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DNS BLD2022-1035+Storm_Drainage_Report+8.4.2022_1.51.18_PM+3033469IEC INSIGHT ENGINEERING CO. 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 Edmonds, WA 98020 Applicant: Landsverk Quality Homes, Inc. 24113 56th Ave W Mountlake Terrace, WA 98043 Contact: IECO P.O. Box 1478 Everett, WA 98206 425-303-9363 Tax Id: 00434600006104, 00434600006105, 00434600006106 IECO Project: 20-1094 Certified Erosion and Sedimentation Control Lead: To be named by contractor Stormwater Site Plan Prepared By: Nicole Maas, E.I.T. R. Stormwater Site Plan Preparation Date: ��' o� WA w May 9, 2022a / v 3fi4" i9 Approximate Construction Date: 99 �sSI oNa[� IS May 1, 2023 06/21/2022 P.O. Box 1478 *Everett, WA 98206• P: 425.303.9363 info@insightengineering.net ;e TABLE OF CONTENTS 1.0 Executive Summary................................................................................................................3 1.1 Minimum Requirements Summary..............................................................................................7 2.0 Existing Conditions.................................................................................................................8 3.0 Offsite Analysis.....................................................................................................................13 3.1 Upstream Analysis.....................................................................................................................13 3.2 Downstream Analysis................................................................................................................13 4.0 Developed Conditions..........................................................................................................16 5.0 Site Hydraulic Analysis.........................................................................................................18 5.1 Existing Basin Summary............................................................................................................18 5.2 Developed Basin Summary........................................................................................................18 6.0 Appendix...............................................................................................................................25 Figures Figure1 - Vicinity Map.................................................................................................................6 Figure2 - Soil Map......................................................................................................................10 Figure 3 - Downstream Analysis Map 1....................................................................................14 Figure 4 - Downstream Analysis Map 2....................................................................................15 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, 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' 2017 requirements and the requirements defined in DOE's 2014 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. There are no critical areas located on the site. 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 19,966 SF. Per Figure 3.1, (Flow Chart for Determining Requirements for Development) from the 2017 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 10' O 110 LF detention pipe located under the proposed drive aisle. The pipe will provide a total detention capacity of 8,276 cf. The detention pipe 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 pipe. Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -3- 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 pipe 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 pipe 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 new 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 nee+ 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 • I - Ajai , ±►-w' id R � t• ��, i rt 1 �y LA a* dR �� .- • i � . ` .ice , � �, -+_ , Taken from Google Maps marf) INSIGHT ENGINEERING CO. P.O. Box 1478, Everett, WA 98206 425-303-9363 Info@insightengineering.net Insight Engineering Co. - Stormwater Site Plan Figure I -Vicinity Map Iron Vista Road Edmonds, Washington SCALE: DATE: 6/21/22 JOB#: 20-1094 NTS FILE NAME: BY: NAM 20-1094/doe/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 2017 requirements and in accordance with DOE's 2014 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: No source control pollutants pertain to the proposed single-family project; therefore, no BMPs are required for the project. 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 pipe 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 Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -7- other hard surfaces will be directed to the proposed detention pipe 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. MR #6 Runoff Treatment: MR #6 water quality will be met by a Contech Stormfilter located downstream of the detention pipe. MR #7 Flow Control: Per Figure 3.1, (Flow Chart for Determining Requirements for Development) from the 2017 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 10' 0 110 LF detention pipe located under the proposed drive aisle. The pipe will provide a total detention capacity of 8,276 cf. The detention pipe has been sized to detain the runoff from the future impervious area in parcel numbers 00434600006102, 00434600006104, 00434600006105, and 00434600006106. Please refer to section 5.0 Site Hydraulic Conditions for more information. 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 190 St SW, 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' 2017 requirements and the requirements defined in DOE's 2014 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. There are no critical areas located on the site. 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 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 mur INSIGHT ENGINEERING CO. P.O. Box 1478, Everett, WA 98206 425-303-9363 Info@insightengineering.net Figure 2 - Soil Map Iron Vista Road Edmonds, Washington ISCALE: I DATE: 6/21/22 I JOB #: 20-1094 I NONE FILE NAME: BY: NAM 1 20-1094/ doc/Stormwater Site Plan 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 • H1 - 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. 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: 6/21/22 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: 6/21/22 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, 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 19,966 SF. Per Figure 3.1, (Flow Chart for Determining Requirements for Development) from the 2017 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 10' O 110 LF detention pipe located under the proposed drive aisle. The pipe will provide a total detention capacity of 8,276 cf. The detention pipe 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 pipe. 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 pipe 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 pipe 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". 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 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* = 0.23 Acres (10,204 SF) Driveway** = 0.06 Acres ( 2,588 SF) Sidewalk*** = 0.03 Acres ( 1,080 SF) Road = 0.14 Acres ( 6,094 SF) Total Impervious = 0.46 Acres (19,966 SF) Pervious Area = 1.23 Acres — 0.46 Acres = 0.77 Acres *The roof area includes 2,588 SFfrom Lot A, 2,616 SFfrom Lot B, 2,440 SFfrom Lot C, and 2,560 SFfrom Lot D. **The driveway area includes 722 SFfrom Lot A, 690 SFfrom Lot B, 489 SFfrom Lot C, and 687 SFfrom Lot D. ***The sidewalk area includes 278 SFfrom Lot A, 280 SFfrom Lot B, 280 SFfrom Lot C, and 242 SFfrom Lot D. Please refer to the developed basin map and the WWHM report in Appendix E for more details. 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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 -22- B. STORMWATER POLLUTION PREVENTION PLAN This Stormwater Pollution Prevention Plan (SWPPP) has been prepared as part of the Construction stormwater permit requirements for the project Iron Vista Road located at 9500 1901h St SW, 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 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. There are no critical areas located on the site. Per NRCS survey of Snohomish County, the project site contains Alderwood soils that have a hydrologic classification of Type "C". 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 19,966 SF. Per Figure 3.1, (Flow Chart for Determining Requirements for Development) from the 2017 Edmonds Stormwater Addendum, Minimum requirements #1 through 9 shall apply for this project. Flow Control requirements will be met by a 10' D 110 LF detention pipe located under the proposed drive aisle. The pipe will provide a total detention capacity of 8,276 cf. Water quality requirements will be met by a Contech Stormfilter located downstream of the detention pipe. The purpose of this SWPPP is to describe the proposed construction activities and all temporary and permanent erosion and sediment control (TESC) measures, pollution prevention measures, inspection/monitoring activities, and recordkeeping that will be implemented during the proposed construction project. The objectives of the SWPPP are to: 1. Implement Best Management Practices (BMPs) to prevent erosion and sedimentation, and to identify, reduce, eliminate or prevent stormwater contamination and water pollution from construction activity. 2. Prevent violations of surface water quality, ground water quality, or sediment management standards. Insight Engineering Co. - Stormwater Site Plan 2/3/2022 - 23 - Prevent, during the construction phase, adverse water quality impacts including impacts on beneficial uses of the receiving water by controlling peak flow rates and volumes of stormwater runoff at the Permittee's outfalls and downstream of the outfalls. This SWPPP was prepared using the Ecology SWPPP Template. This SWPPP was prepared based on the requirements set forth in the Construction Stormwater General Permit and in the Stormwater Management Manual for Western Washington (SWMMWW 2014). The 13 BMP Elements Element #1— Mark Clearing Limits To protect adjacent properties and to reduce the area of soil exposed to construction, the limits of construction will be clearly marked before land -disturbing activities begin. Element #2 — Establish Construction Access 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, and wheel washing, street sweeping, and street cleaning shall be employed to prevent sediment from entering state waters. Install the temporary construction entrance, according to the approved construction plans, prior to any clearing or grading activities. Maintain until the access road is paved. Element #3 — Control Flow Rates 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. Element #4 — Install Sediment Controls Install silt fencing, according to the approved plans, prior to any clearing or grading activities. Maintain until all construction activities are completed. Install catch basin filters, according to the approved construction plans, as catch basins become operable. Maintain until all construction activities are completed. Element #5 — Stabilize Soils Exposed and un-worked soils shall be stabilized with the application of effective BMPs to prevent erosion throughout the life of the project. Apply temporary hydro -seed to exposed and un-worked soils, according to the approved construction plans, as needed to prevent erosion during site grading. Apply permanent hydro -seed to areas at final grade as site grading is completed. Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -24- Apply mulching to exposed and un-worked soils, according to the approved construction plans, as needed to prevent erosion during site grading. Maintain until site grading is completed and permanent hydro -seed is applied. Cover stockpiles with plastic sheeting, according to the approved construction plans, as needed to prevent erosion during site grading. Maintain until stockpiles are removed from site. Element #6 — Protect Slopes All cut and fill slopes will be designed, constructed, and protected in a manner than minimizes erosion. The following specific BMPs will be used to protect slopes for this project. Element #7 — Protect Drain Inlets 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. Element #8 — Stabilize Channels and Outlets Where site runoff is to be conveyed in channels, or discharged to a stream or some other natural drainage point, efforts will be taken to prevent downstream erosion. Element #9 — Control Pollutants 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. Element #10 — Control Dewaterin2 There will be no dewatering expected as part of this proposal. If it occurs, Baker tanks will be used for dewatering. Element #11— Maintain BMPs All temporary and permanent erosion and sediment control BMPs shall be maintained and repaired as needed to assure continued performance of their intended function. Maintenance and repair shall be conducted in accordance with each particular BMP's specifications. Visual monitoring of the BMPs will be conducted at least once every calendar week and within 24 hours of any rainfall event that causes a discharge from the site. If the site becomes inactive, and is temporarily stabilized, the inspection frequency will be reduced to once every month. All temporary erosion and sediment control BMPs shall be removed within 30 days after the final site stabilization is achieved or after the temporary BMPs are no longer needed. Trapped sediment shall be removed or stabilized on site. Disturbed soil resulting from removal of BMPs or vegetation shall be permanently stabilized. Insight Engineering Co. - Stormwater Site Plan 2/3/2022 - 25 - Element #12 — Manage the Proiect Erosion and sediment control BMPs for this project have been designed based on the following principles: Design the project to fit the existing topography, soils, and drainage patterns; Emphasize erosion control rather than sediment control; Minimize the extent and duration of the area exposed; Keep runoff velocities low; Retain sediment on site; Thoroughly monitor site and maintain all ESC measures and Schedule major earthwork during the dry season. The SWPPP shall be modified as necessary to include additional or modified BMPs designed to correct problems identified. Revisions to the SWPPP shall be completed within seven (7) days following the inspection. Element #13 — Protect On -site Stormwater Management BMPs for Runoff from Roofs and Other Hard Surfaces On -site stormwater management BMPs used for runoff from roofs and other hard surfaces include: full dispersion, roof downspout full infiltration or dispersion systems, perforated stubout connections, rain gardens, bioretention systems, permeable pavement, sheetflow dispersion, and concentrated flow dispersion. The areas on the site to be used for these BMPs shall be protected from siltation and compaction during construction by sequencing the construction in a fashion to install these BMPs at the latter part of the construction grading operations, by excluding equipment from the BMPS and the associated areas, and by using the erosion and sedimentation control BMPs listed below. Additional requirements for protecting these BMPs during the construction process, testing functionality, and restoring functionality are needed at the final stage of the construction process. Relevant BMPs BMP C 102: Buffer Zone BMP C103: High Visibility Fence BMP C200: Interceptor Dike and Swale BMP C207: Check Dams BMP C208: Triangular Silt Dike BMP C231: Brush Barrier BMP C233: Silt Fence BMP C234: Vegetated Strip Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -26- C. GEOTECH REPORT Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -27- 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 D. OPERATION & MAINTENANCE MANUAL Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -28- 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 Insight Engineering Co. - Stormwater Site Plan 2/3/2022 -29- WWHM2012 PROJECT REPORT General Model Information Project Name: Linton Lot A Site Name: Linton Lot A Site Address: 9500 190th PI SW City: Lynnwood Report Date: 2/17/2022 Gage: Everett Data Start: 1948/10/01 Data End: 2009/09/30 Timestep: Hourly Precip Scale: 0.800 Version Date: 2019/09/13 Version: 4.2.17 POC Thresholds Low Flow Threshold for POC1: 50 Percent of the 2 Year High Flow Threshold for POC1: 50 Year Linton Lot A 2/17/2022 3:23:35 PM Page 2 Landuse Basin Data Predeveloped Land Use Predeveloped Bypass: No GroundWater: No Pervious Land Use acre C, Forest, Mod 0.08 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 Groundwater Linton Lot A 2/17/2022 3:23:36 PM Page 3 Mitigated Land Use Developed Bypass: GroundWater: Pervious Land Use C, Lawn, Steep Pervious Total Impervious Land Use ROADS FLAT ROADS STEEP ROOF TOPS FLAT DRIVEWAYS FLAT SIDEWALKS FLAT Impervious Total Basin Total Element Flows To: Surface Tank 1 No No acre 0.77 0.77 acre 0.02 0.12 0.23 0.06 0.03 IM. 1.23 Interflow Tank 1 Groundwater Linton Lot A 2/17/2022 3:23:36 PM Page 4 Routing Elements Predeveloped Routing Linton Lot A 2/17/2022 3:23:36 PM Page 5 Mitigated Routing Tank 1 Dimensions Depth: 10 ft. Tank Type: Circular Diameter: 10 ft. Length: 110 ft. Discharge Structure Riser Height: 9 ft. Riser Diameter: 12 in. Orifice 1 Diameter: 0.38 in. Elevation:0 ft. Orifice 2 Diameter: 0.5 in. Elevation:7 ft. Orifice 3 Diameter: 0.75 in. Elevation:8 ft. Element Flows To: Outlet 1 Outlet 2 Tank Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 0.0000 0.000 0.000 0.000 0.000 0.1111 0.005 0.000 0.001 0.000 0.2222 0.007 0.001 0.001 0.000 0.3333 0.009 0.002 0.002 0.000 0.4444 0.010 0.003 0.002 0.000 0.5556 0.011 0.004 0.002 0.000 0.6667 0.012 0.005 0.003 0.000 0.7778 0.013 0.007 0.003 0.000 0.8889 0.014 0.008 0.003 0.000 1.0000 0.015 0.010 0.003 0.000 1.1111 0.015 0.012 0.004 0.000 1.2222 0.016 0.013 0.004 0.000 1.3333 0.017 0.015 0.004 0.000 1.4444 0.017 0.017 0.004 0.000 1.5556 0.018 0.019 0.004 0.000 1.6667 0.018 0.021 0.005 0.000 1.7778 0.019 0.023 0.005 0.000 1.8889 0.019 0.026 0.005 0.000 2.0000 0.020 0.028 0.005 0.000 2.1111 0.020 0.030 0.005 0.000 2.2222 0.021 0.032 0.005 0.000 2.3333 0.021 0.035 0.006 0.000 2.4444 0.021 0.037 0.006 0.000 2.5556 0.022 0.040 0.006 0.000 2.6667 0.022 0.042 0.006 0.000 2.7778 0.022 0.045 0.006 0.000 2.8889 0.022 0.047 0.006 0.000 3.0000 0.023 0.050 0.006 0.000 3.1111 0.023 0.052 0.006 0.000 3.2222 0.023 0.055 0.007 0.000 3.3333 0.023 0.057 0.007 0.000 3.4444 0.024 0.060 0.007 0.000 3.5556 0.024 0.063 0.007 0.000 3.6667 0.024 0.065 0.007 0.000 3.7778 0.024 0.068 0.007 0.000 3.8889 0.024 0.071 0.007 0.000 Linton Lot A 2/17/2022 3:23:36 PM Page 6 4.0000 0.024 0.074 0.007 0.000 4.1111 0.024 0.076 0.007 0.000 4.2222 0.024 0.079 0.008 0.000 4.3333 0.025 0.082 0.008 0.000 4.4444 0.025 0.085 0.008 0.000 4.5556 0.025 0.088 0.008 0.000 4.6667 0.025 0.090 0.008 0.000 4.7778 0.025 0.093 0.008 0.000 4.8889 0.025 0.096 0.008 0.000 5.0000 0.025 0.099 0.008 0.000 5.1111 0.025 0.102 0.008 0.000 5.2222 0.025 0.104 0.009 0.000 5.3333 0.025 0.107 0.009 0.000 5.4444 0.025 0.110 0.009 0.000 5.5556 0.025 0.113 0.009 0.000 5.6667 0.025 0.116 0.009 0.000 5.7778 0.024 0.118 0.009 0.000 5.8889 0.024 0.121 0.009 0.000 6.0000 0.024 0.124 0.009 0.000 6.1111 0.024 0.127 0.009 0.000 6.2222 0.024 0.129 0.009 0.000 6.3333 0.024 0.132 0.009 0.000 6.4444 0.024 0.135 0.009 0.000 6.5556 0.024 0.137 0.010 0.000 6.6667 0.023 0.140 0.010 0.000 6.7778 0.023 0.143 0.010 0.000 6.8889 0.023 0.145 0.010 0.000 7.0000 0.023 0.148 0.010 0.000 7.1111 0.022 0.150 0.012 0.000 7.2222 0.022 0.153 0.013 0.000 7.3333 0.022 0.155 0.014 0.000 7.4444 0.022 0.158 0.015 0.000 7.5556 0.021 0.160 0.015 0.000 7.6667 0.021 0.163 0.016 0.000 7.7778 0.021 0.165 0.016 0.000 7.8889 0.020 0.167 0.017 0.000 8.0000 0.020 0.170 0.017 0.000 8.1111 0.019 0.172 0.023 0.000 8.2222 0.019 0.174 0.025 0.000 8.3333 0.018 0.176 0.028 0.000 8.4444 0.018 0.178 0.029 0.000 8.5556 0.017 0.180 0.031 0.000 8.6667 0.017 0.182 0.032 0.000 8.7778 0.016 0.184 0.034 0.000 8.8889 0.015 0.186 0.035 0.000 9.0000 0.015 0.188 0.036 0.000 9.1111 0.014 0.189 0.427 0.000 9.2222 0.013 0.191 1.084 0.000 9.3333 0.012 0.192 1.723 0.000 9.4444 0.011 0.194 2.129 0.000 Linton Lot A 2/17/2022 3:23:36 PM Page 7 Analysis Results POC 1 0.05 n w 0.04 )v 0.03 Q iL 0.02 0.01 4 e� 10E-4 10E-3 10E-2 10E-1 1 10 100 Percerit Time Exceeding + Predeveloped Predeveloped Landuse Totals for POC #1 Total Pervious Area- 1.23 Total Impervious Area- 0 Mitigated Landuse Totals for POC #1 Total Pervious Area- 0.77 Total Impervious Area- 0.46 Cumulative Probability 0n 001 "1 05 7 2 x Mitigated Flow Frequency Method- Log Pearson Type III 17B Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.02029 5 year 0.031903 10 year 0.039158 25 year 0.047632 50 year 0.053421 100 year 0.058776 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.011345 5 year 0.022274 10 year 0.033623 25 year 0.054658 50 year 0.076812 100 year 0.106213 Annual Peaks Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.003 0.008 1950 0.027 0.010 1951 0.018 0.009 1952 0.015 0.008 1953 0.015 0.007 1954 0.023 0.009 1955 0.038 0.028 1956 0.025 0.030 1957 0.032 0.015 1958 0.027 0.009 uxn gaol 5 70 20 30 50 70 W 90 95 95 99 99.5 7 Linton Lot A 2/17/2022 3:23:36 PM Page 8 1959 0.023 0.010 1960 0.022 0.010 1961 0.022 0.016 1962 0.014 0.008 1963 0.024 0.009 1964 0.022 0.008 1965 0.016 0.010 1966 0.010 0.008 1967 0.031 0.009 1968 0.031 0.010 1969 0.014 0.009 1970 0.014 0.009 1971 0.025 0.033 1972 0.024 0.009 1973 0.012 0.010 1974 0.018 0.010 1975 0.015 0.008 1976 0.016 0.009 1977 0.007 0.008 1978 0.015 0.008 1979 0.040 0.009 1980 0.017 0.008 1981 0.018 0.008 1982 0.023 0.010 1983 0.016 0.009 1984 0.018 0.032 1985 0.029 0.018 1986 0.074 0.149 1987 0.025 0.072 1988 0.017 0.010 1989 0.016 0.007 1990 0.017 0.010 1991 0.020 0.010 1992 0.015 0.010 1993 0.010 0.007 1994 0.009 0.010 1995 0.017 0.016 1996 0.045 0.017 1997 0.083 0.232 1998 0.013 0.009 1999 0.021 0.010 2000 0.012 0.014 2001 0.002 0.006 2002 0.019 0.012 2003 0.012 0.009 2004 0.018 0.015 2005 0.019 0.009 2006 0.048 0.017 2007 0.031 0.016 2008 0.057 0.126 2009 0.017 0.009 Ranked Annual Peaks Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.0830 0.2317 2 0.0739 0.1493 3 0.0565 0.1264 Linton Lot A 2/17/2022 3:23:56 PM Page 9 4 0.0480 0.0721 5 0.0451 0.0326 6 0.0396 0.0319 7 0.0377 0.0299 8 0.0322 0.0283 9 0.0314 0.0177 10 0.0306 0.0174 11 0.0305 0.0167 12 0.0291 0.0163 13 0.0268 0.0163 14 0.0267 0.0157 15 0.0251 0.0151 16 0.0250 0.0146 17 0.0248 0.0141 18 0.0245 0.0124 19 0.0243 0.0103 20 0.0232 0.0103 21 0.0228 0.0102 22 0.0227 0.0101 23 0.0224 0.0101 24 0.0216 0.0101 25 0.0216 0.0099 26 0.0205 0.0098 27 0.0195 0.0097 28 0.0192 0.0097 29 0.0191 0.0096 30 0.0184 0.0096 31 0.0183 0.0096 32 0.0182 0.0095 33 0.0178 0.0094 34 0.0176 0.0093 35 0.0167 0.0093 36 0.0167 0.0092 37 0.0167 0.0090 38 0.0167 0.0090 39 0.0166 0.0089 40 0.0163 0.0088 41 0.0161 0.0087 42 0.0161 0.0087 43 0.0161 0.0087 44 0.0155 0.0086 45 0.0152 0.0086 46 0.0151 0.0086 47 0.0150 0.0086 48 0.0146 0.0082 49 0.0145 0.0082 50 0.0138 0.0082 51 0.0137 0.0082 52 0.0131 0.0082 53 0.0122 0.0081 54 0.0122 0.0078 55 0.0121 0.0078 56 0.0105 0.0076 57 0.0101 0.0076 58 0.0090 0.0074 59 0.0070 0.0072 60 0.0033 0.0070 61 0.0021 0.0063 Linton Lot A 2/17/2022 3:23:56 PM Page 10 Linton Lot A 2/17/2022 3:23:56 PM Page 11 Duration Flows The Facility PASSED Flow(cfs) Predev Mit Percentage Pass/Fail 0.0101 3384 2046 60 Pass 0.0106 3097 1402 45 Pass 0.0110 2845 1366 48 Pass 0.0115 2598 1325 51 Pass 0.0119 2377 1299 54 Pass 0.0123 2165 1259 58 Pass 0.0128 1978 1214 61 Pass 0.0132 1808 1167 64 Pass 0.0136 1666 1098 65 Pass 0.0141 1533 1004 65 Pass 0.0145 1396 930 66 Pass 0.0150 1294 853 65 Pass 0.0154 1189 778 65 Pass 0.0158 1099 694 63 Pass 0.0163 1008 586 58 Pass 0.0167 921 483 52 Pass 0.0171 844 406 48 Pass 0.0176 790 330 41 Pass 0.0180 732 294 40 Pass 0.0185 685 283 41 Pass 0.0189 649 279 42 Pass 0.0193 613 274 44 Pass 0.0198 575 271 47 Pass 0.0202 545 266 48 Pass 0.0206 505 264 52 Pass 0.0211 471 260 55 Pass 0.0215 437 258 59 Pass 0.0219 410 254 61 Pass 0.0224 380 253 66 Pass 0.0228 362 250 69 Pass 0.0233 341 246 72 Pass 0.0237 326 243 74 Pass 0.0241 304 240 78 Pass 0.0246 288 235 81 Pass 0.0250 273 232 84 Pass 0.0254 254 227 89 Pass 0.0259 243 222 91 Pass 0.0263 231 216 93 Pass 0.0268 222 211 95 Pass 0.0272 212 203 95 Pass 0.0276 204 197 96 Pass 0.0281 196 185 94 Pass 0.0285 189 175 92 Pass 0.0289 177 169 95 Pass 0.0294 170 162 95 Pass 0.0298 163 155 95 Pass 0.0303 158 147 93 Pass 0.0307 152 141 92 Pass 0.0311 146 136 93 Pass Linton Lot A 2/17/2022 3:23:56 PM Page 12 0.0333 128 108 84 Pass 0.0338 127 103 81 Pass 0.0342 123 102 82 Pass 0.0346 121 98 80 Pass 0.0351 119 93 78 Pass 0.0355 118 88 74 Pass 0.0359 113 81 71 Pass 0.0364 112 74 66 Pass 0.0368 110 71 64 Pass 0.0372 109 70 64 Pass 0.0377 106 68 64 Pass 0.0381 101 68 67 Pass 0.0386 100 67 67 Pass 0.0390 97 67 69 Pass 0.0394 92 67 72 Pass 0.0399 87 66 75 Pass 0.0403 86 63 73 Pass 0.0407 83 63 75 Pass 0.0412 83 63 75 Pass 0.0416 80 62 77 Pass 0.0421 79 61 77 Pass 0.0425 76 59 77 Pass 0.0429 73 59 80 Pass 0.0434 71 56 78 Pass 0.0438 70 56 80 Pass 0.0442 68 55 80 Pass 0.0447 67 51 76 Pass 0.0451 66 50 75 Pass 0.0456 64 50 78 Pass 0.0460 63 50 79 Pass 0.0464 60 50 83 Pass 0.0469 59 49 83 Pass 0.0473 58 49 84 Pass 0.0477 57 47 82 Pass 0.0482 54 46 85 Pass 0.0486 54 46 85 Pass 0.0490 53 46 86 Pass 0.0495 52 46 88 Pass 0.0499 51 44 86 Pass 0.0504 49 44 89 Pass 0.0508 49 43 87 Pass 0.0512 47 41 87 Pass 0.0517 47 41 87 Pass 0.0521 46 41 89 Pass 0.0525 46 40 86 Pass 0.0530 44 39 88 Pass 0.0534 43 39 90 Pass Linton Lot A 2/17/2022 3:23:56 PM Page 13 Water Quality Water Quality BMP Flow and Volume for POC #1 On-line facility volume: 0 acre-feet On-line facility target flow: 0 cfs. Adjusted for 15 min: 0 cfs. Off-line facility target flow: 0 cfs. Adjusted for 15 min: 0 cfs. Linton Lot A 2/17/2022 3:23:56 PM Page 14 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 Tank 1 POC ❑ 81.75 ❑ 0.00 Total Volume Infiltrated 81.75 0 Oi 1 [i 00 0 00 0.00 0% No Treat. Credit Duration Compliance with LID Analysis Standard 8% of 2-yr to 50% of Result= 2 yr Failed Linton Lot A 2/17/2022 3:23:56 PM Page 15 Model Default Modifications Total of 0 changes have been made. PERLND Changes No PERLND changes have been made. IMPLND Changes No IMPLND changes have been made. Linton Lot A 2/17/2022 3:24:10 PM Page 16 Appendix Predeveloped Schematic redevelopec Linton Lot A 2/17/2022 3:24:10 PM Page 17 Mitigated Schematic Developed 1.23ad SI Tank 1 u Linton Lot A 2/17/2022 3:24:19 PM Page 18 Linton Lot A 2/17/2022 3:24:19 PM Page 18