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PLN20160015-APPROVED DRAINAGE RPT.pdfSelect Homes 8721 218 th St. SW 2-Lot Short Plat 8721 2181" Street SW Edmonds, WA 98026 PLN 20160015 Storm Drainage Report Prepared for: Select Homes Date: March 21, 2016 Revised: August 3, 2016 Revised: October 11, 2016 10/11/201O Prepared by: Rob Long, PE "M 16531 13t" Ave W, Suite A108, Lynnwood WA 98037 (425) 678-6960 RAMengineeringinc.com RECEIVED OCT 1 1 2016 ENGINEERING DIVISION ENGINEERING DIVISION P O D -�.S NOTE^ Data: ijIA6 Job No. 15-032 Select Homes 87212181 St. SW 2-Lot Short Plat 8721 218th Street SW Edmonds, WA 98026 Introduction: This summary report provides site design information for a single family 2-lot short plat by Select Homes. This report includes storm drainage analysis to support permit review and approval. The property is located on the north side 218t" St SW and east of 88t" Ave W, in the northwest 1/4 of Section 30, T 27 N, R 4 E, W.M. Site Address: 8721 218th Street SW Applicant: Select Homes Edmonds, WA 98026 16513 13th Ave W, Suite A108, Lynnwood WA 98037 Tax Parcel Number: 270430-002-064-00 & Contact: Craig Pierce 270430-002-065-00 (425) 299-2600 TABLE OF CONTENTS SECTION PAGES A. Project Summary............................................................................................................................... 5 B. Parcel (Vicinity) Map.......................................................................................................................... 1 C. Site Development Plans...................................................................................................................... 5 D. Aerial Photo....................................................................................................................................... 1 E. Stormwater Control System Summary and Calculations................................................................ 10 F. Drainage Basin Description and Maps............................................................................................... 3 G. Grading & Erosion Control Summary and Soils Map......................................................................... 4 H. Operation and Maintenance Guidelines............................................................................................ 5 RAMEngineering, Inc. Select Homes 8721 218th St. SW Final Engineering and Drainage Report 2-Lot Short Plat RAM No. 15-032 October 11, 2016 Page i A. PROJECT SUMMARY: This report provides engineering information for the proposed construction of a 2-lot single family residence short plat; the project is located on the north side of 218t" St SW and east of 88t" Ave W (8721 218th St SW) in the City of Edmonds. The applicant, Select Homes proposes to remove the existing residence and construct two single family residence on the site. This report provides the evaluation for the proposed 2-lot short plat. Existing Conditions. The total site consists of about 21,209 sf (0.463 acres) and is currently occupied by an existing single family residence with an access drive of 218t" St SW. The existing house is surrounded by open grass lawn area and has scattered trees distributed around the site. The site is bordered by 218t" St SW along the south and single family residences to the west, north, and east (see attached aerial photo - section D). The site generally slopes from northeast to southwest ranging from 2% to 8%. A majority of the site's drainage runoff would sheet flow southwesterly and collect in an existing storm drainage systems located along the north side of 218t" St SW or easterly side of 88t" Ave WA. Minor drainage sheet flow from existing residential properties to the east and north may flow onto the site. 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 F of this report. Developed Conditions. The proposed project includes the construction two single residence and associated driveway and utilities. Lot 1(southerly lot) will access 2181" Ave W and Lot 2 (northerly lot) will also access 218t" St SW with a pan -handle driveway along the westerly side of Lot 1. All 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 detention systems; water; sewer; power; and communications. Due to the existing till soils of the site no infiltration or low impact development technique are proposed to be used to provide storm drainage flow control. 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). To control the stormwater runoff an underground detention tank systems will be installed along the westerly boundary of the project site; all roof drains shall be routed to the proposed detention tank. Due to the fact a majority of the impervious surface is the roof top area with limited pollution generating driveway area (less than 5,000 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. RAM Engineering, Inc. Select Homes 8721 218th St. SW Final Engineering and Drainage Report 2-Lot Short Plat RAM No. 15-032 October 11, 2016 Page A-1 Summary of Minimum Requirements for Small Site Projects: 5.1 Small Site Minimum Requirement #1 — Preparation of Stormwater Site Plan The proposed site development consists of disturbing about 0.487 acres of land and creating/replacing about 9,960 sf (Lot 1- 3,950 sf + Lot 2- 6,010 sf) of impervious surface. Thus, the project is classified as a Small Site- Category 2 project per the City's classification system (see attached Site Classification Worksheet). The civil site development plans have been prepared and reduced copies of the plans are included in section C of this report. 5.2 Small Site 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. The grading quantities are estimated to be 500 CY of cut and 500 CY of fill. 5.3 Small Site 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. 5.4 Small Site Minimum Requirement #4 — Preservation of Natural Drainage Systems and Outfalls A majority of the runoff leaves the site as sheet flow in a southwesterly direction. Site runoff enters an existing catch basins along the north side of 218t" St SW or the east side of 88t" Ave W and enters the City's storm conveyance system. The proposed detention system for each single family residence will discharge flows to the City storm pipe system in 218t" St SW, thus maintaining the existing drainage flow path. The site is located in the Westgate Pond watershed basin and eventually discharge to the Puget Sound (via Shell Creek) per the City of Edmonds maps (see section F). The proposed development will maintain the stormwater flow discharges to the Westgate Pond watershed basin. 5.5 Small Site Minimum Requirement #5 — Onsite Stormwater Management. The developed site conditions include impervious surface roof top, driveway and walkway/patio areas for the proposed residences. All rooftop and exterior area collection drains shall convey stormwater run-off to the on -site detention tank. Due to the underlying dense till soils found onsite, no LID or infiltration type stormwater management systems will be used onsite. An underground detention tank per the City's drainage manual will be provided to control stormwater quantity control (Small Site Category 2). See civil site development plans and section E for additional sizing calculations and construction details. RAMEogineering, Inc. Final Engineering and Drainage Report RAM No. 15-032 Select Homes 8721 218th St. SW 2-Lot Short Plat October 11, 2016 Page A-2 5.6 Small Site 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 3,962 sf (driveways: Lot 1- 1,273 sf + Lot 2- 2,689 sf) pollution generation impervious surfaces; 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. The site's stormwater control system will include a sump and a control tee that will provide some water quality and oil/water separation of the collected runoff. 5.7 Small Site Minimum Requirement #7 — Flow Control. An onsite storm detention tanks will provide flow control of the site's stormwater runoff. The detention tank system has been design to meet the flow control standards of a Small Site- Category 2 project in a creek or lake basin (less than an acre of disturbance and between 5,000 sf and 10,000 sf of impervious surface). The detention tank has been sized using WWHM (9,960 sf) software; a full overview of the proposed storm drainage control facilities calculations is provided in section E. 5.8 Small Site Minimum Requirement #8 — Wetland Protection. No wetlands are known to exist on or adjacent to the site. 5.9 Small Site Minimum Requirement #9 — Operation and Maintenance. An operation and maintenance summary is provided in section H. 5.10 Small Site Minimum Requirement #10 — Offsite Analysis and Mitigation. See section F. Drainage Basin Description and Maps for a qualitative analysis. 5.11 Small Site Minimum Requirement #11 — Financial Liability. Cost estimates and bonds will be provided by the applicant during final construction permit approval. RAMEngineering, Inc. Final Engineering and Drainage Report RAM No. 15-032 Select Homes 8721 218th St. SW 2-Lot Short Plat October 11, 2016 Page A-3 t"j City of Edmonds nl� Site Classification Worksheet Page i of 2 ins ,gqo The project's Site Classification will dictate the specific stormwater management requirements applicable to your site. Completing this worksheet will help determine the amount of regulated impervious surface and whether your project falls into the classification of a Small Site (Category 1 or Category 2), or a Minor Site. Please reference the Cilossary (po. 10-11). Figures D and Epp 8-9) and Examples {p.. I I-12) to assist with completion of this worksheet 1) Is Permeable Pavement Proposed For Use on this Site? Refer to Stormtvater Supplement Chapter 5.1 El Yes N o If YES, the subject area is to be considered impervious for initial site classification purposes. Include total perineable pavement area in the calculation of Non -Regulated Replaced and/or N= impervious surface areas in the table below. 2) Determine the Amount and Type of Existing .0 Proposed Impervious Surface for the Site Refer to Storinwater Supplement Chapter 2 and Fig. C Line 1: Identify the Non -Regulated Impervious Surface Area. I,me 2: Identify the Replaced Impervious Surface Area, dividing the total between Exempt and Regulated; either or both may be zero. Note: For project classification purposes, Replaced Impervious may only be considered exempt under certain conditions. Refer to the Glossary and Figure D. Line 3: Identify the New Impervious Surface Area for your project All impervious areas created post -July 7, 1977 or after the date of annexation into the City are regulated & should be included in this total unless they can be categorized separately as a Replaced -Regulated area. Line 4: Enter the sum of the total Reolaced-Regulated plus the total New impervious areas. Line j: Identify the total area currently mitigated by an existing city -approved stormwater management system. Line 6: Enter the sum of the value in Line 4 less the value in Line 5 to identify the total Regulated area in which stormwater controls have not yet been applied. Line 7. Identify the total area proposed to be mitigated through the use of Low Impact Development Techniques. Line 8: Identify the total area proposed to be mitigated through conventional Stormwater Management Techniques. ** Provide a copy of the following table on the drainage plan sheet for the proposed protect Line Type Area (square feet) 1. Non -Regulated NONE Exempt Regulated 2. Replaced -+ --'�---9,960 0 SF 3. New (Post 1977) 444 4-* 4 444 Total Regulated Impervious Area4. Miti ation required if in excess of 20005 j SF i = 9,960 SF 5. Total Area Mitigated by F_xisting Stormwater Management System(s) Regulated Area Not Yet Mitigated 0 SF ' _ 9:960 $F L7.lArea Proposed to be Mitigated by Low' Impact Development Techniques = 0 SF Aura Proposed to be Mitigated through Conventional SWM Techniques = 9,960 SF t (e.g. porous asphalt, porous concrete, paver blocks, concrete open celled paving grids, or plastic lattices tilled with turf or stone) Revised on 3/t15/2012 E72-SWM Erosion_Controt-03.05.12.doc Page 5 of 12 RAM Engineering, Inc. Select Homes 8721 218th St. SW Final Engineering and Drainage Report 2-Lot Short Plat RAM No. 15-032 October 11, 2016 Page A-4 City of Edmonds G'�01F Fvt,�}yh Site Classification Worksheet Page 2 of 2 .... . .... ___ _.. 3) Determine the Total Area of Land Disturbing Activity 21,209 sf Refer to Storntwater Supplement Chapter 8 4) Determine the Quantity of Grading. Fill and/or Excavation CUT=500 CY FILL=500 CY 5) Will the project convert 'l Acre or'blore of Native Vegetation to Lawn or ❑ Yes � No Landscaped Area? 6) Identify the Watershed the Existing Site Runoff Discharges to Refer to Stormwate►• Supplement Chapter 2.3 Based on Site Location and Watershed Map — Figure-C. Check all that apply. A. ❑ Direct Discharge B. U Creek or Lake Basin ❑ Edmonds Way Basin Westgate Pond ❑ Puget Sound Basin ❑ Puget Sowed Piped Basin DETERMINE PROJECT CLASSIFICATION USING THE INFORMATION ABOVE AND THE PROJECT CLASSIFICATION( CHART (Figure B, pg 4) ❑ Small Site - Category I EISniall Site - Category 2 Minor Site Storntwater Supplement Storrnwater Supplement Storrnwater Supplement Chapter 5 Chapter 5 Chapter 6 Revised on 3I0 12012 E72-SWAT Erosion_Control-03.05.12.doe RAMEngineering, Inc. Final Engineering and Drainage Report RAM No. 15-032 Page 6 of 12 Select Homes 8721 218th St. SW 2-Lot Short Plat October 11, 2016 Page A-5 B. PARCEL (VICINITY) MAP __giIRHTER__- SECTION 1 ... TOWNSHIP N.W.BL NW30 77 4 ...��._� w�..A .K ...,..,. „.....�.,.� Canlenlnp -- - — Gov Lot Moor WMW -- lot Subs iv Other Lot Modt — Sse0on ROW — Quarter YaOROW ---- 10th 017 L1rrna Tax AO ,........... Euanmcnl » I AW*-zwfiw 1,vr�+•rr+» rw...r rm rae r R .�p,w„v,q-rbr e, upar Gma.Mrr,a t,'ur�wy, nwaLrxrwr Minor Meter ._—"_ Other SubdW Vat Let - - - SW-14,27-04 50l1 _ Or ®. or O1 I,0 5 03 - n 1o8 m A or 3 ......Yy1Y... i it _ 10 S , M ® o _-. te m at ] T 2 v S , 02 L U GE 1 5 r 1 4 3 2 10 /aDD TIO 5 87J 8 Nb 4 (529 » ,2 3 a Sr 5 ry D2 E V VIN&:, -W1 56' , z 12 11 10 4 S 06., -IS R' D MAR 3 f 6 5 7 E 3 4 3 e 7 S -10 N 6 61 9) J 16 1 i3 A 10 11 12 13 14 1a 16 O DM NDS f 66) Rf GE 0, ti 02 03 2 3 i 03 € it (02 031pp2 01 03 02 x 10 S , sovmr: , i1 3 r •i 6 ; DD. 02 1 S 00 1 a t =" 0141� 207HPLSYV- c0 Ot €O et K :'02 7 9 S 02 .: 07 ...E-t,hK 5 w s-1 5; 1 (4 �) atr•ausr•w so fi 05 � C D3 01 CC RAMEngineering, Inc. Select Homes 8721 218th St. SW Final Engineering and Drainage Report 2-Lot Short Plat RAM No. 15-032 October 11, 2016 -i mil HADL Page 8-1 C. SITE DEVELOPMENT PLANS NOlOMIN14YM SONOYM3.40AM �usg swoswznnd 9 i�f MS133M16N18LL-Az29 IM IUGH9MS139UISHIG. �iW 4 � Np&A3H Nndln3w�r3a3aaus i� �s z Hof i ai__ 9.?fiR n s Q ai :,ii, INN ��id i i W LU f� # ii 4iYY tl3•:L 'ti & d �K • �u a� 7 g� �yy 44 j{ q{ yky�i A\ l A A to tKit all il RAMEngineering, Inc. Final Engineering and Drainage Report RAM No. 15-032 Select Homes 8721 218th St. SW 2-Lot Short Plat October 11, 2016 Page C-1 rvsc 1Y078J �'wiwrPy rs.e.r.w xtrn.w w Till[ PR07zcrmY11lY0f t! m m O CD y Ca O N � o N ;Z O_ (/) O � lnvA � i AR 0 oRaarMa oulwrmra s Ca 4W.lT MOTCC f 110 N A 101 Y aaaom FATEIf FIIaR1C R1YCl MOf! rM'YC /IKwn R4Ym tl,01m aingNtm Ri+a ltl IY[R,u �.wfY� O �; 11�flII<VaGaTA7111MltTRft/OMIO/T �Rirt yy� � C0Md7R(If.1lONf�lFNCF /. _ h aN4 N O /4i rsa7; o�,.n..a•r.n...w 7V-01 R.4MEngineering, Inc. Final Engineering and Drainage Report RAM No. 15-032 Select Homes 8721 218th St. SW 2-Lot Short Plat October 11, 2016 Page C-4 CD CD co (D CD C/) OD --4 C) N) Cb 00 C/) -4. 0 —0 (/) k 0) TRAFF)C CONTROL TOTES Z— c— .. . ..... ........ RAMI SITE �h E. STORMWATER CONTROL SYSTEM SUMMARY AND CALCULATIONS: The project proposes to create and/or replace approximately 9,960 sf of impervious surface (Lot 1- 3,950 sf + Lot 2- 6,010 sf). To mitigate the development of the site, an underground detention tank system will be installed along the west boundary of the site to control the drainage runoff (flow control). All of the on -site impervious surfaces shall be collected and routed to the on -site detention tank. The stormwater control detention tank has been sized per Table 5-3 City of Edmonds Flow Control Requirements for Small Site Projects- Creek or Lake Basins in the Edmonds Stormwater Code Supplement (April 2010). Per Table 5-3, continuous hydrologic modeling with MGS precipitation data (WWHM 20012) shall be used to model the detention tank system. Project Area Summary: Total Site Area = 21,209 sf Proposed Impervious = 9,960 sf (Lot 1- 3,950 sf + Lot 2- 6,010 sf) Underground Detention Tank Sizing: The detention tank system has been sized for the proposed 9,960 sf (0.229 ac.) of impervious surfaces using WWHM2012 continuous hydrologic modeling. Per Table 5-3 in the Edmonds Stormwater Code Supplement the following flow control standards are required for a Small Site project located within a creek basin: ?s,000 sr Effective Impervious Area For detention BiIPs: 2-year=0,07 cNacre inipenions. I0-year = 0.14 cfs%acre impeivious. and 100-year = 0.33 cNacre impervious, For infiltration BMPs. 2-year = 0,07 cfs/acre impervious, 10-year = 0.25 cfs/acre impervious. and 100-year` OAt c6lacre nnpervious. New and replaced impervious surface Simplified Sizing Approach or continuous hydrologic modeling with MGS'precipitation data CA 2-Year Allowable Release Rate = 0.07 cfs/acre-impervious x 0.229 acres = 0.016 cfs 10-Year Allowable Release Rate = 0.14 cfs/acre-impervious x 0.229 acres = 0.032 cfs 100-Year Allowable Release Rate = 0.33 cfs/acre-impervious x 0.229 acres = 0.076 cfs The developed runoff rates and storage calculations were performed using the DOE 2012 Western Washington Hydrology Model (WWHM2012) continuous runoff model. The required detention system and release rates for the developed conditions are as follows: RAMEngineering, Inc. Final Engineering and Drainage Report RAM No. 15-032 Select Homes 8721 218th St. SW 2-Lot Short Plat October 11, 2016 Page E-1 Proposed Detention Tank: 82 ft — 60" Diameter Pipe with 11116" (0.6875") orifice. Release Rates: Storm Event Mitigated Allowable 2-year = 0.016 cfs 0.016 cfs 10-year = 0.031 cfs 0.032 cfs 100-year = 0.066 cfs 0.076 cfs See WWHM2012 printout on the following pages. RAMEngineering, Inc. Select Homes 8721 218th St. SW Final Engineering and Drainage Report 2-Lot Short Plat RAM No. 15-032 October 11, 2016 Page E-2 WWHM2012 Input/Output Data: WWHM2012 15-032Short Plat File Edit Vie.+ Help Summary Report g r Basin U Schematic O i� C3 Mm 2/an -15R77 Sim PW • Fneh MA 6• Tank 1 Mitigated Facility Name Tank l__ -_�! Facility Type Tarn Outlet 1 Outlet 2 Outlet 3 Downstream Connection 0 r PrecipdationAppled to FaaLy Auto Tank Quick Tank r Evaporation Appliedto Facilty Facility Dimension Diagram Facility Dimensions Outlet Structure Data Facility Bottom Elevation (n) 100 Run HeightI10 4.9 =i Teri GrWx Rua DimretaC ] �� a 0tl 0 ensst (it) L4h w ® Rua Type r- �-. r Notch Type Infiltration NO Orifice Diameter Height Number (n) (it) 1 06875 -q F2--.q 2 r--i F0- 3 FO--4 fo _-:-I TakVd-atRisa Head(.-R) .M7 Show Tank Table Open Table .A Mal Sttaae DO �- Tide Gate I Time Series I Demand �Ct• Basin 1 Mitigated $ Subbasin Name: Basin l i r. Deajnsa.Bytaassla POC Surtax Intereow Groundwater Flows To : lark 1 Tark Area in Basin r 51nw Orly Setetled Available Pervious Ames Available Impervious Acres r A/B; Forest, Fla 0 r RDADS/FLAT 0 �r A/B,Forest Mod 0 r- ROADSMOD 0 jr A/B,Fon d,Steep r ROADS/STEEP iraB,peuue,Flat 17 ROOFTOPS7FW 136 r A/B; Pastue. Mod R DRNEWAYS/FlAT r ;Padue:Sleep r DRNEWAYS/MOD 0� I r.A/B, Lain, Flat 0 r DRNEWAYS/STEEP r NB, Lewn, Mad � W SIDEWM.K- 5 IT/FlA ® l rAR.Lawn Steep �� r SIDEWALKS/MOD -�I� lr C, oud.Fla 0 r SIDEWALKS7STEEP g �r C, Farod; Mad r PARKING/FIA.T _J 9 C,Faeu. Sleep- © r PAR JNG/MOD r C.Pedure.Rd r PAAKING/STEEP 0 r C;Panue,Mod 19 r POND 0 r it Pedue, Slav r Porous, Pavement 0 j r C.Lann,Flet 0 � ':, rL. Lain, Mao r C, Lawn, steep Fla r SAT. FoFls r SAT, Faed,od. Mad r SAT, Forest, Steep Pervious Total Aces Impervious Total ® Aces Basin Total® Acres w Determine O W et With Tide Gate r Use Tide Gate Tide Gate Elevation (0 Downstream Connectian OverBmv Elevamin(h) FoIterations Fiov Frequency ® ILCumulafive __._ Probability .__._.. _- /0 Flotr(e1s) 0001 2 Year 0.0161 5 Year - 0.0240 10 Year - 0.0310 25 Year - 0.0424 50 Year - 0.0531 1 0 aYear - 0.0660 0.1 -. _- _-_.__-__ .1.-1- ++ nal Peaks +++ + 801 1902 0.0169 ++ 1903 0.0140 1904 0.0168 1905 0.0148 1906 0.0127 �xNI1NF 1907 0.0205 + + + +++� 001 190a 1909 0.0154 0.0152 001 0.5 1 2 5 10 20 30 50 70 80 90 95 98 9999.51 1910 0.01Be Stream RolecBcn Duration) LID Dualion Flow Frequency ( Wata Qe VY Hydro 1911 1912 1914 0.0199 0.019 0.0172 Welland Volumes UDRepod Rwhage Duation Rechage Redeveloped I Recha eMirigeted AnalRedatmets Compact WDM Delete Selected ( 1 Puget East 36 Evap 1915 0.0120 2 Puget East 36 Preco 1916 0.0159 501 POC 1 Pred-loped flow 1917 0.0157 7011nlbwto PO,; Mih ated - 1910 0.0160 1000 Tank 1 ALL OUTLETS Mitigated 1919 0.0139 1001 Tank 1 STAGE MRioed 1920 0.0147 1921 0.0140 1922 0.0166 At Deters. Fbw Stage RecP Evap TClj 1923 0.0160 Flood Fregi-y Method 192 1925 0.0134 0.0126 F Log Perim Type III 17B 192 0.015 f W.NA 1927 0.0151 C Cunene 1928 0.0144 f (i n9aken 1929 0.018 RAMEngineering, Inc. Select Homes 8721 218th St. SW Final Engineering and Drainage Report 2-Lot Short Plat RAM No. 15-032 October 11, 2016 Page E-3 WWHM20l2 PROJECT REPORT Project Name: 15-032 Short Plat Site Name: Site Address: City Report Date: 7/19/2016 MGS Regoin Puget East Data Start 1901/10/1 Data End : 2058/09/30 DOT Data Number: 03 Version Date: 2016/02/25 Version : 4.2.12 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, Lawn, Mod .23 Pervious Total 0.23 Impervious Land Use acre Impervious Total 0 Basin Total 0.23 Element Flows To: Surface Interflow Groundwater MITIGATED LAND USE Name : Basin 1 Bypass: No Groundwater: No Pervious Land Use acre Pervious Total 0 Impervious Land Use acre ROOF TOPS FLAT 0.136 DRIVEWAYS FLAT 0.091 SIDEWALKS FLAT 0.002 Impervious Total 0.229 Basin Total 0.229 Element Flows To: Surface Interflow Groundwater Tank 1 Tank 1 Name : Tank 1 Tank Name: Tank 1 Dimensions Depth: 5 ft. Tank Type Circular Diameter 5 ft. Length : 82 ft. RAMEngineering, Inc. Final Engineering and Drainage Report RAM No. 15-032 Select Homes 8721 218th St. SW 2-Lot Short Plat October 11, 2016 Page E-4 Discharge Structure Riser Height: 4.9 ft. Riser Diameter: 6 in. Orifice 1 Diameter: 0.6875 in. Elevation: 2 ft. Element Flows To: Outlet 1 Outlet 2 Tank Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(efs) 100.00 0.000 0.000 0.000 0.000 100.06 0.002 0.000 0.000 0.000 100.11 0.002 0.000 0.000 0.000 100.17 0.003 0.000 0.000 0.000 100.22 0.003 0.000 0.000 0.000 100.28 0.004 0.000 0.000 0.000 100.33 0.004 0.001 0.000 0.000 100.39 0.005 0.001 0.000 0.000 100.44 0.005 0.001 0.000 0.000 100.50 0.005 0.001 0.000 0.000 100.56 0.005 0.002 0.000 0.000 100.61 0.006 0.002 0.000 0.000 100.67 0.006 0.002 0.000 0.000 100.72 0.006 0.003 0.000 0.000 100.78 0.006 0.003 0.000 0.000 100.83 0.007 0.004 0.000 0.000 100.89 0.007 0.004 0.000 0.000 100.94 0.007 0.004 0.000 0.000 101.00 0.007 0.005 0.000 0.000 101.06 0.007 0.005 0.000 0.000 101.11 0.007 0.006 0.000 0.000 101.17 0.008 0.006 0.000 0.000 101.22 0.008 0.007 0.000 0.000 101.28 0.008 0.007 0.000 0.000 101.33 0.008 0.007 0.000 0.000 101.39 0.008 0.008 0.000 0.000 101.44 0.008 0.008 0.000 0.000 101.50 0.008 0.009 0.000 0.000 101.56 0.008 0.009 0.000 0.000 101.61 0.008 0.010 0.000 0.000 101.67 0.008 0.010 0.000 0.000 101.72 0.008 0.011 0.000 0.000 101.78 0.009 0.011 0.000 0.000 101.83 0.009 0.012 0.000 0.000 101.89 0.009 0.012 0.000 0.000 101.94 0.009 0.013 0.000 0.000 102.00 0.009 0.013 0.000 0.000 102.06 0.009 0.014 0.003 0.000 102.11 0.009 0.014 0.004 0.000 102.17 0.009 0.015 0.005 0.000 102.22 0.009 0.015 0.006 0.000 102.28 0.009 0.016 0.006 0.000 102.33 0.009 0.016 0.007 0.000 102.39 0.009 0.017 0.008 0.000 102.44 0.009 0.018 0.008 0.000 102.50 0.009 0.018 0.009 0.000 102.56 0.009 0.019 0.009 0.000 102.61 0.009 0.019 0.010 0.000 102.67 0.009 0.020 0.010 0.000 102.72 0.009 0.020 0.010 0.000 102.78 0.009 0.021 0.011 0.000 102.83 0.009 0.021 0.011 0.000 102.89 0.009 0.022 0.012 0.000 102.94 0.009 0.022 0.012 0.000 RAMEngineering, Inc. Final Engineering and Drainage Report RAM No. 15-032 Select Homes 8721 218th St. SW 2-Lot Short Plat October 11, 2016 Page E-5 103.00 0.009 0.023 0.012 0.000 103.06 0.009 0.023 0.013 0.000 103.11 0.009 0.024 0.013 0.000 103.17 0.009 0.024 0.013 0.000 103.22 0.009 0.025 0.014 0.000 103.28 0.008 0.025 0.014 0.000 103.33 0.008 0.026 0.014 0.000 103.39 0.008 0.026 0.015 0.000 103.44 0.008 0.027 0.015 0.000 103.50 0.008 0.027 0.015 0.000 103.56 0.008 0.028 0.016 0.000 103.61 0.008 0.028 0.016 0.000 103.67 0.008 0.029 0.016 0.000 103.72 0.008 0.029 0.016 0.000 103.78 0.008 0.030 0.017 0.000 103.83 0.008 0.030 0.017 0.000 103.89 0.007 0.030 0.017 0.000 103.94 0.007 0.031 0.017 0.000 104.00 0.007 0.031 0.018 0.000 104.06 0.007 0.032 0.018 0.000 104.11 0.007 0.032 0.018 0.000 104.17 0.007 0.032 0.018 0.000 104.22 0.006 0.033 0.019 0.000 104.28 0.006 0.033 0.019 0.000 104.33 0.006 0.034 0.019 0.000 104.39 0.006 0.034 0.019 0.000 104.44 0.005 0.034 0.020 0.000 104.50 0.005 0.035 0.020 0.000 104.56 0.005 0.035 0.020 0.000 104.61 0.005 0.035 0.020 0.000 104.67 0.004 0.035 0.020 0.000 104.72 0.004 0.036 0.021 0.000 104.78 0.003 0.036 0.021 0.000 104.83 0.003 0.036 0.021 0.000 104.89 0.002 0.036 0.021 0.000 104.94 0.002 0.036 0.071 0.000 105.00 0.000 0.037 0.182 0.000 105.06 0.000 0.000 0.299 0.000 ANALYSIS RESULTS Stream Protection Duration Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.229 Total Impervious Area:O Mitigated Landuse Totals for POC #1 Total Pervious Area:O Total Impervious Area:0.229 Flow Frequency Return Periods for Predeveloped. POC Return Period Flow(cfs) 2 year 0.001811 5 year 0.002732 10 year 0.00334 25 year 0.004095 50 year 0.004646 100 year 0.005185 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.018104 5 year 0.02167 10 year 0.023947 25 year 0.026762 50 year 0.028827 RAMEngineering, Inc. Final Engineering and Drainage Report RAM No. 15-032 Select Homes 8721 218th St. SW 2-Lot Short Plat October 11, 2016 Page E-6 100 year 0.030875 Stream Protection Duration Annual Peaks for Predeveloped and Mitigated Year Predeveloped Mitigated 1949 0.001 0.016 1950 0.002 0.022 1951 0.002 0.019 1952 0.001 0.017 1953 0.001 0.019 1954 0.003 0.022 1955 0.003 0.023 1956 0.002 0.013 1957 0.003 0.017 1958 0.002 0.028 1959 0.002 0.018 1960 0.002 0.016 1961 0.002 0.029 1962 0.001 0.017 1963 0.002 0.023 1964 0.002 0.015 1965 0.002 0.014 1966 0.001 0.015 1967 0.003 0.029 1968 0.003 0.020 1969 0.001 0.023 1970 0.001 0.015 1971 0.002 0.021 1972 0.002 0.027 1973 0.001 0.019 1974 0.002 0.021 1975 0.001 0.019 1976 0.001 0.017 1977 0.001 0.014 1978 0.001 0.013 1979 0.002 0.023 1980 0.002 0.014 1981 0.001 0.015 1982 0.002 0.016 1983 0.002 0.019 1984 0.002 0.018 1985 0.002 0.021 1986 0.006 0.022 1987 0.002 0.019 1988 0.002 0.017 1989 0.001 0.018 1990 0.002 0.014 1991 0.002 0.016 1992 0.001 0.015 1993 0.001 0.016 1994 0.001 0.013 1995 0.002 0.017 1996 0.004 0.017 1997 0.007 0.022 1998 0.001 0.024 1999 0.002 0.014 2000 0.001 0.023 2001 0.000 0.017 2002 0.002 0.014 2003 0.001 0.017 2004 0.002 0.025 2005 0.002 0.020 2006 0.004 0.018 2007 0.003 0.019 2008 0.005 0.020 2009 0.001 0.017 POC #1 RAMEngineering, Inc. Select Homes 8721 218th St. SW Final Engineering and Drainage Report 2-Lot Short Plat RAM No. 15-032 October 11, 2016 Page E-7 Stream Protection Duration Ranked Annual Peaks for Predeveloped and Mitigated Rank Predeveloped Mitigated 1 0.0066 0.0295 2 0.0062 0.0287 3 0.0045 0.0280 4 0.0040 0.0266 5 0.0038 0.0252 6 0.0034 0.0236 7 0.0030 0.0234 8 0.0029 0.0232 9 0.0029 0.0231 10 0.0028 0.0229 11 0.0026 0.0226 12 0.0025 0.0224 13 0.0024 0.0219 14 0.0024 0.0217 15 0.0024 0.0215 16 0.0022 0.0211 17 0.0022 0.0209 18 0.0021 0.0207 19 0.0021 0.0204 20 0.0021 0.0204 21 0.0021 0.0197 22 0.0020 0.0194 23 0.0020 0.0191 24 0.0020 0.0191 25 0.0019 0.0190 26 0.0019 0.0190 27 0.0019 0.0189 28 0.0018 0.0187 29 0.0018 0.0179 30 0.0017 0.0178 31 0.0017 0.0177 32 0.0017 0.0176 33 0.0017 0.0174 34 0.0016 0.0172 35 0.0016 0.0172 36 0.0016 0.0171 37 0.0016 0.0171 38 0.0015 0.0171 39 0.0015 0.0169 40 0.0015 0.0169 41 0.0015 0.0167 42 0.0015 0.0167 43 0.0015 0.0165 44 0.0014 0.0160 45 0.0014 0.0159 46 0.0014 0.0156 47 0.0014 0.0156 48 0.0013 0.0154 49 0.0013 0.0151 50 0.0013 0.0149 51 0.0013 0.0149 52 0.0012 0.0146 53 0.0011 0.0144 54 0.0011 0.0142 55 0.0011 0.0140 56 0.0010 0.0139 57 0.0010 0.0138 58 0.0008 0.0136 59 0.0008 0.0133 60 0.0008 0.0131 61 0.0002 0.0129 Stream Protection Duration POC #1 RAMEngineering, Inc. Final Engineering and Drainage Report RAM No. 15-032 POC #1 Select Homes 8721 218th St. SW 2-Lot Short Plat October 11, 2016 Page E-8 Facility FAILED duration standard for 1+ flows. Flow(cfs) Predev Mit Percentage Pass/Fail 0.0009 13901 167560 1205 Fail 0.0009 12690 165228 1302 Fail 0.0010 11586 162961 1406 Fail 0.0010 10602 160694 1515 Fail 0.0011 9636 158598 1645 Fail 0.0011 8793 156502 1779 Fail 0.0011 8029 154299 1921 Fail 0.0012 7375 152160 2063 Fail 0.0012 6744 149978 2223 Fail 0.0012 6175 147775 2393 Fail 0.0013 5666 145529 2568 Fail 0.0013 5189 143198 2759 Fail 0.0014 4770 140867 2953 Fail 0.0014 4365 138386 3170 Fail 0.0014 3991 135947 3406 Fail 0.0015 3638 133488 3669 Fail 0.0015 3311 130793 3950 Fail 0.0015 3052 128076 4196 Fail 0.0016 2821 125210 4438 Fail 0.0016 2631 122622 4660 Fail 0.0017 2411 120312 4990 Fail 0.0017 2227 118259 5310 Fail 0.0017 2082 116312 5586 Fail 0.0018 1945 114387 5881 Fail 0.0018 1825 112462 6162 Fail 0.0019 1705 110623 6488 Fail 0.0019 1585 108869 6868 Fail 0.0019 1479 107030 7236 Fail 0.0020 1373 105126 7656 Fail 0.0020 1268 103393 8154 Fail 0.0020 1193 101618 8517 Fail 0.0021 1114 99822 8960 Fail 0.0021 1038 97982 9439 Fail 0.0022 985 96121 9758 Fail 0.0022 944 94325 9992 Fail 0.0022 902 92571 10262 Fail 0.0023 860 90646 10540 Fail, 0.0023 816 88721 10872 Fail 0.0023 773 86817 11231 Fail 0.0024 739 84978 11499 Fail 0.0024 696 83160 11948 Fail 0.0025 663 81406 12278 Fail 0.0025 632 79716 12613 Fail 0.0025 608 78197 12861 Fail 0.0026 582 76636 13167 Fail 0.0026 560 75053 13402 Fail 0.0026 543 73599 13554 Fail 0.0027 525 72059 13725 Fail 0.0027 511 70690 13833 Fail 0.0028 497 69257 13935 Fail 0.0028 481 67931 14122 Fail 0.0028 464 66583 14349 Fail 0.0029 455 65257 14342 Fail 0.0029 443 63974 14441 Fail 0.0029 430 62626 14564 Fail 0.0030 420 61236 14580 Fail 0.0030 412 59910 14541 Fail 0.0031 401 58520 14593 Fail 0.0031 395 57087 14452 Fail 0.0031 387 55696 14391 Fail 0.0032 380 54328 14296 Fail 0.0032 371 53001 14285 Fail 0.0032 364 51718 14208 Fail RAMEngineering, Inc. Final Engineering and Drainage Report RAM No. 15-032 Select Homes 8721 218th St. SW 2-Lot Short Plat October 11, 2016 Page E-9 0.0033 350 50478 14422 Fail 0.0033 338 49237 14567 Fail 0.0034 325 48082 14794 Fail 0.0034 316 46970 14863 Fail 0.0034 305 45879 15042 Fail 0.0035 295 44767 15175 Fail 0.0035 289 43655 15105 Fail 0.0036 275 42564 15477 Fail 0.0036 269 41430 15401 Fail 0.0036 262 40382 15412 Fail 0.0037 249 39291 15779 Fail 0.0037 244 38222 15664 Fail 0.0037 237 37174 15685 Fail 0.0038 232 36168 15589 Fail 0.0038 224 35206 15716 Fail 0.0039 220 34265 15575 Fail 0.0039 217 33260 15327 Fail 0.0039 211 32254 15286 Fail 0.0040 208 31420 15105 Fail 0.0040 204 30500 14950 Fail 0.0040 202 29581 14644 Fail 0.0041 196 28704 14644 Fail 0.0041 194 27891 14376 Fail 0.0042 187 27057 14468 Fail 0.0042 183 26287 14364 Fail 0.0042 177 25495 14403 Fail 0.0043 173 24725 14291 Fail 0.0043 169 24020 14213 Fail 0.0043 167 23292 13947 Fail 0.0044 163 22544 13830 Fail 0.0044 155 21859 14102 Fail 0.0045 153 21177 13841 Fail. 0.0045 145 20533 14160 Fail 0.0045 139 19913 14325 Fail 0.0046 136 19278 14175 Fail 0.0046 132 18685 14155 Fail 0.0046 130 18129 13945 Fail The development has an increase in flow durations from 1/2 Predeveloped 2 year flow to the 2 year flow or more than a 10% increase from the 2 year to the 50 year flow. The development has an increase in flow durations for more than 50% of the flows for the range of the duration analysis. 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 RAMEngineering, Inc. Final Engineering and Drainage Report RAM No. 15-032 Select Homes 8721 218th St. SW 2-Lot Short Plat October 11, 2016 Page E-10 F. DRAINAGE BASIN DESCRIPTION: The site is located in the Westgate Pond watershed basin. The Westgate Pond basin is a relatively small urban basin that collects stormwater runoff from primarily residential areas in the City Edmonds and ultimately discharges flows to westerly to Puget Sound via the Shell Creek (see attached watershed map). The collected stormwater runoff from the site will discharge to a pipe and catch basin system located in 218th St SW or 88th Ave W southwest of the site. The proposed detention tank systems for the new lots will discharge to the existing 12" storm drainage system along the north side of 218th St SW; the storm pipe system (consisting of 12 pipe) within 218th St SW flows west (+/-120 ft) to 88th Ave W to the northwest corner of 218th St SW and 88th Ave W. The pipe system continues to flow west along the north side of 218th St SW about 700 feet to a junction catch basin that then directs the pipe system south under 218th St SW and continues south about 250 ft to the outlet side of Westgate Pond; Westgate Pond is approximately 950 feet downstream of the project site. Westgate Pond discharges to the west to 92nd Ave W; the pipe system then turns south to the intersection of 92nd Ave W and 220th St SW (about 1,870 feet downstream of the site). See F-3 Downstream Drainage Facility Map, delineating the downstream path within 1,870 feet of the project site. The system then is directed westerly along 220th St SW to 951h Ave W and extend north to 217th St SW and then heads west again to 96th St SW. At 961h St SW the system is directed north in a collection of 18" to 24" pipes to a discharge to Shell Creek. The Shell Creek discharge point is about 1.25 miles downstream of the site. Shell Creek continues in a northwesterly direction and eventually discharges into the Puget Sound about 2.4 miles from 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; some areas of open channel are found near the conveyance system into and out of Westgate Pond. No apparent flooding or system inadequacies within a % mile 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. RAM Engineering, Inc. Final Engineering and Drainage Report RAM No. 15-032 Select Homes 8721 218th St. SW 2-Lot Short Plat October 11, 2016 Page F-1 F-2. Watershed Basin Map FIGURE B-1 CITY OF EDMONDS - W51' WATERSHEDS Dee, Veek Perrimillie Edmonds Mersin Puget Sound Edmonds wasi ts`Puget Sound Piped fnato.j. shot Creek G..d Hope Pond sh.ubm., "A' r,-k southwest Edmonds A Hindi, Creek 5-vie—st Edmonds B t.1w 0.11mw stilth... C,O.k Who's Gulch Talbot Park A Nle.d..d.e A Taltiot Park 0 M-dowd.f. 8 'i Terrace Creek ly—lotte.. W.,tphs Pond outiall C-1, will— C-1, A in = 4000 is A �$W.Isoun d P42 Anmp d 41 `Wj1tQul Cmok N Ueadowdille A owdste a -W , J L Ito k ! `I'mr1ile un V.11,11det Park 8 M I MM Edmo dsw Southwest EdM*nq.t_,,., od Hope Pond 0" ffw SELECT 218th SITE J a4at rPondHalksCreek Lkn. Miley., RAMEngineering, Inc. Select Homes 8721 218th St. SW Final Engineering and Drainage Report 2-Lot Short Plat RAM No. 15-032 October 11, 2016 Page F-2 F-3. Downstream Drainage Facility Map N% Id 111SR M Id 4198 tmt tt9R, fL58 0 0- 0 pC9Y ot�a °♦ M 0A, tvu o -OLO o It no; o 0 8tJ; 1,: ♦ o M any 4199 a M --'V7TW ' tsa Al Id 4188 e. N sT<c a w eN ~, a♦. 76G .. ,. ic,� 00 0,, t W�h ab*-- .-, 1069 rb C 769 in ' t F ♦ tb ., ac 166 ` 'r4`.R <4q� �0L S tV } ' o ♦ 'o s a M aaV 4106 oar -.,,. W anb N 's Q D 1 � btx,• +Ob- .u: 0 z O N a zuF, N 192ndAv y 92nd Ave W ot(. r.- IhY CZ AA anV P=£6 LL W W Co 3 ° z LL n , gp azr ,h G c -. Bn Id Pi56 t+,. RAMEngineering, Inc. Final Engineering and Drainage Report RAM No. 15-032 Select Homes 8721 218th St. SW 2-Lot Short Plat October 11, 2016 Page F-3 G. GRADING & EROSION CONTROL SUMMARY: This project will require grading to construct the proposed buildings and utilities (including the stormwater detention 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 NRCS Web Soil Survey the on -site soils consist of Alderwood-Urban land complex- 2% to 8% (soil #5). Alderwood soils are moderately well drained soil on till plains formed in glacial till and are categorized as a hydrologic group C soil (see full description attached). The Alderwood till soils are typically not suitable for infiltration of stormwater. 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. Final Engineering and Drainage Report RAM No. 15-032 Select Homes 8721 218th St. SW 2-Lot Short Plat October 11, 2016 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. Grading Quantity Approximation: The below listed grading quantities have been estimated using the AutoCAD 3D modeling of the site; estimated quantities are for permitting purposes only. Estimated grading site development quantities: Cut: 500 CY Fill: 500 CY Conclusion: The final site development construction plans will 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. Final Engineering and Drainage Report RAM No. 15-032 Select Homes 8721 218th St. SW 2-Lot Short Plat October 11, 2016 Page G-2 G-3 Soils Map (NRCS Web Soil Survey) } Sal KV--Snohomish County Area. WWhM'On s n r. cr � .1M .Y. 1. q rm5al.: i,acolatmo,Aw�eaetssxul>�. n €r 1. a i a ,s as reR 0 10 20 ro 6a MvwbmA repaa:uaal...wnwr Ma �SD1 Natural Re3ourccs Web $oit Survey 2/,tt20t8 5 Conserveuon "Mce Natwnal CoWerallve Sal Server Page t W 3 sbpes Totals for Area of Interest 0 b 100.0% RAMEngineering, Inc. Final Engineering and Drainage Report RAM No. 15-032 Select Homes 8721 218th St. SW 2-Lot Short Plat October 11, 2016 Page G-3 SOIL SURVEY OF SNOHOMISH COUNTY AREA, WASHINGTON UNITED STATES DEPARTMENT OF AGRICULTURE, SOIL CONSERVATION SERVICE Alderwood -Urban land complex, (soil #5- 2 to 8 percent slopes) This moderately well drained soil is on till plains. It is moderately deep over a hardpan. The soil formed in glacial till. Areas are long and narrow. They are about 125 acres in size. The native vegetation is mainly conifers and hardwoods. Elevation is 50 to 550 feet. The average annual precipitation is about 40 inches, the average annual air temperature is about 50 degrees F, and the average frost -free season is 170 to 190 days. Typically, the surface layer is very dark grayish brown gravelly sandy loam about 7 inches thick. The upper part of the subsoil is dark yellowish brown and dark brown very gravelly sandy loam about 23 inches thick. The lower part is olive brown very gravelly sandy loam about 5 inches thick. A weakly cemented hardpan is at a depth of about 35 inches. Depth to the hardpan ranges from 20 to 40 inches. Included in this unit are small areas of soils that have a stony or bouldery surface layer and areas of McKenna soils, Norma soils, and Terric Medisaprists in drainageways on plains. Also included are small areas of Everett, Indianola, and Ragnar soils on terraces and outwash plains. Included areas make up about 15 percent of the total acreage. Permeability of this Alderwood soil is moderately rapid above the hardpan and very slow through it. Available water capacity is low. Effective rooting depth is 20 to 40 inches. Runoff is slow, and the hazard of water erosion is slight. A seasonal perched water table is at a depth of 18 to 36 inches from January to March. This unit is used mainly for urban development and as woodland. It is also used for hay and pasture. Douglas -fir is the main woodland species on this unit. On the basis of a 100-year site curve, the mean site index is 142. On the basis of a 50-year site curve, the mean site index is 108. The mean annual increment at culmination (CMAI) for Douglas -fir at age 65 is 148 cubic feet per acre. Among the trees of limited extent are western red cedar, western hemlock, and red alder. Among the common forest under story plants are salal, evergreen huckleberry, Oregon -grape, bracken fern, and western sword fern. This unit is well suited to year-round logging. Logging roads require suitable surfacing for year-round use. Rock for road construction is not readily available on this unit, but gravel is available in areas of adjacent Everett soils. Brush competition is the main limitation for the production of timber. Reforestation can be accomplished by planting Douglas -fir seedlings. If seed trees are present, natural reforestation of cut over areas by red alder occurs periodically. When openings are made in the canopy, invading brushy plants, if not controlled, can prevent the establishment of seedlings. Because the rooting depth is restricted by a cemented pan, trees are subject to windthrow. This unit is suited to hay and pasture. The main limitations are the low available water capacity and the weakly cemented hardpan, which limits the use of the soil in this unit for deep-rooted plants. Grazing when the soil is wet results in compaction of the surface layer, poor tilth, and excessive runoff. The main limitations for homesites and septic tank absorption fields are the depth to the weakly cemented hardpan and wetness because of seasonal high water table. Effluent from absorption fields flows laterally above the hardpan and may seep at the bottom of slopes. Drainage is needed if buildings with basements and crawl spaces are constructed. During construction, disturbed areas need to be seeded and runoff controlled to protect the soil from erosion. Temporary sediment basins can be used in construction areas to reduce the amount of sediment in runoff water. This map unit is in capability subclass IVe RAMEngineering, Inc. Final Engineering and Drainage Report RAM No. 15-032 Select Homes 8721 218th St. SW 2-Lot Short Plat October 11, 2016 Page G-4 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 Storage Detention Tank System. The onsite detention system consists of an underground detention tanks on each individual lots. Onsite storm water runoff from the impervious surfaces are routed to the detention tank and discharged to the City's storm pipe system in 218th St SW. The detention tank is a typical component of a storm water control system for new development. Standard maintenance procedures should be followed. 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. Final Engineering and Drainage Report RAM No. 15-032 Select Homes 8721 218th St. SW 2-Lot Short Plat October 11, 2016 Page H-1 No. 3 —Closed Detention Systems (TanksNaults) Maintenance Component Defect Conditions When Maintenance is Needed Results Expected When Maintenance is Performed Storage Area Plugged Air Vents One-half of the cross section of a vent is blocked at any point or the vent is damaged. Vents open and functioning. Debris and Sediment Accumulated sediment depth exceeds 10% of the diameter of the storage area for 1/2 All sediment and debris removed from length of storage vault or any point depth storage area. exceeds 15% of diameter. (Example: 72-inch storage tank would require cleaning when sediment reaches depth of 7 inches for more than 112 length of tank.) Joints Between Tank/Pipe Section Any openings or voids allowing material to be transported into facility. (Will require engineering analysis to All joint between tank/pipe sections are sealed. determine structural stability). Tank Pipe Bent Out of Shape Any part of tankipipe is bent out of shape more than 10% of its design shape. (Review required by engineer to determine structural Tank/pipe repaired or replaced to design. stability). Vault Structure Includes Cracks in Wall, Bottom, Damage to Frame and/or Top Slab Cracks wider than 1/2-inch and any evidence of soil particles entering the structure through the cracks, or maintenance/inspection personnel determines that the vault is not structurally Vault replaced or repaired to design specifications and is structurally sound. sound. Cracks wider than 1/2-inch at the joint of any No cracks more than inlet/outlet pipe or any evidence of soil particles entering the vault through the walls, 114-inch wide at the joint of the inlet/outlet pipe. Manhole Cover Not in Place Cover is missing or only partially in place. Any open manhole requires maintenance. Manhole is closed. Locking Mechanism Not Working Mechanism cannot be opened by one maintenance person with proper tools. Bolts into frame have less than 1/2 inch of thread Mechanism opens with proper tools. (may not apply to self-locking lids). Cover Difficult to Remove One maintenance person cannot remove lid after applying normal lifting pressure. Intent is to keep cover from sealing off access to Cover can be removed and reinstalled by one maintenance. maintenance person. Ladder Rungs Unsafe Ladder is unsafe due to missing rungs, misalignment, not securely attached to Ladder meets design standards. Allows structure wall, rust, or cracks. maintenance person safe access. Catch Basins See "Catch Basins" (No. 5) See "Catch Basins" (No. 5). See "Catch Basins" (No. 5). Volume V — Runoff Treatment B fPs — December 2014 4-36 RAMEngineering, Inc. Select Homes 8721 218th St. SW Final Engineering and Drainage Report RAM No. 15-032 2-Lot Short Plat October 11, 2016 Page H-2 No. 4 —Control Structure/Flow Restrictor Maintenance Defect Condition When Maintenance is Needed Results Expected Component When Maintenance is Performed General Trash and Debris (Includes Sediment) Material exceeds 25% of sump depth or 1 foot below orifice plate. Control structure orifice is not blocked. All trash and debris removed. Structural Damage Structure is not securely attached to manhole wall. Structure securely attached to wall and outlet pipe. Structure is not in upright position (allow up Structure in correct to 10% from plumb). position. Connections to outlet pipe are not watertight Connections to outlet and show signs of rust. pipe are water tight; structure repaired or replaced and works as designed. Any holes --other than designed holes --in the structure. Structure has no holes other than designed holes. Cleanout Gate Damaged or Missing Cleanout gate is not watertight or is missing. Gate is watertight and works as designed. Gate cannot be moved up and down by one Gate moves up and maintenance person. down easily and is watertight. Chain/rod leading to gate is missing or damaged. Chain is in place and works as designed. Gate is rusted over 50% of its surface area. Gate is repaired or replaced to meet design standards. Orifice Plate Damaged or Missing Control device is not working properly due to missing, out of place, or bent orifice plate. Plate is in place and works as designed. Obstructions Any trash, debris, sediment, or vegetation blocking the plate. Plate is free of all obstructions and works as designed. Overflow Pipe Obstructions Any trash or debris blocking (or having the potential of blocking) the overflow pipe. Pipe is free of all obstructions and works as designed. Manhole See "Closed Detention Systems" (No. 3). See "Closed Detention Systems" (No. 3). See "Closed Detention Systems" (No. 3). Catch Basin See "Catch Basins" (No. 5). See "Catch Basins" (No. 5). See "Catch Basins" 1 (No. 5). Volume V — Runoff Treatment B1YIPs — December 2014 4-37 RAMEngineering, Inc. Final Engineering and Drainage Report RAM No. 15-032 Select Homes 8721 218th St. SW 2-Lot Short Plat October 11, 2016 Page H-3 No. 5 — Catch Basins Maintenance Defect Conditions When Maintenance is Needed Results Expected When Component Maintenance is performed General Trash & Debris Trash or debris which is located immediately in front of the catch basin opening or is blocking inletting capacity of the basin by No Trash or debris located immediately in front of catch basin or on grate more than 10%. opening. Trash or debris (in the basin) that exceeds 60 percent of the sump depth as measured from No trash or debris in 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 a minimum of six inches clearance from the debris surface to the invert of the lowest pipe. Trash or debris in any inlet or outlet pipe Inlet and outlet pipes free blocking more than 1/3 of its height. of trash or debris. Dead animals or vegetation that could generate odors that could cause complaints No dead animals or vegetation present within or dangerous gases (e.g., methane). the catch basin. Sediment Sediment (in the basin) that exceeds 60 No sediment in the catch percent of the sump depth as measured from basin the bottom of basin to invert of the lowest pipe into or out of the basin, but in no case less than a minimum of 6 inches clearance from the sediment surface to the invert of the lowest pipe. Structure Top slab has holes larger than 2 square Top slab is free of holes Damage to inches or cracks wider than 1/4 inch and cracks. Frame and/or Top Slab (intent is to make sure no material is running into basin). Frame not sitting flush on top slab, i.e., Frame is sitting flush on separation of more than 3/4 inch of the frame from the top slab. Frame not securely the riser rings or top slab and firmly attached. attached Fractures or Cracks in Maintenance person judges that structure is unsound. Basin replaced or repaired to design standards. Basin Walls/ Bottom Grout fillet has separated or cracked wider Pipe is regrouted and than 1/2 inch and longer than 1 foot at the secure at basin wall. joint of any inlettoutlet pipe or any evidence of soil particles entering catch basin through cracks. Settlement/ Misalignment If failure of basin has created a safety, function, or design problem. Basin replaced or repaired to design standards. Vegetation Vegetation growing across and blocking more than 10% of the basin opening. No vegetation blocking opening to basin. 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 "Detention Ponds" (No. 1). No pollution present. and Pollution volume V — Runoff Treatment BMPs — December 2014 4-38 RAMEngineering, Inc. Final Engineering and Drainage Report RAM No. 15-032 Select Homes 8721 218th St. SW 2-Lot Short Plat October 11, 2016 Page H-4 No. 5 — Catch Basins Maintenance Defect Conditions When Maintenance is Needed Results Expected When Component Maintenance is performed Catch Basin Cover Not in Cover is missing or only partially in place. Catch basin cover is Cover Place Any open catch basin requires maintenance. closed Locking Mechanism Mechanism cannot be opened by one maintenance person with proper tools. Bolts Mechanism opens with proper tools. Not Working into frame have less than 112 inch of thread. Cover Difficult One maintenance person cannot remove lid Cover can be removed by to Remove after applying normal lifting pressure. one maintenance person. (Intent is keep cover from sealing off access to maintenance.) Ladder Ladder Rungs Unsafe Ladder is unsafe due to missing rungs, not securely attached to basin wall, Ladder meets design standards and allows misalignment, rust, cracks, or sharp edges. maintenance person safe access. Metal Grates Grate opening Grate with opening wider than 7/8 inch. Grate opening meets (If Applicable) Unsafe design standards. Trash and Trash and debris that is blocking more than Grate free of trash and Debris 20% of grate surface inletting capacity. debris. Damaged or Missing. Grate missing or broken member(s) of the grate. Grate is in place and I meets design standards. No. 6 — Debris Barriers (e.g., Trash Racks) Maintenance Defect Condition When Maintenance is Results Expected When Components Needed Maintenance is Performed General Trash and Trash or debris that is plugging more Barrier cleared to design flow Debris than 20% of the openings in the barrier. capacity. Metal Damaged/ Bars are bent out of shape more than 3 Bars in place with no bends more Missing inches. than 3/4 inch. Bars. Bars are missing or entire barrier Bars in place according to design. missing. Bars are loose and rust is causing 50% Barrier replaced or repaired to deterioration to any part of barrier. design standards. InlettOutlet Debris barrier missing or not attached to Barrier firmly attached to pipe Pipe pipe Volume V — Runoff Treatment BMPs — December 2014 4-39 RAMEngineering, Inc. Final Engineering and Drainage Report RAM No. 15-032 Select Homes 8721 218th St. SW 2-Lot Short Plat October 11, 2016 Page H-5