trash and debris Accumulation compost filter bed. removed from the compost filter bed. Sediment in When drain pipes, clean -outs, Drain become full with sediment and/or Sediment and debris Pipes/Clean- debris. removed. Outs Damaged Any part of the pipes that are Pipe repaired and/or Pipes crushed or damaged due to cor- replaced. rosion and/or settlement. Access Cover Cover cannot be opened; one per- Cover repaired to Damaged/Not son cannot open the cover using proper working spe- Working normal lifting pressure, cor- cifications or rosion/deformation of cover. replaced. Cracks wider than 1/2-inch or evid- Vault replaced or ence of soil particles entering the repairs made so that Vault Structure structure through the cracks, or vault meets design Includes maintenance/inspection personnel specifications and is Cracks in Wall, determine that the vault is not struc structurally sound. Bottom, Damage to turally sound. Vault repaired so that Frame and/or Cracks wider than 1/2-inch at the no cracks exist wider Top Slab joint of any inlet/outlet pipe or evid- than 1/4-inch at the ence of soil particles entering joint of the inlet/outlet through the cracks. pipe. Baffles corroding, cracking warp- Baffles repaired or Baffles ing, and/or showing signs of failure replaced to spe- as determined by main- cifications. tenance/inspection person. 2014 Stormwater Management Manual for Western Washington Volume V - Chapter 4 - Page 854 Table V-4.5.2(15) Maintenance Standards - Manufactured Media Filters (continued) Maintenance Condition When Maintenance is Results Expected Component Defect Needed When Maintenance is Performed Ladder is corroded or deteriorated, Ladder replaced or not functioning properly, not repaired and meets Access Ladder securely attached to structure wall, specifications, and is Damaged missing rungs, cracks, and mis- safe to use as determ aligned. fined by inspection personnel. Drawdown of water through the Media cartridges Below Media media takes longer than 1 hour, replaced. Ground Cart- and/or overflow occurs frequently. ridge Type Short Circuiting Flows do not properly enter filter Filter cartridges cartridges. replaced. 2014 Stormwater Management Manual for Western Washington Volume V - Chapter 4 - Page 855 E. WWHM REPORT WWHM2012 PROJECT REPORT Project Name: Vault Site Name: Linton Lot A Site Address: 9500 190th Pl SW City : Lynnwood Report Date: 7/8/2023 MGS Regoin Puget East Data Start 1901/10/1 Data End : 2058/09/30 DOT Data Number: 03 Version Date: 2023/01/27 Version : 4.2.19 Low Flow Threshold for POC 1 : 50 Percent of the 2 Year High Flow Threshold for POC 1: 50 year PREDEVELOPED LAND USE Name : Predeveloped Bypass: No Groundwater: No Pervious Land Use acre C, Forest, Mod .08 C, Forest, Steep 1.15 Pervious Total 1.23 Impervious Land Use acre Impervious Total 0 Basin Total 1.23 Element Flows To: Surface Interflow MITIGATED LAND USE Insight Engineering Co. - Stormwater Site Plan Groundwater 2/3/2022 -28- Name : Developed Bypass: No Groundwater: No Pervious Land Use acre C, Pasture, Steep .73 Pervious Total 0.73 Impervious Land Use acre ROADS FLAT 0.02 ROADS STEEP 0.11 ROOF TOPS FLAT 0.27 DRIVEWAYS FLAT 0.06 SIDEWALKS FLAT 0.04 Impervious Total 0.5 Basin Total 1.23 Element Flows To: Surface Interflow Vault 1 Vault 1 Groundwater Name Vault 1 Width 16 ft. Length 95 ft. Depth: 8 ft. Discharge Structure Riser Height: 7 ft. Riser Diameter: 12 in. Orifice 1 Diameter: 0.5 in. Elevation: 0 ft. Orifice 2 Diameter: 0.5 in. Elevation: 3.23 ft. Orifice 3 Diameter: 1 in. Elevation: 6.8 ft. Element Flows To: Outlet 1 Outlet 2 Vault Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 0.0000 0.034 0.000 0.000 0.000 0.0889 0.034 0.003 0.002 0.000 0.1778 0.034 0.006 0.002 0.000 0.2667 0.034 0.009 0.003 0.000 0.3556 0.034 0.012 0.004 0.000 Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -29- 0.4444 0.034 0.015 0.004 0.000 0.5333 0.034 0.018 0.005 0.000 0.6222 0.034 0.021 0.005 0.000 0.7111 0.034 0.024 0.005 0.000 0.8000 0.034 0.027 0.006 0.000 0.8889 0.034 0.031 0.006 0.000 0.9778 0.034 0.034 0.006 0.000 1.0667 0.034 0.037 0.007 0.000 1.1556 0.034 0.040 0.007 0.000 1.2444 0.034 0.043 0.007 0.000 1.3333 0.034 0.046 0.007 0.000 1.4222 0.034 0.049 0.008 0.000 1.5111 0.034 0.052 0.008 0.000 1.6000 0.034 0.055 0.008 0.000 1.6889 0.034 0.058 0.008 0.000 1.7778 0.034 0.062 0.009 0.000 1.8667 0.034 0.065 0.009 0.000 1.9556 0.034 0.068 0.009 0.000 2.0444 0.034 0.071 0.009 0.000 2.1333 0.034 0.074 0.009 0.000 2.2222 0.034 0.077 0.010 0.000 2.3111 0.034 0.080 0.010 0.000 2.4000 0.034 0.083 0.010 0.000 2.4889 0.034 0.086 0.010 0.000 2.5778 0.034 0.090 0.010 0.000 2.6667 0.034 0.093 0.011 0.000 2.7556 0.034 0.096 0.011 0.000 2.8444 0.034 0.099 0.011 0.000 2.9333 0.034 0.102 0.011 0.000 3.0222 0.034 0.105 0.011 0.000 3.1111 0.034 0.108 0.012 0.000 3.2000 0.034 0.111 0.012 0.000 3.2889 0.034 0.114 0.013 0.000 3.3778 0.034 0.117 0.015 0.000 3.4667 0.034 0.121 0.015 0.000 3.5556 0.034 0.124 0.016 0.000 3.6444 0.034 0.127 0.017 0.000 3.7333 0.034 0.130 0.017 0.000 3.8222 0.034 0.133 0.018 0.000 3.9111 0.034 0.136 0.019 0.000 4.0000 0.034 0.139 0.019 0.000 4.0889 0.034 0.142 0.020 0.000 4.1778 0.034 0.145 0.020 0.000 4.2667 0.034 0.148 0.020 0.000 4.3556 0.034 0.152 0.021 0.000 4.4444 0.034 0.155 0.021 0.000 4.5333 0.034 0.158 0.022 0.000 4.6222 0.034 0.161 0.022 0.000 4.7111 0.034 0.164 0.023 0.000 4.8000 0.034 0.167 0.023 0.000 4.8889 0.034 0.170 0.023 0.000 4.9778 0.034 0.173 0.024 0.000 5.0667 0.034 0.176 0.024 0.000 5.1556 0.034 0.179 0.024 0.000 5.2444 0.034 0.183 0.025 0.000 Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -30- 5.3333 0.034 0.186 0.025 0.000 5.4222 0.034 0.189 0.025 0.000 5.5111 0.034 0.192 0.026 0.000 5.6000 0.034 0.195 0.026 0.000 5.6889 0.034 0.198 0.026 0.000 5.7778 0.034 0.201 0.027 0.000 5.8667 0.034 0.204 0.027 0.000 5.9556 0.034 0.207 0.027 0.000 6.0444 0.034 0.210 0.028 0.000 6.1333 0.034 0.214 0.028 0.000 6.2222 0.034 0.217 0.028 0.000 6.3111 0.034 0.220 0.029 0.000 6.4000 0.034 0.223 0.029 0.000 6.4889 0.034 0.226 0.029 0.000 6.5778 0.034 0.229 0.029 0.000 6.6667 0.034 0.232 0.030 0.000 6.7556 0.034 0.235 0.030 0.000 6.8444 0.034 0.238 0.036 0.000 6.9333 0.034 0.241 0.040 0.000 7.0222 0.034 0.245 0.079 0.000 7.1111 0.034 0.248 0.436 0.000 7.2000 0.034 0.251 0.956 0.000 7.2889 0.034 0.254 1.498 0.000 7.3778 0.034 0.257 1.932 0.000 7.4667 0.034 0.260 2.193 0.000 7.5556 0.034 0.263 2.403 0.000 7.6444 0.034 0.266 2.586 0.000 7.7333 0.034 0.269 2.756 0.000 7.8222 0.034 0.273 2.916 0.000 7.9111 0.034 0.276 3.068 0.000 8.0000 0.034 0.279 3.213 0.000 8.0889 0.034 0.282 3.351 0.000 8.1778 0.000 0.000 3.484 0.000 ANALYSIS RESULTS Stream Protection Duration Predeveloped Landuse Totals for POC #1 Total Pervious Area:1.23 Total Impervious Area:O Mitigated Landuse Totals for POC #1 Total Pervious Area:0.73 Total Impervious Area:0.5 Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -31 - 2 year 5 year 10 year 25 year 50 year 100 year Flow Frequency Return Return Period 2 year 5 year 10 year 25 year 50 year 100 year 0.032887 0.049799 0.058822 0.067915 0.073281 0.077675 Periods for Mitigated Flow (cfs) 0.013591 0.020954 0.027554 0.038326 0.04846 0.060733 Stream Protection Duration Annual Peaks for Predeveloped and Mitigated. Year Predeveloped Mitigated 1902 0.045 0.013 1903 0.016 0.009 1904 0.034 0.011 1905 0.018 0.011 1906 0.013 0.007 1907 0.053 0.019 1908 0.032 0.011 1909 0.036 0.010 1910 0.055 0.015 1911 0.031 0.012 1912 0.085 0.020 1913 0.039 0.023 1914 0.012 0.008 1915 0.016 0.012 1916 0.024 0.011 1917 0.015 0.008 1918 0.028 0.019 1919 0.020 0.012 1920 0.031 0.012 1921 0.031 0.017 1922 0.036 0.018 1923 0.024 0.016 1924 0.016 0.010 1925 0.016 0.010 1926 0.028 0.010 1927 0.036 0.011 1928 0.025 0.011 1929 0.052 0.016 1930 0.029 0.011 1931 0.032 0.011 1932 0.026 0.011 1933 0.026 0.016 1934 0.065 0.027 1935 0.028 0.018 1936 0.041 0.016 Insight Engineering Co. - Stormwater Site Plan POC #k 1 POC #1 2/3/2022 -32- 1937 0.042 0.012 1938 0.035 0.017 1939 0.005 0.009 1940 0.029 0.018 1941 0.030 0.010 1942 0.041 0.029 1943 0.017 0.011 1944 0.050 0.024 1945 0.030 0.012 1946 0.027 0.010 1947 0.021 0.010 1948 0.066 0.022 1949 0.057 0.026 1950 0.028 0.012 1951 0.029 0.015 1952 0.097 0.030 1953 0.081 0.028 1954 0.029 0.018 1955 0.025 0.010 1956 0.016 0.010 1957 0.033 0.016 1958 0.078 0.075 1959 0.046 0.027 1960 0.020 0.010 1961 0.054 0.027 1962 0.032 0.012 1963 0.015 0.011 1964 0.039 0.010 1965 0.060 0.025 1966 0.014 0.010 1967 0.025 0.011 1968 0.029 0.017 1969 0.025 0.010 1970 0.038 0.017 1971 0.068 0.029 1972 0.077 0.020 1973 0.047 0.026 1974 0.031 0.011 1975 0.073 0.027 1976 0.030 0.013 1977 0.019 0.011 1978 0.064 0.025 1979 0.016 0.010 1980 0.029 0.014 1981 0.029 0.018 1982 0.021 0.011 1983 0.050 0.023 1984 0.019 0.011 1985 0.029 0.016 1986 0.025 0.012 1987 0.054 0.027 1988 0.040 0.017 1989 0.031 0.012 1990 0.036 0.017 1991 0.030 0.012 Insight Engineering Co. - Stormwater Site Plan 2/3/2022 - 33 - 1992 0.045 0.021 1993 0.037 0.016 1994 0.064 0.022 1995 0.016 0.010 1996 0.060 0.061 1997 0.035 0.011 1998 0.032 0.016 1999 0.001 0.007 2000 0.023 0.018 2001 0.020 0.008 2002 0.046 0.012 2003 0.033 0.019 2004 0.037 0.017 2005 0.040 0.011 2006 0.023 0.011 2007 0.023 0.016 2008 0.031 0.014 2009 0.020 0.011 2010 0.018 0.013 2011 0.021 0.011 2012 0.046 0.014 2013 0.022 0.011 2014 0.017 0.010 2015 0.072 0.011 2016 0.010 0.009 2017 0.053 0.021 2018 0.076 0.151 2019 0.098 0.030 2020 0.031 0.012 2021 0.042 0.020 2022 0.015 0.009 2023 0.033 0.014 2024 0.074 0.012 2025 0.029 0.016 2026 0.047 0.022 2027 0.024 0.012 2028 0.013 0.009 2029 0.036 0.015 2030 0.069 0.025 2031 0.019 0.009 2032 0.018 0.008 2033 0.016 0.009 2034 0.022 0.010 2035 0.077 0.076 2036 0.037 0.017 2037 0.009 0.008 2038 0.044 0.014 2039 0.004 0.007 2040 0.018 0.012 2041 0.022 0.010 2042 0.085 0.048 2043 0.035 0.021 2044 0.045 0.022 2045 0.028 0.020 2046 0.032 0.022 Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -34- 2047 0.021 0.012 2048 0.034 0.014 2049 0.033 0.015 2050 0.024 0.010 2051 0.042 0.018 2052 0.019 0.011 2053 0.034 0.023 2054 0.044 0.023 2055 0.017 0.008 2056 0.012 0.009 2057 0.020 0.012 2058 0.023 0.012 Stream Protection Duration Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.0985 0.1508 2 0.0973 0.0757 3 0.0852 0.0749 4 0.0852 0.0615 5 0.0809 0.0483 6 0.0775 0.0298 7 0.0767 0.0295 8 0.0766 0.0293 9 0.0763 0.0289 10 0.0742 0.0282 11 0.0732 0.0275 12 0.0721 0.0272 13 0.0692 0.0272 14 0.0680 0.0269 15 0.0655 0.0266 16 0.0652 0.0263 17 0.0636 0.0257 18 0.0636 0.0254 19 0.0600 0.0251 20 0.0599 0.0246 21 0.0567 0.0242 22 0.0550 0.0233 23 0.0540 0.0232 24 0.0536 0.0232 25 0.0531 0.0231 26 0.0529 0.0224 27 0.0522 0.0222 28 0.0504 0.0218 29 0.0496 0.0218 30 0.0475 0.0216 31 0.0474 0.0214 32 0.0464 0.0214 33 0.0459 0.0205 34 0.0456 0.0202 35 0.0451 0.0201 36 0.0448 0.0200 37 0.0447 0.0197 38 0.0445 0.0192 Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -35- 39 0.0440 0.0191 40 0.0424 0.0187 41 0.0422 0.0183 42 0.0419 0.0182 43 0.0410 0.0178 44 0.0409 0.0177 45 0.0402 0.0177 46 0.0400 0.0176 47 0.0394 0.0175 48 0.0388 0.0173 49 0.0380 0.0172 50 0.0374 0.0169 51 0.0372 0.0168 52 0.0371 0.0168 53 0.0364 0.0167 54 0.0363 0.0166 55 0.0359 0.0166 56 0.0358 0.0165 57 0.0355 0.0164 58 0.0354 0.0162 59 0.0352 0.0160 60 0.0350 0.0159 61 0.0340 0.0159 62 0.0339 0.0157 63 0.0339 0.0156 64 0.0334 0.0156 65 0.0334 0.0155 66 0.0329 0.0153 67 0.0327 0.0153 68 0.0325 0.0147 69 0.0319 0.0145 70 0.0318 0.0144 71 0.0318 0.0144 72 0.0315 0.0143 73 0.0313 0.0142 74 0.0311 0.0139 75 0.0311 0.0139 76 0.0309 0.0135 77 0.0309 0.0132 78 0.0308 0.0128 79 0.0306 0.0124 80 0.0303 0.0121 81 0.0300 0.0121 82 0.0296 0.0121 83 0.0295 0.0121 84 0.0295 0.0121 85 0.0294 0.0120 86 0.0294 0.0120 87 0.0293 0.0119 88 0.0292 0.0119 89 0.0291 0.0119 90 0.0291 0.0118 91 0.0290 0.0118 92 0.0285 0.0117 93 0.0284 0.0117 Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -36- 94 0.0283 0.0117 95 0.0281 0.0117 96 0.0278 0.0115 97 0.0277 0.0115 98 0.0268 0.0115 99 0.0257 0.0114 100 0.0256 0.0113 101 0.0255 0.0113 102 0.0253 0.0113 103 0.0252 0.0112 104 0.0249 0.0112 105 0.0246 0.0112 106 0.0240 0.0111 107 0.0239 0.0110 108 0.0237 0.0110 109 0.0236 0.0109 110 0.0231 0.0109 111 0.0230 0.0109 112 0.0230 0.0109 113 0.0229 0.0108 114 0.0224 0.0107 115 0.0224 0.0107 116 0.0216 0.0106 117 0.0214 0.0106 118 0.0214 0.0106 119 0.0213 0.0105 120 0.0212 0.0105 121 0.0204 0.0105 122 0.0203 0.0105 123 0.0202 0.0105 124 0.0200 0.0103 125 0.0197 0.0102 126 0.0192 0.0102 127 0.0191 0.0101 128 0.0188 0.0101 129 0.0185 0.0101 130 0.0180 0.0101 131 0.0179 0.0100 132 0.0178 0.0100 133 0.0177 0.0100 134 0.0170 0.0099 135 0.0169 0.0097 136 0.0168 0.0096 137 0.0164 0.0096 138 0.0163 0.0096 139 0.0163 0.0095 140 0.0162 0.0095 141 0.0161 0.0095 142 0.0160 0.0093 143 0.0159 0.0093 144 0.0157 0.0092 145 0.0150 0.0089 146 0.0146 0.0089 147 0.0146 0.0087 148 0.0135 0.0086 Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -37- 149 0.0130 0.0085 150 0.0127 0.0084 151 0.0119 0.0084 152 0.0118 0.0084 153 0.0099 0.0084 154 0.0092 0.0082 155 0.0045 0.0074 156 0.0040 0.0074 157 0.0012 0.0070 Stream Protection Duration POC #k 1 The Facility PASSED The Facility PASSED. Flow(cfs) Predev Mit Percentage Pass/Fail 0.0164 32920 20545 62 Pass 0.0170 30575 18524 60 Pass 0.0176 28323 16818 59 Pass 0.0182 26314 15370 58 Pass 0.0187 24541 14027 57 Pass 0.0193 22785 12607 55 Pass 0.0199 21249 11417 53 Pass 0.0205 19807 10267 51 Pass 0.0210 18414 9337 50 Pass 0.0216 17154 8169 47 Pass 0.0222 16031 7212 44 Pass 0.0228 14957 6540 43 Pass 0.0233 13977 5758 41 Pass 0.0239 13063 5214 39 Pass 0.0245 12232 4557 37 Pass 0.0251 11450 4018 35 Pass 0.0256 10746 3474 32 Pass 0.0262 10063 2902 28 Pass 0.0268 9447 2342 24 Pass 0.0274 8863 1911 21 Pass 0.0279 8335 1610 19 Pass 0.0285 7878 1295 16 Pass 0.0291 7432 1062 14 Pass 0.0296 7002 795 11 Pass 0.0302 6606 617 9 Pass 0.0308 6221 560 9 Pass 0.0314 5890 543 9 Pass 0.0319 5588 529 9 Pass 0.0325 5325 516 9 Pass 0.0331 5064 498 9 Pass 0.0337 4807 483 10 Pass 0.0342 4562 472 10 Pass 0.0348 4347 459 10 Pass 0.0354 4131 445 10 Pass 0.0360 3930 430 10 Pass 0.0365 3757 414 11 Pass 0.0371 3568 391 10 Pass Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -38- 0.0377 3381 376 11 Pass 0.0383 3202 359 11 Pass 0.0388 3022 334 11 Pass 0.0394 2889 305 10 Pass 0.0400 2750 253 9 Pass 0.0406 2635 203 7 Pass 0.0411 2520 174 6 Pass 0.0417 2427 167 6 Pass 0.0423 2334 157 6 Pass 0.0429 2236 152 6 Pass 0.0434 2146 148 6 Pass 0.0440 2070 140 6 Pass 0.0446 1990 135 6 Pass 0.0451 1912 127 6 Pass 0.0457 1845 119 6 Pass 0.0463 1789 118 6 Pass 0.0469 1723 114 6 Pass 0.0474 1644 111 6 Pass 0.0480 1582 106 6 Pass 0.0486 1516 103 6 Pass 0.0492 1438 98 6 Pass 0.0497 1381 96 6 Pass 0.0503 1316 96 7 Pass 0.0509 1260 94 7 Pass 0.0515 1210 92 7 Pass 0.0520 1164 90 7 Pass 0.0526 1114 89 7 Pass 0.0532 1060 87 8 Pass 0.0538 1011 85 8 Pass 0.0543 974 82 8 Pass 0.0549 937 80 8 Pass 0.0555 903 76 8 Pass 0.0561 874 75 8 Pass 0.0566 846 73 8 Pass 0.0572 819 71 8 Pass 0.0578 784 69 8 Pass 0.0584 754 68 9 Pass 0.0589 718 63 8 Pass 0.0595 691 58 8 Pass 0.0601 651 54 8 Pass 0.0607 626 52 8 Pass 0.0612 587 50 8 Pass 0.0618 558 47 8 Pass 0.0624 529 47 8 Pass 0.0629 491 45 9 Pass 0.0635 463 44 9 Pass 0.0641 438 44 10 Pass 0.0647 418 42 10 Pass 0.0652 383 41 10 Pass 0.0658 363 39 10 Pass 0.0664 346 39 11 Pass 0.0670 330 38 11 Pass 0.0675 309 37 11 Pass 0.0681 289 36 12 Pass 0.0687 269 36 13 Pass Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -39- 0.0693 248 32 12 Pass 0.0698 236 31 13 Pass 0.0704 216 31 14 Pass 0.0710 204 30 14 Pass 0.0716 191 30 15 Pass 0.0721 176 28 15 Pass 0.0727 167 26 15 Pass 0.0733 151 26 17 Pass Water Quality BMP Flow and Volume for POC #1 On-line facility volume: 0.021 acre-feet On-line facility target flow: 0.0106 cfs. Adjusted for 15 min: 0.0106 cfs. Off-line facility target flow: 0.0069 cfs. Adjusted for 15 min: 0.0069 cfs. LID Report LID Technique Used for Total Volume Volume Infiltration Cumulative Percent Water Quality Percent Comment Treatment? Needs Through Volume Volume Volume Water Quality Treatment Facility (ac-ft.) Infiltration Infiltrated Treated (ac-ft) (ac-ft) Credit Vault 1 POC N 238.58 N 0.00 Total Volume Infiltrated 238.58 0.00 0.00 0.00 0.00 0% No Treat. Credit Compliance with LID Standard 8 Duration Analysis Result = Failed Perind and Impind Changes No changes have been made. This program and accompanying documentation are provided 'as -is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc. and the governmental licensee or sublicensees disclaim all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions Inc. be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions Inc. or their authorized representatives have been advised of the possibility of such damages. Software Copyright © by Clear Creek Solutions, Inc. 2005-2023; All Rights Reserved. Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -40- F. PROJECT SITE MAP Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -41 - EX CB 4-71 RIM: 176.14 EX CB 4-268 RIM: 139.17 IE: 130.87 (IN, E) IE: 130.87 (OUT, W) 296 LF18" concr( EX CB 4-246 RIM: 103.31 IE: 96.91 (IN, E) IE: 96.91 (OUT, W) Scale: 1" = 100' Total Site Area - 53,749 SF Total Disturbed Area - 53,749 SF Roof - 10,204 SF Driveway/Sidewalk - 3,668 SF Road - 6,094 SF All pervious and impervious area will flow to the proposed detention pipe. Average Slope - 5 - 35% Infiltration Rate - 0.1 in/hr NRCS Soil Group - Alderwood EX CB 4-263 IE: 172.24 (IN, E) RIM: 154.89 IE: 172.34 (OUT, W) IE: 150.06 (IN, E) IE: 150.06 (OUT, W) 95 LF /1' oncrete Project Boundary 35 LF 18" concrete Offsite Upstream CB #1 Tributary Area RIM: 192.59 i LF 18 concrete IE: 187.59 (IN, S) EX CB 4-210 IE: 187.59 (OUT, NW) RIM: 171.22 IE: 166.02 (IN, E) IE: 166.12 (OUT, W) CB #7 RIM: 247.35 CB #2 IE: 235.50 (OUT, S) , RIM:20328 IE: 198.50 (IN, S) lJ IE: 198.50 (OUT, N) 4. Proposed Drainage System - CB #3 > RIM: 209.31 O IE: 204.50 (IN, E) a IE: 204.50 (OUT, N) CB #4 RIM: 248.00 IE: 232.80 (IN, S) IE: 238.80 (OUT, W) CB #5 RIM: 248.00 IE: 235.25 (IN, E) IE: 232.92 (OUT, N) Proposed Detention Pipe CB #6 RIM:250.24 IE: 235.50 (IN, N) IE: 242.35 (IN, S) IE: 235.50 (OUT, W) CB #8 RIM: 251.21 IE: 246.31 (OUT, N) G. SOURCE CONTROL PLAN Onsite source control BMPs will be used to minimize the impact of pollutant sources. The following BMPs are applicable to this development. See the DOE's 2019 SWMMWW for detailed BMP information. • S406 — BMPs for Streets and Highways • S410 — BMPs for Correcting Illicit Discharges to Storm Drains • S411 — BMPs for Landscaping and Lawn / Vegetation Management • S414 — BMPs for Maintenance and Repair of Vehicles and Equipment • S415 — BMPs for Maintenance of Public and Private Utility Corridors and Facilities • S417 — BMPs for Maintenance of Stormwater Drainage and Treatment Systems • S420 — BMPs for Painting/Finishing/Coating of Vehicles/Boats/Buildings/Equipment • S421 — BMPs for Parking and Storage for Vehicles and Equipment • S430 — BMPs for Urban Streets • S435 — BMPs for Pesticides and an Integrated Pest Management Program • S444 — BMPs for the Storage of Dry Pesticides and Fertilizers • S450 — BMPs for Irrigation • S440 — BMPs for Pest Waste • S442 — BMPs for Labeling Storm Drain Inlets on Your Property • S443 — BMPs for Fertilizer Application • S451 — BMPs for Building, Repair, Remodeling, Painting, and Construction • S453 — BMPs for Formation of a Pollution Prevention Team • S454 — BMPs for Preventative Maintenance / Good Housekeeping • S455 — BMPs for Spill Prevention and Cleanup • S456 — BMPs for Employee Training • S457 — BMPs for Inspections • S458 — BMPs for Record Keeping Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -42- H. CONVEYANCE ANALYSIS A detailed conveyance analysis of the proposed on -site drainage system has been performed using Autodesk Storm and Sanitary Analysis with the Rational methodology. The conveyance system was analyzed for the developed 25 and 100-yr storms. The areas on -site have been separated and connected to catch basins according to their flowpaths. The conveyance analysis was terminated at the existing catch basin on 1901h. Offsite areas draining into the downstream conveyance system were determined using the City of Edmonds GIS Map. Links 06-09 have been made to be 8" diameter pipe to reduce the excavation on steep slopes. This size pipe is sufficient to contain the 100-year flows. The most downstream pipe (Link-09) analyzed has a peak flow of 0.56 cfs in the 100-yr storm, with a capacity of 4.95 cfs. All downstream pipes included in the analysis had additional flow capacity in both the 25 and 100-year storms. The analysis shows that the proposed drainage system pipes have sufficient capacity to convey the runoff from the proposed development. Please refer to the following pages for the analysis results. Insight Engineering Co. - Stormwater Site Plan 2/3/2022 - 43 - Conveyance Map Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -44- EX Outfall CB — Link-09 CB 1 CB 2 Link-07 CB 3 Link-06 CB 4 WQ Link-08 Link-10 \— CB 5 25-Year Conveyance Analysis Insight Engineering Co. - Stormwater Site Plan 2/3/2022 - 45 - Autodesk® Storm and Sanitary Analysis 2016 - Version 13.0.94 (Build 0) ----------------------------------------------------------------------------------------- Project Description ******************* File Name ................. Conveyance Analysis.SPF Analysis Options Flow Units ................ cfs Subbasin Hydrograph Method. Rational Time of Concentration...... User -Defined Link Routing Method ....... Kinematic Wave Storage Node Exfiltration.. None Starting Date ............. DEC-05-2022 00:00:00 Ending Date ............... DEC-06-2022 00:00:00 Report Time Step .......... 00:00:10 ************* Element Count ************* Number of subbasins ....... 5 Number of nodes ........... 9 Number of links ........... 8 **************** Subbasin **************** Summary Subbasin Total Area ID acres Lot C Lot D Lots AB Roadl Road2 ************ Node Summary ************ Node ID CB 1 CB 2 CB 3 CB 4 WQ CB 5 CB 6 CS Ex CB Detention Vault Link Summary ************ Link 0.28 0.32 0.55 0.10 0.07 Element Invert Maximum Ponded External Type Elevation Elev. Area Inflow ft ft ft2 ---------------------------------------------------------- JUNCTION 187.59 192.33 0.00 JUNCTION 198.50 208.65 0.00 JUNCTION 204.50 211.01 0.00 JUNCTION 232.92 251.22 0.00 JUNCTION 246.31 252.18 0.00 JUNCTION 243.85 248.17 0.00 JUNCTION 238.61 245.61 0.00 JUNCTION 172.24 176.14 0.00 STORAGE 238.61 245.61 1552.00 From Node To Node Element Length Slope Manning's Autodesk Storm and Sanitary Analysis ID -------------------------------------------------------------------------------------------- Type ft o Roughness Link-01 CB 6 Detention Vault CONDUIT 35.0 1.4857 0.0150 Link-02 Detention Vault CS CONDUIT 5.0 0.0200 0.0150 Link-03 CB 5 Detention Vault CONDUIT 11.0 12.3636 0.0150 Link-06 CB 4 WQ CB 3 CONDUIT 103.0 27.5922 0.0150 Link-07 CB 3 CB 2 CONDUIT 100.0 6.0000 0.0150 Link-08 CB 2 CB 1 CONDUIT 151.0 7.2252 0.0150 Link-09 CB 1 Ex CB CONDUIT 55.0 27.9091 0.0150 Link-10 CS CB 4 WQ CONDUIT 8.0 42.0000 0.0150 ********************* Cross Section Summary ********************* Link Shape Depth/ Width No. of Cross Full Flow Design ID Diameter Barrels Sectional Hydraulic Flow Area Radius Capacity ft ft ft2 ft cfs ------------------------------------------------------------------------------------------------- Link-01 CIRCULAR 1.00 1.00 1 0.79 0.25 3.76 Link-02 CIRCULAR 1.00 1.00 1 0.79 0.25 0.44 Link-03 CIRCULAR 1.00 1.00 1 0.79 0.25 10.86 Link-06 CIRCULAR 0.67 0.67 1 0.35 0.17 5.50 Link-07 CIRCULAR 0.67 0.67 1 0.35 0.17 2.57 Link-08 CIRCULAR 0.67 0.67 1 0.35 0.17 2.82 Link-09 CIRCULAR 0.67 0.67 1 0.35 0.17 5.53 Link-10 CIRCULAR 1.00 1.00 1 0.79 0.25 20.01 ************************** Volume Depth Runoff Quantity Continuity ************************** acre-ft inches Total Precipitation ...... 0.029 0.260 Continuity Error (%) ..... 0.351 ************************** Volume Volume Flow Routing Continuity ************************** acre-ft Mgallons External Inflow .......... --------- 0.000 --------- 0.000 External Outflow ......... 0.018 0.006 Initial Stored Volume .... 0.000 0.000 Final Stored Volume ...... 0.001 0.000 Continuity Error (%) ..... 0.000 ************************************** Runoff Coefficient Computations Report ************************************** Subbasin Lot C Autodesk Storm and Sanitary Analysis Area Soil Runoff Soil/Surface Description (acres) Group Coeff. ----------------------------------------------------------------------------------------- 0.06 - 0.89 - 0.01 - 0.89 0.21 - 0.52 Composite Area & Weighted Runoff Coeff. 0.28 0.61 Subbasin Lot D Area Soil Runoff Soil/Surface Description (acres) Group Coeff. ----------------------------------------------------------------------------------------- - 0.06 - 0.89 0.02 - 0.89 - 0.24 - 0.52 Composite Area & Weighted Runoff Coeff. 0.32 0.61 Subbasin Lots AB Area Soil Runoff Soil/Surface Description (acres) Group Coeff. ----------------------------------------------------------------------------------------- - 0.12 - 0.89 - 0.03 - 0.89 - 0.01 - 0.89 - 0.39 - 0.52 Composite Area & Weighted Runoff Coeff. 0.55 0.63 Subbasin Roadl Area Soil Runoff Soil/Surface Description (acres) Group Coeff. ----------------------------------------------------------------------------------------- 0.10 - 0.89 Composite Area & Weighted Runoff Coeff. 0.10 0.89 Subbasin Road2 Area Soil Runoff Soil/Surface ----------------------------------------------------------------------------------------- Description (acres) Group Coeff. - 0.07 - 0.89 Composite Area & Weighted Runoff Coeff. 0.07 0.89 Subbasin Runoff Summary --------------------------------------------------------------------------------------- Subbasin Accumulated Rainfall Total Peak Weighted Time of ID Precip Intensity Runoff Runoff Runoff Concentration in in/hr in cfs Coeff days hh:mm:ss --------------------------------------------------------------------------------------- Lot C 0.26 2.60 0.16 0.44 0.610 0 00:06:00 Lot D 0.26 2.60 0.16 0.51 0.610 0 00:06:00 Lots AB 0.26 2.60 0.16 0.90 0.630 0 00:06:00 Roadl 0.26 2.60 0.23 0.23 0.890 0 00:06:00 Road2 --------------------------------------------------------------------------------------- 0.26 2.60 0.23 0.16 0.890 0 00:06:00 Autodesk Storm and Sanitary Analysis Node Depth Summary ----------------------------------------------------------------------------------------- Node Average Maximum Maximum Time of Max Total Total Retention ID Depth Depth HGL Occurrence Flooded Time Time Attained Attained Attained Volume Flooded ft ft ft days hh:mm acre -in minutes hh:mm:ss ----------------------------------------------------------------------------------------- CB 1 0.02 0.12 187.71 0 00:12 0 0 0:00:00 CB 2 0.02 0.13 198.63 0 00:12 0 0 0:00:00 CB 3 0.02 0.13 204.63 0 00:12 0 0 0:00:00 CB 4 WQ 2.34 2.40 235.32 0 00:11 0 0 0:00:00 CB 5 0.00 0.22 246.53 0 00:06 0 0 0:00:00 CB 6 0.00 0.36 244.21 0 00:06 0 0 0:00:00 CS 0.07 0.48 239.09 0 00:11 0 0 0:00:00 Ex CB 3.88 3.90 176.14 0 00:05 0 0 0:00:00 Detention Vault 0.07 0.48 239.09 0 00:11 0 0 0:00:00 ***************** Node Flow Summary ***************** ------------------------------------------------------------------------------------ Node Element Maximum Peak Time of Maximum Time of Peak ID Type Lateral Inflow Peak Inflow Flooding Flooding Inflow Occurrence Overflow Occurrence ------------------------------------------------------------------------------------ cfs cfs days hh:mm cfs days hh:mm CB 1 JUNCTION 0.00 0.20 0 00:12 0.00 CB 2 JUNCTION 0.00 0.20 0 00:12 0.00 CB 3 JUNCTION 0.00 0.21 0 00:12 0.00 CB 4 WQ JUNCTION 0.00 0.21 0 00:11 0.00 CB 5 JUNCTION 1.18 1.18 0 00:06 0.00 CB 6 JUNCTION 1.06 1.06 0 00:06 0.00 CS JUNCTION 0.00 0.21 0 00:11 0.00 Ex CB JUNCTION 0.00 0.20 0 00:12 0.00 Detention Vault STORAGE 0.00 2.23 0 00:06 0.00 Storage Node Summary ------------------------------------------------------------------------------------------------- ------------------------------------ Storage Node ID Maximum Maximum Time of Max Average Average Maximum Maximum Time of Max. Total Ponded Ponded Ponded Ponded Ponded Storage Node Exfiltration Exfiltration Exfiltrated Volume Volume Volume Volume Volume Outflow Rate Rate Volume 1000 £t3 M days hh:mm 1000 ft3 M cfs cfm hh:mm:ss 1000 ft3 Detention Vault 0.749 0.00 0:00:00 0.000 Link Flow Summary ***************** Autodesk Storm and Sanitary Analysis 7 0 00:11 0.102 1 0.21 ------------------------------------------------------------------------------------------------- ------------------------------- Link ID Element Time of Maximum Length Peak Flow Design Ratio of Ratio of Total Reported Type Peak Flow Velocity Factor during Flow Maximum Maximum Time Condition Occurrence Attained Analysis Capacity /Design Flow Surcharged days hh:mm ft/sec cfs cfs Flow Depth minutes ------------------------------------------------------------------------------------------------- ------------------------------- Link-01 CONDUIT 0 00:06 4.68 1.00 1.06 3.76 0.28 0.36 0 Calculated Link-02 CONDUIT 0 00:11 0.55 1.00 0.21 0.44 0.47 0.48 0 Calculated Link-03 CONDUIT 0 00:06 9.07 1.00 1.18 10.86 0.11 0.22 0 Calculated Link-06 CONDUIT 0 00:12 7.53 1.00 0.21 5.50 0.04 0.13 0 Calculated Link-07 CONDUIT 0 00:12 4.41 1.00 0.20 2.57 0.08 0.19 0 Calculated Link-08 CONDUIT 0 00:12 4.71 1.00 0.20 2.82 0.07 0.18 0 Calculated Link-09 CONDUIT 0 00:12 7.56 1.00 0.20 5.53 0.04 0.13 0 Calculated Link-10 CONDUIT 0 00:11 8.20 1.00 0.21 20.01 0.01 0.07 0 Calculated ******************************** Highest Flow Instability Indexes ******************************** All links are stable. WARNING 004 : Minimum elevation drop used for Conduit Link-02. Analysis began on: Fri Apr 12 08:54:40 2024 Analysis ended on: Fri Apr 12 08:54:45 2024 Total elapsed time: 00:00:05 Autodesk Storm and Sanitary Analysis 100-Year Conveyance Analysis Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -46- Autodesk® Storm and Sanitary Analysis 2016 - Version 13.0.94 (Build 0) ----------------------------------------------------------------------------------------- Project Description ******************* File Name ................. Conveyance Analysis.SPF Analysis Options Flow Units ................ cfs Subbasin Hydrograph Method. Rational Time of Concentration...... User -Defined Link Routing Method ....... Kinematic Wave Storage Node Exfiltration.. None Starting Date ............. DEC-05-2022 00:00:00 Ending Date ............... DEC-06-2022 00:00:00 Report Time Step .......... 00:00:10 ************* Element Count ************* Number of subbasins ....... 5 Number of nodes ........... 9 Number of links ........... 8 **************** Subbasin **************** Summary Subbasin Total Area ID acres Lot C Lot D Lots AB Roadl Road2 ************ Node Summary ************ Node ID CB 1 CB 2 CB 3 CB 4 WQ CB 5 CB 6 CS Ex CB Detention Vault Link Summary ************ Link 0.28 0.32 0.55 0.10 0.07 Element Invert Maximum Ponded External Type Elevation Elev. Area Inflow ft ft ft2 ---------------------------------------------------------- JUNCTION 187.59 192.33 0.00 JUNCTION 198.50 208.65 0.00 JUNCTION 204.50 211.01 0.00 JUNCTION 232.92 251.22 0.00 JUNCTION 246.31 252.18 0.00 JUNCTION 243.85 248.17 0.00 JUNCTION 238.61 245.61 0.00 JUNCTION 172.24 176.14 0.00 STORAGE 238.61 245.61 1552.00 From Node To Node Element Length Slope Manning's Autodesk Storm and Sanitary Analysis ID -------------------------------------------------------------------------------------------- Type ft o Roughness Link-01 CB 6 Detention Vault CONDUIT 35.0 1.4857 0.0150 Link-02 Detention Vault CS CONDUIT 5.0 0.0200 0.0150 Link-03 CB 5 Detention Vault CONDUIT 11.0 12.3636 0.0150 Link-06 CB 4 WQ CB 3 CONDUIT 103.0 27.5922 0.0150 Link-07 CB 3 CB 2 CONDUIT 100.0 6.0000 0.0150 Link-08 CB 2 CB 1 CONDUIT 151.0 7.2252 0.0150 Link-09 CB 1 Ex CB CONDUIT 55.0 27.9091 0.0150 Link-10 CS CB 4 WQ CONDUIT 8.0 42.0000 0.0150 ********************* Cross Section Summary ********************* Link Shape Depth/ Width No. of Cross Full Flow Design ID Diameter Barrels Sectional Hydraulic Flow Area Radius Capacity ft ft ft2 ft cfs ------------------------------------------------------------------------------------------------- Link-01 CIRCULAR 1.00 1.00 1 0.79 0.25 3.76 Link-02 CIRCULAR 1.00 1.00 1 0.79 0.25 0.44 Link-03 CIRCULAR 1.00 1.00 1 0.79 0.25 10.86 Link-06 CIRCULAR 0.67 0.67 1 0.35 0.17 5.50 Link-07 CIRCULAR 0.67 0.67 1 0.35 0.17 2.57 Link-08 CIRCULAR 0.67 0.67 1 0.35 0.17 2.82 Link-09 CIRCULAR 0.67 0.67 1 0.35 0.17 5.53 Link-10 CIRCULAR 1.00 1.00 1 0.79 0.25 20.01 ************************** Volume Depth Runoff Quantity Continuity ************************** acre-ft inches Total Precipitation ...... 0.035 0.320 Continuity Error (%) ..... 0.351 ************************** Volume Volume Flow Routing Continuity ************************** acre-ft Mgallons External Inflow .......... --------- 0.000 --------- 0.000 External Outflow ......... 0.022 0.007 Initial Stored Volume .... 0.000 0.000 Final Stored Volume ...... 0.001 0.000 Continuity Error (%) ..... 0.001 ************************************** Runoff Coefficient Computations Report ************************************** Subbasin Lot C Autodesk Storm and Sanitary Analysis Area Soil Runoff Soil/Surface Description (acres) Group Coeff. ----------------------------------------------------------------------------------------- 0.06 - 0.89 - 0.01 - 0.89 0.21 - 0.52 Composite Area & Weighted Runoff Coeff. 0.28 0.61 Subbasin Lot D Area Soil Runoff Soil/Surface Description (acres) Group Coeff. ----------------------------------------------------------------------------------------- - 0.06 - 0.89 0.02 - 0.89 - 0.24 - 0.52 Composite Area & Weighted Runoff Coeff. 0.32 0.61 Subbasin Lots AB Area Soil Runoff Soil/Surface Description (acres) Group Coeff. ----------------------------------------------------------------------------------------- - 0.12 - 0.89 - 0.03 - 0.89 - 0.01 - 0.89 - 0.39 - 0.52 Composite Area & Weighted Runoff Coeff. 0.55 0.63 Subbasin Roadl Area Soil Runoff Soil/Surface Description (acres) Group Coeff. ----------------------------------------------------------------------------------------- 0.10 - 0.89 Composite Area & Weighted Runoff Coeff. 0.10 0.89 Subbasin Road2 Area Soil Runoff Soil/Surface ----------------------------------------------------------------------------------------- Description (acres) Group Coeff. - 0.07 - 0.89 Composite Area & Weighted Runoff Coeff. 0.07 0.89 Subbasin Runoff Summary --------------------------------------------------------------------------------------- Subbasin Accumulated Rainfall Total Peak Weighted Time of ID Precip Intensity Runoff Runoff Runoff Concentration in in/hr in cfs Coeff days hh:mm:ss --------------------------------------------------------------------------------------- Lot C 0.32 3.20 0.20 0.55 0.610 0 00:06:00 Lot D 0.32 3.20 0.20 0.62 0.610 0 00:06:00 Lots AB 0.32 3.20 0.20 1.11 0.630 0 00:06:00 Roadl 0.32 3.20 0.28 0.28 0.890 0 00:06:00 Road2 --------------------------------------------------------------------------------------- 0.32 3.20 0.28 0.20 0.890 0 00:06:00 Autodesk Storm and Sanitary Analysis Node Depth Summary ----------------------------------------------------------------------------------------- Node Average Maximum Maximum Time of Max Total Total Retention ID Depth Depth HGL Occurrence Flooded Time Time Attained Attained Attained Volume Flooded ft ft ft days hh:mm acre -in minutes hh:mm:ss ----------------------------------------------------------------------------------------- CB 1 0.02 0.14 187.73 0 00:12 0 0 0:00:00 CB 2 0.02 0.15 198.65 0 00:12 0 0 0:00:00 CB 3 0.02 0.15 204.65 0 00:11 0 0 0:00:00 CB 4 WQ 2.34 2.41 235.33 0 00:11 0 0 0:00:00 CB 5 0.00 0.25 246.56 0 00:06 0 0 0:00:00 CB 6 0.00 0.41 244.26 0 00:06 0 0 0:00:00 CS 0.07 0.59 239.20 0 00:11 0 0 0:00:00 Ex CB 3.89 3.90 176.14 0 00:05 0 0 0:00:00 Detention Vault 0.07 0.59 239.20 0 00:11 0 0 0:00:00 ***************** Node Flow Summary ***************** ------------------------------------------------------------------------------------ Node Element Maximum Peak Time of Maximum Time of Peak ID Type Lateral Inflow Peak Inflow Flooding Flooding Inflow Occurrence Overflow Occurrence ------------------------------------------------------------------------------------ cfs cfs days hh:mm cfs days hh:mm CB 1 JUNCTION 0.00 0.28 0 00:12 0.00 CB 2 JUNCTION 0.00 0.28 0 00:12 0.00 CB 3 JUNCTION 0.00 0.28 0 00:11 0.00 CB 4 WQ JUNCTION 0.00 0.28 0 00:11 0.00 CB 5 JUNCTION 1.46 1.46 0 00:06 0.00 CB 6 JUNCTION 1.31 1.31 0 00:06 0.00 CS JUNCTION 0.00 0.28 0 00:11 0.00 Ex CB JUNCTION 0.00 0.28 0 00:12 0.00 Detention Vault STORAGE 0.00 2.75 0 00:06 0.00 Storage Node Summary ------------------------------------------------------------------------------------------------- ------------------------------------ Storage Node ID Maximum Maximum Time of Max Average Average Maximum Maximum Time of Max. Total Ponded Ponded Ponded Ponded Ponded Storage Node Exfiltration Exfiltration Exfiltrated Volume Volume Volume Volume Volume Outflow Rate Rate Volume 1000 £t3 M days hh:mm 1000 ft3 M cfs cfm hh:mm:ss 1000 ft3 Detention Vault 0.911 0.00 0:00:00 0.000 Link Flow Summary ***************** Autodesk Storm and Sanitary Analysis 8 0 00:11 0.109 1 0.28 ------------------------------------------------------------------------------------------------- ------------------------------- Link ID Element Time of Maximum Length Peak Flow Design Ratio of Ratio of Total Reported Type Peak Flow Velocity Factor during Flow Maximum Maximum Time Condition Occurrence Attained Analysis Capacity /Design Flow Surcharged days hh:mm ft/sec cfs cfs Flow Depth minutes ------------------------------------------------------------------------------------------------- ------------------------------- Link-01 CONDUIT 0 00:06 4.86 1.00 1.30 3.76 0.35 0.41 0 Calculated Link-02 CONDUIT 0 00:11 0.59 1.00 0.28 0.44 0.65 0.59 0 Calculated Link-03 CONDUIT 0 00:06 9.63 1.00 1.45 10.86 0.13 0.25 0 Calculated Link-06 CONDUIT 0 00:11 8.29 1.00 0.28 5.50 0.05 0.15 0 Calculated Link-07 CONDUIT 0 00:12 4.84 1.00 0.28 2.57 0.11 0.22 0 Calculated Link-08 CONDUIT 0 00:12 5.17 1.00 0.28 2.82 0.10 0.21 0 Calculated Link-09 CONDUIT 0 00:12 8.32 1.00 0.28 5.53 0.05 0.15 0 Calculated Link-10 CONDUIT 0 00:11 9.08 1.00 0.28 20.01 0.01 0.08 0 Calculated ******************************** Highest Flow Instability Indexes ******************************** All links are stable. WARNING 004 : Minimum elevation drop used for Conduit Link-02. Analysis began on: Fri Apr 12 08:56:29 2024 Analysis ended on: Fri Apr 12 08:56:33 2024 Total elapsed time: 00:00:04 Autodesk Storm and Sanitary Analysis