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STORMWATER REPORT 4.20.20For Review 04/22/2020 1234:52 PM 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 �go AS L� 36508W� \� ISTE��/ IONnT , 4/1 j -/2020 Prepared by: Rob Long, PE RAM Engineering, Inc. 16531 13t" Ave W, Suite A108, Lynnwood WA 98037 (425) 678-6960 RAMengineeringinc.corn Job No. 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 5,326 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 1,075 sf pollution generation hard surfaces (driveway 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 5,326 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 (0.015 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. Minimum Requirement #9 — Operation and Maintenance. An operation and maintenance summary is provided in section H. RAMEngineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page A-2 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 fills, moist with iron -oxide weathering; tested infiltration (Volume III, Chapter 3) No 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. Not feasible due to the required expansive trench length and BMP : Downspout Dispersion Systems No dispersion area that is required (10 ft per 700 sf of roof, 55+ (Voluumeme 1I11II, Chapter 3) ft for 3,896 sf of roof) BMP T5.10C: Perforated Stub -out Is feasible due to the relatively shallow depth that a (Volume III, Chapter 3) Yes 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 Sheet flow dispersion for the walkway and patio areas that BMP T5.11: Concentrated Flow Dispersion Yes 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 «. 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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 5,326 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 = Expanded off site Shared driveway (expand to min. 16') = Total Site Development Area = 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 = 8,420 sf (0.193 ac) Proposed Hard Surface = 5,326 sf (0.122 ac) Building Rooftop = 3,896 sf (0.089 ac) Uncovered Patio and Walk = 355 sf (0.008 ac) Onsite Driveway = 685 sf (0.016 ac) Offsite Shared Driveway = 390 sf (0.009 ac) Proposed Previous/Lawn = 7,139 sf (0.164 ac) 12,075 sf 390 sf 13,465 sf (0.286 Ac.) 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 (0.015 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 0.009 Acres Total Areas = 0.286 acres Soil Type(s) (see Geotechnical Report) Alderwood Series Soils (Till) Pre -Developed (pre-1977) 100-year Runoff Rates 0.065 cfs Developed 100-year Runoff Rates 0.080 cfs (0.015 cfs increase) RAMEngineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page C-1 WWHM2012 PROJECT REPORT Project Name: default Site Name: Binder-Veilleux Site Address: 8912 142nd ST SW City : Edmonds Report Date: 4/17/2020 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 .193 Pervious Total 0.193 Impervious Land Use acre ROOF TOPS FLAT 0.041 DRIVEWAYS FLAT 0.045 SIDEWALKS FLAT 0.007 Impervious Total 0.093 Basin Total 0.286 Element Flows To: Surface Interflow MITIGATED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Pasture, Flat .164 Pervious Total 0.164 Impervious Land Use acre ROOF TOPS FLAT 0.098 DRIVEWAYS FLAT 0.016 SIDEWALKS FLAT 0.008 Impervious Total 0.122 Basin Total 0.286 Groundwater Element Flows To: Surface Interflow Groundwater RAMEngineering, Inc. 8912 192nd Street SW RAM No. 20-001 Stormwater Site Plan Report Page C-2 ANALYSIS RESULTS Stream Protection Duration Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.193 Total Impervious Area:0.093 Mitigated Landuse Totals for POC #1 Total Pervious Area:0.164 Total Impervious Area:0.122 Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.025608 5 year 0.034474 10 year 0.040933 25 year 0.049789 50 year 0.056907 100 year 0.064488 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.032386 5 year 0.043243 10 year 0.051101 25 year 0.06182 50 year 0.070398 100 year 0.079499 1.0 T CurnuWve PLa]bablldy N 01 k 0.01 1.0 i 0.01 9 0.5 1 2 5 10 20 30 50 70 90 90 95 98 9999.5 I& 48eem Pd.I. C.T LID Due o Fiow Flequmcy LWMn 4uefar H aph Wetland IMA VAu LID Regal Recharge Oualion Rechmw P Imdnxbpe�d%xhas M Analyze dalasels CarcpectwDM Dekme Selected r Miff I Ap Dat-s Phw Stage P- Ewp POC 3 Fkwd Flee Method F: Lop Pearson Type 111 179 r We" r Eurr,ane r Bi gales RAM Engineering, Inc. RAM No. 20-001 M Flow Frequency rlrnlcP91 Predeveloped Mitigated 2 Year - 0.0256 0.0324 5 Year - 0.0345 0.0432 LC Year - 0.0409 0.0511 25 Year - 0.0498 0.0618 20 Year - 0.0569 0.0704 L00 Year - 0.0645 0.0795 knMe i. Peaks 1902 0.0257 0.0337 1903 0.0209 11.0378 1904 0.0306 0,0470 2.905 0.0168 0.021.3 1906 0.0181 0,0233 1907 0.0291 D.0353 1909 13A231 0.0291 1909 0+0265 0.0347 1910 0.0307 0.0370 2911 0.0252 0.0330 1912 0.0512 0.0675 1913 0.0187 0.0225 1914 0.0603. D.07B4 1915 0.0175 0.0222 1916 0.0252 0.0331 1917 a.0160 0.0205 1918 0.0230 D.0301 1919 0.0153 0.0292 1920 0.0231 0.0289 1921 0.0185 0.0225 1922 0.0248 0.0304 192.1 0.0253 0.0314 1924 0.0277 0.0363 1925 0.0161 0.0206 1926 0.0292 0.0383 1927 0+0222 0.0284 1928 0.0218 0.0273 1929 0.0321 0.0419 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 0.034 1903 0.029 0.038 1904 0.039 0.048 1905 0.017 0.021 1906 0.018 0.023 1907 0.029 0.035 1908 0.023 0.029 1909 0.026 0.035 1910 0.031 0.037 1911 0.025 0.033 1912 0.057 0.067 1913 0.019 0.022 1914 0.060 0.078 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 0.029 1921 0.018 0.023 1922 0.025 0.030 1923 0.025 0.031 1924 0.028 0.036 1925 0.016 0.021 1926 0.029 0.038 1927 0.022 0.028 1928 0.022 0.027 1929 0.032 0.042 1930 0.036 0.047 1931 0.019 0.024 1932 0.022 0.028 1933 0.021 0.026 1934 0.036 0.044 1935 0.018 0.023 1936 0.021 0.026 1937 0.032 0.039 1938 0.020 0.025 1939 0.024 0.031 1940 0.033 0.043 1941 0.027 0.036 1942 0.030 0.037 1943 0.030 0.038 1944 0.045 0.057 1945 0.029 0.037 1946 0.023 0.029 1947 0.018 0.024 1948 0.029 0.035 1949 0.037 0.049 1950 0.017 0.021 1951 0.025 0.032 1952 0.054 0.064 1953 0.051 0.061 1954 0.024 0.030 1955 0.020 0.025 1956 0.015 0.019 1957 0.022 0.028 1958 0.036 0.042 1959 0.031 0.037 1960 0.021 0.027 1961 0.060 0.076 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 0.059 1965 0.029 0.036 1966 0.020 0.025 1967 0.024 0.030 1968 0.021 0.026 1969 0.024 0.030 1970 0.030 0.037 1971 0.032 0.039 1972 0.084 0.105 1973 0.041 0.054 1974 0.033 0.042 1975 0.046 0.055 1976 0.035 0.044 1977 0.015 0.019 1978 0.033 0.040 1979 0.024 0.031 1980 0.026 0.033 1981 0.027 0.035 1982 0.021 0.026 1983 0.030 0.038 1984 0.027 0.034 1985 0.027 0.034 1986 0.019 0.023 1987 0.028 0.034 1988 0.020 0.025 1989 0.017 0.022 1990 0.021 0.026 1991 0.029 0.038 1992 0.034 0.042 1993 0.033 0.044 1994 0.027 0.033 1995 0.015 0.020 1996 0.027 0.032 1997 0.020 0.026 1998 0.028 0.035 1999 0.026 0.034 2000 0.029 0.037 2001 0.024 0.031 2002 0.043 0.052 2003 0.022 0.027 2004 0.031 0.040 2005 0.046 0.059 2006 0.019 0.025 2007 0.027 0.036 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 0.027 2014 0.020 0.027 2015 0.047 0.056 2016 0.017 0.022 2017 0.038 0.049 2018 0.037 0.043 2019 0.047 0.055 2020 0.033 0.041 2021 0.031 0.038 2022 0.034 0.044 2023 0.036 0.048 2024 0.069 0.081 2025 0.020 0.026 2026 0.025 0.030 2027 0.027 0.035 2028 0.012 0.016 2029 0.023 0.029 2030 0.032 0.040 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 0.025 2035 0.033 0.039 2036 0.023 0.027 2037 0.025 0.033 2038 0.030 0.037 2039 0.039 0.051 2040 0.022 0.028 2041 0.025 0.032 2042 0.036 0.042 2043 0.031 0.041 2044 0.025 0.031 2045 0.023 0.028 2046 0.022 0.027 2047 0.026 0.034 2048 0.021 0.028 2049 0.032 0.042 2050 0.022 0.028 2051 0.039 0.048 2052 0.020 0.027 2053 0.021 0.028 2054 0.042 0.051 2055 0.021 0.028 2056 0.027 0.036 2057 0.018 0.023 2058 0.029 0.039 Stream Protection Duration Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.0835 0.1048 2 0.0689 0.0809 3 0.0601 0.0784 4 0.0595 0.0765 5 0.0572 0.0675 6 0.0538 0.0641 7 0.0505 0.0607 8 0.0473 0.0593 9 0.0471 0.0588 10 0.0470 0.0571 11 0.0458 0.0561 12 0.0458 0.0552 13 0.0453 0.0551 14 0.0428 0.0536 15 0.0421 0.0521 16 0.0409 0.0511 17 0.0390 0.0508 18 0.0389 0.0492 19 0.0386 0.0489 20 0.0375 0.0480 21 0.0373 0.0478 22 0.0373 0.0477 23 0.0363 0.0471 24 0.0362 0.0441 25 0.0359 0.0441 26 0.0359 0.0438 27 0.0358 0.0435 28 0.0353 0.0431 29 0.0337 0.0428 30 0.0337 0.0425 31 0.0334 0.0421 32 0.0332 0.0420 33 0.0331 0.0419 34 0.0330 0.0419 RAM Engineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page C-6 35 0.0327 0.0419 36 0.0325 0.0405 37 0.0323 0.0405 38 0.0321 0.0402 39 0.0321 0.0402 40 0.0319 0.0399 41 0.0319 0.0390 42 0.0313 0.0388 43 0.0309 0.0387 44 0.0308 0.0385 45 0.0307 0.0385 46 0.0305 0.0383 47 0.0301 0.0383 48 0.0300 0.0381 49 0.0299 0.0380 50 0.0298 0.0378 51 0.0296 0.0374 52 0.0295 0.0372 53 0.0294 0.0371 54 0.0294 0.0370 55 0.0292 0.0370 56 0.0292 0.0368 57 0.0291 0.0366 58 0.0290 0.0365 59 0.0289 0.0363 60 0.0287 0.0360 61 0.0285 0.0359 62 0.0284 0.0357 63 0.0281 0.0355 64 0.0277 0.0353 65 0.0275 0.0350 66 0.0274 0.0348 67 0.0274 0.0347 68 0.0272 0.0347 69 0.0271 0.0347 70 0.0270 0.0345 71 0.0270 0.0343 72 0.0268 0.0342 73 0.0265 0.0341 74 0.0265 0.0340 75 0.0261 0.0337 76 0.0260 0.0333 77 0.0259 0.0331 78 0.0257 0.0330 79 0.0254 0.0328 80 0.0253 0.0327 81 0.0253 0.0327 82 0.0252 0.0324 83 0.0252 0.0322 84 0.0249 0.0316 85 0.0249 0.0315 86 0.0248 0.0315 87 0.0247 0.0314 88 0.0245 0.0313 89 0.0242 0.0306 90 0.0240 0.0305 91 0.0240 0.0304 92 0.0239 0.0301 93 0.0238 0.0299 94 0.0238 0.0298 95 0.0234 0.0297 96 0.0231 0.0294 97 0.0231 0.0291 98 0.0230 0.0290 99 0.0230 0.0289 100 0.0228 0.0286 101 0.0227 0.0285 RAM Engineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page C-7 102 0.0225 0.0284 103 0.0224 0.0281 104 0.0222 0.0281 105 0.0221 0.0279 106 0.0221 0.0279 107 0.0219 0.0279 108 0.0219 0.0278 109 0.0218 0.0277 110 0.0218 0.0277 ill 0.0218 0.0277 112 0.0217 0.0274 113 0.0214 0.0273 114 0.0214 0.0268 115 0.0213 0.0268 116 0.0209 0.0268 117 0.0208 0.0267 118 0.0208 0.0266 119 0.0208 0.0266 120 0.0208 0.0262 121 0.0207 0.0262 122 0.0205 0.0261 123 0.0205 0.0260 124 0.0204 0.0259 125 0.0203 0.0258 126 0.0202 0.0256 127 0.0200 0.0254 128 0.0199 0.0252 129 0.0198 0.0251 130 0.0196 0.0251 131 0.0195 0.0249 132 0.0194 0.0248 133 0.0190 0.0242 134 0.0189 0.0240 135 0.0187 0.0234 136 0.0185 0.0233 137 0.0185 0.0231 138 0.0182 0.0229 139 0.0181 0.0227 140 0.0177 0.0226 141 0.0176 0.0225 142 0.0175 0.0225 143 0.0175 0.0222 144 0.0174 0.0219 145 0.0171 0.0218 146 0.0169 0.0217 147 0.0168 0.0213 148 0.0165 0.0210 149 0.0161 0.0206 150 0.0160 0.0205 151 0.0156 0.0204 152 0.0154 0.0202 153 0.0153 0.0194 154 0.0152 0.0192 155 0.0148 0.0189 156 0.0141 0.0184 157 0.0124 0.0162 Stream Protection Duration POC #1 The Facility FAILED Facility FAILED duration standard for 1+ flows. Flow(cfs) Predev Mit Percentage Pass/Fail 0.0128 2773 5398 194 Fail 0.0132 2443 4906 200 Fail RAM Engineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page C-8 0.0137 2179 4427 203 Fail 0.0141 1943 4071 209 Fail 0.0146 1727 3721 215 Fail 0.0150 1528 3369 220 Fail 0.0155 1373 3084 224 Fail 0.0159 1235 2843 230 Fail 0.0164 1089 2589 237 Fail 0.0168 985 2342 237 Fail 0.0173 882 2143 242 Fail 0.0177 801 1961 244 Fail 0.0181 728 1785 245 Fail 0.0186 672 1627 242 Fail 0.0190 623 1474 236 Fail 0.0195 567 1355 238 Fail 0.0199 522 1237 236 Fail 0.0204 488 1136 232 Fail 0.0208 444 1032 232 Fail 0.0213 419 940 224 Fail 0.0217 389 859 220 Fail 0.0222 360 796 221 Fail 0.0226 336 735 218 Fail 0.0231 312 690 221 Fail 0.0235 292 639 218 Fail 0.0239 266 600 225 Fail 0.0244 243 554 227 Fail 0.0248 224 514 229 Fail 0.0253 213 475 223 Fail 0.0257 204 450 220 Fail 0.0262 183 431 235 Fail 0.0266 165 411 249 Fail 0.0271 155 388 250 Fail 0.0275 142 369 259 Fail 0.0280 132 340 257 Fail 0.0284 128 318 248 Fail 0.0288 117 298 254 Fail 0.0293 103 280 271 Fail 0.0297 97 264 272 Fail 0.0302 90 250 277 Fail 0.0306 82 235 286 Fail 0.0311 76 225 296 Fail 0.0315 71 213 300 Fail 0.0320 68 205 301 Fail 0.0324 61 192 314 Fail 0.0329 54 182 337 Fail 0.0333 50 174 348 Fail 0.0337 46 164 356 Fail 0.0342 43 148 344 Fail 0.0346 42 138 328 Fail 0.0351 41 126 307 Fail 0.0355 38 118 310 Fail 0.0360 35 113 322 Fail 0.0364 32 105 328 Fail 0.0369 31 101 325 Fail 0.0373 30 94 313 Fail 0.0378 28 88 314 Fail 0.0382 28 78 278 Fail 0.0386 27 69 255 Fail 0.0391 25 65 260 Fail 0.0395 25 65 260 Fail 0.0400 24 64 266 Fail 0.0404 24 60 250 Fail 0.0409 22 55 250 Fail 0.0413 21 55 261 Fail 0.0418 20 54 270 Fail 0.0422 19 46 242 Fail 0.0427 19 43 226 Fail 0.0431 18 41 227 Fail RAM Engineering, Inc. RAM No. 20-001 8912 192nd Street SW Stormwater Site Plan Report Page C-9 0.0435 18 38 211 Fail 0.0440 18 36 200 Fail 0.0444 16 32 200 Fail 0.0449 16 32 200 Fail 0.0453 16 32 200 Fail 0.0458 15 32 213 Fail 0.0462 13 32 246 Fail 0.0467 13 32 246 Fail 0.0471 12 31 258 Fail 0.0476 10 31 310 Fail 0.0480 10 27 270 Fail 0.0484 10 26 260 Fail 0.0489 10 25 250 Fail 0.0493 10 24 240 Fail 0.0498 10 23 230 Fail 0.0502 10 23 230 Fail 0.0507 9 23 255 Fail 0.0511 9 21 233 Fail 0.0516 9 20 222 Fail 0.0520 8 20 250 Fail 0.0525 8 18 225 Fail 0.0529 8 18 225 Fail 0.0533 8 18 225 Fail 0.0538 7 17 242 Fail 0.0542 7 17 242 Fail 0.0547 7 17 242 Fail 0.0551 7 16 228 Fail 0.0556 7 14 200 Fail 0.0560 7 14 200 Fail 0.0565 6 13 216 Fail 0.0569 6 13 216 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 Fruitda|e Creek. Runoff flows from the site sheet flow in a north/northwesterly direction 193"« Street SE. The pipe and catch basin system along 192"" 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 NELSON GEOTECHNICAL N }. A A5SQGIATES, INC. GEOTECHNICAL ENGINEERS & GEOLOGISTS Main office 17311 -- 135" Ave NE, A-500 Woodinville, WA 98072 (425) 486-1669 FAX (425) 481-2510 February 19, 2020 Ms. Deborah Binder 8816 - 20th Place SW Edmonds, Washington VIA Email::jaideborah(a yahoo.com Geotechnical Engineering Evaluation Binder Property Residence Development 8912 —192nd Street SW Edmonds, Washington NGA File No. 1154419 Dear Ms. Binder: Engineering-Gcology Branch 5526 Industry Lane, 42 Fast Wenatchee, WA 98802 (509) 665-7696 • FAX (509) 665-7692 We are pleased to submit the attached report titled "Geotechnical Engineering Evaluation — Binder Property Residence Development — 8912 - 192nd Street SW — Edmonds, Washington." This report summarizes our observations of the existing surface and subsurface conditions within the site, and provides general recommendations for the proposed site development. Our services were completed in general accordance with the proposal signed by you on January 23, 2020. The relatively level to gently sloping, rectangular -shaped subject site is currently occupied by a single- family residence within the northern and south central portion of the site. The property is bordered to the west and south by existing residential properties, to the east by an alley way and to the north by 192" d Street Southwest. We understand that the proposed improvements within the site will consist of removing the existing structures and constructing a new single-family residence. Specific grading and stormwater plans were not available when this report was prepared, however we understand that stormwater may be directed to on -site infiltration facilities, if feasible. In addition to providing recommendations for the development of the new residential structure, we have been requested to evaluate the infiltration capacity of the site soils. The City of Edmonds utilizes the 2019 WSDOE Stormwater Management Manual for Western Washin tg on to determine the design of infiltration facilities. According to this manual, on -site infiltration testing consisting of the small Pilot Infiltration Test (PIT) is used to determine the long-term design infiltration rates. We monitored the excavation of four test pit explorations throughout the property, one of which we utilized for our small-scale PIT testing. Our explorations indicated that the site was underlain by surficial undocumented fill with competent, native glacial soils at depth. It is our opinion that the proposed site development is feasible from a geotechnical engineering standpoint, provided that our recommendations for site development are incorporated into project plans. In general, the competent bearing native glacial soils underlying the site should adequately support the planned structures. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1154419 Binder Property Residence Development February 19, 2020 Edmonds, Washington Summary — Page 2 Foundations should be advanced through any loose and/or undocumented fill soils down to the competent native bearing material for bearing capacity and settlement considerations. These soils should generally be encountered at approximate depths between 2.0 and 4.5 feet below the existing ground surface, based on our explorations. If loose soils or undocumented fill are encountered in unexplored areas of the site, they should be removed and replaced with structural fill for foundation and pavement support. Final stormwater plans have also not been developed, but we understand that on -site infiltration is being considered for this site. Based on our onsite testing, it is our opinion that the onsite soils are not conducive to traditional methods of stormwater infiltration, however low -impact design systems may be feasible. 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 that we interpreted as native glacial soils at relatively shallow depths. We recommend that any low impact stormwater infiltration systems be designed in accordance with the 2019 WSDOE Stormwater Management Manual for Western Washington. In the attached report, we have also provided general recommendations for site grading, slabs -on -grade, structural fill placement, retaining walls, erosion control, and drainage. We should be retained to review and comment on final development plans and observe the earthwork phase of construction. We also recommend that NGA be retained to provide monitoring and consultation services during construction to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes should the conditions revealed differ from those anticipated, and to evaluate whether or not earthwork and foundation installation activities comply with contract plans and specifications. It has been a pleasure to provide service to you on this project. Please contact us if you have any questions regarding this report or require further information. Sincerely, NELSON GEOTECHNICAL ASSOCIATES, INC. Khaled M. Shawish, PE Principal Engineer TABLE OF CONTENTS INTRODUCTION............................................................................................................. 1 SCOPE............................................................................................................................... 1 SITECONDITIONS......................................................................................................... 2 SurfaceConditions....................................................................................................... 2 Subsurface Conditions.................................................................................................. 2 HydrogeologicConditions........................................................................................... 3 SENSITIVE AREA EVALUATION............................................................................... 3 SeismicHazard............................................................................................................. 3 ErosionHazard............................................................................................................. 4 CONCLUSIONS AND RECOMMENDATIONS.......................................................... 4 General......................................................................................................................... 4 ErosionControl............................................................................................................ 5 SitePreparation and Grading....................................................................................... 5 Temporary and Permanent Slopes............................................................................... 6 Foundations.................................................................................................................. 7 RetainingWalls............................................................................................................ 8 StructuralFill................................................................................................................ 9 Slab-on-Grade.............................................................................................................. 9 Pavement Subgrade and Other Hard Surfaces........................................................... 10 Utilities....................................................................................................................... 10 SiteDrainage.............................................................................................................. 10 CONSTRUCTION MONITORING............................................................................. 12 USEOF THIS REPORT................................................................................................ 12 LIST OF FIGURES Figure 1 — Vicinity Map Figure 2 — Site Plan Figure 3 — Soil Classification Chart Figure 4 — Test Pit Logs NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Binder Property Residence Development 8912 — 192nd Street SW Edmonds, Washington INTRODUCTION This report presents the results of our geotechnical engineering investigation and evaluation of the proposed Binder Residence Development project in the Edmonds, Washington. The project site is located at 8912 — 192nd Street SW, as shown on the Vicinity Map in Figure 1. The purpose of this study is to explore and characterize the site's surface and subsurface conditions and to provide geotechnical recommendations for the planned site development. For our use in preparing this report, we have been provided a survey of the property titled "Topographic Survey for: Deborah Binder" dated December 18, 2019 and prepared by Pacific Coast Surveys, Inc. The property is currently occupied by a single-family residence and asphalt driveway and parking area within the south-central and eastern portions of the site, respectively. Vegetation within the site consist mostly of grass yard areas, landscaping areas, and young to mature trees scattered throughout the site. The site is generally level to gently sloping down from the northeast to the southwest. We understand that the proposed development within the site will include constructing a new single-family residence with the possibility of a daylight basement. Final development and grading plans have not been prepared at the time this report was issued. Final stormwater plans have also not been developed, however, we understand that stormwater may be directed to on -site infiltration systems, if feasible. The existing site layout is shown on the Site Plan in Figure 2. SCOPE The purpose of this study is to explore and characterize the site surface and subsurface conditions, and provide general recommendations for site development. Specifically, our scope of services includes the following: Reviewing available soil and geologic maps of the area. 2. Exploring the subsurface soil and groundwater conditions within the site with trackhoe excavated test pits. Trackhoe was subcontracted by NGA. 3. Providing recommendations for earthwork. 4. Providing recommendations for temporary and permanent slopes. 5. Providing recommendations for slab subgrade preparation. 6. Providing recommendations for retaining walls. 7. Determining feasibility of on -site stormwater infiltration. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Binder Property Residence Development Edmonds, Washington NGA File No. 1154419 February 19, 2020 Page 2 8. Providing long-term design infiltration rates based on one on -site Small -Scale Pilot Infiltration Test (PIT) per the 2019 DOE SWMMWW Manual. Location and depth of test was determined by the civil engineer. Water for the test was secured by the client. 9. Providing recommendations for infiltration system installation, as needed. 10. Providing recommendations for site drainage and erosion control. IL Documenting the results of our findings, conclusions, and recommendations in a written geotechnical report. SITE CONDITIONS Surface Conditions The subject site consists of a rectangular -shaped parcel covering approximately 0.28 acres. The site is generally level to gently sloping down from the northeast to the southwest and is currently occupied by a single-family residence and asphalt driveway parking area within the south-central and eastern portions of the site, respectively. Vegetation within the site consists of mostly grass yard areas with landscaping areas and young to mature trees scattered throughout the site. The site is bordered to the west and south by other residences, to the east by an alley, and to the north by 192' Street SW. We did not observe surface water throughout the site during our visit on February 5, 2020. Subsurface Conditions Geology: The geologic units for the overall site are shown on Geologic map of the Edmonds East and part of the Edmonds West quadrangles, Washington, by Minard, J.P. (USGS, 1983). The site is mapped as Vashon till (Qvt). The glacial till is generally described as a non -sorted mixture of clay, silt, sand, pebbles, cobbles, and boulders, all in variable amounts. Our explorations typically encountered surficial undocumented fill underlain by silty fine to medium sand with varying amounts of gravel, which we interpreted as native glacial till soils at depth. Explorations: The subsurface conditions within the site were explored on February 5, 2020 by excavating four test pits to approximate depths in the range of 5.0 to 9.0 feet below the existing ground surface using a mini-trackhoe. The approximate locations of our explorations are shown on the Site Plan in Figure 2. A geologist from NGA was present during the explorations, examined the soils and geologic conditions encountered, obtained samples of the different soil types, and maintained logs of the test pits. The soils were visually classified in general accordance with the Unified Soil Classification System, presented in Figure 3. The logs of our test pits are attached to this report and are presented as Figure 4. We present a brief summary of the subsurface conditions in the following paragraph. For a detailed description of the subsurface conditions, the logs of the test pits should be reviewed. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1154419 Binder Property Residence Development February 19, 2020 Edmonds, Washington Page 3 At the surface of Infiltration Pits 1 and Test Pits 1, 2, and 3, we generally encountered 2.0 to 4.6 feet of loose, dark brown to brown, silty fine to medium sand with gravel, roots, and organics, which we interpreted as undocumented fill soils. Underlying the fill soils in each of our explorations, we generally encountered gray, silty fine to medium sand with gravel, cobbles, and iron -oxide staining, which we interpreted as native glacial soils. Infiltration Pit 1 and Test Pit 1, 2, and 3 were terminated within the native glacial till soils at depths in the range of 5.0 to 9.0 feet below the existing ground surface. Hydrogeologic Conditions We encountered moderate groundwater seepage within Test Pits 2 and 3 at depths in the range of 2.7 to 3.0 feet below the existing ground surface. We interpret the water observed as a perched groundwater condition. Perched water occurs when surface water infiltrates through less dense, more permeable soils and accumulates on top of relatively low permeability materials. The more permeable soils consist of the topsoil/weathered soils and undocumented fill. The low permeability soil consists of relatively silty native deposits. Perched water does not represent a regional groundwater "table" within the upper soil horizons. Perched water tends to vary spatially and is dependent upon the amount of rainfall. We would expect the amount of perched groundwater to decrease during drier times of the year and increase during wetter periods. SENSITIVE AREA EVALUATION Seismic Hazard We reviewed the 2018 International Building Code (IBC) for seismic site classification for this project. Since competent glacial soils are inferred to underlie the site at depth, the site conditions best fit the IBC description for Site Class D. Table 1 below provides seismic design parameters for the site that are in conformance with the 2018 IBC, which specifies a design earthquake having a 2% probability of occurrence in 50 years (return interval of 2,475 years), and the 2008 USGS seismic hazard maps. Table 1 — 2018 IBC Seismic Design Parameters Site Class Spectral Acceleration Spectral Acceleration Site Coefficients Design Spectral at 0.2 sec. (g) at 1.0 sec. (g) Response S, S 1 Parameters Fa Fv SDs SD1 D 1.282 0.503 1.000 1.500 0.855 0.503 The spectral response accelerations were obtained from the USGS Earthquake Hazards Program Interpolated Probabilistic Ground Motion website (2008 data) for the project latitude and longitude. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1154419 Binder Property Residence Development February 19, 2020 Edmonds, Washington Page 4 Hazards associated with seismic activity include liquefaction potential and amplification of ground motion. Liquefaction is caused by a rise in pore pressures in a loose, fine sand deposit beneath the groundwater table. It is our opinion that the medium dense or better native deposits interpreted to underlie the site have a low potential for liquefaction or amplification of ground motion. Erosion Hazard The criteria used for determination of the erosion hazard for affected areas include soil type, slope gradient, vegetation cover, and groundwater conditions. The erosion sensitivity is related to vegetative cover and the specific surface soil types, which are related to the underlying geologic soil units. The Soil Survey of Snohomish County Area, Washington, by the Natural Resources Conservation Service (NRCS) was reviewed to determine the erosion hazard of the on -site soils. The surface soils for this site were mapped as Alderwood-Urban land complex, 8 to 15 percent slopes. The erosion hazard for this material is listed as slight to moderate. This site is relatively level to gently sloping and there are no steep slopes on the property. It is our opinion that the erosion hazard for site soils should be low in areas where the site is not disturbed. CONCLUSIONS AND RECOMMENDATIONS General It is our opinion that the planned development is feasible from a geotechnical standpoint. Our explorations indicated that the site is generally underlain by competent native bearing glacial soils at relatively shallow depths. The native soils encountered at depth should provide adequate support for foundation, slab, and pavement loads. We recommend that the planned structure be designed utilizing shallow foundations. Footings should extend through any loose soil or undocumented fill soils and be founded on the underlying medium dense or better native bearing glacial soils, or structural fill extending to these soils. The medium dense or better native glacial soils should typically be encountered approximately 2.0 to 4.5 feet below the existing surface, based on our explorations. We should note that localized areas of deeper unsuitable soils and/or undocumented fill could be encountered at this site. This condition would require additional excavations in foundation, slab, and pavement areas to remove the unsuitable soils. We have provided detailed recommendations regarding slab -on -grade, pavement and hard surfacing in the Slab -on -Grade and Pavement subgrade and Other Hard Surfaces subsections of this report. Based on the results of our infiltration testing and soil explorations throughout the site, it is our opinion that the onsite native soils are not conducive for traditional methods of stormwater infiltration. This is further discussed in the Site Drainage section of this report. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Binder Property Residence Development Edmonds, Washington NGA File No. 1154419 February 19, 2020 Page 5 Erosion Control The erosion hazard for the on -site soils is interpreted to be moderate for exposed soils, but actual erosion potential will be dependent on how the site is graded and how water is allowed to concentrate. Best Management Practices (BMPs) should be used to control erosion. Areas disturbed during construction should be protected from erosion. Erosion control measures may include diverting surface water away from the stripped or disturbed areas. Silt fences and/or straw bales should be erected to prevent muddy water from leaving the site. Disturbed areas should be planted as soon as practical and the vegetation should be maintained until it is established. The erosion potential of areas not stripped of vegetation should be low. Site Preparation and Grading After erosion control measures are implemented, site preparation should consist of stripping the topsoil, undocumented fill and loose soils from foundation, slab, pavement areas, and other structural areas, to expose medium dense or better native bearing glacial soils. The stripped soil should be removed from the site or stockpiled for later use as a landscaping fill. Based on our observations, we anticipate stripping depths of approximately five feet, depending on the specific locations. However, additional stripping may be required if areas of deeper undocumented fill and/or loose soil are encountered in unexplored areas of the site. After site stripping, if the exposed subgrade is deemed loose, it should be compacted to a non -yielding condition and then proof -rolled with a heavy rubber -tired piece of equipment. Areas observed to pump or weave during the proof -roll test should be reworked to structural fill specifications or over -excavated and replaced with properly compacted structural fill or rock spalls. If loose soils are encountered in the pavement areas, the loose soils should be removed and replaced with rock spalls or granular structural fill. If significant surface water flow is encountered during construction, this flow should be diverted around areas to be developed, and the exposed subgrades should be maintained in a semi -dry condition. If wet conditions are encountered, alternative site stripping and grading techniques might be necessary. These could include using large excavators equipped with wide tracks and a smooth bucket to complete site grading and covering exposed subgrade with a layer of crushed rock for protection. If wet conditions are encountered or construction is attempted in wet weather, the subgrade should not be compacted as this could cause further subgrade disturbance. In wet conditions it may be necessary to cover the exposed subgrade with a layer of crushed rock as soon as it is exposed to protect the moisture sensitive soils from disturbance by machine or foot traffic during construction. The prepared subgrade should be protected from construction traffic and surface water should be diverted around areas of prepared subgrade. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1154419 Binder Property Residence Development February 19, 2020 Edmonds, Washington Page 6 The site soils are considered to be moisture -sensitive and will disturb easily when wet. We recommend that construction takes place during the drier summer months if possible. However, if construction takes place during the wet season, additional expenses and delays should be expected due to the wet conditions. Additional expenses could include the need for placing a blanket of rock spalls on exposed subgrades, construction traffic areas, and paved areas prior to placing structural fill. Wet weather grading will also require additional erosion control and site drainage measures. Some of the native on -site soils may be suitable for use as structural fill, depending on the moisture content of the soil at the time of construction. It is our opinion that the undocumented fill soils encountered within the site are not suitable for structural fill. NGA should be retained to evaluate the suitability of all on -site and imported structural fill material during construction. Temporary and Permanent Slopes Temporary cut slope stability is a function of many factors, including the type and consistency of soils, depth of the cut, surcharge loads adjacent to the excavation, length of time a cut remains open, and the presence of surface or groundwater. It is exceedingly difficult under these variable conditions to estimate a stable, temporary, cut slope angle. Therefore, it should be the responsibility of the contractor to maintain safe slope configurations at all times as indicated in OSHA guidelines for cut slopes. The following information is provided solely for the benefit of the owner and other design consultants and should not be construed to imply that Nelson Geotechnical Associates, Inc. assumes responsibility for job site safety. Job site safety is the sole responsibility of the project contractor. For planning purposes, we recommend that temporary cuts in the upper undocumented fill soils be no steeper than 2 Horizontal to 1 Vertical (2H:IV). Temporary cuts in the competent native glacial soils at depth should be no steeper than 1.5H:IV. If significant groundwater seepage or surface water flow were encountered, we would expect that flatter inclinations would be necessary. We recommend that cut slopes be protected from erosion. The slope protection measures may include covering cut slopes with plastic sheeting and diverting surface runoff away from the top of cut slopes. We do not recommend vertical slopes for cuts deeper than four feet, if worker access is necessary. We recommend that cut slope heights and inclinations conform to appropriate OSHA/WISHA regulations. Permanent cut and fill slopes should be no steeper than 2H:1 V. However, flatter inclinations may be required in areas where loose soils are encountered. Permanent slopes should be vegetated and the vegetative cover maintained until established. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Binder Property Residence Development Edmonds, Washington NGA File No. 1154419 February 19, 2020 Page 7 Foundations Conventional shallow spread foundations should be placed on medium dense or better native bearing soils, or be supported on structural fill or rock spalls extending to those soils. Medium dense soils should be encountered approximately 2.0 to 4.5 feet below ground surface based on our explorations. Where undocumented fill or less dense soils are encountered at footing bearing elevation, the subgrade should be over -excavated to expose suitable bearing soil. The over -excavation may be filled with structural fill, or the footings may be extended down to the competent native bearing soils. If footings are supported on structural fill, the fill zone should extend outside the edges of the footing a distance equal to one half of the depth of the over -excavation below the bottom of the footing. Footings should extend at least 18 inches below the lowest adjacent finished ground surface for frost protection and bearing capacity considerations. Foundations should be designed in accordance with the 2018 IBC. Footing widths should be based on the anticipated loads and allowable soil bearing pressure. Water should not be allowed to accumulate in footing trenches. All loose or disturbed soil should be removed from the foundation excavation prior to placing concrete. For foundations constructed as outlined above, we recommend an allowable bearing pressure of not more than 2,500 pounds per square foot (psf) be used for the design of footings founded on the medium dense or better native bearing soils or structural fill extending to the competent native bearing material. The foundation bearing soil should be evaluated by a representative of NGA. We should be consulted if higher bearing pressures are needed. Current IBC guidelines should be used when considering increased allowable bearing pressure for short-term transitory wind or seismic loads. Potential foundation settlement using the recommended allowable bearing pressure is estimated to be less than 1-inch total and 1/2-inch differential between adjacent footings or across a distance of about 20 feet, based on our experience with similar projects. Lateral loads may be resisted by friction on the base of the footing and passive resistance against the subsurface portions of the foundation. A coefficient of friction of 0.35 may be used to calculate the base friction and should be applied to the vertical dead load only. Passive resistance may be calculated as a triangular equivalent fluid pressure distribution. An equivalent fluid density of 200 pounds per cubic foot (pcf) should be used for passive resistance design for a level ground surface adjacent to the footing. This level surface should extend a distance equal to at least three times the footing depth. These recommended values incorporate safety factors of 1.5 and 2.0 applied to the estimated ultimate values for frictional and passive resistance, respectively. To achieve this value of passive resistance, the foundations should be poured "neat" against the native medium dense soils or compacted fill should be used as backfill against the front of the footing. We recommend that the upper one foot of soil be neglected when calculating the passive resistance. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1154419 Binder Property Residence Development February 19, 2020 Edmonds, Washington Page 8 Retaining Walls Specific grading plans for this project were not available at the time this report was prepared, but retaining walls may be incorporated into the project plans. In general, the lateral pressure acting on retaining walls is dependent on the nature and density of the soil behind the wall, the amount of lateral wall movement which can occur as backfill is placed, wall drainage conditions, and the inclination of the backfill. For walls that are free to yield at the top at least one thousandth of the height of the wall (active condition), soil pressures will be less than if movement is limited by such factors as wall stiffness or bracing (at -rest condition). We recommend that walls supporting horizontal backfill and not subjected to hydrostatic forces, be designed using a triangular earth pressure distribution equivalent to that exerted by a fluid with a density of 40 pcf for yielding (active condition) walls, and 60 pcf for non -yielding (at -rest condition) walls. A seismic design loading of 8H should also be included in the wall design, where H represents the total height of the wall. These recommended lateral earth pressures are for a drained granular backfill and are based on the assumption of a horizontal ground surface behind the wall for a distance of at least the height of the wall, and do not account for surcharge loads. Additional lateral earth pressures should be considered for surcharge loads acting adjacent to walls and within a distance equal to the height of the wall. This would include the effects of surcharges such as traffic loads, floor slab loads, slopes, or other surface loads. We could consult with the structural engineer regarding additional loads on retaining walls during final design, if needed. The lateral pressures on walls may be resisted by friction between the foundation and subgrade soil, and by passive resistance acting on the below -grade portion of the foundation. Recommendations for frictional and passive resistance to lateral loads are presented in the Foundations subsection of this report. All wall backfill should be well compacted as outlined in the Structural Fill subsection of this report. Care should be taken to prevent the buildup of excess lateral soil pressures due to over -compaction of the wall backfill. This can be accomplished by placing wall backfill in 8-inch loose lifts and compacting the backfill with small, hand -operated compactors within a distance behind the wall equal to at least half the height of the wall. The thickness of the loose lifts should be reduced to accommodate the lower compactive energy of the hand -operated equipment. The recommended level of compaction should still be maintained. Permanent drainage systems should be installed for retaining walls. Recommendations for these systems are found in the Subsurface Drainage subsection of this report. We recommend that we be retained to evaluate the proposed wall drain backfill material and observe installation of the drainage systems. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Binder Property Residence Development Edmonds, Washington NGA File No. 1154419 February 19, 2020 Page 9 Structural Fill General: Fill placed beneath foundations, pavement, or other settlement -sensitive structures should be placed as structural fill. Structural fill, by definition, is placed in accordance with prescribed methods and standards, and is monitored by an experienced geotechnical professional or soils technician. Field monitoring procedures would include the performance of a representative number of in -place density tests to document the attainment of the desired degree of relative compaction. The area to receive the fill should be suitably prepared as described in the Site Preparation and Grading subsection prior to beginning fill placement. Materials: Structural fill should consist of a good quality, granular soil, free of organics and other deleterious material, and be well graded to a maximum size of about three inches. All-weather fill should contain no more than five -percent fines (soil finer than U.S. No. 200 sieve, based on that fraction passing the U.S. 3/4-inch sieve). Some of the more granular native on -site soils may be suitable for use as structural fill, but this will be highly dependent on the moisture content of these soils at the time of construction. In our opinion, the surficial undocumented fill soils are not suitable for use as structural fill. We should be retained to evaluate all proposed structural fill material prior to placement. Fill Placement: Following subgrade preparation, placement of structural fill may proceed. All filling should be accomplished in uniform lifts up to eight inches thick. Each lift should be spread evenly and be thoroughly compacted prior to placement of subsequent lifts. All structural fill underlying building areas and pavement subgrade should be compacted to a minimum of 95 percent of its maximum dry density. Maximum dry density, in this report, refers to that density as determined by the ASTM D-1557 Compaction Test procedure. The moisture content of the soils to be compacted should be within about two percent of optimum so that a readily compactable condition exists. It may be necessary to over - excavate and remove wet soils in cases where drying to a compactable condition is not feasible. All compaction should be accomplished by equipment of a type and size sufficient to attain the desired degree of compaction and should be tested. Slab -on -Grade Slabs -on -grade should be supported on subgrade soils prepared as described in the Site Preparation and Grading subsection of this report. However, undocumented fill soils may be encountered at slab subgrade elevations. If some future slab settlement and/or cracking cannot be tolerated, we recommend that at a minimum, the slab subgrade be overexcavated by two feet and the overexcavation backfilled with 1'/4-inch crushed rock compacted to structural fill specifications. The resulting overexcavation subgrade should be compacted to an unyielding condition prior to placement of the crushed rock backfill. Additional reinforcement and doweled cold joints should be incorporated into the slab design. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1154419 Binder Property Residence Development February 19, 2020 Edmonds, Washington Page 10 We recommend that all floor slabs be underlain by at least six inches of free -draining gravel with less than three percent by weight of the material passing Sieve #200 for use as a capillary break. We recommend that the capillary break be hydraulically connected to the footing drain system to allow free drainage from under the slab. A suitable vapor barrier, such as heavy plastic sheeting (6-mil, minimum), should be placed over the capillary break material. An additional 2-inch-thick moist sand layer may be used to cover the vapor barrier. This sand layer may be used to protect the vapor barrier membrane and to aid in curing the concrete. Pavement Subgrade and Other Exterior Hard Surfaces Pavement and walkway subgrade preparation should be completed as recommended in the Site Preparation and Grading and Structural Fill subsections of this report. Depending on tolerance to cracking, we recommend that at least the upper two feet of the existing material be removed and replaced with granular structural fill or crushed rock. The subgrades should be proof -rolled with a heavy, rubber - tired piece of equipment, to identify soft or yielding areas that may require repair prior to placing any structural fill and prior to placing the pavement base course. We should be retained to observe the proof - rolling and to recommend repairs prior to placement of the asphalt or hard surfaces. The hard surface section should be thickened and reinforced with rebar where applicable to further reduce the effects of settlement due to the loose/soft soils, but potential long-term cracking should still be expected if any undocumented fill is left in place below the upper crushed rock backfill. Utilities We recommend that underground utilities be bedded with a minimum six inches of pea gravel prior to backfilling the trench with on -site or imported material. Trenches within settlement sensitive areas should be compacted to 95% of the modified proctor as described in the Structural Fill subsection of this report. Trench backfill should be compacted to a minimum of 95% of the modified proctor maximum dry density. Trenches located in non-structural areas and five feet below roadway subgrade should be compacted to a minimum 90% of the maximum dry density. The trench backfill compaction should be tested. Site Drainage Infiltration: The subsurface soils generally consisted of undocumented fill soils underlain by silty sand with varying amounts of gravel that we interpreted as native glacial deposits to the depths explored. The 2019 WSDOE Stormwater Management Manual for Western Washington was utilized to determine the long term design infiltration rate of the site soils. In accordance with this manual, on -site infiltration testing consisting of the Small Scale Pilot Infiltration Test (Small PIT) was used to determine the long- term design infiltration rates. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1154419 Binder Property Residence Development February 19, 2020 Edmonds, Washington Page 11 We conducted one Small PIT within Infiltration Pit 1 located within the north -central portion of the site, as shown on the attached Site Plan in Figure 2. The pit where the test was conducted measured 4.0-feet long by 3.0-feet wide by 5.0-feet deep. The pit was filled with 12-inches of water at the beginning of the day and we began the soaking period of the PIT for approximately 6 hours. At this time, the water flow rate into the holes was monitored with a Great Plains Industries (GPI) TM 075 water flow meter for the pre-soak period. After the 6-hour soaking period was completed, the water level was maintained at approximately 12- inches for one hour for the steady-state period of the test. The flow rate for Infiltration Pit 1 stabilized at 0.012 gallons per minute (0.74 gallons per hour), which equates to an approximate infiltration rate of 0.10 inches per hour. The water was shut off after the steady-state period and the water level within the pit was monitored every 15 minutes for one hour. After one hour, the water level within the pit had not dropped from 12 inches, resulting in an infiltration rate of 0.0 inches per hour during the falling head portion of the test. Due to the very low rate from the steady-state portion of the test and the zero infiltration during the falling head, it is our opinion that the native glacial till soils encountered at depth throughout the site are not conducive to traditional onsite infiltration. However low -impact design infiltration systems, such as pervious pavements, bioswales, and rain gardens, could be feasible. This should be determined by the civil engineer during the final design. We recommend that any proposed low -impact design infiltration systems be placed as to not negatively impact any proposed or existing nearby structures and also meet all required setbacks from existing property lines, structures, and sensitive areas as discussed in the drainage manual. In general, infiltration systems should not be located within the fill areas associated with site grading or retaining wall backfill as such condition could lead to failures of the placed fills and/or retaining structures. We should be retained to evaluate the infiltration system design and installation during construction. Surface Drainage: The finished ground surface should be graded such that stormwater is directed to an approved stormwater collection system. Water should not be allowed to stand in any areas where footings, slabs, or pavements are to be constructed. Final site grades should allow for drainage away from the residences. We suggest that the finished ground be sloped at a minimum downward gradient of three percent, for a distance of at least 10 feet away from the residences. Surface water should be collected by permanent catch basins and drain lines, and be discharged into an approved discharge system. Subsurface Drainage: If groundwater is encountered during construction, we recommend that the contractor slope the bottom of the excavation and collect the water into ditches and small sump pits where the water can be pumped out and routed into a permanent storm drain. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1154419 Binder Property Residence Development February 19, 2020 Edmonds, Washington Page 12 We recommend the use of footing drains around the structures. Footing drains should be installed at least one foot below planned finished floor elevation. The drains should consist of a minimum 4-inch- diameter, rigid, slotted or perforated, PVC pipe surrounded by free -draining material wrapped in a filter fabric. We recommend that the free -draining material consist of an 18-inch-wide zone of clean (less than three -percent fines), granular material placed along the back of walls. Pea gravel is an acceptable drain material. The free -draining material should extend up the wall to one foot below the finished surface. The top foot of backfill should consist of impermeable soil placed over plastic sheeting or building paper to minimize surface water or fines migration into the footing drain. Footing drains should discharge into tightlines leading to an approved collection and discharge point with convenient cleanouts to prolong the useful life of the drains. Roof drains should not be connected to wall or footing drains. CONSTRUCTION MONITORING We should be retained to provide construction monitoring services during the earthwork phase of the project to evaluate subgrade conditions, temporary cut conditions, fill compaction, and drainage system installation. USE OF THIS REPORT NGA has prepared this report for Ms. Deborah Binder and her agents, for use in the planning and design of the development on this site only. The scope of our work does not include services related to construction safety precautions and our recommendations are not intended to direct the contractors' methods, techniques, sequences, or procedures, except as specifically described in our report for consideration in design. There are possible variations in subsurface conditions between the explorations and also with time. Our report, conclusions, and interpretations should not be construed as a warranty of subsurface conditions. A contingency for unanticipated conditions should be included in the budget and schedule. We recommend that NGA be retained to provide monitoring and consultation services during construction to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes should the conditions revealed differ from those anticipated, and to evaluate whether or not earthwork and foundation installation activities comply with contract plans and specifications. We should be contacted a minimum of one week prior to construction activities and could attend pre -construction meetings if requested. Within the limitations of scope, schedule, and budget, our services have been performed in accordance with generally accepted geotechnical engineering practices in effect in this area at the time this report was prepared. No other warranty, expressed or implied, is made. Our observations, findings, and opinions are a means to identify and reduce the inherent risks to the owner. o-o-o NELSON GEOTECHNICAL ASSOCIATES, INC. Geotcchnical Engineering Evaluation Binder Property Residence Development Edmonds, Washington NGA File No. 1154419 February 19, 2020 Page 13 It has been a pleasure to provide service to you on this project. If you have any questions or require further information, please call. Sincerely, NELSON GEOTECHNICAL ASSOCIATES, INC. Daniel J. O'Dell Staff Geologist I Carston T. Curd, GIT Project Geologist Maher A. Shebl, PhD, PE, M.ASCE Senior Engineer DJO:CTC:MAS:dy Four Figures Attached NELSON GEOTECHNICAL ASSOCIATES, INC. VICINITY MAP N Not to Scale United States Postal Service The Hook Sth PI SWO 18 3� Hutt Park learn St SW 9, SuperBooks Company s FQ 187th SI SW Seaview n n 187th SI SW v s c Elementary School P E R R I N V I L L E m a ca n Project Edmonds Bay D 1891t1 PI S:. Site ou < 189th PI Slq 1901nslsw Adult Care Home "'ek`P' n o_ st' Ctlenry St 19 l os� �a 191s1 192nd St SW C 192nd PI 51\' m N n Just Flowers Q dDe Portofino © Edmonds Q g Q Maplewood Presbyterian Church PLn Restaurant & Bar Adventist Church Faye'Lla' 196m St sw 524 524 Grace Lutheran Church a Iody Ln OEdmonds10 9 Elementary School Tr 198111 S1 SW Hlndley Ln D Viewland Way 3 d) Maplewood 3 ocA e °' z was Park a imonds United t E2 thodist Church Q Maplewood Parent 0 o %oo r 0 � Cooperative v s VW.PI q a' W fHE BOWL o a 0° E Z ' EDMONDS y� 202nd SI SW a o D m nlonas Carol Way F w n 4 o Caen St Glen St ?�rSt SW C ut 9 Pine Ridge a� � -Park Edmonds, WA m Project Number NELSON GEOTECHNICAL No. Date Revision By CK o Binder Residence ASSOCIATES, INC. 1154419 NGA 1 2/12/20 Original DPN DJO Development p GEOTECHNICAL ENGINEERS & GEOLOGISTS E Figure 1 Vicinity Map Woodinville Office East Wenatchee Office OU J 17311-135th Ave. NE, A-500 5526Industry Lane, #2 Woodinville, WA 98072 East Wenatchee, WA 98802 J (425) 486-1669 / Fax: 481-2510 w.nelsonyeotech.com (509) 665-7696 / Fax: 665=7692 = Site Plan N 192nd St SW 27 S� S SS S SS a / d N ` � — N 89'30'26" W 115.00' I DEC 8 M(J14" DEC 8" -- 1 INF-1 J LOT AREA_;_ Q- P-1 I 1 ZO75 SF I o° 16 f k I' 27041800303700 B 1 o �( 16" B 0 ; � 1 18" Aa B 0 o I ROOF PEAK 0 o ELEV.=362.22' o 0 ELEV 344.55' TP-3i z I i ; { I HOUSE J8912 I I - 14� TP-2 M 8.8' I 3 8' 8.2' 6.4 j m I � � 16"x3 ASPHALT N 89'30'26" W 115.00 W X WOOD FENCE x x' r i a 0 LEGEND 0 U — — Property line C Ul INF-1 0 20 40 Number and approximate I location of infiltration test pit TP-1 Scale: 1 inch = 20 feet N —�— Number and approximate o location of test pit o Reference: Site Plan based on a plan dated December 18, 2019 titled "Deborah Binder," prepared by Pacific Coast Surveys, Inc. a` 10 Project Number Binder Residence NELSON GEOTECHNICAL No. Date Revision By CK o 1154419 Development ASSOCIATES, INC. NGA GEOTECHNICAL ENGINEERS & GEOLOGISTS 1 2/12/20 Original DPN DJO E Figure 2 Site Plan Woodinville Office 17311-135th Ave. NE, A-500 Woodinville, WA 98072 East Wenatchee Office 55261ndost y Lane, #2 East Wenatchee, WA 98802 UO J J (425)486-16691 Fax. 481-2510 www.nelsongeotech.com (509)665-7696/Fax: 665-7692 = UNIFIED SOIL CLASSIFICATION SYSTEM GROUP MAJOR DIVISIONS GROUP NAME SYMBOL CLEAN GW WELL -GRADED, FINE TO COARSE GRAVEL COARSE- GRAVEL GRAVEL GP POORLY -GRADED GRAVEL GRAINED MORE THAN 50 GM OF COARSE FRACTION OF SILTY GRAVEL RETAINED ON SOILS NO.4 SIEVE WITH FINES GC CLAYEY GRAVEL SAND CLEAN SW WELL -GRADED SAND, FINE TO COARSE SAND SAND SP POORLY GRADED SAND MORE THAN 50 % RETAINED ON MORE THAN 50 % NO. 200 SIEVE OF COARSE FRACTION SAND SM SILTY SAND PASSES NO. 4 SIEVE WITH FINES SC CLAYEY SAND FINE - SILT AND CLAY ML SILT INORGANIC GRAINED LIQUID LIMIT CL CLAY LESS THAN 50 % SOILS ORGANIC OL ORGANIC SILT, ORGANIC CLAY SILT AND CLAY MH SILT OF HIGH PLASTICITY, ELASTIC SILT INORGANIC MORE THAN 50 % PASSES LIQUID LIMIT CH CLAY OF HIGH PLASTICITY, FAT CLAY NO. 200 SIEVE 50 % OR MORE ORGANIC CH ORGANIC CLAY, ORGANIC SILT HIGHLY ORGANIC SOILS PT PEAT NOTES: 1) Field classification is based on visual SOIL MOISTURE MODIFIERS: examination of soil in general accordance with ASTM D 2488-93. Dry - Absence of moisture, dusty, dry to the touch 2) Soil classification using laboratory tests is based on ASTM D 2488-93. Moist - Damp, but no visible water. 3) Descriptions of soil density or Wet - Visible free water or saturated, consistency are based on usually soil is obtained from interpretation of blowcount data, below water table visual appearance of soils, and/or test data. Project Number NELSON GEOTECHNICAL No. Date Revision By CK 1154419 Binder Residence NGA ASSOCIATES, INC. Development GEOTECHNICAL ENGINEERS & GEOLOGISTS 1 2/12/20 Original DPN DJO Figure 3 Soil Classification Chart Woodinville Office East Wenatchee Office 311-135th Ave. NE, A-500 5526 Lane, 88 Woodinville, WA 98072 East Wenatchee, WA 98602 (425) 486-16691 Fax: 481-2510 w.nelsongeotech.com (509) 665-76961 Fax: 665-7692 LOG OF EXPLORATION DEPTH (FEET) USC SOIL DESCRIPTION INFILTRATION PIT ONE 0.0 - 3.0 GRASS UNDERLAIN BY DARK BROWN TO BROWN, SILTY FINE TO MEDIUM SAND WITH ORGANICS, GRAVEL, ROOTS, AND COBBLES (LOOSE TO MEDIUM DENSE, MOIST) (UNDOCUMENTED FILL) 3.0 - 5.0 SM GRAY TO GRAY -BROWN, SILTY FINE TO MEDIUM SAND WITH IRON OXIDE STAINING, GRAVEL AND COBBLES (MEDIUM DENSE TO DENSE, MOIST) SAMPLES WERE NOT COLLECTED GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 5.0 FEET ON 2/5/2020 TEST PIT ONE 0.0-2.0 GRASS UNDERLAIN BY DARK BROWN TO BROWN, SILTY FINE TO MEDIUM SAND, TRACE COBBLES, GRAVEL, ORGANICS, IRON OXIDE STAINING (LOOSE TO MEDIUM DENSE, MOIST) (UNDOCUMENTED FILL) 2.0-9.0 SM GRAY, SILTY FINE TO MEDIUM SAND WITH GRAVEL, TRACE COBBLES, AND IRON OXIDE STAINING (MEDIUM DENSE TO DENSE, MOIST) SAMPLE WAS COLLECTED AT 8.0 FEET GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 9.0 FEET ON 2/5/2020 TEST PIT TWO 0.0-4.0 GRASS UNDERLAIN BY DARK BROWN, SILTY FINE TO MEDIUM SAND WITH ROOTS, GRAVEL, COBBLES, AND IRON OXIDE STAINING (LOOSE TO MEDIUM DENSE, MOIST) (UNDOCUMENTED FILL) 4.0 - 6.0 SM GRAY, SILTY FINE TO MEDIUM SAND WITH COBBLES, GRAVEL, IRON OXIDE STAINING (MEDIUM DENSE TO DENSE, MOIST) SAMPLES WERE NOT COLLECTED GROUNDWATER SEEPAGE WAS ENCOUNTERED AT 3.0 FEET TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 6.5 FEET ON 2/5/2020 TEST PIT THREE 0.0-4.6 GRASS UNDERLAIN BY DARK BROWN, SILTY FINE TO MEDIUM SAND WITH GRAVEL, COBBLES, ROOTS, ORGANICS, AND IRON OXIDE WEATHERING (LOOSE TO MEDIUM DENSE, MOIST) (UNDOCUMENTED FILL) 4.6 - 5.5 SM GRAY, SILTY FINE TO MEDIUM SAND WITH COBBLES, GRAVEL, AND IRON OXIDE STAINING (MEDIUM DENSE TO DENSE, MOIST) SAMPLES WERE NOT COLLECTED GROUNDWATER SEEPAGE WAS ENCOUNTERED AT 2.7 FEET TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 5.5 FEET ON 2/5/2020 DJO:CTC NELSON GEOTECHNICAL ASSOCIATES, INC. FILE NO 1154419 FIGURE 4 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