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19-014 Purser Lot 2 Drainage Report 2020-03-04Lot 2 of Purser 2-Lot Short Plat 735 15t" Street SW Edmonds, WA 98020 BLD2020 Storm Drainage Report Prepared for: Rob Purser Date: March 4, 2020 goy l� o SIV �O 36508 9 Wei �GISTEg�' 3/-4-/2020 Prepared by: Rob Long, PE RAM Engineering, Inc. 16531 13t" Ave W, Suite A108, Lynnwood WA 98037 (425) 678-6960 RAMengineeringinc.corn Job No. 19-014 Lot 2 of Purser 2-Lot Short Plat 735 15th Street SW Edmonds, WA 98020 Introduction: This summary report provides site design information for Lot 2 of the single family 2- lot short plat by Rob Purser. This report includes storm drainage analysis to support permit review and approval. The property is located on the north side of 15th Street SW between 7th PI S and 8th Ave S, in the southwest 1/4 of Section 25, T 27 N, R 3 E, W.M. Site Address: 735 15th Street SW Applicant: Purser Development Services, LLC Edmonds, WA 98020 Contact: Rob Purser 520 3rd Ave N Tax Parcel Number: 00390000001100 Edmonds, WA 98020 TABLE OF CONTENTS SECTION PAGES A. Project Summary............................................................................................................................... 3 B. Parcel (Vicinity) Map.......................................................................................................................... 1 C. Site Plan............................................................................................................................................. 1 D. Aerial Photo....................................................................................................................................... 1 E. Stormwater Control System Summary............................................................................................... 1 F. Drainage Basin Description and Maps............................................................................................... 3 G. Grading and Erosion Control Summary (SWPPP Evaluation)............................................................ 3 H. Operation and Maintenance Guidelines.......................................................................................... 10 I. Geotechnical Engineering Report.................................................................................................... 18 RAM-noineerina. Inc Lot 2 of Purser 2-Lot Short Plat Engineering and Drainage Report RAM No. 19-014 A. PROJECT SUMMARY: This report provides engineering information for the proposed construction of a single-family residence of Lot 2 of a 2-lot short plat; the project is located on the north side of 15th St SW between 7th PI S and 8th Ave S (735 15th St SW) in the City of Edmonds. Existing Conditions. The total site (both lots of the short plat) consists of about 16,548 sf (0.38 acres) and is currently occupied by an existing single-family residence with a loop access drive between 15th St SW and 7th PI S. The existing house is surrounded by open grass lawn and landscape areas. The site is surrounded by single family residences to the north, 8th Ave S to the east, 15th St SW to the south; and 7th PI S to the west (see attached aerial photo- section D). The site generally slopes in a westerly direction; a majority of the site's drainage runoff would sheet flow westerly to the stormwater collection system in 7th PI S. No stream or wetlands were discovered on or immediately adjacent to the site. The stormwater system within 71h PI S generally flows north/northwesterly in the Willow Creek watershed basin. Additional discussion of the local drainage basin and downstream path is discussed in section F of this report. Developed Conditions. The proposed project includes the construction of a single-family residence and associated driveway and utilities. The proposed house will be located on the easterly portion of the project site of a 2-lot short plat (PLN20190040). The easterly (lot 2) single-family house proposed will have a driveway that directly accesses 7th PI S. via an access easement over lot 1 (westerly lot). All pre-existing structures and impervious 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. New infrastructure improvements include a stormwater conveyance and individual lot infiltration trench; water; sewer; power; and communications. The individual lot infiltration trench system will be designed and sized to meet compliance with the LID performance standard of the Edmonds Community Development Code (ECDC). All disturbed pervious (lawn and landscape) areas will preserve or restore the health and water -holding capacity of the soils by compost -amending (Per DOE BMP T5.13: Post - Construction Soil Quality and Depth). Due to the fact, the pollution generating driveway area are less than 5,000 sf (+/-2,895 sf) no water quality treatment system will be provided. A full overview of the proposed storm drainage control facilities, offsite/downstream analysis and grading and erosion control measures are discussed in the following sections of this report. RAMEngineering, Inc. Engineering and Drainage Report Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Page A-1 Summary of Minimum Requirements for Category 2 Project: 5.1 Minimum Requirement#1—Preparation of Stormwater Site Plan. The proposed easterly lot (lot 2) site development consists of disturbing about 0.23 acres (9,934 sf, which includes access easement area on Lot 1) of land and creating/replacing about 4,830 sf of hard surface area. Thus, the project (2-lot short plat) is classified as a Category 2 project per the City's classification system. The civil site development plans and this report have been prepared to address the projects impacts. 5.2 Minimum Requirement #2 — Construction Stormwater Pollution Prevention. A construction Stormwater Pollution Prevention Plan (SWPPP) has be 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 G. 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. 5.3 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. 5.4 Minimum Requirement #4 —Preservation of Natural Drainage Systems and Outfalls. The site generally slopes in a westerly direction towards 71h PI S; any runoff leaving the site would enter the stormwater system in 71h PI S. The proposed development will install infiltration trenches and amend the disturbed site soils; thus, reducing the site developments runoff to a de minimis amount. Each infiltration system will have a catch basin/trench drain near the edge of 71h PI S that will provide a safe and certain overflow route to the City's storm drainage system within 71h PI S. The City's storm drainage system within 71h PI S flows north within the Willow Creek watershed, thus maintaining the natural outfall watershed basin. The site is located within the Willow Creek watershed basin and eventually discharge to the Puget Sound (via Willow Creek) per the City of Edmonds maps (see section F). 5.5 Minimum Requirement #5 — Onsite Stormwater Management. The developed site conditions include new/replaced hard surface for the roof tops, driveways and walkway/patio areas for the proposed RAMEngineering, Inc. Engineering and Drainage Report Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Page A-2 residence. All rooftop and exterior area collection drains shall convey stormwater run-off to the on -site infiltration trench system. The individual lot infiltration trench system has been designed and sized to comply with the LID performance standard (MR #5) of the Edmonds Community Development Code (ECDC). Additionally, all disturbed pervious (lawn and landscape) areas will preserve or restore the health and water - holding capacity of the soils by compost -amending (Per DOE BMP T5.13: Post -Construction Soil Quality and Depth). See civil site development plans and section E for additional sizing calculations and construction details. 5.6 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 Lot 2 development will create about 2,245 sf pollution generation hard surfaces (driveway); most the site's hard surface is rooftop and walkway/patio areas (non -pollution generation surfaces). Thus, no basic or enhanced water quality treatment system is required. 5.7Minimum Requirement #7— Flow Control. An individual lot infiltration trench will provide flow control of the site's stormwater runoff. The infiltration trench has been designed to meet the flow control standards of a Category 2 project in a creek or lake basin and meet full flow control (due to the fact the project short plat project proposed 8,230 sf of hard surface area, greater than 5,000 sf). The lot stormwater infiltration system has been 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). A full overview of the proposed stormwater control facilities and calculations are provided in section E. 5.8 Minimum Requirement #8— Wetland Protection. No wetlands are known to exist on or adjacent to the site. 5.9 Minimum Requirement #9 — Operation and Maintenance. An operation and maintenance summary is provided in section H. RAMEngineering, Inc. Engineering and Drainage Report Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Page A-3 B. PARCEL (VICINITY) MAP f. ' C - •. T&ANSHP LWSL IGN4C E W M. r:S�" r.� ]fir'—"....• .w�r"".�,r•Li•F.w�..."'S'.. rw.. _ S� ��..� SW� 25 27 3 _•_•.••.•••. ,•••.••• C.msrr. -'•- Lcl � Sealon -•—• Crytr,ro, ram, , .�� .- Gor La — •- 5.+nsr — RO1M C,.rrrr n. na7 14pr vAi w 0L%W La, 4Yt Rd,N __ __ BEM Eaw..rra = } '---......f yf .1......1.E non Y.r r••n..r.. y r. �... „•—•T■ � � rrrgr.. _. . 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ES AT S a 1-078 it l ' Ct' -. 'u '.7ES�g 1-0T9 t7 p �■�ZI � 3 •, 71 SA ... I 7 s a 1 ■ w1 s e, tirti-o/ v NW46-V-03 RAM Engineering, Inc. Engineering and Drainage Report Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Page 8-1 C. SITE PLAN Sp�A:FFR CG[LEER e Y27 15M Sr SK fOU"_, ivA ADR O PARCEL A'O. WON SfAIW d PMR9M !40MY 7M r60h ST Sp{ ELNWI WA sewn PARCCZ N2 Oa39OL1�gO7Oa SAWSMTIR-VvF C)wD e Srefrr scarf r5O7 n Pr, s fp6wms wA qmw PAIICE1 RR A770=94MOO RAM Engineering, Inc. Engineering and Drainage Report YAAf9 CRA iC B� s' � f76A1 (Re-rew) e-f 27a-7O (WF--50 rfa•Accm ANa u near fASPKrOf rm w aflrcm or ear x a• r : 6' i 2r6.7O IrYlf-SEl 14r#f WAYSW Ifs I I ■ � r�- � I —"— s' . I ....... .q I I � .he°• .•., I 11 � I 'I I� � I r � ::•_.:� I I I � . ;` •� I I .-J i —,' SAU ARO DWAO e I_� Z .•.::, .._.� .� f4J5 80 ALE a EWGAA'1S Ncl r PARaEi- AF& WMJIR.U'P9Mf1 aw l'• r �T-J ffa i.azw• � r I I I f I I I '� ree•,re'fa'n• '.7J' Cr,Q76' PtA ij I� � � 1 I i ., ..ram NCA.g Nf 2-BRASS DLr� f w hav[T� S.:�Tr�' M�'•:: � :� afawa r.r• / SYAw SC 7/0 ISMST StlW; FnYpAQ.g ILA 9 20 H . PARLII ACE 07390000OOa1'07 Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Page C-1 - r D. AERIAL PHOTO (City of Edmonds GIS, 2017 photo) RAM Engineering, Inc. Engineering and Drainage Report Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Page D-1 E. STORMWATER CONTROL SYSTEM SUMMARY AND CALCULATIONS: The project proposes to create and/or replace 4,830 sf of hard surface with the construction of the easterly single-family residence (Lot 2, of short plat PLS20190040). To mitigate the construction of the single-family residence, an individual lot stormwater infiltration trench system will be installed to control the drainage runoff (flow control). The project applicant has elected to meet the LID Performance Standard to comply with ECDC 18.30.060.D.b (ii) and (iii), stormwater discharges shall match developed discharge durations to pre -developed durations for the range of pre -developed discharge rates from 8 percent of the 2-year peak flow to 50 percent of the 2-year peak flow from the project site. The following is a summary of the proposed new/replaced hard surface areas for Lot 2: Hard Surface Summary: Lot 2 (House 2,535 + Driveway 2,245 + Sidewalk/Patio 50) = 4,830 sf A site -specific geotechnical evaluation was made to assess the use of infiltration and LID measures onsite. The evaluation determined infiltration is feasible onsite and recommends a long-term infiltration design rate of 7.2 in/hr. The infiltration trench will be located at the easterly end of the access driveway. As stated above the infiltration trench will be designed for the total hard surface of the southerly single-family lot; the hard surface created will be 5,350 sf (0.123 ac). The infiltration trench shall be a minimum of 10 feet wide, 22 feet long and 2.5 feet deep; and filled with %" to 1-%" washed drain rock (35% voids). The below calculations demonstrate that the trench will fully mitigate the increased hard surfaces and the project will 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). The developed runoff rates and storage calculations were performed using the DOE 2012 Western Washington Hydrology Model (WWHM2012) continuous runoff model. See WWHM2012 printout on the following pages. WWHM2012 Input/Output Data: Project Name: 19-014- Lot 2 Site Name: Purser Lot 2 Site Address: 19-014 City Report Date: 3/4/2020 MGS Regoin Puget East Data Start 1901/10/1 Data End : 2058/09/30 DOT Data Number: 03 Version Date: 2018/10/10 Version : 4.2.16 Low Flow Threshold for POC 1 : 50 Percent of the 2 Year High Flow Threshold for POC 1: 50 year RAMEngineering, Inc. Engineering and Drainage Report Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Page E-1 PREDEVELOPED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre A B, Forest, Flat .228 Pervious Total 0.228 Impervious Land Use acre Impervious Total 0 Basin Total 0.228 Element Flows To: Surface Interflow MITIGATED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre A B, Pasture, Flat .117 Pervious Total 0.117 Impervious Land Use acre ROOF TOPS FLAT 0.058 DRIVEWAYS FLAT 0.052 SIDEWALKS FLAT 0.001 Impervious Total 0.111 Basin Total 0.228 Groundwater Element Flows To: Surface Interflow Groundwater Gravel Trench Bed 1 Gravel Trench Bed 1 Name : Gravel Trench Bed 1 Bottom Length: 22.00 ft. Bottom Width: 10.00 ft. Trench bottom slope 1: 0 To 1 RAM Engineering, Inc. Engineering and Drainage Report Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Page E-2 Trench Left side slope 0: 0 To 1 Trench right side slope 2: 0 To 1 Material thickness of first layer: 2.5 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: 7.2 Infiltration safety factor: 1 Total Volume Infiltrated (ac-ft.): 41.202 Total Volume Through Riser (ac-ft.): 0 Total Volume Through Facility (ac-ft.): 41.202 Percent Infiltrated: 100 Total Precip Applied to Facility: 0 Total Evap From Facility: 0 Discharge Structure Riser Height: 0 ft. Riser Diameter: 0 in. Element Flows To: Outlet 1 Outlet 2 Gravel Trench Bed Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) 0.0000 0.005 0.000 0.000 0.000 0.0278 0.005 0.000 0.000 0.036 0.0556 0.005 0.000 0.000 0.036 0.0833 0.005 0.000 0.000 0.036 0.1111 0.005 0.000 0.000 0.036 0.1389 0.005 0.000 0.000 0.036 0.1667 0.005 0.000 0.000 0.036 0.1944 0.005 0.000 0.000 0.036 0.2222 0.005 0.000 0.000 0.036 0.2500 0.005 0.000 0.000 0.036 0.2778 0.005 0.000 0.000 0.036 0.3056 0.005 0.000 0.000 0.036 0.3333 0.005 0.000 0.000 0.036 0.3611 0.005 0.000 0.000 0.036 0.3889 0.005 0.000 0.000 0.036 0.4167 0.005 0.000 0.000 0.036 0.4444 0.005 0.000 0.000 0.036 0.4722 0.005 0.000 0.000 0.036 0.5000 0.005 0.000 0.000 0.036 0.5278 0.005 0.000 0.000 0.036 0.5556 0.005 0.001 0.000 0.036 0.5833 0.005 0.001 0.000 0.036 0.6111 0.005 0.001 0.000 0.036 0.6389 0.005 0.001 0.000 0.036 0.6667 0.005 0.001 0.000 0.036 RAM Engineering, Inc. Engineering and Drainage Report Infilt(cfs) Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Page E-3 0.6944 0.005 0.001 0.000 0.036 0.7222 0.005 0.001 0.000 0.036 0.7500 0.005 0.001 0.000 0.036 0.7778 0.005 0.001 0.000 0.036 0.8056 0.005 0.001 0.000 0.036 0.8333 0.005 0.001 0.000 0.036 0.8611 0.005 0.001 0.000 0.036 0.8889 0.005 0.001 0.000 0.036 0.9167 0.005 0.001 0.000 0.036 0.9444 0.005 0.001 0.000 0.036 0.9722 0.005 0.001 0.000 0.036 1.0000 0.005 0.001 0.000 0.036 1.0278 0.005 0.001 0.000 0.036 1.0556 0.005 0.001 0.000 0.036 1.0833 0.005 0.001 0.000 0.036 1.1111 0.005 0.002 0.000 0.036 1.1389 0.005 0.002 0.000 0.036 1.1667 0.005 0.002 0.000 0.036 1.1944 0.005 0.002 0.000 0.036 1.2222 0.005 0.002 0.000 0.036 1.2500 0.005 0.002 0.000 0.036 1.2778 0.005 0.002 0.000 0.036 1.3056 0.005 0.002 0.000 0.036 1.3333 0.005 0.002 0.000 0.036 1.3611 0.005 0.002 0.000 0.036 1.3889 0.005 0.002 0.000 0.036 1.4167 0.005 0.002 0.000 0.036 1.4444 0.005 0.002 0.000 0.036 1.4722 0.005 0.002 0.000 0.036 1.5000 0.005 0.002 0.000 0.036 1.5278 0.005 0.002 0.000 0.036 1.5556 0.005 0.002 0.000 0.036 1.5833 0.005 0.002 0.000 0.036 1.6111 0.005 0.002 0.000 0.036 1.6389 0.005 0.002 0.000 0.036 1.6667 0.005 0.002 0.000 0.036 1.6944 0.005 0.003 0.000 0.036 1.7222 0.005 0.003 0.000 0.036 1.7500 0.005 0.003 0.000 0.036 1.7778 0.005 0.003 0.000 0.036 1.8056 0.005 0.003 0.000 0.036 1.8333 0.005 0.003 0.000 0.036 1.8611 0.005 0.003 0.000 0.036 1.8889 0.005 0.003 0.000 0.036 1.9167 0.005 0.003 0.000 0.036 1.9444 0.005 0.003 0.000 0.036 1.9722 0.005 0.003 0.000 0.036 2.0000 0.005 0.003 0.000 0.036 2.0278 0.005 0.003 0.000 0.036 2.0556 0.005 0.003 0.000 0.036 2.0833 0.005 0.003 0.000 0.036 2.1111 0.005 0.003 0.000 0.036 2.1389 0.005 0.003 0.000 0.036 2.1667 0.005 0.003 0.000 0.036 2.1944 0.005 0.003 0.000 0.036 RAM Engineering, Inc. Engineering and Drainage Report Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Page E-4 2.2222 0.005 0.003 0.000 0.036 2.2500 0.005 0.004 0.000 0.036 2.2778 0.005 0.004 0.000 0.036 2.3056 0.005 0.004 0.000 0.036 2.3333 0.005 0.004 0.000 0.036 2.3611 0.005 0.004 0.000 0.036 2.3889 0.005 0.004 0.000 0.036 2.4167 0.005 0.004 0.000 0.036 2.4444 0.005 0.004 0.000 0.036 2.4722 0.005 0.004 0.000 0.036 2.5000 0.005 0.004 0.000 0.036 Ij WWHM2012 19.014- Lot 2 File Edit View Help Summary Report ❑ci�0 X %b Ift AI-�] aId®kI•lii�0i■qkla a a� ®9 10 12N 0 © O Predeveloped W0 Mitigated Run Scenario ININIPH Pro Elements _ Commercial T oolbox Move Elements Save xy Load xy I Li Y® KId L' Il p 19 fn c Lot ' Fini RAM Engineering, Inc. Engineering and Drainage Report M • Gravel Trench Bed 1 Mitigated Facility Name Downstream Connection Facility Type r Precipitation Applied to Facility r Kvaoaraiion Arx+ked W Faciits] Gravel Trench Bed t Outlet T Outlet 2 Outlet 3 0 110 Greve)Trench/Bed Quick Trench Facility Dimension Diagram I Facility Dimensions Trench Length (ft) Trench Bottom Width (h) 1l3 Effective Total Depth (ft) 2 Top and bottom slope [HN) 0 Left Side Slope (HN) Right Side Slope (HN) 0 Material Layers for Trench/Red Layer l Thickness (ft) Zg Layer 1 porosity 10.1 ] Q35 Layer 2 Thickness [ft) 0 Layer 2 pou"ly 10.1 ] 0 Layer 3 Thickness (ft) 0 Layer 3 porosily 10.1 ] Infiltration Yes J Measured I nfd4gorr Rate [inlhtl 7.2 Reduction FaVorWiR•factor] 11�-1 Use Wetted Surface Area (sidewaft) NO Total Volume l0krated (ac•ft) 41,202 Total Volume Through Riser [ac•h] 0 Size Infiitralion Trench_ Target %- 100 Outlet Structure Data I Rise) Height [Ilj ��7H Riser Diameter [in] 1u- -:-1 Riser Type Rat Notch Type Orifice Diameter Height Number (in) (ft) 1 2 Fo----I Fo----I 3 F0--- --'A F0-- --.=I TrenchVoWe at Riser Head (ac•ft) M4 Show Trench Open Table Initial Stage (ft) 0 Total Volume Through Fac ly ac 41.202 Percent Infiltrated 100 Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Page E-5 ANALYSIS RESULTS Stream Protection Duration Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.228 Total Impervious Area:O Mitigated Landuse Totals for POC #1 Total Pervious Area:0.117 Total Impervious Area:0.111 Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.000114 5 year 0.000151 10 year 0.000173 25 year 0.000181 50 year 0.000182 100 year 0.000183 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 Stream Protection Duration Annual Peaks for Predeveloped and Mitigated. Year Predeveloped Mitigated 1902 0.000 0.000 1903 0.000 0.000 1904 0.000 0.000 1905 0.000 0.000 1906 0.000 0.000 1907 0.000 0.000 1908 0.000 0.000 1909 0.000 0.000 1910 0.000 0.000 1911 0.000 0.000 1912 0.000 0.000 1913 0.000 0.000 1914 0.000 0.000 1915 0.000 0.000 1916 0.000 0.000 1917 0.000 0.000 1918 0.000 0.000 1919 0.000 0.000 1920 0.000 0.000 RAM Engineering, Inc. Engineering and Drainage Report POC #1 Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Page E-6 1921 0.000 0.000 1922 0.000 0.000 1923 0.000 0.000 1924 0.000 0.000 1925 0.000 0.000 1926 0.000 0.000 1927 0.000 0.000 1928 0.000 0.000 1929 0.000 0.000 1930 0.000 0.000 1931 0.000 0.000 1932 0.000 0.000 1933 0.000 0.000 1934 0.000 0.000 1935 0.000 0.000 1936 0.000 0.000 1937 0.000 0.000 1938 0.000 0.000 1939 0.000 0.000 1940 0.000 0.000 1941 0.000 0.000 1942 0.000 0.000 1943 0.000 0.000 1944 0.000 0.000 1945 0.000 0.000 1946 0.000 0.000 1947 0.000 0.000 1948 0.000 0.000 1949 0.000 0.000 1950 0.000 0.000 1951 0.000 0.000 1952 0.000 0.000 1953 0.000 0.000 1954 0.000 0.000 1955 0.000 0.000 1956 0.000 0.000 1957 0.000 0.000 1958 0.000 0.000 1959 0.000 0.000 1960 0.000 0.000 1961 0.000 0.000 1962 0.000 0.000 1963 0.000 0.000 1964 0.000 0.000 1965 0.000 0.000 1966 0.000 0.000 1967 0.000 0.000 1968 0.000 0.000 1969 0.000 0.000 1970 0.000 0.000 1971 0.000 0.000 1972 0.000 0.000 1973 0.000 0.000 1974 0.000 0.000 1975 0.000 0.000 1976 0.000 0.000 1977 0.000 0.000 1978 0.000 0.000 1979 0.000 0.000 1980 0.000 0.000 1981 0.000 0.000 RAM Engineering, Inc. Engineering and Drainage Report Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Page E-7 1982 0.000 0.000 1983 0.000 0.000 1984 0.000 0.000 1985 0.000 0.000 1986 0.000 0.000 1987 0.000 0.000 1988 0.000 0.000 1989 0.000 0.000 1990 0.000 0.000 1991 0.000 0.000 1992 0.000 0.000 1993 0.000 0.000 1994 0.000 0.000 1995 0.000 0.000 1996 0.000 0.000 1997 0.000 0.000 1998 0.000 0.000 1999 0.000 0.000 2000 0.000 0.000 2001 0.000 0.000 2002 0.000 0.000 2003 0.000 0.000 2004 0.000 0.000 2005 0.000 0.000 2006 0.000 0.000 2007 0.000 0.000 2008 0.000 0.000 2009 0.000 0.000 2010 0.000 0.000 2011 0.000 0.000 2012 0.000 0.000 2013 0.000 0.000 2014 0.000 0.000 2015 0.000 0.000 2016 0.000 0.000 2017 0.000 0.000 2018 0.000 0.000 2019 0.000 0.000 2020 0.000 0.000 2021 0.000 0.000 2022 0.000 0.000 2023 0.000 0.000 2024 0.000 0.000 2025 0.000 0.000 2026 0.000 0.000 2027 0.000 0.000 2028 0.000 0.000 2029 0.000 0.000 2030 0.000 0.000 2031 0.000 0.000 2032 0.000 0.000 2033 0.000 0.000 2034 0.000 0.000 2035 0.000 0.000 2036 0.000 0.000 2037 0.000 0.000 2038 0.000 0.000 2039 0.000 0.000 2040 0.000 0.000 2041 0.000 0.000 2042 0.000 0.000 RAM Engineering, Inc. Engineering and Drainage Report Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Page E-8 2043 0.000 0.000 2044 0.000 0.000 2045 0.000 0.000 2046 0.000 0.000 2047 0.000 0.000 2048 0.000 0.000 2049 0.000 0.000 2050 0.000 0.000 2051 0.000 0.000 2052 0.000 0.000 2053 0.000 0.000 2054 0.000 0.000 2055 0.000 0.000 2056 0.000 0.000 2057 0.000 0.000 2058 0.000 0.000 Stream Protection Duration Ranked Annual Peaks for Predeveloped Rank Predeveloped Mitigated 1 0.0002 0.0000 2 0.0002 0.0000 3 0.0002 0.0000 4 0.0002 0.0000 5 0.0002 0.0000 6 0.0002 0.0000 7 0.0002 0.0000 8 0.0002 0.0000 9 0.0002 0.0000 10 0.0002 0.0000 11 0.0002 0.0000 12 0.0002 0.0000 13 0.0002 0.0000 14 0.0002 0.0000 15 0.0002 0.0000 16 0.0002 0.0000 17 0.0002 0.0000 18 0.0002 0.0000 19 0.0002 0.0000 20 0.0002 0.0000 21 0.0002 0.0000 22 0.0002 0.0000 23 0.0002 0.0000 24 0.0002 0.0000 25 0.0002 0.0000 26 0.0002 0.0000 27 0.0002 0.0000 28 0.0002 0.0000 29 0.0002 0.0000 30 0.0002 0.0000 31 0.0002 0.0000 32 0.0002 0.0000 33 0.0002 0.0000 34 0.0002 0.0000 35 0.0001 0.0000 36 0.0001 0.0000 37 0.0001 0.0000 38 0.0001 0.0000 39 0.0001 0.0000 RAM Engineering, Inc. Engineering and Drainage Report and Mitigated. POC #1 Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Page E-9 40 0.0001 0.0000 41 0.0001 0.0000 42 0.0001 0.0000 43 0.0001 0.0000 44 0.0001 0.0000 45 0.0001 0.0000 46 0.0001 0.0000 47 0.0001 0.0000 48 0.0001 0.0000 49 0.0001 0.0000 50 0.0001 0.0000 51 0.0001 0.0000 52 0.0001 0.0000 53 0.0001 0.0000 54 0.0001 0.0000 55 0.0001 0.0000 56 0.0001 0.0000 57 0.0001 0.0000 58 0.0001 0.0000 59 0.0001 0.0000 60 0.0001 0.0000 61 0.0001 0.0000 62 0.0001 0.0000 63 0.0001 0.0000 64 0.0001 0.0000 65 0.0001 0.0000 66 0.0001 0.0000 67 0.0001 0.0000 68 0.0001 0.0000 69 0.0001 0.0000 70 0.0001 0.0000 71 0.0001 0.0000 72 0.0001 0.0000 73 0.0001 0.0000 74 0.0001 0.0000 75 0.0001 0.0000 76 0.0001 0.0000 77 0.0001 0.0000 78 0.0001 0.0000 79 0.0001 0.0000 80 0.0001 0.0000 81 0.0001 0.0000 82 0.0001 0.0000 83 0.0001 0.0000 84 0.0001 0.0000 85 0.0001 0.0000 86 0.0001 0.0000 87 0.0001 0.0000 88 0.0001 0.0000 89 0.0001 0.0000 90 0.0001 0.0000 91 0.0001 0.0000 92 0.0001 0.0000 93 0.0001 0.0000 94 0.0001 0.0000 95 0.0001 0.0000 96 0.0001 0.0000 97 0.0001 0.0000 98 0.0001 0.0000 99 0.0001 0.0000 100 0.0001 0.0000 RAM Engineering, Inc. Engineering and Drainage Report Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Page E-10 101 0.0001 0.0000 102 0.0001 0.0000 103 0.0001 0.0000 104 0.0001 0.0000 105 0.0001 0.0000 106 0.0001 0.0000 107 0.0001 0.0000 108 0.0001 0.0000 109 0.0001 0.0000 110 0.0001 0.0000 ill 0.0001 0.0000 112 0.0001 0.0000 113 0.0001 0.0000 114 0.0001 0.0000 115 0.0001 0.0000 116 0.0001 0.0000 117 0.0001 0.0000 118 0.0001 0.0000 119 0.0001 0.0000 120 0.0001 0.0000 121 0.0001 0.0000 122 0.0001 0.0000 123 0.0001 0.0000 124 0.0001 0.0000 125 0.0001 0.0000 126 0.0001 0.0000 127 0.0001 0.0000 128 0.0001 0.0000 129 0.0001 0.0000 130 0.0001 0.0000 131 0.0001 0.0000 132 0.0001 0.0000 133 0.0001 0.0000 134 0.0001 0.0000 135 0.0001 0.0000 136 0.0001 0.0000 137 0.0001 0.0000 138 0.0001 0.0000 139 0.0001 0.0000 140 0.0001 0.0000 141 0.0001 0.0000 142 0.0001 0.0000 143 0.0001 0.0000 144 0.0001 0.0000 145 0.0001 0.0000 146 0.0001 0.0000 147 0.0001 0.0000 148 0.0001 0.0000 149 0.0001 0.0000 150 0.0001 0.0000 151 0.0001 0.0000 152 0.0001 0.0000 153 0.0000 0.0000 154 0.0000 0.0000 155 0.0000 0.0000 156 0.0000 0.0000 157 0.0000 0.0000 Stream Protection Duration RAM Engineering, Inc. Engineering and Drainage Report Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Page E-11 POC #1 The Facility PASSED 5W PDC1� Q00 �ti Sao 801 PQC 1 Mhgaked lbw n 0 v D.99 0 J LL QW 19F4 19E-3 13E-2 1SE-1 1� 10 100 F--,�at -T-. l i Exaeedi-O sham Prateclion Duration I UD Duration I Flaw Frapuenay I WOW QUAY I Hydrogmh Welland Input Vokm LID Repot j Recharge Duration I Recharge Redeveloped I Recharge MiinM-i Analyzedatasets CorWWDM I DeisaSoIscled J r Mot#*FF 501 t AN Dalasels Flow j Stege I Pmap, I Evap 7 F3aod FrequeMY Melhod r Lop Pearson Type III 178 r We bup C- Canoe C•" GRgnten Flow(cfs) Predev Mit Percentage Pass/Fail 0.0001 4538 0 0 Pass 0.0001 4411 0 0 Pass 0.0001 4295 0 0 Pass 0.0001 4151 0 0 Pass 0.0001 3943 0 0 Pass 0.0001 3829 0 0 Pass 0.0001 3701 0 0 Pass 0.0001 3599 0 0 Pass 0.0001 3363 0 0 Pass 0.0001 3279 0 0 Pass 0.0001 3176 0 0 Pass 0.0001 3044 0 0 Pass 0.0001 2898 0 0 Pass 0.0001 2807 0 0 Pass 0.0001 2724 0 0 Pass 0.0001 2669 0 0 Pass 0.0001 2536 0 0 Pass 0.0001 2466 0 0 Pass 0.0001 2410 0 0 Pass 0.0001 2324 0 0 Pass 0.0001 2212 0 0 Pass 0.0001 2131 0 0 Pass 0.0001 2080 0 0 Pass 0.0001 1964 0 0 Pass RAM-noineering, Inc. Engineering and Drainage Report O"mm. The Facility PASSIM A rlov(ofs) Predev Mit Percentage Pass/Pail 0.0001 4538 0 0 Pass 0.0001 4411 ❑ O Pass 0.0001 4295 0 0 Pass 0.0001 4151 0 ❑ Pass 0.0001 3943 ❑ 0 Pass 0.0001 3825 ❑ 0 Pass 0.0001 3701 0 0 Pass 0.0001 3599 0 0 Pass 0.0001 3363 ❑ O Pass 0.0001 3279 ❑ 0 Pass 0.0001 3176 0 0 Pass 0.0001 3044 0 0 Pass 0.0001 2898 ❑ O Pass 0.0001 2807 ❑ 0 Pass 0.0001 2721 0 0 Pass 0.0001 2669 0 0 Pass 0.0001 2536 0 0 Pass 0.0001 2466 0 0 Pass 0.0001 2410 0 0 Pass 0.0001 2324 0 0 Pass 0.0001 2212 0 0 Pass 0.0001 2131 ❑ 0 Pass 0.0001 2080 0 0 Pass 0.0001 1.964 0 0 Pass 0.0001 1873 0 0 Pass 0.0001 1326 ❑ ❑ Pass 0.0001 176S 0 0 Pass 0.0001 1651 0 0 Pasa 0.0001 1583 ❑ ❑ Pass 0.0001 1521 ❑ O Pass 0.cool 1462 0 0 Pass 0.0001 1.334 0 0 Pass ❑.coal 1297 a 0 Pass 0.0001 1239 0 0 Pass Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Page E-12 0.0001 1873 0 0 Pass 0.0001 1826 0 0 Pass 0.0001 1765 0 0 Pass 0.0001 1651 0 0 Pass 0.0001 1583 0 0 Pass 0.0001 1521 0 0 Pass 0.0001 1462 0 0 Pass 0.0001 1334 0 0 Pass 0.0001 1297 0 0 Pass 0.0001 1239 0 0 Pass 0.0001 1199 0 0 Pass 0.0001 1134 0 0 Pass 0.0001 1097 0 0 Pass 0.0001 1068 0 0 Pass 0.0001 1029 0 0 Pass 0.0001 955 0 0 Pass 0.0001 934 0 0 Pass 0.0001 893 0 0 Pass 0.0001 848 0 0 Pass 0.0001 831 0 0 Pass 0.0001 809 0 0 Pass 0.0001 797 0 0 Pass 0.0001 756 0 0 Pass 0.0001 735 0 0 Pass 0.0001 716 0 0 Pass 0.0001 691 0 0 Pass 0.0001 621 0 0 Pass 0.0001 605 0 0 Pass 0.0001 590 0 0 Pass 0.0001 553 0 0 Pass 0.0001 498 0 0 Pass 0.0001 489 0 0 Pass 0.0001 480 0 0 Pass 0.0001 458 0 0 Pass 0.0001 423 0 0 Pass 0.0001 409 0 0 Pass 0.0001 397 0 0 Pass 0.0001 371 0 0 Pass 0.0001 354 0 0 Pass 0.0001 341 0 0 Pass 0.0001 332 0 0 Pass 0.0001 310 0 0 Pass 0.0001 306 0 0 Pass 0.0001 302 0 0 Pass 0.0001 292 0 0 Pass 0.0001 265 0 0 Pass 0.0001 246 0 0 Pass 0.0001 242 0 0 Pass 0.0001 240 0 0 Pass 0.0001 227 0 0 Pass 0.0002 212 0 0 Pass 0.0002 203 0 0 Pass 0.0002 189 0 0 Pass 0.0002 186 0 0 Pass 0.0002 179 0 0 Pass 0.0002 171 0 0 Pass 0.0002 159 0 0 Pass 0.0002 145 0 0 Pass 0.0002 128 0 0 Pass 0.0002 127 0 0 Pass 0.0002 118 0 0 Pass RAM Engineering, Inc. Engineering and Drainage Report Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Page E-13 0.0002 116 0 0 Pass 0.0002 103 0 0 Pass 0.0002 98 0 0 Pass 0.0002 88 0 0 Pass 0.0002 79 0 0 Pass 0.0002 75 0 0 Pass 0.0002 69 0 0 Pass 0.0002 55 0 0 Pass 0.0002 50 0 0 Pass 0.0002 48 0 0 Pass 0.0002 44 0 0 Pass 0.0002 30 0 0 Pass 0.0002 24 0 0 Pass 0.0002 17 0 0 Pass 0.0002 2 0 0 Pass LID Report ❑ LID Report POC 1 t+_XW u LID Technique Used for Total Volume Volume Infiltration Cumulative Percent WaterQualkty Percent Comment Treatment') Needs Through volume volume volume water aualPly Treatment Faall[y (ac-ft) Infiltration Infiltrated Treated (ac-R) (ac-ft) Credit Gravel Trenen Bea 1 PDC ❑ 37.49 11 100.00 Total Volume Infiltrated 3749 000 0.00 100.00 0.00 D% 110 Treat Credit Compliance wlth LID Duration Standard 8% of 2-yr to 50% of Analysis 2 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. 2005-2020; All Rights Reserved. RAM-noineerina. Inc Engineering and Drainage Report Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Page E-14 F. DRAINAGE BASIN DESCRIPTION: The site is located within the City of Edmonds Willow Creek watershed basin. The Willow Creek basin is a centralized urban basin that collects stormwater runoff from primarily residential areas in the City Edmonds and ultimately discharges flows westerly to Puget Sound via Willow Creek (see attached watershed map). The proposed stormwater infiltration trench systems are designed to infiltrate most the site stormwater flows into the underlying outwash soils. Flows that don't infiltrate into the soils will sheet flow off in a westerly direction towards 7th PI S. The infiltration systems include a collection catch basin/trench drians that will overflow into 7th PI in the event of an extraordinary rainfall event. Any overflow would flow towards 71h PI S and enter the pipe and catch basin system of 71h PI S. The stormwater system in 71h PI S directs runoff north and eventually discharges to Willow Creek about 1,100 feet north of the project site. Willow Creek continues in a west/northwesterly direction and eventually discharges into the Puget Sound about 1.9 miles northwest of the site A majority of the downstream conveyance system within a % mile of the site consists of a man-made pipe and catch basin system and Willow Creek stream channel. No apparent flooding or system inadequacies within a % mile downstream of the site were discovered during site visits or research of the downstream system. Due to the fact the site is bordered by 8th Ave S on its uphill (easterly) side; the site receives minimum upstream run-on flows and are considered negligible. See attached watershed and downstream drainage facility map for the local downstream path. RAMEngineering, Inc. Engineering and Drainage Report Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Page F-1 F-2. Watershed Basin Map FIGURE B-1 WiM CITY OF EDMONDS WATERSHEDS D Creek PrinrimrIll. Edmonds Marsh Puget Sound Edmond, Way Puget Sound Piped Fmitclal. Shell Creek Good Hope Pond Shdlab.rger Halls Creek Southwest Edmond, A Hindley Creek Southwest Edmonds B l U,Ilin,,,r 1111l Creek ,cN Gulch Talbot Park A Me3didale A Talbot Park a Mead —dal. S Terrace Creek N.rl Westgate Pond Ci,tf.V Creek Will— Creek I.— s.000 1 in = 2,DDO ft —P.,thn P1 .. N .. I— Puget Sound Piped "A Shell Creek Sheltab,rge, D-4 Puget Sou led,_ Talbot Park A Talb ot Park B virl N Rd Meadowda;e A M@Wowdale B ado 16fth Sr SN Terrace Creek. Pel od Hope Pond .M Halls Cl I Deer Creek 7 F W11h.— Rd Edmonds Way S. hwest' F lake a Ballinger Sea.ithwest Edmonds R L--------------------------------------------------- --- -------- - ------ RAMEngineering, Inc. Engineering and Drainage Report Creek Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Page F-2 F-3. Downstream Drainage Facility Map (City of Edmonds GIS) DISCHARGE TO I ' 3g �► r WILLOW CREEK 12 r_ J. 3( 13TH. WAY S221t+V 2i1 M2-47 P01242 1401 '� 2Cy 1 ; I3 FiL71 1116 i415 11 , 36 j w � � 17 � '�''yI 14225143 r 51I 1 815 1434 �, i43 I 1 ; 00 1 SITE Y Jam, II 1.13 9 807 1909 1457 145 Sale 1: 2257 r STH 5T 5 RAM Engineering, Inc. Engineering and Drainage Report Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Page F-3 G. GRADING and EROSION CONTROL SUMMARY: The project will require grading to construct the proposed buildings and utilities (including the stormwater infiltration trench 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, soil application of polyacrylamide (pam), 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. Soils: In accordance with the project's site specific geotechnical engineering study by Earth Solutions NW, LLC the on -site soils consist of loose to medium dense poorly graded sand (Unified Soil Classification System: SP) outwash deposits. Overall soil relative density increases with depth. The subject site is underlain by outwash (Qva) deposits; Everett series soils. Everett soils are well drained soil and are categorized as a hydrologic group A soil. Earth Solutions NW, LLC. Recommends a long-term design infiltration rate of 7.2 inches per hour. Full soils description is included in the project's site specific geotechnical engineering study by Earth Solutions NW, LLC. 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: Due to the underlying outwash soils no flow control system (ie: temporary pond) is proposed. 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. RAMEngineering, Inc. Engineering and Drainage Report Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Page G-1 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. 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: During construction the proposed infiltration trench systems areas shall be protected from sediment accumulation, sediment -laden runoff and soils, and compaction from construction equipment. Soils restoration and/or replacement may be needed if soils are compacted or contaminated with sediment. Conclusion: The final site development construction plans include specific grading and drainage improvement notes and details. With proper installation, maintenance and inspections of the proposed construction the project should have minimal impact to the surrounding environment. RAMEngineering, Inc. Engineering and Drainage Report Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Page G-2 G-1. Soils Map Figure $-2 City of Edmonds Soil Map Units (SCS 1983) LEGEND -- CAy of Edmonds Boundary 5oil Map Vnns SOIL NAME Alder d Gravely sandy loam, 2-B % slopes rwoo Alded Gravelly sandy loam, &15 %slopes Aldenrood Gravely sandy loam, 1�25 % dopes Aldenwod Udean land comple:.2•S %sopes Aldernnad Urban land complex, &15 %slopes Alden O-Everetl Gravelly sandy Warns, 25-70 custprine sandy morn EveroC 1'avell sand uany 0� `.'E sl es Evarek mall sand loam 9-75 %slo es Even:n gravelty sand loam, 15-25 % sopes Fwawents. ndal 111sap silt loam, 0-8 1 slopes I<ll., silt loam, B-25 %slopes 7dci(ema 9mvelry sill Iparn, M %alppea �•! Mukilteo muck � pds llydan [and p 1.1,P7o 2000 4,00P S5.uw 6,W0 Feet 1 in = 2,000 R rw wn,ta,�ry dory xurl, o-,�dao-y a.ry,a�y, re—, — -d L.0dy ux�ntpwiy Vih Yrwlui[ P ISITE ➢ a 2 w alem — I � F1 5 6m a to :e— I � =r•` I � 1 ti — J& ... l _ -v A RAM Engineering, Inc. Engineering and Drainage Report e MiL lease WM k�CF,JI � I y I % ,-� :s Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Page G-3 H. 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 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 owner and used as a reference to identify drainage facilities outlined in this manual. Conveyance Systems. The design objective in pipe sizing was to convey the large storm events without the water surface exceeding the ground elevation. Frequent overtopping of the pipe system in a particular area might indicate a downstream blockage. Overtopping of the drain systems at the catch -basins is an indication that maintenance is required. Stormwater Infiltration Trench System. The private onsite infiltration trench systems consist of excavated trench filled with drain rock per the City Standard detail (Handout #E72 B, Figure A-3). 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 upstream 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. RAMEngineering, Inc. Engineering and Drainage Report Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Page H-1 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.htmI 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 7gineering, In, Engineering and Drainage Report Page H-2 Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 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 Defect Conditions When Results Expected When Component Maintenance Is Needed 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. Any poisonous or nuisance vegetation which may constitute No danger of poisonous General 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). Contaminants and Any evidence of oil, gasoline, No contaminants or pollutants Pollution contaminants or other pollutants present. RAMEngineering, Inc. Engineering and Drainage Report Page H-3 Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Table V-A.1: Maintenance Standards - Detention Ponds Maintenance Defect Conditions When Results Expected When Component Maintenance Is Needed Maintenance Is Performed (Coordinate removal/cleanup 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; coordinate with Ecology Dam piping through dam or berm via Safety Office if pond exceeds 10 rodent holes. 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) Eroded damage over 2 inches Side Slopes of Pond Erosion deep where cause of damage is Slopes should be stabilized still present or where there is using appropriate erosion potential for continued erosion. control measure(s); e.g.,rock RAMEngineering, Inc. Engineering and Drainage Report Page H-4 Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Table V-A.1: Maintenance Standards - Detention Ponds Maintenance Defect Conditions When Results Expected When Component Maintenance Is Needed Maintenance Is Performed reinforcement, planting of grass, Any erosion observed on a compaction. compacted berm embankment. If erosion is occurring on compacted berms a licensed 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 berm or outlet works. A licensed Ponds Berms engineer in the state of (Dikes) Washington should be consulted to determine the source of the settlement. Discernable water flow through pond berm. Ongoing erosion with potential for erosion to continue. Piping Piping eliminated. Erosion potential resolved. (Recommend a Goethechnical engineer be called in to inspect and evaluate condition and recommend repair of condition. Emergency Tree Growth Tree growth on emergency Trees should be removed. If root Overflow/ Spillway spillways creates blockage system is small base less than RAMEngineering, Inc. Engineering and Drainage Report Page H-5 Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Table V-A.1: Maintenance Standards - Detention Ponds Maintenance Defect Conditions When Results Expected When Component Maintenance Is Needed Maintenance Is Performed and Berms over 4 problems and may cause failure 4 inches) the root system may feet in height of the berm due to uncontrolled be left in place. Otherwise the overtopping. roots should be removed and the berm restored. A licensed engineer in the state of Tree growth on berms over 4 Washington should be consulted feet in height may lead to piping for proper berm/spillway through the berm which could restoration. lead to failure of the berm. 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 Conditions When Maintenance Is Results Expected Component Defect Needed When Maintenance Is Performed See Table V-A.1: Trash & Debris See Table V-A.1: Maintenance Maintenance Standards - Detention Ponds Standards - Detention Ponds General Poisonous/Noxious See Table V-A.1: Maintenance See Table V-A.1: Vegetation Standards - Detention Ponds Maintenance RAMEngineering, Inc. Engineering and Drainage Report Page H-6 Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 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: 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 Emergency See Table V-A.1: Overflow Spillway Tree Growth See Table V-A.1: Maintenance Maintenance and Berms over 4 Standards - Detention Ponds Standards - Detention Ponds feet in height. RAMEngineering, Inc. Engineering and Drainage Report Page H-7 Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 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: 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 No Trash or debris front of the catch basin opening or is blocking located immediately in inletting capacity of the basin by more than front of catch basin or 10%. on grate opening. Trash or debris (in the basin) that exceeds 60 No trash or debris in General Trash &Debris percent of the sump depth as measured from the catch basin. the bottom of basin to invert of the lowest pipe into or out of the basin, but in no case less than Inlet and outlet pipes a minimum of six inches clearance from the free of trash or debris. debris surface to the invert of the lowest pipe. No dead animals or Trash or debris in any inlet or outlet pipe vegetation present blocking more than 1/3 of its height. within the catch basin. RAMEngineering, Inc. Engineering and Drainage Report Page H-8 Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Table V-A.5: Maintenance Standards - Catch Basins Maintenance Results Expected Component Defect Conditions When Maintenance is Needed When Maintenance is performed 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 secure at basin t basin wall. particles entering catch basin through cracks. Settlement/ If failure of basin has created a safety, function, Basin replaced or repaired design Misalignment or design problem. standards. Vegetation growing across and blocking more No vegetation blocking than 10 /o of the basin opening. opening to basin. Vegetation 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 RAMEngineering, Inc. Engineering and Drainage Report Page H-9 Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 Table V-A.5: Maintenance Standards - Catch Basins Maintenance Results Expected Component Defect Conditions When Maintenance is Needed When Maintenance is performed 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 /o 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, and is installed and Missing. grate. aligned with the flow path. RAMEngineering, Inc. Engineering and Drainage Report Page H-10 Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 I. GEOTECHNICAL ENGINEERING REPORT Geotechnical Evaluation Prepared by: Earth Solutions NW, LLC Revision Date: July 29, 2019 Pages: 17 RAMEngineering, Inc. Engineering and Drainage Report Page 1-1 Lot 2 of Purser 2-Lot Short Plat RAM No. 19-014 July 29, 2019 ES-6749 Purser Development Services, LLC 520 — 31d Avenue North Edmonds, Washington 98020 Attention: Mr. Rob Purser Subject: Geotechnical Evaluation Proposed Single -Family Residences 735 — 15t" Street Southwest Edmonds, Washington Reference: Northpeak Associates LLC Topographic Survey May 28, 2019 Edmonds City Code (ECC) Geologically Hazardous Areas — Chapter 23.80 Earth 4 Solutions NWLLC Earth Solutions NW LLC Geotechnical Engineering, Construction Observation/Testing and Environmental Services Washington State Department of Ecology City of Edmonds Stormwater Addendum (ESA) to the 2014 Stormwater Management Manual for Western Washington (SWMMWW) James P. Minard Geologic Map of the Washington, 1983 Dear Mr. Purser: Edmonds East and Part of the Edmonds West Quadrangles As requested, Earth Solutions NW, LLC (ESNW) has prepared geotechnical evaluation report for the proposed single-family residences. Our scope of services included subsurface investigation, engineering analysis, and preparation of this report with recommendations pertinent to the geotechnical aspects of the project. As part of the subsurface investigation, ESNW observed the excavation of three test pits on June 12, 2019. 1805 - 136th Place N.E., Suite 201 • Bellevue, WA 98005 • (425) 449-4704 0 FAX (425) 449-4711 Purser Development Services, LLC July 29, 2019 Project Description ES-6749 Page 2 The subject site is located at 735 — 15th Street Southwest in Edmonds, Washington, as illustrated on the Vicinity Map (Plate 1). The site consists of a single residential tax parcel (Snohomish County parcel number 00390000001100) covering approximately 0.38 acres of land area. The site is currently developed with a single-family residence and associated improvements. The site gently descends toward the northwestern site corner, with about 12 feet of total elevation change. Based our discussions with Client, the existing structure and improvements will be removed and the site will be redeveloped with two new single-family residences and associated improvements. We understand the stormwater design will incorporate infiltration to the extent feasible. Based on the existing grades, we estimate cuts and fills to establish building pad and foundation subgrade elevations will be on the order four to five feet. However, grading plans were not available at the time this report was prepared. 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 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 evaluation. 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 June 12, 2019, excavated at accessible locations within the proposed development area, using a mini-trackhoe and operator retained by our firm. The approximate locations of the test pits are depicted on Plate 2 (Test Pit Location Plan). Please refer to the test pit logs (attached) 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 (USDA) methods and procedures. Topsoil and Fill Topsoil was observed extending to depths of approximately six inches below existing grades. The topsoil was characterized by dark brown color and fine organic material. Some root zones were observed to extend below the topsoil. No fill was encountered within the test pit locations. If fill is encountered during construction, ESNW should be consulted to verify the suitability for support of the proposed structure and/or reuse as structural fill. Earth Solutions NW, LLC Purser Development Services, LLC July 29, 2019 Native Soil ES-6749 Page 3 Underlying topsoil, native soils were encountered as poorly graded sand with gravel, poorly graded sand with silt and gravel, and poorly graded gravel with silt and sand (USCS: SP, SP-SM, and GP -GM, respectively), consistent with the typical makeup of outwash deposits. The native soil deposits were observed to be generally in a medium dense condition beginning at depths of approximately one to two feet below existing grades and were generally damp to moist at the time of our exploration. Geologic Setting Geologic mapping of the area indicates the site is underlain by Vashon advance outwash deposits (Qva). According to the geologic map resource, the advance outwash is characterized as a well - sorted sand and gravel. The referenced WSS resource identifies Everett very gravelly sandy loam (Map Unit Symbol: 17) as the primary soil unit underlying the subject site. The Everett series was formed in esker, moraines, and kames. Based on our field observations, native soils on the subject site are consistent with outwash deposits. Groundwater Groundwater seepage was not encountered at the test pit locations at the time of our June 2019 subsurface exploration. However, perched seepage may be encountered in site excavations depending on the time of the year excavations take place. Groundwater seepage rates and elevations fluctuate depending on many factors, including precipitation duration and intensity, the time of year, and soil conditions. In general, groundwater flow rates are higher during the winter, spring, and early summer months. Geologic Hazard Areas Assessment Based on review of ECC 23.80, the subject site is not mapped within, or adjacent to, any geologically hazardous areas. Based on our subsurface exploration performed at the subject site, it is our opinion the site is properly mapped outside of ECC geologically hazardous areas. Foundations The proposed residential structures can be supported on conventional continuous and spread footing foundations bearing on competent native soil, recompacted native soil, or new structural fill placed directly on competent native soils. Competent native soil suitable for support of foundations will likely be encountered beginning at depths of about two to four feet below existing grades. Where loose or unsuitable soil conditions are exposed at foundation subgrade elevations, compaction of soils to the specifications of structural fill, or overexcavation and replacement with suitable structural fill, will be necessary. Earth Solutions NW, LLC Purser Development Services, LLC ES-6749 July 29, 2019 Page 4 Provided the foundations will be supported as prescribed, the following parameters may be used for design: i Allowable soil bearing capacity 2,500 psf Passive earth pressure 0 Coefficient of friction 300 pcf (equivalent fluid) 0.40 A one-third increase in the allowable soil bearing capacity may be assumed for short-term wind and seismic loading conditions. The above passive pressure and friction values include a factor - of -safety of 1.5. With structural loading as expected, total settlement in the range of one inch and differential settlement of about one-half inch is anticipated. The majority of the settlements should occur during construction, as dead loads are applied. Seismic Design The 2015 International Building Code recognizes the American Society of Civil Engineers (ASCE) for seismic site class definitions. In accordance with Table 20.3-1 of the ASCE Minimum Design Loads for Buildings and Other Structures manual, Site Class D should be used for design. The referenced liquefaction susceptibility map indicates the subject site possesses low liquefaction susceptibility. Liquefaction is a phenomenon where saturated and loose sandy soils suddenly lose internal strength and behave as a fluid. This behavior is in response to increased pore water pressures resulting from an earthquake or other intense ground shaking. In our opinion, site susceptibility to liquefaction may be considered low. This opinion is based on the composition of the native soil and the absence of evidence of a shallow groundwater table. Slab -on -Grade Floors Slab -on -grade floors for the proposed structures should be supported on competent and well - compacted, firm and unyielding subgrades. Unstable or yielding subgrade areas should be recompacted, or overexcavated and replaced with suitable structural fill, prior to slab construction. A capillary break consisting of at least four inches of free -draining crushed rock or gravel should be placed below each slab. The free -draining material should have a fines content of 5 percent or less (where the fines content is defined as the percent passing the Number 200 sieve, based on the minus three -quarter -inch fraction). In areas where slab moisture is undesirable, installation of a vapor barrier below the slab should be considered. If a vapor barrier is to be used, it should be a material specifically designed for use as a vapor barrier and should be installed in accordance with the specifications of the manufacturer. Earth Solutions NW. LLC Purser Development Services, LLC July 29, 2019 Retaining Walls ES-6749 Page 5 Retaining walls must be designed to resist earth pressures and applicable surcharge loads. The following parameters may be used for design: • Active earth pressure (unrestrained condition) • At -rest earth pressure (restrained condition) Traffic surcharge (passenger vehicles) 0 Passive earth pressure • Coefficient of friction Seismic surcharge Where applicable * Where H equals the retained height (in feet) 35 pcf (equivalent fluid) 55 pcf 70 psf (rectangular distribution)* 250 pcf (equivalent fluid) Fly, re 6H psf** The passive earth pressure and coefficient of friction values include a safety factor of 1.5. The above design parameters are based on a level backfill condition and level grade at the wall toe. Revised design values will be necessary if sloping grades are to be used above or below retaining walls. Additional surcharge loading from adjacent foundations, sloped backfill, or other relevant loads should be included in the retaining wall design. Retaining walls should be backfilled with free -draining material that extends along the height of the wall and a distance of at least 18 inches behind the wall. The upper 12 inches of the wall backfill may consist of a less permeable soil, if desired. A sheet drain may also be considered in lieu of a free -draining backfill section. A perforated drainpipe should be placed along the base of the wall and connected to an approved discharge location. A typical retaining wall drainage detail is provided on Plate 3. If drainage is not provided, hydrostatic pressures should be included in the wall design. Drainage Groundwater seepage may be encountered in site excavations depending on the time of year grading operations take place. ESNW should be consulted during earthwork activities to further evaluate groundwater conditions and provide additional recommendations. Finish grades must be designed to direct surface drain water away from structures and slopes. Water must not be allowed to pond adjacent to structures or slopes. In our opinion, foundation drains should be installed along building perimeter footings. A typical foundation drain detail is provided on Plate 4. Earth Solutions NK LLC Purser Development Services, LLC July 29, 2019 Infiltration Feasibility ES-6749 Page 6 Our evaluation of site infiltration capacity was completed in general accordance with applicable requirements and procedures of the ESA, to the extent practicable. Two small-scale Pilot Infiltration Tests (PIT) were performed within accessible areas of the subject site during our June 2019 subsurface exploration. One PIT was performed within TP-2 at a depth of about three feet bgs and one PIT was performed within TP-3 at a depth of about three and one-half feet bgs. In accordance with USDA textural analysis, native soils at the bottom of the PITs classified as very gravelly sand and very gravelly coarse sandy loam, with fines contents ranging between about 5 and 10 percent. The following measured infiltration rates and correction factors should be used for design of proposed infiltration facilities: 0 Short-term (measured) infiltration rate 24 inches per hour ■ CF„ (site variability) 0.67 Q CFT (test method) 0.50 (small-scale PIT) CFm (plugging) 0.90 (typical) • Long-term (design) infiltration rate 7.2 inches per hour Based on our field observations, the following is offered: In accordance with the ESA, the native material is feasible for infiltration design. We acknowledge that final site layouts and/or designs may affect infiltration feasibility, concerning maximum allowable setbacks from structures and property lines. • Infiltration trenches and drywells may be sized for medium sands. ESNW should have the opportunity to review final drainage plans. ESNW should also be retained to observe installation of site infiltration facilities. Supplementary recommendations may be provided at the time of construction, where warranted. 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. We understand the proposed development intends to add over 5,000 square feet of new hard surface and therefore must comply with Minimum Requirements (MRs) 1 through 9. MR 5 concerns on -site stormwater management, and the viability of specific BMPs are to be evaluated for each type of proposed surface. The table below summarizes our evaluation of the required BMPs for MR 5, 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 Purser Development Services, LLC July 29, 2019 ES-6749 Page 7 BMP Viable? mitations or Infeasibility Criteria i Lawns and Landscaped Area_ s T5.13: Post -construction soil quality and None. No slopes greater than 33 Yes de th Volume V, Chapter 5) percent are present. Roofs T5.30: Full dispersion (Volume V, Chapter The proposed project will not 5) No preserve at least 65 percent of the site. T5.10A: Downspout full infiltration systems Downspout infiltration systems can Yes (Volume III, Chapter 3) be sized based on medium sand soils or 7.2 inches per hour. T7.30: Bioretention (Volume V, Chapter 7) Infiltrating bioretention and rain T5.14A: Rain Gardens (Volume V, Yes garden systems can be sized based Chapter 5) on medium sand soils or 7.2 inches per hour. T5.10B: Downspout dispersion systems NO Proper setbacks and vegetated flow Volume III, Chapter 3 paths are not available. T5.10C: Perforated stub -out connections Yes None. Volume III, Chapter 3 Other Hard Surfaces T5.30: Full dispersion (Volume V, Chapter The proposed project will not 5) No preserve at least 65 percent of the site. Infiltration surface must be T5.15: Permeable pavement (Volume V advanced to suitable soils Chapter 5) Yes anticipated at depths below one to two feet. T7.30: Bioretention (Volume V, Chapter 7) T5.14A: Rain Gardens (Volume V, Chapter 5) T5.12: Sheet flow dispersion T5.11: Concentrated flow dispersion (Volume V, Chapter 5) Infiltrating bioretention and rain garden systems can be sized based on medium sand soils or 7.2 inches per hour. Sheet flow dispersion and concentrated flow dispersion may No be feasible; however, proper setbacks and vegetated flow paths may not be available. Earth Solutions NW, LLC Purser Development Services, LLC July 29, 2019 Limitations ES-6749 Page 8 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 letter if variations are encountered. Should you require additional information, or have questions, please call. Sincerely, EARTH SOLUTIONS NW, LLC A ;Z/-;! - - Kyler T. Kelly Staff Geologist Attachments: Plate 1 — Vicinity Map Plate 2 — Test Pit Location Plan Plate 3 — Retaining Wall Drainage Detail Plate 4 — Footing Drain Detail Test Pit Logs Grain Size Distribution Henry T. Wright, P.E. Senior Project Manager cc: RAM Engineering, Inc. Attention: Mr. Rob Long, P.E. (Email only) Earth Solutions NW, LLC Reference: NORTH Snohomish County, Washington K8ap474 8yThe Thomas Guide ' Rand McNally 32ndEdition NOTE: This plate may contain areas ofcolor. ESNWcannot be responsible for any subsequent misinterpretation of the information resulting from black & white reproductions nfthis plate. Checked KTK Date June 2019 Plate 1 I I 280 / I IN 80%�TP2 --- T� I / _ j T—p �l W 290 > I TP-31 C \- 00 s 0 I LEGEND TP-1 Approximate Location of — ■ — ESNW Test Pit, Proj. No. ES-6749, June 2019 Subject Site Existing Building NOTE: The graphics shown on this plate are not intended for design purposes or precise scale measurements, but only to illustrate the approximate test locations relative to the approximate locations of existing and / or proposed site features. The information illustrated is largely based on data provided by the client at the time of our study. ESNW cannot be responsible for subsequent design changes or interpretation of the data by others. NORTH 0 25 50 100 1 "=50' gala in Fact Test Pit Location Plan 735 — 15th Street S.W. Edmonds, Washington NOTE: This plate may contain areas of color. ESNW cannot be Drwn. MRS Date 06/25/2019 Proj. No. 6749 responsible for any subsequent misinterpretation of the information Checked KTK Date June 2019 Plate 2 resulting from black & white reproductions of this plate. 18" Min. 00 0� o oUoo 00 00 oo00�0 �o 00000 o B 00 o o 0 o00 0 0 0 o 0 0 0 00 0o 'o o o �o o oao 0 0000oo 8o 00 0 0 0 o o 0 o O o 0 oo Oo 00 o -0 000 o 0 0 0 o 0 o 0 0 o 0 0 0 0 o0 00C 0 o 0 0o oo0 'o o O o O o0 0 0 O coo 00 0 0 0o Oo O oo o 0 0 oo o o ogoo o�000 oo oo o o 6 o o o 0 o00�00 0 oo o 0 oo ogo 0000 0 o o oo o ° o o 000 0 o oo 0 0 0 0o 0 o 0 d o o 0 6 o o O000 0 0o O o o 0 o 0 �r.'r ?� NOTES: • Free -draining Backfill should consist of soil having less than 5 percent fines. Percent passing No. 4 sieve should be 25 to 75 percent. • Sheet Drain may be feasible in lieu of Free -draining Backfill, per ESNW recommendations. • Drain Pipe should consist of perforated, rigid PVC Pipe surrounded with 1-inch Drain Rock. LEGEND: Oo0o O 0 o0 00 Free -draining Structural Backfill 1-inch Drain Rock .}.r.r.r. Structural Fill Perforated Rigid Drain Pipe (Surround in Drain Rock) SCHEMATIC ONLY - NOT TO SCALE NOT A CONSTRUCTION DRAWING Retaining Wall Drainage Detail 735 — 15th Street S.W. Edmonds, Washington Drwn. MRS Date 06/25/2019 Proj. No. 6749 Checked KTK Date June 2019 1 Plate 3 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. ti.ti•ti•ti• 1-inch Drain Rock r�r�r�r�r ti•ti•ti•ti• Perforated Rigid Drain Pipe (Surround in Drain Rock) SCHEMATIC ONLY - NOT TO SCALE NOT A CONSTRUCTION DRAWING Drwn. MRS Date 06/25/2019 Proj. No. 6749 Checked KTK Date June 2019 Plate 4 Earth Solutions NWLLC SOIL CLASSIFICATION CHART MAJOR DIVISIONS SYMBOLS TYPICAL DESCRIPTIONS GRAPH LETTER GRAVEL AND CLEAN GRAVELS ' �' ' `� • * .0 ■� GW WELL -GRADED GRAVELS, GRAVEL - SAND MIXTURES, LITTLE OR NO FINES ■C o d o paQ Q Q np GP POORLY-GRADED GRAVELS, GRAVEL- SAND MIXTURES, LITTLE OR NO FINES GRAVELLY SOILS (LITTLE OR NO FINES) COARSE GRAINED SOILS MORE THAN 50% OF COARSE GRAVELS WITH FINES ' Q ° �° ° D a GM SILTY GRAVELS, GRAVEL -SAND - SILT MIXTURES FRACTION GC CLAYEY GRAVELS, GRAVEL - SAND - CLAY MIXTURES RETAINED ON NO. 4 SIEVE (APPRECIABLE AMOUNT OF FINES) SAND AND CLEAN SANDS SW WELL -GRADED SANDS, GRAVELLY SANDS, LITTLE OR NO FINES MORE THAN 50% OF MATERIAL IS 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 S`+ CLAYEY SANDS, SAND - CLAY MIXTURES PASSING ON NO. 4 SIEVE (APPRECIABLE AMOUNT OF FINES) 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 -u OL ORGANIC SILTS AND ORGANIC SILTY CLAYS OF LOW PLASTICITY MORE THAN 50% OF MATERIAL IS MH INORGANIC SILTS, MICACEOUS OR DIATOMACEOUS FINE SAND OR SMALLER THAN NO.200 SIEVE SILTY SOILS SIZE SILTS LIQUID LIMIT AND CLAYS GREATER THAN 50 CH INORGANIC CLAYS OF HIGH PLASTICITY OH ORGANIC CLAYS OF MEDIUM TO HIGH PLASTICITY. ORGANIC SILTS HIGHLY ORGANIC SOILS T' ' ' ' ' ' 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. Earth Solutions NW TEST PIT NUMBER TP-1 1805 - 136th Place N.E., Suite 201 Bellevue, Washington 98005 PAGE 1 OF 1 Telephone: 425-449-4704 Fax: 425-449-4711 PROJECT NUMBER ES-6749 PROJECT NAME 735 — 15th Street S.E. DATE STARTED 6/12/19 COMPLETED 6/12/19 GROUND ELEVATION 282 ft TEST PIT SIZE EXCAVATION CONTRACTOR NW Excavating GROUND WATER LEVELS: EXCAVATION METHOD AT TIME OF EXCAVATION LOGGED BY KTK CHECKED BY HTW AT END OF EXCAVATION NOTES Depth of Topsoil & Sod 6":-grass AFTER EXCAVATION --- w Hw U a- TESTS Q O MATERIAL DESCRIPTION o_:) z C7 co 0 TPSL '= '' 0.5 Dark brown TOPSOIL, trace roots to 5' 281.5 Brown poorly graded SAND with silt and gravel, loose, damp -becomes moist SP- -light iron oxide staining to 4', becomes medium dense MC = 9.50% SM MC = 12.50% -minor caving to BOH 14.5 277.5 Gray poorly graded SAND with gravel, medium dense, moist 5 MC = 3.00% -increased gravel content SP MC = 11.80% 70 275.0 Test pit terminated at 7.0 feet below existing grade. No groundwater encountered during excavation. Caving observed from 3.0 feet to BOH. Bottom of test pit at 7.0 feet. Earth Solutions NW TEST PIT NUMBER TP-2 1805 - 136th Place N.E., Suite 201 Bellevue, Washington 98005 PAGE 1 OF 1 Telephone: 425-449-4704 Fax: 425-449-4711 PROJECT NUMBER ES-6749 PROJECT NAME 735 — 15th Street S.E. DATE STARTED 6/12/19 COMPLETED 6/12/19 GROUND ELEVATION 282 ft TEST PIT SIZE EXCAVATION CONTRACTOR NW Excavating GROUND WATER LEVELS: EXCAVATION METHOD AT TIME OF EXCAVATION --- LOGGED BY KTK CHECKED BY HTW AT END OF EXCAVATION --- NOTES Depth of Topsoil & Sod 6": grass AFTER EXCAVATION --- w a- }W Co U w- _jW TESTS O MATERIAL DESCRIPTION Q Z C7 U) 0 TPSL — ` 0_5 Dark brown TOPSOIL 281.5 Brown poorly graded SAND with silt and gravel, loose, damp SP- SM 2 0 280.0 Gray poorly graded GRAVEL with silt and sand, medium dense, damp to moist MC = 1.60% -infiltration test at T, minor caving to BOH Fines = 10.40% GP o [USDA Classification: very gravelly coarse sandy LOAM] GM a a MC = 8.90% 5.0 277.0 Gray poorly graded SAND with gravel, medium dense, moist SP MC = 7.40% 8.5 [USDA Classification: very gravelly SAND] 273 Fines = 1.60% Test pit terminated at 8.5 feet below existing grade. No groundwater encountered during excavation. Caving observed from 2.5 feet to BOH. Bottom of test pit at 8.5 feet. Earth Solutions NW TEST PIT NUMBER TP-3 1805 - 136th Place N.E., Suite 201 Bellevue, Washington 98005 PAGE 1 OF 1 NowTelephone: 425-449-4704 Fax: 425-449-4711 PROJECT NUMBER ES-6749 PROJECT NAME 735 — 15th Street S-E. DATE STARTED 6/12/19 COMPLETED 6/12/19 GROUND ELEVATION 288 ft TEST PIT SIZE EXCAVATION CONTRACTOR NW Excavating GROUND WATER LEVELS: EXCAVATION METHOD AT TIME OF EXCAVATION --- LOGGED BY KTK CHECKED BY HTW AT END OF EXCAVATION --- NOTES Depth of Topsoil & Sod 6": grass AFTER EXCAVATION --- _ w a-UJ U _ w W g TESTS � 2 0- p MATERIAL DESCRIPTION p Z of Q 0 TPSL 1.5 Dark brown TOPSOIL, trace roots to 5' 2.8_7_5_ Brown poorly graded SAND with silt and gravel, loose to medium dense, damp MC = 6.00% -moderate iron oxide staining to 3' becomes weakly cemented, becomes moist = MC 16.60% minor caving to BOH, becomes gray MC = 3.80% SM -infiltration test at 3.5' Fines = 5.30% [USDA Classification: very gravelly SAND] 5 MC = 15.20% 6.0 282.0 Gray poorly graded SAND with gravel, medium dense, moist SP MC = 5.80% 8.0 [USDA Classification: very gravelly coarse SAND] 0-0 Test pit terminated at 8.0 feet below existing grade. No groundwater encountered during Fines = 1.00% excavation. Caving observed from 2.5 feet to BOH. Bottom of test pit at 8.0 feet. BONN liiiimmiiii ilmmiiiii Hill 1 lllismillill NEIIII liimiiiiiilmm I lllomillill Millilli oil so on 1 111111111111 lllomil lllomillillismillill ME III RIB lowillillin IINEII liiinm"iliilm iiiiiiiimmiiiiiilmmii IN mmiiiiiiimmlli iiiiiiiiisllilli lismillill M 11111111 lin I NINE '11. liiiiiinmiiiiiiimm I MINE lismillillin�Milli IONE llmmiiiiiiimmiiii ismillillimmillillinEll , llmmiiiiiiimmiiiiii III INN I Ills inmiiiiiilomiiiiii 11 liiiiiimmii 111111 litlomillillismil III ME I 111 ME III in IN 11 liiiiiino iiiismi IN I iiiiiiinmiiiiiii 011!!Mllllmmllllllmm 0.1 0.01 0.001 GRAIN SIZE IN MILLIMETERS COBBLES GRAVEL I SAND I — SILT OR CLAY coarse I fine I coarse medium I fine Specimen Identification Classification Cc Cu 50 TP-02 3.Oft. USDA: Gray Very Gravelly Coarse Sandy Loam. USCS: GP -GM with Sand. 0.71 88. y m TP-02 8.5ft. USDA: Gray Very Gravelly Sand. USCS: SP with Gravel. 0.10 35.16 • TP-03 3.5ft. USDA: Gray Very Gravelly Sand. USCS: SP-SM with Gravel 1 0.19 25.14 r * TP-03 8.Oft. USDA: Gray Very Gravelly Coarse Sand. USCS: SP with Gravel. 0.45 12.93 s Specimen Identification D100 D90 D60 D30 D10 LL PL PI %Silt %Clay 0 TP-02 3.Oft. 37.5 31.331 14.517 0.622 10.4 m TP-02 8.5ft. 19 15.94 9.126 0.492 0.26 1.6 • TP-03 3.5ft. 19 14.753 5.022 1 0.442 0.2 5.3 * TP-03 8.Oft. 37.5 29.95 4.625 0.859 0.358 1.0 ENGINEERING, INC. Civil Engineering /Land Planning