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APPROVED STM 82nd Townhomes Stormwater Report 2020-11-1282"' Townhouses 21222 82nd PI W Edmonds, WA 98026 Stormwater Site Plan Report Prepared for: Select Homes Date: April 21, 2020 Revised: November 12, 2020 11/12/2020 Prepared by: Rob Long, PE RAM Engineering, Inc. 16531 13t" Ave W, Suite A108, Lynnwood WA 98037 (425) 678-6960 RAMengineeringinc.corn Job No. 20-003 82"d Townhouses 21222 82nd PI W Introduction: This summary report provides site design information for a four -unit residential townhouse development by Select Homes. This report includes storm drainage analysis to support permit review and approval. The property is located at 21222 82nd Place W, in the northeast 1/4 of Section 30, T 27 N, R 3 E, W.M. Site Address: 21222 82nd Place W Applicant: Select Homes Edmonds, WA 98026 16513 13th Ave W, Suite A108, Lynnwood WA 98037 Tax Parcel Number: 004674 000 006 00 Contact: Kayla Clark (425) 742-6044 TABLE OF CONTENTS SECTION A. Project Overview................................................................................. B. Existing Conditions Summary.............................................................. C. Developed Site Hydrology................................................................... D. Soils Report.......................................................................................... E. Construction SWPPPP Requirements................................................... F. Operation and Maintenance Guidelines ............................................... RAMEngineering, Inc. RAM No. 20-003 PAGES ......................................... 5 ......................................... 1 ....................................... 20 ....................................... 20 ......................................... 2 ......................................... 5 82nd Townhouses Stormwater Site Plan Report A. PROJECT OVERVIEW. This report provides engineering information for the proposed construction of a four -unit residential townhouse project on an 11,520 sf (0.26 ac) lot; the project is located at 21222 82"d Place W in the City of Edmonds. The applicant, Select Homes proposes to remove the existing residence. This report provides the evaluation for the proposed residential townhouse 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 0.3 acres of land and creating/replacing about 9,510 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 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. Residential properties 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 an easterly direction towards 82"d PI W; there are no concentrated flows or existing defined conveyance systems located onsite; any site runoff leaves the site as sheet -flow. Stormwater runoff leaving the site collects in the existing stormwater systems (ditch and pipe/catch basins) along the west side of 82"1 RAMEngineering, Inc. RAM No. 20-003 82" d Townhouses Stormwater Site Plan Report Page A-1 PI W and flows north. The 82nd PI W stormwater system routes runoff norther under 212t" St SW and eventually outfalls to Good Hope Pond about 0.35 miles north of the site. The proposed development will discharge the collected stormwater discharge to the existing stormwater system along the east side of 82n1 PI W. The stormwater system along the easterly side of 82nd PI W merges with the system on the west side of 82nd PI W about 115 feet north of the site. Thus, discharges of the site maintain the maintaining the existing stormwater discharge basin outfall of the site (within a % mile of site). The site is located within the upper reach of the Good Hope Pond watershed basin per the City of Edmonds maps (see section C). Minimum Requirement #5—OnsiteStormwater Management. Asite-specificgeotechnical evaluation (see section D) of the site demonstrates that infiltration based systems are not recommended onsite due to the underlying site soils. The subsurface soils generally consisted of till soils with a shallow depth to hardpan (or other low permeability layer). Furthermore, the proposed site development has limited pervious (lawn and landscape) areas to implement dispersion BMPs onsite. On -site flow control detention will be provided in an R-tank detention system, thus meeting the Edmonds detention vaults or pipes BMP in accordance with the Edmonds Stormwater Addendum. Post -Construction Soil Quality and Depth (BMP T5.13) for pervious surfaces are considered feasible stormwater BMPs for the site development and shall be applied post construction. See LID BMP feasibility evaluation table (below), civil site development plans and Section Cfor additional stormwater BMP 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 3,800 sf pollution generation hard surfaces (driveway and road frontage 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. An onsite stormwater R-tank detention system will provide flow control of the site's stormwater runoff. The detention vault system has been designed to meet the flow control standards of a Category 2 project in a creek or lake basin (restrict the stormwater discharge duration for half the 2-year to 50-year storm events using a continuous storm event model). The R-tank detention system has been sized using WWHM software; a full overview of the project's stormwater flow control measures is 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. 20-003 82nd Townhouses 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 Yes BMP T5.13 shall be applied to the site post construction. (Volume V, Chapter 5) Roofs: BMP T5.30: Full Dispersion Infeasibility: The developed site does not allow for native (Volume V, Chapter 5) No vegetation retention and flow path areas (100 ft) need to meet full dispersion requirements. Infeasibility: Shallow depths to hardpan (or other low BMP T5.10A: Downspout Full Infiltration Systems permeability layer) from final grade and/or bottom of facility (Volume III, Chapter 3) No elevation will not satisfy minimum required. See additional discussion in the geotechnical evaluation by Earth Solutions Northwest. Bioretention No Infeasibility: The underlying soils consists of shallow depths to (Volume V, Chapter 7) hardpan (or other low permeability layer) BMP T5.106: Downspout Dispersion Systems No Not feasible due to the required expansive trench length and (Volume III, Chapter 3) dispersion flow path area that is required (10 ft per 700 sf of roof) BMP T5.10C: Perforated Stub -out The underlying soils consists of shallow depths to hardpan (or (Volume III, Chapter 3) No other low permeability layer) and limited areas to place a system onsite. Detention vaults or pipes in accordance with the Yes A shallow detention tank system (R-tank) is feasible onsite. Edmonds Stormwater Addendum Other Hard Surfaces: BMP T5.30: Full Dispersion Infeasibility: The developed site does not allow for native (Volume V, Chapter 5) No vegetation retention and flow path areas (100 ft) need to meet full dispersion requirements. BMP T5.15: Permeable Pavement No Infeasibility: The underlying soils consists of shallow depths to (Volume V, Chapter 5) hardpan (or other low permeability layer) Bioretention (Volume V, Chapter 7) No Infeasibility: The underlying soils consists of shallow depths to hardpan (or other low permeability layer) BMP T5.12: Sheet Flow Dispersion Infeasibility: The developed site does not allow for adequate BMP T5.11: Concentrated Flow Dispersion No vegetative flow path areas. (Volume V, Chapter 5) Feasible: An R-tank stormwater detention system has been Detention System (ECDC 18.30) Yes provided in the project's site development plans to control stormwater runoff generated by the project development. RAMEngineering, Inc. RAM No. 20-003 82" d Townhouses Stormwater Site Plan Report Page A-3 Parcel (Vicinity) Map: QUARTER SECTION TOWNSHIP N.W.B. , RANGE E.W.M. 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EXISTING CONDITIONS SUMMARY Existing Conditions. The total site consists of about 11,520 sf (0.26 acres) and is currently occupy by an existing house. The existing house onsite is surrounded by grass lawn and landscape areas with a few mature trees. The subject property is bordered by 82nd Place W along the east boundary, single family lot to the north and south, and the church property to the west (see attached aerial photo). The site generally slopes in an easterly direction towards 82nd PI W in a range between 2% and 5%. No define drainage courses are found on -site and stormwater runoff would sheet flow easterly direction to a roadside ditch along the westerly side of 82nd PI W. 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 evaluation by Earth Solutions NW, LLC the on -site soils consist of silty sand with gravel (USCS: SM) glacial till deposits. The subject site is underlain by glacial till deposits (Qvt, Alderwood series soils). Full soils description is included in the project's site specific geotechnical evaluation by Earth Solutions NW, LLC. Aerial Photo (City of Edmonds GIS, 2017 photo): R.4MEngineering, Inc. RAM No. 20-003 82nd Townhouses Stormwater Site Plan Report Page 8-1 C. DEVELOPED SITE HYDROLOTY. The proposed project includes the construction of a four -unit residential townhouse building and associated frontage improvements, driveways and utilities. All existing structures and hard surface onsite will be removed/replaced with the site development; landscaping and grass lawn around the new residence will stabilize the site upon building construction. The project proposes to create and/or replace 9,510 sf of hard surface with the complete site development, all existing onsite hard surface will be removed with the project site development. The following is a summary of the proposed new/replaced hard surface areas: Total Hard Surface New/Replaced Proposed = 9,510 sf (0.219 ac) Building Rooftop = 4,710 sf Uncovered Patio and Walk = 500 sf Onsite Driveway Area = 3,230 sf (PGHS) ROW Frontage = 570 sf (PGHS) ROW Sidewalk = 500 sf 82nd PI W ROW Net Run-on Area = 1,100 sf (0.025 ac) (PGHS) Total Hard Surface (Site + Upstream) = 10,610 sf (0.224 ac) Total Pervious Surface (Lawn) = 3,080 sf (0.070 ac) New/Replace Pollution Generating Hard Surfaces (PGHS) = 3,800 sf Off -site Run-on Pollution Generating Hard Surface (PGHS) = 1,100 sf Total PGHS Collected by Site = 4,900 sf An underground R-tank detention system will be installed along the northerly portion townhouse building. The R-tank system will provide flow control of the project's stormwater runoff (Minimum Requirement #7). The hydrologic analysis uses WWHM2012 software to model historical storm events in the existing and proposed developed conditions. Per the City of Edmonds (DOE 2019) drainage manual, the project shall meet the site discharge duration for half the 2-year to 50-year storm events using a continuous storm event model (WWHM). Net Upstream Collection Area Summary: Due to placement of existing and proposed stormwater catch basins along 98t" Ave SW additional existing roadway (hard surface) from 98' Ave SW will flow into the project's stormwater system and some minor areas of by-pass will be created. The below evaluation summarizes the net upstream area tributary to the project's stormwater collection and detention system. The net upstream area has been included and accounted for in the below stormwater modeling calculations. Upstream Right of Way "Run-on" Areas Collected = 1,350 sf (existing 82nd PI W pavement collected along frontage) Redeveloped Site and Right-of-way Areas By-passed = - 250 sf (non -collected areas north of collection catch basin) Net Upstream Run-on 82nd PI W Right-of-way Area = 1,100 sf RAMEngineering, Inc. RAM No. 20-003 82nd Townhouses Stormwater Site Plan Report Page C-1 Low Impact Development (LID) BMPs. All disturbed pervious (lawn and landscape) areas will preserve or restore the health and water -holding capacity of the soils by compost -amending (Per DOE BMP T5.13: Post - Construction Soil Quality and Depth). Attached are the DOE summary criteria of BMP T5.13: Post -Construction Soil Quality and Depth. V-11 Miscellaneous LID BMPs V-11.1 Introduction to Miscellaneous LID BMPs BMPs in this chapter have been grouped because they have the following in common: . They employ Low Impact Development (LID) Principles • They cannot be used to meet 1-3.4.6 MR6: Runoff Treatment . They cannot, by themselves, be used to meet the Flow Control Performance Standard or the LID Performance Standard. Some of the BMPs in this chapter do allow for some amount of Flow Control credit. See the guidance for each individual BMP for details. . The design methods for each BMP in this chapter are unique. They do not have strong enough design similarities to other BMPs in this volume to place them in the other BMP cat- egories identified in this volume. BMP T5.13: Post -Construction Soil Quality 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 functions are 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 RAMEngineering, Inc. RAM No. 20-003 2019 Stormwater Management Manual for Western Washington Volume V - Chapter 11- Page 927 82" d Townhouses Stormwater Site Plan Report Page C-2 meet this BMP 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: 1. 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: Bioretention, 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. b. Calculated amendment rates maybe 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 220-13, Test- ing Parameters, in WAC 173-350-220. The resulting soil should be conducive to the type of vegetation to be established. RAMEngineering, Inc. RAM No. 20-003 2019 Stormwater Management Manual for Western Washington Volume V - Chapter I I - Page 928 82" d Townhouses Stormwater Site Plan Report Page C-3 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. Planning/Permitting/inspectionNerification Guidelines & 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 soil quality and depth design criteria may be entered into approved runoff mod- els as "Pasture" rather than "Lawn/Landscaping". RAMEngineering, Inc. RAM No. 20-003 2019 Stormwater Management Manual for Western Washington Volume V - Chapter 11- Page 929 82" d Townhouses Stormwater Site Plan Report Page C-4 Stormwater Modeling. Attached is the stormwater analysis documentation output from the Washington State Department of Ecology's WWHM2012 stormwater modeling software as referenced above. An underground R-tank detention system installed under the shared drive aisle along the north boundary of the site will provide onsite stormwater detention for the project. A R-tank system is about 14.4 ft wide, 65.7 ft long and 4.2 ft deep will provide 3,782 cf of storage to control the project's stormwater runoff. See summary table on modeling input/output below. Project Area: 11,520 sf (Site) + 1,070 sf (ROW) + 1,100 (Net Upstream) = 13,690 sf (0.314 ac) Total Hard (Impervious) Surface (Site + Upstream) = 10,610 sf (0.224 ac) Developed Total Pervious = 3,080 sf (0.070 ac) Flow Control Summary Table: Project Areas Site Area + ROW Redevelopment + Upstream ROW 0.314 Acres Type of Storage Proposed Underground R-Tank 14.4 ft (w) x 65.7 ft (1) x 4.2 ft (d) (Triple R-tank Stack) Approx. Detention Storage Volume (cf) 3,782 cf Soil Type(s) (see Geotechnical Report) Alderwood Series Soils (Till) Pre -Existing Runoff Release Rates Q (cfs.) 2 yr. 0.0090 cfs 50 yr. 0.0238 cfs 100 yr. 0.0275 cfs Post -development Runoff Rates (without quantity controls) Q (cfs.) 2 yr. 0.0607 cfs 50 yr. 100 yr. Post -development Runoff Rates (with quantity controls) Q (cfs.) 2 yr. 50 yr. 100 yr. 0.1276 cfs 0.1433 cfs 0.0048 cfs 0.0156 cfs 0.0193 cfs RAM =ngineering, Inc. RAM No. 20-003 82nd Townhouses Stormwater Site Plan Report Page C-5 R-Tank System: The proposed design R-tank' system consist of 308 Triple units (11 units wide, 28 units long and 3 units high) providing a design storage volume of 3,782 cf. Below is a summary calculation of the total volume storage within the R-tank system: Design R-Tank System:* Total R-tank System = 308 Triple HD units for a total of 924 HD R-tank units HD Triple R-tank Unit = 2.35' (1) x 1.31'(w) x 4.20'(d) HD Double Unit Volume = 12.28 cf (95%void) Total Volume of System = 3,782 cf System Size = 11 units wide (14.438 ft) x 28 units long (65.683 ft) x HD Double Unit (4.20 ft) Equivalent Open Vault Used in WWHM Modeling = 13.715 ft (14.438 x 95%) x 65.683 ft x 4.20 ft. *Note: For stability and a symmetrical layout of the R-tank system an additional Triple R-tank stack will be added to the system layout; thus the construction plans shows a total of 309 Triple R-tank units. WWHM Input/output Data: WWHM2012 PROJECT REPORT Project Name: 20-003 Rtank Site Name: 82nd Townhouses Site Address: City : Edmonds Report Date: 11/12/2020 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 Is 1aWOLVAN093aall71P\IIBM6*10 Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Forest, Flat .289 Pervious Total 0.289 Impervious Land Use acre ROADS FLAT 0.025 Impervious Total 0.025 Basin Total 0.314 Element Flows To: Surface Interflow Groundwater RAMEngineering, Inc. 82nd Townhouses RAM No. 20-003 Stormwater Site Plan Report Page C-6 MITIGATED LAND USE Name : Basin 1 Bypass: No Groundwater: No Pervious Land Use acre A B, Pasture, Flat .07 Pervious Total 0.07 Impervious Land Use acre ROADS FLAT 0.038 ROOF TOPS FLAT 0.108 DRIVEWAYS FLAT 0.074 SIDEWALKS FLAT 0.024 Impervious Total 0.244 Basin Total 0.314 Element Flows To: Surface Interflow Groundwater Vault 1 Vault 1 Name Vault 1 Width 13.715 ft. Length 65.683 ft. Depth: 4.2 ft. Discharge Structure Riser Height: 4.1 ft. Riser Diameter: 8 in. Orifice 1 Diameter: 0.354331 in. Elevation: 0.8 ft. Orifice 2 Diameter: 0.5 in. Elevation: 3 ft. Element Flows To: Outlet 1 Outlet 2 Vault Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) 0.0000 0.020 0.000 0.000 0.000 0.0467 0.020 0.001 0.000 0.000 0.0933 0.020 0.001 0.000 0.000 0.1400 0.020 0.002 0.000 0.000 0.1867 0.020 0.003 0.000 0.000 0.2333 0.020 0.004 0.000 0.000 0.2800 0.020 0.005 0.000 0.000 0.3267 0.020 0.006 0.000 0.000 0.3733 0.020 0.007 0.000 0.000 0.4200 0.020 0.008 0.000 0.000 0.4667 0.020 0.009 0.000 0.000 0.5133 0.020 0.010 0.000 0.000 0.5600 0.020 0.011 0.000 0.000 0.6067 0.020 0.012 0.000 0.000 0.6533 0.020 0.013 0.000 0.000 0.7000 0.020 0.014 0.000 0.000 0.7467 0.020 0.015 0.000 0.000 0.7933 0.020 0.016 0.000 0.000 0.8400 0.020 0.017 0.000 0.000 0.8867 0.020 0.018 0.001 0.000 0.9333 0.020 0.019 0.001 0.000 0.9800 0.020 0.020 0.001 0.000 1.0267 0.020 0.021 0.001 0.000 1.0733 0.020 0.022 0.001 0.000 1.1200 0.020 0.023 0.001 0.000 1.1667 0.020 0.024 0.002 0.000 RAM Engineering, Inc. RAM No. 20-003 Infilt(cfs) 82nd Townhouses Stormwater Site Plan Report Page C-7 1.2133 0.020 0.025 0.002 0.000 1.2600 0.020 0.026 0.002 0.000 1.3067 0.020 0.027 0.002 0.000 1.3533 0.020 0.028 0.002 0.000 1.4000 0.020 0.029 0.002 0.000 1.4467 0.020 0.029 0.002 0.000 1.4933 0.020 0.030 0.002 0.000 1.5400 0.020 0.031 0.002 0.000 1.5867 0.020 0.032 0.003 0.000 1.6333 0.020 0.033 0.003 0.000 1.6800 0.020 0.034 0.003 0.000 1.7267 0.020 0.035 0.003 0.000 1.7733 0.020 0.036 0.003 0.000 1.8200 0.020 0.037 0.003 0.000 1.8667 0.020 0.038 0.003 0.000 1.9133 0.020 0.039 0.003 0.000 1.9600 0.020 0.040 0.003 0.000 2.0067 0.020 0.041 0.003 0.000 2.0533 0.020 0.042 0.003 0.000 2.1000 0.020 0.043 0.003 0.000 2.1467 0.020 0.044 0.004 0.000 2.1933 0.020 0.045 0.004 0.000 2.2400 0.020 0.046 0.004 0.000 2.2867 0.020 0.047 0.004 0.000 2.3333 0.020 0.048 0.004 0.000 2.3800 0.020 0.049 0.004 0.000 2.4267 0.020 0.050 0.004 0.000 2.4733 0.020 0.051 0.004 0.000 2.5200 0.020 0.052 0.004 0.000 2.5667 0.020 0.053 0.004 0.000 2.6133 0.020 0.054 0.004 0.000 2.6600 0.020 0.055 0.004 0.000 2.7067 0.020 0.056 0.004 0.000 2.7533 0.020 0.056 0.004 0.000 2.8000 0.020 0.057 0.004 0.000 2.8467 0.020 0.058 0.004 0.000 2.8933 0.020 0.059 0.004 0.000 2.9400 0.020 0.060 0.005 0.000 2.9867 0.020 0.061 0.005 0.000 3.0333 0.020 0.062 0.006 0.000 3.0800 0.020 0.063 0.007 0.000 3.1267 0.020 0.064 0.007 0.000 3.1733 0.020 0.065 0.008 0.000 3.2200 0.020 0.066 0.008 0.000 3.2667 0.020 0.067 0.008 0.000 3.3133 0.020 0.068 0.009 0.000 3.3600 0.020 0.069 0.009 0.000 3.4067 0.020 0.070 0.009 0.000 3.4533 0.020 0.071 0.010 0.000 3.5000 0.020 0.072 0.010 0.000 3.5467 0.020 0.073 0.010 0.000 3.5933 0.020 0.074 0.010 0.000 3.6400 0.020 0.075 0.011 0.000 3.6867 0.020 0.076 0.011 0.000 3.7333 0.020 0.077 0.011 0.000 3.7800 0.020 0.078 0.011 0.000 3.8267 0.020 0.079 0.012 0.000 3.8733 0.020 0.080 0.012 0.000 3.9200 0.020 0.081 0.012 0.000 3.9667 0.020 0.082 0.012 0.000 4.0133 0.020 0.083 0.012 0.000 4.0600 0.020 0.084 0.013 0.000 4.1067 0.020 0.084 0.017 0.000 4.1533 0.020 0.085 0.100 0.000 4.2000 0.020 0.086 0.233 0.000 4.2467 0.024 0.098 0.388 0.000 RAM Engineering, Inc. RAM No. 20-003 82nd Townhouses Stormwater Site Plan Report Page C-8 ANALYSIS RESULTS Stream Protection Duration Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.289 Total Impervious Area:0.025 Mitigated Landuse Totals for POC #1 Total Pervious Area:0.07 Total Impervious Area:0.244 Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.009048 5 year 0.013048 10 year 0.016055 25 year 0.020283 50 year 0.023753 100 year 0.027509 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.004795 5 year 0.007173 10 year 0.009254 25 year 0.012578 50 year 0.015646 100 year 0.019303 4 1.0 T 3i Cumulative Probability 1.0 0.1 0.1 � x x x x + 501 +t + x 701 LL 0.01 � 801 0.001 0.001 0.5 1 2 5 10 20 30 50 70 80 90 95 98 9999.51 Stream Protection Duration I LID Duration Flow Frequency I Water quality Hydrograph Wetland Input Volumes LID Report Recharge Duration Recharge Predeveloped I Recharge Mitigated Analyze datasets Compact WDM I Delete Selected r Monthly FF 501 POC 1 Redeveloped flow 701 Inflow to POC 1 Mitigated 801 POC 1000 Vault 1 ALL OUTLETS Mitigated All Datasets Flow Stage Precip Evap POC 1 Flood Frequency Method G Log Pearson Type III 178 C' Weibull C' Cunnane C Gringoden RAM Engineering, Inc. RAM No. 20-003 W� Flow Frequency Flow(cfs) 0501 hr 0701 hr 0801 hr 2 Year = 0.0090 0.0607 0.0048 5 Year = 0.0130 0.0800 0.0072 10 Year = 0.0161 0.0939 0.0093 25 Year = 0.0203 0.1126 0.0126 50 Year = 0.0238 0.1276 0.0156 100 Year = 0.0275 0.1433 0.0193 Annual Peaks 1902 0.0109 0.0675 0.0047 1903 0.0078 0.0756 0.0037 1904 0.0137 0.0854 0.0038 1905 0.0052 0.0398 0.0045 1906 0.0051 0.0449 0.0033 1907 0.0134 0.0609 0.0051 1908 0.0085 0.0539 0.0038 1909 0.0097 0.0694 0.0043 1910 0.0147 0.0620 0.0063 1911 0.0089 0.0660 0.0041 1912 0.0279 0.1073 0.0046 1913 0.0095 0.0397 0.0073 1914 0.0160 0.1548 0.0036 1915 0.0058 0.0416 0.0045 1916 0.0075 0.0661 0.0040 1917 0.0050 0.0408 0.0037 1918 0.0083 0.0603 0.0047 1919 0.0056 0.0355 0.0044 1920 0.0086 0.0525 0.0042 1921 0.0083 0.0387 0.0045 1922 0.0102 0.0530 0.0062 1923 0.0099 0.0560 0.0046 1924 0.0075 0.0725 0.0038 1925 0.0052 0.0395 0.0039 1926 0.0081 0.0765 0.0038 1927 0.0087 0.0545 0.0040 1928 0.0078 0.0498 0.0040 1929 0.0141 0.0829 0.0045 82nd Townhouses Stormwater Site Plan Report Page C-9 Stream Protection Duration Annual Peaks for Predeveloped and Mitigated Year Predeveloped Mitigated 1902 0.011 0.005 1903 0.008 0.004 1904 0.014 0.004 1905 0.005 0.004 1906 0.005 0.003 1907 0.013 0.005 1908 0.008 0.004 1909 0.010 0.004 1910 0.015 0.006 1911 0.009 0.004 1912 0.028 0.005 1913 0.010 0.007 1914 0.016 0.004 1915 0.006 0.005 1916 0.008 0.004 1917 0.005 0.004 1918 0.008 0.005 1919 0.006 0.004 1920 0.009 0.004 1921 0.008 0.005 1922 0.010 0.006 1923 0.010 0.005 1924 0.007 0.004 1925 0.005 0.004 1926 0.008 0.004 1927 0.009 0.004 1928 0.008 0.004 1929 0.014 0.005 1930 0.010 0.004 1931 0.008 0.004 1932 0.008 0.004 1933 0.008 0.005 1934 0.017 0.010 1935 0.007 0.005 1936 0.009 0.004 1937 0.012 0.004 1938 0.008 0.004 1939 0.007 0.004 1940 0.009 0.005 1941 0.008 0.004 1942 0.011 0.012 1943 0.008 0.004 1944 0.016 0.012 1945 0.008 0.004 1946 0.009 0.004 1947 0.006 0.004 1948 0.014 0.009 1949 0.014 0.012 1950 0.008 0.004 1951 0.008 0.004 1952 0.026 0.013 1953 0.022 0.011 1954 0.009 0.005 1955 0.007 0.003 1956 0.005 0.004 1957 0.008 0.005 1958 0.020 0.013 1959 0.014 0.011 1960 0.007 0.004 1961 0.016 0.011 1962 0.008 0.004 1963 0.004 0.004 RAM Engineering, Inc. RAM No. 20-003 POC #1 82nd Townhouses Stormwater Site Plan Report Page C-10 1964 0.014 0.004 1965 0.015 0.010 1966 0.005 0.004 1967 0.008 0.004 1968 0.008 0.005 1969 0.008 0.004 1970 0.012 0.005 1971 0.016 0.010 1972 0.022 0.005 1973 0.014 0.011 1974 0.010 0.007 1975 0.020 0.011 1976 0.012 0.004 1977 0.005 0.004 1978 0.015 0.008 1979 0.007 0.004 1980 0.009 0.004 1981 0.007 0.005 1982 0.006 0.004 1983 0.012 0.008 1984 0.007 0.004 1985 0.008 0.005 1986 0.007 0.004 1987 0.013 0.012 1988 0.009 0.005 1989 0.007 0.004 1990 0.008 0.005 1991 0.008 0.004 1992 0.012 0.005 1993 0.009 0.005 1994 0.014 0.008 1995 0.005 0.004 1996 0.016 0.012 1997 0.008 0.004 1998 0.009 0.004 1999 0.007 0.003 2000 0.008 0.005 2001 0.006 0.003 2002 0.017 0.004 2003 0.009 0.005 2004 0.011 0.005 2005 0.015 0.004 2006 0.008 0.004 2007 0.007 0.004 2008 0.008 0.004 2009 0.007 0.004 2010 0.007 0.008 2011 0.006 0.004 2012 0.010 0.005 2013 0.007 0.004 2014 0.006 0.003 2015 0.018 0.004 2016 0.004 0.004 2017 0.014 0.011 2018 0.022 0.023 2019 0.024 0.026 2020 0.012 0.004 2021 0.012 0.007 2022 0.009 0.004 2023 0.010 0.004 2024 0.032 0.004 2025 0.007 0.005 2026 0.012 0.008 2027 0.008 0.004 2028 0.004 0.003 2029 0.009 0.004 2030 0.017 0.008 RAM Engineering, Inc. RAM No. 20-003 82nd Townhouses Stormwater Site Plan Report Page C-II 2031 0.005 0.004 2032 0.006 0.003 2033 0.005 0.004 2034 0.007 0.004 2035 0.017 0.040 2036 0.011 0.005 2037 0.007 0.004 2038 0.013 0.008 2039 0.010 0.003 2040 0.006 0.004 2041 0.006 0.004 2042 0.019 0.014 2043 0.010 0.008 2044 0.011 0.006 2045 0.009 0.004 2046 0.009 0.007 2047 0.007 0.004 2048 0.007 0.005 2049 0.010 0.005 2050 0.007 0.004 2051 0.011 0.008 2052 0.006 0.005 2053 0.008 0.008 2054 0.016 0.008 2055 0.006 0.003 2056 0.007 0.004 2057 0.006 0.004 2058 0.008 0.004 Stream Protection Duration Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.0320 0.0402 2 0.0279 0.0260 3 0.0260 0.0232 4 0.0241 0.0138 5 0.0225 0.0131 6 0.0223 0.0128 7 0.0216 0.0121 8 0.0203 0.0121 9 0.0196 0.0117 10 0.0191 0.0115 11 0.0181 0.0115 12 0.0171 0.0115 13 0.0171 0.0114 14 0.0171 0.0112 15 0.0170 0.0109 16 0.0161 0.0108 17 0.0161 0.0107 18 0.0160 0.0102 19 0.0157 0.0101 20 0.0156 0.0098 21 0.0155 0.0086 22 0.0153 0.0082 23 0.0148 0.0082 24 0.0147 0.0081 25 0.0145 0.0081 26 0.0144 0.0080 27 0.0141 0.0080 28 0.0139 0.0080 29 0.0139 0.0076 30 0.0138 0.0076 31 0.0137 0.0076 32 0.0137 0.0075 33 0.0137 0.0073 34 0.0136 0.0072 RAM Engineering, Inc. RAM No. 20-003 82nd Townhouses Stormwater Site Plan Report Page C-12 35 0.0134 0.0069 36 0.0130 0.0067 37 0.0129 0.0063 38 0.0123 0.0063 39 0.0122 0.0062 40 0.0122 0.0052 41 0.0121 0.0051 42 0.0121 0.0050 43 0.0119 0.0049 44 0.0118 0.0048 45 0.0116 0.0048 46 0.0113 0.0048 47 0.0110 0.0048 48 0.0109 0.0047 49 0.0109 0.0047 50 0.0108 0.0047 51 0.0108 0.0047 52 0.0105 0.0047 53 0.0103 0.0047 54 0.0102 0.0047 55 0.0101 0.0047 56 0.0101 0.0046 57 0.0100 0.0046 58 0.0099 0.0046 59 0.0098 0.0046 60 0.0097 0.0046 61 0.0097 0.0046 62 0.0095 0.0046 63 0.0095 0.0045 64 0.0093 0.0045 65 0.0093 0.0045 66 0.0092 0.0045 67 0.0092 0.0045 68 0.0091 0.0045 69 0.0090 0.0045 70 0.0090 0.0045 71 0.0090 0.0045 72 0.0089 0.0045 73 0.0089 0.0045 74 0.0088 0.0045 75 0.0087 0.0044 76 0.0087 0.0044 77 0.0086 0.0044 78 0.0086 0.0044 79 0.0085 0.0044 80 0.0085 0.0044 81 0.0085 0.0044 82 0.0085 0.0044 83 0.0084 0.0043 84 0.0084 0.0043 85 0.0084 0.0043 86 0.0083 0.0043 87 0.0083 0.0043 88 0.0083 0.0043 89 0.0083 0.0043 90 0.0083 0.0043 91 0.0083 0.0043 92 0.0083 0.0043 93 0.0083 0.0042 94 0.0082 0.0042 95 0.0082 0.0042 96 0.0081 0.0042 97 0.0081 0.0042 98 0.0081 0.0042 99 0.0081 0.0042 100 0.0079 0.0042 101 0.0078 0.0042 RAM Engineering, Inc. RAM No. 20-003 82nd Townhouses Stormwater Site Plan Report Page C-13 102 0.0078 0.0042 103 0.0078 0.0042 104 0.0077 0.0041 105 0.0077 0.0041 106 0.0076 0.0041 107 0.0075 0.0041 108 0.0075 0.0041 109 0.0075 0.0040 110 0.0075 0.0040 111 0.0075 0.0040 112 0.0073 0.0040 113 0.0073 0.0040 114 0.0072 0.0040 115 0.0072 0.0040 116 0.0072 0.0040 117 0.0071 0.0039 118 0.0071 0.0039 119 0.0070 0.0039 120 0.0070 0.0039 121 0.0070 0.0039 122 0.0070 0.0039 123 0.0070 0.0039 124 0.0069 0.0039 125 0.0069 0.0039 126 0.0068 0.0039 127 0.0067 0.0039 128 0.0067 0.0039 129 0.0066 0.0038 130 0.0065 0.0038 131 0.0065 0.0038 132 0.0064 0.0038 133 0.0064 0.0038 134 0.0061 0.0038 135 0.0061 0.0038 136 0.0060 0.0038 137 0.0059 0.0037 138 0.0058 0.0037 139 0.0058 0.0037 140 0.0058 0.0037 141 0.0057 0.0037 142 0.0056 0.0037 143 0.0056 0.0037 144 0.0056 0.0036 145 0.0053 0.0036 146 0.0052 0.0036 147 0.0052 0.0036 148 0.0051 0.0035 149 0.0051 0.0035 150 0.0050 0.0034 151 0.0049 0.0034 152 0.0048 0.0034 153 0.0048 0.0033 154 0.0046 0.0033 155 0.0045 0.0033 156 0.0044 0.0032 157 0.0036 0.0032 RAM Engineering, Inc. RAM No. 20-003 82nd Townhouses Stormwater Site Plan Report Page C-14 Stream Protection Duration POC #1 The Facility PASSED R 0.02 0.01 0 J 0.01 0.00 t0E-4 10E-3 10E-2 10E-1 1 10 Percent Time Exceeding 501 POC 1 Predeveblted 801 POC 1 Mtigated flow 100 Stream Protection Duration LID Duration Flow FrequencyI Water Quality I Hydrograph Welland Input Volumes I LID Report I Recharge Duration I Recharge Predeveloped I Recharge Mitigated Analyze datasets Compact WDM Delete Selected r Monthly FF F] 501 POCII 801 POC 7 All Datasets I Flow jStage _tTEipj Evap pOC_1_.. Flood Frequency Method R Log Pearson Type III 17B r Weibull Cunnane C' Giingorten The Facility PASSED. Flow(cfs) Predev Mit Percentage Pass/Fail 0.0045 5808 4602 79 Pass 0.0047 5165 3058 59 Pass 0.0049 4594 2022 44 Pass 0.0051 4137 1495 36 Pass 0.0053 3713 1430 38 Pass 0.0055 3342 1391 41 Pass 0.0057 3020 1353 44 Pass 0.0059 2735 1321 48 Pass 0.0061 2494 1280 51 Pass 0.0063 2291 1232 53 Pass 0.0065 2095 1201 57 Pass 0.0067 1896 1153 60 Pass 0.0069 1740 1113 63 Pass 0.0070 1574 1065 67 Pass 0.0072 1448 997 68 Pass 0.0074 1318 952 72 Pass 0.0076 1202 899 74 Pass 0.0078 1109 854 77 Pass 0.0080 1022 804 78 Pass 0.0082 928 758 81 Pass 0.0084 849 727 85 Pass 0.0086 788 680 86 Pass 0.0088 734 643 87 Pass RAM Engineering, Inc. RAM No. 20-003 C Facility PASSED Flow(cfs) Predev Mit Percentage Pass/Fail 0.0045 5808 4602 79 Pass 0.0047 5165 3058 59 Pass 0.0049 4594 2022 44 Pass 0.0051 4137 1495 36 Pass 0.0053 3713 1430 38 Pass 0.0055 3342 1391 41 Pass 0.0057 3020 1353 44 Pass 0.0059 2735 1321 48 Pass 0.0061 2494 1280 51 Pass 0.0063 2291 1232 53 Pass 0.0065 2095 1201 57 Pass 0.0067 1896 1153 60 Pass 0.0069 1740 1113 63 Pass 0.0070 1574 1065 67 Pass 0.0072 1448 997 68 Pass 0.0074 1318 952 72 Pass 0.0076 1202 899 74 Pass 0.0078 1109 854 77 Pass 0.0080 1022 804 78 Pass 0.0082 928 758 81 Pass 0.0084 849 727 85 Pass 0.0086 788 680 86 Fass 0.0088 734 643 87 Pass 0.0090 689 606 87 Pass 0.0092 634 560 88 Pass 0.0094 584 523 89 Pass 0.0096 537 485 90 Pass 0.0098 496 440 88 Pass 0.0100 463 411 88 Pass 0.0102 432 381 88 Pass 0.0104 399 342 85 Pass 0.0105 379 302 79 Pass 0.0107 364 257 70 Pass 0.0109 330 225 68 Pass v 82nd Townhouses Stormwater Site Plan Report Page C-15 0.0090 689 606 87 Pass 0.0092 634 560 88 Pass 0.0094 584 523 89 Pass 0.0096 537 485 90 Pass 0.0098 496 440 88 Pass 0.0100 463 411 88 Pass 0.0102 432 381 88 Pass 0.0104 399 342 85 Pass 0.0105 379 302 79 Pass 0.0107 364 257 70 Pass 0.0109 330 225 68 Pass 0.0111 304 200 65 Pass 0.0113 280 178 63 Pass 0.0115 262 145 55 Pass 0.0117 244 111 45 Pass 0.0119 219 96 43 Pass 0.0121 204 80 39 Pass 0.0123 186 64 34 Pass 0.0125 171 58 33 Pass 0.0127 157 47 29 Pass 0.0129 142 38 26 Pass 0.0131 133 21 15 Pass 0.0133 124 17 13 Pass 0.0135 118 17 14 Pass 0.0137 106 15 14 Pass 0.0138 96 13 13 Pass 0.0140 89 13 14 Pass 0.0142 84 13 15 Pass 0.0144 78 12 15 Pass 0.0146 71 12 16 Pass 0.0148 65 12 18 Pass 0.0150 63 12 19 Pass 0.0152 58 12 20 Pass 0.0154 55 11 20 Pass 0.0156 49 10 20 Pass 0.0158 44 10 22 Pass 0.0160 40 10 25 Pass 0.0162 36 10 27 Pass 0.0164 35 10 28 Pass 0.0166 34 10 29 Pass 0.0168 32 10 31 Pass 0.0170 31 10 32 Pass 0.0171 26 10 38 Pass 0.0173 23 10 43 Pass 0.0175 23 10 43 Pass 0.0177 23 10 43 Pass 0.0179 20 9 45 Pass 0.0181 20 9 45 Pass 0.0183 19 9 47 Pass 0.0185 18 9 50 Pass 0.0187 18 9 50 Pass 0.0189 18 9 50 Pass 0.0191 17 8 47 Pass 0.0193 16 8 50 Pass 0.0195 15 8 53 Pass 0.0197 14 8 57 Pass 0.0199 14 8 57 Pass 0.0201 14 8 57 Pass 0.0203 13 8 61 Pass 0.0205 12 8 66 Pass 0.0206 12 8 66 Pass 0.0208 12 8 66 Pass 0.0210 12 8 66 Pass 0.0212 12 8 66 Pass 0.0214 12 8 66 Pass 0.0216 11 7 63 Pass 0.0218 11 7 63 Pass RAM Engineering, Inc. RAM No. 20-003 82nd Townhouses Stormwater Site Plan Report Page C-16 0.0220 11 6 54 Pass 0.0222 11 6 54 Pass 0.0224 10 6 60 Pass 0.0226 9 6 66 Pass 0.0228 9 6 66 Pass 0.0230 9 6 66 Pass 0.0232 8 6 75 Pass 0.0234 8 5 62 Pass 0.0236 7 5 71 Pass 0.0238 6 5 83 Pass Water Quality BMP Flow and Volume for POC #1 On-line facility volume: 0.0081 acre-feet On-line facility target flow: 0.0051 cfs. Adjusted for 15 min: 0.0052 cfs. Off-line facility target flow: 0.0028 cfs. Adjusted for 15 min: 0.0028 cfs. LID Report C LID Technique Used for Total Volume Volume Infiltration Cumulative Percent Water Quality Percent Comment Treatment'? Needs Through Volume Volume Volume Water Quality Treatment Facility (ac-fit) Infiltration Infiltrated Treated (ac-ft) (ac-ft) Credit Vault 1 POC ❑ 84.33 E3 0 00 Total Volume Infiltrated 84.33 0.00 0.00 0 00 0.00 0% Treat r Credit C Duration Compliance with LID Analysis Standard 8% of 2-yrto 50% of Result = 2 yr Failed 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. 20-003 82nd Townhouses Stormwater Site Plan Report Page C-17 ACFwESTjmc. G E O S Y N T H E T I C S ACF West Inc. 15540 Woodinville -Redmond Rd. Bldg. A#400 Woodinville, WA 98072 Rob Long, P.E. RAM Engineering, Inc. 16531 13th Ave W Suite A108 Lynnwood, WA 98037 October 28, 2020 SUBJECT: 82nd Townhomes - Edmond, WA R-Tank Plan Review and Construction Oversight Commitment Dear Rob, Thank you for forwarding the plans of the proposed 82nd Townhome project in Edmonds, Washington to ACF West for review. Our team has reviewed the R-Tank plans dated 10-28-20 which call for the installation of a stormwater tank utilizing 309 "Triple" R-TankHD modules for storage. Below is a summary of our observations of the proposed system: • The dimensions and layout pattern or the R-Tank Triple Modules are consistent with our recommendations. • There are 2 maintenance ports located in the system which meet our standards. These maintenance ports also serve as inspection points. • Both Inlet and Outlet locations have been verified on the East end of the system and will require pipe boots as shown in the attached cross section details. • Trash Guard location in the upstream CB has been verified and cross-section view is shown on the plans. Overall, ACF takes no exceptions to the location and application of the R-Tank system for this project. RAM Engineering, Inc. RAM No. 20-003 1 1 P a g e 82nd Townhouses Stormwater Site Plan Report Page C-18 Regarding the installation, ACF West will host a preconstruction meeting with the site contractor and will visit the site several times during the installation to ensure the installation is being conducted in accordance with our standard installation procedures and specifications. Please review and contact me with any questions from your office. We look forward to working with you on this project. Sincerely, Joshua Venters, P.G. Engineered Product Solutions ACF West Inc. Cc: Aaron Schmidt., ACF West Attached: R-Tank flans for 82nd Townhomes Edmonds, WA RAM Engineering, Inc. RAM No. 20-003 2 1 P a g 82nd Townhouses Stormwater Site Plan Report Page C-19 Offsite Analysis. The site is located within the City of Edmonds Good Hope Pond watershed basin. Good Hope Pond basin is a centralized urban basin that collects stormwater runoff from primarily residential areas in the City Edmonds and ultimately discharges flows westerly to Shell Creek and on to the Puget Sound (see attached watershed map). Site runoff leaves the site as sheet -flow runoff that flows in an easterly direction. Runoff leaving the site sheet -flows across the site and enter the roadside ditch and culvert system along the west side of 82nd PI W. The storm system along 82nd PI W crosses to the east side of 82nd PI W about 75 feet north of the site and continues north in a pipe and catch basin system along 82nd PI W. The stormwater system continues north under 212th St SW through the Solaire Condominium complex and back in to the 82nd PI W right-of-way north of the condominium property. The stormwater system continues north and shifts west to 83rd Ave W at 210th PI SW; at 2081h St SW the system turns west and discharges into Good Hope Pond about 0.35 miles downstream of the site. Good Hope Pond discharges westerly to Shell Creek and eventually discharges to the Puget Sound about 2.6 miles from the site. The downstream system primarily consists of a man-made pipe and catch basin system within the 0.35 miles from the site to Good Hope Pond. No apparent flooding or system inadequacies within downstream of the site were discovered during site visits or research of the downstream system. See attached watershed and downstream drainage facility map for the local downstream path. RAMEngineering, Inc. RAM No. 20-003 82"d Townhouses Stormwater Site Plan Report Page C-20 Watershed Basin Map v FIGURE B-1 N CITY OF EDMONDS g WATERSHEDS 3 I - I Deer Creek -Perrinville�- Vtil I Edmonds Marsh - Puget Sound 9Neadowdale A.; --- j Edmonds Way - Puget Sound Piped u Fruitdale - Shell Creek �"1- w °ie Rd -' Good Hope Pond - Shellabarger 1"th St sw Halls Creek _Southwest Edmonds A 7 Hindley Creek Southwest Edmonds B 1 �\ ----- --' - f� 1I Cree;Stilthouse Cr a i' ! Lake Ballinger Stilthouse Creek j I-�Lund 's Gulch -Talbot ParkA �ttralhocPa r•Th"�`. i -I Meadowdale A - Talbot Park B a� - -- in i -- Meadowdale B -Terrace Creek Terrace Creek Northstream Westgate Pond Outfall Creek Willow Creek 3 3 0 1,00g z,Doo a,aoo 6,g00 e,000 P 'nville Feet Pug ntE, . :`2. aQ ri m Ei lin=2,000ft j No warranty of airy sort, Including accuracy, fitness, ar rn—hantability ! accompanythisprcEuct. 17P - I March 30, 2mo N lFruitdale - 3 �.9�get Dt� If 1 196th St SW C�sperse= o` .. zaan usw i Good Hope Pond yip \ ' i 206th St SW I .,\"et Sound Pipp�4-- ��, bayt '• 6- t � * --zoam St. sw rids It 3— oinwv i \U Shell Creek �• 212th St sw i �. Shelffbargen� ; P C` GAVestgate Pon Halls Creek / ! ! ! I.. �illptwCreek� .� SITE CT-..... zzatn St sw m Cre nd, Wy ♦j $ i� 3 i y\ i If z3sst st sw /n E.4, 3 I1. F Ur- a> W—h—en Rd \ I S �ii� Edmonds Way 1 it F Lake Ballinger 24011, Sbuthwest Edmonds'$ ! -----'------------------------------------------------- N ry zosth 51/24am S, s W------. RAMEngineering, Inc. RAM No. 20-003 82"d Townhouses Stormwater Site Plan Report Page C-21 Downstream Drainage Facility Map (City of Edmonds GIS) O PD9.37 ooa PD9-11 0 T PD9' ♦O iD13.0 RAM Engineering, Inc. RAM No. 20-003 0 0 0 0 Good Hope Pond 0 d PD9-43 ❑ O + I O b Discharge to Good Hope Pond about 0.35 miles downstream of site. II O u O I PD9d9 PD9- 18 PD1?-iO 16 Oo O.=O 0CR P P11 O36 O 00 OS 0 CD 0 g>OPf Qt'.39r_ 7 L'. a� 82"d Townhouses Stormwater Site Plan Report Page C-22 D. SOILS REPORT. Geotechnical Evaluation Letter Prepared by: Earth Solutions NW, LLC Date: April 21, 2020 RAMEngineering, Inc. RAM No. 20-003 82" d Townhouses Stormwater Site Plan Report Page D-1 E. CONSTRUCTION SWPPP REQUIREMENTS: The project will require grading to construct the proposed building and utilities (including the stormwater R-tank detention system). Standard erosion control measures are proposed to be used during construction. The primary erosion and sediment control BMP during construction will be proper soil stabilization methods. Exposed soils shall be stabilized by application of effective BMPs that protect the soil from the erosive forces of raindrops, flowing water, and wind. Applicable practices include, but not limited to, temporary and permanent seeding, sodding, mulching, plastic covering, erosion control fabrics, matting, 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 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. RAMEngineering, Inc. RAM No. 20-003 82" d Townhouses 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: Compaction (i.e. vehicle and equipment traffic or storage; and/or placement of stockpiles) to the soils in the area of the stormwater BMPs (Post - Construction Soil Quality and Depth BMP T5.13 shall be avoided (or restored) during construction. RAMEngineering, Inc. RAM No. 20-003 82" d Townhouses 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 (pipes and R-tank detention system) on the project site to ensure it operates as designed. The City has developed an inspection program to ensure private property owners are properly maintaining their stormwater systems. City System: City crews perform maintenance activities on the entire storm drainage system, including inspection and cleaning of catch basins, street sweeping, emergency flooding response, creek maintenance, inspection and monitoring of private stormwater detention systems. Operation and Maintenance Requirements for private property owner system: This manual is not comprehensive; although it explains the intended operation of the various components of the drainage system, and suggests a routine of inspection and maintenance, it cannot anticipate every problem. Once a historical record of maintenance is established, it may be prudent to alter the routine. It is recommended that maintenance records be kept, and that the records be reviewed periodically. Concept of Operation: The drainage design is shown and described in the site development engineering plans and report. The approved site development plans and report should be retained by the owner and used as a reference to identify stormwater BMP facilities outlined in this manual. Conveyance Systems. The design objective in pipe sizing was to convey the large storm events without the water surface exceeding the ground elevation. Frequent overtopping of the pipe system in an area might indicate a downstream blockage. Overtopping of the drain systems at the catch -basins is an indication that maintenance is required. The following pages outline standard general maintenance criteria for the project's drainage facilities For additional and updated maintenance information visit the Washington State Department of Ecology's web -site at: http://www.ecy.wa.gov/programs/wq/wghome.html 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 party 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. RAMEngineering, Inc. RAM No. 20-003 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. 82nd Townhouses Stormwater Site Plan Report Page F-1 v (D T N O v (D co C/) r CD a O Z3 N O _1 co Table V-A.S: Maintenance Standards - Catch Basins Maintenance Defect Conditions When Maintenance is Needed Results Expected When Maintenance is per - Component formed 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%. No Trash ordebris located immediately in front of 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 gout of the catch basin a on grate opening. basin, but in no case less than a minimum of six inches clearance from the debris surface to the invert of the lowest pipe. No trash ordebris in the catch basin. Trash & Debris Trash or debris in an inlet a outlet blocking more than 1/3 of its height. Y pipe 9 9 Intel and outlet pipes free of trash or debris. Dead animals or vegetation that could generate odors that could cause complaints or dangerous gases (e.g., methane). No dead animals or vegetation present within the catch basin. Sediment (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 Sediment 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 General Structure Damage to T slab has holes la than 2 square inches or cracks widerthan 1/4 inch. Intent is to make sure no material is runninginto basin Top � q ( basin). Top slab is free of holes and cracks. Frame and/or Top Slab 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 Frame is sitting flush on the riser rings or top slab and finely attached. Fractures a Cracks in Maintenance person judges that structure is unsound. Basin replaced or repaired to design standards. Basin Walls/ Bottom Grout fillet has separated or cracked wider than 1/2 inch and longer than 1 foot at the joint of any inlet/outlet pi pe or any evidence of soil particles entering Pipe is regrouted and secure at basin wall. catch basin through cracks. Settlement] Mis- If failure of basin has created a safety, function, ordesign problem. Basin replaced or repaired to design standards. alignment Vegetation growing across and blocking more than 10% of the basin opening. No vegetation blocking opening to basin. Vegetation Vegetation growing in inleUoutlet pipejoints that is more than six inches tall and less than six inches apart. No vegetation or root growth present. Contamination and Pol- See Table V-A.1: Maintenance Standards - Detention Ponds No pollution present. lution 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 Catch Basin Locking Mechanism Mechanism cannot be opened by one maintenance person with proper tools. Bolts into frame have less than 112 inch of thread. Mechanism opens with proper tools. Cover Not Waking Cover Difficult to One maintenance person cannot remove lid after applying normal lifting pressure. Cover can be removed by one maintenance per - Remove (Intent is keep cover from sealing off access to maintenance.) son. 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 main- tenance person safe access. Grate opening Unsafe Grate with opening wider than 7/8 inch. Grate opening meets design standards. Metal Grates Trash and Debris Trash and debris that is blocking more than 20% of grate surface inletting capacity. Grate free of trash and debris. (If Applicable) Grate is in place, meets the design standards, and Damaged a Missing. Grate missing a broken member(s) of the grate. is installed and aligned with the flow path. T W O v (D Co C0 r (D a O v � Z N O � co Table V-A.6: Maintenance Standards - Debris Barriers (e.g., Trash Racks) Maintenance Components Defect Condition When Maintenance is Needed Results Expected When Maintenance is Performed General Trash and Debris Trash or debris that is plugging more than 20% of the openings in the barrier. Barrier cleared to design flow capacity. Bars are bent out of shape more than 3 inches. Bars in place with no bends more than 314 inch. Damaged/ Missing Bars. Bars are missing or entire barrier missing. Bars in place according to design. Metal Bars are loose and rust is causing 50% deterioration to any part of barrier. Barrier replaced or repaired to design standards. Inlet/Outlet Pipe Debris barrier missing or rat attached to pipe Banner firmly attached to pipe Table V-A.7: Maintenance Standards - Energy Dissipators Maintenance Com- Defect Conditions When Maintenance is Needed Results Expected When Maintenance is ponents Performed External: Rack Pad Missing or Moved Rock Only one layer of rock exists above native soil in area five square feet or larger, or any exposure of native soil. Rock pad replaced to design standards. Erosion Soil erosion in or adjacent to rock pad. Rock pad replaced to design standards. Pipe Plugged with Sediment Accumulated sediment that exceeds 20%of the design depth. Pipe cleaned/flushed so that it matches design. Not Discharging Water Property Visual evidence of water discharging at concentrated points along trench (normal condition is a "sheet flow" of water along trench). Trench redesigned or rebuilt to standards. Intent is to prevent erosion damage. Dispersion Trench perforations Plugged. Over 1/2 of perforations in pipe are plugged with debris and sediment. Perforated pipe cleaned or replaced. Water Flows Out Top of "Distributor" Maintenance person observes or receives credible report of waterflowing out during any storm less than the design storm or its causing Facility rebuilt or redesigned to standards. Catch Basin. or appears likely to cause damage. Receiving Area Oversaturated Water in receiving area is causing or has potential of causing landslide problems. No danger of landslides. Internal: Worn or Damaged Post, Baffles, Side Structure dissipating Flow deteriorates to 1/2 of original size or any concentrated worn spot exceeding one square foot which would Structure replaced to design standards. Manhole/Chamber of Chamber make structure unsound. Other Defects See Table V-A.S: Maintenance Standards - Catch Basins See Table V-A.S: Maintenance Standards - Catch Basins O TECHNICAL T ANK STORMWATER MANAGEMENT 0 RJANK MAINTENANCE Designing an underground stormwater detention system with future maintenance in mind is a simple process that includes three primary objectives: PREVENT debris from entering the system by using good pre-treatment systems, ISOLATE debris and sediments that manage to enter the system, and PROTECT the body of the system by providing backflush mechanisms to ensure longevity. L PREVENT Keeping debris and sediment out of the system by pre -treating runoff is one of the smartest things an engineer can do when designing underground detention systems. It makes no sense to allowtrash and sedimentstoflow unrestricted into an underground system where removal will be expensive. Instead, capture pollutants simply and inexpensively in the inlets, where removal is easy. There are several ways this can be accomplished with minimal cost impacts to your project. Trask Guard Plus® Trash Guard Plus is a patented stormwater pretreatment device that traps debris, sediment and floatables in the inlet. It helps extend maintenance cycles by using the full volume of the inlet structure for sediment capacity. And it is easy to Trash Guard Plusm maintain by accessing pollutants through the manhole lid. Trash Guard Plus works by both screening debris out of the runoff and by slowing the flow of runoff, causing sediments to fall to the bottom of the inlet. Testing at NC State has shown the Trash Guard to be effective at removingtrash, sediment, nutrients, and metals. Gratemaster 4!L To treat a single inlet that serves as a ju nction fora larger drainage area, consider an insert like the Gratemaster. Ideal for capturing sediment and trash, it makes clean-up Grate —ter a snap by holding all the pollutants right near the surface for easy extraction. R-Tank Screening For a more centralized approach, some engineers prefer to create an opening in the inlet structures to allow the R-Tank modules to penetrate the structure to act as a trash screen. This works best with a structure that includes a sump (see drawing below). RAM -ngineering, Inc. RAM No. 20-003 82"d Townhouses Stormwater Site Plan Report Page F-4 ail►�l'Ilalill�ilai 2. ISOLATE Some pollutants may elude the pre-treatment systems. Trap these materials inside the maintenance row (see drawing to right). Consolidating sediments in a single location makes them easy to remove. Maintenance rows are formed by using maintenance modules, which have open internal components that are fully accessible by conventional jet -vac systems. These modules are set in a row (or multiple rows) to your desired length. Longer maintenance rows should include an access structure on both ends. Extremely long rows may require access from the middle of the row, as well. The maintenance row is always wrapped in geotextile independently from the rest of the system. The geotextile retains trash, sediments, and other solids, preventing contamination of the rest of the system. The maintenance row should be sized to treat the first flush (usually 1 ") of runoff. Use a bypass structure to divert that flow into the maintenance row, and allow larger flows to continue to a downstream inlet where they can enter the R-Tank outside of the maintenance row. The maintenance row is only available in LID, HD, and UD modules. For SD and XD modules, consider creating a forebay around the inlet locations to collect sediment. This is done by using a taller module installed at a lower invert. Geotextile baffles between the forebay and the rest of the system can help retain sediments. Concentrate Maintenance Ports (see PROTECT below) in the forebay to ensure access to sediment for removal. & PROTECT Every good system has a fall -back plan. You can ensure a long system life by including maintenance ports throughout the system footprint to remove any pollutants that evade the pretreatment system and maintenance row. Maintenance ports should be specified within 10' of inlet and outlet connections, and roughly 50' on center (see maintenance port detail to right). LET'S GET IT DONE 800.448.3636 acfenvironmental.com RAMEngineering, Inc. RAM No. 20-003 82"d Townhouses Stormwater Site Plan Report Page F-5 TECHNICAL STORMWATER MANAGEMENT TiTANK RJANK OPERATION, INSPECTION & MAINTENANCE Operation Your ACF R-Tank System has been designed to function in conjunction with the engineered drainage system on your site, the existing municipal infrastructure, and/orthe existing soils and geography of the receiving watershed. Unless your site included certain unique and rare features, the operation of your R-Tank System will be driven by naturally occurring systems and will function autonomously. However, upholding a proper schedule of Inspection & Maintenance is critical to ensuring continued functionality and optimum performance of the system. Inspection Both the R-Tank and all stormwater pre-treatment features incorporated into your site must be inspected regularly. Inspection frequency for your system must be determined based on the contributing drainage area, but should never exceed one year between inspections (six months during the first year of operation). Inspections may be required more frequently for pre-treatment systems. You should refer to the manufacturer requirements for the proper inspection schedule. With the right equipment your inspection and measurements can be accomplished from the surface without physically entering any confined spaces. If your inspection does require confined space entry, you MUST follow all local/regional requirements as well as OSHA standards. R-Tank Systems may incorporate Inspection Ports, Maintenance Ports, and/or adjoining manholes. Each of these features are easily accessed by removing the lid at the surface. With the cover removed, a visual inspection can be performed to identify sediment deposits within the structure. Using a flashl ight, ALL access points should be examined to complete a thorough inspection. Inspection Ports Usually located centrally in the R-Tank System, these perforated columns are designed to give the user a base -line sediment depth across the system floor. Maintenance Ports Usually located near the inlet and outlet connections, you'll likely find deeper deposits of heavier sediments when compared to the Inspection Ports. Manholes Mostsystemswill include at least two manholes -one at the inlet and another at the outlet. There may be more than one location where stormwater enters the system, which would result in additional manholes to inspect. Bear in mind that these manholes often include a sump below the invert of the pipe connecting to the R-Tank. These sumps are designed to capture sediment before it reaches the R-Tank, and they should be kept clean to ensure theyfunction properly. However, existence of sediment in the sump does NOT necessarily mean sediment has accumulated in the R-Tank. After inspecting the bottom of the structure, use a mirror on a pole (or some other device) to check for sediment or debris in the pipe connecting to the R-Tank. RAM Engineering, Inc. RAM No. 20-003 82"d Townhouses Stormwater Site Plan Report Page F-6 If sediment or debris is observed in any of these structures, you should determine the depth of the material. This is typically accomplished with a stadia rod, but you should determine the best way to obtain the measurement. All observations and measurements should be recorded on an Inspection Log kept on file. We've included a form you can use at the end of this guideline. Maintenance The R Tank System should be back -flushed once sediment accumulation has reached 6" or 15% of the total system height. Use the chart below as a guideline to determine the point at which maintenance is required on your system. 1 P ,. Mini 9.5" 1.5" Single 17" 3" Double 34" 5" Triple 50" 6" Quad 67" 6" Pent 94" 6" Before any maintenance is performed on your system, he sure to plug the outlet pipe to prevent contamination of the adjacent systems. To back -flush the R-Tank, water is pumped into the system through the Maintenance Ports as rapidly as possible. Water should be pumped into ALL Maintenance Ports. The turbulent action of the water moving through the R-Tank will suspend sediments which may then be pumped out. If your system includes an Outlet Structure, this will be the ideal location to pump contaminated water out of the system. However, removal of back -flush water may be accomplished through the Maintenance Ports, as well. For systems with large footprints that would require extensive volumes of water to properly flush the system, you should consider performing your maintenance within 24 hours of a rain event. Stormwater entering the system will aid in the suspension of sediments and reduce the volume of water required to properly flush the system. Once removed, sediment -laden water may be captured for disposal or pumped through a DirtbagTM (if permitted by the locality). 2831 Cardwell Road ® Richmond, Virginia, 23234 800.448.3636 FAX 804.743.7779 LET'S GET IT DONE acfenvironmental.com RAMEngineering, Inc. RAM No. 20-003 82nd Townhouses Stormwater Site Plan Report Page F-7 Step -By -Step Inspection & Maintenance Routine 1) Inspection a. Inspection Port I. Remove Cap ii. Use flashlight to detect sediment deposits ill. If present, measure sediment depth with stadia rod iv. Record results on Maintenance Log v. Replace Cap b. Maintenance Port/s i. Remove Cap ii. Use flashlight to detect sediment deposits ill. If present, measure sediment depth with stadia rod iv. Record results on Maintenance Log v. Replace Cap vi. Repeat for ALL Maintenance Ports c. Adjacent Manholes i. Remove Cover ii. Use flashlight to detect sediment deposits ill. If present, measure sediment depth with stadia rod, accounting for depth of sump (if present) iv. Inspect pipes connecting to R-Tank v. Record results on Maintenance Log vi. Replace Cover vii. Repeat for ALL Manholes that connect to the R-Tank 2) Maintenance a. Plug system outlet to prevent discharge of back -flush water b. Determine best location to pump out back -flush water c. Remove Cap from Maintenance Port d. Pump water as rapidly as possible (without over -topping port) into system until at least 1" of water covers system bottom e. Replace Cap f. Repeat at ALL Maintenance Ports g. Pump out back -flush water to complete back -flushing h. Vacuum all adjacent structures and any other structures or stormwater pre-treatment systems that require attention i. Sediment -laden water may be captured for disposal or pumped through a DirtbagTM. j. Replace any remaining Caps or Covers k. Record the back -flushing event in your Maintenance Log with any relevant specifics RAMEngineering, Inc. RAM No. 20-003 82nd Townhouses Stormwater Site Plan Report Page F-8 v 0 m T na 3 A GF I� o ,(D LET S GET IT DOL,F o m o =� CIO :z Site Name: 3 Location: System Owner: 0 v m 'I co C/) N) CD a � o v g m o -0 _ � � R-Tank Maintenance Log Company Responsible for Maintenance: Conta Phone Number: For more information about our products, contact Inside Sales at 800.448.3636 or email at info@acfenv.com STORMWATER PRETREATMENT DEVICE THAT CAPTURES DEBRIS, SEDIMENT AND FLOATABLES Trash Guard Plus is a patented catch basin filter designed to trap and filter solid materials and floatables out of stormwater runoff while maintaining water flow. These devices have been proven through extensive testing and come in three screen sizes for use with discharge pipes with <24" diameter. A calculator to help design professionals select the appropriate screen size is available. Each screen can be adjusted at installation to accommodate low flow stormwater events of 10 cfs or more. Installation of a Trash Guard Plus screen is relatively straightforward and quick with no heavy equipment required. As with any catch basin filter, regularly scheduled maintenance to reduce clogging or flooding is necessary. With the Trash Guard Plus, it is recommended that these units be inspected and cleaned every 3 months (or after any major weather event). �f r, �f (A ADVANTAGES: Made from 100% HDPE Optional bottom plate available for rounded bottoms Optional retaining rails available for plate removal Simple retrofits to existing catch basin RAMEngineering, Inc. RAM No. 20-003 - Installs easily without heavy equipment - Adjusts to irregular catch basin bottoms and/or walls - Helps eliminate stormwater trash at public parks, beaches, and within the waterways 82nd Townhouses Stormwater Site Plan Report Page F-10 TRASH GUARD PLUS® INSTALLATION: Trash Guard Plus can be installed in a variety of catch basin configurations (or field conditions). In general the Trash Guard Plus is mounted on the catch basin wall, centered over the outlet pipe. Before installing the device, a hydraulic calculation should be performed to determine maximum flow rate based on depth of the catch basin and size of Trash Guard Plus used. This calculated model will determine maximum flow rate with no obstructions orvarying amounts of trash build up, and determine the drainage area required to support the calculated flow rate. Allowable trash build up and drainage area required fortrash build up will determine maintenance frequency. Every3 months is recommended at minimum, with additional cleanings after major weather events. If catch basin conditions allow an increased flow rate and additional vertical capacity is desired, a model can be calculated to determine flow rate when extending Trash Guard Plus from 1 " - 7" from the catch basin wall. As above, this calculated model will determine maximum flow rate with no obstructions or varying amounts of trash build up. For assistance with calculations, please reach out to our team. Plat -Bottom Catch Basin - Trash Guard Plus Installation Several other installation options are available. Rounded Bottom Catch Basin - Trash Guard Plus Installation WARNING: Improper installation of the Trash Guard Plus® or failure to keep the area around the Trash Guard Plus® free from sediment, debris and litter after installation may result in clogging of the stormwater drainage system and increase the risk of flooding during times of heavy rainfall. It is important to clear sediment, debris and litter from around the Trash Guard Plus® at least four (4) times a year and more frequently in areas with large amounts of vegetation or litter. Please contact your local Trash Guard Plus® distributor with any questions regarding the installation or regular maintenance requirements of the Trash Guard Plus® RAM ngineering, Inc. RAM No. 20-003 A GF LET'S GET IT DONE 800.448.3636 acfenvironmental,com 82"d Townhouses Stormwater Site Plan Report Page F-II ENGINEERING, INC. Civil Engineering /Land Planning