Loading...
APPROVED-Stormwater Report 2020-06-25BLD2020-0412 8912192 nd St SW Single Family Residence Edmonds, WA 98026 Stormwater Site Plan Report Prepared for: Deborah Binder and Gaetan Veilleux Date: April 17, 2020 Revised: June 25, 2020 RESUB Jun 25 2020 CITY OF EDMONDS DEVELOPMENT SERVICES DEPARTMENT COMPLIES WITH APPLICABLE go WA.8�� l� d 36508 9W \IDNAL��� 0/25/2020 Prepared by: Rob Long, PE STORMWATER NOTE: BY DESIGN, THIS SITE ACCEPTS RUNOFF FROM THE ADJACENT PRIVATE ACCESS ROAD/DRIVEWAY. BY PROCEEDING WITH CONSTRUCTION OF THE IMPROVEMENTS SHOWN HEREIN, THE APPLICANT ACKNOWLEDGES THIS CONDITIONS AND THE RESULTING REQUIREMENT TO MANAGE THE IMPACTS AND AGREES TO CONVEY SUCH INFORMATION TO SUBSEQUENT OWNERS, SUCCESSORS, OR ASSIGNED. RAM Enqineerinq, Inc. 16531 13t" Ave W, Suite A108, Lynnwood WA 98037 (425) 678-6960 RAMengineeringinc.com Job No. 20-001 8912192nd St SW Single Family Residence Introduction: This summary report provides site design information for a single-family residential lot development by Deborah Binder and Gaetan Veilleux. This report includes storm drainage analysis to support permit review and approval. The property is located at 8912 192nd Street SW, in the southwest 1/4 of Section 18, T 27 N, R 4 E, W.M. Site Address: 8912 192nd Street SW Edmonds, WA 98026 Tax Parcel Number: 270418 003 037 00 Applicant: Deborah Binder and Gaetan Veilleux 8816 207th Place SW Edmonds WA 98026 TABLE OF CONTENTS SECTION PAGES A. Project Overview.............................................................................................................................. 5 B. Existing Conditions Summary........................................................................................................... 2 C. Developed Site Hydrology.............................................................................................................. 22 D. Soils Report..................................................................................................................................... 21 E. Construction SWPPPP Requirements................................................................................................ 2 F. Operation and Maintenance Guidelines.......................................................................................... 10 RAM-noineering, Inc. 8912 192nd Street SW RAM No. 20-001 Stormwater Site Plan Report A. PROJECT OVERVIEW. This report provides engineering information for the proposed construction of a single-family residence on an 12,075 sf (0.28 ac) lot; the project is located at 9812 192nd Street SW in the City of Edmonds. The applicant, Deborah Binder and Gaetan Veilleux proposes to remove an existing house and all existing hard surface to construct one single family residence on the project site. This report provides the evaluation for the proposed single family residence development. Summary of Minimum Requirements for Category 2 Project: Minimum Requirement #1 —Preparation of Storm water Site Plan. The proposed site development consists of disturbing about 0.30 acres of land and creating/replacing about 5,246 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. Minimum Requirement #3 —Source Control of Pollution. Specific source controls are not required for single family residential sites. General requirements for these sites include preventing the discharge of pollutants to the City's storm drainage system per Edmonds City Code Chapter 7.200 (Illicit Discharges). This includes common household items such as pesticides, herbicides, fertilizers, detergents and fluids from vehicle maintenance. Single family residences shall incorporate DOE's S411 BMPs for landscape and lawn vegetation management. Lawn and vegetation management can include control of objectionable weeds, insects, mold, bacteria, and other pests with pesticides. Examples include weed control on golf course lawns, access roads, and utility corridors and during landscaping; sap stain and insect control on lumber and logs; rooftop moss removal; killing nuisance rodents; fungicide application to patio decks, and residential lawn/plant care. It is possible to release toxic pesticides such as pentachlorophenol, carbamates, and organometallics to the environment by leaching and dripping from treated parts, container leaks, product misuse, and outside storage of pesticide contaminated materials and equipment. Poor management of the vegetation and poor application of pesticides or fertilizers can cause appreciable stormwater contamination. Minimum Requirement #4 — Preservation of Natural Drainage Systems and Outfalls. The site generally slopes in a northerly towards 192nd Street SW right-of-way. There are no concentrated flows or existing defined conveyance systems located onsite, any site runoff leaves the site as sheet -flow. Discharge of site stormwater to 192nd Street SW will be maintained by the project. The site is located within the upper reach of the Fruitdale watershed basin per the City of Edmonds maps (see section C). RAMEngineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page A-1 Minimum Requirement #5—OnsiteStormwaterManagement. Asite-specificgeotechnical evaluation (see section D) of the site demonstrates that an infiltration trench is not recommended onsite due to the underlying site soils. The subsurface soils generally consisted of surficial undocumented fill soils underlain by silty fine to medium sand with varying amounts of gravel and iron -oxide weathering interpreted as native glacial soils at relatively shallow depths. Onsite stormwater BMPs to be implemented consists of Perforated Stub -out Connections (BMP T5.10C) and Sheet Flow Dispersion (BMP T5.12) for hard surfaces; and Post - Construction Soil Quality and Depth (BMP T5.13) for pervious surfaces are considered feasible stormwater BMPs for the site development. See LID BMP feasibility evaluation table (below), civil site development plans and Section Cfor additional stormwater BMP evaluation and construction details. Minimum Requirement #6 — Runoff Treatment. The project does not propose to create/replace more than 5,000 sf of pollution -generation impervious surface onsite. The project will create about 955 sf pollution generation hard surfaces (driveway and private road areas); 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. Minimum Requirement #7— Flow Control. The project will not exceed any of the required thresholds to provide flow control onsite. In accordance with ECDC 18.30.060.D.7 there are three thresholds: 1) Projects in which the total of effective impervious surfaces is 10,000 square feet or more in a threshold discharge area, or The project total new and replace effective impervious surfaces is 5,246 sf. 2) Projects that convert 0.75 acres or more of vegetation to lawn or landscape, or convert 2.5 acres or more of native vegetation to pasture in a threshold discharge area, and from which there is a surface discharge in a natural or man-made conveyance system from the site, or The site is currently developed with an existing single-family residence and there are no native vegetation areas onsite. 3) Projects that through a combination of hard surfaces and converted vegetation areas cause a 0.10 cubic feet per second (cfs) increase or greater in the 100-year flow frequency from a threshold discharge area as estimated using the Western Washington Hydrology Model or other approved model and one -hour time steps (or a 0.15 cfs increase or greater using 15-minute time steps). The existing house onsite was constructed in 1930 per public records (prior to 1977) and thus will be included in the as a predevelopment condition. WWHM modeling calculations demonstrate that the 100-year flow frequency from the proposed development (0.014 cfs) does not increased by more than 0.10 cfs. See WWHM modeling calculations provided in Section C below. Minimum Requirement #8 — Wetland Protection. No wetlands are known to exist on or adjacent to the site. RAMEngineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page A-2 Minimum Requirement #9 — Operation and Maintenance. An operation and maintenance summary is provided in section H. LID BMP Performance Standards Evaluation Lawn and landscaped areas: BMP Viable Limitations / Infeasibility Criteria BMP T5.13: Post -Construction Soil Quality and Depth Limitation: Considered infeasible on slopes greater than 33 (Volume V, Chapter 5) Yes percent are present., BMP T5.13 shall be applied to the site post construction. Roofs: BMP T5.30: Full Dispersion Infeasibility: Comprehensive Plan and Zoning minimum (Volume V, Chapter 5) No density requirements do not allow for large native vegetation retention and flow path areas (100 ft) need to meet full dispersion requirements. Infeasibility: The underlying soils consists of undocumented BMP T5.10A: Downspout Full Infiltration Systems No fills, moist with iron -oxide weathering; tested infiltration (Volume III, Chapter 3) capacity is very low. See additional discussion in the geotechnical evaluation by Nelson Geotechnical Associates. Bioretention Infeasibility: The underlying soils consists of undocumented (Volume V, Chapter 7) No fills, moist with iron -oxide weathering; tested infiltration capacity is very low. BMP : Downspout Dispersion Systems Not feasible due to the required expansive trench length and (Voluumeme 1I11II, Chapter 3) No dispersion area that is required (10 ft per 700 sf of roof, 55+ ft for 3,896 sf of roof) BMP T5.10C: Perforated Stub -out Yes Is feasible due to the relatively shallow depth that a (Volume III, Chapter 3) perorated stub -out could be constructed. Detention vaults or pipes in accordance with the Yes A shallow detention tank system is feasible onsite. Edmonds Stormwoter Addendum Other Hard Surfaces: BMP T5.30: Full Dispersion No See BMP T5.30 dispersion infeasibility discussion above. (Volume V, Chapter 5) BMP T5.15: Permeable Pavement Infeasibility: The underlying soils consists of undocumented (Volume V, Chapter 5) No fills, moist with iron -oxide weathering (evidence of high seasonal ground water). Infeasibility: The underlying soils consists of undocumented Bioretention (Volume V, Chapter 7) No fills, moist with iron -oxide weathering (evidence of high seasonal ground water). BMP T5.12: Sheet Flow Dispersion Yes Sheet flow dispersion for the walkway and patio areas that BMP T5.11: Concentrated Flow Dispersion require a minimum 10-foot vegetative flow path is feasible (Volume V, Chapter 5) RAMEngineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page A-3 Parcel (Vicinity) Map: QUARTER SECTION TUWN814P N W-B.✓_ RANGE E.W.M., SW 18 ZT 4 _ CerNerllneLot Bock —•- Section ----- Ciry LFnits r - Ga Lot ..- Sul lv — ROW — Quarter _ _--- Tax Acct •"'Al S11..:'�.. - -. •:. - Major water other Lot ------- Vac Row - - - - 16lh ---- Easement n-U— M� K..e..,,.�rr.....:. -Lnx3xmirh f'xuutl', Aa.l.ingrxn Mirror Water Other 5uhdiv � Vac Lot NW-18-27-04 &211S T,7e 01 _ D4 t i a ,T.»,....�..��.� ... a „ . � 03 _ _ :-a8 07 Q5 ,..� P� ol�oaa 6 . a 1t1is tl5 .. A1Ms...�..�.�,.��. f ..,»,..,.�. - 06! 01 »...., vei=_u-xrt�°r,, 03 - 0 2 ❑2 06 a Ol OS ; _ QS Q 05 w _ 02 ? N 03 02 2 t 12 7 22 P3 2d:`y07 tACT{83 91 675 E 2 SW _ FINOYER._�-. __—.- _—_g5� -i£ TJ---�488TN_$7HA�2aN 1 W 2 3 6 Ja 9 10 W 0110•'10 145- R .S . R . - S ¢ I P 201 0046 �' ",• 01 {{ tY1 ! U4 p 48_ 04 a � F .... O1 2g - 2 to 02 i OZ 'x D1 HEAaali.T- Ix $ 5 g $ EIGHTS t1 «. SP8-2u�163 ..•w.w. i n »•••••.• .� ,.w�.n 7 W - 04 05 C. 32 03 7 i g 1T 18 = 21 7 3 07 3 W 1] SP S-28-8.,� �., j 12 8 GQ HOMELtAND 10 1 100 03 = y SH RO : H€IGHTS 22 1 2 ❑ + 12 """"•' tt a H DF �:: 4e = 04 t z s ` a s 12 ` to T5 .t 9 os W OSC EE a O ­} D7 :, . 26 G2 ': 6 m 11 fg 20 .» M gg [4r T�., Uz - 189TH- PL- SW a 8 DS jj06 _ H ! T54E 6 g »10 00 OS 09 S a }.17.v. t1 10 9 g= 7 S 1 2 3 a 5 -'h 08..,.. j 5 5a. _ iFi ' - 0B s 4.. 2 g t 9 - 07 u E - PL — 'N0= 2'- 15 - BIpR ES TES 728fi) {7260uy I -1-9JQTH ST 10 09 15 04, 03 D2 C2 04 �. ;„, . 02 D3 01 - ..,.,, - a H 1g r�., f wa ..,..,.. ,1-1.....,, '"• - i.�„��..� = -3D'75 11 'i t 9 [ 02 03 i Q$ FT 1d f 3 cn 49 .:,� 1 p7 a DB µ I ... :. v . ' - v Q4 HA O HAV N 12 s g ,..».,..»..... i tl5 _ �» 02 16 13 14 313 8 22 .S VIEjN t 1a 2 SITE w 2 r 7.,2 aa a 4'01 m 05 �wm 05 » 7B.. 05 01 - --'f915TP�- 6 SlJB BA N ` 04 i-••,••, i1 d ❑ 3 4 a 7918T 87SW ~,11 W q, 'y,N S UN 1 5 2 5 6 4 05 6 w.....».., 3�8 •�.,., "n7s'� 19 „» {87 } 23 .,. 05 fg ESTATES:NO2 10 CLL ., ¢ ❑7 _. DO 2 06 c- 02 pg t 2 . 2 Ww LC D7.,.m..�..�„ 29 . E.Sx DT N tU7^y4 ] 2 M 3 02 pg ..» i 06 06 _ EDMODS $EA VEWT C 4346 a s 1 aD5' as = 03 D5� ROT 07 201 012 5812} _ _ -t n SP 5- $ 00 8 m 2- 09 — --t -- — — -- -- --- -- --- 192W-D—SF.---SW. --- — —.--- m ui 4 a 02 - __ .- ...—. -i--- - 792iJ{] w rn' "v. x 53 3-007 2-008 3-0273.023 8 ��., 3p�x p5� S 2 S - % 'gQAg7 ill .�,._ .«.P.,.,..Ha _ .- 4 c� »ra.'SI,.. 3 2 t 3.070 . 3-069 _ 4 A e R r 3-W9 ?° 3-028 $ - 7 "t 3-083 ! .n g M 3-951 {..,.•......,,,....,... Si �; ..,3-005(` 3 134s 3-02T'.3-108; 3��. �.��i.��.�„.d..,...,., .•...,...,.,, S; t 3-059 _ .,...,.,.,,1 3-063 f 7 y 147-,..,.,v„d.............. �...... . .„..........al 3-D45 :3044 3, 088 v,.}..� ..,..= 4 s i......,M.,-..,... .-_-. t1 3-D19 3-025 3.022 = 3-038 3-043 »3 4 ---fit ^, 3-980 7 e 3-U�-066= 25' 2a 23 2P s g ..i«M.... a«.»,. ? 3-086 M =_ N'Y WOO❑ 6261 ....,..:�� ..-t767 ..,w..».,»I.. s q' EA g = a _�.�'�:� ,,::':" ..,.:.,.",. .....• I , yyILS N' "=w ' 3.072x ... jF .3-071.. .. 2S 13 1 5a ,."3P P E » 3-085 '- s 2 t 3-077 3-120i • • ....,.i,.... .. 4 rF, M _ "^"^"....M. 3-060 -1" 6= x� za ❑ ,a 3.065 »,�✓�-4 3-028 i 2 3 5 «............n„w, M3-087 57 x t TRACT (4346) gLA AFN 199912' 05 iP 8-12-31 n 1S 8408290222 58 D1 ,17 24 2 03 05 3-030 183ROPLSVV 3-12p :3.076 _ 1y o>, 15 y F 1 (6405j 3.018 3-135 11.•1fi .437 5 1 6 ° ' ..,.........M....,. s SP 0 94-62 18 :, 18 sPPLN1.2QlO•oo19 AD (61R6) 3-078 3-G08 4-008 IV A 62 5721 - - - - f 5 5-3-72 q N TR m1 3-112 3-094 M 3Pf EW _ Qfl 3074 TWIN FIRS APL L .., ............«.», t }} 7 i � s cv i 3-1G3 I 3 6 3-038 = 3.O5C a s 6 4 r3 4. 3-114 a 2' 1 _. SP �a^-3T- 8 9 T PL. . �..."....,. m.,.,,...., u7$ I z ?t 3.115'•... 4 H3 3-055 - .. :' B4ZH W �: ,,..,w,.�.,...........:�..,. 5 g I ..... ��.i..,.. ., i �1 srs &039 3-001 2 ,.3.n�- F .--1 3«105 4-tl24 5 s O 2 883E �ti. 3'•.. 3-0@fi COU T 3-076-�`','»" 6 s RO 3-051 �t 3-f23 2 3-033 3-032 ..��";=3.1?3- 1 6U19 a 'nFN 061+ = 3-128 .3_}2,q ; STERLING CREST 3-102 .N-p0`{ "R 7 IA CONS70) l890ij }.,.,.. a y4 a:.... ,........... -003,,.. �,... .•F• 3-003 n F 3-C73 4-023 ,N DMONOS T4ii'MNlMt7BL-t b9'EHYI7Y]- N W-19.27-04 RAM Engineering, Inc. RAM No. 20-001 PUGEr VI MAPLEWCOD 2-OOi RAC8[- 92} j f MANORs D11201i EI s _CONDOMINIUM s a02 a a 2 2- (4552) a � 28 1-14 006 7 ❑ ... 27 � 8912 192"°' Street SW Stormwater Site Plan Report Page A-4 Site Plan: RAMEngineering, Inc. 8912 192nd Street SW RAM No. 20-001 Stormwater Site Plan Report Page A-5 B. EXISTING CONDITIONS SUMMARY Existing Conditions. The total site consists of about 12,075 sf (0.28 acres) and is currently occupied by an existing single-family residence. The existing house and driveway are surrounded by grass lawn and landscape areas. The site is surrounded by single family residences to the west, south and east; and 192nd Street SW north (see attached aerial photo). The site generally slopes in the north/northwesterly direction in a range between 2% and 4%. No define drainage courses are found on -site and stormwater runoff would sheet flow in a north/northwesterly direction towards the 192nd Street SW right-of-way. No stream or wetlands were discovered on or immediately adjacent to the site. Additional discussion of the local drainage basin and downstream path is discussed in Section C of this report. Soils: In accordance with the project's site -specific geotechnical engineering evaluation by Nelson Geotechnical Associates, Inc the on -site subsurface soils generally consisted of surficial undocumented fill soils underlain by silty fine to medium sand with varying amounts of gravel and iron -oxide weathering interpreted as native glacial soils at relatively shallow depths. The investigation confirm that the site soils are generally consistent with Alderwood series soil (till). Full soils description is included in the project's site -specific geotechnical engineering study by Nelson Geotechnical Associates, Inc. Aerial Photo (City of Edmonds GIS, 2017 photo; includes pre-existing house onsite): RAMEngineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page 8-1 USDA Natural Resource Soil Conservation Service (NRCS) Web Soil Survey Map Unit Legend Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI 6 Alderwood-Urban land complex, 8 to 15 percent slopes 4.3 100.0 Totals for Area of Interest 0.3 100.0% RAM Engineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page 8-2 C. DEVELOPED SITE HYDROLOTY. Developed Conditions. The proposed project includes the construction of a 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 5,246 sf of hard surface with the complete site development, all existing hard surface will be removed with the project site development. The following is a summary of the proposed site areas and the new/replaced hard surface areas: Project Area Summary: Lot Area = 12,075 sf Expanded off site Shared driveway (expand to min. 16') = 355 sf Total Site Development Area = 12,430 sf (0.285 Ac.) Pre -developed (pre-1977) Hard Surface = 4,045 sf (0.093 ac) Building Rooftop = 1,800 sf (0.041 ac) Uncovered Patio and Walk = 300 sf (0.007 ac) Onsite Driveway = 1,945 sf (0.045 ac) Pre -developed (pre-1977) Previous/Lawn = 8,385 sf (0.192 ac) Proposed Hard Surface = 5,246 sf (0.120 ac) Note: 995 SF of driveway would be Building Rooftop = 3,896 sf (0.089 ac) allowable as bypass per MR #5 (under P c�-355 sf (0.008 ac) 1,000 SF), but is actually routed through Onsite Driveway = 640 sf (0.015 ac) the perforated pipe connection in order Offsite Shared Driveway = 355 sf (0.008 ac to provide some degree of mitigation. Propose r a s a s a The following DOE 2012 Western Washington Hydrology Model (WWHM2012) continuous runoff model summary and calculations show that the increase in the 100-year storm event (0.014 cfs) is less than 0.10 cfs and thus full flow control is not required of the project. Stormwater Modeling Summary Table: Site Area 0.277 Acres Off -site Driveway Area 0.008 Acres Total Areas = 0.285 acres Soil Type(s) (see Geotechnical Report) Alderwood Series Soils (Till) Pre -Developed (pre-1977) 100-year Runoff Rates 0.064 cfs Developed 100-year Runoff Rates 0.078 cfs (0.014 cfs increase) R.4M Engineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page C-1 WWHM2012 PROJECT REPORT Project Name: 20-001 Site Flows Site Name: Binder-Veilleux Site Address: 8912 142nd ST SW City : Edmonds Report Date: 6/25/2020 MGS Regoin Puget East Data Start 1901/10/1 Data End : 2058/09/30 DOT Data Number: 03 Version Date: 2019/09/13 Version : 4.2.17 Low Flow Threshold for POC 1 : 50 Percent of the 2 Year High Flow Threshold for POC 1: 50 year PREDEVELOPED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Pasture, Flat .192 Pervious Total 0.192 Impervious Land Use acre ROOF TOPS FLAT 0.041 DRIVEWAYS FLAT 0.045 SIDEWALKS FLAT 0.007 Impervious Total 0.093 Basin Total 0.285 Element Flows To: Surface Interflow Groundwater MITIGATED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Pasture, Flat .165 Pervious Total 0.165 Impervious Land Use acre ROADS FLAT 0.008 ROOF TOPS FLAT 0.089 DRIVEWAYS FLAT 0.015 SIDEWALKS FLAT 0.008 Impervious Total 0.12 Basin Total 0.285 Element Flows To: Surface Interflow Groundwater RAM Engineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page C-2 ANALYSIS RESULTS Stream Protection Duration Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.192 Total Impervious Area:0.093 Mitigated Landuse Totals for POC #1 Total Pervious Area:0.165 Total Impervious Area:0.120 Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.025594 5 year 0.034451 10 year 0.040902 25 year 0.049746 50 year 0.056855 100 year 0.064425 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.031903 5 year 0.04261 10 year 0.050362 25 year 0.060939 50 year 0.069404 100 year 0.078387 611 10 01 LL Cumulative Probability µ+++++ + + + + +++xx 1.0 0.07 0 01 0.5 1 2 5 10 A 30 50 70 80 9U 95 1 99 99.5 1 Slream Rmw6on Daation I LID Or+alion Fhw Frsqudicy WAMr Rr y Hydrogrtph Welland Input Voirr�es WD Repo! Recharge Duelion R"Amfge Pr�edav-eloFed�Recharge Mitigated Analyze datasets Compact WDM J Oelde Se6ct.d f- Mmft FF I J e •r All DasasNs Flow j Slag. IPr.cy Evap PDG 1 Fiord Fregwncy Method r% Log Pearson Type 111 170 r Wea.i r' Ciuuaane r' Gr�.pweerr RAM Engineering, Inc. RAM No. 20-001 Flow Frequency n Flow(cfs) Predeveloped Mitigated 2 Year . 0.0236 0.0319 5 Year = 0.0345 0.0426 10 Year - 0.0409 0.0504 25 Year - 0.0491 0.06119 50 Year 0.0369 0.0694 100 Year 0.0644 0.0784 Annual Peaks 1902 0.0257 O.Oa32 1903 0.0289 0.0372 1904 0.0386 0.0472 1905 0.0168 0.0210 1906 0.0101 0.0229 1907 0.0290 0.U348 1908 0.0231 0.0287 1909 0.0265 0.0342 1910 0.0307 0.0365 1911 0.0252 0.0325 1912 0.0571 0.0667 1913 0.0187 0.0222 1914 0.0601 0.0771 1915 0.0175 0.0218 1916 0.0252 0.0325 1917 0.6160 0.0202 1918 0.0230 0.0296 1919 0.0153 0.0190 1920 0.0231 0.0285 1921 0.0185 0.0222 1922 0.0248 0.0300 1925 0.0253 0.0310 1924 0.0277 0.0357 1925 0.0161 0.0203 1926 0.0292 0.0376 1927 0.0221 0.0280 192e 0.0217 0.0269 1929 0.0321 0.0412 8912 192nd Street SW Stormwater Site Plan Report Page C-3 Stream Protection Duration Annual Peaks for Predeveloped and Mitigated Year Predeveloped Mitigated 1902 0.026 0.033 1903 0.029 0.037 1904 0.039 0.047 1905 0.017 0.021 1906 0.018 0.023 1907 0.029 0.035 1908 0.023 0.029 1909 0.026 0.034 1910 0.031 0.037 1911 0.025 0.032 1912 0.057 0.067 1913 0.019 0.022 1914 0.060 0.077 1915 0.017 0.022 1916 0.025 0.033 1917 0.016 0.020 1918 0.023 0.030 1919 0.015 0.019 1920 0.023 0.028 1921 0.018 0.022 1922 0.025 0.030 1923 0.025 0.031 1924 0.028 0.036 1925 0.016 0.020 1926 0.029 0.038 1927 0.022 0.028 1928 0.022 0.027 1929 0.032 0.041 1930 0.036 0.046 1931 0.019 0.024 1932 0.022 0.027 1933 0.021 0.025 1934 0.036 0.043 1935 0.018 0.022 1936 0.021 0.026 1937 0.032 0.038 1938 0.020 0.025 1939 0.024 0.031 1940 0.033 0.042 1941 0.027 0.035 1942 0.030 0.036 1943 0.029 0.038 1944 0.045 0.056 1945 0.029 0.037 1946 0.023 0.028 1947 0.018 0.024 1948 0.029 0.035 1949 0.037 0.048 1950 0.017 0.021 1951 0.025 0.032 1952 0.054 0.063 1953 0.050 0.060 1954 0.024 0.029 1955 0.020 0.025 1956 0.015 0.019 1957 0.022 0.027 1958 0.036 0.041 1959 0.030 0.037 1960 0.021 0.026 1961 0.059 0.075 1962 0.023 0.029 1963 0.016 0.020 POC #1 RAMEngineering, Inc. 8912 192nd Street SW RAM No. 20-001 Stormwater Site Plan Report Page C-4 1964 0.047 0.058 1965 0.029 0.035 1966 0.020 0.025 1967 0.024 0.029 1968 0.021 0.026 1969 0.024 0.029 1970 0.030 0.036 1971 0.032 0.038 1972 0.083 0.103 1973 0.041 0.053 1974 0.033 0.042 1975 0.046 0.054 1976 0.035 0.043 1977 0.015 0.019 1978 0.033 0.040 1979 0.024 0.031 1980 0.026 0.032 1981 0.027 0.034 1982 0.021 0.026 1983 0.030 0.037 1984 0.027 0.034 1985 0.027 0.034 1986 0.019 0.023 1987 0.028 0.033 1988 0.020 0.025 1989 0.017 0.022 1990 0.021 0.025 1991 0.029 0.037 1992 0.034 0.041 1993 0.033 0.043 1994 0.027 0.032 1995 0.015 0.020 1996 0.027 0.032 1997 0.020 0.026 1998 0.028 0.034 1999 0.026 0.034 2000 0.029 0.037 2001 0.024 0.031 2002 0.043 0.051 2003 0.022 0.026 2004 0.031 0.040 2005 0.046 0.058 2006 0.019 0.025 2007 0.027 0.035 2008 0.022 0.029 2009 0.022 0.028 2010 0.025 0.033 2011 0.017 0.023 2012 0.030 0.037 2013 0.021 0.026 2014 0.020 0.026 2015 0.047 0.055 2016 0.017 0.021 2017 0.038 0.048 2018 0.037 0.043 2019 0.047 0.054 2020 0.033 0.040 2021 0.031 0.038 2022 0.034 0.043 2023 0.036 0.047 2024 0.069 0.080 2025 0.020 0.026 2026 0.025 0.030 2027 0.027 0.034 2028 0.012 0.016 2029 0.023 0.028 2030 0.032 0.039 RAM Engineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page C-5 2031 0.014 0.018 2032 0.017 0.022 2033 0.018 0.023 2034 0.019 0.024 2035 0.032 0.038 2036 0.023 0.027 2037 0.025 0.032 2038 0.030 0.036 2039 0.039 0.050 2040 0.022 0.027 2041 0.025 0.031 2042 0.036 0.042 2043 0.031 0.040 2044 0.025 0.030 2045 0.023 0.028 2046 0.022 0.026 2047 0.026 0.033 2048 0.021 0.028 2049 0.032 0.041 2050 0.022 0.027 2051 0.039 0.047 2052 0.020 0.026 2053 0.021 0.027 2054 0.042 0.050 2055 0.021 0.027 2056 0.027 0.035 2057 0.018 0.022 2058 0.029 0.038 Stream Protection Duration Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.0835 0.1033 2 0.0688 0.0799 3 0.0601 0.0771 4 0.0595 0.0753 5 0.0571 0.0667 6 0.0537 0.0633 7 0.0505 0.0599 8 0.0472 0.0583 9 0.0470 0.0580 10 0.0469 0.0562 11 0.0458 0.0554 12 0.0457 0.0545 13 0.0453 0.0544 14 0.0428 0.0527 15 0.0421 0.0514 16 0.0409 0.0502 17 0.0389 0.0502 18 0.0389 0.0484 19 0.0386 0.0481 20 0.0375 0.0474 21 0.0373 0.0472 22 0.0373 0.0469 23 0.0363 0.0463 24 0.0362 0.0434 25 0.0359 0.0433 26 0.0358 0.0431 27 0.0357 0.0430 28 0.0353 0.0427 29 0.0337 0.0421 30 0.0336 0.0418 31 0.0334 0.0415 32 0.0332 0.0414 33 0.0331 0.0414 34 0.0330 0.0413 RAM Engineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page C-6 35 0.0327 0.0412 36 0.0325 0.0400 37 0.0323 0.0399 38 0.0321 0.0396 39 0.0321 0.0396 40 0.0319 0.0393 41 0.0318 0.0384 42 0.0312 0.0383 43 0.0309 0.0382 44 0.0308 0.0379 45 0.0307 0.0379 46 0.0305 0.0377 47 0.0301 0.0376 48 0.0300 0.0374 49 0.0299 0.0374 50 0.0298 0.0372 51 0.0296 0.0368 52 0.0295 0.0367 53 0.0294 0.0365 54 0.0294 0.0365 55 0.0292 0.0365 56 0.0292 0.0363 57 0.0290 0.0361 58 0.0290 0.0360 59 0.0289 0.0357 60 0.0287 0.0354 61 0.0285 0.0354 62 0.0284 0.0352 63 0.0281 0.0349 64 0.0277 0.0348 65 0.0275 0.0346 66 0.0274 0.0343 67 0.0273 0.0342 68 0.0272 0.0342 69 0.0271 0.0342 70 0.0269 0.0340 71 0.0269 0.0337 72 0.0268 0.0337 73 0.0265 0.0335 74 0.0265 0.0334 75 0.0261 0.0332 76 0.0259 0.0328 77 0.0259 0.0325 78 0.0257 0.0325 79 0.0254 0.0323 80 0.0253 0.0322 81 0.0252 0.0321 82 0.0252 0.0319 83 0.0252 0.0317 84 0.0249 0.0311 85 0.0249 0.0310 86 0.0248 0.0310 87 0.0247 0.0310 88 0.0245 0.0308 89 0.0242 0.0302 90 0.0240 0.0301 91 0.0240 0.0300 92 0.0238 0.0296 93 0.0238 0.0294 94 0.0238 0.0294 95 0.0234 0.0293 96 0.0231 0.0289 97 0.0231 0.0287 98 0.0230 0.0285 99 0.0230 0.0285 100 0.0228 0.0282 101 0.0226 0.0281 RAM Engineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page C-7 102 0.0225 0.0280 103 0.0224 0.0277 104 0.0222 0.0276 105 0.0221 0.0275 106 0.0220 0.0274 107 0.0219 0.0274 108 0.0218 0.0274 109 0.0218 0.0273 110 0.0218 0.0273 ill 0.0217 0.0273 112 0.0217 0.0271 113 0.0214 0.0269 114 0.0214 0.0265 115 0.0213 0.0264 116 0.0209 0.0264 117 0.0208 0.0263 118 0.0208 0.0262 119 0.0208 0.0262 120 0.0207 0.0258 121 0.0207 0.0258 122 0.0205 0.0257 123 0.0205 0.0256 124 0.0204 0.0255 125 0.0203 0.0254 126 0.0202 0.0253 127 0.0200 0.0250 128 0.0199 0.0248 129 0.0198 0.0247 130 0.0196 0.0247 131 0.0195 0.0245 132 0.0194 0.0244 133 0.0190 0.0238 134 0.0189 0.0237 135 0.0187 0.0231 136 0.0185 0.0229 137 0.0185 0.0228 138 0.0181 0.0225 139 0.0181 0.0223 140 0.0177 0.0222 141 0.0176 0.0222 142 0.0175 0.0222 143 0.0175 0.0218 144 0.0174 0.0216 145 0.0171 0.0215 146 0.0169 0.0213 147 0.0168 0.0210 148 0.0165 0.0207 149 0.0161 0.0203 150 0.0160 0.0202 151 0.0156 0.0201 152 0.0154 0.0199 153 0.0153 0.0191 154 0.0152 0.0190 155 0.0148 0.0186 156 0.0141 0.0181 157 0.0124 0.0159 Stream Protection Duration POC #1 The Facility FAILED Facility FAILED duration standard for 1+ flows. Flow(cfs) Predev Mit Percentage Pass/Fail 0.0128 2770 5195 187 Fail 0.0132 2437 4694 192 Fail RAM Engineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page C-8 0.0137 2179 4280 196 Fail 0.0141 1943 3910 201 Fail 0.0146 1722 3556 206 Fail 0.0150 1528 3242 212 Fail 0.0155 1371 2975 216 Fail 0.0159 1234 2713 219 Fail 0.0164 1091 2444 224 Fail 0.0168 985 2227 226 Fail 0.0172 882 2042 231 Fail 0.0177 800 1852 231 Fail 0.0181 727 1691 232 Fail 0.0186 671 1530 228 Fail 0.0190 623 1389 222 Fail 0.0195 566 1281 226 Fail 0.0199 523 1167 223 Fail 0.0204 488 1062 217 Fail 0.0208 442 976 220 Fail 0.0213 419 879 209 Fail 0.0217 389 818 210 Fail 0.0221 360 761 211 Fail 0.0226 336 703 209 Fail 0.0230 312 654 209 Fail 0.0235 292 608 208 Fail 0.0239 267 562 210 Fail 0.0244 243 524 215 Fail 0.0248 224 486 216 Fail 0.0253 213 458 215 Fail 0.0257 204 436 213 Fail 0.0261 182 414 227 Fail 0.0266 167 393 235 Fail 0.0270 155 373 240 Fail 0.0275 142 344 242 Fail 0.0279 132 320 242 Fail 0.0284 128 300 234 Fail 0.0288 117 285 243 Fail 0.0293 103 268 260 Fail 0.0297 97 251 258 Fail 0.0302 90 234 260 Fail 0.0306 83 226 272 Fail 0.0310 77 212 275 Fail 0.0315 71 204 287 Fail 0.0319 68 193 283 Fail 0.0324 61 182 298 Fail 0.0328 54 173 320 Fail 0.0333 50 162 324 Fail 0.0337 47 147 312 Fail 0.0342 43 138 320 Fail 0.0346 42 127 302 Fail 0.0350 41 118 287 Fail 0.0355 38 ill 292 Fail 0.0359 35 105 300 Fail 0.0364 32 101 315 Fail 0.0368 31 92 296 Fail 0.0373 29 87 300 Fail 0.0377 28 76 271 Fail 0.0382 28 69 246 Fail 0.0386 27 66 244 Fail 0.0391 25 65 260 Fail 0.0395 25 64 256 Fail 0.0399 24 59 245 Fail 0.0404 24 55 229 Fail 0.0408 22 55 250 Fail 0.0413 21 51 242 Fail 0.0417 20 45 225 Fail 0.0422 19 42 221 Fail 0.0426 19 41 215 Fail 0.0431 18 38 211 Fail RAM Engineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page C-9 0.0435 18 34 188 Fail 0.0439 18 32 177 Fail 0.0444 17 32 188 Fail 0.0448 16 32 200 Fail 0.0453 16 32 200 Fail 0.0457 15 32 213 Fail 0.0462 13 32 246 Fail 0.0466 13 31 238 Fail 0.0471 11 29 263 Fail 0.0475 10 26 260 Fail 0.0480 10 26 260 Fail 0.0484 10 25 250 Fail 0.0488 10 24 240 Fail 0.0493 10 23 230 Fail 0.0497 10 23 230 Fail 0.0502 10 22 220 Fail 0.0506 9 20 222 Fail 0.0511 9 20 222 Fail 0.0515 9 18 200 Fail 0.0520 8 18 225 Fail 0.0524 8 18 225 Fail 0.0528 8 17 212 Fail 0.0533 8 17 212 Fail 0.0537 7 17 242 Fail 0.0542 7 17 242 Fail 0.0546 7 15 214 Fail 0.0551 7 14 200 Fail 0.0555 7 13 185 Fail 0.0560 7 13 185 Fail 0.0564 6 12 200 Fail 0.0569 6 12 200 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 damages. Software Copyright © by : Clear Creek Solutions, Inc. 2005-2020; All Rights Reserved. RAM Engineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page C-10 Site LID BMP Analysis. In accordance with the Edmonds City Code (18.30) Category 2 projects shall meet MR 5 and MR 7 (see discussion in Section A above) and provide on -site stormwater management and flow control. To meet these criteria, the proposed hard surfaces of the site shall implement BMPs from "List No. 2" or meet the LID performance standard. Onsite stormwater BMPs to be implemented consists of Perforated Stub -out Connections (BMP T5.10C) and Sheet Flow Dispersion (BMP T5.12) for hard surfaces; and Post - Construction Soil Quality and Depth (BMP T5.13) for pervious surfaces are considered feasible stormwater BMPs for the site development. Attached are the DOE summary criteria of BMP T5.10C: Perforated Stub -out Connections, Sheet Flow Dispersion (BMP T5.12), and BMP T5.13: Post -Construction Soil Quality and Depth. BMP T5.10C: Perforated Stub -out Connections A perforated stub out connection is a length of perforated pipe within a gravel filled trench that is placed between roof downspouts and a stub out to the local drainage system. Figure V-4.7: Per- forated Stub -Out Connection illustrates a perforated stub out connection. These systems are inten- ded to provide some infiltration during drier months. During the wet winter months, they may provide little or no Flow Control. RAMEngineering, Inc. RAM No. 20-001 2019 Stormwater Management Manual for Western Washington Volume V - Chapter 4 - Page 719 8912 192nd Street SW Stormwater Site Plan Report Page C-11 Applications g Limitations Perforated stub -outs are not appropriate when the seasonal water table is less than one foot below the trench bottom. 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 maintenance. do not locate the per- forated pipe portion of the system under impervious or heavily compacted (e.g.. driveways and park- ing areas) surfaces. Use the same setbacks as for infiltration trenches in 6MP T5.10A: Downspout Full Infiltration. Have a licensed geologist. hydrogeologist. or engineering geologist evaluate potential runoff dis- charges 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 licensed engineer in the state of Washington with geotechnical expertise or qualified geologist and jurisdiction approval. For sites with septic systems. the perforated portion of the pipe must be downgradient of the drain - field primary and reserve areas. This requirement can be waived if site topography will clearly pro- hibit flows from intersecting the drainfiield 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 pipe 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 ftterfabric and 6 inches of Fill (see Figure V-4.7: Perforated Stub -Out Con- nection). Runoff Model Representation Any flow reducton is variable and unpredictable. No computer modeling techniques are allowed that would predict any reduction in flow rates and volumes from the connected area. RAM -ngineering, Inc. RAM No. 20-001 2019 Stormwater Management Manual for Western Washington Volume V - Chapter Q - Page 720 8912 192nd Street SW Stormwater Site Plan Report Page C-12 Figure V-4.7: Perforated Stub -Out Connection random Al 'r R'—� 9 ''� k't,%_ s A:14� filter fabric Trench X-Section SirspP r Plan View of Roof 1n rnarl dramagr. system 2' x 1 p' level trench yr per! pipe NOT TO SCALE Perforated Stub -Out Connection Revised dune2016 DEPRPTMENTOF ECOLOGY please see nf[p/Avwrv.B[y.1hp.QwhapyrVhl.hhnlfor copyright notice urcludog permissions, State of Washington bmWionofliabitly.and disdaimer. RAM Engineering, Inc. RAM No. 20-001 2019 Stormwater Management Manual for Western Washington Volume V - Chapter 4 - Page 721 8912 192nd Street SW Stormwater Site Plan Report Page C-13 BMP T5.12: Sheet Flaw Dispersion Purpose and Definition Sheet flow dispersion is the simplest method of runoff control. This BMP can be used for any imper- vious or pervious surface that is graded to avoid concentrating flows. Because flows are already dis- persed as they leave the surface, they need only traverse a narrow band of adjacent vegetation for effective on -site stormwatef management. Applications and Limitations Use this BMP for flat or moderately sloping (< 15% slope) surfaces such as driveways, sports courts, patios, roofs without gutters, lawns, pastures; or any situation where concentration of Flows can be avoided. Design Guidelines See Figure V-3.2: Sheet Flow Dispersion for Driveways for details for driveways. See BMP T5.1013: Downspout Dispersion Systems for dispersion trench design criteria. Provide a 2-foot-wide transition zone to discourage channeling between the edge of the imper- vious surface (or building eaves) and the downslope vegetation. This transition zone may con- sist of an extension of subgrade material (crushed rock), modular pavement, drain rock, or other material acceptable to the Local Plan Approval Authority. Provide a 10-foot-wide vegetated buffer for up to 20 feet of width of paved or impervious sur- face. Provide an additional 10 feet of vegetated buffer width for each additional 20 feet of impervious surface width or fraction thereof. For example, if a driveway is 30 feet wide and 60 feet long provide a 20-foot wide by 60-foot long vegetated buffer, with a 2-foot by 60-foot trans- ition zone. The design must not result in erosion or flooding of downstream properties. Runoff discharge toward landslide hazard areas must be evaluated by a geotechnical engin- eer or a qualified geologist. Do not allow sheet flow on or above slopes greater than 20%, or above erosion hazard areas, without evaluation by a geotechnicai engineer or qualified geo- logist and approval by the Local Plan Approval Authority. For sites with septic systems, the discharge area must be ten feet downgradient of the drain - field primary and reserve areas (VVAC 246-272A-0210). A Local Plan Approval Authority may waive this requirement if site topography clearly prohibits flows from intersecting the drain - field. Runoff Model Representation Where this BMP is used to disperse impervious area runoff into an undisturbed native landscape area or an area that meets SMP T5.13: Post -Construction Soil Quality and Depth, the impervious area should be modeled as a lateral flow impervious area. Do this in WWHM on the Mitigated RAM =ngineering, Inc. RAM No. 20-001 2019 Stormwater Management Manual for Western Washington Volume V - Chapter 3 - Page 692 8912 192nd Street SW Stormwater Site Plan Report Page C-14 Scenario screen by connecting the lateral flow impervious area element (representing the area that is dispersed) to the lawnflandscape lateral flow soil basin element (representing the area that will be used far dispersion). RAM =ngineering, Inc. RAM No. 20-001 2019 Stormwater- Management Manual for Westem Washington Volume V - Chapter 3 - Page 693 8912 192nd Street SW Stormwater Site Plan Report Page C-15 Figure V 3.2: Sheet Flaw Dispersion for Driveways Source: Ding County Department of Nalural Resources, 1993 � I T r S ILocate drain 25' from P RQVV 9 drivevray wI � slopes toard sheet. l sq, ft. max. between berm Drive" 510 e 1 1 "1 IUI ICYI V C3 I&`JE�S `_ ❑iagonol =�-_- 25'vegetated berm with flo npsth 25 dispersion ftrench Plan Driveway Dispersion Trench Driveway Slope Varies and Slopes Toward Street r J J Max. 2° Driveway � cross slope/ Slope I f ` --- 25' J Plan N� PP r i Sheet Flow Dispersion from a Drivewaye� Flat to Moderately Sloping Driveways Iliiilre in NOT TO SCALE Sheet Flow Dispersion for Driveways Revised December 2016 DEPART MENT OF ECOLOGYplease see htfp:lAvww-ecy wa.gov/copyright html for copyright notice including permissions, State of Washingtonl limitation of liability, and disclalmer. RAM Engineering, Inc. RAM No. 20-001 2019 Stormwater Management Manual for Western Washington Volume V - Chapter 3 - Page 694 8912 192nd Street SW Stormwater Site Plan Report Page C-16 BMP T5.13: Post -Construction Soil Duality and Depth Purpose and Definition Naturally occurring (undisturbed) soil and vegetation provide important stormwater functions includ- ing: water infiltration, nutrient, sediment, and pollutant adsorption. sediment and pollutant biofiltra- tion; water interflow storage and transmission; and pollutant decomposition. These functionsare largely lost when development strips away native soil and vegetation and replaces it with minimal top- soil and sod Not only are these important stormwater functions lost. but such landscapes them- selves 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 pol- lutants that accompany roadside litter. Establishing soil quality and depth regains greater stormwater functions in the post development landscape, provides increased treatment of pollutants and sediments that result from development and habitation, and minimizes the need for some landscaping chemicals, thus reducing pollution through prevention. Applications and Limitations Establishing a minimum soil quality and depth is not the same as preservation of naturally occurring soil and vegetation. However, establishing a minimum soil quality and depth will provide improved on -site management of stormwater flow and water quality. Soil organic matter can be attained through numerous materials such as compost, composted woody material. biosolids. and forest product residuals. It is important that the materials used to RAM =ngineering, Inc. RAM No. 20-001 2019 Stormwater Management Manual for Western Washington Volume V - Chapter 11- Page 927 8912 192nd Street SW Stormwater Site Plan Report Page C-17 meet this BM 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 Guidelines Soil Retention Retain, in an undisturbed state, the duff layer and native topsoil to the maximum extent practicable. In any areas requiring grading, remove and stockpile the duff layer and topsoil on site in a des- ignated, controlled area. not adjacent to public resources and critical areas. to be reapplied to other portions of the site where feasible. Soil Quality All areas subject to clearing and grading that have not been covered by impervious surface, incor- porated into a drainage facility or engineered as structural fill or slope shall. at project completion, demonstrate the following: A topsoil layer with a minimum organic matter content of 10% dry weight in planting beds. and 5% organic matter 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 minimum depth of eight inches except where tree roots limit the depth of incorporation of amendments needed to meet the criteria. Subsoils below the topsoil layer should be scarified at least 4 inches with some incorporation of the upper material to avoid stratified layers, where Feasible. 2. Mulch planting beds with 2 inches of organic material. 3. Use compost and other materials that meet the following organic content requirements: a. The organic content for "pre -approved" amendment rates can be met only using com- post meeting the compost specification for BMP T7.30: 6ioretention, with the exception that the compost may have up to 35% 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 region. Calculated amendment rates may be met through use of composted material meeting (a.) above: or other organic materials amended to meet the carbon to nitrogen ratio requirements, and not exceeding the contaminant limits identified in Table 220-B, Test- ing Parameters, in WAC 173-350-220. The resulting soil should be conducive to the type of vegetation to be established. 2019 Stormwater Management Manual for Western Washington RAM =ngineering, Inc. RAM No. 20-001 Volume V - Chapter 11 - Page 928 8912 192nd Street SW Stormwater Site Plan Report Page C-18 Implementation Options The soil quality design guidelines listed above can be met by using one of the methods listed below: 1. Leave undisturbed native vegetation and soil, and protect from compaction during con- struction. 2. Amend existing site topsoil or subsoil either at default "pre -approved" rates. or at custom cal- culated rates based on tests of the soil and amendment. 3. Stockpile existing topsoil during grading. and replace it prior to planting. Stockpiled topsoil must also be amended if needed to meet the organic matter or depth requirements, either at a default -pre-approved" rate or at a custom calculated rate. 4. Import topsoil mix of sufficient organic content and depth to meet the requirements. More than one method may be used on different portions of the same site. Soil that already meets the depth and organic matter quality standards, and is not compacted, does not need to be amended. PlanninglPermittingllnspectionNerification Guidelines 8 Procedures Local governments are encouraged to adopt guidelines and procedures similar to those recom- mended in Building Soil: Guidelines and Resources for Implementing Soil Quality and Depth BMP T5.13 in WDOE Stormwater Management Manual for Western Washington [Stenn et al.. 2016.} 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 Representation All areas meeting the sail quality and depth design criteria may be entered into approved runoff mod- els as -Pasture" rather than "Law nlLandscaping" 2019 Stormwater Management Manual for Western Washington RAM =ngineering, Inc. RAM No. 20-001 Volume V - Chapter 11 - Page 929 8912 192nd Street SW Stormwater Site Plan Report Page C-19 Figure V-11.1: Planting Bed Cross -Section Mulch Loose snit vnlh risible dark organic matter Looso or [raclured subsoil Reprinted f rom OvAI&AFnes and Rowarces For ImplamrintkV Solt Quakily and Depth BMP T5.13 in WDOE SAormwoter Management A0.3rrual for WeVern N47 70 SCALE WushingW. 2010. Washington Organic Recycling Council Planting Bed Cross -Section Revised June 2016 DEPARTVEfJT OF ECOLOGYPlease &ea htlplRv►avv.Bcy.wa.gpvlcpp"hf.h" for cnpyrighI nolice including permissions. State of Washmatonbrnoation oftiabiWy,and disckrirner. 2019 Stormwater Management Manual for Western Washington RAM Engineering, Inc. RAM No. 20-001 Volume V - Chapter 11 - Page 930 8912 192nd Street SW Stormwater Site Plan Report Page C-20 Offsite Analysis. The site is located within the City of Edmonds' "Fruitdale" watershed basin. The Fruitdale basin is a relatively small creek basin consisting of developed urban residential properties that discharge to the Puget Sound via Fruhda|e Creek. Runoff flows from the site sheet flow in a north/northwesterly direction 193"« Street SE. The pipe and catch basin system along 193"" STSE flows westerly and eventually discharges to the Puget Sound about U7Smiles from the site (see attached watershed map). See the below downstream drainage facility map and watershed map for the local downstream path. Downstream Drainage Facility Map (City ofEdmonds G|S) , � ` g \ ~ '" y ~ K,.=""LN! ^�� + � RAMEngineerin�Inc. RAM No. 20-001 `. � ... p~° ~^~~— 8912192" Sheet SW / M Page C-21 Watershed Basin Map N FIGURE B - 1 A CITY OF EDMONDS"`' N iLund:� Gulch`°% °•10'° WATERSHEDS 4 ® Deer creek Perrinville- - ® Edmonds Marsh _ Puget sound 1 Meadowdale A �---= Edmonds Way Puget Sound Piped Meadowdale H I� Fruitdale '_ _' Shell Creek Goad Hope Pond SheEfa6arger Halls Creek - Southwest Edmonds r�Y:;i� tearh sts % Hindley Creek ® Lake Bal€'roger Lund sGulch Southwest Edmonds B Stilthouse Creek - Talbot Park A Op II [reeRSGlouse Creek. ' MeadawdaleA Talbot Parka Terrace Creak• ! �_ Meadawdale B Terrace Creek j Narths[ream l_ Westgate Pond outfall Creek rr Willow Creek P 'nville o yom 2,om 4,000 r,000 apao i o feet Puget sound x Talbot Park A14 - Talbot Park B No warranty °I any sort. IrrcIudm9 e—n ,, farness, or mcrh bli ry _ MromPanY=reread $912 192nd St SW March 30, lm0 `� N �Fruitdale . a __ � -14h sl sw E. rthstream _ I zoom sr sw Handley Good Hope Pond 1 --^. quern ssw 'i -;,7trget Sound Piped- ozv� ` 'G I Edmonds Marsh aawanl^wv % - Shell Creek - ztzrh srsw i Shellabarger' j — ---------- ---- Westgate Pond Halls Crleek i� - r-------------=z:ornstsw------- T .. `Willow Creek j _ i zzatnsrsw� I" _l 'Deer Creek N,\ 23tnstsw 'a 3 Edmonds Way i i Sbuthwest Edmonds A .- Lake Ballinger Q rI Raetfi StSW Southwest Edmonds B �--------'--- -—- — -----— —-———-----..—- _----`--'----�zosn'susmm�..�w. RAM Engineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page C-22 D. SOILS REPORT. Geotechnical Engineering Evaluation Letter Prepared by: Nelson Geotechnical Associates, Inc Date: February 19, 2020 Pages: 20 RAM =ngineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page D-1 E. CONSTRUCTION SWPPP REQUIREMENTS: The project will require grading to construct the proposed building and utilities (including the stormwater infiltration system). Standard erosion control measures are proposed to be used during construction. The primary erosion and sediment control BMP during construction will be proper soil stabilization methods. Exposed soils shall be stabilized by application of effective BMPs that protect the soil from the erosive forces of raindrops, flowing water, and wind. Applicable practices include, but not limited to, temporary and permanent seeding, sodding, mulching, plastic covering, erosion control fabrics, matting, the early application of gravel base on areas to be paved, and dust control. The contractor shall select a soil stabilization method best suited for the particular situation. Stock piles must be stabilized and protected with sediment trapping measures. In addition, site containment of exposed soils shall be sustained by using silt fence barriers along the down -slope boundaries of the site's disturbance areas. See the site development plan for details. Construction Stormwater Pollution Prevention Plan (SWPPP): The following is a summary of the site's erosion control measures that evaluates the typical DOE 13 elements of a SWPPP: Element 1: Mark Clearing Limits: Clearing limits have been delineated on the engineering site development plans. Element 2: Establish Construction Access: A construction access has been delineated on the engineering site development plans. Element 3: Control Flow Rates: During construction silt fencing will provide attenuation of site runoff and upon project completion and stabilization (established lawns and landscape of exposed soils), the infiltration storm system will provide flow control. Element 4: Install Sediment Controls: Filter fabric fence has been delineated and detailed on the engineering site development plans. At a minimum, silt fence will be installed along the down gradient perimeter of the disturbed area that will receive sediment -laden runoff. Element 5: Stabilize Soils: Soils will be stabilized per the TESC notes listed on the engineering site development plans. Element 6: Protect Slopes: Exposed slopes shall be stabilized per the TESC notes listed on the engineering site development plans. Element 7: Protect Drain Inlets: Drain inlet protection will be installed on all catch basins that will receive sediment -laden runoff. See the engineering site development plans for locations and detail. Element 8: Stabilize Channels and Outlets: This element is not applicable since there are no temporary channels or outlets proposed. RAMEngineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page E-1 Element 9: Control Pollutants: Pollutants shall be managed as described in the TESC notes listed on the engineering site development plans. Element 10: Control De -Watering: Highly turbid or contaminated de -watering water shall be handled separately from stormwater. The water from all de -watering systems for trenches and foundations shall be treated or disposed prior to discharging from the site. Element 11: Maintain BMPs: BMPs shall be maintained and removed at the end of the project as follows: i. All temporary and permanent erosion and sediment control BMPs shall be inspected, maintained and repaired in accordance with the Drainage Manual or as approved or required by the City to assure continued performance of their intended function in accordance with BMP specifications. ii. The applicant may remove temporary BMPs when they are no longer needed. iii. All temporary erosion and sediment control BMPs shall be removed within 30 days after construction is completed and the City has determined that the site is stabilized. Element 12: Manage the Project: The owner of the site is responsible for managing the installation and maintenance of the site BMPs. Element 13. Protect Low Impact Development BMPs: During construction the proposed perforated roof drain stub -out connection area 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. RAMEngineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page E-2 F. OPERATION AND MAINTENANCE GUIDELINES: These guidelines are intended to provide operation and maintenance instructions for the project's storm drainage control facilities. The owner is responsible for maintenance of storm drainage facilities within the property (private property owner system); the owner is not responsible for maintenance within the public right-of-way (City system). Private Property Owners: Private property owners are responsible for properly maintaining the stormwater infrastructure on their property to ensure it operates as designed. The 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. Perforated Roof Drain Stub -out Connection. The private onsite roof drains perforated stub -out connection (PSOC) system consist of a section of perforated pipe in an excavated trench filled with drain rock. The PSOC system are been designed to temporary store and infiltrate a portion of the collected stormwater in the drain rock of the system. Over a period siltation of the PSOC bed can occur (especially if the system and upstream catch basin are not inspected and cleaned regularly) and replacement of the rock in the infiltration system may be required. The following pages outline standard general maintenance criteria for the project's drainage facilities. For additional and updated maintenance information visit the Washington State Department of Ecology's web -site at: http://www.ecy.wa.gov/programs/wq/wghome.html RAMEngineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page F-1 MAINTENANCE REQUIREMENTS ECDC Section 18.30.090 requires privately -owned stormwater management facilities, such as LID BMPs be properly maintained. The owner of the property is the responsible parry for such maintenance. The system must be kept in good working order. The entire system should be inspected once per year. An improperly maintained BMP may cause private property or street flooding. Contact the City Engineering Division for maintenance information. The City may make periodic inspections of BMPs to ensure they are operating properly. ECDC Section 18.30.100 contains the enforcement provisions the City can use to ensure the system is properly maintained. General Infiltration Maintenance Criteria Provision should be made for regular and perpetual maintenance of the infiltration basin/trench, including replacement and/or reconstruction of the any media that are relied upon for treatment purposes. Maintenance should be conducted when water remains in the basin or trench for more than 24 hours after the end of a rainfall event, or when overflows occur more frequently than planned. For example, off-line infiltration facilities should not have any overflows. Infiltration facilities designed to completely infiltrate all flows to meet flow control standards should not overflow. Removal of accumulated debris/sediment in the basin/trench should be conducted every 6 months or as needed to prevent clogging, or when water remains in the pond for greater than 24 hours after the end of a rainfall event. RAM ngineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page F-2 Appendix V-A: BMP Maintenance Tables Ecology intends the facility -specific maintenance standards contained in this section to be conditions for determining if maintenance actions are required as identified through inspection. Recognizing that Permittees have limited maintenance funds and time, Ecology does not require that a Permittee perform all these maintenance activities on all their stormwater BMPs. We leave the determination of importance of each maintenance activity and its priority within the stormwater program to the Permittee. We do expect, however, that sufficient maintenance will occur to ensure that the BMPs continue to operate as designed to protect ground and surface waters. Ecology doesn't intend that these measures identify the facility's required condition at all times between inspections. In other words, exceedance of these conditions at any time between inspections and/or maintenance does not automatically constitute a violation of these standards. However, based upon inspection observations, the Permittee shall adjust inspection and maintenance schedules to minimize the length of time that a facility is in a condition that requires a maintenance action. Table V-A.1: Maintenance Standards - Detention Ponds Maintenance Component Defect Conditions When Maintenance Is Needed Results Expected When Maintenance Is Performed Any trash and debris which exceed 1 cubic feet per 1,000 square feet. In general, there should be no visual evidence of Trash &Debris dumping. Trash and debris cleared from site If less than threshold all trash and debris will be removed as part of next scheduled maintenance. General Any poisonous or nuisance vegetation which may constitute No danger of poisonous a hazard to maintenance vegetation where maintenance personnel or the public. personnel or the public might normally be. (Coordinate with Poisonous Any evidence of noxious weeds local health department) Vegetation and as defined by State or local noxious weeds regulations. Complete eradication of noxious weeds may not be possible. (Apply requirements of adopted Compliance with State or local IPM policies for the use of eradication policies required herbicides). RAMEngineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page F-3 Table V-A.1: Maintenance Standards - Detention Ponds Maintenance Defect Conditions When Results Expected When Component Maintenance Is Needed Maintenance Is Performed Any evidence of oil, gasoline, contaminants or other pollutants Contaminants and No contaminants or pollutants Pollution (Coordinate removal/cleanup present. with local water quality response agency). Any evidence of rodent holes if Rodents destroyed and dam or facility is acting as a dam or berm repaired. (Coordinate with Rodent Holes berm, or any evidence of water local health department; piping through dam or berm via coordinate with Ecology Dam rodent holes. Safety Office if pond exceeds 10 acre-feet.) Facility is returned to design function. Beaver Dams Dam results in change or function of the facility. (Coordinate trapping of beavers and removal of dams with appropriate permitting agencies) Insects destroyed or removed When insects such as wasps from site. Insects and hornets interfere with maintenance activities. Apply insecticides in compliance with adopted IPM policies Tree growth does not allow maintenance and inspection access or interferes with maintenance activity (i.e., slope mowing, silt removal, vactoring, Trees do not hinder or equipment movements). If maintenance activities. trees are not interfering with Harvested trees should be Tree Growth and access or maintenance, do not recycled into mulch or other Hazard Trees remove beneficial uses (e.g., alders for firewood). If dead, diseased, or dying trees are identified Remove hazard Trees (Use a certified Arborist to determine health of tree or removal requirements) RAMEngineering, Inc. 8912 192" d Street SW RAM No. 20-001 Stormwater Site Plan Report Page F-4 Table V-A.1: Maintenance Standards - Detention Ponds Maintenance Defect Conditions When Results Expected When Component Maintenance Is Needed Maintenance Is Performed Slopes should be stabilized using appropriate erosion Eroded damage over 2 inches control measure(s); e.g.,rock deep where cause of damage is reinforcement, planting of grass, still present or where there is compaction. Side Slopes of Pond Erosion potential for continued erosion. If erosion is occurring on Any erosion observed on a compacted berms a licensed compacted berm embankment. engineer in the state of Washington should be consulted to resolve source of erosion. Accumulated sediment that exceeds 10% of the designed Sediment cleaned out to Sediment pond depth unless otherwise designed pond shape and specified or affects inletting or depth; pond reseeded if Storage Area outletting condition of the necessary to control erosion. facility. Liner (if Applicable) Liner is visible and has more Liner repaired or replaced. Liner than three 1/4-inch holes in it. is fully covered. Any part of berm which has settled 4 inches lower than the design elevation If settlement is apparent, measure berm to determine amount of settlement Dike is built back to the design Settlements elevation. Settling can be an indication of more severe problems with the Ponds Berms berm or outlet works. A licensed (Dikes) engineer in the state of Washington should be consulted to determine the source of the settlement. Discernable water flow through pond berm. Ongoing erosion with potential for erosion to Piping eliminated. Erosion Piping continue. potential resolved. (Recommend a Goethechnical engineer be called in to inspect RAMEngineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page F-5 Table V-A.1: Maintenance Standards - Detention Ponds Maintenance Defect Conditions When Results Expected When Component Maintenance Is Needed Maintenance Is Performed and evaluate condition and recommend repair of condition. Tree growth on emergency Trees should be removed. If root spillways creates blockage system is small (base less than problems and may cause failure 4 inches) the root system may of the berm due to uncontrolled be left in place. Otherwise the Tree Growth overtopping. roots should be removed and the berm restored. A licensed Tree growth on berms over 4 engineer in the state of feet in height may lead to piping Washington should be consulted Emergency through the berm which could for proper berm/spillway Overflow/ Spillway lead to failure of the berm. restoration. and Berms over 4 feet in height Discernable water flow through pond berm. Ongoing erosion with potential for erosion to continue. Piping Piping eliminated. Erosion potential resolved. (Recommend a Geotechnical engineer be called in to inspect and evaluate condition and recommend repair of condition. Only one layer of rock exists above native soil in area five square feet or larger, or any Emergency Emergency exposure of native soil at the Rocks and pad depth are Overflow/Spillway Overflow/Spillway top of out flow path of spillway. restored to design standards. (Rip -rap on inside slopes need not be replaced.) Erosion See "Side Slopes of Pond" Table V-A.2: Maintenance Standards - Infiltration Maintenance Defect Conditions When Maintenance Is Component I I Needed General Trash & Debris See Table V-A.1: Maintenance Standards - Detention Ponds RAMEngineering, Inc. RAM No. 20-001 Results Expected When Maintenance Is Performed See Table V-A.1: Maintenance 8912 192nd Street SW Stormwater Site Plan Report Page F-6 Table V-A.2: Maintenance Standards - Infiltration Maintenance Conditions When Maintenance Is Results Expected Component Defect Needed When Maintenance Is Performed Standards - Detention Ponds See Table V-A.1: Poisonous/Noxious See Table V-A.1: Maintenance Maintenance Vegetation Standards - Detention Ponds Standards - Detention Ponds See Table V-A.1: Contaminants and See Table V-A.1: Maintenance Maintenance Pollution Standards - Detention Ponds Standards - Detention Ponds See Table V-A.1: Rodent Holes See Table V-A.1: Maintenance Maintenance Standards - Detention Ponds Standards - Detention Ponds Water ponding in infiltration pond after rainfall ceases and appropriate time allowed for infiltration. Treatment basins should infiltrate Water Quality Design Storm Volume within 48 hours, and Sediment is removed empty within 24 hours after cessation of and/or facility is Storage Area Sediment most rain events. cleaned so that infiltration system works according to (A percolation test pit or test of facility design. indicates facility is only working at 90% of its designed capabilities. Test every 2 to 5 years. If two inches or more sediment is present, remove). Filter Bags (if Filled with Sediment Sediment and debris fill bag more than Filter bag is replaced applicable) and Debris 1/2 full. or system is redesigned. By visual inspection, little or no water Gravel in rock filter is Rock Filters Sediment and Debris flows through filter during heavy rain replaced. storms. See Table V-A.1: Side Slopes of Erosion See Table V-A.1: Maintenance Maintenance Pond Standards - Detention Ponds Standards - Detention Ponds RAMEngineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page F-7 Table V-A.2: Maintenance Standards - Infiltration Maintenance Conditions When Maintenance Is Results Expected Component Defect Needed When Maintenance Is Performed See Table V-A.1: Tree Growth See Table V-A.1: Maintenance Maintenance Standards - Detention Ponds Standards - Detention Ponds Emergency Overflow Spillway and Berms over 4 feet in height. See Table V-A.1: Piping See Table V-A.1: Maintenance Maintenance Standards - Detention Ponds Standards - Detention Ponds See Table V-A.1: Rock Missing See Table V-A.1: Maintenance Maintenance Standards - Detention Ponds Standards - Detention Ponds Emergency Overflow Spillway See Table V-A.1: Erosion See Table V-A.1: Maintenance Maintenance Standards - Detention Ponds Standards - Detention Ponds Pre -settling Ponds Facility or sump filled 6" or designed sediment trap depth of and Vaults with Sediment and/or sediment. Sediment is removed. debris Table V-A.S: Maintenance Standards - Catch Basins Maintenance Component Defect Conditions When Maintenance is Needed Results Expected When Maintenance is performed Trash or debris which is located immediately in front of the catch basin opening or is blocking No Trash or debris inletting capacity of the basin by more than located immediately in General 10%. front of catch basin or Trash & Debris on grate opening. Trash or debris (in the basin) that exceeds 60 percent of the sump depth as measured from No trash or debris in the bottom of basin to invert of the lowest pipe the catch basin. into or out of the basin, but in no case less than RAMEngineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page F-8 Table V-A.5: Maintenance Standards - Catch Basins Maintenance Results Expected Component Defect Conditions When Maintenance is Needed When Maintenance is performed a minimum of six inches clearance from the debris surface to the invert of the lowest pipe. Inlet and outlet pipes free of trash or debris. Trash or debris in any inlet or outlet pipe blocking more than 1/3 of its height. No dead animals or vegetation present within the catch basin. Dead animals or vegetation that could generate odors that could cause complaints or dangerous gases (e.g., methane). Sediment (in the basin) that exceeds 60 percent of the sump depth as measured from the bottom of basin to invert of the lowest pipe into or out of the basin, but in no case less than No sediment in the Sediment a minimum of 6 inches clearance from the catch basin sediment surface to the invert of the lowest pipe. Top slab has holes larger than 2 square inches Top slab is free of or cracks wider than 1/4 inch. (Intent is to make holes and cracks. Structure Damage sure no material is running into basin). to Frame and/or Frame is sitting flush Top Slab Frame not sitting flush on top slab, i.e., on the riser rings or top separation of more than 3/4 inch of the frame slab and firmly from the top slab. Frame not securely attached attached. Maintenance person judges that structure is Basin replaced or unsound. repaired to design Fractures or standards. Cracks in Basin Grout fillet has separated or cracked wider than Walls/ Bottom 1/2 inch and longer than 1 foot at the joint of Pipe is and any inlet/outlet pipe or any evidence of soil a t basin wall. secure at basin particles entering catch basin through cracks. Settlement/ If failure of basin has created a safety, function, Basin replaced or repaired to design Misalignment or design problem. standards. Vegetation Vegetation growing across and blocking more No vegetation blocking than 10 /o of the basin opening. opening to basin. RAMEngineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page F-9 Table V-A.S: Maintenance Standards - Catch Basins Maintenance Results Expected Component Defect Conditions When Maintenance is Needed When Maintenance is performed Vegetation growing in inlet/outlet pipe joints No vegetation or root that is more than six inches tall and less than growth present. six inches apart. Contamination See Table V-A.1: Maintenance Standards - No pollution present. Detention Ponds and Pollution Cover/grate is in place, Cover Not in Cover is missing or only partially in place. Any meets design Place open catch basin requires maintenance. standards, and is secured Locking Mechanism cannot be opened by one Mechanism opens with Catch Basin Mechanism Not maintenance person with proper tools. Bolts proper tools. Cover Working into frame have less than 1/2 inch of thread. One maintenance person cannot remove lid after applying normal lifting pressure. Cover can be removed Cover Difficult to by one maintenance Remove (Intent is keep cover from sealing off access to person. maintenance.) Ladder is unsafe due to missing rungs, not Ladder meets design Ladder Ladder Rungs securely attached to basin wall, misalignment, standards and allows Unsafe rust, cracks, or sharp edges. maintenance person safe access. Grate opening Grate with opening wider than 7/8 inch. Grate opening meets Unsafe design standards. Trash and Debris Trash and debris that is blocking more than Grate free of trash and Metal Grates 20 /o of grate surface inletting capacity. debris. (If Applicable) Grate is in place, meets Damaged or Grate missing or broken member(s) of the the design standards, Missing. grate. and is installed and aligned with the flow path. RAMEngineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page F-10 Flikrin ENGINEERING, INC. Civil Engineering 1 Land Planning