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APPROVED STM RESUB 1+PLN2021-0021+Stormwater Report+4.21.2022_12.08.32_PM+2818905
88th Ave W Short Plat 3-Lot Short Plat 19508 88th Avenue W Edmonds, WA 98026 PLN 2021- 0021 Stormwater Site Plan Report Prepared for: Select Homes Date: May 4, 2021 Revision #4: April 20, 2022 4/20/2022 Prepared by: Rob Long, PE RAM Engineering, Inc. 19109 36th Ave W, Suite 100, Lynnwood WA 98036 (425) 678-6960 RAMengineeringinc.com Job No. 21-001 RESUB CITY OF EDMONDS DEVELOPMENT SERVICES DEPARTMENT APR 21 2022 COMPLIES WITH APPLICABLE CITY STORMWATER CODE 07/15/2022 RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page i 88th Ave W Short Plat 3-Lot Short Plat Introduction: This summary report provides site design information for a three lot short plat development by Select Homes. This report includes storm drainage analysis to support permit review and approval. The property is located at 19508 88th Avenue W, in the southwest 1/4 of Section 18, T 27 N, R 4 E, W.M. Site Address: 19508 88th Avenue W Edmonds, WA 98026 Tax Parcel Number: 270418 003 03400 Applicant: Select Homes 16513 13th Ave W, Suite A108, Lynnwood WA 98037 Contact: Kayla Clark Nichols (425) 742-6044 TABLE OF CONTENTS SECTION PAGES A. Project Overview .............................................................................................................................. 4 B. Existing Conditions Summary ........................................................................................................... 1 C. Developed Site Hydrology .............................................................................................................. 17 D. Soils Report ..................................................................................................................................... 19 E. Construction SWPPPP Requirements ................................................................................................ 2 F. Operation and Maintenance Guidelines .......................................................................................... 15 RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 1 PROJECT OVERVIEW: This report provides engineering information for the proposed construction of a three lot short plat on a 41,826 sf (0.96 ac) lot; the project is located at 19508 88th Avenue W in the City of Edmonds. The applicant, Select Homes proposes to retain the existing house and construct two new single family residence on the project site. This report provides the evaluation for the proposed short plat residential development. Summary of Minimum Requirements for Category 2 Project: Minimum Requirement #1 – Preparation of Stormwater Site Plan. The proposed site development consists of disturbing about 0.96 acres of land and creating/replacing about 10,904 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 been 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 (gross site = 0.96 acres), 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 westerly direction. There are no concentrated flows or existing defined conveyance systems located onsite, any site runoff leaves the site as sheet-flow. Per the geotechnical report the underlying soils consists of silty sands that are able infiltrate stormwater; thus, it is assumed a majority of the local RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 2 stormwater infiltrates and dissipates into the ground. The site is located within the upper reach of the Fruitdale Creek watershed basin per the City of Edmonds maps (see section C). Onsite stormwater BMPs (infiltration trench and Post-Construction Soil Quality and Depth) will be implemented with the site development; these stormwater BMPs will mimic the natural infiltration and dissipation of stormwater into the underlying soils. Minimum Requirement #5 – Onsite Stormwater Management. A site-specific geotechnical evaluation (see section D) of the site demonstrates that an infiltration trench 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 civil site development plans and Section C for 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 4,670 sf pollution generation hard surfaces (shared private road and driveways; thus, no basic or enhanced water quality treatment system is required. The site’s stormwater infiltration system will be proceeded by a catch basin with a sump and a floatable tee that will provide some water quality and oil/water separation of the collected runoff. Minimum Requirement #7 – Flow Control. An onsite infiltration trench will provide flow control of the site development’s stormwater runoff. The infiltration trench system is designed to fully mitigate the increased hard surfaces and be in full compliance with the LID Standard and full flow control (match flow durations between 8 percent of the 2-year flow through the full 50-year flow). Flow control (storm water infiltration) designs and sizing calculations are provided in Section E of this report. 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 are provided in section H. RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 3 Parcel (Vicinity) Map: RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 4 Site Plan: RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 1 EXISTING CONDITIONS SUMMARY Existing Conditions. The total site consists of about 41,826 sf (0.96 acres) and is currently occupied by an existing single-family residence. The existing house and driveway are surrounded by grass lawn and landscape areas. Access to the site is via 88th Avenue W that abuts the easterly boundary of the subject site. The site is surrounded by single family residences to the north, west and south; and 88th Ave W to the east (see attached aerial photo). The site generally slopes in a westerly direction in a range between 2% and 10%. No define drainage courses are found on-site and stormwater runoff would sheet flow in a westerly/northwesterly direction towards the Puget Sound within the Fruitdale Creek basin. No runoff from the east and 88th Ave W right- of-way flows onto the site due to an existing thickened edge and stormwater conveyance system (pipes and catch basins) that collects and routs runoff north to Fruitdale Creek. 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 study by Earth Solutions NW, LLC the on-site soils consist of silty sands (USCS: SM). Mapping shows that the subject site is underlain by Vashon till (Qvt). Full soils description is included in the project’s site specific geotechnical engineering study by Earth Solutions NW, LLC. Aerial Photo (City of Edmonds GIS, 2017 photo): RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 1 DEVELOPED SITE HYDROLOTY: Developed Conditions. The proposed project includes the construction of a shared private road to access the existing house (to remain) and two new single-family residences, driveways and supporting utilities. The existing house onsite will remain on Lot 1 of the short plat; new impervious surface will be allocated to Lot 1 to construct a new driveway and walkway to the existing house. Per City of Edmonds standards, 25% of the existing hard surface associated with the existing house to remain shall be accounted for in the stormwater infiltration system; however due to the fact the existing house hard surface flows to the project infiltration system, all the Lot 1 hard surface will be accounted for in the design of the infiltration trench system. Landscaping and grass lawn around the new residence will stabilize the site upon building construction. The project proposes to create and/or replace 12,460 sf of hard surface, which includes all of the hard surface on Lot 1 (new, replaced and existing). The following is a summary of the proposed new/replaced and existing hard surface areas: Total Hard Surface to Mitigated = 12,460 sf (0.286 ac) Lot 1 Hard Surface to Mitigate = 2,775 sf Existing House/covered patio to remain = 2,075 sf New Driveway for Area = 430 sf New Walkway/Patio Area = 270 sf Lot 2 Hard Surface to Mitigate = 3,425 sf Roof Area = 2,680 sf Driveway Area = 625 sf Walkway/Patio Area = 120 sf Lot 3 Hard Surface to Mitigate = 3,720 sf Roof Area = 2,610 sf Driveway Area = 1,075 sf Walkway/Patio Area = 35 sf Shared Private Road = 2,540 sf Total Pervious Surface (Lawn) = 29,366 sf (0.674 ac) The project proposes to implement full (100%) infiltration for all new and replaced hard surfaces onsite. In accordance with City Code (ECDC 18.30.060.D.5.b.i.), existing hard surfaces to remain shall apply stormwater management BMPs to a minimum of 25% of the existing unmanaged surfaces to remain. However, due to the fact the existing house hard surface flows to the project’s infiltration system it has been sized to accommodate 100% of the Lot 1 hard surface (2,775 sf). The joint infiltration trench will be sized using the DOE 2012 Western Washington Hydrology Model (WWHM2012) continuous runoff model. RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 2 The infiltration trench will be constructed along the westerly side of the project site within easements on the westerly portions of Lots 2 and 3. The infiltration trench will be designed for the total development area; the total hard surface mitigated will be 12,460 sf (0.286 ac). The infiltration trench shall be a minimum 29 feet wide, 136 feet long and 4.0 feet deep; filled with 1-½” to 3” washed drain rock (35% voids). Due to the fact the site does not have a well-defined stormwater conveyance system to discharge or overflow to, a stormwater pump system has been included in the design. The stormwater pump will provide a safe and certain overflow route. The stormwater pump system design is provided below. A site specific geotechnical evaluation was made to assess the use of infiltration onsite. The evaluation determined infiltration is feasible onsite and recommends a long-term infiltration design rate of 0.28 in/hr. The onsite measured infiltration rate was 1.25 in/hr and a design rate of 0.28 in/hr has been recommended by the geotechnical engineer. The recommended rate includes conservative design correction factors of 0.5 for both site variability and test method. Therefore, the design infiltration rate of 0.28 in/hr is a conservative design rate and is believed to be achievable post-construction. The site is constrained by its natural slope and does not have a direct available receiving stormwater system (pipe, catch basin and/or ditch) and thus infiltration has been proposed to control stormwater. The design rate is low, however a large footprint (with void storage volume in the trench rock) is proposed. Catch basin 1, at the lower northwest corner of the site will provide an overflow for the infiltration systems that will discharge overflows in the existing natural runoff path along neighboring back yards west of the site. As discussed in the 2014 DOE Stormwater Manual (Vol. III, Section 3.3); if the measured post-construction infiltration rates are below the design rates (0.28 in/hr), the underlying soils can be amended/ rehabilitated. Additionally, the layout and design can be adjusted/expanded during construction to create an expanded trench footprint to increase the infiltration capacity of the system. During the soil test pit excavation and infiltration testing, light groundwater seepages from the infiltration testing were observed at a depth of five feet. The seepages were determined to be flows from the nearby infiltration testing that was being conducted at the same time; no groundwater seepages were encounter in the other test pit onsite. The geotechnical engineering will be onsite to observe the construction of the infiltration trench and will be able to adjust the location and size, and test the actual infiltration rates in the areas the trench is constructed. To facilitate flexibility during construction an expanded private drainage easement area has been provided. The developed runoff rates and storage calculations were performed using the DOE 2012 Western Washington Hydrology Model (WWHM2012) continuous runoff model. The below calculations demonstrate that the trenches will fully mitigate (100% infiltration) the increased hard surfaces, see WWHM2012 input/printout on the following pages. RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 3 ___________________________________________________________________ WWHM2012 PROJECT REPORT ___________________________________________________________________ Project Name: 21-001 Prelim Infil(2) Site Name: 88th 3-Lot Site Address: 21-001 City : Report Date: 10/12/2021 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, Forest, Mod .96 Pervious Total 0.96 Impervious Land Use acre Impervious Total 0 Basin Total 0.96 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ MITIGATED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Pasture, Mod .674 Pervious Total 0.674 Impervious Land Use acre ROADS MOD 0.058 ROOF TOPS FLAT 0.169 DRIVEWAYS MOD 0.049 SIDEWALKS MOD 0.01 Impervious Total 0.286 Basin Total 0.96 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater Gravel Trench Bed 1 Gravel Trench Bed 1 ___________________________________________________________________ RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 4 Name : Gravel Trench Bed 1 Bottom Length: 136.00 ft. Bottom Width: 29.00 ft. Trench bottom slope 1: 0 To 1 Trench Left side slope 0: 0 To 1 Trench right side slope 2: 0 To 1 Material thickness of first layer: 4 Pour Space of material for first layer: 0.35 Material thickness of second layer: 0 Pour Space of material for second layer: 0 Material thickness of third layer: 0 Pour Space of material for third layer: 0 Infiltration On Infiltration rate: 0.28 Infiltration safety factor: 1 Total Volume Infiltrated (ac-ft.): 169.07 Total Volume Through Riser (ac-ft.): 0 Total Volume Through Facility (ac-ft.): 169.07 Percent Infiltrated: 100 Total Precip Applied to Facility: 0 Total Evap From Facility: 0 Discharge Structure Riser Height: 4 ft. Riser Diameter: 8 in. Element Flows To: Outlet 1 Outlet 2 ___________________________________________________________________ RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 5 Gravel Trench Bed Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 0.0000 0.090 0.000 0.000 0.000 0.0444 0.090 0.001 0.000 0.025 0.0889 0.090 0.002 0.000 0.025 0.1333 0.090 0.004 0.000 0.025 0.1778 0.090 0.005 0.000 0.025 0.2222 0.090 0.007 0.000 0.025 0.2667 0.090 0.008 0.000 0.025 0.3111 0.090 0.009 0.000 0.025 0.3556 0.090 0.011 0.000 0.025 0.4000 0.090 0.012 0.000 0.025 0.4444 0.090 0.014 0.000 0.025 0.4889 0.090 0.015 0.000 0.025 0.5333 0.090 0.016 0.000 0.025 0.5778 0.090 0.018 0.000 0.025 0.6222 0.090 0.019 0.000 0.025 0.6667 0.090 0.021 0.000 0.025 0.7111 0.090 0.022 0.000 0.025 0.7556 0.090 0.023 0.000 0.025 0.8000 0.090 0.025 0.000 0.025 0.8444 0.090 0.026 0.000 0.025 0.8889 0.090 0.028 0.000 0.025 0.9333 0.090 0.029 0.000 0.025 0.9778 0.090 0.031 0.000 0.025 1.0222 0.090 0.032 0.000 0.025 1.0667 0.090 0.033 0.000 0.025 1.1111 0.090 0.035 0.000 0.025 1.1556 0.090 0.036 0.000 0.025 1.2000 0.090 0.038 0.000 0.025 1.2444 0.090 0.039 0.000 0.025 1.2889 0.090 0.040 0.000 0.025 1.3333 0.090 0.042 0.000 0.025 1.3778 0.090 0.043 0.000 0.025 1.4222 0.090 0.045 0.000 0.025 1.4667 0.090 0.046 0.000 0.025 1.5111 0.090 0.047 0.000 0.025 1.5556 0.090 0.049 0.000 0.025 1.6000 0.090 0.050 0.000 0.025 1.6444 0.090 0.052 0.000 0.025 1.6889 0.090 0.053 0.000 0.025 1.7333 0.090 0.054 0.000 0.025 1.7778 0.090 0.056 0.000 0.025 1.8222 0.090 0.057 0.000 0.025 1.8667 0.090 0.059 0.000 0.025 1.9111 0.090 0.060 0.000 0.025 1.9556 0.090 0.062 0.000 0.025 2.0000 0.090 0.063 0.000 0.025 2.0444 0.090 0.064 0.000 0.025 2.0889 0.090 0.066 0.000 0.025 2.1333 0.090 0.067 0.000 0.025 2.1778 0.090 0.069 0.000 0.025 2.2222 0.090 0.070 0.000 0.025 2.2667 0.090 0.071 0.000 0.025 2.3111 0.090 0.073 0.000 0.025 2.3556 0.090 0.074 0.000 0.025 2.4000 0.090 0.076 0.000 0.025 2.4444 0.090 0.077 0.000 0.025 2.4889 0.090 0.078 0.000 0.025 2.5333 0.090 0.080 0.000 0.025 2.5778 0.090 0.081 0.000 0.025 2.6222 0.090 0.083 0.000 0.025 2.6667 0.090 0.084 0.000 0.025 2.7111 0.090 0.085 0.000 0.025 2.7556 0.090 0.087 0.000 0.025 2.8000 0.090 0.088 0.000 0.025 RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 6 2.8444 0.090 0.090 0.000 0.025 2.8889 0.090 0.091 0.000 0.025 2.9333 0.090 0.093 0.000 0.025 2.9778 0.090 0.094 0.000 0.025 3.0222 0.090 0.095 0.000 0.025 3.0667 0.090 0.097 0.000 0.025 3.1111 0.090 0.098 0.000 0.025 3.1556 0.090 0.100 0.000 0.025 3.2000 0.090 0.101 0.000 0.025 3.2444 0.090 0.102 0.000 0.025 3.2889 0.090 0.104 0.000 0.025 3.3333 0.090 0.105 0.000 0.025 3.3778 0.090 0.107 0.000 0.025 3.4222 0.090 0.108 0.000 0.025 3.4667 0.090 0.109 0.000 0.025 3.5111 0.090 0.111 0.000 0.025 3.5556 0.090 0.112 0.000 0.025 3.6000 0.090 0.114 0.000 0.025 3.6444 0.090 0.115 0.000 0.025 3.6889 0.090 0.116 0.000 0.025 3.7333 0.090 0.118 0.000 0.025 3.7778 0.090 0.119 0.000 0.025 3.8222 0.090 0.121 0.000 0.025 3.8667 0.090 0.122 0.000 0.025 3.9111 0.090 0.123 0.000 0.025 3.9556 0.090 0.125 0.000 0.025 4.0000 0.090 0.126 0.000 0.025 RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 7 ___________________________________________________________________ ANALYSIS RESULTS Stream Protection Duration ___________________________________________________________________ Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.96 Total Impervious Area:0 ___________________________________________________________________ Mitigated Landuse Totals for POC #1 Total Pervious Area:0.674 Total Impervious Area:0.286 ___________________________________________________________________ 2 year 0.016377 5 year 0.027191 10 year 0.033328 25 year 0.039728 50 year 0.043597 100 year 0.046812 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0 5 year 0 10 year 0 25 year 0 50 year 0 100 year 0 ___________________________________________________________________ RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 8 Stream Protection Duration Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1902 0.023 0.000 1903 0.008 0.000 1904 0.015 0.000 1905 0.009 0.000 1906 0.004 0.000 1907 0.025 0.000 1908 0.016 0.000 1909 0.018 0.000 1910 0.028 0.000 1911 0.014 0.000 1912 0.049 0.000 1913 0.024 0.000 1914 0.006 0.000 1915 0.008 0.000 1916 0.013 0.000 1917 0.006 0.000 1918 0.016 0.000 1919 0.012 0.000 1920 0.015 0.000 1921 0.016 0.000 1922 0.018 0.000 1923 0.012 0.000 1924 0.008 0.000 1925 0.008 0.000 1926 0.014 0.000 1927 0.018 0.000 1928 0.012 0.000 1929 0.026 0.000 1930 0.015 0.000 1931 0.015 0.000 1932 0.011 0.000 1933 0.013 0.000 1934 0.036 0.000 1935 0.013 0.000 1936 0.021 0.000 1937 0.017 0.000 1938 0.018 0.000 1939 0.001 0.000 1940 0.014 0.000 1941 0.014 0.000 1942 0.021 0.000 1943 0.007 0.000 1944 0.018 0.000 1945 0.016 0.000 1946 0.014 0.000 1947 0.010 0.000 1948 0.033 0.000 1949 0.027 0.000 1950 0.015 0.000 1951 0.017 0.000 1952 0.048 0.000 1953 0.042 0.000 1954 0.013 0.000 1955 0.011 0.000 1956 0.008 0.000 1957 0.019 0.000 1958 0.045 0.000 1959 0.027 0.000 1960 0.010 0.000 1961 0.028 0.000 1962 0.014 0.000 1963 0.007 0.000 1964 0.013 0.000 RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 9 1965 0.033 0.000 1966 0.006 0.000 1967 0.013 0.000 1968 0.017 0.000 1969 0.012 0.000 1970 0.019 0.000 1971 0.035 0.000 1972 0.023 0.000 1973 0.026 0.000 1974 0.015 0.000 1975 0.037 0.000 1976 0.017 0.000 1977 0.010 0.000 1978 0.032 0.000 1979 0.009 0.000 1980 0.016 0.000 1981 0.016 0.000 1982 0.011 0.000 1983 0.026 0.000 1984 0.007 0.000 1985 0.016 0.000 1986 0.012 0.000 1987 0.026 0.000 1988 0.020 0.000 1989 0.015 0.000 1990 0.020 0.000 1991 0.015 0.000 1992 0.023 0.000 1993 0.019 0.000 1994 0.033 0.000 1995 0.008 0.000 1996 0.037 0.000 1997 0.017 0.000 1998 0.016 0.000 1999 0.001 0.000 2000 0.012 0.000 2001 0.009 0.000 2002 0.023 0.000 2003 0.018 0.000 2004 0.018 0.000 2005 0.022 0.000 2006 0.012 0.000 2007 0.013 0.000 2008 0.017 0.000 2009 0.011 0.000 2010 0.008 0.000 2011 0.011 0.000 2012 0.015 0.000 2013 0.012 0.000 2014 0.008 0.000 2015 0.032 0.000 2016 0.004 0.000 2017 0.026 0.000 2018 0.045 0.000 2019 0.049 0.000 2020 0.014 0.000 2021 0.022 0.000 2022 0.008 0.000 2023 0.018 0.000 2024 0.038 0.000 2025 0.014 0.000 2026 0.025 0.000 2027 0.011 0.000 2028 0.005 0.000 2029 0.018 0.000 2030 0.035 0.000 2031 0.010 0.000 RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 10 2032 0.008 0.000 2033 0.009 0.000 2034 0.010 0.000 2035 0.040 0.000 2036 0.021 0.000 2037 0.004 0.000 2038 0.020 0.000 2039 0.002 0.000 2040 0.007 0.000 2041 0.011 0.000 2042 0.041 0.000 2043 0.018 0.000 2044 0.025 0.000 2045 0.016 0.000 2046 0.019 0.000 2047 0.012 0.000 2048 0.016 0.000 2049 0.015 0.000 2050 0.010 0.000 2051 0.016 0.000 2052 0.009 0.000 2053 0.017 0.000 2054 0.022 0.000 2055 0.007 0.000 2056 0.006 0.000 2057 0.011 0.000 2058 0.013 0.000 ___________________________________________________________________ Stream Protection Duration Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.0493 0.0000 2 0.0492 0.0000 3 0.0478 0.0000 4 0.0452 0.0000 5 0.0446 0.0000 6 0.0424 0.0000 7 0.0412 0.0000 8 0.0396 0.0000 9 0.0383 0.0000 10 0.0373 0.0000 11 0.0369 0.0000 12 0.0358 0.0000 13 0.0352 0.0000 14 0.0349 0.0000 15 0.0333 0.0000 16 0.0332 0.0000 17 0.0328 0.0000 18 0.0323 0.0000 19 0.0322 0.0000 20 0.0278 0.0000 21 0.0277 0.0000 22 0.0274 0.0000 23 0.0272 0.0000 24 0.0264 0.0000 25 0.0263 0.0000 26 0.0262 0.0000 27 0.0260 0.0000 28 0.0257 0.0000 29 0.0254 0.0000 30 0.0251 0.0000 31 0.0250 0.0000 32 0.0244 0.0000 33 0.0229 0.0000 34 0.0228 0.0000 RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 11 35 0.0227 0.0000 36 0.0227 0.0000 37 0.0224 0.0000 38 0.0220 0.0000 39 0.0219 0.0000 40 0.0213 0.0000 41 0.0212 0.0000 42 0.0205 0.0000 43 0.0204 0.0000 44 0.0200 0.0000 45 0.0196 0.0000 46 0.0189 0.0000 47 0.0187 0.0000 48 0.0185 0.0000 49 0.0185 0.0000 50 0.0183 0.0000 51 0.0183 0.0000 52 0.0180 0.0000 53 0.0180 0.0000 54 0.0179 0.0000 55 0.0179 0.0000 56 0.0177 0.0000 57 0.0177 0.0000 58 0.0176 0.0000 59 0.0175 0.0000 60 0.0175 0.0000 61 0.0175 0.0000 62 0.0173 0.0000 63 0.0172 0.0000 64 0.0168 0.0000 65 0.0166 0.0000 66 0.0165 0.0000 67 0.0165 0.0000 68 0.0163 0.0000 69 0.0161 0.0000 70 0.0160 0.0000 71 0.0158 0.0000 72 0.0158 0.0000 73 0.0158 0.0000 74 0.0158 0.0000 75 0.0156 0.0000 76 0.0156 0.0000 77 0.0156 0.0000 78 0.0154 0.0000 79 0.0153 0.0000 80 0.0152 0.0000 81 0.0149 0.0000 82 0.0148 0.0000 83 0.0148 0.0000 84 0.0148 0.0000 85 0.0147 0.0000 86 0.0147 0.0000 87 0.0146 0.0000 88 0.0145 0.0000 89 0.0144 0.0000 90 0.0144 0.0000 91 0.0143 0.0000 92 0.0142 0.0000 93 0.0142 0.0000 94 0.0141 0.0000 95 0.0140 0.0000 96 0.0134 0.0000 97 0.0132 0.0000 98 0.0132 0.0000 99 0.0132 0.0000 100 0.0129 0.0000 101 0.0129 0.0000 RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 12 102 0.0128 0.0000 103 0.0128 0.0000 104 0.0124 0.0000 105 0.0123 0.0000 106 0.0122 0.0000 107 0.0120 0.0000 108 0.0117 0.0000 109 0.0117 0.0000 110 0.0116 0.0000 111 0.0116 0.0000 112 0.0116 0.0000 113 0.0115 0.0000 114 0.0114 0.0000 115 0.0110 0.0000 116 0.0109 0.0000 117 0.0109 0.0000 118 0.0108 0.0000 119 0.0106 0.0000 120 0.0106 0.0000 121 0.0104 0.0000 122 0.0100 0.0000 123 0.0098 0.0000 124 0.0098 0.0000 125 0.0098 0.0000 126 0.0096 0.0000 127 0.0094 0.0000 128 0.0092 0.0000 129 0.0089 0.0000 130 0.0088 0.0000 131 0.0086 0.0000 132 0.0085 0.0000 133 0.0083 0.0000 134 0.0082 0.0000 135 0.0079 0.0000 136 0.0079 0.0000 137 0.0079 0.0000 138 0.0078 0.0000 139 0.0078 0.0000 140 0.0078 0.0000 141 0.0076 0.0000 142 0.0074 0.0000 143 0.0072 0.0000 144 0.0069 0.0000 145 0.0068 0.0000 146 0.0066 0.0000 147 0.0064 0.0000 148 0.0063 0.0000 149 0.0059 0.0000 150 0.0057 0.0000 151 0.0054 0.0000 152 0.0045 0.0000 153 0.0039 0.0000 154 0.0037 0.0000 155 0.0018 0.0000 156 0.0011 0.0000 157 0.0008 0.0000 ___________________________________________________________________ RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 13 Stream Protection Duration POC #1 The Facility PASSED The Facility PASSED. Flow(cfs) Predev Mit Percentage Pass/Fail 0.0081 53267 0 0 Pass 0.0084 49006 0 0 Pass 0.0087 45136 0 0 Pass 0.0091 41761 0 0 Pass 0.0094 38645 0 0 Pass 0.0097 35805 0 0 Pass 0.0100 33228 0 0 Pass 0.0103 30916 0 0 Pass 0.0106 28879 0 0 Pass 0.0109 26964 0 0 Pass 0.0112 25202 0 0 Pass 0.0115 23473 0 0 Pass 0.0118 21871 0 0 Pass 0.0121 20347 0 0 Pass 0.0124 18943 0 0 Pass 0.0127 17693 0 0 Pass 0.0130 16493 0 0 Pass 0.0133 15469 0 0 Pass 0.0136 14473 0 0 Pass 0.0139 13520 0 0 Pass 0.0142 12629 0 0 Pass 0.0145 11792 0 0 Pass 0.0148 11065 0 0 Pass 0.0151 10427 0 0 Pass RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 14 0.0154 9848 0 0 Pass 0.0157 9309 0 0 Pass 0.0160 8786 0 0 Pass 0.0163 8296 0 0 Pass 0.0166 7850 0 0 Pass 0.0169 7415 0 0 Pass 0.0172 7035 0 0 Pass 0.0175 6667 0 0 Pass 0.0178 6353 0 0 Pass 0.0181 6045 0 0 Pass 0.0184 5742 0 0 Pass 0.0187 5474 0 0 Pass 0.0190 5222 0 0 Pass 0.0193 4993 0 0 Pass 0.0196 4763 0 0 Pass 0.0199 4538 0 0 Pass 0.0202 4335 0 0 Pass 0.0205 4128 0 0 Pass 0.0208 3943 0 0 Pass 0.0211 3772 0 0 Pass 0.0214 3631 0 0 Pass 0.0217 3495 0 0 Pass 0.0220 3369 0 0 Pass 0.0223 3258 0 0 Pass 0.0227 3145 0 0 Pass 0.0230 3054 0 0 Pass 0.0233 2966 0 0 Pass 0.0236 2877 0 0 Pass 0.0239 2779 0 0 Pass 0.0242 2681 0 0 Pass 0.0245 2587 0 0 Pass 0.0248 2493 0 0 Pass 0.0251 2387 0 0 Pass 0.0254 2278 0 0 Pass 0.0257 2181 0 0 Pass 0.0260 2080 0 0 Pass 0.0263 1999 0 0 Pass 0.0266 1927 0 0 Pass 0.0269 1866 0 0 Pass 0.0272 1790 0 0 Pass 0.0275 1719 0 0 Pass 0.0278 1663 0 0 Pass 0.0281 1595 0 0 Pass 0.0284 1537 0 0 Pass 0.0287 1482 0 0 Pass 0.0290 1420 0 0 Pass 0.0293 1360 0 0 Pass 0.0296 1298 0 0 Pass 0.0299 1242 0 0 Pass 0.0302 1188 0 0 Pass 0.0305 1146 0 0 Pass 0.0308 1100 0 0 Pass 0.0311 1045 0 0 Pass 0.0314 1000 0 0 Pass 0.0317 954 0 0 Pass 0.0320 916 0 0 Pass 0.0323 877 0 0 Pass 0.0326 832 0 0 Pass 0.0329 788 0 0 Pass 0.0332 754 0 0 Pass 0.0335 710 0 0 Pass 0.0338 666 0 0 Pass 0.0341 627 0 0 Pass 0.0344 595 0 0 Pass 0.0347 554 0 0 Pass 0.0350 516 0 0 Pass 0.0353 461 0 0 Pass RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 15 0.0356 423 0 0 Pass 0.0360 392 0 0 Pass 0.0363 360 0 0 Pass 0.0366 334 0 0 Pass 0.0369 306 0 0 Pass 0.0372 286 0 0 Pass 0.0375 264 0 0 Pass 0.0378 247 0 0 Pass 0.0381 233 0 0 Pass ___________________________________________________________________ Water Quality BMP Flow and Volume for POC #1 On-line facility volume: 0 acre-feet On-line facility target flow: 0 cfs. Adjusted for 15 min: 0 cfs. Off-line facility target flow: 0 cfs. ___________________________________________________________________ LID Report ___________________________________________________________________ Perlnd and Implnd 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. 2005-2021; All Rights Reserved. RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 16 Overflow Stormwater Pump Design. Due to the lack of an outfall overflow stormwater conveyance system a stormwater pump system has been incorporated in the design to accommodate potential overflow release from the infiltration system. The overflow stormwater pump system is conservatively designed to pump the 100-year developed peak flow frequency (0.259 cfs). A dual-pump alternating system (Zoeller 284 Series with 2.5” discharge force main) will be located as an overflow release system for the infiltration system. A single pump will operate during smaller overflow events, and the pumps will alternate between starts. Both pumps may operate simultaneously during larger overflow event. The operating flow rate of each pump will have the capacity to pump half of the 100-year peak flow rates (half = 0.1295 cfs), thus providing the full 100-year discharge (0.259 cfs) with both pumps are on (full on). Each pump will operate at 58.1 gpm (0.1295 cfs) against 27.5 feet of total head. Total head calculations and manufacturer documentation for the Zoeller 284 Series (including pump performance curves and specification) are provided below. Total Head: Total Head = Static Head + Dynamic Head Static Head = 359.07 ft. – 346.00 ft. = 13.07 ft. Dynamic Head, use the following equation to determine friction loss: where: f = friction loss per 100 ft. of pipe C = flow coefficient 150 for PVC Q = 58.1 gpm Di = inside diameter of pipe, in. 2.5 in. 𝑓=.02083 ൬100 150൰ ଵ.଼ହ ቆ58.1ଵ.଼ହଶ 2.5ସ.଼ହହቇ = 2.11 ft. per 100 ft. of pipe Restricting Globe Valve = 472 ft. (equiv. length of 2.5 in.)- adjust to restrict flows Swing Check Valve = 22.0 ft. (equiv. length of 2.5 in.) Control Gate Valve (open) = 1.7 ft. (equiv. length of 2.5 in.) 90° Bend (2) = 2*9.3 ft. = 18.6 ft. (equiv. length of 2.5 in.) Tee- Branch Flow = 13.0 ft. (equiv. length of 2.5 in.) Total Equivalent Pipe for Fitting Losses = 527.30 ft. Length of pipe between pump and outfall = 157 ft Dynamic Head = (527.3 ft. + 157 ft.) * 2.11 ft. / 100 ft. = 14.43 ft. Total Head = 13.07 ft. (static) + 14.43 ft. (dynamic) = 27.5 ft. Single Pump Required Design Performance: 58.1 gpm with 27.5 ft. of Total Head 8655.4 852.185.11002083.0 iD Q Cf RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 17 Pump Manufacturer Information: RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 18 Offsite Analysis. The site is located within the Fruitdale Creek watershed basin. The Fruitdale Creek basin is a relatively small urban basin that collects stormwater runoff from primarily residential areas in the City Edmonds and ultimately discharges flow westerly/northwesterly to Puget Sound via Fruitdale Creek (see attached watershed map). Runoff from the site sheet-flows in a westerly direction towards Fruitdale Creek. Stormwater runoff would flow westerly across private property entering a small ravine that directs the local drainage north to Fruitdale Creek about 1,000 feet from the site. A majority of the site runoff would leave the site near northwest corner of the project and flow westerly along the back yards of properties west of the site. The westerly flow path across the neighboring private properties is the existing and natural flow path of the runoff from the site. The proposed development of the site will install an infiltration system to reduce runoff flows from the site. The infiltration system has been designed to infiltrate 100% of the WWHM2012 design storms. To provide a safe a certain overflow route a stormwater pump system has been included in the stormwater control system. If the stormwater flows exceed the capacity of the infiltration trench system, the flows will overflow into a stormwater pump system that will pump the flows to the stormwater pipe conveyance system along 88th Ave W that flows north to Fruitdale Creek. The potential pumped overflow flows would merge with the natural downstream path about 1,000 feet downstream of the site. Therefore, both the existing and potential overflow routes are within the same threshold discharge area (within ¼ mile of convergence). With the installation of the proposed 100% infiltration system there are no additional adverse impact anticipated as a result of the proposed site development. Fruitdale Creek continues in a westerly/northwesterly direction and eventually discharges into the Puget Sound about 0.9 miles from the site. See the below downstream drainage facility map and watershed map for the local downstream path. RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 19 Downstream Drainage Facility Map (City of Edmonds GIS) RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 20 Watershed Basin Map RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 1 SOILS REPORT: Geotechnical Evaluation Letter Prepared by: Earth Solutions NW, LLC Date: May 4, 2021 Pages: 18 Addendum Geotechnical Evaluation Letter Prepared by: Earth Solutions NW, LLC Date: October 13, 2021 Pages: 2 RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 1 CONSTRUCTION SWPPP REQUIREMENTS: The project will require grading to construct the proposed buildings, driveways, shared private road 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. Stockpiles 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. RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 2 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: No project specific de-watering system is proposed for the project. However, the contractor shall control any highly turbid or contaminated de-watering water and keep it separate 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 BMP’s: BMPs shall be maintained and removed at the end of the project as follows: i. All temporary and permanent erosion and sediment control BMPs shall be inspected, maintained and repaired in accordance with the Drainage Manual or as approved or required by the City to assure continued performance of their intended function in accordance with BMP specifications. ii. The applicant may remove temporary BMPs when they are no longer needed. iii. All temporary erosion and sediment control BMPs shall be removed within 30 days after construction is completed and the City has determined that the site is stabilized. Element 12: Manage the Project: The owner of the site is responsible for managing the installation and maintenance of the site BMPs. Element 13. Protect Low Impact Development BMPs: During construction the proposed infiltration trench 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. RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 1 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 joint stormwater system (pipes, catch basins, and joint infiltration trench) which benefits all three lots shall be maintained collectively and equally by all three property owners. 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 property owners and used as a reference to identify drainage facilities outlined in this manual. Stormwater Infiltration Trench System. The private joint infiltration trench system consists of excavated trench filled with drain rock. The infiltration trench system has been designed to infiltrate most storm event; if an extraordinary event was to occur or multiple back to back large storm events occurred the upstream catch-basins may overtop and overflow into the street system. If regular overtopping of the catch basin is experienced the system shall be thoroughly cleaned and inspected. Over a period of time siltation of the infiltration bed can occur (especially if the system and upstream catch basin are not inspected and cleaned regularly) and replacement of the rock in the infiltration system may be required. 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/wqhome.html RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 2 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 Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 3 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 General Trash & Debris Any trash and debris which exceed 1 cubic feet per 1,000 square feet. In general, there should be no visual evidence of dumping. If less than threshold all trash and debris will be removed as part of next scheduled maintenance. Trash and debris cleared from site Poisonous Vegetation and noxious weeds Any poisonous or nuisance vegetation which may constitute a hazard to maintenance personnel or the public. Any evidence of noxious weeds as defined by State or local regulations. (Apply requirements of adopted IPM policies for the use of herbicides). No danger of poisonous vegetation where maintenance personnel or the public might normally be. (Coordinate with local health department) Complete eradication of noxious weeds may not be possible. Compliance with State or local eradication policies required RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 4 Table V-A.1: Maintenance Standards - Detention Ponds Maintenance Component Defect Conditions When Maintenance Is Needed Results Expected When Maintenance Is Performed Contaminants and Pollution Any evidence of oil, gasoline, contaminants or other pollutants (Coordinate removal/cleanup with local water quality response agency). No contaminants or pollutants present. Rodent Holes Any evidence of rodent holes if facility is acting as a dam or berm, or any evidence of water piping through dam or berm via rodent holes. Rodents destroyed and dam or berm repaired. (Coordinate with local health department; coordinate with Ecology Dam Safety Office if pond exceeds 10 acre-feet.) Beaver Dams Dam results in change or function of the facility. Facility is returned to design function. (Coordinate trapping of beavers and removal of dams with appropriate permitting agencies) Insects When insects such as wasps and hornets interfere with maintenance activities. Insects destroyed or removed from site. Apply insecticides in compliance with adopted IPM policies Tree Growth and Hazard Trees Tree growth does not allow maintenance and inspection access or interferes with maintenance activity (i.e., slope mowing, silt removal, vactoring, or equipment movements). If trees are not interfering with access or maintenance, do not remove If dead, diseased, or dying trees are identified (Use a certified Arborist to determine health of tree or removal requirements) Trees do not hinder maintenance activities. Harvested trees should be recycled into mulch or other beneficial uses (e.g., alders for firewood). Remove hazard Trees RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 5 Table V-A.1: Maintenance Standards - Detention Ponds Maintenance Component Defect Conditions When Maintenance Is Needed Results Expected When Maintenance Is Performed Side Slopes of Pond Erosion Eroded damage over 2 inches deep where cause of damage is still present or where there is potential for continued erosion. Any erosion observed on a compacted berm embankment. Slopes should be stabilized using appropriate erosion control measure(s); e.g.,rock reinforcement, planting of grass, compaction. If erosion is occurring on compacted berms a licensed engineer in the state of Washington should be consulted to resolve source of erosion. Storage Area Sediment Accumulated sediment that exceeds 10% of the designed pond depth unless otherwise specified or affects inletting or outletting condition of the facility. Sediment cleaned out to designed pond shape and depth; pond reseeded if necessary to control erosion. Liner (if Applicable) Liner is visible and has more than three 1/4-inch holes in it. Liner repaired or replaced. Liner is fully covered. Ponds Berms (Dikes) Settlements 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 Settling can be an indication of more severe problems with the berm or outlet works. A licensed engineer in the state of Washington should be consulted to determine the source of the settlement. Dike is built back to the design elevation. Piping Discernable water flow through pond berm. Ongoing erosion with potential for erosion to continue. (Recommend a Goethechnical engineer be called in to inspect Piping eliminated. Erosion potential resolved. RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 6 Table V-A.1: Maintenance Standards - Detention Ponds Maintenance Component Defect Conditions When Maintenance Is Needed Results Expected When Maintenance Is Performed and evaluate condition and recommend repair of condition. Emergency Overflow/ Spillway and Berms over 4 feet in height Tree Growth Tree growth on emergency spillways creates blockage problems and may cause failure of the berm due to uncontrolled overtopping. Tree growth on berms over 4 feet in height may lead to piping through the berm which could lead to failure of the berm. Trees should be removed. If root system is small (base less than 4 inches) the root system may be left in place. Otherwise the roots should be removed and the berm restored. A licensed engineer in the state of Washington should be consulted for proper berm/spillway restoration. Piping Discernable water flow through pond berm. Ongoing erosion with potential for erosion to continue. (Recommend a Geotechnical engineer be called in to inspect and evaluate condition and recommend repair of condition. Piping eliminated. Erosion potential resolved. Emergency Overflow/Spillway Emergency Overflow/Spillway Only one layer of rock exists above native soil in area five square feet or larger, or any exposure of native soil at the top of out flow path of spillway. (Rip-rap on inside slopes need not be replaced.) Rocks and pad depth are restored to design standards. Erosion See "Side Slopes of Pond" Table V-A.2: Maintenance Standards - Infiltration Maintenance Component Defect Conditions When Maintenance Is Needed Results Expected When Maintenance Is Performed General Trash & Debris See Table V-A.1: Maintenance Standards - Detention Ponds See Table V-A.1: Maintenance RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 7 Table V-A.2: Maintenance Standards - Infiltration Maintenance Component Defect Conditions When Maintenance Is Needed Results Expected When Maintenance Is Performed Standards - Detention Ponds Poisonous/Noxious Vegetation See Table V-A.1: Maintenance Standards - Detention Ponds See Table V-A.1: Maintenance Standards - Detention Ponds Contaminants and Pollution See Table V-A.1: Maintenance Standards - Detention Ponds See Table V-A.1: Maintenance Standards - Detention Ponds Rodent Holes See Table V-A.1: Maintenance Standards - Detention Ponds See Table V-A.1: Maintenance Standards - Detention Ponds Storage Area Sediment 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 empty within 24 hours after cessation of most rain events. (A percolation test pit or test of facility 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). Sediment is removed and/or facility is cleaned so that infiltration system works according to design. Filter Bags (if applicable) Filled with Sediment and Debris Sediment and debris fill bag more than 1/2 full. Filter bag is replaced or system is redesigned. Rock Filters Sediment and Debris By visual inspection, little or no water flows through filter during heavy rain storms. Gravel in rock filter is replaced. Side Slopes of Pond Erosion See Table V-A.1: Maintenance Standards - Detention Ponds See Table V-A.1: Maintenance Standards - Detention Ponds RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 8 Table V-A.2: Maintenance Standards - Infiltration Maintenance Component Defect Conditions When Maintenance Is Needed Results Expected When Maintenance Is Performed Emergency Overflow Spillway and Berms over 4 feet in height. Tree Growth See Table V-A.1: Maintenance Standards - Detention Ponds See Table V-A.1: Maintenance Standards - Detention Ponds Piping See Table V-A.1: Maintenance Standards - Detention Ponds See Table V-A.1: Maintenance Standards - Detention Ponds Emergency Overflow Spillway Rock Missing See Table V-A.1: Maintenance Standards - Detention Ponds See Table V-A.1: Maintenance Standards - Detention Ponds Erosion See Table V-A.1: Maintenance Standards - Detention Ponds See Table V-A.1: Maintenance Standards - Detention Ponds Pre-settling Ponds and Vaults Facility or sump filled with Sediment and/or debris 6" or designed sediment trap depth of sediment. Sediment is removed. Table V-A.5: Maintenance Standards - Catch Basins Maintenance Component Defect Conditions When Maintenance is Needed Results Expected When Maintenance is performed General Trash & Debris Trash or debris which is located immediately in front of the catch basin opening or is blocking inletting capacity of the basin by more than 10%. Trash or debris (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 Trash or debris located immediately in front of catch basin or on grate opening. No trash or debris in the catch basin. RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 9 Table V-A.5: Maintenance Standards - Catch Basins Maintenance Component Defect Conditions When Maintenance is Needed Results Expected When Maintenance is performed a minimum of six inches clearance from the debris surface to the invert of the lowest pipe. Trash or debris in any inlet or outlet pipe blocking more than 1/3 of its height. Dead animals or vegetation that could generate odors that could cause complaints or dangerous gases (e.g., methane). Inlet and outlet pipes free of trash or debris. No dead animals or vegetation present within the catch basin. Sediment 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 a minimum of 6 inches clearance from the sediment surface to the invert of the lowest pipe. No sediment in the catch basin Structure Damage to Frame and/or Top Slab Top slab has holes larger than 2 square inches or cracks wider than 1/4 inch. (Intent is to make sure no material is running into basin). Frame not sitting flush on top slab, i.e., separation of more than 3/4 inch of the frame from the top slab. Frame not securely attached Top slab is free of holes and cracks. Frame is sitting flush on the riser rings or top slab and firmly attached. Fractures or Cracks in Basin Walls/ Bottom Maintenance person judges that structure is unsound. Grout fillet has separated or cracked wider than 1/2 inch and longer than 1 foot at the joint of any inlet/outlet pipe or any evidence of soil particles entering catch basin through cracks. Basin replaced or repaired to design standards. Pipe is regrouted and secure at basin wall. Settlement/ Misalignment If failure of basin has created a safety, function, or design problem. Basin replaced or repaired to design standards. Vegetation Vegetation growing across and blocking more than 10% of the basin opening. No vegetation blocking opening to basin. RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 10 Table V-A.5: Maintenance Standards - Catch Basins Maintenance Component Defect Conditions When Maintenance is Needed Results Expected When Maintenance is performed Vegetation growing in inlet/outlet pipe joints that is more than six inches tall and less than six inches apart. No vegetation or root growth present. Contamination and Pollution See Table V-A.1: Maintenance Standards - Detention Ponds No pollution present. Catch Basin Cover Cover Not in Place Cover is missing or only partially in place. Any open catch basin requires maintenance. Cover/grate is in place, meets design standards, and is secured Locking Mechanism Not Working Mechanism cannot be opened by one maintenance person with proper tools. Bolts into frame have less than 1/2 inch of thread. Mechanism opens with proper tools. Cover Difficult to Remove One maintenance person cannot remove lid after applying normal lifting pressure. (Intent is keep cover from sealing off access to maintenance.) Cover can be removed by one maintenance person. Ladder Ladder Rungs Unsafe Ladder is unsafe due to missing rungs, not securely attached to basin wall, misalignment, rust, cracks, or sharp edges. Ladder meets design standards and allows maintenance person safe access. Metal Grates (If Applicable) Grate opening Unsafe Grate with opening wider than 7/8 inch. Grate opening meets design standards. Trash and Debris Trash and debris that is blocking more than 20% of grate surface inletting capacity. Grate free of trash and debris. Damaged or Missing. Grate missing or broken member(s) of the grate. Grate is in place, meets the design standards, and is installed and aligned with the flow path. RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 11 RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 12 RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 13 RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 14 RAM Engineering, Inc. 88th Ave W Short Plat RAM No. 21-001 Stormwater Site Plan Report Page 15