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APPROVED STM BLD2021-0020+Storm_Drainage_Report+2.15.2021_1.00.11_PM+2047672RECEIVED Feb 17 2021 CITY OF MONDS DEVELOPMENT SERVICES civil &structural DEPARTMENT MENT ENGINEERING engineering & planning DRAINAGE REPORT 76t" Ave Townhomes 7528 215th Street SW Edmonds, WA 98026 APPLIES WITH APPLICABLE CITY STROMWATER CODE 0211212021 CG Project No.: 17206.20 250 4ch Ave S Ste 200 Edmonds, WA 98020 Phone: (425) 778-8500 Fax: (425) 778-5536 Table of Contents Section I — Project Overview Section II — Off -Site Analysis Section III — Permanent Stormwater Control Plan Section IV —Construction Stormwater Pollution Prevention Plan Section V — Special Reports and/or Studies Section VI — Other Permits Section VII — Bond Quantities & Operation and Maintenance Manual 4 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com 76th Ave Townhomes - CG #17206.20 February 12, 2021 Drainage Report Section I, Page 1 Section I — Project Overview Section I Summa Overview Existing Condition Developed Condition Minimum Requirements Overview This stormwater site plan has been written for a new four -unit townhome building on a 0.24 ac lot located at 7528 215th Street SW in Edmonds, WA (Tax Parcel Number: 00501200001600). The building will have a footprint of approximately 3,500 sf (0.08 ac), along with an associated driveway and walkways. There is an existing single-family residential house with attached garage and associated walkways and driveway that will be demolished. The project will meet minimum requirements 1 through 9 per the Edmonds Stormwater Addendum and ECDC 18.30.060. Existing Condition The site is currently developed with a house, attached garage, driveway and walkways on a rectangular, approximately 10,250 sf (0.24 ac) lot. Other ground cover includes large and small trees, shrubs and grass. The site soils consist of "Existing Fill Soils", which are loose to medium dense, silty sand and "Glacial Till Deposits", which are dense to very dense, silty sand with gravel. More about the soils can be found in Section V in the Geotechnical Engineering Report. Another single-family residence borders the site on the east side of the site, 76th Avenue borders the west side, and a hospital parking lot borders the site on the south side. The front of the house faces 2151h Street and access to the driveway is on this street. Stormwater that collects on the driveway slopes down to the driveway edge and sheets off into the grass on the east side toward the adjacent property. Stormwater that collects elsewhere either infiltrates through the grass or runs off the east and south edges of the site. Utilities are located in the south edge of 2151h Street and include the sewer, water, and storm mains. There are 3 existing catch basins along the north edge of the property. The site generally slopes downward from west to east with an average slope of 8%. The site does not appear to take on any significant upstream flows. The site is located in the Hall Creek Watershed. The existing impervious areas are as follows: Impervious Areas Roof: 1,604 sf (0.037 ac) Sidewalk: 784 sf (0.018 ac) Driveway, Mod: 469 sf (0.011 ac) Total: 2,857 sf (0.066 ac) 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com 76th Ave Townhomes - CG #17206.20 Drainage Report February 12, 2021 Section I, Page 2 Develoned Condition The project consists of the construction of a 4-unit townhome building with associated walkways and driveway, as well as street improvements in 215t" Street and sidewalk improvements on 761" Avenue and 215t" Street. The total of new plus replaced impervious surface is 8,517 sf (0.196 ac). Disturbance will affect the entire site. The site will utilize a 24" detention pipe with a flow control structure in the driveway that will discharge to the city's MS4 before ultimately discharging to Hall Creek. All runoff on -site will drain to the detention pipe. The west side of the site will be sloped down towards the townhouse and runoff will enter area drains which will tie into roof drains that will discharge into the detention pipe. All other runoff will sheet flow to the driveway area and enter the detention pipe through a catch basin/manhole. Setbacks and proximity to structures and property lines can be seen in the civil drawings on sheet C3.1. See page 7, Section VII for vegetation management plan. The proposed impervious areas (including ROW) are as follows: Impervious Areas Roof: Sidewalk: Driveway, flat: ROW Sidewalk, mod ROW Road, mod: Tota 1: 3,423 sf (0.079 ac) 236 sf (0.005 ac) 2,683 sf (0.062 ac) 1,360 sf (0.031 ac) 806 sf (0.019 ad 8,517 sf (0.196 ac) M E:TOTAL (MITGATED)215TH (COLLECTED) 76TH (BYPASS) The new and replaced pollution -generating impervious areas are as follows: Pollution -generating impervious areas Driveway, flat: 2,683 sf (0.062 ac) ROW Road, mod: 806 sf (0.019 ad Total: 3,489 sf (0.080 ac) 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com 76th Ave Townhomes - CG #17206.20 February 12, 2021 Drainage Report Section I, Page 3 0 2 H DETENTION PIPE 0 7 � 15 40 � 7 T101! � ,, J r- PROJECT SITE : z TTotal hard urfaces: 0.20 ac otal project area: 0.24 ac 2i s��.., PGHS/PGiS: 0.07 ac Total disturbed area: 0.24 ac Average slope: 8% 7W NRCS soil group: B Ic Figure 1-1. Vicinity map. 14-13 1421 � — 215 ThC�Sw-- ?" F,ETF 14146 14-145 14426 142214231424 1425 l 140.43 If :..J Q°N° 0 0 0 0� o rn n N PD1414 i, 14-1 3 PD"' 21516 Figure 1-2. Map with pipe material. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com 76th Ave Townhomes - CG #17206.20 February 12, 2021 Drainage Report Section I, Page 4 Figure 1-2. Aerial photograph (stars show approximate boring locations). Minimum Requirements Stormwater requirements were determined per the December 2016 Addendum to Edmonds Community Development Code Chapter 18.30 (Edmonds Stormwater Addendum), the Edmonds Community Development Code (ECDC) Chapter 18.30, and the 2014 Stormwater Management Manual for Western Washington by the Department of Ecology (SWMMWW). This report is based on the steps recommended in Chapter 7 of the Edmonds Stormwater Addendum. Using Figure 1-3 (Figure 3.1 from the Edmonds Stormwater Addendum), the project is classified as a Category 2 Project and will comply with Minimum Requirements #1-9. Minimum Requirement #1: Preparation of Stormwater Site Plans: The stormwater site plan consists of this report and the civil drawings, and is prepared in accordance with Chapter 3 of Volume 1 of the SWMMWW and the requirements in the Edmonds Stormwater Addendum. Project checklists by the City of Edmonds to facilitate compliance with this minimum requirement have not been made available at the time of this submittal. 4M 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com 76th Ave Townhomes - CG #17206.20 February 12, 2021 Drainage Report Section I, Page 5 Minimum Requirement #2: Construction Stormwater Pollution Prevention Plan (SWPPP): The SWPPP shall include a narrative and drawings. The SWPPP narrative shall include documentation that addresses the 13 elements of Construction Stormwater Pollution Prevention. See Section IV and the civil drawings. Minimum Requirement #3: Source Control of Pollution: All known, available and reasonable source control BMPs must be required for all projects approved by the City. All single-family residential projects shall, at a minimum, incorporate required BMPs from SWMMWW Volume IV, S411 — BMPs for Landscaping and Lawn/Vegetation Management. The Operation & Maintenance Manual found in Section VII addresses Lawn/Vegetation management. Minimum Requirement #4: Preservation of Natural Drainage Systems and Outfalls: Natural drainage patterns shall be maintained, and discharges from the project site shall occur at the natural location, to the maximum extent practicable. The manner by which runoff is discharged from the project site must not cause a significant adverse impact to downstream receiving waters and down gradient properties. All projects shall submit an off -site qualitative analysis. A qualitative analysis of the upstream and downstream system entering the site is presented in Section II. Minimum Requirement #5: On -Site Stormwater Management: The proposed project is a Category 2 project per the Edmonds Stormwater Addendum that discharges to the City's MS4. It shall either use On - Site Stormwater Management BMPs from List No. 2 (per ECDC 18.30.060.D.5.e) for all new plus replaced hard surfaces and land disturbed, or demonstrate compliance with the LID Performance Standard (per ECDC 18.30.060.D.5.c ). The project will use On -Site Stormwater Management BMPs from List No. 2. See Section III for feasibility review. The total area of vegetation to be retained is approximately 0.090 acres. Post -construction soil quality and depth in accordance with BMP T5.13 in Chapter 5 of Volume V of the SWMMWW will be used for all disturbed pervious areas. Two trees on -site are to be retained and these can be seen on the Grading and Drainage Plan. Minimum Requirement #6: Runoff Treatment: This requirement applies to the new plus replaced hard surfaces and the converted vegetation areas. The following require construction of stormwater treatment facilities: i.) Projects in which the total of pollution -generating hard surface (PGHS) is 5,000 square feet or more in a threshold discharge area of the project, or ii.) projects in which the total of pollution -generating pervious surfaces (PGPS) — not including permeable pavements is 0.75 acres or more in a threshold discharge area, and from which there will be a surface discharge in a natural or man-made conveyance system from the site. This project's total of PGHS is less than 5,000 square feet and runoff treatment is not required. Minimum Requirement #7: Flow Control: Projects must provide flow control to reduce the impacts of stormwater runoff from hard surfaces and land cover conversions. The requirement below applies to projects that discharge stormwater directly, or indirectly through a conveyance system, into a fresh waterbody. Flow control is not required for projects that discharge directly to, or indirectly through the City's MS4 to Puget Sound. The following circumstances require achievement of the standard flow control requirement for western Washington: i.) Projects in which the total of effective impervious surfaces is 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com 76th Ave Townhomes - CG #17206.20 February 12, 2021 Drainage Report Section I, Page 6 10,000 square feet or more in a threshold discharge area, or ii.) projects that convert 0.75 acres or more of vegetation to lawn or landscape, or iii.) projects that through a combination of hard surfaces and converted vegetation areas cause a 0.15 cubic feet per second (cfs) increase or greater in the 100-year flow frequency from a threshold discharge area as estimated using the Western Washington Hydrology Model or other approved model and 15-minute time steps. The project's targeted new and replaced hard surfaces are approximately 8,517 sf (see areas tabulation and civil plans). Based on the proposed clearing limits (see civil plans), on -site land disturbance is approximately 9,800 sf. Using 15-minute time steps in WWHM2012, the project will cause a 0.06 cfs increase in flows between the existing and developed 100-year flow frequencies. Therefore, this project does not meet any of the aforementioned circumstances and standard flow control is not required. Minimum Requirement #8: Wetlands Protection: Projects shall comply with Guide Sheets #1 through #3 in Appendix I-D of the SWMMWW. The hydrologic analysis shall use the existing land cover condition to determine the existing hydrologic conditions unless directed otherwise by a regulatory agency with jurisdiction. The requirements apply only to projects whose stormwater discharges into a wetland, either directly or indirectly through a conveyance system. This project site's stormwater does not discharge into a wetland and does not require wetland protection. Minimum Requirement #9: Operation and Maintenance: An operation and maintenance manual that is consistent with the provisions in Volume I and Volume V of the SWMMWW is required for proposed Stormwater Treatment and Flow Control BMPs/facilities. The party (or parties) responsible for maintenance and operation shall be identified in the operation and maintenance manual. For private facilities approved by the City, a copy of the operation and maintenance manual shall be retained on -site or within reasonable access to the site, and shall be transferred with the property to the new owner. For public facilities, a copy of the operation and maintenance manual shall be retained in the appropriate department. A log of maintenance activity that indicates what actions were taken shall be kept and be available for inspection. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com 76th Ave Townhomes - CG #17206.20 Drainage Report February 12, 2021 Section I, Page 7 Dcx:s the project result in 2,000 square feet, or greater, urnew plus replaced hard surface area? OR Ikx s the land disturbing activity total 7,000 square feet or greater? 140 Minimum RequircmcnLs No. I through 5 apply Minimum Requircmcnt No. 2 applies Next Quesfi m Dees the project add 5,000 square feet or more of new plus replaced hard surfaces? OR Convert 0.75 acres or more of vegetation to lawn or landscaped areas? OR Convert 2.5 acres or mart of native vegetation to pasture? (H) Yes 1 Is this a road related project` All Minimum Rcqu"rements apply to the new and replaeed Yet hard surfaces and converted vegetation areas_ All Minimum Requirements apply to the new hard surfaces and converted vegetation arcaa. Yes Does the project acid 5,000 square feet or more of new hard surfaces? Yes Do new hard surfaces add 50%gar more to the existing hard surface within the project limits? No No IND Noadditional I rcquirements. Figure 1-3. Flow Chart for determining requirements for development (Figure 3.1 in the Edmonds Stormwater Addendum). 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com 76th Ave Townhomes - CG #17206.20 February 12, 2021 Drainage Report Section II, Page 1 Section II — Off -Site Analysis Section II Summary Task 1— Define and map the study area Task 2 — Review all available information of the study area Task 3 — Field inspect the area Task 4 - Describe the drainage system, and its existing and predicted problems Task 1— Define and map the study area An initial qualitative analysis shall document potential off -site impacts of stormwater discharges for each upstream drainage system entering a site, and each downstream drainage system leaving a site according to Section 6.2 of the Edmonds Stormwater Addendum. The downstream analysis shall extend from the project site to the receiving water, or up to one -quarter mile, whichever is less. Runoff from the site enters the City's MS4 within one -quarter mile since the project proposes to connect into the public storm main along the project frontage. The receiving water is Hall Creek which is about 0.50 mi downstream of the site. The downstream flowpath is outlined below in Figure II-1 from the City GIS map. O PD14.7 PD14a8 O O 0 0♦ 0 PD14-10 O PD14-40 �D O _ 0 O ° H '.' O O POoa408 O �D O 0 - VF PD14411 1 �---r--� 643.40 ft O % t; I I 1 _ 414 -4.12,� PD1413 0 14-15 ♦ O 0. O Q f 0 - _... ° O P014=51 O 445 PROJECT SITE0 q� D14 55 `J 610 N �� 0D13-22 06) <�? 480.00 ft 2,) 3, :� ft ,i PD14-52 ♦O O O-� ♦ O 466 97 ft `r � ° OUTFACE , 0 ° 0 PD14-53 PDa,434 O ,� 0 00 P014-17 6) 0 0 0 0 ♦ 00 1 �1 O 00 ♦ V� �D1433 Ofl4'SO O 0 0 O O PD14�9 O• ,i %; 0 00 � O I Figure II-1. Study area. Task 2 — Review all available information on the study area Existing stormwater improvements were determined from the survey and the City GIS map. There is a 12" concrete stormwater main along 215t" St running east that is adjacent to the site. The 12" concrete main then daylights into a ditch a few houses down in front of 7514 215" St. The flow path includes the ditch 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com 76th Ave Townhomes - CG #17206.20 February 12, 2021 Drainage Report Section II, Page 2 followed by 12" concrete pipe running under driveway and daylighting back into a ditch. The flow enters a 12" concrete pipe in front of 7420 215th St and does not daylight again. The concrete main continues down 73rd Ave to 216th St, where it becomes an 18" concrete main (0.25 miles downstream from site). The main continues east and becomes a 36" concrete main at 72nd Ave (0.33 miles downstream from site). The main continues east crossing Highway 99 and discharges into Hall Creek just 500 feet east of Highway 99. Per the City GIS map, the site may contain erosion hazard areas. An erosion hazard area map can be seen below in Figure II-2. The site is within the Hall Creek Watershed. Hall Creek is a category 5 water body due to bacteria according to DOE's 303(d) list. City of Edmonds GIS Legend - x < � L �o — Critical Areas /_'1 I ■ 41_ Lf-).Mq Lr) ON = Creeks CD 0 N ® seismic Hazard Areas i PROJECT SITE L Earth Subsidence and Landslide Area L Minimum Buffer Adjacent to Hazard i Wetlands �I — Wetlands Boundary __ Wetland Boundaries Not Completely II (N � O Delineated ^ rn Nt = Wetland Known Extents ■ I� ® Floodplains — Landslide and Erosion Hazard . Landslide Hazard Area 40% ' T severe Erosion Hazard 15%-40% ❑ Erosion Hazard Areas 15%-40% �%,p Legend Landslide... v o so eon Figure II-2. Erosion hazard area map. Task 3 — Field inspect the study area A site visit was done on the afternoon of June 27, 2017. The weather was clear and it had not rained that day. From evaluating surrounding conditions, the site does not appear to take on significant upstream runoff as it is near the top of the hill, which can be seen below in Figure II-3. The project proposes to tie all impervious areas to a detention pipe prior to connecting to the 12" concrete main along 215th St. On the 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com 76th Ave Townhomes - CG #17206.20 Drainage Report February 12, 2021 Section II, Page 3 following page, Figure II-4 shows a picture from the NW corner of the site looking downstream. The catch basins along 215th St appeared to be free of problems. Figures II-5 and II-6 show areas where the stormwater daylights into ditches. These areas have become overgrown with grass and sediment and may need to be addressed to facilitate stormwater flow properly. If they are not addressed, it is possible that stormwater will pool to a certain point and overflow into the ditch as it is supposed to do. This might also erode the overgrown areas and fix the problem naturally. Figure II-3. Front of house (house facing north). 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com 76th Ave Townhomes - CG #17206.20 Drainage Report February 12, 2021 Section II, Page 4 Figure II-4. 2151h St, NW corner of site looking east. h" c- - u 4 Vr F .M 3 A� Figure II-5. Daylight into ditch, east edge of 7514 215th St driveway. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com 76th Ave Townhomes - CG #17206.20 Drainage Report February 12, 2021 Section II, Page 5 Figure II-6. Daylight into ditch, east edge of 7520 2151h St west driveway. Task 4 — Describe the drainage system, and its existing and predicted problems Existing stormwater improvements were determined from the survey and the City GIS map. This is described in Task 2. The project proposes to route all runoff from impervious surfaces of the site to a 24" detention pipe system to meet the on -site stormwater management requirements (see Section III). The system will be tied into the 12" concrete main that runs along 215th Street. From Task 3 (field inspection) and Figures II- 5 and II-6, it can be seen that where the storm pipes daylight into ditches, these areas have become overgrown with grass and sediment and may pose problems for proper storm drainage. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com 76th Ave Townhomes - CG #17206.20 February 12, 2021 Drainage Report Section III Page 1 Section III — Permanent Stormwater Control Plan Section III Summary Narrative Feasibility Review Calculations WWHM2012 Report Narrative The proposed project is a Category 2 project per the Edmonds Stormwater Addendum that discharges to the City's MS4. It shall either use On -Site Stormwater Management BMPs from List No. 2 (per ECDC 18.30.060.D.5.e) for all new plus replaced hard surfaces and land disturbed, or demonstrate compliance with the LID performance standard (per ECDC 18.30.060.D.5.c ). The project proposes to use On -site Stormwater Management BMPs from List No. 2 (per ECDC 18.30.060.D.5.e). Runoff treatment and standard flow control are not required for this project (see Minimum Requirements #6 & #7 in Section I and WWHM report later in this section). Feasibility Review The project must implement on -site stormwater management BMPs to the maximum extent feasible per Minimum Requirement #5. The following BMPs were evaluated per List No. 2 of the On -site Stormwater Management BMPs for Projects Triggering Minimum Requirements #1 through #9: Lawn and landscaped areas: 1. Post -construction soil quality and depth in accordance with BMP T5.13 in Chapter 5 of Volume V of the SWMMWW will be used for all disturbed pervious areas. Roofs: 1. Full Dispersion in accordance with BMP T5.30 is infeasible because a 65 to 10 ratio of forested or native vegetation area to impervious area cannot be achieved. Downspout Full Infiltration Systems in accordance with BMP T5.10A is infeasible because the geotechnical evaluation advises against infiltration due to "the very low permeability of the dense to very dense glacial till deposits". 2. Rain Gardens in accordance with BMP T5.14A and Bioretention in accordance with Chapter 7 are infeasible because the geotechnical evaluation points out that "the feasibility for... rain gardens, permeable pavement, and surface dispersion appears low". 3. Downspout Dispersion Systems in accordance with BMP T5.1013 are infeasible because the geotechnical evaluation points out that "the feasibility for... rain gardens, permeable pavement, and surface dispersion appears low". 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com 76th Ave Townhomes - CG #17206.20 Drainage Report February 12, 2021 Section III Page 2 4. A Perforated Stub -Out Connection in accordance with BMP T5.10C is infeasible because the only location available for the perforated stub -out connection is under impervious or heavily compacted soils. 5. Detention vaults or pipes in accordance with the Edmonds Stormwater Addendum are feasible and detention pipes will be used to manage runoff for the townhouse roof. Roof drains will collect runoff and route to detention pipes in proposed driveway on -site. Other Hard Surfaces: 1. Full Dispersion in accordance with BMP T5.30 is infeasible because a 65 to 10 ratio of forested or native vegetation area to impervious area cannot be achieved. 2. Permeable pavement in accordance with BMP T5.15 in Chapter 5 of Volume V of the SWMMWW is infeasible because the geotechnical evaluation points out that "the feasibility for... rain gardens, permeable pavement, and surface dispersion appears low". 3. Rain Gardens in accordance with BMP T5.14A and Bioretention in accordance with Chapter 7 are infeasible because the geotechnical evaluation points out that "the feasibility for... rain gardens, permeable pavement, and surface dispersion appears low". 4. Sheet Flow Dispersion in accordance with BMP T5.12, or Concentrated Flow Dispersion in accordance with BMP T5.11 in Chapter 5 of Volume V of the SWMMWW is infeasible because the geotechnical evaluation points out that "the feasibility for... rain gardens, permeable pavement, and surface dispersion appears low". 5. Detention vaults or pipes in accordance with the Edmonds Stormwater Addendum are feasible and detention pipes will be used to manage runoff for the site. Area drains will collect runoff on the west side of the site and route to detention pipes and all other runoff will be collected through a manhole/catch basin in the driveway area. rnlridntinnc Since the project meets the exemptions from flow control, detention pipes may be sized according to the prescriptive equation in Chapter 6.3.1 of the Edmonds Stormwater Addendum to meet the On -Site Stormwater Management requirement. The detention pipe was sized for length as a 24" diameter pipe using the equation L = 0.019*A, where L is length of pipe (ft) and A is contributing surface area (ftz). L = 0.019*(8,517ft2) = 161.8 ft. Therefore, a 24" diameter, 162 ft long detention pipe was selected for this project. See civil plans for more. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com 76th Ave Townhomes - CG #17206.20 Drainage Report February 12, 2021 Section III Page 3 WWHM2012 PROJECT REPORT FLOW CONTROL CHECK 15-minute time steps Project Name: 76th Ave Flow Control Check 02.09.21 Site Name: 76th Ave Townhomes Site Address: 7528 215th St SW City Edmonds Report Date: 2/9/2021 MGS Regoin Puget East 36 Data Start 1901/10/01 00:00 Data End : 2058/09/30 00:00 DOT Data Number: 02 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, Lawn, Flat .2 Pervious Total 0.2 Impervious Land Use acre ROADS MOD 0.02 ROOF TOPS FLAT 0.04 DRIVEWAYS MOD 0.01 SIDEWALKS FLAT 0.02 Impervious Total 0.09 Basin Total 0.29 Element Flows To: Surface Interflow MITIGATED LAND USE Name : Basin 1 Bypass: No GroundWater: No Groundwater 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com 76th Ave Townhomes - CG #17206.20 Drainage Report February 12, 2021 Section III Page 4 Pervious Land Use C, Lawn, Mod acre .09 Pervious Total 0.09 Impervious Land Use acre ROADS MOD 0.02 ROOF TOPS FLAT 0.08 DRIVEWAYS FLAT 0.06 SIDEWALKS FLAT 0.04 Impervious Total 0.2 Basin Total 0.29 Element Flows To: Surface Interflow Groundwater ANALYSIS RESULTS Stream Protection Duration Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.2 Total Impervious Area:0.09 Mitigated Landuse Totals for POC #1 Total Pervious Area:0.09 Total Impervious Area:0.2 Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.033113 5 year 0.049233 10 year 0.062719 25 year 0.083456 50 year 0.101937 100 year 0.123334 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0. 06324 NO CREDIT TAKEN FOR MR #5 BMP; 5 year 0.087716 10 year 0.106719 PROJECT IS FLOW CONTROL EXEMPT 25 year 0.134165 WITHOUT DETENTION TANK 50 year 0.157281 100 year 0.18284 (difference of 0.06 cfs; < 0.15 cfs increase between predeveloped and mitigated flows Perind and Impind Changes No changes have been made. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com 76th Ave Townhomes - CG #17206.20 Drainage Report February 12, 2021 Section III Page 5 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. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com 76th Ave Townhomes - CG #17206.20 February 12, 2021 Drainage Report Section IV, Page 1 Section IV — Construction Stormwater Pollution Prevention Plan Section IV Summary: Narrative Erosion control details are provided consistent with the City of Edmonds guidelines. Erosion control plan sheets are provided in full size as a part of the civil drawing set. For sites under one acre in area, the Department of Ecology does not require completion of the Construction SWPPP or the Construction Stormwater General Permit. Therefore, a Construction SWPPP is not required for this site. The elements for construction pollution prevention are discussed as follows: Element 1: Mark clearing limits To protect adjacent properties and to reduce the area of soil exposed to construction, the limits of construction will be clearly marked before land -disturbing activities begin. Clearing limits will be to the extents of necessary land disturbance for the new townhome building and associated driveways and walkways. The BMPs relevant to marking the clearing limits that will be applied for this project include: High Visibility Plastic or Metal Fence (BMP C103) Element 2: Establish construction access Construction access or activities occurring on unpaved areas shall be minimized, yet where necessary, access points shall be stabilized to minimize the tracking of sediment onto public roads. The existing driveway may be used as a stabilized construction entrance and expanded to the 15' minimum as necessary: Stabilized Construction Entrance (BMP C105) Element 3: Control Flow Rates The site slopes on average about 8% from west to east. The site is small enough that a silt fence used in Element 4 may be used to control flow rates. Element 4: Install sediment controls All stormwater runoff from disturbed areas shall pass through an appropriate sediment removal BMP before leaving the construction site or prior to being discharged. Silt fences will be installed on the downstream ends. Pollution prevention facilities on the erosion control plan must be constructed prior to or in conjunction with all clearing and grading so as to ensure that the transport of sediment to surface 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com 76th Ave Townhomes - CG #17206.20 February 12, 2021 Drainage Report Section IV, Page 2 waters and adjacent properties is minimized. The specific BMPs to be used for controlling sediment on this project include: Silt Fence (BMP C233) Element 5: Stabilize Soils Exposed and unworked soils shall be stabilized with the application of effective BMPs to prevent erosion throughout the life of the project. The specific BMPs for soil stabilization that shall be used on this project include: Temporary and Permanent Seeding (BMP C120) Mulching (BMP C121) Nets and Blankets (BMP C122) Plastic Covering (BMP C123) Sodding (BMP C124) Topsoiling/Composting (BMP C125) Surface Roughening (BMP C130) Dust Control (BMP C140) Element 6: Protect Slopes There are existing surfaces that will be removed as part of the development. Exposed slopes shall be stabilized with BMPs found in Element 5. Element 7: Protect Drain Inlets Drain inlets along 215th Street and as made operable on -site will be protected from sedimentation. Stormwater shall not enter the conveyance system without first being filtered or treated to remove sediment. Inlet protection devices shall be cleaned or removed and replaced when sediment has filled one-third of the available storage (or as specified by the manufacturer). The specific BMPs to be used for protecting drain inlets are: Storm Drain Inlet Protection (BMP C220) Element 8: Stabilize Channels and Outlets Conveyance channels are not located on or in the immediate vicinity of the site. Element 9: Control Pollutants Design, install, implement and maintain effective pollution prevention measures to minimize the discharge of pollutants. The suggested BMPs are: Concrete Handling (BMP C151) Sawcutting and Surfacing Pollution Prevention (BMP C152) Material Delivery, Storage and Containment (BMP C153) 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com 76th Ave Townhomes - CG #17206.20 Drainage Report February 12, 2021 Section IV, Page 3 Element 10: Control Dewatering De -watering is not anticipated. Element 11: Maintain BMPs All temporary and permanent erosion and sediment control BMPs shall be maintained and repaired as needed to assure continued performance of their intended function. Element 12: Manage the Project • Phase development projects to the maximum degree practicable and take into account seasonal work limits. • Inspection and monitoring— Inspect, maintain, and repair all BMPs as needed to assure continued performance of their intended function. Conduct site inspections and monitoring in accordance with the Construction Stormwater General Permit or local plan approval authority. • Maintain an Updated Construction SWPPP - This SWPPP shall be retained on -site or within reasonable access to the site. - The SWPPP shall be modified whenever there is a change in the design, construction, operation, or maintenance at the construction site that has, or could have, a significant effect on the discharge of pollutants to waters of the state. - The SWPPP shall be modified if, during inspections or investigations conducted by the owner/operator, or the applicable local or state regulatory authority, it is determined that the SWPPP is ineffective in eliminating or significantly minimizing pollutants in stormwater discharges from the site. The SWPPP shall be modified as necessary to include additional or modified BMPs designed to correct problems identified. Revisions to the SWPPP shall be completed within seven (7) days following the inspection. Element 13: Protect Low Impact Development BMPs A 24" detention pipe is proposed as an on -site stormwater management BMP and will be located under the driveway on the east side of the site. Protection of LID BMPs is not anticipated. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com 76th Ave Townhomes - CG #17206.20 Drainage Report February 12, 2021 Section V, Page 1 Section V — Special Reports and/or Studies Section V Summary: Narrative The following reports are included in this section: 1. Geotechnical Engineering Report by ZipperGeo, Geoprofessional Consultants dated May 26, 2017. 2. Natural Resources Conservation Service Soil Map dated June 29, 2017. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com GEOTECHNICAL ENGINEERING REPORT 76T" AVENUE WEST TOWNHOMES 7528 215TH STREET SW EDMONDS, WASHINGTON Project No. 1817.01 May 26, 2017 Prepared for: Northlake Capital & Development Prepared by: ZipperGeo Geoprofessional Consultants 19023 36t" Ave West, Suite D I Lynnwood, WA 98036 1 Phone: 425.582.9928 1 zippergeo.com Zipp Geo Geoprofessional Consultants Project No. 1817.01 May 26, 2017 Northlake Capital & Development c/o CDA + Pirscher Architects 23114 100 Avenue West Edmonds, Washington 98020 Attention: Mr. Jim Thorpe Subject: Geotechnical Engineering Report 76th Avenue West Townhomes 7528 215th Street SW Edmonds, Washington 98026 Dear Mr. Thorpe, In accordance with your request and written authorization, Zipper Geo Associates, LLC (ZGA) has completed the subsurface evaluation and geotechnical engineering report for the above -referenced project. This report presents the findings of the subsurface evaluation and geotechnical recommendations for the project. Our work was completed in general accordance with our Proposal for Geotechnical Engineering Services (Proposal No. P17160) dated April 12, 2017. Written authorization to proceed was provided by Northlake Capital & Development on April 29, 2017. We appreciate the opportunity to be of service to you on this project. If you have any questions concerning this report, or if we may be of further service, please contact us. Sincerely, Zipper Geo Associates, LLC o1 W a a y5126117 ` . ��+ 1783 �• ed G$0 4AMEs P. GEORGIS James P. Georgis, LG, LEG Principal Copies: Addressee (1) Thomas A. Jones, PE Managing Principal 19023 36th Ave West, Suite D I Lynnwood, WA 98036 1 Phone: 425.582.9928 I zippergeo.com TABLE OF CONTENTS Page INTRODUCTION...........................................................................................................................................1 SITEDESCRIPTION.....................................................................................................................................1 PROJECT UNDERSTANDING.....................................................................................................................2 SUBSURFACECONDITIONS......................................................................................................................2 RegionalGeology.............................................................................................................................................2 SoilConditions.................................................................................................................................................2 GroundwaterConditions.................................................................................................................................3 Summary of Laboratory Testing......................................................................................................................4 CONCLUSIONS AND RECOMMENDATIONS............................................................................................4 General..........................................................................................................................................................4 SitePreparation...............................................................................................................................................4 Structural Fill Materials and Preparation........................................................................................................7 Temporary and Permanent Slopes..................................................................................................................9 Seismic Design Considerations......................................................................................................................10 ShallowFoundations.....................................................................................................................................11 On -Grade Concrete Slabs..............................................................................................................................12 BackfilledRetaining Walls.............................................................................................................................13 DrainageConsiderations...............................................................................................................................14 Infiltration Considerations.............................................................................................................................14 Pavements.....................................................................................................................................................15 Existing Retaining Wall Considerations.........................................................................................................16 CLOSURE................................................................................................................................................... 17 FIGURES Figure 1— Site and Exploration Plan APPENDICES Appendix A —Subsurface Exploration Procedures and Logs Appendix B — Laboratory Testing Procedures and Results Cover Photo Credit: Google Earth 2017 GEOTECHNICAL ENGINEERING REPORT 76T" AVENUE WEST TOWNHOMES 7528 215T" STREET SW EDMONDS, WASHINGTON Project No. 1817.01 MAY 26, 2017 INTRODUCTION This report documents the surface and subsurface conditions encountered at the site and our geotechnical engineering recommendations for the proposed 76th Avenue West Townhomes project. The project description, site conditions, and our geotechnical conclusions and design recommendations are presented in the text of this report. Supporting data including detailed exploration logs and field exploration procedures, results of laboratory testing, and other supporting information are presented as appendices. Our geotechnical engineering scope of services for the project included a literature review, site reconnaissance, subsurface exploration, laboratory testing, geotechnical engineering analysis, and preparation of this report. The subsurface evaluation consisted of completing two exploratory borings (13- 1 and B-2) across the site. The borings extended to a depth of approximately 21% feet below the ground surface. SITE DESCRIPTION The site is located at 7528 2151h Street Southwest in Edmonds, Washington. The rectangular parcel is bordered by 215th Street Southwest to the north, 76th Avenue West to the west, a single-family residential parcel to the east, and an access drive and parking lot for Swedish Hospital to the south. The site includes a single -story, single-family residence with a daylight basement located in the north central portion of the site. It appears that the basement level is limited to the eastern half of the residence. In general, the site slopes gently down from west to east with about 3 feet of relief across the site. The single-family parcel to the east is lower than the subject property and a concrete masonry unit (CMU) block wall is located near the common property line. The northern half of the wall is about 4 feet tall. The southern half of the wall consists of two tiers with a combined height of about 9 to 10 feet. The horizontal distance from the face of the upper wall to the face of the lower wall is about 2% feet. Site vegetation includes ornamental shrubs such as rhododendron, arborvitae, and laurel with the majority of the yard north, west, and south of the existing residence covered with lawn. The property includes several moderately large trees including three conifers up to about 2 feet in diameter north of the house, two to three conifers up to about 1 foot in diameter west of the house, and about 7 to 9 conifers up to about 2% feet in diameter in the southwest corner of the site. Page 1 Zi pperGeo Geoprofessional Consultants PROJECT UNDERSTANDING 76T" Avenue West Townhomes Project No. 1817.01 May 26, 2017 We understand that the proposed project includes razing the existing residence and associated structures and construction of a three-story, four -unit townhome building located slightly west of the center of the lot. We understand that the bottom level will consist of daylight basement garages open to vehicle access from a driveway located along the east side of the site. A grading plan was not available at the time this report was prepared. However, we anticipate that excavations for foundation construction would likely extend about one to two feet below the basement level of the existing residence at elevation 405 feet. Existing site features and a preliminary development plan are shown on the enclosed Site and Exploration Plan, Figure 1. We understand that infiltration of roof and surface water runoff is currently under consideration. We anticipate that the design of infiltration systems will be completed in accordance with the City of Edmonds Bulletin # E72B and Appendix C of the City of Edmonds Stormwater Supplement. We anticipate that infiltration systems could include permeable pavement, rain gardens, drywells, infiltration trenches, and subsurface infiltration galleries such as StormTech systems. SUBSURFACE CONDITIONS Regional Geology We assessed the geologic setting of the site and surrounding vicinity by reviewing the Geologic Map of the Edmonds East and Part of the Edmonds West Quadrangle, Washington, U.S. Geological Survey, Map MF-1541, by J.P. Minard 1983. The geologic map locates the site near the contact between Vashon glacial till (Qvt) and Vashon advance outwash (Qva) deposits. The Vashon till is described as a compact, poorly sorted mixture of clay, sand, pebbles, cobbles, and boulders. Vashon till is often referred to as "hardpan" in its unweathered state due to its very dense nature caused by compaction resulting from the weight of an overriding glacial mass thousands of years ago, which was hundreds of meters thick in some areas. The Vashon advance outwash deposit is described as typically consisting of a thick section of mostly clean, gray, pebbly sand with increasing amounts of gravel higher up in the deposit. The advance outwash was deposited by meltwater flowing from the advancing front of the glacier and was compacted by the overriding glacial mass. The Vashon advance outwash is younger than the Vashon glacial till and is often encountered stratigraphically below the glacial till deposits. The soil conditions encountered in the boring were generally consistent with the Vashon glacial till unit. Soil Conditions The subsurface evaluation for this project included two borings (B-1 and B-2) completed on the north and south sides of the existing residence. The borings extended to a depth of about 21% feet below the ground surface. The approximate exploration locations are shown on the enclosed Site and Exploration Plan, Figure 1. Page 2 Zi pperGeo 76T" Avenue WestTownhomes Project No. 1817.01 Geoprofessional Consultants May 26, 2017 Soils observed in the borings were visually classified in general accordance with the Unified Soil Classification System. Descriptive logs of the subsurface explorations and the procedures utilized in the subsurface exploration program are presented in Appendix A. A generalized description of soil conditions encountered in the borings is presented below. Please refer to the boring logs in Appendix for a more detailed description of the conditions encountered at the exploration locations. The subsurface conditions encountered in the explorations were relatively consistent with respect to soil type and relative density. In general, the explorations encountered about 2 to 3 inches of grass sod over fill soils over glacial till deposits. Description of the existing fill soils and underlying glacial till deposits are presented below. Existing Fill Soils: Soils interpreted as fill were encountered in borings B-1 and B-2 to depths of about 3% and 2 feet below existing grade, respectively. In general, the fill consisted of loose to medium dense, silty sand with organics and roots. Glacial Till Deposits: Glacial till deposits were encountered below the surficial fill in both explorations. The glacial till consisted of dense to very dense, silty sand with gravel to sand with silt and gravel. The glacial till deposits extended to the total depth explored of about 21% feet below existing grade. Soil types and conditions can vary between explorations. The nature and extent of variations between the explorations may not become evident until construction. Stratification boundaries on the boring logs represent the approximate depth of changes in soil types, although the transition between materials may have been gradual. If variations become apparent during construction, it may be necessary to reevaluate the recommendations of this report Groundwater Conditions Groundwater in the form of seepage at the exploration locations was not observed at the time of drilling. However, given the dense to very dense nature and low permeability of the glacial till soils encountered below the existing surficial fill, near surface perched groundwater conditions are expected to develop due to variations in the amount of precipitation, runoff, and other factors not evident at the time the exploration was performed. The periodic development of near -surface perched groundwater conditions is supported by iron oxide staining and soil mottling observed in in the upper portion of the glacial till deposits. Groundwater conditions should be expected to fluctuate due to variations in the amount of rainfall, runoff, and other factors not evident at the time the exploration was performed. Therefore, groundwater levels during construction or at other times in the life of the structure may vary from those indicated on the logs. Page 3 Zi pperGeo Geoprofessional Consultants 76TH Avenue West Townhomes Project No. 1817.01 May 26, 2017 Summary of Laboratory Testing Laboratory testing was completed on selected samples obtained from our explorations. Testing included moisture content and grain size analyses. The results of moisture content testing are presented on the boring logs. The results of the grain size analyses are presented in Appendix B. Moisture Content: Moisture content tests completed on glacial till samples indicate in -situ moisture contents ranging from about 9 to 11 percent within the upper 10 feet of existing site grade. Grain Size Analyses: Grain size analysis tests completed on samples of glacial till collected at depths of about 5 and 10 feet below grade indicate fines contents (silt and clay size particles passing a US No. 200 sieve) of about 28 and 35 percent, respectively. CONCLUSIONS AND RECOMMENDATIONS General Based on our subsurface exploration program and analysis, we conclude that the proposed development is feasible from a geotechnical standpoint, contingent on proper design and construction practices. Based on our analyses, conventional spread footings and slab -on -grade concrete floors can be used for the new development. The site borings completed in currently landscaped portions of the site encountered about 2 to 3% feet of organic rich undocumented fill. We do not recommend supporting new foundations on existing undocumented fill soils. Undocumented fill soils encountered within the proposed building area should be removed and the excavation thoroughly cleaned prior to backfill placement and/or construction. Geotechnical engineering recommendations for foundation systems and other earthwork related phases of the project are outlined below. The recommendations contained in this report are based upon the results of field and laboratory testing (which are presented in Appendices A and B), engineering analyses, and our current understanding of the proposed project. ASTM and Washington State Department of Transportation (WSDOT) specification codes cited herein respectively refer to the current manual published by the American Society for Testing & Materials and the current edition of the Standard Specifications for Road, Bridge, and Municipal Construction, (M41-10). Site Preparation Existing Structure Removal: The site is currently developed with a single-family residence, a concrete driveway, and concrete walkways. We recommend that any existing foundation elements or other below grade structures be completely demolished and removed from the proposed building footprint. Existing Utility Removal: We recommend that abandoned underground utilities within the proposed building envelope be completely removed. Utility pipes outside the building envelope could be abandoned in place, provided they are fully grouted with controlled density fill (CDF) and the trench Page 4 Zi pperGeo 76T" Avenue WestTownhomes Project No. 1817.01 Geoprofessional Consultants May 26, 2017 backfill is density tested to verify that it meets the compaction levels presented in the project specifications. Localized excavations made for removal of utilities or existing unsuitable trench backfill should be backfilled with structural fill as outlined in the following section of this report. Erosion Control Measures: Stripped surfaces and soil stockpiles are typically a source of runoff sediments. We recommend that silt fences, berms, and/or swales be installed around the downslope side of stripped areas and stockpiles in order to capture runoff water and sediment. If earthwork occurs during wet weather, we recommend that all stripped surfaces be covered with straw to reduce runoff erosion, whereas soil stockpiles should be protected with anchored plastic sheeting. Temporary Drainage: Stripping, excavation, grading, and subgrade preparation should be performed in a manner and sequence that will provide drainage at all times and provide proper control of erosion. The site should be graded to prevent water from ponding in construction areas and/or flowing into and/or over excavations. Exposed grades should be crowned, sloped, and smooth -drum rolled at the end of each day to facilitate drainage if inclement weather is forecasted. Accumulated water must be removed from subgrades and work areas immediately and prior to performing further work in the area. Equipment access may be limited and the amount of soil rendered unfit for use as structural fill may be greatly increased if drainage efforts are not accomplished in a timely manner. Clearing and Stripping: The site is surfaced with a concrete driveway and walkways. As such, extensive clearing, grubbing, and topsoil stripping activities in paved areas are not anticipated. Our explorations were completed in landscaped portions of the site and encountered about 2 to 3% feet of organic rich fill. In our opinion, these organic rich fill soils are not suitable for use as structural fill. As such, clearing, grubbing, and topsoil stripping activities in landscaped portion of the site are anticipated to range from about 2 to 4 feet. The site currently supports a number of relatively large conifer trees and it appears that the site may have supported more trees prior to development. Thicker deposits of organic rich soil and tree root systems may be encountered were trees were previously removed or currently exist. Topsoil or other organic rich soils should be removed and utilized for non-structural landscape fill or be disposed of at a suitable off -site location. Any excavations that extend below finish grades should be backfilled with structural fill as outlined in the Structural Fill section in this report. Subgrade Preparation: Existing organic -rich fill soils were encountered in the site explorations to depths ranging from 2 to 3% feet below existing grade. We do not recommend the construction of building foundations, interior floor slabs, or pavements over undocumented fill soils. Based on the proposed daylight basement configuration of the building, it appears that most of the fill soils will be removed from the building envelope as part of the planned excavation. We recommend that existing fill soils be removed from below foundation and floor slab areas and replaced with structural fill as outlined in the Structural Fill section of this report. Existing fill soils encountered in pavement areas should be evaluated by ZGA at the time of construction relative to pavement support. Page 5 Zi pperGeo 76T" Avenue WestTownhomes Project No. 1817.01 Geoprofessional Consultants May 26, 2017 Once site preparation is complete, all areas that are at design subgrade elevation or areas that will receive new structural fill should be compacted to a firm and non -yielding condition and to a compaction level of at least 95 percent of the maximum laboratory density (per ASTM D 1557) within the upper 12 inches. Some moisture conditioning of site soils may be required to achieve an appropriate moisture content for compaction within ±2 percent of the soils laboratory optimum moisture content. Our laboratory testing indicates that, at the time our explorations were completed, in -situ moisture contents of the glacial till soils ranging from 9 to 11 percent with within the upper 10 feet of existing site grades. These moisture contents are near to slightly above the estimated optimum moisture content of the site soils. Asa result, we expect that moisture conditioning of site soils during construction may be required to achieve suitable moisture contents (plus or minus two percent of optimum) for compaction in areas. Earthwork should be completed during drier periods of the year when soil moisture content can be controlled by aeration and drying if possible. If earthwork or construction activities take place during extended periods of wet weather, if will be difficult to achieve a firm, non -yielding surface and recommended compaction levels. In the event the exposed subgrade becomes unstable, yielding, or unable to be compacted due to high moisture conditions, we recommend that the materials be removed to a sufficient depth in order to develop stable subgrade soils that can be compacted to the minimum recommended levels. The severity of construction problems will be dependent, in part, on the precautions that are taken by the contractor to protect the subgrade soils. Once compacted, subgrades should be evaluated through density testing and, if possible, proof rolling with a loaded dump truck or heavy rubber -tired construction equipment weighing at least 20 tons to assess the subgrade adequacy and to detect soft and/or yielding soils. In the event that soft or yielding areas are detected during proof rolling, the upper 12 inches of subgrade should be scarified, moisture conditioned and re -compacted as necessary to obtain at least 95 percent of the maximum laboratory density (per ASTM D 557) and a firm, non -yielding condition. Those soils which are soft, yielding, or unable to be compacted to the specified criteria should be over -excavated and replaced with suitable on -site or imported material as recommended in the Structural Fill section of this report. Once subgrades are compacted, depending on the time of year, it may be desirable to protect prepared foundation and floor slab subgrades from wet weather. To protect stable subgrades, we recommend using crushed rock or crushed recycled concrete. The thickness of the protective layer should be determined at the time of construction and be based on the moisture condition of the soil and the amount of anticipated traffic. Freezing Conditions: If earthwork takes place during freezing conditions, all exposed subgrades should be allowed to thaw and then be compacted prior to placing subsequent lifts of structural fill. Alternatively, the frozen material could be stripped from the subgrade to expose unfrozen soil prior to placing subsequent lifts of fill or foundation components. The frozen soil should not be reused as structural fill until allowed to thaw and adjusted to the proper moisture content, which may not be possible during winter months. Page 6 Zi pperGeo Geoprofessional Consultants 76TH Avenue West Townhomes Project No. 1817.01 May 26, 2017 Structural Fill Materials and Preparation Structural fill includes any material placed below foundations and pavement sections, within utility trenches, and behind retaining walls. Prior to the placement of structural fill, all surfaces to receive fill should be prepared as previously recommended in the Site Preparation section of this report. Laboratory Testing: Representative samples of on -site and imported soils to be used as structural fill should be submitted for laboratory testing at least 4 days in advance of its intended use in order to complete appropriate laboratory testing. Re -Use of Site Soils as Structural Fill: The existing fill soils encountered in our explorations generally consisted of silty sand with organics and roots and are not suitable for reuse as structural fill. Field and laboratory test data indicates that the native glacial till soils encountered below the existing fill are generally suitable for reuse as structural fill from a compositional standpoint provided the soil is placed and compacted in accordance with the compaction recommendations presented in this report. However, based on drilling action and depositional environment, some oversized material may be encountered in the glacial till soils. Material greater than 3-inches in diameter should be removed from soils to be reused as structural fill. Site glacial till soils at the time of our evaluation appeared to be near to slightly wet of their estimated optimum moisture content. Excavations completed during extended wet periods may encounter perched groundwater and as a result, drying of wet, over -optimum soils may be required for re -use of site soils as structural fill. Drying of over -optimum moisture soils may be achieved by scarifying or windrowing surficial materials during extended periods of dry weather. If encountered, soils which are dry of optimum may be moistened through the application of water and thorough blending to facilitate a uniform moisture distribution in the soil prior to compaction. We recommend that site soils used as structural fill have less than 4 percent organics by weight and have no woody debris greater than % inch in diameter. We recommend that all pieces of organic material greater than % inch in diameter be picked out of the fill before it is compacted. Any organic -rich soil derived from earthwork activities should be utilized in landscape areas or wasted from the site. Imported Structural Fill: Imported structural fill may be required for raising site grades or as replacement fill for unsuitable site soils. The appropriate type of imported structural fill will depend on the prevailing weather conditions. During extended periods of dry weather, we recommend imported fill, at a minimum, meet the requirements of Common Borrow as specified in Section 9-03.14(3) of the 2016 Washington State Department of Transportation, Standard Specifications for Road, Bridge, and Municipal Construction (WSDOT Standard Specifications). During wet weather, higher -quality structural fill might be required, as Common Borrow may contain sufficient fines to be moisture sensitive. During wet weather we recommend that imported structural fill meet the requirements of Gravel Borrow as specified in Section 9-03.14(1) of the WSDOT Standard Specifications. Page 7 Zi pperGeo 76T" Avenue West Townhomes Project No. 1817.01 Geoprofessional Consultants May 26, 2017 Pavement Subgrades: Any structural fill used within the upper one foot below pavement sections should have a minimum California Bearing Ratio (CBR) of 15 when compacted to a minimum of 95 percent of the modified Proctor maximum dry density. A CBR value of 15 is representative of the on -site soils and Common Borrow import fill, and has been used to develop our pavement section recommendations. Samples of proposed imported fill should be submitted for laboratory testing and approval prior to use. Moisture Content: The suitability of soil for use as structural fill will depend on the time of year, the moisture content of the soil, and the fines content (that portion passing the U.S. No. 200 sieve) of the soil. As the amount of fines increases, the soil becomes increasingly sensitive to small changes in moisture content. Soils containing more than about 5 percent fines cannot be consistently compacted to the appropriate levels when the moisture content is more than approximately 2 percent above or below the optimum moisture content (per ASTM D 1557). Optimum moisture content is that moisture content which results in the greatest compacted dry density with a specified compactive effort. Moisture content of fill at the time of placement should be within plus or minus 2 percent of optimum moisture content for compaction as determined by the ASTM D 1557 test method. Fill Placement: Structural fill should be placed in horizontal lifts not exceeding 10 inches in loose thickness. Each lift of fill should be compacted using compaction equipment suitable for the soil type and lift thickness. Compaction Criteria: Each lift of fill should be compacted to the minimum levels recommended in the table below based on the maximum laboratory dry density as determined by the ASTM D 1557 Modified Proctor Compaction Test. Structural fill placed in municipal rights -of -way should be placed and compacted in accordance with the jurisdiction codes and standards. We recommend that a geotechnical engineer be present during grading so that an adequate number of density tests may be conducted as structural fill placement occurs. In this way, the adequacy of the earthwork may be evaluated as it proceeds. RECOMMENDED SOIL COMPACTION LEVELS Location Minimum Percent Compaction* Stripped native subgrade soils, prior to fill placement (upper 12 inches) 95 All fill below building floor slabs and foundations 95 Upper 2 feet of fill below pavements 95 Pavement fill below two feet 92 Upper two feet of utility trench backfill 95 Utility trenches below two feet 92 Landscape Areas 90 * ASTM D 1557 Modified Proctor Maximum Dry Density Page 8 Zi pperGeo 76T" Avenue WestTownhomes Project No. 1817.01 Geoprofessional Consultants May 26, 2017 Placing Fill on Slopes: Permanent fill placed on slopes steeper than 5H:1V (Horizontal:Vertical) should be keyed and benched into natural soils of the underlying slope. We recommend that the base downslope key be cut into undisturbed native soil. The key slot should be at least 8 feet wide and 3 feet deep. The hillside benches cut into the native soil should be at least 4 feet in width. The face of the embankment should be compacted to the same relative compaction as the body of the fill. This may be accomplished by over -building the embankment and cutting back to the compacted core. Alternatively, the surface of the slope may be compacted as it is built, or upon completion of the embankment fill placement. Temporary and Permanent Slopes Temporary excavation slope stability is a function of many factors, including: • The presence and abundance of groundwater; • The type and density of the various soil strata; • The depth of cut; • Surcharge loadings adjacent to the excavation; and • The length of time the excavation remains open. As the cut is deepened, or as the length of time an excavation is open, the likelihood of bank failure increases; therefore, maintenance of safe slopes and worker safety should remain the responsibility of the contractor, who is present at the site, able to observe changes in the soil conditions, and monitor the performance of the excavation. It is exceedingly difficult under the variable circumstances to pre -establish a safe and "maintenance -free" temporary cut slope angle. Therefore, it should be the responsibility of the contractor to maintain safe temporary slope configurations since the contractor is continuously at the job site, able to observe the nature and condition of the cut slopes, and able to monitor the subsurface materials and groundwater conditions encountered. Unsupported vertical slopes or cuts deeper than 4 feet are not recommended if worker access is necessary. The cuts should be adequately sloped, shored, or supported to prevent injury to personnel from local sloughing and spalling. The excavation should conform to applicable Federal, State, and Local regulations. According to Chapter 296-155 of the Washington Administrative Code (WAC), the contractor should make a determination of excavation side slopes based on classification of soils encountered at the time of excavation. Temporary cuts may need to be constructed at flatter angles based upon changes in soil moisture and groundwater conditions during construction. Adjustments to the slope angles should be determined by the contractor at that time. We recommend that all permanent cut or fill slopes constructed in native soils or with imported structural fill be designed at a 2H: 1V (Horizontal: Vertical) inclination or flatter. All permanent cut and fill slopes should be adequately protected from erosion both temporarily and permanently. If the slopes are exposed to prolonged rainfall before vegetation becomes established, the surficial soils will be prone to erosion and possible shallow sloughing. We recommend covering permanent slopes with a rolled erosion Page 9 Zi pperGeo 76T" Avenue WestTownhomes Project No. 1817.01 Geoprofessional Consultants May 26, 2017 protection material, such as Jute matting or Curlex II, if vegetation has not been established by the regional wet season (typically November through May). Seismic Design Considerations The seismic performance of the development was evaluated relative to seismic hazards resulting from ground shaking associated with the Maximum Considered Earthquake Geometric Mean (MCEG) Peak Ground Acceleration and the Risk -Targeted Maximum Considered Earthquake (MCER) Ground Motion Response Acceleration in accordance with the 2012/2015 International Building Code (IBC). Conformance to the above criteria for seismic excitation does not constitute any kind of guarantee or assurance that significant structural damage or ground failure will not occur if a maximum considered earthquake occurs. The primary goal of the IBC seismic design procedure is to protect life and not to avoid all damage, since such design may be economically prohibitive. Following a major earthquake, a building may be damaged beyond repair, yet not collapse. Ground Surface Rupture: We evaluated the potential for seismic ground surface rupture at the site by reviewing the USGS Quaternary Fault Web Mapping Application. The mapping application indicates that there are no mapped Quaternary faults within 5 miles of the site. It is our opinion that the risk of ground surface rupture at the site is low. Landsliding: Based on the topography of the site and surrounding vicinity and the density of the site glacial till soils, the risk of earthquake -induced landsliding is low. Soil Liquefaction & Lateral Spread: Liquefaction is a phenomenon wherein saturated cohesionless soils build up excess pore water pressures during earthquake loading. Liquefaction typically occurs in loose soils, but may occur in denser soils if the ground shaking is sufficiently strong. The explorations primarily encountered glacially consolidated glacial till deposits. Based on the dense to very dense nature of these soils, it is our opinion that the potential for liquefaction at the site is low. Lateral spreading is a phenomenon in which soil deposits which underlie a site can experience significant lateral displacements associated with the reduction in soil strength caused by soil liquefaction. This phenomenon tends to occur most commonly at sites where the soil deposits can flow toward a "free - face", such as a water body. Due to the lack of liquefiable soils at the site and the lack of a nearby "free - face" condition, it is our opinion that the risk of lateral spreading at the site is low. IBC Seismic Design Parameters: 2012/2015 IBC Seismic Design parameters are summarized on the table below. Page 10 Zi pperGeo Geoprofessional Consultants 76TH Avenue West Townhomes Project No. 1817.01 May 26, 2017 Code Used Site Classification 2012/2015 International Building Code (IBC) 1 C 2 Ss Spectral Acceleration for a Short Period 1.271g (Site Class B) S1Spectral Acceleration for a 1-Second Period 0.496g (site Class B) Fa Site Coefficient for a Short Period 1.000 (Site Class C) F Site Coefficient for a 1-Second Period 1.304 (Site Class C) SMs Maximum considered spectral response acceleration 1.271g (Site Class C) for a Short Period SMi Maximum considered spectral response acceleration 0.647g (Site Class C) for a 1-Second Period Sos Five -percent damped design spectral response 0.847g (Site Class C) acceleration for a Short Period Sol Five -percent damped design spectral response 0.431g (Site Class C) acceleration for a 1-Second Period 1. In general accordance with the 201212015 International Building Code, Section 1613.3.2 and ASCE 7-10, Chapter 20. IBC Site Class is based on the average characteristics of the upper 100 feet of the subsurface profile. 2. The borings completed for this study extended to a maximum depth of 21% feet below grade. ZGA therefore determined the Site Class assuming that dense to very dense glacially consolidated soils extend to 100 feet as suggested by published geologic maps for the project area. Shallow Foundations Based on our analyses, conventional spread footings will provide adequate support for the proposed building and retaining walls provided that the foundation subgrades are properly prepared. We anticipate that foundation subgrade soils will generally consist of medium dense to very dense silty sand with gravel to sand with silt and gravel. Borings completed in landscaped portions of the site encountered about 2 to 3% feet of organic -rich fill and the proposed townhome building encompasses about half of the existing building footprint and extends north and south into currently landscaped areas. We do not recommend supporting new foundations on existing undocumented fill soils. If fills are encountered within the proposed building area, such fills should be removed and the excavation thoroughly cleaned prior to backfill placement and/or construction. We recommend that any over -excavation of unsuitable fill soils extend outside the limits of the footings a distance equal to the depth of over -excavation. Design recommendations for foundations and related structural elements are presented in the following sections. Allowable Bearing Pressure: Continuous and isolated column footings bearing on medium dense to very dense glacial till soils or structural fill placed and compacted in accordance with this report may be designed for a maximum allowable, net, bearing capacity of 3,000 psf. A one-third increase of the bearing Page 11 Zi pperGeo 76T" Avenue WestTownhomes Project No. 1817.01 Geoprofessional Consultants May 26, 2017 pressure may be used for short-term transient loads such as wind and seismic forces. The above - recommended allowable bearing pressure includes a 3.0 factor of safety. Shallow Foundation Depth and Width: For frost protection, the bottom of all exterior footings should bear at least 18 inches below the lowest adjacent outside grade, whereas the bottoms of interior footings should bear at least 12 inches below the surrounding slab surface level. We recommend that all continuous wall and isolated column footings be at least 12 and 24 inches wide, respectively. Lateral Resistance: Resistance to lateral loads can be calculated assuming an ultimate passive resistance of 450 pcf equivalent fluid pressure (triangular distribution) and an ultimate base friction coefficient of 0.60. An appropriate safety factor (or load/resistance factors) should be included for calculating resistance to lateral loads. For allowable stress design, we recommend a minimum 1.5 safety factor. We recommend that passive resistance be neglected in the upper 18 inches of embedment. Estimated Static Settlement: Assuming the foundation subgrade soils are prepared in accordance with recommendations presented herein, we estimate that total and differential settlements will be less than 1 inch and % inch over a distance of about 50 feet, respectively. On -Grade Concrete Slabs Floor slabs for the proposed building may be supported on the medium dense to very dense glacial till deposits or new structural fill placed in accordance with the recommendations provided in this report. Floor slabs should not be supported on existing fill soils. If unsatisfactory fills are encountered within the slab area, such fills should be removed and the excavation thoroughly cleaned prior to backfill placement and/or construction The following sections provide recommendations for on -grade floor slabs. Subgrade Preparation: Subgrades for on -grade slabs should be prepared in accordance with the Site Preparation and Structural Fill sections of this report. Capillary Break: To provide a capillary break, uniform slab bearing surface, and a minimum subgrade modulus of 150 pci, we recommend the on -grade slabs be underlain by a 5-inch thick layer of compacted, crushed rock meeting the requirements of WSDOT Standard Specification Section 9-03.9(3), Crushed Surfacing Top Course, with the modification of a maximum of 7 percent passing the U.S. No. 200 sieve. Alternatively, a clean angular gravel such as No. 7 aggregate per WSDOT: 9-03.1(4)C could be used for this purpose. Alternative capillary break materials should be submitted to the geotechnical engineer for review and approval before use. Vapor Retarder: From a geotechnical standpoint, a vapor barrier is not considered to be necessary for the proposed building. Where potential slab moisture is a concern or where moisture sensitive floor coverings are planned, we recommend using a puncture -resistant 10- to 15-mil thick product such as Stego Wrap, or an approved equivalent, that is classified as a Class A vapor retarder in accordance with ASTM E 1745. Page 12 Zi pperGeo 76T" Avenue WestTownhomes Project No. 1817.01 Geoprofessional Consultants May 26, 2017 To avoid puncturing of the vapor barrier, construction equipment should not be allowed to drive over any vapor retarder material. Where pipes and other objects penetrate the barrier, we recommend taping these per the manufacturer's recommendations. We recommend the slab designer and slab contractor refer to ACI 302 and ACI 360 for procedures and cautions regarding the use and placement of a vapor retarder/barrier. Backfilled Retaining Walls We expect the project to include backfilled, cast -in -place (c.i.p.) concrete retaining walls for the proposed daylight basement level of the building, and possibly other minor site walls. For recommended bearing capacities and lateral resistance parameters, refer to the Shallow Foundations section of this report. Retaining walls must be founded on suitable native soils or compacted structural fill placed above suitable native soils. If fills are encountered, we recommend that the fill be removed and replaced with structural fill. Additional recommendations for retaining walls are provided below. Lateral Earth Pressures: The lateral soil pressures acting on backfilled retaining walls will depend on the nature and density of the soil behind the wall, and the ability of the wall to yield in response to the earth loads. Yielding walls (i.e. walls that are free to translate or rotate) that are able to displace laterally at least 0.001H, where H is the height of the wall, may be designed for active earth pressures. Non -yielding walls (i.e. walls that are not free to translate or rotate) should be designed for at -rest earth pressures. Non -yielding walls include walls that are braced to another wall or structure, and wall corners. If walls are backfilled and drained as described in the following paragraphs, we recommend that yielding walls supporting horizontal backfill be designed using an equivalent fluid density of 35 pcf (active earth pressure). Non -yielding walls should be designed using an equivalent fluid density of 55 pcf (at -rest earth pressure). Design of permanent retaining walls should consider additional earth pressure resulting from the design seismic event. For the seismic case, walls should be designed for an additional uniform, total seismic earth pressure distribution of 11H. The above -recommended lateral earth pressures do not include the effects of sloping backfill surfaces, surcharges such as traffic loads, other surface loading, or hydrostatic pressures. If such conditions exist, we should be consulted to provide revised earth pressure recommendations. Drainage: Adequate drainage measures must be installed to collect and direct subsurface water away from subgrade walls. All backfilled walls should include a drainage aggregate zone extending two feet from the back of wall for the full height of the wall. The drainage aggregate should consist of material meeting the requirements of WSDOT 9-03.12(2) Gravel Backfill for Walls. A minimum 4-inch diameter, perforated PVC drain pipe should be provided at the base of backfilled walls to collect and direct subsurface water to an appropriate discharge point. We recommend placing a non -woven geotextile, such as Mirafi 140N, or equivalent, around the free draining backfill material. Wall drainage systems should be independent of other drainage systems such as roof drains. Page 13 Zi pperGeo Geoprofessional Consultants Drainage Considerations 76T" Avenue West Townhomes Project No. 1817.01 May 26, 2017 Surface Drainage: Final site grades should be sloped to carry surface water away from the building and other drainage -sensitive areas. Additionally, site grades should be designed such that concentrated runoff on softscape surfaces is avoided. Any surface runoff directed towards softscaped slopes should be collected at the top of the slope and routed to the bottom of the slope and discharged in a manner that prevents erosion. Building Perimeter Footing Drains and Retaining Wall Drains: We recommend that the new building and retaining walls be provided with a footing drain system to reduce the risk of future moisture problems and the buildup of hydrostatic pressures. The footing drains should consist of a minimum 4-inch diameter, Schedule 40, rigid, perforated PVC pipe placed at the base of the heel of the footing with the perforations facing down. The pipe should be surrounded by a minimum of 6 inches of clean free -draining granular material conforming to WSDOT Standard Specification 9-03.12(4), Gravel Backfill for Drains. A non -woven filter fabric such as Mirafi 140N, or equivalent, should envelope the free -draining granular material. At appropriate intervals such that water backup does not occur, the drainpipe should be connected to a tightline system leading to a suitable discharge. Cleanouts should be provided for future maintenance. The tightline system must be separate from the roof drain system. Roof drains should be connected to a separate solid wall PVC tightline system and routed to a suitable discharge location. Infiltration Considerations We understand that infiltration of roof and surface water runoff is currently under consideration. We anticipate that the design of infiltration systems will be completed in accordance with the City of Edmonds Bulletin # E72B and Appendix C of the City of Edmonds Stormwater Supplement. We anticipate that infiltration systems could include permeable pavement, rain gardens, drywells, infiltration trenches, and subsurface infiltration galleries such as StormTech systems. In general, the site is mantled by about 2 to 3% feet of fill over dense to very dense glacial till deposits. The upper portion of the glacial till exhibits mottling and iron oxide staining indicative of near -surface perched groundwater conditions. Given the very low permeability of the dense to very dense glacial till deposits and indications of shallow perched groundwater, it is our opinion that the feasibility for shallow infiltration systems such as rain gardens, permeable pavement, and surface dispersion appears low and we anticipate that the use of these systems could result in wet or soggy ground surface conditions during the wet season. In addition, infiltrated water would tend to migrate along the top of the low permeability, dense to very dense glacial till soils to the basement walls, thereby contributing the water in the wall and footing drain systems and an increased potential for groundwater intrusion into the building. Deeper infiltration systems such as conventional infiltration trenches, gravelless chambers, and drywells would be socketed into impermeable glacial till deposits and are not considered feasible. We therefore recommend that surface water and groundwater collected by the wall/footing drain system be tightlined to a City stormwater or combined storm/sewer system, if feasible. Page 14 Zi pperGeo Geoprofessional Consultants Pavements 76T" Avenue West Townhomes Project No. 1817.01 May 26, 2017 We anticipate that the access driveway for the four townhome units will consist of flexible asphalt pavement or rigid concrete pavement. The following sections provide pavement recommendations for the development. Asphalt Pavement Pavement Life and Maintenance: It should be realized that asphaltic pavements are not maintenance - free. The following pavement sections represent our minimum recommendations for an average level of performance during a 20-year design life; therefore, an average level of maintenance will likely be required. A 20-year pavement life typically assumes that an overlay will be placed after about 12 years. Thicker asphalt, base, and subbase courses would offer better long-term performance, but would cost more initially. Conversely, thinner courses would be more susceptible to "alligator" cracking and other failure modes. As such, pavement design can be considered a compromise between a high initial cost and low maintenance costs versus a low initial cost and higher maintenance costs. The recommendations presented below are based on AASHTO Low -Volume Road Design methodologies as presented in the 1993 AASHTO Guide for Design of Pavement Structures. Traffic Design Values: No traffic loading was provided for this project. We have assumed relatively low traffic volumes. Soil Design Values: Pavement subgrade soils are anticipated to consist of on -site soils or, at a minimum, imported structural fill meeting the requirements of Common Borrow. Our analysis assumes the imported fill will have a minimum California Bearing Ration (CBR) value of 15. Recommended Pavement Sections: For light -duty pavements, we recommend 2 inches of asphalt concrete over 4 inches of crushed rock base course. For heavy-duty pavements, we recommend 3 inches of asphalt concrete over 6 inches of crushed rock base course. Materials and Construction: We recommend the following regarding asphalt pavement materials and pavement construction. • Subgrade Preparation and Compaction: Upper 12 inches of native stripped subgrade should be prepared in accordance with the recommendations presented in the Subgrade Preparation section of this report, and all fill should be compacted in accordance with the recommendations presented in the Structural Fill section of this report. • Asphalt Concrete: We recommend that the asphalt concrete conform to Section 9-02.1(4) for PG 58-22 or PG 64-22 Performance Graded Asphalt Binder as presented in the 2016 WSDOT Standard Specifications. We also recommend that the gradation of the asphalt aggregate conform to the Page 15 Zi pperGeo Geoprofessional Consultants 76TH Avenue West Townhomes Project No. 1817.01 May 26, 2017 aggregate gradation control points for %-inch mixes as presented in Section 9-03.8(6), HMA Proportions of Materials. • Base Course: We recommend that the crushed aggregate base course conform to Section 9- 03.9(3) of the WSDOT Standard Specifications. • Compaction and Paving: All base material should be compacted to at least 95 percent of the maximum dry density determined in accordance with ASTM D 1557. We recommend that asphalt be compacted to a minimum of 92 percent of the Rice (theoretical maximum) density or 96 percent of Marshall (Maximum laboratory) density. Placement and compaction of asphalt should conform to requirements of Section 5-04 of the 2016 WSDOT Standard Specifications Concrete Pavement Concrete Properties and Thickness: Concrete pavement design recommendations are based on an assumed modulus of rupture of 600 psi and a minimum compressive strength of4,000 psi forthe concrete. For light duty pavements, we recommend 5 inches of concrete over 3 inches of crushed aggregate base. For heavy duty pavements, we recommend 6 inches of concrete over 3 inches of crushed aggregate base. Concrete Pavement Joints and Reinforcing: Based on the soils encountered, we recommend that concrete pavements should be lightly reinforced to control cracking and have relatively closely spaced control joints on the order of 10 to 12 feet. We recommend that minimum reinforcement consist of 6x6-W2.OxW2.0 welded wire fabric or equivalent. Existing Retaining Wall Considerations The single-family parcel to the east is lower than the subject property and a concrete masonry unit (CMU) block wall is located near the common property line. The northern half of the wall is about 4 feet tall. The southern half of the wall consists of two tiers with a combined height of about 9 to 10 feet. The horizontal distance from the face of the upper wall to the face of the lower wall is about 2% feet. The CMU wall appears to include grout between horizontal layers of block, but does not include grout between vertical block joints (presumably to provide drainage through the wall face). It is not currently known if the CMU units are filled with concrete or include steel reinforcement. The foundation system for the walls is also unknown at this time. An invasive investigation of the walls and wall foundations was not completed by ZGA as the walls appear to be located off the subject property and the owner of the property to the east was not at home during our site visits (the home appears to be under renovation). At the time of our evaluation the existing walls appeared to be in serviceable condition with no obvious indications of distress or damage. The preliminary plan shows a private driveway for the 4 townhome units located within a few feet of the existing off -site retaining walls. Surcharge loads from construction equipment and post construction vehicle traffic including passenger vehicle and moving trucks could impart a significant load on the existing walls. The magnitude and effect of the surcharge load will depend greatly on the elevation of the driveway, which is currently unknown, relative to the bottom of wall elevation. Page 16 Zi pperGeo 76T" Avenue WestTownhomes Project No. 1817.01 Geoprofessional Consultants May 26, 2017 A conservative approach would be to replace the existing retaining walls with new walls designed for anticipated loading conditions. Alternatively, it appears feasible from a geotechnical perspective to proceed with the planned construction leaving the existing off -site walls as -is provided that the east edge of the new driveway is beyond a 1H:1V plane extending up and to the west from the front toe of the existing wall face. ZGA is available to further evaluate the existing off -site walls from a geotechnical perspective once final site grades have been established and access to the wall has been arranged with the adjacent property owner. A structural evaluation of the walls would likely require a structural engineer. CLOSURE The analysis and recommendations presented in this report are based, in part, on the explorations completed for this study. The number, location, and depth of the explorations were completed within the constraints of budget and site access so as to yield the information to formulate our recommendations. Project plans were in the preliminary stage at the time this report was prepared. We therefore recommend Zipper Geo Associates, LLC be provided an opportunity to review the final plans and specifications when they become available in order to assess that the recommendations and design considerations presented in this report have been properly interpreted and implemented into the project design. The performance of earthwork, structural fill, foundations, floor slabs, and pavements depend greatly on proper site preparation and construction procedures. We recommend that Zipper Geo Associates, LLC be retained to provide geotechnical engineering services during the foundation construction phases of the project. If variations in subsurface conditions are observed at that time, a qualified geotechnical engineer could provide additional geotechnical recommendations to the contractor and design team in a timely manner as the project construction progresses. This report has been prepared for the exclusive use of Northlake Capital and Development, and its agents, for specific application to the project discussed and has been prepared in accordance with generally accepted geotechnical engineering practices. No warranties, express or implied, are intended or made. Site safety, excavation support, and dewatering requirements are the responsibility of others. In the event that changes in the nature, design, or location of the project as outlined in this report are planned, the conclusions and recommendations contained in this report shall not be considered valid unless Zipper Geo Associates, LLC reviews the changes and either verifies or modifies the conclusions of this report in writing. Page 17 ANGLE N i i° 1 5 7 T I o f o2 14 2 1I ��ti D�411.9 6�/.p / / i � h T 412.22 \ �I D�� i' // O�1' �O 1N ii cgco 412.30 _ \\ I I `o(0 405.36 • �O 80.00' Q v-2 I� I —-----�---- ----� \IIIII II o,\a ��---�_ i TI—r------ --'-- Oj -;IIII I I m I Q 00Ln Cn / • i m. —IuII I� LLJ A. 01 \ > 3—STORY TOWNHOME W/ 15,_m„ 2 CAR GARAGE, 3 oIp � fRMT sEMACK 4•j� TYP— + ol° r I ° L SIDE j\-1 — — SEA o i ii 00 SF —I ' J / PER bLR, TYP ��°" / N I d O / �ao7 1 N `— N I Co I 410. 4 }� .. O/ / I Y I \\� O I II L-FO Oo'� \—-------7------------- -----+—' --•---- T - 30.01';' 12" CED�R N88'02'01"W/ 80.00' a� / �� o 00 !; Cb, REFERENCE: SITE PLAN PREPARED BY CDA + PIRSCHER ARCHITECTS, DATED FEBRUARY 24, 2017. LEGEND 76th AVENUE WEST TOWNHOMES 7528 215th Street SW B_ BORING NUMBER AND Edmonds, WA APPROXIMATE LOCATION SITE AND EXPLORATION PLAN 20 0 10 20 DATE: MAY 2017 Job No. 1817.01 Zipper Geo Associates, LLC FIGURE SCALE IN FEET 19023 36th Ave. W.,Suite D Lynnwood, WA SHT. 1 of 1 APPENDIX A SUBSURFACE EXPLORATION PROCEDURES AND LOGS APPENDIX A SUBSURFACE EXPLORATION PROCEDURES AND LOGS Field Exploration Description Our field exploration for this project included two borings completed in May 2017. The approximate exploration locations are shown on the enclosed Site and Exploration Plan, Figure 1. The exploration locations were determined by measuring distances from existing site features with a fiberglass tape relative to Site Plan prepared by CDA+ Pirscher Architects dated February 24, 2017. As such, the exploration locations should be considered accurate only to the degree implied by the means and methods used to define them. Soil Borings The borings were advanced using a limited- access, track -mounted drill rig operated by an independent drilling company (Geologic Drilling, Inc.) working under subcontract to ZGA. The borings were advanced using hollow stem auger drilling methods. A geologist from our firm continuously observed the borings, logged the subsurface conditions encountered, and obtained representative soil samples. All samples were stored in moisture -tight containers and transported to our laboratory for further evaluation and testing. Samples were obtained by means of the Standard Penetration Test at 2.5- to 5-foot intervals throughout the drilling operation. The Standard Penetration Test (ASTM D 1586) procedure consists of driving a standard 2-inch outside diameter steel split spoon sampler 18 inches into the soil with a 140-pound hammer free falling 30 inches. The number of blows required to drive the sampler through each 6-inch interval is recorded, and the total number of blows struck during the final 12 inches is recorded as the Standard Penetration Resistance, or "blow count" (N value). If a total of 50 blows are struck within any 6- inch interval, the driving is stopped and the blow count is recorded as 50 blows for the actual penetration distance. The resulting Standard Penetration Resistance values indicate the relative density of granular soils and the relative consistency of cohesive soils. The enclosed boring logs describes the vertical sequence of soils and materials encountered in the borings, based primarily upon our field classifications. Where a soil contact was observed to be gradational, our logs indicate the average contact depth. Where a soil type changed between sample intervals, we inferred the contact depth. Our logs also graphically indicates the blow count, sample type, sample number, and approximate depth of each soil sample obtained from the borings. Groundwater monitoring wells were installed in all three borings completed for this project to monitor fluctuations in groundwater levels over time. Boring Location: See Figure 1, Site and Exploration Plan Drilling Company: Geologic Drill Bore Hole Dia.: 4.5 Inches Top Elevation: 410.5 Feet Drilling Method: HSA Hammer Type: Cathead 6-1 Date Drilled: 5/9/2017 Drill Rig: Mini -track Logged by_: JST E a) SOIL DESCRIPTION �� E J n U) � - a ° (D PENETRATION RESISTANCE (blows/foot) co o U m 0) ~ The stratification lines represent the approximate boundaries between soil types. The transition may be gradual. Refer to report text and appendices for additional information. Standard Penetration Test Q Hammer Weight and Drop: 0 20 40 60 2 inches grass sod. -----------------------------------------'� IIII ',II IIIIIIIII IIII -IIIIIIII IIIIIIIII Illlii 7TI-17Y�rt—I-Y rtrtYYTY7TT rTTYT r r - :_... Medium dense, moist, brown, silt SAND, with organics. Fill Y g (Fill) T S-1 6" IIII II 13 -f-I-IT_717-f711 IIIII I -fT7TTTTTT IIIIIIIII TTTTTTT _ IIIIIII. ------------------------------------------- Dense, moist, gray SAND, with silt and gravel. (Glacial Till) 111 S-2 12,E �JJJJJJJ IIIIIIIII -IIIIIIII 11.11111.11 IIIIIIIII IIIIIIIII 1LLLLLLL IIIIIIII IIIIIIII 49 IIIIIIII IIIIIIIII IIII IIIIIIIII IIIIIIIII IIIIIIIII IIIIIIIII IIII . IIIIIIII Medium dense to dense, moist, gray SAND with silt and gravel. (Glacial Till) Dense, moist, gray, silty SAND with gravel, slight iron oxide staining. (Glacial Till) S-3 18" s-a I 1a 1 -I-IT-f7 IIIIIIIII IIIIIIIII I I I I I I I I I 77TT TTTT I�I II,IIIII,II IIIIIIIII I I I I I I I I I TTTTTTT -.. IIIIILLI IIIIIII I I I I I I I I 30 as +.� IIIII111I + IIIIIIIII IIIIIIII IIIIIIII --I11_f++t- IIIIIIII IIIIIIIII ++t t t t.t.t t IIIIIIIII IIi1I1'... IIII Very dense, moist, gray, silty SAND with gravel. (Glacial Till) S-s I 16 IIIIIIII IIIIIIIII IIIIIII soi4" .'...IIIIIIII IIIIIII IIIIIIIII IIIIIIIII IIIIIIII IIIIIIII IIIIIIII IIIIIIIII IIII IIIIIIIII +-1++++-4+ IIIIIIIII IIIIIIIII ++a-++++++ IIIIIIIII IIII +++a- - IIII -i��rtrtrtrtY IIIIIIIII rtrtYYYrt7rtr IIIIIIIII III trrrrr IIIIIIIII IIIIIIII IIIIIIIII IIIIIIIII f7 '..�IIIIII TTTTTTTTT III�I111� TTTTTi-T '- IIIIIII Very dense, moist, gray, silty SAND, with gravel. (Glacial Till) S-s T 12" 1 so 4" (� IIIIIIIII IIIIIIIII -+--4-i-4+ IIIIIIIII IIIIIIIII ++44+++++ IIII IIII +++44- 1-- -- Boring completed at about 21.5 feet. No groundwater observed at time of drilling. g. IIIIIIIII 11 f-t-r-t- IIIIIIIII IIIIIIIII fiat t t t.tt t IIIIIIIII IIII tt r - - , IIII�� IIIIIIIII IIIIIIIII IIIIIIII 7I77Y777 YTTTTTTTT TTTTTTT:- SAMPLE LEGEND GROUNDWATER LEGEND O % Fines (<0.075 mm) I2-inch O.D. split spoon sample Clean Sand 0 % Water (Moisture) Content 3-inch I.D. Shelby tube sample ® Bentonite Plastic Limit Liquid Limit Grout/Concrete Natural Water Content ® Screened Casing 76th Ave. West Townhomes TESTING KEY n Blank Casing 7528 215th Street SW GSA = Grain Size Analysis V Groundwater level at Edmonds, WA time of drilling (ATD) or 200W = 200 Wash Analysis_ on date of Date: May 2017 Project No.: 1817.01 Consol. = Consolidation Test measurement. Zipper Geo Associates BORING Att. = Atterberq Limits B-1 19023 36th Ave. W, Suite D LOG; Lynnwood, WA Page 1 of 1 Boring Location: See Figure 1, Site and Exploration Plan Drilling Company: Geologic Drill Bore Hole Dia.: 4.5 Inches Top Elevation: 410.5 Feet Drilling Method: HAS Hammer Type: Cathead B-2 Date Drilled: 5/9/2017 Drill Rig: Mini -track Logged by_: JST SOIL DESCRIPTION - PENETRATION RESISTANCE (blows/foot) �� E co o 0) Standard Penetration Test E The stratification lines represent the approximate boundaries J n a Q Hammer Weight and Drop: U a) between soil types. The transition may be gradual. Refer to ~ report text and appendices for additional information. U) � ° m (D 0 20 40 60 3 inches grass sod. , -----------------------------------------'—�I Loose to medium dense, moist, brown, silty SAND, with III .II (IIIIIIII (III organics and roots. (Fill) -------------------------------------------- �� rrt rrt -IIIIIIII rt 1 T7TT IIIIIIIII rrrrrrrr_ Dense, moist, gray -brown SAND, with silt and gravel, Wthd Glacial Till moderate iron oxide staining. (Weathered ) s-1 18" IIIIIIII 42 ��T�� (III III 77 T T TTTTT IIIIIIIII �TTTTTT - IIIIII -------------------------------------------- Ve dense, moist, gray SAND, with silt and ravel. ry 9 Y g (Glacial Till) S-2 12' IIIIIIIII -IIIIIIII 11.1II LLL IIIIIIIII IIIIIIIII 1LILLLLs IIIIIIII IIIIIIII 51 GSA 1111 IIIIIIII (IIIIIIIII III IIIII IIIIIIIII Ili � - (III �.._I7yrtttrtrt '..IIIIIII IIIIIIIII rtt-t t t t..ttt IIIIIIIII (III t t...- t- r ` :... IIIIIIII Ve dense, moist, gray, silt SAND, with ravel, slight iron rY 9 Y Y 9 9 T S-3 I 1$" I 63 i I-I-1�777 7777T TTTT TTTTTTT � oxide staining. (Glacial Till) Very dense, moist, gray, silty SAND, with gravel. (Glacial Till) 11 S-4 181, IIIIIIIII IIIIIIIII I I I I I I I I I 1 1 1 1 1 1 1 1 1 II,,,IIIII,II IIIIIIIII I I I I I I I I I 1 1 1 1 1 1 IIIIILL -s.. IIIIIII'. I I I I I I I I 64 GSA + IIIIIIIII IIIIIIIII ��-f _f _f _f_+ 11111111 IIIIIIIII IIIIIIIII tttttt 111111111 (III (III '... ttt 1111 Very dense, moist, gray, silty SAND, with gravel. (Glacial Till) s-5 10.5° 1-I-17 111 11 r7- 11111 50i4.5° -�-�T-irt I� '11111111 � t r-r-r7�-r-r 111111111 -r-r-r rTTT 11111111 1 r11 0 11 111111111 1111 ...11 ...11 I1111111 111111111 111111111 1111 1111 -I��rtrtrtrtrt 111111111 rttrt7rtrt7rtr 111111111 r T_ trrrrr.. 11111111i 11111111 111111111 111111111 77-177-17 f7 -IIIIIIII 77777TTTT III�I111� TTTTTTT '- 1111�111 Very dense, moist, gray, silty SAND, with gravel. (Glacial Till) S-6 I n° 50/5" 111111111 111111111 IIIIIIIII IIIIIIIII +++++++++ (III (III ++++- r Boring completed at about 21.5 feet. 1 No groundwater observed at time of drilling. g g IIIIIIIII -r11-f-t-t-t-t 111111111 IIIIIIIII fittttt.+tt 111111111 (III tt-rrr 1111�� 111111111 111111111 11111111 T11T7T77 77777TTTT TTTTTTT:- SAMPLE LEGEND GROUNDWATER LEGEND O % Fines (<0.075 mm) I2-inch O.D. split spoon sample Clean Sand 0 % Water (Moisture) Content 3-inch I.D. Shelby tube sample ® Bentonite Plastic Limit Liquid Limit Grout/Concrete Natural Water Content ® Screened Casing 76th Ave. West Townhomes TESTING KEY n Blank Casing 7528 215th Street SW GSA = Grain Size Analysis V Groundwater level at Edmonds, WA time of drilling (ATD) or 200W = 200 Wash Analysis _ on date of Date: May 2017 Project No.: 1817.01 Consol. = Consolidation Test measurement. BORING Zipper Geo Associates Att. = Atterberq Limits B-2 19023 36th Ave. W, Suite D LOG; Lynnwood, WA Page 1 of 1 APPENDIX B LABORATORY TESTING PROCEDURES AND RESULTS APPENDIX B LABORATORY TESTING PROCEDURES AND RESULTS A series of laboratory tests were performed by ZGA during the course of this study to evaluate the index and geotechnical engineering properties of the subsurface soils. Descriptions of the types of tests performed are given below. Visual Classification Samples recovered from the exploration locations were visually classified in the field during the exploration program. Representative portions of the samples were carefully packaged in moisture tight containers and transported to our laboratory where the field classifications were verified or modified as required. Visual classification was generally done in accordance with ASTM D 2488. Visual soil classification includes evaluation of color, relative moisture content, soil type based upon grain size, and accessory soil types included in the sample. Soil classifications are presented on the exploration logs in Appendix A. Moisture Content Determinations Moisture content determinations were performed on representative samples obtained from the explorations in order to aid in identification and correlation of soil types. The determinations were made in general accordance with the test procedures described in ASTM D 2216. Moisture contents are presented on the exploration logs in Appendix A. Grain Size Analysis A grain size analysis indicates the range in diameter of soil particles included in a particular sample. Grain size analyses were performed on representative samples in general accordance with ASTM D 422. The results of the grain size determinations for the samples were used in classification of the soils, and are presented in this appendix. GRAIN SIZE ANALYSIS Test Results Summary ASTM D 422 100 90 = 80 W ?� 70 Im IW 60 W Z 50 Z W tU W 40 W a 30 20 10 0 1000.000 100.000 10.000 1.000 0.100 0.010 0.001 PARTICLE SIZE IN MILLIMETERS Coarse Fine Coarse Medium Fine Silt Clay BOULDERS COBBLES GRAVEL SAND FINE GRAINED Comments: Exploration Sample Depth (feet) Moisture (%) Fines (%) Description B-2 S-2 5.0 9.1 27.9 SAND with silt and gravel Project No.: 1817.01 PROJECT NAME: Zipper Geo Associates, LLC Geotechnical and Environmental Consultants DATE OF TESTING: 5/11/2017 76th Ave. W. Townhomes GRAIN SIZE ANALYSIS Test Results Summary ASTM D 422 100 90 = 80 W ?� 70 Im IW 60 W Z 50 Z W tU W 40 W a 30 20 10 0 1000.000 100.000 10.000 1.000 0.100 0.010 0.001 PARTICLE SIZE IN MILLIMETERS Coarse Fine Coarse Medium Fine Silt Clay BOULDERS COBBLES GRAVEL SAND FINE GRAINED Comments: Exploration Sample Depth (feet) Moisture (%) Fines (%) Description B-2 S-4 10.0 9.9 35.2 Silty SAND with gravel Project No.: 1817.01 PROJECT NAME: Zipper Geo Associates, LLC Geotechnical and Environmental Consultants DATE OF TESTING: 5/11/2017 76th Ave. W. Townhomes USDA United States Department of Agriculture N RCS Natural Resources Conservation Service A product of the National Cooperative Soil Survey, a joint effort of the United States Department of Agriculture and other Federal agencies, State agencies including the Agricultural Experiment Stations, and local participants Custom Soil Resource Report for Snohomish County Area, Washington 76th Ave Townhomes Contents SoilMap.................................................................................................................. 3 SoilMap................................................................................................................3 Legend..................................................................................................................4 MapUnit Legend.................................................................................................. 5 MapUnit Descriptions.......................................................................................... 5 Snohomish County Area, Washington............................................................ 7 5—Alderwood-Urban land complex, 2 to 8 percent slopes ......................... 7 6—Alderwood-Urban land complex, 8 to 15 percent slopes ....................... 8 47o 48' 16' N rn Custom Soil Resource Report 3 Soil Map 0 NV N 549743 549749 549755 549761 549767 549M 1 •i• lie 16 i' ■ •aii JA r PE , 5 it Map may 47° 48' 15" N 549743 549749 549755 549761 549767 549M 3 co R Map Scale: 1:255 if printed on A portrait (8.5" x 11") sheet. N Meters 0 3 7 14 21 Feet 0 10 20 40 60 Map projection: Web Mercator Comer coordinates: WGS84 Edge tics: UTM Zone 1ON WGS84 3 3 �o 0 NV N 549779 41 4616" N L 47° 48' 15' N 549779 3 co N a MAP LEGEND Area of Interest (AOI) Area of Interest (AOI) Soils 0 Soil Map Unit Polygons rwr Soil Map Unit Lines Soil Map Unit Points Special Point Features Uo Blowout ® Borrow Pit Clay Spot Closed Depression Gravel Pit Gravelly Spot Landfill Lava Flow Marsh or swamp + Mine or Quarry Miscellaneous Water Perennial Water Rock Outcrop Saline Spot d Sandy Spot Severely Eroded Spot Sinkhole Slide or Slip oa Sodic Spot Custom Soil Resource Report MAP INFORMATION Spoil Area The soil surveys that comprise your AOI were mapped at 1:24,000. Stony Spot Very Stony Spot Warning: Soil Map may not be valid at this scale. Wet Spot Enlargement of maps beyond the scale of mapping can cause Other misunderstanding of the detail of mapping and accuracy of soil .- Special Line Features line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed Water Features scale. Streams and Canals Transportation Please rely on the bar scale on each map sheet for map 1 1 F Rails measurements. Interstate Highways Source of Map: Natural Resources Conservation Service r.x US Routes Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Major Roads Local Roads Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts Background distance and area. A projection that preserves area, such as the Aerial Photography Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: Snohomish County Area, Washington Survey Area Data: Version 22, Jun 4, 2020 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Sep 2, 2018—Sep 25, 2018 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Custom Soil Resource Report Map Unit Legend Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI 5 6 Alderwood-Urban land complex, 2 to 8 percent slopes Alderwood-Urban land complex, 8 to 15 percent slopes 0.3 0.0 86.2% 13.8% Totals for Area of Interest 0.3 100.0% Map Unit Descriptions The map units delineated on the detailed soil maps in a soil survey represent the soils or miscellaneous areas in the survey area. The map unit descriptions, along with the maps, can be used to determine the composition and properties of a unit. A map unit delineation on a soil map represents an area dominated by one or more major kinds of soil or miscellaneous areas. A map unit is identified and named according to the taxonomic classification of the dominant soils. Within a taxonomic class there are precisely defined limits for the properties of the soils. On the landscape, however, the soils are natural phenomena, and they have the characteristic variability of all natural phenomena. Thus, the range of some observed properties may extend beyond the limits defined for a taxonomic class. Areas of soils of a single taxonomic class rarely, if ever, can be mapped without including areas of other taxonomic classes. Consequently, every map unit is made up of the soils or miscellaneous areas for which it is named and some minor components that belong to taxonomic classes other than those of the major soils. Most minor soils have properties similar to those of the dominant soil or soils in the map unit, and thus they do not affect use and management. These are called noncontrasting, or similar, components. They may or may not be mentioned in a particular map unit description. Other minor components, however, have properties and behavioral characteristics divergent enough to affect use or to require different management. These are called contrasting, or dissimilar, components. They generally are in small areas and could not be mapped separately because of the scale used. Some small areas of strongly contrasting soils or miscellaneous areas are identified by a special symbol on the maps. If included in the database for a given area, the contrasting minor components are identified in the map unit descriptions along with some characteristics of each. A few areas of minor components may not have been observed, and consequently they are not mentioned in the descriptions, especially where the pattern was so complex that it was impractical to make enough observations to identify all the soils and miscellaneous areas on the landscape. The presence of minor components in a map unit in no way diminishes the usefulness or accuracy of the data. The objective of mapping is not to delineate pure taxonomic classes but rather to separate the landscape into landforms or landform segments that have similar use and management requirements. The delineation of such segments on the map provides sufficient information for the development of resource plans. If intensive use of small areas is planned, however, Custom Soil Resource Report onsite investigation is needed to define and locate the soils and miscellaneous areas. An identifying symbol precedes the map unit name in the map unit descriptions. Each description includes general facts about the unit and gives important soil properties and qualities. Soils that have profiles that are almost alike make up a soil series. Except for differences in texture of the surface layer, all the soils of a series have major horizons that are similar in composition, thickness, and arrangement. Soils of one series can differ in texture of the surface layer, slope, stoniness, salinity, degree of erosion, and other characteristics that affect their use. On the basis of such differences, a soil series is divided into soil phases. Most of the areas shown on the detailed soil maps are phases of soil series. The name of a soil phase commonly indicates a feature that affects use or management. For example, Alpha silt loam, 0 to 2 percent slopes, is a phase of the Alpha series. Some map units are made up of two or more major soils or miscellaneous areas. These map units are complexes, associations, or undifferentiated groups. A complex consists of two or more soils or miscellaneous areas in such an intricate pattern or in such small areas that they cannot be shown separately on the maps. The pattern and proportion of the soils or miscellaneous areas are somewhat similar in all areas. Alpha -Beta complex, 0 to 6 percent slopes, is an example. An association is made up of two or more geographically associated soils or miscellaneous areas that are shown as one unit on the maps. Because of present or anticipated uses of the map units in the survey area, it was not considered practical or necessary to map the soils or miscellaneous areas separately. The pattern and relative proportion of the soils or miscellaneous areas are somewhat similar. Alpha -Beta association, 0 to 2 percent slopes, is an example. An undifferentiated group is made up of two or more soils or miscellaneous areas that could be mapped individually but are mapped as one unit because similar interpretations can be made for use and management. The pattern and proportion of the soils or miscellaneous areas in a mapped area are not uniform. An area can be made up of only one of the major soils or miscellaneous areas, or it can be made up of all of them. Alpha and Beta soils, 0 to 2 percent slopes, is an example. Some surveys include miscellaneous areas. Such areas have little or no soil material and support little or no vegetation. Rock outcrop is an example. Custom Soil Resource Report Snohomish County Area, Washington 5—Alderwood-Urban land complex, 2 to 8 percent slopes Map Unit Setting National map unit symbol: 2hz9 Elevation: 50 to 800 feet Mean annual precipitation: 25 to 60 inches Mean annual air temperature: 48 to 52 degrees F Frost -free period: 180 to 220 days Farmland classification: Not prime farmland Map Unit Composition Alderwood and similar soils: 60 percent Urban land: 25 percent Minor components: 15 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Alderwood Setting Landform: Till plains Parent material: Basal till Typical profile H1 - 0 to 7 inches: gravelly ashy sandy loam H2 - 7 to 35 inches: very gravelly ashy sandy loam H3 - 35 to 60 inches: gravelly sandy loam Properties and qualities Slope: 2 to 8 percent Depth to restrictive feature: 20 to 40 inches to densic material Drainage class: Moderately well drained Capacity of the most limiting layer to transmit water (Ksat): Very low to moderately low (0.00 to 0.06 in/hr) Depth to water table: About 18 to 36 inches Frequency of flooding: None Frequency of ponding: None Available water capacity. Low (about 3.0 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 4s Hydrologic Soil Group: B Forage suitability group: Limited Depth Soils (G002XN302WA) Other vegetative classification: Limited Depth Soils (G002XN302WA) Hydric soil rating: No Minor Components Terric medisaprists, undrained Percent of map unit: 5 percent Landform: Depressions Other vegetative classification: Wet Soils (G002XN102WA) Hydric soil rating: Yes Custom Soil Resource Report Norma, undrained Percent of map unit: 5 percent Landform: Depressions Other vegetative classification: Wet Soils (G002XN102WA) Hydric soil rating: Yes Mckenna Percent of map unit: 5 percent Landform: Depressions Other vegetative classification: Wet Soils (G002XN102WA) Hydric soil rating: Yes 6—Alderwood-Urban land complex, 8 to 15 percent slopes Map Unit Setting National map unit symbol: 2hzn Elevation: 50 to 800 feet Mean annual precipitation: 25 to 60 inches Mean annual air temperature: 48 to 52 degrees F Frost -free period: 180 to 220 days Farmland classification: Not prime farmland Map Unit Composition Alderwood and similar soils: 60 percent Urban land: 25 percent Minor components: 5 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Alderwood Setting Landform: Till plains Parent material: Basal till Typical profile H1 - 0 to 7 inches: gravelly ashy sandy loam H2 - 7 to 35 inches: very gravelly ashy sandy loam H3 - 35 to 60 inches: gravelly sandy loam Properties and qualities Slope: 8 to 15 percent Depth to restrictive feature: 20 to 40 inches to densic material Drainage class: Moderately well drained Capacity of the most limiting layer to transmit water (Ksat): Very low to moderately low (0.00 to 0.06 in/hr) Depth to water table: About 18 to 36 inches Frequency of flooding: None Frequency of ponding: None Available water capacity: Low (about 3.0 inches) Custom Soil Resource Report Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 4s Hydrologic Soil Group: B Forage suitability group: Limited Depth Soils (G002XN302WA) Other vegetative classification: Limited Depth Soils (G002XN302WA) Hydric soil rating: No Minor Components Norma, undrained Percent of map unit: 5 percent Landform: Drainageways Other vegetative classification: Wet Soils (G002XN102WA) Hydric soil rating: Yes 76th Ave Townhomes - CG #17206.20 Drainage Report February 12, 2021 Section VI, Page 1 Section VI — Other Permits Section VI Summary: Narrative The site will not require permits beyond those from the City of Edmonds. C � ENGINEERING 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com 76th Ave Townhomes - CG #17206.20 February 12, 2021 Drainage Report Section VI I, Page 1 Section VII — Bond Quantities, Declaration of Covenant, & Operation and Maintenance Manual Section VII Summ Narrative The Bond Quantity Worksheet is a standalone document that is also being submitted to the City of Edmonds separately from this document. A Declaration of Covenant is provided for the onsite BMPs proposed. The Operation and Maintenance Manual is a standalone document that will be given to the owners following the construction of the project. nInrrntivo The maintenance covenant contained herein is for the 76t" Avenue Townhomes building project. The contractor will be responsible for the maintenance and operation of all stormwater structures and BMPs requiring maintenance during construction and, after construction, responsibility will pass to the home owner's association. The project contractor will be responsible for passing along the information in this maintenance manual to the owner. Upon request by the City, it shall be made available for their inspection. It is generally expected that few to none of these defects will be present upon the yearly inspection of each facility. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com After recording return to: City Clerk City of Edmonds 121 Fifth Avenue North Edmonds, WA 98020 Document Title(s) Declaration of Covenant - Private Stormwater Facility Reference Number(s) of Related Documents N/A Grantor(s) (Last, First and Middle Initial) Forde, Keith M. Grantee(s) (Last, First and Middle Initial) City of Edmonds Legal Description (abbreviated form; i.e., lot, plat or section,. township, range, quarter/quarter) LOT 16, NW 1/4, NW 1/4, SECTION 29, TOWNSHIP 27 NORTH, RANGE 4 EAST, W.M. Assessor's Property Tax Parcel/Account Number at the Time of Recording: 00501200001600 The Auditor/Recorder will rely on the information provided on this form. The staff will not read the document to verify the accuracy or completeness of the indexing information provided herein. DECLARATION OF COVENANT Private Stormwater Facility WHEREAS, the undersigned Declarant(s) have installed a stormwater facility under Edmonds Community Development Code Chapter 18.30 known as a "low impact development best management practices (LID BMP)" in lieu of other required more conventional stormwater systems, as selected below: ❑ Permeable Pavement ❑ Rain Garden / Bioretention Cell ❑ Infiltration Trench ❑ Drywell ❑ Gravelless Chamber © Other Detention Pipe WHEREAS, the City of Edmonds has allowed installation of the LID BMP, subject to the execution and recording of this Declaration of Covenant; NOW, THEREFORE, THE UNDERSIGNED DECLARANT(S), being the owners of the real property ("the Property") located at the following address: 7528 215th Street SW in the City of Edmonds, Washington, and legally described on Exhibit A attached hereto and incorporated herein by this reference as if set forth in full, hereby covenants and agrees, on behalf of himself/herself/themselves/itself and his/her/their/its successors and assigns, as follows: Declarant(s) warrant that he/she/they are the owners of the property described on Exhibit A and have the authority to impose this covenant on the property and bind all future owners, successors, and assigns of the Declarant(s). The Declarant(s), future owners, successors, and assigns of the Declarant(s) shall be referred to collectively as "Owners." 2. The Owners of the property described on Exhibit A agree that the property contains a stormwater management facility called a "LID BMP," which was installed to mitigate the stormwater quantity and quality impacts of some or all of the impervious or non-native pervious surfaces on the property. "Low impact development" means development conducted in a way that seeks to minimize or completely prevent alterations to the natural hydrology of the site. Low impact development includes site planning and design to reduce alterations of natural soil and vegetation cover, minimize impervious surfaces, and specific practices that help to replicate natural hydrology such as permeable pavements, green roofs, soil amendments, bioretention systems, and dispersion of runoff. 3. The Owners of the property described on Exhibit A shall maintain the size, placement, and design of the LID BMP as depicted on the approved site plan, Exhibit B, and design details shall be maintained and may not be changed without written approval either from the Engineering Division of the City of Edmonds or through a future development permit from the City of Edmonds. Chemical fertilizers and pesticides shall not be used where LID BMP is located. . All costs of maintenance and repair shall be the sole responsibility of the Owners. 4. The Owners of the property described on Exhibit A shall inspect LID BMPs annually for physical defects. After major storm events, the system shall also be checked to ensure that the overflow system is working properly. The Owners also shall maintain all LID BMP so it functions as designed on a year-round basis. 5. The City of Edmonds is hereby granted by the Owners the right, but not the obligation, to enter upon the property described on Exhibit A at all reasonable times for the purpose of inspecting the private stormwater LID BMP facility. If, as the result of any such inspection the City of Edmonds determines that the LID BMP is in disrepair, requires maintenance or repair, or is otherwise not functioning as provided in the BMP site plan, the City Engineer or his designee shall have the right, but not the obligation, to order the Owners of the property described on Exhibit A to maintain or repair the same. 6. If the City of Edmonds determines that the LID BMP requires maintenance or repair pursuant to Section 5, the City of Edmonds shall provide notice to the Owners of the deadline within which such maintenance or repair must be completed. Said notice may further advise that, should the violator fail to perform required maintenance or make repairs within the established deadline, the work may be done by the city or a contractor designated by the City Engineer and the expense thereof shall be charged to the Owners. The City's officers, agents, employees, and contractors shall have the right, which is hereby granted by the Owners, to enter upon the property described on Exhibit A in order to perform such work. The Owners shall bear the cost of all work performed. 7. The Owners shall indemnify, defend and hold harmless the City of Edmonds, its officers, officials, employees and agents from any and all claims, demands, suits, penalties, losses, damages, judgments, attorneys' fees and/or costs of any kind whatsoever, arising out of or in any way resulting from the approval of the LID BMP, the installation and presence of the LID BMP, and the acts or omissions of the Owners, their officers, employees, contractors, and agents relating to the construction, operation and maintenance of the LID BMPs on the property, except for the City's intentional and willful tortious acts, and waive and release the City of Edmonds from any and all claims for damages and injunctive relief which the Owners may themselves have now or in the future, by reason of the construction, maintenance and operation of said LID BMPs. 8. This covenant shall run with the land and be binding upon the Declarant(s), as the owner of the property described on Exhibit A, and on Declarant's successors and assigns as to such property. Dated: DECLARANT(S): (Signature) (Print Name) (Signature) (Print Name) State of Washington M1 County of Snohomish APPROVED: CITY OF EDMONDS (Signature) (Print Name) (Title) On this day personally appeared before me { Declarant(s) } to me known to be the individual, or individuals described in and who executed the within and foregoing instrument, and acknowledged that he/she/they signed the same as his/her/their free and voluntary act and deed, for the uses and purposes therein mentioned. SUBSCRIBED AND SWORN before me this day of , 201_. (Signature) (Name legibly printed or stamped) Notary Public in and for the State of Washington. Residing at: My commission expires Exhibit A LOT 16, LUSCHEN'S TRACTS DIVISION NO 2, ACCORDING TO THE PLAT THEREOF RECORDED IN VOLUME 17 OF PLATS, PAGE 21, RECORDS OF SNOHOMISH COUNTY, STATE OF WASHINGTON. Exhibit B 0 MINI = 4uz.00 O IE=400.35 12"RCP O E & W SSMH 408.79 215TH ST SW SITE BENCH 0 RIM = 0 CTR CHANNEL ELEV: = 405.87; O = 399.49 HP - HP — 80.0 _ CATCH BASIN W/ FLOW CONTROL STRUCTURE DETENTION PIPE SYSTEM w � IQ 4-UNITTOWNHOME JILI I I^ BLDG FFE: 405.0 w N W U) CATCH BASIN II AIL OHP 1 - - - - GAS pN87`57'45°tq� 80.00' — — -- G1N et-7 A S UGP 76th Ave Townhomes - CG #17206.20 Drainage Report February 12, 2021 Section VII, Page 2 76th Ave Townhomes 7528 215th Street SW Edmonds, WA 98026 OPERATION AND MAINTENANCE MANUAL Date: February 2021 C � ENGINEERING 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com 76th Ave Townhomes - CG #17206.20 February 12, 2021 Drainage Report Section VI I, Page 3 Operation and Maintenance Manual This Operation and Maintenance Manual has been created for the 76th Ave Townhomes, a 3,500 ft2 building project on a 0.24 acre lot. The proposed storm system consists of a catch basin/manhole located in the driveway area that collects all on -site runoff from the driveway and roof, area, and footing drains and routes it to a flow -through detention pipe system. Included in this Operation and Maintenance Manual is an 11" x 17" grading and drainage plan sheet showing the location of the system. Please note that this map is generated during the design phase and may not reflect all changes made in permitting and construction. CG Engineering may be contacted for an updated copy of this map once the as -built drawings are completed forthe site. The contractor will be responsible forthe maintenance and operation of all stormwater structures and BMPs requiring maintenance during construction and, after construction, responsibility will pass to the home owner's association. A map of the project area can be seen on the following page in Figure VII-1. Included in this manual are maintenance sheets taken from the 2014 Stormwater Management Manual for Western Washington for the following facilities/activities: Catch Basins: Concrete structures with steel grates that collect stormwater runoff from the site and act as junctions for storm conveyance pipes. Control Structures: Control structures are catch basins or manholes with a restrictor device for controlling outflow from a facility to meet the desired performance. Detention Pipes/Tanks: Detention tanks are underground storage facilities typically constructed with large diameter corrugated metal pipe. Vegetation Management: Landscaping can include grading, soil transfer, vegetation removal, pesticide and fertilizer applications, and watering. Stormwater contaminants include toxic organic compounds, heavy metals, oils, total suspended solids, coliform bacteria, fertilizers, and pesticides. Facilities shall be inspected for defects listed in the following facility sheets. Most maintenance tasks are generally reactionary to a defect being found, rather than a matter of constant upkeep. It is generally expected that few to none of these defects will be present upon the yearly inspection of each facility. The facility sheets list the potential conditions warranting maintenance and the expected result following any maintenance. Several engineer's notes for specific tasks are provided within the facility sheets. Unless otherwise noted on the facility sheets the maintenance tasks should be performed on an "as needed" basis: (a) when the described defect is visible to whomever performs the yearly inspection, or (b) should any defect become apparent between inspections. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com 76th Ave Townhomes - CG #17206.20 Drainage Report February 12, 2021 Section VII, Page 4 Figure VII-1. Map of project area. -14 4M 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com NW 1 /4, NW 1 /4, SECTION 29, TOWNSHIP 27 NORTH, RANGE 4 EAST, W.M. 11 cn ` Ells cns_rt-Ells- _ _ CB TYF�E 1 \ RPm = 402)55 IE=406.35 12"R�--P E &',W SWH 2,'I i_M/ - /". 9 Fl,Z�,M =e\i 0° 8 / /TR CHANCEL L i_ L= z99.4c)/ ____ , //� _�TODRIVE Al_ I 1 _T _S__W1 ____ IE FOOTING DRARi II _I I ___-_/___- - O TDOWNSTREAyOF /'U 17 °.4, 8DETENTIo 40t.06o / / °I ° I �4. -12 .9°5�` 411.11 4 .48 II I 40 I °s II TI 41 a i 411 , al 33 409.9 a 1" 409. 411.11 TOC 411.62 \ 1� ROOF IE: \ j � 405.1 ` \ / ' � 411.57 \\ / 409.9 wI Ti \ a T yx ° TOW 411.0 \ 410.65 a I P 409.9 I \. To 10.5 I 430.57 \ 3 1° 4 .0 41 \ �DBB4' I gb .11 _g I \\ I 1 _ 14 14 2 406.36 I I 141 1 405.25 I 16 LF - 12" PVC @ 0.5% 406.74 vU _ I TOC 405.75 FTG IE: ROOF IE: gp2.pp v ROOF IE: �" BOC 405.25 404.6 R III302.8 6"VERTICAL III I _ CURB I III 195 407.4 ROOF & FOOTING / 6" YARD DRAIN 1 405.05 ✓ .� IE: 401.74 6fJ0.0 eDRAINS RIM: 403.4 /}30.0 �-1E<"51:403.4 'II III I pra _ 1 I TOC 405.25 BOC 405.25 / 18 LF^'.�." PVC @ I... FTG DRN � 6.1% � li �,I: _ _ d - - -'1 j IE: 404.0 G GARAGE ENTRY /7 405.0 I, I-- 407.63 e v SEE C5.1 FOR LOT LINE LENGTHSANID $ ,'�" 35 LF - 2' MAX C5. HEIGHT RETAINING LIGHTWELL BEARINGS, BLDG 408.0 SETBACK LINES, 0 5,1 WALL. SEE NOTE 3 j AND LOT ARE I GRADE BREAK 6 � < --- -- z -- TOW 406.5 BOW 405.25 / LIGHTWELL GARAGE ENTRY 408.0 405.0 p o OG 407.5 4-UNITTOWNHOM I� o z ilg a 408.02 BLDG FFE: 405.0 BOO\61405.15 d Ot5408.05 / 4I4.90 , 9 olel �/ ,�\ 4 8 ml 408.14 ' /4 �/ LLI N j TOW 406.5 BOW 405.0 ENTRY-_ OG 408.5 1 ,81 408.64 / 77 _ TOC 405.5 `\ / KK 404.70 i�_ ` \ 408.57 / GARAGE ENTRY I \\ I 405.0 \ I I 3 LF " 24"0 N-12 LIGHTWELL j DETENTION PIPE, 408.0 / ROOF TYP e / 402.1414 408.5 I 66J 'I ?L = 6yE g'_Py,[.@y09jL 10 TOC 405.5 BOC 405.0 II 3 408.44 / UGHT\• ELL GARAGE ENTRY / 6" VERTICAL 408.0 405.0 7 i , 404.72 i i I CURB i aossl i 1 404.80 II TOW 401.51 I BOW 405.5 II ROOF IE: I OG 408.75 II 402.48 I 6 YARD DRAIN 1 / I RIM: 408.5 1 IE (6"N): 407.0 II p \ 408.58 I TOWBOW 409.5 \I I I TOW 409.75 OG 4000 II BOW 405.5 1 OG 409.7 405.92 I I N87'57't4~"87- nE'� 9 _ .,..� �-cns-Gas-fTYgbq,9++ � �_�` ___cns=-�G-�-a�%tA5_-___._ , P V� IVU� f� y /i 'I'- GRADING AND DRAINAGE PLAN 1 SCALE: 10 0 5 10 zo CATCH BASIN SCHEDULE MARK TYPE RIM ELEV INV ELEV NOTES /1 1Y' (E)=400.47 0J TYPE 1 405.0 12" (W)=400.57 REPLACE EXISTING 12" (S) = 400.57 O 54"TYPE II 405.17 = 12" (N)400.6524"(S)=400.65 FLOW CONTROL STRUCTUR 3 O 54"TYPE II 404.69 24" IN & E) = 400.65 8" (NW) = 401.53 SOLID LID 6"(W) 402.10 ® TYPE 404.60 8'(N)=401.69 - 8" (S) 401.59 OS TYPE 404.88 6'(N)=402.31 8'(S) 402.21 © 4" AREA 409.80 4' (E)=408.90 TYPICAL AT (6) LOCATIONS; DRAIN TIE INTO ROOF DRAINS 70 �J 4" AREA g08.0 4" (E) = 407.0 TYPICAL AT (4) LOCATIONS; DRAIN TIE INTO ROOF DRAINS 4" DIA PERFORATED PVC PIPE WITH 6" OF 1" MINUS GRAVEL 8" MIN FROM WOOD. ALL AROUND, WRAPPED IN SEE STRUCTURAL DRAWINGS NON -WOVEN GEOTEXTILE FABRIC, SLOPE AT 0.5% MIN. TURN DOWN PERFORATIONS AS SHOWN II ;II' 6" DOWNSPOUT TIGHTLINE TO FINISHED GRADE CONVEYANCE SYSTEM @ 0.5% MIN. PLACE NEXT TO FOOTING DRAINOR ASSHOWNON j-III- III GRADING & DRAINAGE PLAN - (CONTRACTOR MAY LOCATE ON EITHER SIDE OF FOOTING DRAIN) 00000 ° OaO° pO LINE OF MAX EXCAVATION. O O0Q'4 IF SOIL IS OVEREXCAVATED, O 0 ° 00 ° d REPLACE WITH LEAN MIX D o 0� o CONCRETE / � FOOTING i 1 1 TING AND ROOF_DRAIN SECTION 2 FOOSCALE: NTS (� STD LOCKING MH FRAME & I COVER MARKED "DRAIN" 0.5 MIN FREEBOARD iOVERFLOW IE=402.65 ,-- l I I I I I OUTLET CUTEn �IE=400.65 .. , C � ENGINEERING NEW/REPLACED IMPERVIOUS AREAS: 250 4TH AVE. S., SUITE 200 EDMONDS, WASHINGTON 98020 ROOF: 3,924 SQ FT PHONE (425) 778-8500 WALKWAYS: 236 SQ FT FAX (425) 778-5536 DRIVEWAY: 2,190 SQ FT ROW SIDEWALK: 1,360 SQ FT ROW ROAD: 806 SQ FT TOTAL 8,517 SQ FT GRADING AND DRAINAGE PLAN NOTES: 1. 3' SEPARATION 15 REQUIRED BETWEEN THE DRY UTILITIES (POWER, GAS, PHONE, CABLE, ETC.) AND SEWER, WATER, AND STORM AND 5 FROM ANY CITY MAIN LINES. 2. YARD DRAINS SHALL BE 9' z9' NDS CB (PART #900) OR APPROVED EQUAL YARD DRAINS TO HAVE A SOLID BASE. 3. TOWAND BOW REFERTO FINISHED GRADE ATTHE TOP AND GU D Q' ryc✓ BOTTOM OF THE RETAINING WALL, RESPECTIVELY. OG REFERS TO ORIGINAL GRADE, PRIOR TO CONSTRUCTION. SEE B/C5.2 FOR ADDITIONAL DETAIL 4 SHOP DRAWINGS FOR DETENTION PIPE SHALL VERIFY uVOO u u Q OOp� CAN ACCOMMODATE 72,00 LB GROSS VEHICLE WEIGHITE A AND 43,200 LB POINT LOAD FOR FIRE TRUCK AT PIPE COVER 02/ 12/ 2021 DEPICTED ON PLANS (2' MIN). 5. ROCKERY FOOTING DRAINS NEAR THE LIGHT WELLS ARE TO TIE INTO THE BUILDING FOOTING DRAINS. 6. IF THE RIM TO INVERT ELEVATION EXCEEDS 5-FEETTHEN A TYPE II MANHOLE WILL BE REQUIRED. 7. ALL PIPE SHALL BE HAVE A MINIMUM OF T OF COVER UNDER DRIVABLE SURFACES AND 1' OF COVER UNDER LANDSCAPE AREAS. PAVING LEGEND a - NEW ASPHALT o o o tz - OVERLAY EXISTING ASPHALT/UTILITY SAWCUT z tz 00 m NEW CONCRETE O m F z s F F w w d F w w w r r N z 0 0 0 s s OMuuuuuuaa RETAINING WALL NOTE: TOW AND BOW REFER TO FINISHED GRADE AT THE TOP AND BOTTOM OF THE RETAINING WALL, RESPECTIVELY. OG REFERS TO ORIGINAL GRADE, PRIOR TO CONSTRUCTION. SEE STRUCTURAL PLANS FOR ACTUAL WALL SPECS. FINISHED GRADE -\ SOLID LID z� �O '- ELEV=402.65 LADDER PER COE ELEV = 402.65 STD GU-423 / C5. e 3 LF ^ 24" N-12 \\ CONNECTOR \ BETWEEN PIPES 3 LF ^' 24" N-12 CONNECTOR II BETWEEN PIPES I I \ ELEV=400.65 LEVEL DETENTION TANK GRADING QUANTITIES TOTAL EXCAVATION (CUT) - 1,150 CU YDS TOTAL EMBANKMENT(FILL)- 50 CU YDS TOTAL 1,200 CU YDS THE QUANTITIES SHOWN ABOVE ARE FOR THE PERMIT PROCESS ONLY. THESE VALUES ARE APPROXIMATE. DO NOT USE FOR BIDDING, PAYMENT, OR ESTIMATING PURPOSES. APPROVED FOR CONSTRUCTION CITY OF EDMONDS DATE: BY: - CITY ENGNEERING DIVISION DESIGN: TAF DRAWN: JCS CHECK: JPU JOB NO: 17206.20 DATE: 07/20/17 I..I..I V Q Z_ Q V) (n i Ld O O N Do Z 0)Z 0 O Q Q Lo j N V Z Q Q N Z O C) Q Z °r-W �< 0CL w SHEET C3.1 76th Ave Townhomes - CG #17206.20 Drainage Report February 12, 2021 Section VI I, Page 5 SAMPLE ACTIVITY LOG DATE FACILITY MAINTENANCE PERFORMED RESULTS / NOTES 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com 3.2.2 Detention Tanks Detention tanks are underground storage facilities typically constructed with large diameter corrugated metal pipe. Standard detention tank details are shown in Figure 3.2.6 and Figure 3.2.7. Control structure details are shown in Section 3.2.4. Design Criteria General. Typical design guidelines are as follows: Tanks may be designed as flow -through systems with manholes in line (see Figure 3.2.6) to promote sediment removal and facilitate maintenance. Tanks may be designed as back-up systems if preceded by water quality facilities, since little sediment should reach the inlet/control structure and low head losses can be expected because of the proximity of the inlet/control structure to the tank. 2. Locate the detention tank bottom 0.5 feet below the inlet and outlet to provide dead storage for sediment. 3. Use a 36-inch minimum pipe diameter. 4. Tanks larger than 36 inches may be connected to each adjoining structure with a short section (2-foot maximum length) of 36-inch minimum diameter pipe. 5. Refer to the details of outflow control structures in Section 3.2.4. Note: Control and access manholes should have additional ladder rungs to allow ready access to all tank access pipes when the catch basin sump is filled with water (see Fri ure 3.2.9, plan view). Materials. Galvanized metals leach zinc into the environment, especially in standing water situations. This can result in zinc concentrations that can be toxic to aquatic life. Therefore, use of galvanized materials in stormwater facilities and conveyance systems is discouraged. Where other metals, such as aluminum or stainless steel, or plastics are available, they should be used. Volume III — Hydrologic Analysis and Flow Control BMPs — December 2014 3-37 Pipe material, joints, and protective treatment for tanks should be in accordance with Section 9.05 of the WSDOT/APWA Standard Specification. Structural Stability. Tanks must meet structural requirements for overburden support and traffic loading if appropriate. Accommodate H-20 live loads for tanks lying under parking areas and access roads. Design metal tank end plates for structural stability at maximum hydrostatic loading conditions. Flat end plates generally require thicker gage material than the pipe and/or require reinforcing ribs. Place tanks on stable, well consolidated native material with a suitable bedding. Do not place tanks in fill slopes, unless analyzed in a geotechnical report for stability and constructability. Buoyancy. In moderately pervious soils where seasonal ground water may induce flotation, balance buoyancy tendencies by either ballasting with backfill or concrete backfill, providing concrete anchors, increasing the total weight, or providing subsurface drains to permanently lower the ground water table. Calculations that demonstrate stability must be documented. Access. The following guidelines for access may be used. 1. The maximum depth from finished grade to tank invert should be 20 feet. 2. Position access openings a maximum of 50 feet from any location within the tank. 3. All tank access openings may have round, solid locking lids (usually 1/2 to 5/8-inch diameter Allen -head cap screws). 4. Thirty -six-inch minimum diameter CMP riser -type manholes (Figure 3.2.7) of the same gage as the tank material may be used for access along the length of the tank and at the upstream terminus of the tank in a backup system. The top slab is separated (1-inch minimum gap) from the top of the riser to allow for deflections from vehicle loadings without damaging the riser tank. 5. Make all tank access openings readily accessible by maintenance vehicles. 6. Tanks must comply with the OSHA confined space requirements, which includes clearly marking entrances to confined space areas. This may be accomplished by hanging a removable sign in the access riser(s), just under the access lid. Access Roads. Access roads are needed to all detention tank control structures and risers. Design and construct access roads as specified for detention ponds in Section 3.2.1. Right -of -Way. Right-of-way may be needed for detention tank maintenance. It is recommended that any tract not abutting public Volume III — Hydrologic Analysis and Flow Control BMPs — December 2014 3-38 right-of-way have a 15 to 20-foot wide extension of the tract to accommodate an access road to the facility. Setbacks. It is recommended that facilities be a minimum of 20 feet from any structure, property line, and any vegetative buffer required by the local government and from any septic drainfield. However, the setback requirements are generally specified by the local government, uniform building code, or other statewide regulation and may be different from those mentioned above. All facilities must be a minimum of 50 feet from the top of any steep (greater than 15%) slope. A geotechnical analysis and report must be prepared addressing the potential impact of the facility on a slope steeper than 15%. Maintenance. Build in provisions to facilitate maintenance operations into the project when it is installed. Maintenance must be a basic consideration in design and in determination of first cost. See Table 4.5.2. in Volume V for specific maintenance requirements. Volume III — Hydrologic Analysis and Flow Control BMPs December 2014 3-39 Methods of Analysis Detention Volume and Outflow inlet pipe ' where allowed) !�� A t control structure control structure (FMP•T shown) The volume and outflow design for detention tanks must be in accordance with Minimum Requirement #7 in Volume I and the hydrologic analysis and design methods in Chapter 2. Restrictor and orifice design are given in Section 3.2.4. opfional parallel tank -- - - - - - - - ---------------- - - - - -, � access risers F _ � �' ' - - - - - - - (nm spacing shown below) - - - - - - '- - i men. diameter 2' mina same as UM pipe A a� flow �' inlet pipe (flow through) access risers See Figure 2.11 type 2 CB required for flow through system only PLAN VIEW NTS `Flow -through" system shown solid. Designs tor'Ncw backup' system and paraNel tanks shown dashed 2' min. diameter air vent 1W max pipe welted to tank MY max access risers (required it no access --� ` riseron.tank) 0.5' sediment storage level W min. \detention tank diameter (typ) size as required NOTE: All metal parts corrosion resistant. Steel parts galvanized and asphalt coated (Treatment 1 or better). SECTION A -A NTS "Flow through' system shown solid_ Figure 3.2.6 - Typical Detention Tank Volume III — Hydrologic Analysis and Flow Control BMPs — December 2014 3-40 standard type 2-60" diam. CB concrete top slab 36" CM P riser standard locking M.H. frame & cover compacted pipe bedding M.H. steps 12" C.C. weld or bolt standard M.H. steps PLAN NTS I SECTION NTS frame locking lid (marked "DRAIN' mounted over 24" diam. eccentric opening maintain Is gap between bottom of slab & top of riser — provide pliable gasket to exclude dirt riser, 36" diam. min., same material & gage as tank welded or fused to tank detention tank Notes: 1. Use adjusting blocks as required to bring frame to grade. 2. All materials to be aluminum or galvanized and asphalt coated (Treatment 1 or better). 3. Must be located for access by maintenance vehicles. 4. May substitute WSDOT special Type IV manhole (RCP only). Figure 3.2.7 - Detention Tank Access Detail 3 .3 et �ti r6 V It D en' n v Its re x-s pe n gr nd ora fa ' iti t 'all co ruc d w' r ' fo ed ncr e. sta ar ete io au det ' is OW n F' ur .2. . C tro tru re etai ar o i ect' n 3. D Sig Cri ria a ral cal esi gu' eli s ar as to Volume III — Hydrologic Analysis and Flow Control BMPs — December 2014 3-41 p ' ab O at' al M • El' in u e to asadi ar s t tose er, oui at , or rfa w er.: / onv u e to isc rg to an' ry we f a weal by,tlie to se er tho y, to e pp e ea en • Ob in ro iat tat nd oca e is th e d' cha es.:" e m en d dit' nal pe do al P . At in rcX an du ial cil' 'es, nd t a ry of ast at dis ar co ec ns to o dra' s a to rf e w er fol ws• !` • on ct iel su y ui in , pa cu y der it gs 'nd o er i us al as to to rai Er b ' di a pa d sur ces of h e t e j 'n t pu is s rm rai ). • ur' g n -st er nd' on 'ns t e s rm ai or 'n- s ter isc rge . Re rd e 1 ati so 11 n-s rm ater is ar I ud 11 rm' ed 'sch ge • us 1, ep e a ap ea ar . S w th a he o I o atio of o ew s, s it se ers nd er ed d np i d ' ch es er' p os ay us 1. e re rds s ch pi g s e ics o f of n n s' e s er on do an ho the o e ap. on ' er in in e, e, o the Ica al s t s t et co ec 'ons etw en o c ve nc ys s .. (e , p ces a a sto w er). de rab , c duc 'TV sp do of e s rm rai an ec t fo ge v' eot e. om re e o se d 1 ati s o co ect' ns ith e ' o do o e ap d r is e ap co in . N e s pe co ecf ns at e i ons' ten it e eld ry • ent' a co ect' ns st er or su ace at an tak th cti s s cif d a ve a is e $•VIPs LZ S411 BMPs for Landscaping and Lawn/ Vegetation Management Description of Pollutant Sources: Landscaping can include grading, soil transfer, vegetation removal, pesticide and fertilizer applications, and watering. Stormwater contaminants include toxic organic compounds, heavy metals, oils, total suspended solids, coliform bacteria, fertilizers, and pesticides. 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 Volume IV - Souree Control BMPs — Deeember 2014 2-21 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. Pollutant Control Approach: Control of fertilizer and pesticide applications, soil erosion, and site debris to prevent contamination of stormwater. Develop and implement an Integrated Pest Management Plan (IPM) and use pesticides only as a last resort. Carefully apply pesticides/ herbicides, in accordance with label instructions. Maintain appropriate vegetation, with proper fertilizer application where practicable, to control erosion and the discharge of stormwater pollutants. Where practicable grow plant species appropriate for the site, or adjust the soil properties of the subject site to grow desired plant species. Applicable Operational BMPs for Landscaping: • Install engineered soil/landscape systems to improve the infiltration and regulation of stormwater in landscaped areas. Do not dispose of collected vegetation into waterways or storm sewer systems. Recommended Additional Operational BMPs for Landscaping: • Conduct mulch -mowing whenever practicable • Dispose of grass clippings, leaves, sticks, or other collected vegetation, by composting, if feasible. • Use mulch or other erosion control measures on soils exposed for more than one week during the dry season or two days during the rainy season. • Store and maintain appropriate oil and chemical spill cleanup materials in readily accessible locations when using oil or other chemicals. Ensure that employees are familiar with proper spill cleanup procedures. • Till fertilizers into the soil rather than dumping or broadcasting onto the surface. Determine the proper fertilizer application rate for the types of soil and vegetation encountered. • Till a topsoil mix or composted organic material into the soil to create a well -mixed transition layer that encourages deeper root systems and drought -resistant plants. • Use manual and/or mechanical methods of vegetation removal rather than applying herbicides, where practical. Volume IV - Source Control BMPs — December 2014 2-22 Applicable Operational BMPs for the Use of Pesticides: • Develop and implement an IPM (See section on IPM in ,4pplicable Operational BM Ps for Ve,,etation Manyems) and use pesticides only as a last resort. • Implement a pesticide -use plan and include at a minimum: a list of selected pesticides and their specific uses; brands, formulations, application methods and quantities to be used; equipment use and maintenance procedures; safety, storage, and disposal methods; and monitoring, record keeping, and public notice procedures. All procedures shall conform to the requirements of Chapter 17.21 RCW and Chapter 16-228 WAC (Appendix IV-D R.7). • Choose the least toxic pesticide available that is capable of reducing the infestation to acceptable levels. The pesticide should readily degrade in the environment and/or have properties that strongly bind it to the soil. Conduct any pest control activity at the life stage when the pest is most vulnerable. For example, if it is necessary to use a Bacillus thuringiens application to control tent caterpillars, apply it to the material before the caterpillars cocoon or it will be ineffective. Any method used should be site -specific and not used wholesale over a wide area. • Apply the pesticide according to label directions. Do not apply pesticides in quantities that exceed manufacturer's instructions. • Mix the pesticides and clean the application equipment in an area where accidental spills will not enter surface or ground waters, and will not contaminate the soil. • Store pesticides in enclosed areas or in covered impervious containment. Do not discharge pesticide contaminated stormwater or spills/leaks of pesticides to storm sewers. Do not hose down the paved areas to a storm sewer or conveyance ditch. Store and maintain appropriate spill cleanup materials in a location known to all near the storage area. • Clean up any spilled pesticides. Keep pesticide contaminated waste materials in designated covered and contained areas. • The pesticide application equipment must be capable of immediate shutoff in the event of an emergency. • Spraying pesticides within 100 feet of open waters including wetlands, ponds, and rivers, streams, creeks, sloughs and any drainage ditch or channel that leads to open water may have additional regulatory requirements beyond just following the pesticide product label. Additional requirements may include: • Obtaining a discharge permit from Ecology. • Obtaining a permit from the local jurisdiction. • Using an aquatic labeled pesticide. Volume IV - Source Control BMPs — December 2014 2-23 • Flag all sensitive areas including wells, creeks, and wetlands prior to spraying. • Post notices and delineate the spray area prior to the application, as required by the local jurisdiction or by Ecology. Conduct spray applications during weather conditions as specified in the label direction and applicable local and state regulations. Do not apply during rain or immediately before expected rain. Recommended Additional Operational BMPs for the use of pesticides: Consider alternatives to the use of pesticides such as covering or harvesting weeds, substitute vegetative growth, and manual weed control/moss removal. • Consider the use of soil amendments, such as compost, that are known to control some common diseases in plants, such as Pythium root rot, ashy stem blight, and parasitic nematodes. The following are three possible mechanisms for disease control by compost addition (USEPA Publication 530-F-9-044): 1. Successful competition for nutrients by antibiotic production; 2. Successful predation against pathogens by beneficial microorganism; and 3. Activation of disease -resistant genes in plants by composts. Installing an amended soil/landscape system can preserve both the plant system and the soil system more effectively. This type of approach provides a soil/landscape system with adequate depth, permeability, and organic matter to sustain itself and continue working as an effective stormwater infiltration system and a sustainable nutrient cycle. • Once a pesticide is applied, evaluate its effectiveness for possible improvement. Records should be kept showing the effectiveness of the pesticides considered. Develop an annual evaluation procedure including a review of the effectiveness of pesticide applications, impact on buffers and sensitive areas (including potable wells), public concerns, and recent toxicological information on pesticides used/proposed for use. If individual or public potable wells are located in the proximity of commercial pesticide applications, contact the regional Ecology hydrogeologist to determine if additional pesticide application control measures are necessary. • Rinseate from equipment cleaning and/or triple -rinsing of pesticide containers should be used as product or recycled into product. For more information, contact the Washington State University (WSU) Extension Home -Assist Program, (253) 445-4556, or Bio-Integral Resource Center (BIRC), P.O. Box 7414, Berkeley, CA.94707, or EPA to Volume IV - Source Control BMPs — December 2014 2-24 obtain a publication entitled "Suspended, Canceled, and Restricted Pesticides " which lists all restricted pesticides and the specific uses that are allowed. Applicable Operational BMPs for Vegetation Management: Use at least an eight -inch "topsoil' layer with at least 8 percent organic matter to provide a sufficient vegetation -growing medium. Amending existing landscapes and turf systems by increasing the percent organic matter and depth of topsoil can substantially improve the permeability of the soil, the disease and drought resistance of the vegetation, and reduce fertilizer demand. This reduces the demand for fertilizers, herbicides, and pesticides. Organic matter is the least water-soluble form of nutrients that can be added to the soil. Composted organic matter generally releases only between 2 and 10 percent of its total nitrogen annually, and this release corresponds closely to the plant growth cycle. Return natural plant debris and mulch to the soil, to continue recycling nutrients indefinitely. Select the appropriate turfgrass mixture for the climate and soil type. Certain tall fescues and rye grasses resist insect attack because the symbiotic endophytic fungi found naturally in their tissues repel or kill common leaf and stem -eating lawn insects. However, they do not, repel root -feeding lawn pests such as Crane Fly larvae, and are toxic to ruminants such as cattle and sheep. The fungus causes no known adverse effects to the host plant or to humans. Endophytic grasses are commercially available; use them in areas such as parks or golf courses where grazing does not occur. Local agricultural or gardening resources such as Washington State University Extension office can offer advice on which types of grass are best suited to the area and soil type. • Use the following seeding and planting BMPs, or equivalent BMPs to obtain information on grass mixtures, temporary and permanent seeding procedures, maintenance of a recently planted area, and fertilizer application rates: Temporary and Permanent Seeding, Mulching, Plastic Covering, and Sodding as described in Volume II. Adjusting the soil properties of the subject site can assist in selection of desired plant species. For example, design a constructed wetland to resist the invasion of reed canary grass by layering specific strata of organic matters (e.g., composted forest product residuals) and creating a mildly acidic pH and carbon -rich soil medium. Consult a soil restoration specialist for site -specific conditions. • Aerate lawns regularly in areas of heavy use where the soil tends to become compacted. Conduct aeration while the grasses in the lawn are growing most vigorously. Remove layers of thatch greater than 3/4-inch deep. Volume IV - Source Control BMPs — December 2014 2-25 Mowing is a stress -creating activity for turfgrass. Grass decreases its productivity when mown too short and there is less growth of roots and rhizomes. The turf becomes less tolerant of environmental stresses, more disease prone and more reliant on outside means such as pesticides, fertilizers, and irrigation to remain healthy. Set the mowing height at the highest acceptable level and mow at times and intervals designed to minimize stress on the turf. Generally mowing only 1/3 of the grass blade height will prevent stressing the turf. Irrigation: The depth from which a plant normally extracts water depends on the rooting depth of the plant. Appropriately irrigated lawn grasses normally root in the top 6 to 12 inches of soil; lawns irrigated on a daily basis often root only in the top 1 inch of soil. Improper irrigation can encourage pest problems, leach nutrients, and make a lawn completely dependent on artificial watering. The amount of water applied depends on the normal rooting depth of the turfgrass species used, the available water holding capacity of the soil, and the efficiency of the irrigation system. Consult with the local water utility, Conservation District, or Cooperative Extension office to help determine optimum irrigation practices. Fertilizer Management: Turfgrass is most responsive to nitrogen fertilization, followed by potassium and phosphorus. Fertilization needs vary by site depending on plant, soil, and climatic conditions. Evaluation of soil nutrient levels through regular testing ensures the best possible efficiency and economy of fertilization. For details on soils testing, contact the local Conservation District, a soils testing professional, or a Washington State University Extension office. Apply fertilizers in amounts appropriate for the target vegetation and at the time of year that minimizes losses to surface and ground waters. Do not fertilize when the soil is dry. Alternatively, do not apply fertilizers within three days prior to predicted rainfall. The longer the period between fertilizer application and either rainfall or irrigation, the less fertilizer runoff occurs. Use slow release fertilizers such as methylene urea, IDBU, or resin coated fertilizers when appropriate, generally in the spring. Use of slow release fertilizers is especially important in areas with sandy or gravelly soils. Time the fertilizer application to periods of maximum plant uptake. Ecology generally recommends application in the fall and spring, although Washington State University turf specialists recommend four fertilizer applications per year. Volume IV - Source Control BMPs — December 2014 2-26 • Properly trained persons should apply all fertilizers. Apply no fertilizer at commercial and industrial facilities, to grass swales, filter strips, or buffer areas that drain to sensitive water bodies unless approved by the local jurisdiction. Integrated Pest Management An IPM program might consist of the following steps: Step 1: Correctly identify problem pests and understand their life cycle Step 2: Establish tolerance thresholds for pests. Step 3: Monitor to detect and prevent pest problems. Step 4: Modify the maintenance program to promote healthy plants and discourage pests. Step 5: Use cultural, physical, mechanical or biological controls first if pests exceed the tolerance thresholds. Step 6: Evaluate and record the effectiveness of the control and modify maintenance practices to support lawn or landscape recovery and prevent recurrence. For an elaboration of these steps, refer to Appendix IV-F. 5412`BM.Ps for Loading and Unloadin Ar s ..ferLiqui: or S'blid Material ; Dt ri io f P ut t ur s: era rs is y c du og/ oa g li d a s d er' s a 'nd ria nd c in cia aci ' ies s pi an ec in , ou de ora in are , et . ria tra fe d c in de ro cts aw ate Is e di pr uc , w e ter' s, els, cra et s, e . L s d sp' so el ,oil , po er or ics ea m als alt aci , al lis c. rin ra er ay us to a co a ati . S is om h ra c li br s ea in on obl a oa g cks Po to C tr Ap oa ver nd nt ' th oa 'ng/ to in ea er nec sar to eve ru on st inw er d of f / c a at -to w er. A is a er io B s• At L di / U oa ' g ea sig ' is a un f d ris an cu lat at o si , un ve d o ng/ to in re a . S ep ese rf es qu tly re ove ose at ial at c I ont in e st ter. we ar s to or ily ve d a r r ov of e c ta' ers ogs r o er at al ver' g t gr nd ace rip ans or o er pr ria to or co ai en ev' e, a to do w re 1 s sp' s y o ur ch ho co ec 'ons ose eel nd le oz s. wa us dri a wh m in nd Volume IV - Source Control BMPs — December 2014 2-27 No. 3 — Closed Detention Systems (Tanks/Vaults) Maintenance Defect Conditions When Maintenance is Needed Results Expected Component When Maintenance is Performed Storage Area Plugged Air Vents One-half of the cross section of a vent is Vents open and blocked at any point or the vent is damaged. functioning. Debris and Sediment Accumulated sediment depth exceeds 10% All sediment and of the diameter of the storage area for 1/2 debris removed from length of storage vault or any point depth storage area. exceeds 15% of diameter. (Example: 72-inch storage tank would require cleaning when sediment reaches depth of 7 inches for more than 1/2 length of tank.) Joints Between Any openings or voids allowing material to All joint between Tank/Pipe Section be transported into facility. tank/pipe sections (Will require engineering analysis to are sealed. determine structural stability). Tank Pipe Bent Out Any part of tank/pipe is bent out of shape Tank/pipe repaired or of Shape more than 10% of its design shape. (Review replaced to design. required by engineer to determine structural stability). Vault Structure Cracks wider than 1/2-inch and any Vault replaced or Includes Cracks in evidence of soil particles entering the repaired to design Wall, Bottom, structure through the cracks, or specifications and is Damage to Frame maintenance/inspection personnel structurally sound. and/or Top Slab determines that the vault is not structurally sound. Cracks wider than 1/2-inch at the joint of any No cracks more than inlet/outlet pipe or any evidence of soil 1/4-inch wide at the particles entering the vault through the walls. joint of the inlet/outlet pipe. Manhole Cover Not in Place Cover is missing or only partially in place. Manhole is closed. Any open manhole requires maintenance. Locking Mechanism Mechanism cannot be opened by one Mechanism opens Not Working maintenance person with proper tools. Bolts with proper tools. into frame have less than 1/2 inch of thread (may not apply to self-locking lids). Cover Difficult to One maintenance person cannot remove lid Cover can be Remove after applying normal lifting pressure. Intent removed and is to keep cover from sealing off access to reinstalled by one maintenance. maintenance person. Ladder Rungs Unsafe Ladder is unsafe due to missing rungs, Ladder meets design misalignment, not securely attached to standards. Allows structure wall, rust, or cracks. maintenance person safe access. Catch Basins See "Catch Basins" See "Catch Basins" (No. 5). See "Catch Basins" (No. 5) (No. 5). Volume V — Runoff Treatment BMPs — December 2014 4-36 No. 4 - Control Structure/Flow Restrictor Maintenance Defect Condition When Maintenance is Needed Results Expected Component When Maintenance is Performed General Trash and Debris Material exceeds 25% of sump depth or 1 Control structure (Includes Sediment) foot below orifice plate. orifice is not blocked. All trash and debris removed. Structural Damage Structure is not securely attached to Structure securely manhole wall. attached to wall and outlet pipe. Structure is not in upright position (allow up Structure in correct to 10% from plumb). position. Connections to outlet pipe are not watertight Connections to outlet and show signs of rust. pipe are water tight; structure repaired or replaced and works as designed. Any holes --other than designed holes --in the Structure has no structure. holes other than designed holes. Cleanout Gate Damaged or Missing Cleanout gate is not watertight or is missing. Gate is watertight and works as designed. Gate cannot be moved up and down by one Gate moves up and maintenance person. down easily and is watertight. Chain/rod leading to gate is missing or Chain is in place and damaged. works as designed. Gate is rusted over 50% of its surface area. Gate is repaired or replaced to meet design standards. Orifice Plate Damaged or Missing Control device is not working properly due to Plate is in place and missing, out of place, or bent orifice plate. works as designed. Obstructions Any trash, debris, sediment, or vegetation Plate is free of all blocking the plate. obstructions and works as designed. Overflow Pipe Obstructions Any trash or debris blocking (or having the Pipe is free of all potential of blocking) the overflow pipe. obstructions and works as designed. Manhole See "Closed See "Closed Detention Systems" (No. 3). See "Closed Detention Systems" Detention Systems" (No. 3). (No. 3). Catch Basin See "Catch Basins" See "Catch Basins" (No. 5). See "Catch Basins" (No. 5). (No. 5). Volume V — Runoff Treatment BMPs — December 2014 4-37 No. 5 — Catch Basins Maintenance Defect Conditions When Maintenance is Needed Results Expected When Component Maintenance is performed General Trash & Trash or debris which is located immediately No Trash or debris located Debris in front of the catch basin opening or is immediately in front of blocking inletting capacity of the basin by catch basin or on grate more than 10%. opening. Trash or debris (in the basin) that exceeds 60 No trash or debris in the percent of the sump depth as measured from catch basin. the bottom of basin to invert of the lowest pipe into or out of the basin, but in no case less than a minimum of six inches clearance from the debris surface to the invert of the lowest pipe. Trash or debris in any inlet or outlet pipe Inlet and outlet pipes free blocking more than 1/3 of its height. of trash or debris. Dead animals or vegetation that could No dead animals or generate odors that could cause complaints vegetation present within or dangerous gases (e.g., methane). the catch basin. Sediment Sediment (in the basin) that exceeds 60 No sediment in the catch percent of the sump depth as measured from basin the bottom of basin to invert of the lowest pipe into or out of the basin, but in no case less than a minimum of 6 inches clearance from the sediment surface to the invert of the lowest pipe. Structure Top slab has holes larger than 2 square Top slab is free of holes Damage to inches or cracks wider than 1/4 inch and cracks. Frame and/or Top Slab (Intent is to make sure no material is running into basin). Frame not sitting flush on top slab, i.e., Frame is sitting flush on separation of more than 3/4 inch of the frame the riser rings or top slab from the top slab. Frame not securely and firmly attached. attached Fractures or Maintenance person judges that structure is Basin replaced or repaired Cracks in unsound. to design standards. Basin Walls/ Bottom Grout fillet has separated or cracked wider Pipe is regrouted and than 1/2 inch and longer than 1 foot at the secure at basin wall. joint of any inlet/outlet pipe or any evidence of soil particles entering catch basin through cracks. Settlement/ If failure of basin has created a safety, Basin replaced or repaired Misalignment function, or design problem. to design standards. Vegetation Vegetation growing across and blocking more No vegetation blocking than 10% of the basin opening. opening to basin. Vegetation growing in inlet/outlet pipe joints No vegetation or root that is more than six inches tall and less than growth present. six inches apart. Contamination See "Detention Ponds" (No. 1). No pollution present. and Pollution Volume V — Runoff Treatment BMPs — December 2014 4-38 No. 5 — Catch Basins Maintenance Defect Conditions When Maintenance is Needed Results Expected When Component Maintenance is performed Catch Basin Cover Not in Cover is missing or only partially in place. Catch basin cover is Cover Place Any open catch basin requires maintenance. closed Locking Mechanism cannot be opened by one Mechanism opens with Mechanism maintenance person with proper tools. Bolts proper tools. Not Working into frame have less than 1/2 inch of thread. Cover Difficult One maintenance person cannot remove lid Cover can be removed by to Remove after applying normal lifting pressure. one maintenance person. (Intent is keep cover from sealing off access to maintenance.) Ladder Ladder Rungs Ladder is unsafe due to missing rungs, not Ladder meets design Unsafe securely attached to basin wall, standards and allows misalignment, rust, cracks, or sharp edges. maintenance person safe access. Metal Grates Grate opening Grate with opening wider than 7/8 inch. Grate opening meets (If Applicable) Unsafe design standards. Trash and Trash and debris that is blocking more than Grate free of trash and Debris 20% of grate surface inletting capacity. debris. Damaged or Grate missing or broken member(s) of the Grate is in place and Missing. grate. meets design standards. Volume V — Runoff Treatment BMPs — December 2014 4-39