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BLD2022-1087+Storm_Drainage_Report+8.15.2022_1.25.27_PM+30511847918 203rd Street SW 2-Lot Short Plat Introduction: This summary report provides site design information for a residential 2-lot short plat development by Select Homes. This report includes storm drainage analysis to support permit review and approval. The property is located at 7918 203rd Street SW, in the northeast 1/4 of Section 19, T 27 N, R 4 E, W.M. Site Address: 7918 203rd Street SW Applicant: Select Homes Edmonds, WA 98026 16513 13th Ave W, Suite A108, Lynnwood WA 98037 Tax Parcel Number: 270419 001 127 00 Contact: Kayla Clark Nichols (425) 742-6044 TABLE OF CONTENTS SECTION A. Project Overview................................................................................. B. Existing Conditions Summary.............................................................. C. Developed Site Hydrology................................................................... D. Soils Report.......................................................................................... E. Construction SWPPPP Requirements................................................... F. Operation and Maintenance Guidelines ............................................... PAGES ......................................... 4 ......................................... 1 ....................................... 17 ....................................... 16 ......................................... 2 ....................................... 10 RAMEngineering, Inc. Select Homes: 2-Lot SP, 7902 203rd Street SW RAM No. 17-033 Stormwater Site Plan Report A. PROJECT OVERVIEW: This report provides engineering information for the proposed construction of a 2-lot residential short plat on a 22,559 sf (0.518 ac) lot; the project is located at 7918 203rd Street SW in the City of Edmonds. The applicant, Select Homes proposes to remove the existing residence and all existing hard surface to construct two single family residences on the project site. This report provides the evaluation for the proposed single family residence development. Summary of Minimum Requirements for Category 2 Project: Minimum Requirement #1—Preparation of Storm water Site Plan. The proposed site development consists of disturbing about 0.54 acres of land and creating/replacing about 9,640 sf of hard surface area. Thus, the project is classified as a Category 2 project per the City's classification system. Per ECDC 18.30, Category 2 projects must comply with Minimum Requirements No. 1 through No. 9. The civil site development plans and this report have been prepared to address the projects impacts. Minimum Requirement #2 — Construction Stormwater Pollution Prevention (SWPPP). A construction Stormwater Pollution Prevention Plan (SWPPP) has been incorporated into the site development plans. A summary of the site's erosion control measures that evaluates the typical 13 elements of a SWPPP are included in section E. The total site disturbance area of the project is less than one acre, thus a formal Notice of Intent application for NPDES coverage will not be made to the Department of Ecology. Minimum Requirement #3 —Source Control of Pollution. Specific source controls are not required for single family residential sites. General requirements for these sites include preventing the discharge of pollutants to the City's storm drainage system per Edmonds City Code Chapter 7.200 (Illicit Discharges). This includes common household items such as pesticides, herbicides, fertilizers, detergents and fluids from vehicle maintenance. Single family residences shall incorporate DOE's S411 BMPs for landscape and lawn vegetation management. Lawn and vegetation management can include control of objectionable weeds, insects, mold, bacteria, and other pests with pesticides. Examples include weed control on golf course lawns, access roads, and utility corridors and during landscaping; sap stain and insect control on lumber and logs; rooftop moss removal; killing nuisance rodents; fungicide application to patio decks, and residential lawn/plant care. It is possible to release toxic pesticides such as pentachlorophenol, carbamates, and organometallics to the environment by leaching and dripping from treated parts, container leaks, product misuse, and outside storage of pesticide contaminated materials and equipment. Poor management of the vegetation and poor application of pesticides or fertilizers can cause appreciable stormwater contamination. Minimum Requirement #4 —Preservation of Natural Drainage Systems and Outfalls. The site generally slopes in a west/northwesterly direction and the existing developed areas (house and driveway, built in 1942) generally slope in a north/northwesterly direction. Any stormwater runoff leaving the site would sheet -flow due to the fact there are no concentrated flows or existing defined conveyance systems located onsite. As described above a majority of the existing developed areas of the site flow in a west/northwesterly and eventually is directed to 203rd St SW; 203rd St SW directs runoff in a westerly direction along the south edge of pavement and gravel shoulder of the street. RAMEngineering, Inc. Select Homes: 2-Lot SP, 7918 203rd Street SW RAM No. 20-020 Stormwater Site Plan Report Page A-1 Discharge flows for the developed hard surfaces of the site will be collected and infiltrated in an onsite infiltration system. The infiltration system will have an overflow system that will be directed to 203rd St SW; thus, the proposed site development will maintain the natural drainage outfall of the site. The site is located within the upper reach of the Good Hope Pond watershed basin per the City of Edmonds maps (see section C). Minimum Requirement #5 — Onsite Stormwater Management. A site -specific geotechnical evaluation (see section D) of the site demonstrates that an infiltration trench for hard surfaces; and Post - Construction Soil Quality and Depth (BMP T5.13) for pervious surfaces are considered feasible stormwater BMPs for the site development. See civil site development plans and Section C for additional stormwater BMP evaluation and construction details. Minimum Requirement#6—Runoff Treatment. The project does not propose to create/replace more than 5,000 sf of pollution -generation impervious surface onsite. The project will create about 3,150 sf pollution generation hard surfaces (road and driveway areas); a majority of the site's impervious surface is rooftop and walkway/patio areas (non -pollution generation surfaces). Thus, no basic or enhanced water quality treatment system is required. Minimum Requirement#7—Flow Control. An onsite infiltration trench will provide flow control of the site development's stormwater runoff. The infiltration trench system is designed to fully mitigate the increased hard surfaces and be in full compliance with the LID Standard and full flow control (match flow durations between 8 percent of the 2-year flow through the full 50-year flow). Flow control (storm water infiltration) designs and sizing calculations are provided in Section E of this report. Minimum Requirement #8 — Wetland Protection. No wetlands are known to exist on or adjacent to the site. Minimum Requirement #9 — Operation and Maintenance. An operation and maintenance summary is provided in section F. RAMEngineering, Inc. RAM No. 20-020 Select Homes: 2-Lot SP, 7918 203rd Street SW Stormwater Site Plan Report Page A-2 Parcel (Vicinity) Map: NE 19 27 4 Centerline ------ Lot BioOk Section -- -- City Limits —, Gov Lot —••• Subdiv — ROW — Quarter --- Tax Acct s INch--200f i Major Water -- Other Lot ------- Vac ROW - - - - 16th ---- Easement; A pnMucr rflhr Aasesfur'n Ogee .Mapp dared 29.2— Snohomish Courtly,, N•ashiaglan Minor Water Other Subdiv— Vac Lot ----- SE-1 U-f27-04 3 " a 14 19 14 Z uI m_ a W W w V w� i o n 4-023 2 G 15 o$ O 4-010 0r46 64 01 W p ca "' 6 a w�o 7; 6 e m I 1 m 16 19 17 18 15 =¢ZO a a$p a0 AD- "O 3 $ 26 W V I U U V U F d 3 2 - — ¢ S L' (8589, }96T+}-�TTSW------ Sty-524--- fNvf- "' 2-00 ----' 1 ---- OP1Cl3-TOi-Yi^INbNOt9D-F/IOtNf�Y 1 2 3 4 1 1 g MEADOWOOD Sp"q 3 IM 28 1.141 1 TOWNHOUSES 1 1 2 3 2 CONDO 9101 ayn 4 a z-aos ( Su S 1-006 �z0� 01 1-009 o 27 2 3 7 8 196T11-PLBVJ / P -007 " t87iH-srsw 3 Q w I 6 co m �g. 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RAM No. 20-020 Fl �iFSiE'L1 I 2-04 _198TH._ __ST._- 1 15 14 13 12 11 pry. o,1v � tiry , y ,.y zry A yy ' 3N3 -2937 _.Yt a1�`l Select Homes: 2-Lot SP, 7918 203r°' Street SW Stormwater Site Plan Report Page A-3 Site Plan: I � f I I I I I I EX157TNG FIRE C6 2 HYDRANT rwr 1 VANED GRATE PVT; TEE RIM 424.10 6" 1E 421.60 (OUT-5� SOCOT 6" CLEANOUT RIM 424.32 6' IE 421.50 (IN-N) 6' IE 421.50 (OUT-S) lNFl0RADON TRENCH 7' WTDE x 120' LONG X 4 DEEP j WITH 6' P£RF PYC PIPES (SEE DETAIL THIS SHEET) I 25' DRAINAGE & J(NNT URUTT EASEMENT CT7P) 15'PR/YATE ACCESS EASEMENT I Ca 1 VANED GRATE PVC TEE RIM 42AJ6 6' IE 421.50 (IN-N) 6' lE 521.50 (IN-E) 6" IE 421.50 (OUT-S) — 15 PRI DRVATE DRAINAGE EASEMENT I SOLO f ' 6" CLEANOUT I' 6- IF 421.50 (IN-N) I I I I It L_—J 1 I I; I I I I I I RAM Engineering, Inc. RAM No. 20-020 INSTALL 1' WATER SERNCES lE 12 CPP E =4222 —WITH 3= 7EIi_7_S —ss—�--ss-- J 10' ROW DED/GA77ON p ,' / 1 JI III ' I 1-1/2- PE (200 PSI) I ; 1 'I ETER TO HOUSE I 1 (TRACER WIRE TO BE r III j I., WITH WATER \ I` PROPOSED SE 1 i I i^o 1 i f_________ ____� PROPO HOUSE FF = f2e.0 i i I i i I 2 I 1 I I — — — — — I II -----11 ;I 1 1 I E RE' TEN TTON%MlPGA 7TON AREA (CROSS -HATCHED AREA) I 00 1 LWE EL': 41203 I i ` ®� — T- SSCO R/M 418.06 SAN/TARP SEWER CO ® R0W LINE 2 REOV CONSTRUCT PER OVND STD PUN S-5 IF 420.5.1 IE=42 .0 (SSCO TO HAVE 12' CAST IRON LAMPHOLE COVER WITH }'HEX BOLTS, T/P) �-INSTALL 6' PVC SEWER SERiNCE LINE A 2.09 MIN LOT 1 -W PR/Vi TE SEWER EASEMEI%T `SSCO lE 42$.5 SHORT PLAT S-99.167 A.F. NO. 200007055001 L LOT2 Select Homes: 2-Lot SP, 7918 203rd Street SW Stormwater Site Plan Report Page A-4 B. EXISTING CONDITIONS SUMMARY Existing Conditions. The total site consists of about 22,559 sf (0.518 acres) and is currently occupied by an existing single-family residence with a looped access driveway off 203rd St SW. The existing house is surrounded by open grass lawn, landscape areas and several trees throughout the site. The site is surrounded by single family residences to the west, east and south; and 203rd St SW to the north (see attached aerial photo). The site is generally slopes in a wester/northwesterly direction; there are no define drainage courses found on -site and stormwater runoff would sheet flow in west/northwesterly direction. A majority of the site improvements (hard surface) flows in a northwesterly direction to the south side of 203rd St SW. No stream or wetlands were discovered on or immediately adjacent to the site. Additional discussion of the local drainage basin and downstream path is discussed in Section C of this report. Soils: In accordance with the project's site specific geotechnical evaluation by Earth Solutions NW, LLC the on -site soils consist of silty sand with gravel and poorly graded gravel with silt (USCS: SM and GP -GM, respectively). The subject site is underlain by glacial till deposits (Vashon till Qvt, Alderwood series soils). Full soils description is included in the project's site specific geotechnical evaluation by Earth Solutions NW, LLC. Aerial Photo (City of Edmonds GIS, 2017 photo): RAMEngineering, Inc. RAM No. 20-020 Select Homes: 2-Lot SP, 7918 203rd Street SW Stormwater Site Plan Report Page 8-1 C. DEVELOPED SITE HYDROLOGY: Developed Conditions. The proposed project includes the construction of two single residence and associated driveways and utilities. All existing structures and impervious (hard) surface onsite will be removed/replaced with the site development; landscaping and grass lawn around the new residence will stabilize the site upon building construction. The project proposes to create and/or replace 9,625 sf of hard surface with the complete site development, all existing onsite hard surface will be removed with the project site development. The following is a summary of the proposed new/replaced hard surface areas: Total Hard Surface to Mitigated = 9,625 sf (0.221 ac) Lot 1 Hard Surface to Mitigate = 3,650 sf Roof Area = 2,670 sf Driveway Area = 600 sf Walkway/Patio Area = 380 sf Lot 2 Hard Surface to Mitigate = 3,950 sf Roof Area = 2,800 sf Driveway Area = 1,100 sf Walkway/Patio Area = 50 sf Shared Private Driveway = 1,150 sf Frontage Road Widening = 300 sf Frontage Sidewalks = 575 sf Total Pervious Surface (Lawn)=13,809 sf (0.317 ac) The project proposes to implement full (100%) hard surface infiltration onsite. The joint infiltration trench will be sized using the DOE 2012 Western Washington Hydrology Model (WWHM2012) continuous runoff model. The infiltration trench will be installed along the shared private driveway for the lots along the easterly boundary of the project site. The infiltration trench will be designed for the total development area; the total hard surface mitigated will be 9,625 sf (0.221 ac). The infiltration trench shall be a minimum 7 feet wide, 120 feet long and 4.0 feet deep; filled with 1-%" to 3" washed drain rock (35% voids). A site specific geotechnical evaluation was made to assess the use of infiltration onsite. The evaluation determined infiltration is feasible onsite and recommends a long-term infiltration design rate of 1.7 in/hr. The developed runoff rates and storage calculations were performed using the DOE 2012 Western Washington Hydrology Model (WWHM2012) continuous runoff model. The below calculations demonstrate that the trenche will fully mitigate (100% infiltration) the increased hard surfaces, see WWHM2012 input/printout on the following pages. RAMEngineering, Inc. RAM No. 20-020 Select Homes: 2-Lot SP, 7918 203rd Street SW Stormwater Site Plan Report Page C-1 WWHM2012 PROJECT REPORT Project Name: 20-020 Storm modeling Site Name: 17-033 Site Address: 7902 203rd City : Edmonds Report Date: 5/13/2021 MGS Regoin Puget East Data Start 1901/10/1 Data End : 2058/09/30 DOT Data Number: 03 Version Date: 2019/09/13 Version : 4.2.17 Low Flow Threshold for POC 1 : 50 Percent of the 2 Year High Flow Threshold for POC 1: 50 year PREDEVELOPED LAND USE Name : Basin 1 Bypass: No Groundwater: No Pervious Land Use acre C, Forest, Flat .538 Pervious Total 0.538 Impervious Land Use acre Impervious Total 0 Basin Total 0.538 Element Flows To: Surface Interflow Groundwater MITIGATED LAND USE Name : Basin 1 Bypass: No Groundwater: No Pervious Land Use acre C, Pasture, Flat .317 Pervious Total 0.317 Impervious Land Use acre ROADS FLAT 0.007 ROOF TOPS FLAT 0.126 DRIVEWAYS FLAT 0.065 SIDEWALKS FLAT 0.023 Impervious Total 0.221 Basin Total 0.538 Element Flows To: Surface Interflow Groundwater Gravel Trench Bed 1 Gravel Trench Bed 1 RAM Engineering, Inc. RAM No. 20-020 Select Homes: 2-Lot SP, 7918 203rd Street SW Stormwater Site Plan Report Page C-2 Name : Gravel Trench Bed 1 Bottom Length: 120.00 ft. Bottom Width: 7.00 ft. Trench bottom slope 1: 0 To 1 Trench Left side slope 0: 0 To 1 Trench right side slope 2: 0 To 1 Material thickness of first layer: 4 Pour Space of material for first layer: 0.35 Material thickness of second layer: 0 Pour Space of material for second layer: 0 Material thickness of third layer: 0 Pour Space of material for third layer: 0 Infiltration On Infiltration rate: 1.7 Infiltration safety factor: 1 Total Volume Infiltrated (ac-ft.): 111.744 Total Volume Through Riser (ac-ft.): 0.002 Total Volume Through Facility (ac-ft.): 111.746 Percent Infiltrated: 100 Total Precip Applied to Facility: 0 Total Evap From Facility: 0 Discharge Structure Riser Height: 3.95 ft. Riser Diameter: 100 in. Element Flows To: Outlet 1 Outlet 2 Gravel Trench Bed Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) 0.0000 0.019 0.000 0.000 0.000 0.0444 0.019 0.000 0.000 0.033 0.0889 0.019 0.000 0.000 0.033 0.1333 0.019 0.000 0.000 0.033 0.1778 0.019 0.001 0.000 0.033 0.2222 0.019 0.001 0.000 0.033 0.2667 0.019 0.001 0.000 0.033 0.3111 0.019 0.002 0.000 0.033 0.3556 0.019 0.002 0.000 0.033 0.4000 0.019 0.002 0.000 0.033 0.4444 0.019 0.003 0.000 0.033 0.4889 0.019 0.003 0.000 0.033 0.5333 0.019 0.003 0.000 0.033 0.5778 0.019 0.003 0.000 0.033 0.6222 0.019 0.004 0.000 0.033 0.6667 0.019 0.004 0.000 0.033 0.7111 0.019 0.004 0.000 0.033 0.7556 0.019 0.005 0.000 0.033 0.8000 0.019 0.005 0.000 0.033 0.8444 0.019 0.005 0.000 0.033 0.8889 0.019 0.006 0.000 0.033 0.9333 0.019 0.006 0.000 0.033 0.9778 0.019 0.006 0.000 0.033 1.0222 0.019 0.006 0.000 0.033 1.0667 0.019 0.007 0.000 0.033 1.1111 0.019 0.007 0.000 0.033 1.1556 0.019 0.007 0.000 0.033 1.2000 0.019 0.008 0.000 0.033 1.2444 0.019 0.008 0.000 0.033 1.2889 0.019 0.008 0.000 0.033 1.3333 0.019 0.009 0.000 0.033 1.3778 0.019 0.009 0.000 0.033 1.4222 0.019 0.009 0.000 0.033 1.4667 0.019 0.009 0.000 0.033 1.5111 0.019 0.010 0.000 0.033 1.5556 0.019 0.010 0.000 0.033 RAM Engineering, Inc. RAM No. 20-020 Infilt(cfs) Select Homes: 2-Lot SP, 7918 203rd Street SW Stormwater Site Plan Report Page C-3 1.6000 0.019 0.010 0.000 0.033 1.6444 0.019 0.011 0.000 0.033 1.6889 0.019 0.011 0.000 0.033 1.7333 0.019 0.011 0.000 0.033 1.7778 0.019 0.012 0.000 0.033 1.8222 0.019 0.012 0.000 0.033 1.8667 0.019 0.012 0.000 0.033 1.9111 0.019 0.012 0.000 0.033 1.9556 0.019 0.013 0.000 0.033 2.0000 0.019 0.013 0.000 0.033 2.0444 0.019 0.013 0.000 0.033 2.0889 0.019 0.014 0.000 0.033 2.1333 0.019 0.014 0.000 0.033 2.1778 0.019 0.014 0.000 0.033 2.2222 0.019 0.015 0.000 0.033 2.2667 0.019 0.015 0.000 0.033 2.3111 0.019 0.015 0.000 0.033 2.3556 0.019 0.015 0.000 0.033 2.4000 0.019 0.016 0.000 0.033 2.4444 0.019 0.016 0.000 0.033 2.4889 0.019 0.016 0.000 0.033 2.5333 0.019 0.017 0.000 0.033 2.5778 0.019 0.017 0.000 0.033 2.6222 0.019 0.017 0.000 0.033 2.6667 0.019 0.018 0.000 0.033 2.7111 0.019 0.018 0.000 0.033 2.7556 0.019 0.018 0.000 0.033 2.8000 0.019 0.018 0.000 0.033 2.8444 0.019 0.019 0.000 0.033 2.8889 0.019 0.019 0.000 0.033 2.9333 0.019 0.019 0.000 0.033 2.9778 0.019 0.020 0.000 0.033 3.0222 0.019 0.020 0.000 0.033 3.0667 0.019 0.020 0.000 0.033 3.1111 0.019 0.021 0.000 0.033 3.1556 0.019 0.021 0.000 0.033 3.2000 0.019 0.021 0.000 0.033 3.2444 0.019 0.021 0.000 0.033 3.2889 0.019 0.022 0.000 0.033 3.3333 0.019 0.022 0.000 0.033 3.3778 0.019 0.022 0.000 0.033 3.4222 0.019 0.023 0.000 0.033 3.4667 0.019 0.023 0.000 0.033 3.5111 0.019 0.023 0.000 0.033 3.5556 0.019 0.024 0.000 0.033 3.6000 0.019 0.024 0.000 0.033 3.6444 0.019 0.024 0.000 0.033 3.6889 0.019 0.024 0.000 0.033 3.7333 0.019 0.025 0.000 0.033 3.7778 0.019 0.025 0.000 0.033 3.8222 0.019 0.025 0.000 0.033 3.8667 0.019 0.026 0.000 0.033 3.9111 0.019 0.026 0.000 0.033 3.9556 0.019 0.026 0.036 0.033 4.0000 0.019 0.027 0.989 0.033 RAM Engineering, Inc. RAM No. 20-020 Select Homes: 2-Lot SP, 7918 203rd Street SW Stormwater Site Plan Report Page C-4 ANALYSIS RESULTS Stream Protection Duration Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.538 Total Impervious Area:O Mitigated Landuse Totals for POC #1 Total Pervious Area:0.317 Total Impervious Area:0.221 Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.009046 5 year 0.013978 10 year 0.016646 25 year 0.019354 50 year 0.020961 100 year 0.022281 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0 5 year 0 10 year 0 25 year 0 50 year 0 100 year 0 1arIrY 0.0001 Cumulative Probability xxx x x x xxxxxxxxooacxs=�- - + Flop Frequency 1.0 Flow(cfs) 0501 15m 2 Year = 0.0090 5 Year = 0.0140 10 Year = 0.0166 0.1 25 Year = 0.0194 50 Year = 0.0210 100 Year = 0.0223 501 Annual Peaks ).0001 0 0.5 1 2 5 10 20 30 50 70 80 90 95 98 9999.5100 Stream Protection Duration LID Duration Flow Frequency I Water Q uality_j Hydrograph I Wetland Input Volumes I LID Report I Recharge Duration I Recharge Predeveloped I Recharge Mitigated Analyze dalasets Compact WDM I Delete Selected I F- Monthly FF FE 501 POC 1 Predeveloped flow 701 Inflow to POC 1 Mitigated a •t T GravelTrenchBed1ALLOUTLETSMitigated 1001 Gravel Trench Bed 1 OUTLET 1 Mitigated 1002 Gravel Trench Bed 1 OUTLET 2 Mitigated All Datasets Flow Stage I Precip Flood Frequency Method Evap POC 1 POC 2 (: Log Pearson Type III 17B C Weibull Cunnane C' Gringorten RAMEngineering, Inc. RAM No. 20-020 n 0701 15m 0801 15m 0.0695 0.0000 0.0945 0.0000 0.1132 0.0000 0.1395 0.0000 0.1610 0.0000 0.1843 0.0000 1902 0.0127 0.0783 0.0000 1903 0.0045 0.0855 0.0000 1904 0.0082 0.1002 0.0000 1905 0.0052 0.0465 0.0000 1906 0.0021 0.0490 0.0000 1907 0.0142 0.0693 0.0000 1908 0.0090 0.0586 0.0000 1909 0.0098 0.0716 0.0000 1910 0.0156 0.0707 0.0000 1911 0.0081 0.0737 0.0000 1912 0.0225 0.1471 0.0000 1913 0.0137 0.0479 0.0000 1914 0.0032 0.1956 0.0000 1915 0.0047 0.0451 0.0000 1916 0.0074 0.0834 0.0000 1917 0.0036 0.0424 0.0000 1918 0.0087 0.0663 0.0000 1919 0.0065 0.0398 0.0000 1920 0.0084 0.0592 0.0000 1921 0.0089 0.0484 0.0000 1922 0.0100 0.0674 0.0000 1923 0.0065 0.0587 0.0000 1924 0.0044 0.0923 0.0000 1925 0.0044 0.0429 0.0000 1926 0.0079 0.0845 0.0000 1927 0.0102 0.0631 0.0000 1928 0.0067 0.0552 0.0000 1929 0.0142 0.0902 0.0000 Select Homes: 2-Lot SP, 7918 203rd Street SW Stormwater Site Plan Report Page C-5 Stream Protection Duration Annual Peaks for Predeveloped and Mitigated Year Predeveloped Mitigated 1902 0.013 0.000 1903 0.004 0.000 1904 0.008 0.000 1905 0.005 0.000 1906 0.002 0.000 1907 0.014 0.000 1908 0.009 0.000 1909 0.010 0.000 1910 0.016 0.000 1911 0.008 0.000 1912 0.023 0.000 1913 0.014 0.000 1914 0.003 0.000 1915 0.005 0.000 1916 0.007 0.000 1917 0.004 0.000 1918 0.009 0.000 1919 0.006 0.000 1920 0.008 0.000 1921 0.009 0.000 1922 0.010 0.000 1923 0.007 0.000 1924 0.004 0.000 1925 0.004 0.000 1926 0.008 0.000 1927 0.010 0.000 1928 0.007 0.000 1929 0.014 0.000 1930 0.009 0.000 1931 0.009 0.000 1932 0.006 0.000 1933 0.008 0.000 1934 0.020 0.000 1935 0.007 0.000 1936 0.012 0.000 1937 0.010 0.000 1938 0.010 0.000 1939 0.001 0.000 1940 0.008 0.000 1941 0.008 0.000 1942 0.012 0.000 1943 0.004 0.000 1944 0.010 0.000 1945 0.009 0.000 1946 0.008 0.000 1947 0.006 0.000 1948 0.019 0.000 1949 0.015 0.000 1950 0.008 0.000 1951 0.010 0.000 1952 0.027 0.000 RAM Engineering, Inc. RAM No. 20-020 POC #1 Select Homes: 2-Lot SP, 7918 203rd Street SW Stormwater Site Plan Report Page C-6 1953 0.024 0.000 1954 0.007 0.000 1955 0.006 0.000 1956 0.004 0.000 1957 0.011 0.000 1958 0.025 0.000 1959 0.015 0.000 1960 0.005 0.000 1961 0.016 0.000 1962 0.008 0.000 1963 0.004 0.000 1964 0.006 0.000 1965 0.018 0.000 1966 0.003 0.000 1967 0.007 0.000 1968 0.010 0.000 1969 0.007 0.000 1970 0.010 0.000 1971 0.020 0.000 1972 0.013 0.000 1973 0.015 0.000 1974 0.008 0.000 1975 0.021 0.000 1976 0.009 0.000 1977 0.006 0.000 1978 0.018 0.000 1979 0.005 0.000 1980 0.009 0.000 1981 0.009 0.000 1982 0.006 0.000 1983 0.015 0.000 1984 0.004 0.000 1985 0.009 0.000 1986 0.007 0.000 1987 0.015 0.000 1988 0.011 0.000 1989 0.009 0.000 1990 0.011 0.000 1991 0.008 0.000 1992 0.013 0.000 1993 0.010 0.000 1994 0.019 0.000 1995 0.004 0.000 1996 0.021 0.000 1997 0.010 0.000 1998 0.009 0.000 1999 0.000 0.000 2000 0.007 0.000 2001 0.005 0.000 2002 0.011 0.000 2003 0.010 0.000 2004 0.010 0.000 2005 0.011 0.000 2006 0.007 0.000 RAM Engineering, Inc. RAM No. 20-020 Select Homes: 2-Lot SP, 7918 2O3rd Street SW Stormwater Site Plan Report Page C-7 2007 0.007 0.000 2008 0.009 0.000 2009 0.006 0.000 2010 0.005 0.000 2011 0.006 0.000 2012 0.008 0.000 2013 0.007 0.000 2014 0.005 0.000 2015 0.014 0.000 2016 0.003 0.000 2017 0.015 0.000 2018 0.025 0.000 2019 0.027 0.031 2020 0.008 0.000 2021 0.012 0.000 2022 0.004 0.000 2023 0.010 0.000 2024 0.019 0.000 2025 0.008 0.000 2026 0.014 0.000 2027 0.006 0.000 2028 0.003 0.000 2029 0.010 0.000 2030 0.020 0.000 2031 0.005 0.000 2032 0.004 0.000 2033 0.005 0.000 2034 0.006 0.000 2035 0.022 0.000 2036 0.011 0.000 2037 0.002 0.000 2038 0.011 0.000 2039 0.001 0.000 2040 0.004 0.000 2041 0.006 0.000 2042 0.023 0.000 2043 0.010 0.000 2044 0.014 0.000 2045 0.009 0.000 2046 0.010 0.000 2047 0.006 0.000 2048 0.009 0.000 2049 0.008 0.000 2050 0.005 0.000 2051 0.009 0.000 2052 0.005 0.000 2053 0.009 0.000 2054 0.011 0.000 2055 0.004 0.000 2056 0.004 0.000 2057 0.006 0.000 2058 0.007 0.000 RAM Engineering, Inc. RAM No. 20-020 Select Homes: 2-Lot SP, 7918 2O3rd Street SW Stormwater Site Plan Report Page C-8 Stream Protection Duration Ranked Annual Peaks for Predeveloped and Mitigated Rank Predeveloped Mitigated 1 0.0268 0.0306 2 0.0266 0.0003 3 0.0251 0.0000 4 0.0250 0.0000 5 0.0238 0.0000 6 0.0228 0.0000 7 0.0225 0.0000 8 0.0222 0.0000 9 0.0210 0.0000 10 0.0207 0.0000 11 0.0201 0.0000 12 0.0197 0.0000 13 0.0196 0.0000 14 0.0194 0.0000 15 0.0187 0.0000 16 0.0186 0.0000 17 0.0184 0.0000 18 0.0181 0.0000 19 0.0156 0.0000 20 0.0156 0.0000 21 0.0154 0.0000 22 0.0152 0.0000 23 0.0148 0.0000 24 0.0148 0.0000 25 0.0147 0.0000 26 0.0146 0.0000 27 0.0142 0.0000 28 0.0142 0.0000 29 0.0141 0.0000 30 0.0140 0.0000 31 0.0137 0.0000 32 0.0137 0.0000 33 0.0129 0.0000 34 0.0128 0.0000 35 0.0127 0.0000 36 0.0123 0.0000 37 0.0119 0.0000 38 0.0119 0.0000 39 0.0115 0.0000 40 0.0115 0.0000 41 0.0114 0.0000 42 0.0113 0.0000 43 0.0112 0.0000 44 0.0111 0.0000 45 0.0110 0.0000 46 0.0106 0.0000 47 0.0105 0.0000 48 0.0104 0.0000 49 0.0104 0.0000 50 0.0103 0.0000 51 0.0102 0.0000 RAM Engineering, Inc. RAM No. 20-020 POC #1 Select Homes: 2-Lot SP, 7918 203rd Street SW Stormwater Site Plan Report Page C-9 52 0.0101 0.0000 53 0.0101 0.0000 54 0.0100 0.0000 55 0.0099 0.0000 56 0.0099 0.0000 57 0.0099 0.0000 58 0.0098 0.0000 59 0.0098 0.0000 60 0.0098 0.0000 61 0.0097 0.0000 62 0.0097 0.0000 63 0.0096 0.0000 64 0.0094 0.0000 65 0.0093 0.0000 66 0.0093 0.0000 67 0.0092 0.0000 68 0.0091 0.0000 69 0.0090 0.0000 70 0.0090 0.0000 71 0.0089 0.0000 72 0.0089 0.0000 73 0.0089 0.0000 74 0.0088 0.0000 75 0.0088 0.0000 76 0.0087 0.0000 77 0.0087 0.0000 78 0.0086 0.0000 79 0.0086 0.0000 80 0.0085 0.0000 81 0.0084 0.0000 82 0.0083 0.0000 83 0.0083 0.0000 84 0.0082 0.0000 85 0.0082 0.0000 86 0.0082 0.0000 87 0.0081 0.0000 88 0.0081 0.0000 89 0.0081 0.0000 90 0.0080 0.0000 91 0.0080 0.0000 92 0.0079 0.0000 93 0.0079 0.0000 94 0.0078 0.0000 95 0.0078 0.0000 96 0.0075 0.0000 97 0.0074 0.0000 98 0.0074 0.0000 99 0.0074 0.0000 100 0.0072 0.0000 101 0.0072 0.0000 102 0.0072 0.0000 103 0.0069 0.0000 104 0.0069 0.0000 105 0.0068 0.0000 RAM Engineering, Inc. RAM No. 20-020 Select Homes: 2-Lot SP, 7918 2O3rd Street SW Stormwater Site Plan Report Page C-10 106 0.0067 0.0000 107 0.0066 0.0000 108 0.0065 0.0000 109 0.0065 0.0000 110 0.0065 0.0000 ill 0.0065 0.0000 112 0.0064 0.0000 113 0.0064 0.0000 114 0.0062 0.0000 115 0.0061 0.0000 116 0.0061 0.0000 117 0.0061 0.0000 118 0.0060 0.0000 119 0.0059 0.0000 120 0.0058 0.0000 121 0.0057 0.0000 122 0.0056 0.0000 123 0.0055 0.0000 124 0.0055 0.0000 125 0.0055 0.0000 126 0.0054 0.0000 127 0.0053 0.0000 128 0.0052 0.0000 129 0.0050 0.0000 130 0.0049 0.0000 131 0.0048 0.0000 132 0.0048 0.0000 133 0.0047 0.0000 134 0.0046 0.0000 135 0.0045 0.0000 136 0.0044 0.0000 137 0.0044 0.0000 138 0.0044 0.0000 139 0.0044 0.0000 140 0.0044 0.0000 141 0.0042 0.0000 142 0.0042 0.0000 143 0.0040 0.0000 144 0.0039 0.0000 145 0.0038 0.0000 146 0.0037 0.0000 147 0.0036 0.0000 148 0.0035 0.0000 149 0.0033 0.0000 150 0.0032 0.0000 151 0.0030 0.0000 152 0.0025 0.0000 153 0.0022 0.0000 154 0.0021 0.0000 155 0.0010 0.0000 156 0.0006 0.0000 157 0.0005 0.0000 RAM Engineering, Inc. RAM No. 20-020 Select Homes: 2-Lot SP, 7918 2O3rd Street SW Stormwater Site Plan Report Page C-11 Stream Protection Duration POC #1 The Facility PASSED A :.nal,..;is ® U.U2 n 0.02 0 >v > 0.01 0 J 0.01 0.00 1 Percent Time Exceeding . 501 POC 1 Predevefoped iligated flow DO Stream Protection Duration LID Duration Flow Frequency Water Quality Hydrograph Wetland Input Volumes I LID Report I Recharge Duration I Recharge Redeveloped I Recharge Mitigated Analyze datasets Compact WDM I Delete Selected I r Monthly FF 501 POC 1 Predeveloped flow 801 POC Evap`................POC_1POC 2 Flood Frequency Method AlDatasets Flow Stage Precip l.' Log Pearson Type III 1 JB C Weibull C Cunnane f Gringoden The Facility PASSED. Flow(cfs) Predev Mit Percentage Pass/Fail 0.0045 54379 4 0 Pass 0.0047 50129 4 0 Pass 0.0049 46187 4 0 Pass 0.0050 42741 4 0 Pass 0.0052 39581 4 0 Pass 0.0054 36719 4 0 Pass 0.0055 34104 4 0 Pass 0.0057 31747 4 0 Pass 0.0059 29689 4 0 Pass 0.0060 27762 4 0 Pass 0.0062 25907 4 0 Pass 0.0063 24195 4 0 Pass 0.0065 22615 4 0 Pass 0.0067 21079 4 0 Pass 0.0068 19642 4 0 Pass 0.0070 18326 3 0 Pass 0.0072 17121 3 0 Pass 0.0073 16064 3 0 Pass 0.0075 15051 3 0 Pass 0.0077 14076 3 0 Pass 0.0078 13157 3 0 Pass 0.0080 12315 3 0 Pass 0.0082 11517 3 0 Pass RAM Engineering, Inc. RAM No. 20-020 Facility PASSED Flow(cfs) Predev Nit Percentage Pass/Fail 0.0045 54379 4 0 Pass 0.0047 50129 4 0 Pass 0.0049 46187 4 0 Pass 0.0050 42741 4 0 Pass 0.0052 39581 4 0 Pass 0.0054 36719 4 0 Pass 0.0055 34104 4 0 Pass 0.0057 31747 4 0 Pass 0.0059 29689 4 0 Pass 0.0060 27762 4 0 Pass 0.0062 25907 4 0 Pass 0.0063 24195 4 0 Pass 0.0065 22615 4 0 Pass 0.0067 21079 4 0 Pass 0.0068 19642 4 0 Pass 0.0070 18326 3 0 Pass 0.0072 17121 3 0 Pass 0.0073 16064 3 0 Pass 0.0075 15051 3 0 Pass 0.0077 14076 3 0 Pass 0.0078 13157 3 0 Pass 0.0080 12315 3 0 Pass 0.0082 11517 3 0 Pass 0.0083 10850 3 0 Pass 0.0085 10239 3 0 Pass 0.0087 9683 3 0 Pass 0.0088 9199 3 0 Pass 0.0090 8643 3 0 Pass 0.0092 8202 2 0 Pass 0.0093 7751 2 0 Pass 0.0095 7344 2 0 Pass 0.0097 6980 2 0 Pass 0.0098 6612 2 0 Pass 0.0100 6309 2 0 Pass Select Homes: 2-Lot SP, 7918 203r°' Street SW Stormwater Site Plan Report Page C-12 0.0083 10850 3 0 Pass 0.0085 10239 3 0 Pass 0.0087 9683 3 0 Pass 0.0088 9199 3 0 Pass 0.0090 8643 3 0 Pass 0.0092 8202 2 0 Pass 0.0093 7751 2 0 Pass 0.0095 7344 2 0 Pass 0.0097 6980 2 0 Pass 0.0098 6612 2 0 Pass 0.0100 6309 2 0 Pass 0.0102 6022 2 0 Pass 0.0103 5731 2 0 Pass 0.0105 5457 2 0 Pass 0.0107 5220 2 0 Pass 0.0108 4984 2 0 Pass 0.0110 4773 2 0 Pass 0.0112 4550 2 0 Pass 0.0113 4340 2 0 Pass 0.0115 4146 2 0 Pass 0.0117 3948 2 0 Pass 0.0118 3799 2 0 Pass 0.0120 3651 2 0 Pass 0.0122 3508 2 0 Pass 0.0123 3380 2 0 Pass 0.0125 3276 2 0 Pass 0.0127 3172 2 0 Pass 0.0128 3073 2 0 Pass 0.0130 2981 2 0 Pass 0.0132 2898 2 0 Pass 0.0133 2803 2 0 Pass 0.0135 2719 2 0 Pass 0.0137 2618 2 0 Pass 0.0138 2518 2 0 Pass 0.0140 2426 2 0 Pass 0.0142 2317 2 0 Pass 0.0143 2217 2 0 Pass 0.0145 2129 2 0 Pass 0.0147 2025 2 0 Pass 0.0148 1961 2 0 Pass 0.0150 1898 2 0 Pass 0.0151 1833 2 0 Pass 0.0153 1763 2 0 Pass 0.0155 1691 2 0 Pass 0.0156 1637 2 0 Pass 0.0158 1573 2 0 Pass 0.0160 1511 2 0 Pass 0.0161 1456 2 0 Pass 0.0163 1396 2 0 Pass 0.0165 1339 2 0 Pass 0.0166 1277 2 0 Pass 0.0168 1221 2 0 Pass 0.0170 1173 2 0 Pass 0.0171 1124 2 0 Pass 0.0173 1082 2 0 Pass 0.0175 1033 2 0 Pass 0.0176 984 2 0 Pass 0.0178 938 2 0 Pass 0.0180 903 2 0 Pass 0.0181 863 2 0 Pass 0.0183 812 2 0 Pass 0.0185 778 2 0 Pass 0.0186 742 2 0 Pass 0.0188 703 2 0 Pass 0.0190 661 2 0 Pass 0.0191 617 2 0 Pass 0.0193 582 2 0 Pass RAM Engineering, Inc. RAM No. 20-020 Select Homes: 2-Lot SP, 7918 203rd Street SW Stormwater Site Plan Report Page C-13 0.0195 548 2 0 Pass 0.0196 507 2 0 Pass 0.0198 462 2 0 Pass 0.0200 415 2 0 Pass 0.0201 387 2 0 Pass 0.0203 360 2 0 Pass 0.0205 339 2 0 Pass 0.0206 304 2 0 Pass 0.0208 286 2 0 Pass 0.0210 265 2 0 Pass 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. LID Report Ised for Total Volume Volume Infiltration Cumulative Percent Water Quality Percent Comment reatment? Needs Through Volume Volume Volume Water Quality Treatment Facility (ac-ft) Infiltration Infiltrated Treated (ac-ft) (ac-ft) Credit ❑ 101.69 ❑ 100.00 101.69 0.00 0.00 100.00 0.00 0% No Treat Credit Duration Analysis Result = Passed Perind and Impind Changes No changes have been made. This program and accompanying documentation are provided 'as -is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc. and the governmental licensee or sublicensees disclaim all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions Inc. be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions Inc. or their authorized representatives have been advised of the possibility of such damages. Software Copyright © by : Clear Creek Solutions, Inc. 2005-2021; All Rights Reserved. RAM Engineering, Inc. RAM No. 20-020 Select Homes: 2-Lot SP, 7918 203rd Street SW Stormwater Site Plan Report Page C-14 Offsite Analysis. The site is located within the City of Edmonds Good Hope Pond watershed basin. The Good Hope Pond basin is a centralized urban basin that collects stormwater runoff from primarily residential areas in the City Edmonds and ultimately discharges stormwater runoff westerly to Puget Sound via Shell Creek (see attached watershed map). The site generally slopes in a west/northwesterly direction; there is no define channels onsite or adjacent to the site and thus stormwater runoff would leave the site as sheet -flow. A majority of the runoff from the site is generated by the existing house and driveway; runoff from these hard surfaces flow in a north/northwesterly direction to the south side of 203rd St SW collecting into the City's municipal separate storm sewer system (MS4) at the westerly street of 203rd St SW. The pipe system (MS4) continues west to 81" Ave W and is routed north along east side of 81St Ave W. The pipe and catch basin system then routes west along a shared private road at 20126/20128/20130 81St Ave W; the system continues westerly to 83rd Ave W and then is directed south at the intersection of 83rd Ave W and 202nd PI SW (about 1,050 feet from the site). The system continues south along 83rd Ave W and discharges into Good Hope Pond (about 2,700 ft from the site). Good Hope Pond discharges via pipe system that routes discharge flows in a southwesterly direction and daylights to the headwaters of Shell Creek along the north side of Shelly Valley Rd (about 5,600 feet from the site). Shell Creek generally flows in a northwesterly direction and eventually discharges to the Puget Sound about 2.7 miles from the site. No apparent flooding or system inadequacies within downstream of the site were discovered during site visits or research of the downstream system. See attached watershed and downstream drainage facility map for the local downstream path. RAMEngineering, Inc. RAM No. 20-020 Select Homes: 2-Lot SP, 7918 203rd Street SW Stormwater Site Plan Report Page C-15 Watershed Basin Map Y FIGURE B-1 CITY OF EDMONDS 6 WATERSHEDS Deer Creek _ Perrinville Edmonds Marsh - Puget Sound Edmonds Way _ Puget Sound Piped Fruitdale - Shell Creek Good Hope Pond _ Shellabarger Halls Creek _ Southwest Edmonds Hindley Creek i Southwest Edmonds B Lake Ballinger Stilthouse Creek Lund's Gulch ® Talbot Park MeadowdaleA Talbot Park MeadowdaleEl C1 Terrace Creek Northstream Westgate Pond i /hqd '3 `Tlfeadowd. kA'. i G` I 1691M1 9r , �\— 4.40. 11 rre Ithouse e i i as �{ ?.. a S i Terrace Creek ! OutEall Creek Willow Creek 3 os a 1poo zGW 40% soon a,gao mec Puget Sound, 1 in = 2,OD0 h Talbot Park A - Talbot Park B no warranty of am stln, i rci,ding accurary, fl—, or—hantablliry ."r, 0, 201s product , ' March 30. 1010 \ i 1Pruitdale e, 1 ,brthstream s o zoom sr sw e Hindleym Good Hopca Ponc S 2ocrh 5l SW Puget Sound Piped R- 17918 203rd St SW I f' — i_, Edmonds Marsh Shell Creek ztzrn sr sw // Shellabarger _______ vine sr o, 3 Westgate Pond Halls Craek i / e I� `Olilllolw Creek I i 224th Se5W W r- - ._._i r_J a Deer Creek ---- I— . I P, 131st StSW G Edmonds WayI, Southwest Edmonds A Lake Ballinger Q L249th S, SW Southwest Edmonds B _ --- __----- ------g4osrh5Vz44tn sr 5w a3p9 RAM =ngineering, Inc. Select Homes: 2-Lot SP, 7918 203rd Street SW RAM No. 20-020 Stormwater Site Plan Report Page C-16 Downstream Drainage Facility Map (City of Edmonds GIS) O 0 O O O a 0 0 0 ji I Oq � 4 RAMEngineering, Inc. RAM No. 20-020 Select Homes: 2-Lot SP, 7918 203rd Street SW Stormwater Site Plan Report Page C-17 D. SOILS REPORT: Geotechnical Evaluation Letter Prepared by: Earth Solutions NW, LLC Date: May 14, 2020 Pages: 15 RAMEngineering, Inc. RAM No. 20-020 Select Homes: 2-Lot SP, 7918 203rd Street SW Stormwater Site Plan Report Page D-1 May 14, 2021 ES-7572 Select Homes, Inc. 16531 — 1311 Avenue West, A107 Lynnwood, Washington 98037 Attention: Ms. Kayla Nichols Subject: Geotechnical Evaluation Proposed Single -Family Residence 7918 — 203rd Street Southwest Edmonds, Washington Earth Solutions N W «C Earth Solutions NW LLC Geotechnical Engineering, Construction Observation/Testing and Environmental Services Reference: Department of Ecology Stormwater Management Manual for Western Washington Amended December 2014 James P. Minard Geologic Map of the Edmonds East and Part of the Edmonds West Quadrangles Washington, 1983 Web Soil Survey (WSS) Edmonds City Code (ECC) Chapter 23.80 (Geologically Hazard Areas) City of Edmonds Edmonds Stormwater Addendum, dated June 8, 2017 Dear Ms. Nichols: As requested, Earth Solutions NW, LLC (ESNW) has prepared this geotechnical evaluation report for the proposed single-family residence project. As part of our scope of services, we completed a subsurface exploration, laboratory and engineering analyses, and prepared this written report with our findings and recommendations for the proposed project. Based on our evaluation, the proposed project is feasible from a geotechnical standpoint. Project Description The subject site is located at 7918 — 203rd Street Southwest in Edmonds, Washington, as illustrated on the attached Vicinity Map (Plate 1). The site consists of one tax parcel (Snohomish County parcel number 27041900112700) covering 0.51 acres. The property is currently developed with a single-family residence and associated improvements. Based on ESNW's understanding of the proposed development, the boundary lines will be adjusted to create a new residential lot. Site topography is relatively level with less than about five feet of elevation change. The subject site is bordered by single-family residences on the east, south, and west and 203rd Street Southwest to the north. 15365 N.E. 90th Street, Suite 100 0 Redmond, WA 98052 0 (425) 449-4704 • FAX (425) 449-4711 Select Homes, Inc. ES-7572 May 14, 2021 Page 2 We anticipate grading activities will include cuts and fills of about two to four feet to establish the planned building alignments. We understand infiltration and low impact development methods are being evaluated for stormwater management. Site improvements will also include underground utility installations. At the time this report was prepared, specific building load values were not available. However, we anticipate the proposed residential structures will consist of relatively lightly loaded wood framing supported on conventional foundations. Based on our experience with similar developments, we estimate wall loads on the order of one to two kips per linear foot and slab -on - grade loading of 150 pounds per square foot (psf). If the above design assumptions are incorrect or change, ESNW should be contacted to review the recommendations in this report. ESNW should review the final design to verify the geotechnical recommendations provided in this report have been incorporated into the plans. Subsurface Conditions As part of this geotechnical evaluation, an ESNW representative observed, logged, and sampled three test pits on December 4, 2020, excavated at accessible locations within the proposed development area, using a mini-trackhoe and operator provided by the client. The approximate locations of the test pits are depicted on the Test Pit Location Plan (Plate 2). Please refer to the test pit logs provided as an attachment to this report for a more detailed description of subsurface conditions. Representative soil samples collected at the test pit locations were analyzed in general accordance with the Unified Soil Classification System (USCS) and United States Department of Agriculture methods and procedures. Topsoil and Fill Topsoil was observed extending to a depth of approximately three to six inches below existing ground surface (bgs). The topsoil was characterized by dark brown color and fine organic material. Fill was encountered at test pit location TP-3 extending about six inches bgs. The fill was characterized primarily as silty gravel, crushed minus rock and was encountered in a moist condition at the time of exploration; the surficial fill was underlain by topsoil. Fill may be present, to some degree, around existing improvements and, where encountered, should be evaluated by ESNW during construction. Native Soil Underlying the topsoil and limited fill, native soil conditions at the test pit locations was observed to consist primarily of silty sand with gravel and poorly graded gravel with silt (USCS: SM and GP -GM, respectively). Overall soil relative density increased with depth, extending to the maximum exploration depth of about seven feet bgs. The native soil was generally observed in a weakly cemented condition at about four to five feet bgs. Earth Solutions NW. LLC Select Homes, Inc. May 14, 2021 Geologic Setting ES-7572 Page 3 The referenced geologic map resource identifies Vashon till (Qvt) across the site and surrounding areas. As reported on the geologic map resource, Vashon till typically consists of a nonsorted mixture of clay, silt, sand, pebbles, cobbles, and boulders. The till was deposited directly by ice advanced over previously deposited sediment and rocks. In addition, the referenced WSS resource identifies Alderwood-urban land complex (Map Unit Symbol: 5) as the primary soil units underlying the subject site. The Alderwood series was formed in glacial till plains. Based on our field observations, native soils on the subject site generally consist of advance outwash with a weakly cemented till cap. Groundwater Groundwater seepage was not observed at the test pit locations during the fieldwork (December 2020). However, seepage should be expected in deeper excavations at this site, particularly during the winter, spring, and early summer months. Groundwater seepage rates and elevations fluctuate depending on many factors, including precipitation duration and intensity, the time of year, and soil conditions. Geologically Hazardous Areas Assessment As part of this geotechnical evaluation, the referenced chapter of the ECC was reviewed. Based on our investigation and review, there are no geologically hazardous areas present on or adjacent to the site. Foundations The proposed structure can be supported on conventional spread and continuous footings bearing on undisturbed, competent native soil, compacted native soil, or new structural fill. Competent native soils, suitable for support of the foundation, should be encountered beginning at depths of approximately two to three feet bgs. Where loose or unsuitable soil conditions are encountered at foundation subgrade elevations during site preparation activities, compaction of the soils to the specifications of structural fill, or overexcavation and replacement with granular structural fill will be necessary. Structural fill should consist of suitable granular soils compacted to 95 percent of Modified Proctor (ASTM D1557). Compaction of the soil to the levels necessary for use as structural fill will be difficult during wet weather conditions. Organic material exposed at foundation subgrade elevations must be removed and grades restored with structural fill. Provided the structure will be supported as described above, the following parameters can be used for design of the new foundation: • Allowable soil bearing capacity 2,500 psf • Passive earth pressure 300 pcf (equivalent fluid) • Coefficient of friction 0.40 Earth Solutions NW. LLC Select Homes, Inc. ES-7572 May 14, 2021 Page 4 The passive earth pressure and coefficient of friction values include a safety factor of 1.5. A one- third increase in the allowable soil bearing capacity can be assumed for short-term wind and seismic loading conditions. With structural loading as expected, total settlement in the range of one inch is anticipated, with differential settlement of about one-half inch. The majority of the settlements should occur during construction, as dead loads are applied. Seismic Considerations The 2015 and 2018 International Building Code recognizes the American Society of Civil Engineers (ASCE) for seismic site class definitions. In accordance with Table 20.3-1 of ASCE, Minimum Design Loads for Buildings and Other Structures, Site Class D, should be used for design. In our opinion, the site susceptibility to liquefaction is negligible. The native soil relative density and the absence of an established, shallow groundwater table are the primary bases for this opinion. Drainage Temporary measures to control surface water runoff during construction would likely involve passive elements such as interceptor trenches and sumps. ESNW should be consulted during preliminary grading activities to evaluate seepage areas and provide recommendations to reduce the potential for seepage -related instability. Finish grades should be designed to direct surface water away from structures and slopes. Grades adjacent to the building should be sloped away at a gradient of either at least 2 percent for a horizontal distance of up to 10 feet or the maximum allowed by adjacent structures. In our opinion, foundation drains should be installed along building perimeter footings. A typical footing drain detail is attached to this letter (Plate 3). Infiltration Evaluation As indicated in the Subsurface Conditions section, native soils encountered during our fieldwork were characterized primarily as advance outwash with a weakly cemented till cap. Based on the results of USDA textural analyses, the native soils at depth were classified as gravelly sandy loam with fines contents of about 12 to 23 percent. In -situ testing was completed in accordance with the Small-scale Pilot Infiltration Test (PIT) procedure, as outlined in Volume III, Chapter 3, Page 526 of the 2014 SMMWW. The testing was completed at a depth of approximately four feet at TP-1. The in -situ rate obtained during testing was 5.5 inches per hour. Because the infiltration rate obtained from in -situ testing is considered to be a short-term rate, correction factors must be applied in order to determine a long-term design rate. The correction factors outlined below were used in accordance with Table 111-3.3.1 of the 2014 SMMWW outlined in Volume III, Chapter 3, Page 529. Earth Solutions NW. LLC Select Homes, Inc. ES-7572 May 14, 2021 Page 5 The correction factors, along with the measured infiltration rate, were incorporated into the following equation: Ksat design = Ksat initial x CFv x CFr x CFm. • Measured (Ksat initial) 5.5 inches per hour • Site variability CF„ = 0.7 • Test method CFt = 0.5 • Degree of influent control CFm = 0.9 • Long-term design infiltration rate (Ksat design) 1.7 inches per hour • Infiltration trench or drywell sizing sandy loam The design infiltration rate is applicable to facilities located in proximity to the infiltration test location and at a depth that may infiltrate into the native soil at depth. Emergency overflow provisions should be included in the design. ESNW should be retained to observe the construction of infiltration facilities on the subject site in order to confirm soil conditions are as anticipated and perform confirmation infiltration testing at the infiltration design depth and locations. Overexcavation of low permeability lenses may be required. Supplementary geotechnical recommendations may be provided at the time of construction, where necessary. On -site Stormwater Management Pursuant to City of Edmonds stormwater management requirements, implementation of on -site stormwater BMPs are required for proposed developments in accordance with specified thresholds, standards, and lists. The intent of BMP implementation is to infiltrate, disperse, and retain stormwater runoff on site to the extent feasible. The table below summarizes our evaluation of low impact development methods, as outlined in the referenced stormwater manual, from a geotechnical standpoint. It is instructed in the referenced stormwater manual that BMPs are to be considered in the order listed (from top to bottom) for each surface type, and the first BMP that is determined to be viable should be used. For completeness, however, we have evaluated each listed BMP for the proposed surface types. Earth Solutions NW. LLC Select Homes, Inc. May 14, 2021 ES-7572 Page 6 BMP Viable? Limitations or Infeasibility Criteria Lawns and Landscaped Areas T5.13: Post -construction soil quality and depth (Volume V, Yes None. Chapter 5 Roofs T5.30: Full dispersion (Volume Maybe* Adequate vegetative flow paths will likely not be V, Chapter 5) available. T5.10A: Downspout full infiltration systems (Volume III, Yes Low permeability lenses may need to be overexcavated. Chapter 3) Roofs Bioretention (Volume V, Chapter Yes Low permeability lenses may need to be 7) overexcavated. T5.10B: Downspout dispersion systems (Volume III, Chapter 3) Maybe* Adequate vegetative flow paths are likely not available. T5.10C: Perforated stub -out connections (Volume III, Chapter Yes None 3 T5.30: Full dispersion (Volume V, Chapter 5) Maybe* Adequate vegetative flow paths are likely not available. T5.15: Permeable pavement Yes Low permeability lenses may need to be (Volume V, Chapter 5) overexcavated. Bioretention (Volume V, Chapter Yes Low permeability lenses may need to be overexcavated. 7) T5.12: Sheet flow dispersion T5.11: Concentrated flow dispersion (Volume V, Chapter Maybe* Adequate vegetative flow paths are likely not available. 5 * Viability to be determined by storm designer. Limitations The recommendations and conclusions provided in this geotechnical evaluation report are professional opinions consistent with the level of care and skill that is typical of other members in the profession currently practicing under similar conditions in this area. A warranty is not expressed or implied. Variations in the soil and groundwater conditions observed at the test pit locations may exist and may not become evident until construction. ESNW should reevaluate the conclusions in this geotechnical evaluation report if variations are encountered. Earth Solutions NW. LLC Select Homes, Inc. May 14, 2021 Additional Services ES-7572 Page 7 ESNW should be retained to provide additional geotechnical services in association with this project, including testing and consulting services during construction. ESNW should have an opportunity to review final project plans with respect to geotechnical recommendations provided in this letter. We trust this letter meets your current needs. Should you have questions, or if any additional information is required, please call. Sincerely, EARTH SOLUTIONS NW, LLC Adam Z. Shier, L.G. Project Geologist _ _.. I/2021 Henry T. Wright, P.E. Senior Project Manager Attachments: Plate 1 — Vicinity Map Plate 2 — Test Pit Location Plan Plate 3 — Footing Drain Detail Test Pit Logs Grain Size Distribution cc: RAM Engineering, Inc. Attention: Mr. Rob Long, P.E. (Email only) Earth Solutions NW. LLC N 187th Street Southwest ❑ ❑ O Goo, I ❑ �06 188th Street Southwest a Lynndole -' I odooPo as omgd� 188th Street Southwest aPork Penny Lane n °se 3 O / 189th Place South e t 189th Place Southwes� v o 190th Street Southwes[. ^ ¢ 191 StStreet Southwl 1915 t Street Southwest 192nd Street _ m ❑, P �0 �� '� u u 192no Place Sou �q,PSt r$nd P\ace Southwest e C eP n P t 193rd Place Southwest f Ulida IL 193rd Street southwest b ,��❑� L�ao Q Lynnwood WA 524 9 —196th S_tne Southwest_ _ _ WA 524 - _196th Stre_e[ S_o_uthwest__ fLe�'>. Crossr `m a6 0------------- a� ay o M nJnl — 199th Street Southwest WA 200th Street Southwest _ Edmonds. - = 200th Street Southwest I c'c Community t� Ista Place D 201 st street Southwest o College a 202nd Street Southwest 202nd Street Southwest 3 `w 202nd Place Southwest S ° ° ° ^ ° 3rd Street Southwest Lynnwood MunlclpaI / °.' SITE Golf Course dmonds E= s Street Southwest � ds Streei c'206th ,° n College ^ ^ � m Place Middle s � .. .. � School v —< — -- Main Street_ � � _ -. - N 208th Street Southwest Seattle' Heights) meek 210th Street s 4outhwest] Yost Park 3a \\ 3 w3`aPc — — �p / 4 �< Edmondsl Woodway Apartme [s�� '' Poo9q 7S High school Bo"cloin �oo poo a m 3m ad Sou 216[h 50¢ei thwest ro dbl ^ Chase Lokes 216tn street southwest 216tn street southwest .215ih Street Southwest Elementar 216th Street Southwest _�1 _ WA 99 J;r`� School y pca yt° `�J © 217th Street southwest m {11 1 ENF-'u .i L _�� /mot �� D�o i6❑a �a� w218th Shee°Southwest �3�� C� qqp� " 0 Lo, o.: ooa ❑oa be ;ova ud❑ . a. ❑ ° 4°�a0°o�°�,III fl.b n Ptl ao dco ❑ . h q I' = p� _ t _ 220th St[eet.Southwest_ a_220th Street Southwes Y Reference: NORTH , Snohomish County, Washington i OpenStreetMap.org Vicinity Map 203rd Street SFR Edmonds, Washington Drwn. MRS Date 12/16/2020 Proj. No. 7572 NOTE: This plate may contain areas of color. ESNW cannot be responsible for any subsequent misinterpretation of the information resulting from black & white reproductions of this plate. Checked AZS Date Dec. 2020 Plate 1 VIM rrc !ojnpow ESLIP OP2GLA:ff'IOU\l62f'IIJ9 gUq EIJAILOIJWG JCUI 2GLAICG2 CGO�GcPlJlc l Eu$IUGGLIu$' COu2CLncgou Lip goinj!ouie IAM,-,-c NOTES: • Do NOT tie roof downspouts to Footing Drain. • Surface Seal to consist of 12" of less permeable, suitable soil. Slope away from building. LEGEND: Surface Seal: native soil or other low -permeability material. 1-inch Drain Rock ti•ti•ti•ti• r1r�r��1r Perforated Rigid Drain Pipe (Surround in Drain Rock) SCHEMATIC ONLY - NOT TO SCALE NOT A CONSTRUCTION DRAWING Drwn. MRS Date 12/29/2020 Proj. No. 7572 Checked AZS Date Dec. 2020 Plate 3 Earth Solutions NWLLC SOIL CLASSIFICATION CHART MAJOR DIVISIONS SYMBOLS TYPICAL DESCRIPTIONS GRAPH LETTER GRAVEL AND CLEAN GRAVELS �' �� • �•• 46 •� GW WELL -GRADED GRAVELS, GRAVEL - SAND MIXTURES, LITTLE OR NO FINES GRAVELLY SOILS (LITTLE OR NO FINES) ° (Y o B, o DOo D Q oQ Q GP POORLY -GRADED GRAVELS, GRAVEL - SAND MIXTURES, LITTLE OR NO FINES COARSE GRAINED SOILS MORE THAN 50% OF COARSE FRACTION GRAVELS WITH FINES ° o 0 �0 o D GM SILTY GRAVELS, GRAVEL - SAND - SILT MIXTURES RETAINED ON NO. 4 SIEVE (APPRECIABLE AMOUNT OF FINES) GC CLAYEY GRAVELS, GRAVEL - SAND - CLAY MIXTURES MORE THAN 50% OF MATERIAL IS SAND AND CLEAN SANDS SW WELL -GRADED SANDS, GRAVELLY SANDS, LITTLE OR NO FINES �. :. SP POORLY -GRADED SANDS, GRAVELLY SAND, LITTLE OR NO FINES LARGER THAN NO. 200 SIEVE SIZE SANDY SOILS (LITTLE OR NO FINES) SANDS WITH FINES SM SILTY SANDS, SAND - SILT MIXTURES MORE THAN 50% OF COARSE FRACTION PASSING ON NO. 4 SIEVE (APPRECIABLE AMOUNT OF FINES) SC CLAYEY SANDS, SAND - CLAY MIXTURES INORGANIC SILTS AND VERY FINE ML SANDS, ROCK FLOUR, SILTY OR CLAYEY FINE SANDS OR CLAYEY SILTS WITH SLIGHT PLASTICITY FINE GRAINED SOILS SILTS LIQUID LIMIT AND LESS THAN 50 CLAYS CL INORGANIC CLAYS OF LOW TO MEDIUM PLASTICITY, GRAVELLY CLAYS, SANDY CLAYS, SILTY CLAYS, LEAN CLAYS OL ORGANIC SILTS AND ORGANIC SILTY CLAYS OF LOW PLASTICITY MORE THAN 50% OF MATERIAL IS SMALLER THAN NO. 200 SIEVE MH INORGANIC SILTS, MICACEOUS OR DIATOMACEOUS FINE SAND OR SILTY SOILS SIZE SILTS AND LIQUID LIMIT CLAYS GREATER THAN 50 CH INORGANIC CLAYS OF HIGH PLASTICITY OH ORGANIC CLAYS OF MEDIUM TO HIGH PLASTICITY, ORGANIC SILTS HIGHLY ORGANIC SOILS PT PEAT, HUMUS, SWAMP SOILS WITH HIGH ORGANIC CONTENTS DUAL SYMBOLS are used to indicate borderline soil classifications. The discussion in the text of this report is necessary for a proper understanding of the nature of the material presented in the attached logs. 'I �Mrrc o�n�iou Egu�N 'I �Mrrc o�n�iou Egu�N 'I �Mrrc o�n�iou Egu�N r,Zm7 dC Eff� i E. CONSTRUCTION SWPPP REQUIREMENTS: The project will require grading to construct the proposed buildings and utilities (including the stormwater detention pipe system). Standard erosion control measures are proposed to be used during construction. The primary erosion and sediment control BMP during construction will be proper soil stabilization methods. Exposed soils shall be stabilized by application of effective BMPs that protect the soil from the erosive forces of raindrops, flowing water, and wind. Applicable practices include, but not limited to, temporary and permanent seeding, sodding, mulching, plastic covering, erosion control fabrics, matting, the early application of gravel base on areas to be paved, and dust control. The contractor shall select a soil stabilization method best suited for the particular situation. Stock piles must be stabilized and protected with sediment trapping measures. In addition, site containment of exposed soils shall be sustained by using silt fence barriers along the down -slope boundaries of the site's disturbance areas. See the site development plan for details. Construction Stormwater Pollution Prevention Plan (SWPPP): The following is a summary of the site's erosion control measures that evaluates the typical DOE 13 elements of a SWPPP: Element 1: Mark Clearing Limits: Clearing limits have been delineated on the engineering site development plans. Element 2: Establish Construction Access: A construction access has been delineated on the engineering site development plans. Element 3: Control Flow Rates: During construction silt fencing will provide attenuation of site runoff and upon project completion and stabilization (established lawns and landscape of exposed soils), the infiltration storm system will provide flow control. Element 4: Install Sediment Controls: Filter fabric fence has been delineated and detailed on the engineering site development plans. At a minimum, silt fence will be installed along the down gradient perimeter of the disturbed area that will receive sediment -laden runoff. Element 5: Stabilize Soils: Soils will be stabilized per the TESC notes listed on the engineering site development plans. Element 6: Protect Slopes: Exposed slopes shall be stabilized per the TESC notes listed on the engineering site development plans. Element 7: Protect Drain Inlets: Drain inlet protection will be installed on all catch basins that will receive sediment -laden runoff. See the engineering site development plans for locations and detail. Element 8: Stabilize Channels and Outlets: This element is not applicable since there are no temporary channels or outlets proposed. RAMEngineering, Inc. RAM No. 20-020 Select Homes: 2-Lot SP, 7918 203rd Street SW Stormwater Site Plan Report Page E-1 Element 9: Control Pollutants: Pollutants shall be managed as described in the TESC notes listed on the engineering site development plans. Element 10: Control De -Watering: Highly turbid or contaminated de -watering water shall be handled separately from stormwater. The water from all de -watering systems for trenches and foundations shall be treated or disposed prior to discharging from the site. Element 11: Maintain BMPs: BMPs shall be maintained and removed at the end of the project as follows: i. All temporary and permanent erosion and sediment control BMPs shall be inspected, maintained and repaired in accordance with the Drainage Manual or as approved or required by the City to assure continued performance of their intended function in accordance with BMP specifications. ii. The applicant may remove temporary BMPs when they are no longer needed. iii. All temporary erosion and sediment control BMPs shall be removed within 30 days after construction is completed and the City has determined that the site is stabilized. Element 12: Manage the Project: The owner of the site is responsible for managing the installation and maintenance of the site BMPs. Element 13. Protect Low Impact Development BMPs: Compaction (i.e. vehicle and equipment traffic or storage; and/or placement of stockpiles) to the soils in the area of the stormwater BMPs (Post - Construction Soil Quality and Depth BMP T5.13 and Perforated Stub -out Connections BMP T5.10C) shall be avoided during construction. RAMEngineering, Inc. RAM No. 20-020 Select Homes: 2-Lot SP, 7918 203rd Street SW Stormwater Site Plan Report Page E-2 F. OPERATION AND MAINTENANCE GUIDELINES: These guidelines are intended to provide operation and maintenance instructions for the project's storm drainage control facilities. The owner is responsible for maintenance of storm drainage facilities within the property (private property owner system); the owner is not responsible for maintenance within the public right-of-way (City system). Private Property Owners: Private property owners are responsible for properly maintaining the stormwater infrastructure on their property to ensure it operates as designed. The joint stormwater system (pipes, catch basins, and joint infiltration trench) which benefits both lots of the short plat shall be maintained collectively and equally by both property owners. The City has developed an inspection program to ensure private property owners are properly maintaining their stormwater systems. City System: City crews perform maintenance activities on the entire storm drainage system, including inspection and cleaning of catch basins, street sweeping, emergency flooding response, creek maintenance, inspection and monitoring of private stormwater detention systems. Operation and Maintenance Requirements for private property owner system: This manual is not comprehensive; although it explains the intended operation of the various components of the drainage system, and suggests a routine of inspection and maintenance, it cannot anticipate every problem. Once a historical record of maintenance is established, it may be prudent to alter the routine. It is recommended that maintenance records be kept, and that the records be reviewed periodically. Concept of Operation: The drainage design is shown and described in the site development engineering plans and report. The approved site development plans and report should be retained by the property owners and used as a reference to identify drainage facilities outlined in this manual. Stormwater Infiltration Trench System. The private joint infiltration trench system consists of excavated trench filled with drain rock. The infiltration trench system has been designed to infiltrate most storm event; if an extraordinary event was to occur or multiple back to back large storm events occurred the connected catch -basins may overtop and overflow into the street system. If regular overtopping of the catch basin is experienced the system shall be thoroughly cleaned and inspected. Over a period of time siltation of the infiltration bed can occur (especially if the system and upstream catch basin are not inspected and cleaned regularly) and replacement of the rock in the infiltration system may be required. The following pages outline standard general maintenance criteria for the project's drainage facilities For additional and updated maintenance information visit the Washington State Department of Ecology's web -site at: http://www.ecy.wa.gov/programs/wq/wghome.html RAMEngineering, Inc. RAM No. 20-020 Select Homes: 2-Lot SP, 7918 203rd Street SW Stormwater Site Plan Report Page F-1 MAINTENANCE REQUIREMENTS ECDC Section 18.30.090 requires privately -owned stormwater management facilities, such as LID BMPs be properly maintained. The owner of the property is the responsible party for such maintenance. The system must be kept in good working order. The entire system should be inspected once per year. An improperly maintained BMP may cause private property or street flooding. Contact the City Engineering Division for maintenance information. The City may make periodic inspections of BMPs to ensure they are operating properly. ECDC Section 18.30.100 contains the enforcement provisions the City can use to ensure the system is properly maintained. General Infiltration Maintenance Criteria Provision should be made for regular and perpetual maintenance of the infiltration basin/trench, including replacement and/or reconstruction of the any media that are relied upon for treatment purposes. Maintenance should be conducted when water remains in the basin or trench for more than 24 hours after the end of a rainfall event, or when overflows occur more frequently than planned. For example, off-line infiltration facilities should not have any overflows. Infiltration facilities designed to completely infiltrate all flows to meet flow control standards should not overflow. Removal of accumulated debris/sediment in the basin/trench should be conducted every 6 months or as needed to prevent clogging, or when water remains in the pond for greater than 24 hours after the end of a rainfall event. RAM ngineering, Inc. RAM No. 20-020 Select Homes: 2-Lot SP, 7918 203rd Street SW Stormwater Site Plan Report Page F-2 Appendix V-A: BMP Maintenance Tables Ecology intends the facility -specific maintenance standards contained in this section to be conditions for determining if maintenance actions are required as identified through inspection. Recognizing that Permittees have limited maintenance funds and time, Ecology does not require that a Permittee perform all these maintenance activities on all their stormwater BMPs. We leave the determination of importance of each maintenance activity and its priority within the stormwater program to the Permittee. We do expect, however, that sufficient maintenance will occur to ensure that the BMPs continue to operate as designed to protect ground and surface waters. Ecology doesn't intend that these measures identify the facility's required condition at all times between inspections. In other words, exceedance of these conditions at any time between inspections and/or maintenance does not automatically constitute a violation of these standards. However, based upon inspection observations, the Permittee shall adjust inspection and maintenance schedules to minimize the length of time that a facility is in a condition that requires a maintenance action. Table V-A.1: Maintenance Standards - Detention Ponds Maintenance Component Defect Conditions When Maintenance Is Needed Results Expected When Maintenance Is Performed Any trash and debris which exceed 1 cubic feet per 1,000 square feet. In general, there should be no visual evidence of Trash &Debris dumping. Trash and debris cleared from site If less than threshold all trash and debris will be removed as part of next scheduled maintenance. General Any poisonous or nuisance vegetation which may constitute No danger of poisonous a hazard to maintenance vegetation where maintenance personnel or the public. personnel or the public might normally be. (Coordinate with Poisonous Any evidence of noxious weeds local health department) Vegetation and as defined by State or local noxious weeds regulations. Complete eradication of noxious weeds may not be possible. (Apply requirements of adopted Compliance with State or local IPM policies for the use of eradication policies required herbicides). RAMEngineering, Inc. RAM No. 20-020 Select Homes: 2-Lot SP, 7918 203rd Street SW Stormwater Site Plan Report Page F-3 Table V-A.1: Maintenance Standards - Detention Ponds Maintenance Defect Conditions When Results Expected When Component Maintenance Is Needed Maintenance Is Performed Any evidence of oil, gasoline, contaminants or other pollutants Contaminants and No contaminants or pollutants Pollution (Coordinate removal/cleanup present. with local water quality response agency). Any evidence of rodent holes if Rodents destroyed and dam or facility is acting as a dam or berm repaired. (Coordinate with Rodent Holes berm, or any evidence of water local health department; piping through dam or berm via coordinate with Ecology Dam rodent holes. Safety Office if pond exceeds 10 acre-feet.) Facility is returned to design function. Beaver Dams Dam results in change or function of the facility. (Coordinate trapping of beavers and removal of dams with appropriate permitting agencies) Insects destroyed or removed When insects such as wasps from site. Insects and hornets interfere with maintenance activities. Apply insecticides in compliance with adopted IPM policies Tree growth does not allow maintenance and inspection access or interferes with maintenance activity (i.e., slope mowing, silt removal, vactoring, Trees do not hinder or equipment movements). If maintenance activities. trees are not interfering with Harvested trees should be Tree Growth and access or maintenance, do not recycled into mulch or other Hazard Trees remove beneficial uses (e.g., alders for firewood). If dead, diseased, or dying trees are identified Remove hazard Trees (Use a certified Arborist to determine health of tree or removal requirements) RAMEngineering, Inc. Select Homes: 2-Lot SP, 7918 203rd Street SW RAM No. 20-020 Stormwater Site Plan Report Page F-4 Table V-A.1: Maintenance Standards - Detention Ponds Maintenance Defect Conditions When Results Expected When Component Maintenance Is Needed Maintenance Is Performed Slopes should be stabilized using appropriate erosion Eroded damage over 2 inches control measure(s); e.g.,rock deep where cause of damage is reinforcement, planting of grass, still present or where there is compaction. Side Slopes of Pond Erosion potential for continued erosion. If erosion is occurring on Any erosion observed on a compacted berms a licensed compacted berm embankment. engineer in the state of Washington should be consulted to resolve source of erosion. Accumulated sediment that exceeds 10% of the designed Sediment cleaned out to Sediment pond depth unless otherwise designed pond shape and specified or affects inletting or depth; pond reseeded if Storage Area outletting condition of the necessary to control erosion. facility. Liner (if Applicable) Liner is visible and has more Liner repaired or replaced. Liner than three 1/4-inch holes in it. is fully covered. Any part of berm which has settled 4 inches lower than the design elevation If settlement is apparent, measure berm to determine amount of settlement Dike is built back to the design Settlements elevation. Settling can be an indication of more severe problems with the Ponds Berms berm or outlet works. A licensed (Dikes) engineer in the state of Washington should be consulted to determine the source of the settlement. Discernable water flow through pond berm. Ongoing erosion with potential for erosion to Piping eliminated. Erosion Piping continue. potential resolved. (Recommend a Goethechnical engineer be called in to inspect RAMEngineering, Inc. RAM No. 20-020 Select Homes: 2-Lot SP, 7918 203rd Street SW Stormwater Site Plan Report Page F-5 Table V-A.1: Maintenance Standards - Detention Ponds Maintenance Defect Conditions When Results Expected When Component Maintenance Is Needed Maintenance Is Performed and evaluate condition and recommend repair of condition. Tree growth on emergency Trees should be removed. If root spillways creates blockage system is small (base less than problems and may cause failure 4 inches) the root system may of the berm due to uncontrolled be left in place. Otherwise the Tree Growth overtopping. roots should be removed and the berm restored. A licensed Tree growth on berms over 4 engineer in the state of feet in height may lead to piping Washington should be consulted Emergency through the berm which could for proper berm/spillway Overflow/ Spillway lead to failure of the berm. restoration. and Berms over 4 feet in height Discernable water flow through pond berm. Ongoing erosion with potential for erosion to continue. Piping Piping eliminated. Erosion potential resolved. (Recommend a Geotechnical engineer be called in to inspect and evaluate condition and recommend repair of condition. Only one layer of rock exists above native soil in area five square feet or larger, or any Emergency Emergency exposure of native soil at the Rocks and pad depth are Overflow/Spillway Overflow/Spillway top of out flow path of spillway. restored to design standards. (Rip -rap on inside slopes need not be replaced.) Erosion See "Side Slopes of Pond" Table V-A.2: Maintenance Standards - Infiltration Maintenance Defect Conditions When Maintenance Is Component I I Needed General Trash & Debris See Table V-A.1: Maintenance Standards - Detention Ponds RAMEngineering, Inc. RAM No. 20-020 Results Expected When Maintenance Is Performed See Table V-A.1: Maintenance Select Homes: 2-Lot SP, 7918 203rd Street SW Stormwater Site Plan Report Page F-6 Table V-A.2: Maintenance Standards - Infiltration Maintenance Conditions When Maintenance Is Results Expected Component Defect Needed When Maintenance Is Performed Standards - Detention Ponds See Table V-A.1: Poisonous/Noxious See Table V-A.1: Maintenance Maintenance Vegetation Standards - Detention Ponds Standards - Detention Ponds See Table V-A.1: Contaminants and See Table V-A.1: Maintenance Maintenance Pollution Standards - Detention Ponds Standards - Detention Ponds See Table V-A.1: Rodent Holes See Table V-A.1: Maintenance Maintenance Standards - Detention Ponds Standards - Detention Ponds Water ponding in infiltration pond after rainfall ceases and appropriate time allowed for infiltration. Treatment basins should infiltrate Water Quality Design Storm Volume within 48 hours, and Sediment is removed empty within 24 hours after cessation of and/or facility is Storage Area Sediment most rain events. cleaned so that infiltration system works according to (A percolation test pit or test of facility design. indicates facility is only working at 90% of its designed capabilities. Test every 2 to 5 years. If two inches or more sediment is present, remove). Filter Bags (if Filled with Sediment Sediment and debris fill bag more than Filter bag is replaced applicable) and Debris 1/2 full. or system is redesigned. By visual inspection, little or no water Gravel in rock filter is Rock Filters Sediment and Debris flows through filter during heavy rain replaced. storms. See Table V-A.1: Side Slopes of Erosion See Table V-A.1: Maintenance Maintenance Pond Standards - Detention Ponds Standards - Detention Ponds RAMEngineering, Inc. RAM No. 20-020 Select Homes: 2-Lot SP, 7918 203rd Street SW Stormwater Site Plan Report Page F-7 Table V-A.2: Maintenance Standards - Infiltration Maintenance Conditions When Maintenance Is Results Expected Component Defect Needed When Maintenance Is Performed See Table V-A.1: Tree Growth See Table V-A.1: Maintenance Maintenance Standards - Detention Ponds Standards - Detention Ponds Emergency Overflow Spillway and Berms over 4 feet in height. See Table V-A.1: Piping See Table V-A.1: Maintenance Maintenance Standards - Detention Ponds Standards - Detention Ponds See Table V-A.1: Rock Missing See Table V-A.1: Maintenance Maintenance Standards - Detention Ponds Standards - Detention Ponds Emergency Overflow Spillway See Table V-A.1: Erosion See Table V-A.1: Maintenance Maintenance Standards - Detention Ponds Standards - Detention Ponds Pre -settling Ponds Facility or sump filled 6" or designed sediment trap depth of and Vaults with Sediment and/or sediment. Sediment is removed. debris Table V-A.S: Maintenance Standards - Catch Basins Maintenance Component Defect Conditions When Maintenance is Needed Results Expected When Maintenance is performed Trash or debris which is located immediately in front of the catch basin opening or is blocking No Trash or debris inletting capacity of the basin by more than located immediately in General 10%. front of catch basin or Trash & Debris on grate opening. Trash or debris (in the basin) that exceeds 60 percent of the sump depth as measured from No trash or debris in the bottom of basin to invert of the lowest pipe the catch basin. into or out of the basin, but in no case less than RAAf Engineering, Inc. RAM No. 20-020 Select Homes: 2-Lot SP, 7918 203rd Street SW Stormwater Site Plan Report Page F-8 Table V-A.5: Maintenance Standards - Catch Basins Maintenance Results Expected Component Defect Conditions When Maintenance is Needed When Maintenance is performed a minimum of six inches clearance from the debris surface to the invert of the lowest pipe. Inlet and outlet pipes free of trash or debris. Trash or debris in any inlet or outlet pipe blocking more than 1/3 of its height. No dead animals or vegetation present within the catch basin. Dead animals or vegetation that could generate odors that could cause complaints or dangerous gases (e.g., methane). Sediment (in the basin) that exceeds 60 percent 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 less than No sediment in the Sediment a minimum of 6 inches clearance from the catch basin sediment surface to the invert of the lowest pipe. Top slab has holes larger than 2 square inches Top slab is free of or cracks wider than 1/4 inch. (Intent is to make holes and cracks. Structure Damage sure no material is running into basin). to Frame and/or Frame is sitting flush Top Slab Frame not sitting flush on top slab, i.e., on the riser rings or top separation of more than 3/4 inch of the frame slab and firmly from the top slab. Frame not securely attached attached. Maintenance person judges that structure is Basin replaced or unsound. repaired to design Fractures or standards. Cracks in Basin Grout fillet has separated or cracked wider than Walls/ Bottom 1/2 inch and longer than 1 foot at the joint of Pipe is and any inlet/outlet pipe or any evidence of soil a t basinn wall. secure at basin particles entering catch basin through cracks. Settlement/ If failure of basin has created a safety, function, Basin replaced or repaired to design Misalignment or design problem. standards. Vegetation Vegetation growing across and blocking more No vegetation blocking than 10 /o of the basin opening. opening to basin. RAMEngineering, Inc. RAM No. 20-020 Select Homes: 2-Lot SP, 7918 203rd Street SW Stormwater Site Plan Report Page F-9 Table V-A.S: Maintenance Standards - Catch Basins Maintenance Results Expected Component Defect Conditions When Maintenance is Needed When Maintenance is performed Vegetation growing in inlet/outlet pipe joints No vegetation or root that is more than six inches tall and less than growth present. six inches apart. Contamination See Table V-A.1: Maintenance Standards - No pollution present. Detention Ponds and Pollution Cover/grate is in place, Cover Not in Cover is missing or only partially in place. Any meets design Place open catch basin requires maintenance. standards, and is secured Locking Mechanism cannot be opened by one Mechanism opens with Catch Basin Mechanism Not maintenance person with proper tools. Bolts proper tools. Cover Working into frame have less than 1/2 inch of thread. One maintenance person cannot remove lid after applying normal lifting pressure. Cover can be removed Cover Difficult to by one maintenance Remove (Intent is keep cover from sealing off access to person. maintenance.) Ladder is unsafe due to missing rungs, not Ladder meets design Ladder Ladder Rungs securely attached to basin wall, misalignment, standards and allows Unsafe rust, cracks, or sharp edges. maintenance person safe access. Grate opening Grate with opening wider than 7/8 inch. Grate opening meets Unsafe design standards. Trash and Debris Trash and debris that is blocking more than Grate free of trash and Metal Grates 20% of grate surface inletting capacity. debris. (If Applicable) Grate is in place, meets Damaged or Grate missing or broken member(s) of the the design standards, Missing. grate. and is installed and aligned with the flow path. RAMEngineering, Inc. RAM No. 20-020 Select Homes: 2-Lot SP, 7918 203rd Street SW Stormwater Site Plan Report Page F-10 Ft ALI I ENGINEERING, INC. Civil Engineering I Land Planning