Loading...
Staff Report Attachments 4-5.pdfCity of Edmonds PLN20180024 `t ` I 121�8 - �12�17 �N' ; 121�3. A206 �,. Legend 0 ReZones 1 \` � a PRD Plan Overlays Activity Center 1140 112 \ . 1 �\\ �\\ \ Corridor Development L j p r I Hi -Rise Node L — PPark School Zoning \\ t • • �' NA RSW-12 RS-20 RS-MP %� S �` �� \ RM-3 1\103 \ �� �� \\ �x\1`a` RM-EW +. BD2 �` '\\\•C`\\ ��' \`` ; �\ 3D4 3D5 \. \=j \` \ �'�\` �\� �� 1: 1,652 O Notes 0 68.85 137.7 Feet WGS_1984_Web_Mercator_Auxiliary_Sphere © City of Edmonds This map is a user generated static output from an Internet mapping site and is for reference only. Data layers that appear on this map may or may not be accurate, current, or otherwise reliable. THIS MAP IS NOT TO BE USED FOR DESIGN OR CONSTRUCTION Select Homes 2-Lot Short Plat 1122 Olympic Ave. Select Homes Viewland Short Plat 2-Lot Short Plat 1122 Olympic Avenue Edmonds, WA 98020 Storm Drainage Report Prepared for: Select Homes Date: March 26, 2018 Revised: May 24, 2018 G �v��opGo��z�a S/24/2012 Prepared by: Rob Long, PE RAM ngineering, nc. 16531 13t" Ave W, Suite A108, Lynnwood WA 98037 (425) 678-6960 RAMengineeringinc.com Job No. 16-001 ATTACHMENT 5 Select Homes Viewland Short Plat 1122 Olympic Avenue Edmonds, WA 98020 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 east side of Olympic Ave and south of Viewland Way, in the northeast 1/4 of Section 24, T 27 N, R 3 E, W.M. Site Address: 1122 Olympic Avenue Applicant: Select Homes Edmonds, WA 98020 16513 13th Ave W, Suite A108, Lynnwood WA 98037 Tax Parcel Number: 005489-000-019-03 Contact: Kayla Clark (425) 742-6044 TABLE OF CONTENTS SECTION PAGES A. Project Summary............................................................................................................................... 2 B. Parcel (Vicinity) Map......................................................................................................................... 1 C. Site Plan............................................................................................................................................. 1 D. Aerial Photo....................................................................................................................................... 1 E. Stormwater Control System Summary.............................................................................................. 6 F. Drainage Basin Description and Maps.............................................................................................. 3 G. Grading and Erosion Control Summary (SWPPP Evaluation)............................................................ 2 H. Operation and Maintenance Guidelines............................................................................................ 3 I. Geotechnical Engineering Report..................................................................................................... 1 RAMEngineering, Inc. RAM No. 16-001 Page i Select Homes Viewland Short Plat Stormwater Site Plan Report A. PROJECT SUMMARY: This report provides engineering information for the proposed construction of a single-family residential 2-Lot short plat on a 24,350 sf (0.56 ac) lot; the project is located at 1122 Olympic Avenue in the City of Edmonds. The applicant, Select Homes proposes to remove the existing residence and all existing hard surface to construct two single family residences on the project site. This report provides the evaluation for the proposed 2-lot single-family residence development. Summary of Minimum Requirements for Category 1 Project: Minimum Requirement #1 — Preparation of Stormwater Site Plan. The proposed site development consists of disturbing about 0.56 acres of land and creating/replacing about 9,990 sf (greater than 5,000 sf) of hard surface area. Thus, the project is classified as a Category 2 project per the City's classification system. Per ECDC 18.30, Category 2 projects must comply with Minimum Requirements No. 1 through No. 9. The civil site development plans and this report have been prepared to address the projects impacts. Minimum Requirement #2 — Construction Stormwater Pollution Prevention (SWPPP). A construction Stormwater Pollution Prevention Plan (SWPPP) has 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 E. The total site disturbance area of the project is less than one acre, thus a formal Notice of Intent application for NPDES coverage will not be made to the Department of Ecology. The grading quantities are estimated to be 100 CY of cut and 100 CY of fill. 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. RAMEngineering, Inc. Select Homes Viewland Short Plat RAM No. 16-001 Stormwater Site Plan Report Page A-1 Minimum Requirement #4 —Preservation of Natural Drainage Systems and Outfalls. The site generally slopes in a westerly direction, stormwater leaving the site would sheet flow westerly to Olympic Ave and enter the stormwater pipe and catchbasin system along the easterly side of Olympic Ave. Discharge flows for the developed site will either continue to sheet flow (lower lawn areas) or will be tight -line (roof and yard drains) into a storm system along the east side of Olympic Ave. The proposed site development will maintain the natural drainage outfall of the site (stormwater system along the easterly side of Olympic Ave). The local stormwater system within Olympic Ave discharges westerly to Hindley Creek and eventually discharges to the Puget Sound about 0.7 miles from the site. The site is located within the Hindley Creek watershed basin per the City of Edmonds maps, see section C for additional discussion of the downstream system. Minimum Requirement #5 — Onsite Stormwater Management. A site specific geotechnical evaluation of the site recommends two stormwater BMPs for the site; BMP T5.13: Post -Construction Soil Quality and Depth and BMP T5.10C: Perforated Stub -out Connections based on the site's soil conditions. In accordance with Edmonds Code, lawn and landscape areas will be managed by post -construction soil quality and depth (soil amendments); roof tops will be managed by perforated stub -out connections; and other hard surfaces will be managed by detention a pipe designed in accordance with the Edmonds Stormwater Addendum. See civil site development plans and Section Cfor additional stormwater BMP evaluation 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 hard surface onsite. The project will create about 1,815 sf pollution generation hard surfaces (driveways and frontage improvements); 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. 5.7 Minimum Requirement #7— Flow Control. The project does not propose to create/replace more than 10,000 sf of effective imperious surfaces, or convert 0.75 acres or more of vegetation to lawn or landscape. The 0.56 acer project proposed to create/replace 9,990 sf of hard surface; thus exempt from flow control per ECDC 18.30.060.D.7.b. As discussed above each lot will implement BMP T5.13: Post - Construction Soil Quality and Depth; BMP T5.10C: Perforated Stub -out Connections; and install a detention a pipe (per Edmonds Stormwater Addendum) onsite stormwater management BMPs. 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. Select Homes Viewland Short Plat RAM No. 16-001 Stormwater Site Plan Report Page A-2 B. PARCEL (VICINITY) MAP Gumlin t0'h s—%WL IWtGii N v 1 ...... NE 24 27 3 C2 G� L.1 sww� — ROW 0�,W I*.A00 kla<+ W+tw 0-Mo Lot Vx ROW loth [.wm.N 44— hh— Ww Ot", Sub&, — V�. Lot 3) He SP 5.11,19, S 5 ONE 0%11 iul, ..'e' 7 o COND 11 Q41 ".4-11 A $I Sw SR 52• U4 g 3 ON) A IRE rHIJRT'T-1--1 I O;f 01116 IN 3 1 1 6RACKET7 LAND0jG RD 24, 12 J6C ,awn SP 'I lit PT WAY 13 , I I PUGCT SOUND 11 0 (19 49430? 3 "Ll �-- �• VIEW M 4�4 --.— — VIEW ADD, ,, PUGET z 18 u 1 01 Ni FE 4 1 20 'N IA78IR VIEW EI.STATES 01 J A 2 MACHINERY DEPOT TR lot a It WIP YATES -y 4 3 2 V' v W jr�R."R t C. NOR V ME 1. NO V IN TrSiLL.ea 2 to 9 0511 118 02 2T O 01 SP S.fg to 11 I�711 CIO&GNr- S A lift — 13 • 10 it 12 oA 01 as C4 V1 EK' QVz E= 02 ' is 07 (11 4 L W 0ot . . C' 17 1615 li....... IrTEP, I , —1. ...— -- -- Is 04 q7 0; VISTA I 07 01 ' Lu z 31 IR� W. OF 03 21 ile 01 1. . 15 AW& III es us 1 14019 -WAM OR A 0 fi 03 2W CAROL 'NAY SP s4ou!'.) 1! 5 271 1756j to&; s "A7:4.1 11. �11 S-2.31 i 1. 2 2 0 GLEN cl: F 72 SSGO1 4 63 it 4 4 ST 'A 71 f'] T-7 F 1 7 �p .1 SE-24-2743 RAMEngineering, Inc. RAM No. 16-001 Page B- I Select Homes Viewland Short Plat Stormwater Site Plan Report C. SITE PLAN N •,_I, vrl.4 �a r;., rrtr1,.,rs I• ,.. amn � srr•u.r fir. ay.. ( �uc•cvl. Cwu11 bNfl •a — =I T ♦`. > F a lI> I1 _ - � I ' � /A'.�<:ao e Ca_ � I d .M', C '"f � .�I� i IKi n;' • nY v ,c.i .. -.._. � . .�— �,_� __ C" •1 Ce 4jv I��f ISM hr � ' o VIEWLAND WAY •.na__ _ _ �ri o f I. IiS I• � _yam _ n• car s a_{. i:1 ('_ _ =v I r= _ - .. ..SGs „<'X2 { ( ro VDrrY .T• wrY ruw • °...4.ee4t �� //��/� 6' :•.., x'IG I Fs ,Gi - 11 r42M2^ 4'.4 � , '$r i __�� (.if♦�I � �'�.. I-(/Y /ADI : r'.0 , 19 !si +, PW A]C PIY r>q/ly tDW61Nv ,.e0J J5 ! tS) _ { saes N ua cor r a In V uvao /YIw01a �i{ £�.1 /W'Kutl RAW 191q Nro O IY (� /, wui LONER iK 7l000t Ire Li • a rp N eC.A` F PAO^O$w HOUSE .•"N' .fly ! MAM,I 17100 f { 1 LOMER fF 165003 cor 1 co,z I• a 1p 0* (_; Q i. i ara 1 •l�lr T.r� t' MD.� �/ OOIMGR>1 1 j .: I'" rl ,u sa1.ul two •rn 1.r ':f I ���/7LTW!___ �1•+'_.My4v1 �1 aI IIyy�1 � We X9. r ,, a'•'sre.n FNlnva� 1 •' I 'O � lly ` �—SIi•3/r- 'ie V baiII11. r ':;.i:o:•Gria � -� 4u•H+? ( I nC,OI aV `.ra e,1,'eJ e'f.•3ir5'w Y _ i i--SS-+_"'•... ;..fl..-..y—at.._�. ...�y..r..-'•M. ss Sf +,�. a ai�� .1�eNJY• J:•.�'r;, . '1:•4 iie � s,o,•ae o nl ..�,I�� ; :. 1..• 1 tI.1[d � e��s�e Is1,M1f>t% \ Zrr. F/T� tt V':'.4� a •. •. ( ( { �•( r ,IALe '•4i.; c:s(v5(� v': Lv f.�iNi' >hii Cl'sri4r x9�rtl�5.: • /N: .r4/ � •r'IrA: •i •:J ': i { ' .. �.: i Y ,.a'µivT ..-. it �'� •`� " I t tf raACr to 111rOCTSOONOMACH)WOr M-01 fAVA AV- I11,410 vW1.91, P-111 RAMEngineering, Inc. RAM No. 16-001 Page C-1 Select Homes Viewland Short Plat Stormwater Site Plan Report D. AERIAL PHOTO (City of Edmonds GIS, 2015 photo) RAMEngineering, Inc RAM No. 16-001 Page D-1 Select Homes Viewland Short Plat Stormwater Site Plan Report E. STORMWATER CONTROL SYSTEM SUMMARY AND CALCULATIONS: Developed Conditions. The proposed project includes the construction of two single residence and associated driveway and utilities. 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. The project proposes to create and/or replace 9,995 sf of hard surface with the complete site development (Lot 1 =4,280 sf, Lot 2 = 3,930 sf, and 1,785 sf of frontage improvements). All existing onsite hard surface will be removed with the project site development. The following is a summary of the proposed new/replaced hard surface areas: Hard Surface Summary: Lot 1 (House 3,620 + Driveway 610 + Sidewalk/Patio 50) = 4,280 sf Lot 2 (House 3,190 + Driveway 610 + Sidewalk/Patio 130) = 3,930 sf Right -of -Way (Road 595 + Sidewalk 1,190) = 1,785 sf Lot Hard Surface = 9,995 sf (0.229 ac) In accordance with the Edmonds City Code (18.30) Category 2 projects shall meet MR 5 and provide on - site stormwater management. To meet these criteria, the proposed hard surfaces of the site shall implement BMPs from "List No. 2" or meet the LID performance standard. The attached geotechnical evaluation letter assesses the feasibility criteria of each stormwater BMP; per the evaluation only BMP T5.10C: Perforated Stub -out Connections, and BMP T5.13: Post -Construction Soil Quality and Depth are considered feasible (dispersion, infiltration, rain gardens, and bioretention are all considered infeasible). The proposed 3,620 sf (Lot 1) and 3,190 sf (Lot 2) roof areas (less than 5,000 sf each), will be collected and routed through individual lot perforated stub -out prior to discharging from the site; and thus, will be considered a manage hard surface and no other BMPs are necessary for the roof area. The driveway, patio and walk ways and frontage improvement areas ("other hard surfaces") will total 3,185 sf (lot 1= 660 sf, lot 2 = 740 sf, frontage = 1,785 sf). A detention a pipe designed in accordance with the Edmonds Stormwater Addendum will be installed to manage the "other hard surfaces" proposed. In accordance with the Edmonds Stormwater Addendum (Section 6.3), 61 feet of 24" detention pipe will mitigate the 3,185 sf of other hard surface area (L = 0.019 x 3,185 = 60.5 ft). A detention pipe will be installed along the westerly boundary of the site to manage the additional proposed "other hard surfaces". Some of the hard surfaces of the project's frontage improvements will bypass the collection system of the onsite detention pipe. The below frontage area exhibit demonstrates that additional run-on from Viewland Way street will be collected and adequately compensate/swap for the non -collected frontage improvements. 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). R.4MEngineering, Inc Select Homes Viewland Short Plat RAM No. 16-001 Stormwater Site Plan Report Page E-1 Frontage Area Exhibit: 1 � �y� l�/69M(✓F Np aEtGl-!P'S nH-iGF7.Pl5d— a Vot.U.1f," i.i, PACF."OA 'r CW C 156.,f (5 eO r n1 Cewsmucr Culls' UPSTREAI.1 GurfR t 97K" S� I e' CavC It 15e.19 RU11011 AREA 1,7J0 SF EX CASFO CMCPErE x r 1 Yaq ww wof 7' e" CGVC Ir7j" 1 e" COY C Q ter ry ,7• PIC Y IA9,71 !�alr I 1 AMASS CAP MM R� ICP r3D 177 I e' •� - c1 f P e'PW 1tE Mft CDOID 11or KRY MY D.L XAi$ lW SfPUCR1RE !941 CP *AMP f _ S'Gy SD — BY -PASS —' '- PROJECT AREA zoo SF s x 16410.(a r aI; VIEWLANO WAY { cu+: n rc vA .� t�r —3}vt yo' r- _ l rop fa." - R.t ter-e• OW c� fa- coreT n•s1(+q � I RrrtACE'rx �. Ir cave IE r9s.r. �r,-- - r?'CaSC re ISSr1f eS— _ =f 6. 09NC +E IS9.61 S -- _ v11AI1 r' WA frA % I i-rY a�rP uAtltE wnI 1- A o. EX CASED C(WCRETF ! , (� 10• Py�1C ug1+7Y /-/{y— MAI£R urgR 6• P4C C 1.nm (CJ C.uavummr wM ' lASpgNr J �_,_/ MA 7£R e" PtC f f9J.J5 ts INYERIED NAA �• MAW MY(gY,IrY cdryc11a1 SrWS 10-EACH L0r RIR 15 72 V_ C RV 1NLE1 ' B+ 2F56P156.77 (W f-E) • I .al ! 6[7 PROPOSED HOUSE $ a 1�YrG II °'"E 1 mwYrCPON 4A/N FF roo.ao LONER FF 180.003 R4MEngineering, Inc. Select Homes Viewland Short Plat RAM No. 16-001 Stormwater Site Plan Report Page E-2 Attached below are the DOE summary criteria of BMP T5.10C: Perforated Stub -out Connections and BMP T5.13: Post -Construction Soil Quality and Depth. 3.1.3 Perforated Stub -Out Connections (BMP T6.10C) A perforated stub -out connection is a length of perforated pipe within a gravel -filled trench that is placed between roof donznspouts and a stab -out to the local drainage system. Firrure 3.1.8 illustrates a perforated stub -out connection. These systems are intended to provide some infiltration during drier months During the vet hinter months. they may provide little or no flow control. Applications S Perforated snub -outs are not appropriate when seasonal water table is less Lintitations than one foot below trench bottom. In projects subject to Mitumtuu Requacinent :5 (see Volume F). perforated stub -out connections may be used only when all other higher priority on -site stornni water management BMPs are not feasible. per the criteria for each of those BMPs Select the location of the connection to allow a maximum amount of runoff to infiltrate into the ground (ideally a dry. relatively well drained. location). To facilitate nnalntenance. do not locate the perforated pipe portion of the system under uupervious or heavily compacted (e.g.. driveways and parking areas) surfaces. Use the same setbacks as for infiltration trenches in Section 3.1.1. Have a licensed geologist, hydrogeologist_ or engineering geologist evaluate potential runoff discharges towards landslide hazard areas. Do not place the perforated portion of the pipe on or above slopes greater than 20% or above erosion hazard areas without evaluation by a professional engineer with geoteclmical expertise or qualified geologist and jurisdiction approval. For sites with septic systems. the perforated portion of the pipe must be dowrngradieru of the dianifield prunary and reserve areas. Tills requirement can be waived if site topography will clearly prohibit flows from intersecting the drainfneld or where site conditions (soil permeability. distance between systems. etc.) indicate that this is unnecessary. Design Criteria Perforated stub -out connections consist of at least 10 feet of perforated pule per 5.000 square feet of roof area laid in a level. 2-foot wide trench backfilled with washed drain rock. Extend the drain rock to a depth of at least 8 Inches below the bottom of the pipe and cover the pipe. Lay the pipe level and cover the rock trench with filter fabric and 6 inches of fill (see Figure 3.1.8). Runoff.11odel Any flow reduction is variable and unpredictable. No computer modeling Represeutarion techniques are allowed that would predict any reduction in flow rates and volumes from the connected area. i oli me III - Hydrologic Anat.sis and Flo►r Controi BAIPs - December 2014 3-17 RAMEngineering, Inc Select Homes Viewland Short Plat RAM No. 16-001 Stormwater Site Plan Report Page E-3 _ . rrwom ri •' P+e Pb •o e o �o o• r•r• •re � :. � °• ere � :; -� 21•mn� TRENCH X•SECT14M NTS w losd drrYrpr gym$ zx+n wvW "nch WWP+w PLAN nEW OF BQQ NTS Source: King County Figure 3.1.8 - Perforated Stub -Out Connection Volume HI —Hydrologic Anolrsis and Flow Control BAIPs —December 2014 3-18 RAMEngineering, Inc. RAM No. 16-001 Page E-4 Select Homes Viewland Short Plat Stormwater Site Plan Report BMP T5.13: Post -Construction Soil Quality and Depth Purpose and Nattrally occurring (undisturbed) soil and vegetation provide important Definition sto1 invater functions including: hater infiltration: nutrient. sediment. and pollutant adsorption. sedinent and pollutant biofiltration: water interflow storage and transmission: and pollutant decomposition, These functions are largely lost when development strips away native soil and vegetation and replaces it with nnininnal topsoil and sod. Not only are these important stonnwater function,, lost. but such landscapes themselves become pollution generating pervious surfaces due to increased use of pesticides. fertilizers and other landscaping and household industrial chemicals. the concentration of pet \wastes, and pollutants that accompany roadside litter. Establishing soil quality and depth regains greater stortllwater functions in the post development landscape. provides increased treatment of pollutants and sediments that result froin development and habitation. and lnni iiinizes the need for sonic landscaping clnenlicals. thus reducing pollution through prevention. Applications and Establishing a nnininnuunn soil quality and depth is not the same as Limitations preservation of naturally occurring soil and vegetation. However. establishing a niilinlum soil quality and depth will provide improved oil - site management of stortnuvater flow and water quality. Soil organic matter can be attained through numerous materials such as compost. cornposted woody material. biosolids. and forest product residuals. It is important that the materials used to meet the soil quality and depth B11iP be appropriate and beneficial to the plant cover to be established. Likewise. it is important that imported topsoils improve soil conditions and do not have an excessive percent of clay fines. This BMP can be considered infeasible on till soil slopes greater than 33 Percent. Design Soil retention. Retain. in all undisturbed state. the duff layer and Guidelines dative topsoil to the inaxinnuu extent practicable. In any areas requiring grading remove and stockpile the duff layer and topsoil on site in a designated. controlled area. not adjacent to public resources and critical areas. to be reapplied to other portions of the site ,,,-here feasible. RAMEngineering, Inc. RAM No. 16-001 • Soil quality. All areas subject to clearing and grading that have not been covered by impervious surface. incorporated into a drainage facility or engineered as structural fill or slope shall. at project completion. denlorlstrate the following: 1. A topsoil layer with a ininirnunn organic platter content of 10% dry weight in planting beds. and 5% or'gallic platter content in turf areas. and a pH from 6.0 to 8.0 or matching the pH of the undisturbed soil. The topsoil layer shall have a mirlinlnrnn depth of Yolunre V — Runoff Tr eannent BVIPs — December 2014 5-S Page E-5 Select Homes Viewland Short Plat Stormwater Site Plan Report RAMEngineering, Inc. RAM No. 16-001 eight inches except where tree roots limit the depth of incorporation of amendments needed to meet the criteria. Subsoils belotl• the topsoil layer should be scarified at least 4 inches with some incorporation of the upper material to avoid stratified layers. n•here feasible. 2. Mulch planting beds with 3 inches of organic material 3. Use compost and other materials that ineet these organic content requirements: a. The organic content for -'pre-approved" amendment rates can be met only using compost meeting the compost specification for Bioretention (BMP T7.30). with the exception that the compost may have up to 3 5% biosolids or manure. The compost must also have an organic matter content of 40% to 65%. and a carbon to nitrogen ratio below 25:1. The carbon to nitrogen ratio may be as high as 35:1 for plantings composed entirely of plants native to the Puget .Sound Lowlands regiorn. - b. Calculated annendiuent rates may be met through use of composted material meeting (a.) above: or other organic naterials amended to meet the carbon to nitrogen ratio requirements. and not exceeding the contaminant lirnnits Identified in Table 220-B. Testing Parameters. in WAC 173- 350-220. The resulting soil should be conducive to the type of vegetation to be established. • Implementation Options: The soil quality design -guidelines listed above can be met by using one of the inethods listed below: 1. Leave undisturbed nature vegetation and soil, and protect from compaction during construction. �. Amend existing site topsoil or subsoil either at default "pre - approved" rates. or at custom calculated rates based on tests of the soil and amendment. 3. Stockpile existing topsoil dtuing grad ng. and replace it prior to planting. Stockpiled topsoil must also be amended if needed to meet the organic nnatter or depth requirements. either at a default --pre-approved" rate or at a custom calculated rate. 4, Import topsoil nux of sufficient organic content and depth to ineet the requirements. More than one method inay be used on different portions of the same site. Soil that already meets the depth and organic matter quality standards. and is not connpaeted. does not need to be amended. Voltnne V — Runoff Treannent B IPs — December 2014 5-0 Page E-6 Select Homes Viewland Short Plat Stormwater Site Plan Report Planning/Pernnitt Local goveitunents are encouraged to adopt guidelines quid ing/Inspection/Ve procedures similar to those reconuneuded in Guidelines and rification Resom ces Fo• Bnplementing Soil Qnaliry and Depth BMP T5.13 in Guidelines & WDOE Sr01711iaater Management Manual fo• Westem Washington_ Procedures This document is available at: llttty'\\'\\'\\'.SO11Sf01'Sa1111011.01'apdf Soil BINiP Manual.udf Maintenance Establish soil quality and depth toward the end of construction and once established. protect from compaction. such as from large machinery use. and from erosion. • Plant vegetation and mulch the amended soil area after installation. • Leave plant debris or its equivalent on the soil surface to replenish organic matter. • Reduce and adjust. where possible. the use of irrigation. fertilizers. herbicides and pesticides. rather than continuing to implement formerly established practices. Runoff Model Areas meeting the design guidelines may be entered into approved runoff Representation models as "Pasture" rather than "Lawn." RAMEngineering, Inc. RAM No. 16-001 Floe reduction credits can be taken in runoff modeling when BMP T5.13 is used as part of a dispersion design under the conditions described in: BMP'r5.IUB Downspout Dispersion B\1P T5.11 Concentrated Flow Dispersion BMP T5.12 Sheet Flow Dispersion B%1P T5.1 S Reverse Slope Side\\'alks BMP T5.30 Full Dispersion (for public road projects) Volmone V - Rmmnoff Treatment BVM - December 2014 5-10 Page E-7 Select Homes Viewland Short Plat Stormwater Site Plan Report F. DRAINAGE BASIN DESCRIPTION: The site is located within the City of Edmonds Hindley Creek watershed basin. The Hindley Creek basin is a centralized urban basin that collects stormwater runoff from primarily residential areas in the City Edmonds and ultimately discharges westerly to Puget Sound via the Hindley and Shell Creek (see attached watershed map). Site stormwater runoff leaves the site as sheet -flow, flowing in a westerly direction to Olympic Ave collecting in the stormwater conveyance pipe system along the easterly side of Olympic Ave. The pipe and catch basin system along Olympic Avenue flows north to the southeast corner of Olympic Ave and Viewland Way (near the site's northwest corner) and is directed west under Olympic Ave down Viewland Way. The stormwater system continues west along the south side of Edmonds Elementary School and under 9t" Ave N eventually daylighting into Hindley Creek about 1,450 feet west of the site. Hindley Creek continues west and merges with Shell Creek about 0.5 miles from the site and then ultimately discharges to the Puget Sound about 0.7 miles from the site. Minor areas of run-on from the residential properties east of the site may occur; however, these flows are primarily from lawn areas and are considered insignificant. No apparent flooding or system inadequacies within downstream of the site were discovered during site visits or research of the downstream system. See attached watershed and downstream drainage facility map for the local downstream path. RAMEngineering, Inc. RAM No. 16-001 Page F-1 Select Homes Viewland Short Plat Stormwater Site Plan Report F-2. Watershed Basin Map FIGURE B-1 CITY OF EDMONDS WATERSHEDS Dm Creek Perrinvilisr Edmonds Marsh Pullet Sound Edmonds My j Puget SOWW Piped fnikdde C- Shall OVA I Good HW Pend Sh*lWWW Halt Creek Southwest Edmonds A Wridley Creek i Souttwesit Edmonds 6 LAW ""we" somiouse 0*0 hind's Gulch Talbot Perk A Meadowdelle A Talbot Park 6 —I Meadowdsle 6 f -7 Terrace Cisio Lu(WsGulch Me.idowdale A j Meadowdato 8 sv ClutfalI Creek5bli Ouse Creep L Terrace Creek NonfOreism �l Westgate Pond OWall Creek VAllow Creek P nVille Puget sound 4 1 M - 2.000ift 1,Albot Pa M wb," air ON ZWL kvu&v amumev. ftnsix w mwchw,-Wkv Mamh M 2010 FS I T El TorootPark e Rultdale rthWeafri !Mindley Good Hope Pond ugelt Sound P.;)L d idnioild" Mnh st S%V hp; :.West ate Pond Halt-, Crv(4. RAM Engineering, Inc. Select Homes Viewland Short Plat RAM No. 16-001 Stormwater Site Plan Report Page F-2 F-3. Downstream Drainage Facility Map (City of Edmonds GIS) RAMEngineering, Inc. RAM No. 16-001 Page F-3 T- Select Homes Viewland Short Plat Stormwater Site Plan Report G. GRADING and EROSION CONTROL SUMMARY: The project will require grading to construct the proposed buildings and utilities (including the stormwater infiltration trench systems). 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 silty sand with gravel (Unified Soil Classification System: SM) outwash deposits. Overall soil relative density increases with depth. Per geologic mapping the subject site is underlain by outwash (Qva) deposits, however the near -surface conditions observed at the test pit locations were generally not consistent with outwash soils. Areas of fill, up to five feet deep were discovered in geotechnical test pits conducted onsite. Earth Solutions NW, LLC. recommends the limited use of the stormwater BMPs (Post -Construction Soil Quality and Depth BMP T5.13 and Perforated Stub - out Connections BMP T5.10C) due to the existing fill soils present on site. A full soils description is included in the 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: Mork Clearing Limits: Clearing limits have been delineated on the engineering site development plans. Element 2: Establish Construction Access: A construction access has been delineated on the engineering site development plans. Element 3: Control Flow Rates: During construction silt fencing will provide attenuation of site runoff and upon project completion and stabilization (established lawns and landscape of exposed soils), the infiltration storm system will provide flow control. Element 4: Install Sediment Controls: Filter fabric fence has been delineated and detailed on the engineering site development plans. At a minimum, silt fence will be installed along the down gradient perimeter of the disturbed area that will receive sediment -laden runoff. Element 5: Stabilize Soils: Soils will be stabilized per the TESC notes listed on the engineering site development plans. RAMEngineering, Inc. Select Homes Viewland Short Plat RAM No. 16-001 Stormwater Site Plan Report Page G-1 Element 6: Protect Slopes: Exposed slopes shall be stabilized per the TESC notes listed on the engineering site development plans. Element 7: Protect Drain Inlets: Drain inlet protection will be installed on all catch basins that will receive sediment -laden runoff. See the engineering site development plans for locations and detail. Element 8: Stabilize Channels and Outlets: This element is not applicable since there are no temporary channels or outlets proposed. 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: L All temporary and permanent erosion and sediment control BMPs shall be inspected, maintained and repaired in accordance with the Drainage Manual or as approved or required by the City to assure continued performance of their intended function in accordance with BMP specifications. ii. The applicant may remove temporary BMPs when they are no longer needed. iii. All temporary erosion and sediment control BMPs shall be removed within 30 days after construction is completed and the City has determined that the site is stabilized. Element 12: Manage the Project: The owner of the site is responsible for managing the installation and maintenance of the site BMPs. Element 13. Protect Low Impact Development BMPs: Compaction (i.e. vehicle and equipment traffic or storage; and/or placement of stockpiles) to the soils in the area of the stormwater BMPs (Post -Construction Soil Quality and Depth BMP T5.13 and Perforated Stub -out Connections BMP T5.10C) shall be avoided during construction. 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: 100 CY Fill: 100 CY 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. RAM Engineering, Inc Select Homes Viewland Short Plat RAM No. 16-001 Stormwater Site Plan Report Page G-2 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 stormwater BMP 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 an area might indicate a downstream blockage. Overtopping of the drain systems at the catch -basins is an indication that maintenance is required. The following pages outline standard general maintenance criteria for the project's drainage facilities. For additional and updated maintenance information visit the Washington State Department of Ecology's web -site at: http://www.ecy.wa.gov/programs/wq/wghome.htmI MAINTENANCE REQUIREMENTS ECDC Section 18.30.090 requires privately -owned stonnwater management facilities, such as LID BMPs be properly maintained. The owner of the property is the responsible party for sueh maintenance. The system nmst 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 enforcentent provisions the City can use to ensure the system is properly maintained. RAMEngineering, Inc Select Homes Viewland Short Plat RAM No. 16-001 Stormwater Site Plan Report Page H-1 No. 3—Closed Detention Systems (Tan ksNau Its) 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 1/2length 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 tank/pipe 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 voider 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. 1/4-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 112 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 BMPs — December 2014 4-36 RAMEngineering, Inc Select Homes Viewland Short Plat RAM No. 16-001 Stormwater Site Plan Report 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 and show signs of rust Connections to outlet pipe are watertight; 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). 1 See "Catch Basins" (No. 5). RAMEngineering, Inc. RAM No. 16-001 Volume V — Runoff Treatment BMPs — December 2014 4-37 Page H-3 Select Homes Viewland Short Plat Stormwater Site Plan Report 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 No Trash or debris located immediately in front of blocking inletting capacity of the basin by 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 or dangerous gases (e.g., methane), No dead animals or vegetation present within 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 Damage to Top slab has holes larger than 2 square inches or cracks wider than 114 inch Top slab is free of holes 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., separation of more than 3/4 inch of the frame from the top slab. Frame not securely Frame is sitting flush on 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 than 1/2 inch and longer than 1 foot at the Pipe is regrouted and secure at basin wall. joint of any inlet/outlet 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 that is more than six inches tall and less than No vegetation or root growth present six inches apart. Contamination See "Detention Ponds" (No. 1). No pollution present and Pollution RAMEngineering, Inc RAM No. 16-001 Volume V— Runoff Treatment BMPs— December 2014 4-38 Page H-4 Select Homes Viewland Short Plat Stormwater Site Plan Report No. 5 — Catch Basins Maintenance Defect Conditions When Maintenance is Needed Results Expected When Component Maintenance is performed Catch Basin Cover Cover Not in Place Cover is missing or only partially in place. Any open catch basin requires maintenance. Catch basin cover is 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 1/2 inch of thread. Cover Difficult to Remove One maintenance person cannot remove lid after applying normal lifting pressure. Cover can be removed by 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, misalignment, rust, cracks, or sharp edges. Ladder meets design standards and allows maintenance person safe access. Metal Grates (If Applicable) Grate opening Unsafe Grate with opening wider than 718 inch. Grate opening meets design standards. Trash and Debris Trash and debris that is blocking more than 20% of grate surface inletting capacity. Grate free of trash and debris. Damaged or Missing. Grate missing or broken member(s) of the grate. Grate is in place and 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/ Missing Bars are bent out of shape more than 3 inches Bars in place with no bends more 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. Inlet/Outlet Debris barrier missing or not attached to Barrier firmly attached to pipe Pipe pipe RAM Engineering, Inc. RAM No. 16-001 Volume V — Runoff Treatment BMPs —December 2014 4-39 Page H-5 Select Homes Viewland Short Plat Stormwater Site Plan Report No. 7 — Energy Dissipaters Maintenance Defect Conditions When Maintenance is Results Expected When Components Needed Maintenance is Performed External: Rock Pad f.tissing or Only one layer of rock exists above Rock pad replaced to design Moved Rock native soil in area fire square feet or standards - larger, or any exposure of native soil Erosion Soil erosion in or adjacent to rock pad Rock pad replaced to design standards Dispersion Trench Pipe ACCU1111.1lated sediment that exceeds Pipe cl eanediflu shed so that it Plugged v.ith 201% of the design depth. matches design Sediment Not Visual evidence of water discharging at Trench redesigned or rebuilt to Discharging concentrated points along trench (normal standards. Water condition is a 'sheet flow"of water along Property trench). Intent is to prevent erosion damage. Perforations Over 1/2 of perforations in pipe are Perforated pipe cleaned or Plugged. plugged with debris and sediment replaced. Water Flows Maintenance person observes or Facility rebuilt or redesigned to Out Top of receives credible report of water flowing standards `Distributor out during any storm less than the design Catch Basin. storm or its causing or appears likely to cause damage. Receiving Water in receiving area is causing or has No danger of landslides. Area Over- potential of causing landslide problems Saturated internal- Manhole/Chamber Worn or Structure dissipating flow deteriorates to Structure replaced to design Damaged 112 of original size or any concentrated standards. Post, worn spot exceeding one square toot Baffles, Side which would make structure Unsound, of Chamber Other See "Catch Basins" (No, 5). See "Catch Basins" (No. 5), Defects RAM Engineering, Inc RAM No. 16-001 Volrone V — Rrmoff Treatment B.11Ps — Decembe?- 2014 4-40 Page H-6 Select Homes Viewland Short Plat Stormwater Site Plan Report I. GEOTECHNICAL ENGINEERING REPORT Geotechnical Engineering Study. Prepared by: Earth Solutions NW, LLC Date: June 8, 2017, Updated March 24, 2018 (under separate cover) RAMEngineering, Inc. RAM No. 16-001 Page 1-1 Select Homes Viewland Short Plat Stormwater Site Plan Report