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APPROVED STM RESUB3 BLD2023-0799+Storm_Drainage_Report+9.3.2024_9.52.07_AM+4476079C � ENGINEERING civil & structural engineering & planning DRAINAGE REPORT Cochran Residence 8475 Frederick Place BLD2023-0799 Edmonds, WA 98026 250 4th Ave S Ste 200 Edmonds, WA 98020 Phone: (425) 778-8500 Fax: (425) 778-5536 Applicant: Ryan & Syndey Cochran RESUB 902 N 8151, Seattle WA, 98103 Sep 03 2024 425.308.3872 CITY OF EDMONDS ryanrcochran@gmail.com DEVELOPMENT SERVICES DEPARTMENT Contact: Sarah Thompson 23020 Edmonds Way #113, Edmonds WA, 98020 206.542.3734 sarah@h2darchitects.com Contractor: TBD Project Engineer: Greg Guillen, PE 250 4th Ave S, Suite 200, Edmonds WA, 98020 425.778.8500 grego@cgengineering.com 0611612023 0212312 024 0512812024 Submittal Date: 0812312024 CG Project No.: 23038.20 COMPLIES WITH APPLICABLE CITY STORMWATER CODE 10/07/2024 Cochran Residence - CG #23038.20 August 23, 2024 Drainage Report Section I, Page 2 Contents SectionI — Project Site Maps.......................................................................................................... 3 Section II — Project Overview.......................................................................................................... 7 Section III — Off -Site Analysis........................................................................................................ 14 Section IV — Permanent Stormwater Control Plan....................................................................... 21 Section V —Construction Stormwater Pollution Prevention Plan ................................................ 33 Section VI — Special Reports and/or Studies................................................................................. 37 Section VI I — Other Permits........................................................................................................... 38 Section VIII — Bond Quantities, Declaration of Covenant, & Operation and Maintenance Manual ....................................................................................................................................................... 39 Appendix A —Attached Reports.................................................................................................... 44 Appendix B — Maintenance Covenant.......................................................................................... 45 250 4th Avenue South, Suite 200 CM Edmonds, WA 98020 2 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com Cochran Residence - CG #23038.20 Drainage Report August 23, 2024 Section I, Page 3 Section I — Project Site Maps Please see below for the attached project site maps. 250 4th Avenue South, Suite 200 CM Edmonds, WA 98020 3 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com -jj� City of Edmonds Map Title — -- �- �_ ----�� p03�1 APPROX. FLOW r' Legend f Wo DIRECTION OF _ a INFILTRATED 00i ` 00 RUNOFF. 00 4 _ Storm Catch Basins o Edmonds cc Ln o O l-n O M PROJECT SITE I w � N p Private Infiltration Storm Manholes 00 p Edmonds II O Private y 8475 9 Infiltration I Detention Facilities I Culvert ' <all other values> . Yes - — — Co o Facility Feature co APPROX. LOCATION N Wo N = Creeks 00 OF PROPOSED O W Storm Line O tT INFIL. TRENCH. — <all other values> 8522 No, BNSF; No, COUNTY; No, LYNI MOUNTLAKE TERRACE; No, POF SHORELINE; No, STATE; No, WO, — Yes, EDMONDS; Yes, PRIVATE; 1 Facility Lines Perrinville Creek Storm Ditch - - Sections Boundary Sections Snohomish i_ Edmonds Boundary County Park ArcSDE.GIS.PROPERTY BUILDING 1: 1,516 O ArrSDF_GIS.STRFFT rFNTFRLINF! Notes 0 126.30 2S2.6 Feet 188.1 This ma is a user 2,257 P generated static output from an Internet mapping site and is for B P PP g reference only. Data layers that appear on this map may or may not be accurate, WGS_1984_Web-Mercator _Auxiliary -Sphere current, or otherwise reliable. © City of Edmonds THIS MAP IS NOT TO BE USED FOR DESIGN OR CONSTRUCTION DISCHARGE POOL POOL FOOTING DRAIN PROPOSED AREA DRAIN FOR PROPOSED 9 LF - 4" PVC FOOTING DRAINS TO LINES (PERF PIPE AROUND CONCRETE PATIO PATIO RUNOFF. TIE CONCRETE PATIO @ 0.5% MIN 4'x4'x4' DRYWELL LOT 1 POOL WALLS AND SOLID FIFE: 51.80 INTO ROOF DRAIN LINE FENCE CDR FFE: 52.30 PLN-2017-002 • PVC FOR CONVEYANCE) A0.0 OF LINE PROP COR FROM 4 LF 3.7' TALL MAX SDCO, TYP RETAR/CAP HEIGHT CONCRETE 0. D IRON PIPE Nz _ GRADE POOL DECK TO °'°, OF LINE & _� - i 1 RETAINING WALL 0.41'S F M PROP CDR ` N 85°0 182.00' i FLOW TOWARDS 8" SE `� ��ROOF DRAIN �� SDCO, TYP AREA DRAIN AS INDICATED FOOTING DRAIN (PERF \ FENCE BY FLOW ARROWS PIPE AROUND BUILDING I II �� -� 12" AREA DRAIN AND WALLS AND SOLID I _ / WITH OPEN GRATE PROPOSED POOL DECK Fo;w_ i PVC FOR CONVEYANCE) RIM: 51.80 FIFE: 46.70 / 46.90 SDCO, TYP l IE (TRENCH DRAIN, E): 51.30 PROPOSED POOL �` -- / I IE (6", SE): 48.30 46.90 12" AREA DRAIN �� / TRENCH DRAIN TO i PROPOSED PARTIALLY -143 SF OF UNCOVERED WITH OPEN GRATE 46.7 COLLECT DRIVEWAY �COVERED DECK DECK TO BE DRIP THROUGH I � RIM: 46.57 46.87 FIFE: 51.80 RUNOFF IE (6" SW): 43.57 p9 46.80 j 46.67 -102 - _ / I Fj.fF Z 10 LF - 6" PVC @ 28.0% j IN 1 / / / TP 2 I o SDCO, TYP 46.77 46.70 PLANTER TYPE I CB, SOLID LID °' ZA SDCO PROPOSED HOUSE i _` TP-2 RIM: 45.7 Z� FIFE: 51.80 a PROPOSED CONCRETE TYP IE (6" NE, E): 40.80 A 46 60 SDCO, UPPER FLOOR FIFE: 62.10'jl a ¢�' o DRIVEWAY AND PARKING IE (4"E): 40.80 46.70 TYP LOWER FLOOR FIFE: 42.40' I a o FIFE: 51.80 IE (6" SW): 40.70 I "d-,0= I 51.90 IE (6" W, OVERFLOW): 41.30 o 46.67 TP-1 / AREA DRAIN FOR BASEMENT i PROPOSED DRIVEWAY BOT: 38.70 g 46.70 ACCESS RUNOFF. TIE INTO ROOF DRAIN LINE i SDCO, TYP DISCHARGE 1.2' I °� a i a� „ / _ J 12 AREA DRAIN OVERFLOW TO I 51.80 �' - -e WITH OPEN GRATE 4'x4'x4' DRYWELL I / FENCE RIM: 51.60 27 LF - 6" PVC �� _ f�/I IAA i ry a- ° II IE (6" SE): 48.10 @ 0.5/o MIN 1 I �P SDCO, TYP SDCO, TYP II' 4" OBSERVATION FODUN4 TACK/LEAD ::.. � / PROPOSED ACCESS 1 NCF END o.,'w o.os•N of LINE & WELL, TYP OFF I :::: P• qj 16 LF - 4" PVC TO BASEMENT I OM PROP CDR 0.,2'W FROM PROP CDR RIM:45.50 o - - ENCDR @ 0.5/o MIN FIFE: 42.40 & 3 9'NFROM LINE/ SDCO, TYP PROP C /� / - TOTAL PROJECT AREA: 0.31 ACRES RIM:45.50 �S1P i - -r�5o9'00" E 1a2oo' I � _ *TOTAL HARD SURFACE: 8,294 SF IE (6" PERF PIPE): 39.30�r� 15 LF ^ 6" PVC @ 0.5% MIN �PROPOSED PGIS: 1,657 SF --- PROPOSED PGPS: 0 SF I\ EXISTING UNMANAGED HARD SURFACE: 0 SF 8 LF ^ 6" PVC @ 17.5% MIN W ice- 6 LF ___-1 _ -- FOUND IRON PIP 29.0' x 9.5' x 3.0' 0.,,•W OF LINE \ EXISTING TOTAL DISTURBED AREA: 0.31 ACRES 0.18'S FROM PROP OR z A W 3SC0 W/ COVERT - 6" PVC AVERAGE SLOPE: 10% INFILTRATION TRENCH N� �� \ °°"°RE�3�` W- I @ 0.5% MIN ESTIMATED ULTIMATE INFILTRATION RATE: 10 INCH/HR TOP: 41.30 o_ I £ / / / n' - W RIM: 4415' I VV APPROX. LOCATION �� D r ^ I � I/ I p L \ - VY PER RECORDS (TYP) tr-( r\ 1 -- NRCS SOIL GROUP: ALDERWOOD-URBAN LAND COMPLEX BOT: 38.30 W �I GROUNDWATER: 37.30±ALL AREAS EXCEPT THE OFFSITE DRIVEWAY APRON (SEE GEOTECH REPORT) GRADING AND DRAINAGE PLAN (216 SF) AND SLATTED DRIP THROUGH DECK (143 SF) 144.54' fi- WILL BE COLLECTED AND ROUTED TO PROPOSED = AREAS FLOWING TO INFIL. TRENCH (-7,935 SF) '4mwtSCALE: 1" = 20' INFILTRATION TRENCH. PLEASE SEE CIVIL PLANS. E5$TrpS 20 0 10 20 40 40- PDS Map Portal Snohomish County Pianmog & Development Services Map Title 1 /4/2024 190.4 0 95.22 190.4 Feet All maps, data, and information set forth herein ("Da a"), are for illustrative purposes only and are not to be considered an official citation to, or representation of, the Snohomish County Code. Amendments and updates to the Data, together with other applicable County Code provisions may apply which are not depicted herein. Snohomish County makes no.—or--ty concerning the content accuracy, currency, ompleta— or quality of the Data contained herein and expressly disclaims any warranty of merchantability or fitness for any particular purpose. All persons accessing or otherwise using this Data assume all responsibility for use thereof and agree to hold Snohomish County Projection: NAD_1983_StatePlane_Washington North_FIPS_4601_Feet harmless from and api-any damages,loss, claim or liability a,ising —of any error, defect or omission contained within aid Data. Planning and Development Services, Snohomish Count =hinegton SW,e .,,Ch. -56nRCW, p,hibrcs state and local agen es from providing ac—tnli,ts of individuals intended for aee for g p y rcial purposes and, thus, o c mme cial use may be made of any Data comprising lists of individuals contained herein. r-"< r-- f I Legend SW quad NW quad NE quad SE quad Snohomish County Tax Parcels © Airports to> Fire Stations l:l Hospitals a Police Stations ® Schools fn Bus Stops ® Community Transit Park and Rid( © Ferry Terminals Buildings - Ferry Routes - County Lines 600 - 1,200 Stillaguamish Indian Reservation Boundary Tulalip Indian Reservation Boundary Cities 600 - 1,200 Streets 600 - 1,200 Interstate State Route Ramps Major Road; Major Road Minor Road; Minor Road Access Road Water Features County Parks 600 - 1,200 Cities 600 - 1,200 National Forest 600 - 1,200 1: 1,143 Notes This map was automatically generated using Geocortex Essentials. Cochran Residence - CG #23038.20 August 23, 2024 Drainage Report Section II, Page 7 Section II — Project Overview Section I Summary Overview Existing Condition Developed Condition Minimum Requirements Overview This drainage report has been written for a new single family home on a 0.46 ac lot located at 8475 Frederick Place in Edmonds, WA (TPN: 00594400006402). The building will have a roof area of approximately 4,714 sf (0.108 ac) and the project's area of disturbance will total approximately 0.31 ac. The development also consists of a new driveway, new patios, and a new swimming pool. The site is currently undeveloped and consists of pasture and forested areas. The project will meet minimum requirements 1 through 9 of the 2019 Department of Ecology Stormwater Management Manual for Western Washington (herein referred to as the DOE Manual) and comply with those requirements as modified in the Edmonds Community Development Code Chapter 18.30 (herein referred to as ECDC 18.30) and the December 2022 Addendum to ECDC 18.30 (herein referred to as the Edmonds Stormwater Addendum). Existing Condition The site is part of a 0.46-acre parcel which is elongated with the longer side being aligned parallel with Frederick Place. The area of work is located centrally. The site soil primarily consists of fine to medium sand with varying amounts of silt extending to about 5'-9.5' below grade. The top of the groundwater table was located at 8.7' below grade during the time of the testing in early February. The design infiltration rate was calculated to be approximately 10 in/hr. More about site soils can be found in the Geotechnical Engineering Report by NGA in Section V. The site is bordered by Frederick Place to the south, and residential properties to the north, west, and east. A water meter and sewer cleanout connection to mains are provided along the south property line, and runoff from the site sheet flows to the northwest. Developed Condition The project consists of the construction of a 4,714-sf home along with an associated driveway, patios, and pool totaling 8,078 sf new and replaced hardscape onsite. The total new plus replaced impervious area (including ROW) is 8,328 sf (0.19 ac). Disturbance will affect 0.31 ac of the project parcel. Site runoff will be routed to an onsite infiltration trench. The proposed impervious areas (including ROW) are as follows: Roof: 4,714 sf (0.108 ac) Driveway: 1,441 sf (0.033 ac) *New Patios/Walkways: 1,431 sf (0.033 ac) New Swimming Pool: 492 sf (0.011 ac) 250 4th Avenue South, Suite 200 Edmonds, WA 98020 7 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com Cochran Residence - CG #23038.20 August 23, 2024 Drainage Report Section II, Page 8 ROW Dr Total: 216 sf (0.005 ac) 8,294 sf (0.190 ac) *Approximately 143 sf of the walkway areas shown on site consist of slatted drip through deck areas confirmed with the client. These areas were included in the hardscape calculations, however, are to sheet flow through the deck slats. The new and replaced pollution -generating impervious areas are as follows: Concrete Driveway: 1,657 sf (0.038 ac) Total: 1,657 sf (0.038 ac) The building roof will not be considered as pollution -generating as the roof will be made with non - leachable material. Total parcel area: 0.46 ac Total hard surfaces: 0.190 ac PGHS/PGIS: 0.038 ac Total disturbed area: 0.31 ac kI 7� i rr rr - — ----- PROJECT SIT 1•y (OVERALL 1 PROPERTY Figure II-1. Vicinity map (from Edmonds GIS). Snohomish Coungi Park 250 4th Avenue South, Suite 200 Edmonds, WA 98020 8 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com Cochran Residence - CG #23038.20 August 23, 2024 Drainage Report Section II, Page 9 Figure II-2. Map with storm pipe material (from Edmonds GIS). 250 4th Avenue South, Suite 200 CM Edmonds, WA 98020 9 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com Cochran Residence - CG #23038.20 August 23, 2024 Drainage Report Section 11, Page 10 Figure II-3. Aerial Photograph (from Edmonds GIS). Minimum Requirements Stormwater requirements were determined per the Edmonds Stormwater Addendum, ECDC 18.30, and the DOE Manual. This report is based on the steps recommended in Chapter 7 of the Edmonds Stormwater Addendum and Section 3.1.7 of the DOE Manual. The project is classified as a Category 2 because it will result in more than 5,000 sf of new plus replaced hard surfaces. Following the flow chart in Figure 1-4, Minimum Requirements #1-9 will apply to all new and replaced hard surfaces. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 10 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com Cochran Residence - CG #23038.20 August 23, 2024 Drainage Report Section II, Page 11 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 DOE Manual and the requirements in the Edmonds Stormwater Addendum. 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. Mandatory Operational Source Control BMPs must be implemented by forming a pollution prevention team, good housekeeping practices, preventive maintenance, spill prevention and cleanup, employee training, inspections, and record keeping. See Section IV for a source control discussion and Section VIII for source control guide sheets from the DOE Manual. 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 III. Minimum Requirement #5: On -Site Stormwater Management: The proposed project is classified as a Category 2 per the Edmonds Stormwater Addendum and does not discharge into the city's MS4. The project must comply with Minimum Requirements #1-9 (per ECDC 18.30.060.C) shall either use On -site Stormwater Management BMPs from List #2 or demonstrate compliance with the LID Performance Standard. The project has proposed to install one infiltration trench per BMP T5.10A for all proposed hardscape areas. This is discussed in Section III. Minimum Requirement #6: Runoff Treatment: This requirement applies to the new plus replaced hard surfaces and the converted vegetated areas that will generate pollutants and be conveyed to the public storm system through stormwater runoff. Runoff treatment is not required because the project will result less than 5,000 sf of pollution -generating hard surfaces in a threshold discharge area. Additionally, all new impervious surfaces are to be 100% infiltrated. This is discussed in Section III. Minimum Requirement #7: Flow Control: Projects must provide flow control to reduce the impacts of stormwater runoff from hard surfaces and land cover conversions. As the project is located within the Perrinville Creek watershed additional requirements are to be followed per 18.30.060.D.7.d. However, flow control is not required as this project proposed less than 10,000 sf of new/replaced impervious surface, does not propose to convert 0.75 acres or more of vegetation to lawn area, does not proposed to convert 2.5 acres or more of native vegetation to pasture, and has proposed to 100% infiltrated all 250 4th Avenue South, Suite 200 CM Edmonds, WA 98020 11 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com Cochran Residence - CG #23038.20 August 23, 2024 Drainage Report Section II, Page 12 proposed hardscape. Infiltrating the proposed hardscape 100% is shown to meet all requirements for projects within the Perrinville Creek Watershed. Minimum Requirement #8: Wetlands Protection: Not applicable. There are no wetlands located in the immediate downstream vicinity of the site. 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 On -Site Stormwater Management 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 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 CM Edmonds, WA 98020 12 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com Cochran Residence - CG #23038.20 Drainage Report August 23, 2024 Section II, Page 13 Does the project result in 2,000 square feet, or greater, of new plus replaced hard surface area? OR Does the land disturbing activity total 7,000 square feet or greater? No Minimum Requirements No. I through 5 apply I Minimum Requirement No. 2 applies Nett Question Does 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 more of native vegetation to pasture? No Yes yes Is this a road related project? All Minimum Requirements apply to the nee% and replaced yes hard surfaces and con cried vegetation areas. All Minimum Requirements apply to the new hard surfaces and converted vegetation areas. Does the project add 5,000 square feet or more of new hard surfaces? yes Do new hard surfaces add 50% or more to the existing hard surfaces within the project limits? No NO No No additional requirements. Figure II-4. Flow chart for determining requirements for development (Figure 3.1 in the Edmonds Stormwater Addendum). 250 4th Avenue South, Suite 200 Edmonds, WA 98020 13 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com Cochran Residence - CG #23038.20 August 23, 2024 Drainage Report Section III, Page 14 Section III — Off -Site Analysis Section II Summa 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 will be fully infiltrated. The runoff will continue along the natural drainage path and the infiltrated flow is expected to continue to disperse beneath the surface in a general north westerly direction. The natural drainage direction is in a northwesterly direction and portions of the runoff get picked up by the City's storm main and catch basins conveyed for approximately 690 feet on the south side of Talbot Road in an easterly direction. It is then routed in a northwesterly direction for approximately 490 feet until it outfalls into the Puget Sound. The remaining runoff continues to flow subsurface from the site in a northerly direction beneath Talbot Road and the properties to the north until it flows into the Puget Sound, approximately 580 feet north of the site. The downstream flow path is outlined below in Figure III-1 from the City GIS map. The site is located in the Perrinville Creek Piped Watershed. 250 4th Avenue South, Suite 200 C CM 14 Edmonds, WA 98020 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com Cochran Residence - CG #23038.20 August 23, 2024 Drainage Report Section III, Page 15 Figure III-1. Vicinity map showing stormwater flow path and distance to outfall (from Edmonds GIS). Task 2 — Review all available information on the study area Existing stormwater improvements were determined from the survey, the initial site visit, and the City GIS map. Runoff from the site will be fully infiltrated and will flow along the natural drainage path to the northwest. A portion of the infiltrated runoff may be picked up by the City's storm main and catch basins will convey the runoff for approximately 690 feet on the south side of Talbot Road in an easterly direction through a series of catch basins, 18" concrete, and 30" PVC storm drain pipes. It will then be routed in a northwesterly direction for approximately 490 feet through a series of manholes, catch basins, and 30" PVC storm drainpipes, until it outfalls into the Puget Sound. The remaining runoff will continue to flow subsurface from the site in a northerly direction beneath Talbot Road and the properties to the north until it flows into the Puget Sound, approximately 580 feet north of the site. 250 4th Avenue South, Suite 200 C CM 15 Edmonds, WA 98020 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com Cochran Residence - CG #23038.20 August 23, 2024 Drainage Report Section III, Page 16 Task 3 — Field inspect the study area A site visit was done on the morning of February 27, 2023. The weather was overcast. From evaluating surrounding conditions, the site does not appear to take on significant upstream runoff. Pavement from the areas to the south of the project site is sloped westerly. The project proposes to tie all roof drains and all other hardscape drains to the onsite infiltration trench. Please see below for the site drainage walk photos. Figure III-2. From the north side of Frederick Place looking westerly. 250 4th Avenue South, Suite 200 C CM 16 Edmonds, WA 98020 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com _ '.�+%y��rr �• r-A • `a� 'a�• •,_y�siti kal''=07� ..il _ �:',J. _fjj '-.� `!'�. Y tn , ^�a a� � • r ' ��\' ♦+ : R ..�t� !�; s ��y1 • • - ="'"6 ¢ �' .. � - '` }i•� ty �r-+ r 'V' � - gyp: w,j. � ! �V to C _ Cochran Residence - CG #23038.20 August 23, 2024 Drainage Report Section III, Page 18 t�9259 SUBSURFACE FLOWS TO OUTLET TO PUGET SOUND 4 Figure III-4. From a downstream catch basin facing east on the south side of Talbot Road. (Should a portion of the runoff surface, it will be picked up by this catch basin and further downstream catch basins. Otherwise, the runoff will continue below the surface in the direction shown above.) 250 4th Avenue South, Suite 200 C 18 Edmonds, WA 98020 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com Cochran Residence - CG #23038.20 August 23, 2024 Drainage Report Section III, Page 19 All I C CM ENGINEERING � 1� ��, .� � � "� r• mow_ Figure III-5. Facing westerly from the south side of Talbot Road. 250 4th Avenue South, Suite 200 19 Edmonds, WA 98020 ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Cochran Residence - CG #23038.20 Drainage Report August 23, 2024 Section III, Page 20 V Figure III-6. Facing northerly from the north side of Talbot Road. Task 4 — Describe the drainage system, and its existing and predicted problems The site is in the Perrinville Creek Piped Watershed. The project proposes to route all runoff to the onsite proposed 29'x9.5'x3' infiltration trench per BMP T7.20. There are no predicted problems with the drainage system so long as the installation and maintenance of drainage facilities are done properly. C GM ENGINEERING 250 4th Avenue South, Suite 200 20 Edmonds, WA 98020 ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Cochran Residence - CG #23038.20 Drainage Report August 23, 2024 Section IV, Page 21 Section IV — Permanent Stormwater Control Plan Section III Summary Narrative Feasibility Review Runoff Treatment Water Quality WWHM Alnrrntiva The project is a Category 2 project per the Edmonds Stormwater Addendum. 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. 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. 2. Downspout Full Infiltration Systems in accordance with BMP T5.10A is feasible. The project has proposed to infiltrate all the proposed hardscape into one 29x9.5x3 infiltration trench per BMP T5.10A. See calculations below. Sized to meet LID standards. 3. Bioretention in accordance with BMP T7.30 is infeasible because the only available area for siting would not allow for a proper overflow connection to the city's storm drain conveyance system. 4. Downspout Dispersion Systems in accordance with BMP T5.1013 are infeasible because a minimum vegetated flowpath of at least 50 ft between the outlet property lines cannot be achieved. 5. Detention vaults or pipes in accordance with the Edmonds Stormwater Addendum are infeasible as there is not a viable location downstream of the site to connect to the city's storm drain conveyance system. 6. A Perforated Stub -Out Connection in accordance with BMP T5.10C is infeasible as there is not a viable location downstream of the site to connect to the city's storm drain conveyance system. C 4M ENGINEERING 250 4th Avenue South, Suite 200 Edmonds, WA 98020 21 ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Cochran Residence - CG #23038.20 August 23, 2024 Drainage Report Section IV, Page 22 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. Full Infiltration per BMP T5.10A in Volume III of the SWMMWW or Permeable pavement in accordance with BMP T5.15 in Chapter 5 of Volume V of the SWMMWW is feasible. The project has proposed to infiltrate all the proposed hardscape into one 29x9.5x3 infiltration trench per BMP T5.10A. See calculations below. Sized to meet LID standards. 3. Bioretention in accordance with Chapter 7 is infeasible because the only available area for siting would not allow for a proper overflow connection to the city's storm drain conveyance system. 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 a 10-foot-wide vegetation buffer for dispersion of the adjacent 20 feet of contributing surface cannot be achieved in a downstream direction. 5. Detention vaults or pipes in accordance with the Edmonds Stormwater Addendum are infeasible as there is not a viable location downstream of the site to connect to the city's storm drain conveyance system. Calculations Please see the below WWHM calculations for the proposed 29'x9.5'x3' infiltration trench sizing. WWHM2012 PROJECT REPORT Project Name: Cochran Trench Site Name: Cochran Residence Site Address: 8475 Frederick P1 City : Edmonds Report Date: 8/20/2024 Gage : Everett Data Start : 1948/10/01 Data End : 2009/09/30 Precip Scale: 0.80 Version Date: 2023/01/27 Version : 4.2.19 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 250 4th Avenue South, Suite 200 Edmonds, WA 98020 22 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com Cochran Residence - CG #23038.20 Drainage Report August 23, 2024 Section IV, Page 23 Pervious Land Use acre C, Forest, Mod .19 Pervious Total 0.19 Impervious Land Use acre Impervious Total 0 Basin Total 0.19 Element Flows To: Surface Interflow MITIGATED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre Pervious Total Impervious Land Use ROADS FLAT ROADS MOD ROOF TOPS FLAT SIDEWALKS FLAT POND Impervious Total Basin Total 0 Groundwater acre 0.023 *Onsite driveway and apron 0.015 *Onsite driveway 0.108 *Total roof 0.033 *Patios & walkways 0.011 *Proposed pool 0.19 0.19 Element Flows To: Surface Interflow Groundwater Gravel Trench Bed 1 Gravel Trench Bed 1 Name : Gravel Trench Bed 1 Bottom Length: 29.00 ft. Bottom Width: 9.50 ft. Trench bottom slope 1: 0 To 1 Trench Left side slope 0: 0 To 1 250 4th Avenue South, Suite 200 C Edmonds, WA 98020 23 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com Cochran Residence - CG #23038.20 Drainage Report August 23, 2024 Section IV, Page 24 Trench right side slope 2: 0 To 1 Material thickness of first layer: 3 Pour Space of material for first layer: 0.3 Material thickness of second layer: 0 Pour Space of material for second layer: 0 Material thickness of third layer: 0 Pour Space of material for third layer: 0 Infiltration On Infiltration rate: 10 Infiltration safety factor: 1 Total Volume Infiltrated (ac-ft.): 22.773 Total Volume Through Riser (ac-ft.): 0.001 Total Volume Through Facility (ac-ft.): 22.774 Percent Infiltrated: 100 Total Precip Applied to Facility: 0.835 Total Evap From Facility: 0.131 Discharge Structure Riser Height: 2.95 ft. Riser Diameter: 12 in. Element Flows To: Outlet 1 Outlet 2 Gravel Trench Bed Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 0.0000 0.006 0.000 0.000 0.000 0.0333 0.006 0.000 0.000 0.063 0.0667 0.006 0.000 0.000 0.063 0.1000 0.006 0.000 0.000 0.063 0.1333 0.006 0.000 0.000 0.063 0.1667 0.006 0.000 0.000 0.063 0.2000 0.006 0.000 0.000 0.063 0.2333 0.006 0.000 0.000 0.063 0.2667 0.006 0.000 0.000 0.063 0.3000 0.006 0.000 0.000 0.063 0.3333 0.006 0.000 0.000 0.063 0.3667 0.006 0.000 0.000 0.063 0.4000 0.006 0.000 0.000 0.063 0.4333 0.006 0.000 0.000 0.063 0.4667 0.006 0.000 0.000 0.063 0.5000 0.006 0.000 0.000 0.063 0.5333 0.006 0.001 0.000 0.063 0.5667 0.006 0.001 0.000 0.063 0.6000 0.006 0.001 0.000 0.063 0.6333 0.006 0.001 0.000 0.063 0.6667 0.006 0.001 0.000 0.063 0.7000 0.006 0.001 0.000 0.063 0.7333 0.006 0.001 0.000 0.063 0.7667 0.006 0.001 0.000 0.063 0.8000 0.006 0.001 0.000 0.063 0.8333 0.006 0.001 0.000 0.063 0.8667 0.006 0.001 0.000 0.063 0.9000 0.006 0.001 0.000 0.063 250 4th Avenue South, Suite 200 Edmonds, WA 98020 24 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com Cochran Residence - CG #23038.20 Drainage Report August 23, 2024 Section IV, Page 25 0.9333 0.006 0.001 0.000 0.063 0.9667 0.006 0.001 0.000 0.063 1.0000 0.006 0.001 0.000 0.063 1.0333 0.006 0.002 0.000 0.063 1.0667 0.006 0.002 0.000 0.063 1.1000 0.006 0.002 0.000 0.063 1.1333 0.006 0.002 0.000 0.063 1.1667 0.006 0.002 0.000 0.063 1.2000 0.006 0.002 0.000 0.063 1.2333 0.006 0.002 0.000 0.063 1.2667 0.006 0.002 0.000 0.063 1.3000 0.006 0.002 0.000 0.063 1.3333 0.006 0.002 0.000 0.063 1.3667 0.006 0.002 0.000 0.063 1.4000 0.006 0.002 0.000 0.063 1.4333 0.006 0.002 0.000 0.063 1.4667 0.006 0.002 0.000 0.063 1.5000 0.006 0.002 0.000 0.063 1.5333 0.006 0.002 0.000 0.063 1.5667 0.006 0.003 0.000 0.063 1.6000 0.006 0.003 0.000 0.063 1.6333 0.006 0.003 0.000 0.063 1.6667 0.006 0.003 0.000 0.063 1.7000 0.006 0.003 0.000 0.063 1.7333 0.006 0.003 0.000 0.063 1.7667 0.006 0.003 0.000 0.063 1.8000 0.006 0.003 0.000 0.063 1.8333 0.006 0.003 0.000 0.063 1.8667 0.006 0.003 0.000 0.063 1.9000 0.006 0.003 0.000 0.063 1.9333 0.006 0.003 0.000 0.063 1.9667 0.006 0.003 0.000 0.063 2.0000 0.006 0.003 0.000 0.063 2.0333 0.006 0.003 0.000 0.063 2.0667 0.006 0.003 0.000 0.063 2.1000 0.006 0.004 0.000 0.063 2.1333 0.006 0.004 0.000 0.063 2.1667 0.006 0.004 0.000 0.063 2.2000 0.006 0.004 0.000 0.063 2.2333 0.006 0.004 0.000 0.063 2.2667 0.006 0.004 0.000 0.063 2.3000 0.006 0.004 0.000 0.063 2.3333 0.006 0.004 0.000 0.063 2.3667 0.006 0.004 0.000 0.063 2.4000 0.006 0.004 0.000 0.063 2.4333 0.006 0.004 0.000 0.063 2.4667 0.006 0.004 0.000 0.063 2.5000 0.006 0.004 0.000 0.063 2.5333 0.006 0.004 0.000 0.063 2.5667 0.006 0.004 0.000 0.063 2.6000 0.006 0.004 0.000 0.063 2.6333 0.006 0.005 0.000 0.063 2.6667 0.006 0.005 0.000 0.063 2.7000 0.006 0.005 0.000 0.063 2.7333 0.006 0.005 0.000 0.063 2.7667 0.006 0.005 0.000 0.063 2.8000 0.006 0.005 0.000 0.063 250 4th Avenue South, Suite 200 CCMEdmonds, WA 98020 25 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com Cochran Residence - CG #23038.20 Drainage Report August 23, 2024 Section IV, Page 26 2.8333 0.006 0.005 0.000 0.063 2.8667 0.006 0.005 0.000 0.063 2.9000 0.006 0.005 0.000 0.063 2.9333 0.006 0.005 0.000 0.063 2.9667 0.006 0.005 0.022 0.063 3.0000 0.006 0.005 0.118 0.063 ANALYSIS RESULTS Stream Protection Duration Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.19 Total Impervious Area:O Mitigated Landuse Totals for POC #1 Total Pervious Area:O Total Impervious Area:0.19 Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.00231 5 year 0.003586 10 year 0.004376 25 year 0.005293 50 year 0.005916 100 year 0.006492 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0 5 year 0 10 year 0 25 year 0 50 year 0 100 year 0 Stream Protection Duration Annual Peaks for Predeveloped and Mitigated Year Predeveloped Mitigated 1949 0.000 0.000 1950 0.003 0.000 1951 0.002 0.000 1952 0.002 0.000 1953 0.001 0.000 1954 0.003 0.000 1955 0.004 0.000 1956 0.003 0.000 1957 0.004 0.000 POC #1 250 4th Avenue South, Suite 200 Edmonds, WA 98020 26 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com Cochran Residence - CG #23038.20 Drainage Report August 23, 2024 Section IV, Page 27 1958 0.003 0.000 1959 0.002 0.000 1960 0.002 0.000 1961 0.003 0.024 1962 0.002 0.000 1963 0.002 0.000 1964 0.002 0.000 1965 0.002 0.000 1966 0.001 0.000 1967 0.003 0.000 1968 0.003 0.000 1969 0.002 0.000 1970 0.002 0.000 1971 0.003 0.000 1972 0.003 0.000 1973 0.001 0.000 1974 0.002 0.000 1975 0.002 0.000 1976 0.002 0.000 1977 0.001 0.000 1978 0.002 0.000 1979 0.003 0.000 1980 0.002 0.000 1981 0.002 0.000 1982 0.003 0.000 1983 0.002 0.000 1984 0.002 0.000 1985 0.003 0.000 1986 0.009 0.000 1987 0.003 0.000 1988 0.002 0.000 1989 0.001 0.000 1990 0.002 0.000 1991 0.003 0.000 1992 0.002 0.000 1993 0.001 0.000 1994 0.001 0.000 1995 0.002 0.000 1996 0.005 0.000 1997 0.010 0.000 1998 0.001 0.000 1999 0.002 0.000 2000 0.001 0.000 2001 0.000 0.000 2002 0.002 0.000 2003 0.001 0.000 2004 0.002 0.000 2005 0.002 0.000 2006 0.005 0.000 2007 0.004 0.000 2008 0.005 0.000 2009 0.002 0.000 Stream Protection Duration Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 250 4th Avenue South, Suite 200 C Edmonds, WA 98020 27 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com Cochran Residence - CG #23038.20 Drainage Report August 23, 2024 Section IV, Page 28 1 0.0097 0.0236 2 0.0087 0.0000 3 0.0053 0.0000 4 0.0052 0.0000 5 0.0051 0.0000 6 0.0040 0.0000 7 0.0037 0.0000 8 0.0036 0.0000 9 0.0034 0.0000 10 0.0033 0.0000 11 0.0033 0.0000 12 0.0033 0.0000 13 0.0032 0.0000 14 0.0030 0.0000 15 0.0030 0.0000 16 0.0029 0.0000 17 0.0027 0.0000 18 0.0027 0.0000 19 0.0026 0.0000 20 0.0026 0.0000 21 0.0026 0.0000 22 0.0025 0.0000 23 0.0025 0.0000 24 0.0025 0.0000 25 0.0025 0.0000 26 0.0024 0.0000 27 0.0023 0.0000 28 0.0023 0.0000 29 0.0023 0.0000 30 0.0023 0.0000 31 0.0023 0.0000 32 0.0022 0.0000 33 0.0022 0.0000 34 0.0021 0.0000 35 0.0021 0.0000 36 0.0020 0.0000 37 0.0020 0.0000 38 0.0020 0.0000 39 0.0020 0.0000 40 0.0020 0.0000 41 0.0019 0.0000 42 0.0019 0.0000 43 0.0019 0.0000 44 0.0018 0.0000 45 0.0018 0.0000 46 0.0017 0.0000 47 0.0017 0.0000 48 0.0016 0.0000 49 0.0015 0.0000 50 0.0015 0.0000 51 0.0014 0.0000 52 0.0014 0.0000 53 0.0014 0.0000 54 0.0013 0.0000 55 0.0013 0.0000 56 0.0013 0.0000 57 0.0012 0.0000 C � ENGINEERING 250 4th Avenue South, Suite 200 Edmonds, WA 98020 28 ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Cochran Residence - CG #23038.20 Drainage Report August 23, 2024 Section IV, Page 29 58 0.0009 0.0000 59 0.0008 0.0000 60 0.0003 0.0000 61 0.0003 0.0000 Stream Protection Duration POC #k 1 The Facility PASSED The Facility Flow(cfs) Predev Mit Percentage Pass/Fail 0.0012 21881 3 0 Pass 0.0012 20048 3 0 Pass 0.0013 18320 3 0 Pass 0.0013 16767 3 0 Pass 0.0013 15297 3 0 Pass 0.0014 13995 3 0 Pass 0.0014 12846 3 0 Pass 0.0015 11832 3 0 Pass 0.0015 10846 3 0 Pass 0.0016 9967 3 0 Pass 0.0016 9184 3 0 Pass 0.0017 8481 3 0 Pass 0.0017 7837 3 0 Pass 0.0018 7249 3 0 Pass 0.0018 6701 3 0 Pass 0.0019 6192 3 0 Pass 0.0019 5715 3 0 Pass 0.0020 5249 3 0 Pass 0.0020 4834 3 0 Pass 0.0021 4451 3 0 Pass 0.0021 4122 3 0 Pass 0.0022 3805 3 0 Pass 0.0022 3540 3 0 Pass 0.0023 3275 3 0 Pass 0.0023 3020 3 0 Pass 0.0024 2796 3 0 Pass 0.0024 2609 3 0 Pass 0.0025 2443 3 0 Pass 0.0025 2304 3 0 Pass 0.0025 2182 3 0 Pass 0.0026 2055 3 0 Pass 0.0026 1952 3 0 Pass 0.0027 1860 3 0 Pass 0.0027 1743 3 0 Pass 0.0028 1656 3 0 Pass 0.0028 1558 3 0 Pass 0.0029 1456 3 0 Pass 0.0029 1372 3 0 Pass 0.0030 1308 3 0 Pass 0.0030 1242 3 0 Pass 0.0031 1196 3 0 Pass 0.0031 1156 3 0 Pass 0.0032 1117 3 0 Pass 0.0032 1076 3 0 Pass 250 4th Avenue South, Suite 200 CCMEdmonds, WA 98020 29 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com Cochran Residence - CG #23038.20 Drainage Report August 23, 2024 Section IV, Page 30 0.0033 1032 3 0 Pass 0.0033 997 3 0 Pass 0.0034 966 3 0 Pass 0.0034 936 3 0 Pass 0.0035 903 3 0 Pass 0.0035 868 3 0 Pass 0.0036 834 3 0 Pass 0.0036 796 3 0 Pass 0.0037 769 3 0 Pass 0.0037 738 3 0 Pass 0.0038 720 3 0 Pass 0.0038 690 3 0 Pass 0.0038 669 3 0 Pass 0.0039 649 3 0 Pass 0.0039 637 3 0 Pass 0.0040 615 3 0 Pass 0.0040 592 3 0 Pass 0.0041 577 3 0 Pass 0.0041 565 3 0 Pass 0.0042 550 3 0 Pass 0.0042 538 3 0 Pass 0.0043 524 3 0 Pass 0.0043 513 3 0 Pass 0.0044 504 3 0 Pass 0.0044 495 3 0 Pass 0.0045 482 3 0 Pass 0.0045 471 3 0 Pass 0.0046 456 3 0 Pass 0.0046 440 3 0 Pass 0.0047 427 3 0 Pass 0.0047 417 3 0 Pass 0.0048 406 3 0 Pass 0.0048 390 3 0 Pass 0.0049 376 3 0 Pass 0.0049 360 3 0 Pass 0.0050 345 3 0 Pass 0.0050 327 3 0 Pass 0.0051 319 3 0 Pass 0.0051 312 3 0 Pass 0.0051 303 3 0 Pass 0.0052 294 3 1 Pass 0.0052 289 3 1 Pass 0.0053 283 3 1 Pass 0.0053 277 3 1 Pass 0.0054 272 3 1 Pass 0.0054 268 3 1 Pass 0.0055 265 3 1 Pass 0.0055 261 3 1 Pass 0.0056 257 3 1 Pass 0.0056 250 3 1 Pass 0.0057 245 3 1 Pass 0.0057 241 3 1 Pass 0.0058 237 3 1 Pass 0.0058 232 3 1 Pass 0.0059 227 3 1 Pass 0.0059 224 3 1 Pass 250 4th Avenue South, Suite 200 C Edmonds, WA 98020 30 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com Cochran Residence - CG #23038.20 Drainage Report August 23, 2024 Section IV, Page 31 Water Quality BMP Flow and Volume for POC #1 On-line facility volume: 0 acre-feet On-line facility target flow: 0 cfs. Adjusted for 15 min: 0 cfs. Off-line facility target flow: 0 cfs. Adjusted for 15 min: 0 cfs. LID Report LID Technique Used for Total Volume Volume Infiltration Cumulative Percent Water Quality Percent Comment Treatment? Needs Through Volume Volume Volume Water Quality Treatment Facility (ac-ft.) Infiltration Infiltrated Treated (ac-ft) (ac-ft) Credit Gravel Trench Bed 1 POC N 20.72 N 100.00 Total Volume Infiltrated 20.72 0.00 0.00 100.00 0.00 0% No Treat. Credit Compliance with LID Standard 8 Duration Analysis Result = Passed Perind and Impind Changes No changes have been made. This program and accompanying documentation are provided 'as -is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc. and the governmental licensee or sublicensees disclaim all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions Inc. be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions Inc. or their authorized representatives have been advised of the possibility of such damages. Software Copyright © by Clear Creek Solutions, Inc. 2005-2024; All Rights Reserved. 250 4th Avenue South, Suite 200 C Edmonds, WA 98020 31 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com Cochran Residence - CG #23038.20 Drainage Report August 23, 2024 Section IV, Page 32 Runoff Treatment Runoff treatment is not required because the project will result in less than 5,000 sf of pollution - generating hard surfaces in a threshold discharge area. Additionally, all new impervious surfaces are to be 100% infiltrated. 250 4th Avenue South, Suite 200 CM Edmonds, WA 98020 32 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com Cochran Residence - CG #23038.20 August 23, 2024 Drainage Report Section V, Page 33 Section V— 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 (DOE) does not require completion of the full Construction SWPPP or the Construction Stormwater General Permit. Therefore, a Construction SWPPP is not required for this site. The following is an abbreviated format of the SWPPP that addresses each of the 13 elements of construction pollution prevention for the City review. Please note that the project may apply for a DOE permit regardless due to the contaminated soil considerations. 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 building and this can be seen on drawing sheet C2.1. 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. A stabilized construction entrance should be utilized as needed when possible, to prevent sediment tracking. See C2.1 for placement. The BMPs relevant to establishing construction access that will be applied for this project include: Stabilized Construction Entrance (BMP C105) Element 3: Control Flow Rates The site slopes on average about 9% from southeast to northwest. The site is small enough that a silt fence used for Element 4 can be used to control flow rates, however, this alone is not recommended. Additionally, the project has been directed to utilize BMP C235 Wattles for soils exposed and experiencing construction delays, over the winter months, and when permanent vegetation has yet to be established. Wattles (BMP C235) C 4M ENGINEERING 250 4th Avenue South, Suite 200 Edmonds, WA 98020 33 ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Cochran Residence - CG #23038.20 August 23, 2024 Drainage Report Section V, Page 34 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. A silt fence is proposed to be installed around the site development area and will prevent unfiltered runoff from flowing to adjacent properties. This can be seen on the Temporary Erosion Control Plan, C2.1. Pollution prevention facilities on the erosion control plan must be constructed prior to or in conjunction with all clearing and grading to ensure that the transport of sediment to surface 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 Catch basins along Admiral Way 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. C 4M ENGINEERING 250 4th Avenue South, Suite 200 Edmonds, WA 98020 34 ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Cochran Residence - CG #23038.20 Drainage Report August 23, 2024 Section V, Page 35 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) Element 10: Control Dewatering Perched groundwater was encountered during geotechnical explorations, however, is not anticipated to be an issue during construction. However, if groundwater is encountered during construction, it is recommended that the contractor slope the bottom of the excavation and collect the water into ditches and small sump pits where the water can be pumped out of the excavation and routed into a suitable outlet. A note to this effect has been added to the erosion control plan (C2.1). Element 11: Maintain BMPs All temporary and permanent erosion and sediment control BMPs shall be maintained and repaired as needed to ensure continued performance of their intended function. Element 12: Manage the Project • Phase development projects to the maximum degree practicable and consider seasonal work limits. • Follow the recommendations and requirements of the EMMP. • 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 Low -Impact Development BMPs are not proposed for this project. Location of the proposed infiltration trench should be protected from compaction where applicable. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 35 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com Cochran Residence - CG #23038.20 Drainage Report August 23, 2024 Section V, Page 36 Cntirrc rnntrnlc This project should incorporate required BMPs from Volume IV of the DOE Manual: S407 — BMPs for Dust Control at Disturbed Land Areas and Unpaved Roadways and Parking Lots; S411 — BMPs for Landscaping and Lawn/Vegetation Management; and S417 — BMPs for Maintenance of Stormwater Drainage and Treatment Systems. The Operation & Maintenance Manual found in Section VII contains guide sheets for the aforementioned BMPs. The proposed pool drain/overflow will be managed per the 2019 SWMMWW S433 BMPs for Pools, Spas, Hot Tubs, and Fountains. This BMP states "If the water feature must be drained, convey discharges (within hoses or pipes) to a sanitary sewer if approved by the local sewer authority or to a storm sewer following the conditions outlined below. Do not discharge to a septic system since it may cause the system to fail. No discharge to the ground or to surface water should occur, unless permitted by the proper regulatory authority'. Therefore, the pool's drain/overflow will be connected to the proposed onsite pump and will discharge to the sanitary sewer system within Frederick Place. 250 4th Avenue South, Suite 200 CM Edmonds, WA 98020 36 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com Cochran Residence - CG #23038.20 Drainage Report August 23, 2024 Section VI, Page 37 Section VI — Special Reports and/or Studies Section V Summary: Narrative The following described in the section are located in Appendix A: 1. Geotechnical Engineering Evaluation by Nelson Geotechnical Associates, Inc. dated February 02, 2018. 2. Geotechnical Engineering Comment Response by Nelson Geotechnical Associates, Inc. dated March 01, 2024. 3. Geotechnical Engineering Evaluation by Nelson Geotechnical Associates, Inc. dated May 02, 2024. 4. Soil Resource Report from the USDA and NRCS Web Soil Survey dated June 12, 2023. 250 4th Avenue South, Suite 200 CM Edmonds, WA 98020 37 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com Cochran Residence - CG #23038.20 Drainage Report August 23, 2024 Section VII, Page 38 Section VII — Other Permits Section VI Summary: Narrative Other permits are not anticipated to be required for this project besides those from the City of Edmonds. 250 4th Avenue South, Suite 200 CM Edmonds, WA 98020 38 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com Cochran Residence - CG #23038.20 August 23, 2024 Drainage Report Section VIII, Page 39 Section VIII — Bond Quantities, Declaration of Covenant, & Operation and Maintenance Manual Section VII Summary: Narrative The Bond Quantity Worksheet is a standalone document that can also be submitted to the City of Edmonds separately from this document. A Declaration of Covenant is provided for the proposed on -site BMP. The Operation and Maintenance Manual is a standalone document that will be given to the owner(s) following the construction of the project. The maintenance manual contained herein is for the Cochran Residence single-family 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 house owner(s). The project contractor will be responsible for passing along the information in this maintenance manual to the owner(s). 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. C 4M ENGINEERING 250 4th Avenue South, Suite 200 Edmonds, WA 98020 39 ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Cochran Residence - CG #23038.20 Drainage Report August 23, 2024 Section VIII, Page 40 Cochran Residence 8475 Frederick Place Edmonds, WA 98026 OPERATION AND MAINTENANCE MANUAL Date: August 2024 250 4th Avenue South, Suite 200 Edmonds, WA 98020 40 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com Cochran Residence - CG #23038.20 August 23, 2024 Drainage Report Section VIII, Page 41 Operation and Maintenance Manual This Operation and Maintenance Manual has been created for the Cochran Residence: a 4,714 sf single- family residence project on a 0.46-acre lot. The proposed storm system consists of routing a trench drain, area drains, and roof drains to a infiltration trench system. Included in this Operation and Maintenance Manual is an 11" x 17" grading and drainage plan sheet showing the location of the infiltration 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 for the site. 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). An aerial image of the project area can be seen on the following page in Figure VII-1. Attached at the end of this section are maintenance sheets taken from the 2019 Stormwater Management Manual for Western Washington (DOE Manual). Guide sheets for source controls are also included that were taken from the DOE Manual. Maintenance sheets are included for the following facilities: Yard/Area Drains: Concrete structures with metal grates that collect stormwater runoff from the site and act as junctions for storm conveyance pipes. See "No. 5" for maintenance. Trench Drains: Drainage pipes with metal grates crossing driveways to collect stormwater runoff. See "No. 5" for maintenance. Infiltration Trenches: Gravel filled trenches used to infiltrate stormwater runoff through existing soils. 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. C 4M ENGINEERING 250 4th Avenue South, Suite 200 Edmonds, WA 98020 41 ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com NE 1 /4, SW 1 /4, SECTION 07, TOWNSHIP 27 NORTH, RANGE 04 EAST, W.M. C SOIL LOGS: II I SET TEST PIT ONE FOUND IRON PIPE I o+ - - /�� RE9AR/CAP (ELEV:46FEET) ENGINEERING 0.30'W OF LINE & DISCHARGE POOL 182.00' i' I / �1 0.0-0.1 TOPSOIL 250 4TH AVE. 5., SUITE 200 RAVE FROM PROP CUR FOOTING DRAINS TO C33 N 85'D9 D� E / / 1 4UP 3.7'TALL MAX I .4i EDMONDS, WASHINGTON 98020 4'x4'x4'DRYWELL - - e HEIGHT CONCRETE Y� ��J7(� PHONE 425 778-8500 RETAINING WALL I `V 0.1-1.5 SM BROWN SILTY FINE TO MEDIUM SAND WITH ROOTS AND TRACE IRON OXIDATION STAINING (LOOSE, DRY) (� ) / FAX 425 778-5536 \11 I M I FENCE 1.5-2.3 SP-SM LIGHT YELLOW -TAN FINE TO COARSE SAND WITH SILT (MEDIUM DENSE, DRY -MOIST) 9 L 0.5%PVC \ I 2 FOOTING DRAIN (PERF \ II PROPOSED TOW: 56.0 0 BE 2.3-7.1 SP-SM LIGHT GRAY -TAN FINE TO MEDIUM SAND WITH SILT AND TRACE FINE GRAVEL AND IRON OXIDATION STAINING (DENSE, MOIST) @0.5%MIN 1 e PIPE ARALLSAN BUILDING \ PROPOSED I I CONCRETE PATIO POOL FOOTING DRAIN 1 / BOW: 52.30 I AND WALLS AND SOLID CONCRETE PATIO I FFE: 52.30 LINES (PERF PIPE AROUND 11 PVC FOR CONVEYANCE) p FFE: 51.80 1 / j 7.1-8.0 SM BROWN SILTY FINE TO MEDIUM SAND WITH TRACE COARSE SAND AND IRON OXIDATION STAINING (MEDIUM DENSE, MOIST) POOL WALLS AND SOLID 2 SDCO, TVP / / FENCE m / SDCO, TYR PVC FOR CONVEYANCE) e SOLO, TYR II / I 8.0-9.5 SM GRAY SILTY FINE TO COARSE SAND WITH IRON OXIDATION STAINING (DENSE, WET) / ROOF DRAIN 2 `` I GRADE POOL DECK TO FLOW \ �, R F�F / SAMPLES WERE COLLECTED AT 3.5, 4.5, 7.3, 7.5, AND 8.2 FEET TOWARD58"SE AREA DRAIN AS 46'9a0 DECK FIE TO BE 30" / / R��FR _F ----- I I MODERATE GROUNDWATER SEEPAGE WAS ENCOUNTERED AT 8.7 FEET INDICATED BY FLOW ARROWS 30 "� OR LESS ABOVER� x- I / \, r - FINISHED GRADE R _FR =-F----F--- r-�F-- _F�--- TEST PIT CAVING WAS NOT ENCOUNTERED III / TEST PIT WAS COMPLETED AT9.5FEETON1/17/18 FOR REPORT USE 46.90FR _f- AREA DRAIN FOR II j Fyn-�-_----- / TEST PIT TWO - -/- / PATIO RUNOFF. TIE T I �.\ PROPOSED PARTIALLY INTO ROOF DRAIN LINE I (ELEV:57 FEET) ONLY PROPOSED POOL DECK, \ I ALL WALL FOOTING ' /. COVERED DECK I III I I FEE 46.70 /. �' 4677 1 FFE: 51.80 / ( PRAINSED TIE INTO 0.0-0.4 LIGHT GRAY SILT AND FINE TO MEDIUM SAND WITH ROOTS AND FINE GRAVEL (LOOSE, DRY-MOIST)(FILL) I PROPOSED CONCRETE le d l 111 II PROPOSED HOUSE ^143 SF O F UNCO�E RED / DRIVEWAY AND PARKING PROPOSED POOL 46.87 7 / I+•" I� FOOTING DRAINS. 0.4-1.7 SM RED -BROWN SILTY FINE TOMEDIUM SAND WITH GRAVEL AND TRACE ROOTS (LOOSE -MEDIUM DENSE, M0157) \ I.' � DECK TO BE DRIP THROUGH FFE: 51.80 I I / / (4" PVC PERF PIPE) \\ I- I'I HA-102 I �/' I I • I I I\ 1.7-3.8 SM YELLOW -GRAY SILTY FINE TO MEDIUM SAND WITH TRACE FINE GRAVEL (DENSE, MOIST) 12"AREA DRAIN \ I PLANTER / HA-1 III FE E� \ • I �, TRENCH DRAIN TO / I 2'E \ WITH OPEN GRATE 6 I/ d 46.67 - I /' `h COLLECT DRIVEWAY TOW: 56.90 / 11�� I 3.8-9.0 SM GRAY SILTY FINE TO MEDIUM SAND WITH TRACE IRON OXIDATION STAINING (DENSE, MOIST) RIM: 46.57 TOW: 49.30 12' AREA DRAIN TP-2 C3. - RUNOFF I E (6" SW): 43.57 I e �I BOW: 42.40 \ WITH OPEN GRATE 3 BOW: 51.80 • Z 46.80 46.70 d I I 1 SAMPLES WERE COLLECTED AT NO ENCOUNTERED FEET qy RIM: 51.80 GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED 101 0 LF ^ 6'.' PVC @ 28.0% I SDCO, TYP / 7/ 24 LF 9' TALL MAX HEIGHT IE (TRENCH DRAIN, E): 51.30 j / I m I ? TEST PIT CAVING WAS NOT ENCOUNTERED TYPE CB, SOLID LID / CONCRETE RETAINING 1 cn t(, C3.3 IE (6", SE): 48.30 9p TEST PIT WAS COMPLETED AT 9.0 FEET ON 1/17/18 I INF-1M / WALL (SEE STRUCTURAL) r 1.0' RIM:45.7 1 46.77 1 HANDAUGERONE IE (6" NE, E): 40.80 1 8 8. - l TOW: 51.30 1 / _�R / I Z IE 4"E:40.80 1 O TOW: a / BOW: 42.40 PROPOSED HOUSEI CONNECT TO / - T / (ELEV.53 FEET) ( ) 1 BOW: 47.40 1 ROOF DRAIN LINE e c q �/ SDCO, TYR a r II/ I PI IEI6"SW):40.70 1 I `Tow:aaso FFE:51.80' '11 0 IE IS OVERFLOW): 41.30 p I � 146.60 / BOW: 4240 I / I R d ,ram: i 0.0-0.3 LIGHT GRAY SILT AND FINE TO MEDIUM SAND WITH ROOTS AND ORGANIC AND ANTHROPOGENIC DEBRIS (LOOSE, DRY) (FILL) Y / UPPER FLOOR FFEt 62.10' I J� �� BOT: 38.70 LI I� p l +'I �e IE:-41.47/ TOW 4790 LOWER FLOOR FFE: 42.40' I 1 p /�I, '�'� / m o 0.3-2.0 SM RED -BROWN SILTY FINE TO MEDIUM SAND WITH GRAVELANO TRACE ROOTS (LOOSE -MEDIUM DENSE, MOIST) C3. C3. / I R I °BOW 47.40 I TOW: 51.30 I I I o SOLO, TOW: 51.30 Ip a4i a d ea4 y e I 2.0-3.6 SM YELLOW -GRAY SILTY FINE TO MEDIUM SAND WITH TRACE FINE GRAVEL(DENSE, MOIST) I \\\ d 70 46.70 HA-101p" TYP AREA DRAIN FOR BASEMENT I I I l I\ - e S'j III a a a �/46.67 I ACCESS RUNOFF. TIE INTO / I I TOW: 57.90 I 51.90 \ I 3.6-5.0 SM GRAY SILTY FINE TO MEDIUM SAND WITH TRACE IRON OXIDATION STAINING (DENSE, MOIST) Q \ I I �/ m BOW: 52.30 ROOF LINE I ® { I 2 2 2 'o 46.70 e c RIM: SW): CONNECT TOIN O I �i I TOW: 42.90 IE 6"SW :40.93 b _4 \ e / GROUND ATE COLLECTED z WAS O \ BOW: 42.40 ( ) ROOF DRAIN LINE / e ® 4e \ O m w w w GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED 8 UP-6"PVC / I PROPOSED ACCESS / / a \ - / m TEST PIT CAVING WAS NOT ENCOUNTERED 7 MAIN ENTRY w 3o TO BASEMENT / / I v \ \ I / II I HAND AUGER WAS TERMINATED AT 5.0 FEET ON I/17/18 d z o @ 17.5% I q SDCO, TVP FFE: 51.80 I I 4` H 1= H H FEE: 42.40 I / °2 DISCHARGE \I / 15 LF ^' 6" 26 LF 8' TALL MAX / _ 1 I �' a '� % e I INFILTRATION PIT ONE O w w O w w w w OVERFLOWTO / __ _ --- - "'"i (ELEV:46 FEET) ICI I \ HEIGHT CONCRETE 1 �� a4 \ PROPOSED DRIVEWAY I a d a d 4'x4'x4'DRYWELL / \ I 0.5%MIN RETAINING WALL I C3.3 I \ III 0.0-0.9 DARK BROWN SILTY FINE TO MEDIUM SAND WITH TRACE FINE GRAVEL AND ROOTS (LOOSE, MOIST)(TOPSOIL) / TP 1 I i I (SEE STRUCTURAL) 3 27 LF - 6" PVC 7 LL a u i �d R I SDCO, TYP TOW: 54.40 59 LF G' TALL MAX \ N ti ti C3.3 I @0.5%MIN Fy PROFILE C3. _ ---- �� a'a� FENCE 0.9-2.0 SM RED -BROWN FINETOMEDIUM SAND WITH GRAVELANDTRACE ROOTS(LOOSE-MEDIUM DENSE, MOIST) / l� WA i R-�- d ' I -BOW: 51.80 I HEIGHT CONCRETE e 1 16 LF"'4"PVCW ® b 51.80 F �F F RETAINING WALL C33 20-5.0 SM YELLOW -GRAY SILTY FINE TO MEDIUM SAND WITH TRACE FINE GRAVEL (DENSE, MOIST) C, 1 @0.5%MIN I ry' _F (SEE STRUCTURAL) O O O X RIM: SDCO,TYP I I TOW: T FSDCO, TYP j® 6UP-6"PVC 1 ' SAMPLES WERE COLLECTED AT 0.5 AND 2.5 FEET RIM: 45.50 SDCO, TYP ® p / - BOW: 42.40 @0.5%MIN ed.GA \ GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED a IE (6" PERF PIPE): 39.30 / / tq TOW: 52.0 1 ,{, TOW: 57.40 \ TEST PITCAVING WAS NOT ENCOUNTERED Q IE:'"41.45 TOW:48.90 BOW: 51.80 / 12"AREA DRAIN 11 ° ® ,jj BOW: 55.20 I INFILTRATION TEST PIT WAS TERMINATED AT 5.0 AT DEPTH ON 1/17/2018 IN BOW: 42.40 WITH OPEN GRATE I _ _ I �, I - LsUND y 14490CK/u / 10.0 M 1 63 LF 3'TALL / RIM: 51.60 I HAND AUGER 101 DESIGN: NAT 10.0' �.:.- - / / NCE END 0.1'W 0.05'N OF LINE MIN / / / (22'0i l `G C3.3 MAX HEIGHT / IE IS" SE): 48.10 / j OM PROP COR 0.12'W FROM PI (ELEV:48 FEET) DRAWN: JCP SGOO CONCRETE _ \ / 4" OBSERVATION p RIM: 48.36 RETAINING WALL % / r - 1 0.0-1.0 DARK BROWN SILTY FINE TO MEDIUM SAND WITH TRACE FINE GRAVEL AND ROOTS (LOOSE, MOIST)(TOPSOIL) FENCE COR �p/_r6 WELL, TYR 9 / / IE(6"N,S): 41.40 j _ _ -" - / CHECK: JPU 1.2'E OF LINE 1 RIM: 45.50 C3 / .IE(6"NE):40.88 - - - - ,( TOW: 57.50\ 1.0-2.0 SM RED -BROWN SILTY FINE TO MEDIUM SAND WITH GRAVEL AND TRACE ROOTS (LOOSE -MEDIUM DENSE, MOIST) JOB NO: 23038.20 & 3.9'N FROM \\ / IE (6"W): 40.88 - ,7XBOW: 57.0 PROP COR \ / 2.0-9.0 SM GRAY SILTY FINE TO MEDIUM SAND WITH TRACE IRON OXIDATION STAINING (DENSE, MOIST) DATE: 06 1 6 23 10' MIN RADIUS 1 D ! SAMPLES WERE NOT COLLECTED GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED _ 29.0' x9.5'x3.0' cc�� I `�� A HA ND AUGER CAVING WAS NOT ENCOUNTERED INFILTRATION TRENCH `Y I _ I �� HAND AUGER WAS COMPLETED AT 9.0 FEET ON 2/8/23 TOP: 41.30 I I � > / PROPOSED DRIVEWAY 3 BUT 38.30 I \ �I i/ APPROACH SHALL NOT EXCEED HAND AUGER 102 GROUNDWATER: 37.30± � I 24' IN WIDTH. DRIVEWAY C3. I W C3. HAND FEET) FOUND IRON PIPE I (SEE GEOTECH REPORT) 1 \\\ �W W 1 APPROACH MATERIAL SHALL BE (T1�� \ 8''pl W 24.0' 0.11'W OF LINE & I Z j I EXISTING 6"I \ \I /W�'N 1 ASPHALT FROM PAVED ROAD 0.0-1.0 DARK BROWN SILTY FINE TO MEDIUM SAND WITH TRACE FINE GRAVEL AND ROOTS (LOOSE, MOIST)(TOPSOIL) 18'S FROM PROP COR A W \ SGCO W/ COVE WSW I TO PROPERTY LINE OR 20, / �o 3 CONCRETE II WAIN W� I `� WHICHEVER IS GREATER, AT MIN 1.0-3.0 SM RED -BROWN SILTY FINE TO MEDIUM SAND WITH GRAVEL AND TRACE ROOTS (LOOSE -MEDIUM DENSE, MOIST) IM: 51.3W�W 1 1 I ASPHALT \� APPROX. LOCATION I I PAVEMENT 3.0-9.0 SM GRAY SILTY FINE TO MEDIUM SAND WITH TRACE IRON OXIDATION STAINING DENSE, MOIST �W IE: 44.15 I IL \ I ( I �W PER RECORDS (TYR) DERICK SAMPLES WERE NOT COLLECTED GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED GRADING AND DRAINAGE PLAN © HAND AUGER WASING COMPETEDAT90FEET ON2/8/23 � SCALE: 1" = 10' 10 0 5 10 20 1. SOILS REPORT REPORT NUMBER: 1021818 PREPARED BY: NELSON GEOTECHNICAL ASSOCIATES, INC DATED: FEB 02, 2018 2. A MINIMUM OF 3' HORIZONTAL SEPARATION AND 1' VERTICAL SEPARATION IS REQUIRED BETWEEN DRY UTILITIES (POWER, GAS, PHONE, CABLE, ETC) AND SEWER, WATER AND STORM, AND A MINIMUM OF 5' HORIZONTAL SEPARATION AND 1' VERTICAL SEPARATION FROM ANY CITY OWNED LINES. 3. ALL DISTURBED AREAS TO BE COMPOST AMENDED PER 2019 SW MM W W EMIR T5.13. SEE DETAIL 4/C3.2. 4. ATYPE II MANHOLE IS REQUIRED WHENEVER RIM TO INVERT EXCEEDS 5'. 5. A MINIMUM OF 2' OF COVER IS REQUIRED FOR ALL PIPES LOCATED UNDER DRIVABLE SURFACES AND VICE COVER UNDER LANDSCAPE AND OTHER HARD SURFACES. ALL PIPES HAVE BEEN DESIGNED WITH A MIN T OF COVER. 6. DRIVEWAY TO BE INSTALLED PER ECDC 18.80.060. PROPOSED DRIVEWAY NOT TO EXCEED 14% SLOPE. 7. PER CHAPTER 5-05 PF THE COE EDDS, CLEANOUTS ARE REQUIRED UPSTREAM OF EACH WYE OR TEE CONNECTION. REQUIRED SDCO HAVE BEEN SHOWN IN PLAN VIEW. GRADING QUANTITIES PAVING LEGEND TOTAL EXCAVATION(CUT)- 1,100 CUVDS TOTAL NEW ASPHALT/UTILITY SAWCUT EMBANKMENT (FILL) 755 CUVDS NEW CONCRETE TOTAL 1,855 CU YDS THE QUANTITIES SHOWN ABOVE ARE FOR THE PERMIT PROCESS ON LV. THESE VALUES ARE APPROXIMATE. DO NOT USE FOR BIDDING, PAYMENT, OR ESTIMATING PURPOSES. IMPERVIOUS SURFACES SURFACE SURFACE AREA (SF) STORMWATER CONTROL MEASURE NEW BUILDING 4,714 RUNOFF ROUTED TO INFILTRATION TRENCH THROUGH ROOF DRAINS. NEW DRIVEWAY 1,441 RUNOFF COLLECTED VIA TRENCH DRAIN AND ROUTED THROUGH PERIMETER DRAINS TO INFILTRATION TRENCH. NEW PATIOS & WALKWAYS ,1431 COLLECTED BY AREA DRAINS AND ROUTED THROUGH PERIMETER DRAINS TO INFILTRATION TRENCH. NEW POOL 492 THE POOL AREA HAS BEEN INCLUDED IN THE INFILTRATION TRENCH SIZING CALCULATIONS. SSCO DESIGNED WITHIN 50' OF POOL. NEW DWI (ROW) 116 NEW OFFSITE DRIVEWAY WILL SHEET FLOW WITHIN ROW. NOTE: TOTAL NEW/REPLACED IMPERVIOUS SURFACES ON -SITE ARE 8,294 SF • APPROX 143 OF THE WALKWAY AREAS SHOWN IN PLAN VIEW ARE SLATTED DRIP THROUGH DECK AREAS AND ARE NOT TO BE COUNTED AS IMPERVIOUS HOWEVER, HAS BEEN INCLUDED IN CALCULATIONS PER CITY REQUEST. 4" CIA PERFORATED PVC PIPE WITH 6" OF 1" MINUS GRAVEL ALL AROUND, WRAPPED IN NON -WOVEN GEOTEXTILE FABRIC, SLOPE 8" MIN FROM WOOD. AT 0.5%MIN. TURN DOWN SEE STRUCTURAL DRAWINGS PERFORATIONS AS SHOWN 6" DOWNSPOUTTIGHTLINE III 70 CONVEYANCE SYSTEM FINISHED GRADE @ 0.5%MIN. PLACE NEXT < TO FOOTING DRAIN OR AS SHOWN ON GRAD I NG& DRAINAGE PLAN 1 I (CONTRACTOR MAY LOCATE ON EITHER SIDE OF 0 FOOTING DRAIN) . OO , o n O O.O° p9 a e O Q a LINE OF MAX EXCAVATION. O O OO °0 n e IF SOIL 15 OVEREXCAVATED, REPLACE WITH LEAN MIX / CONCRETE / a 1 FOOTING FOOTING AND ROOF DRAIN SECTION G % SCALE: NTS FINISHED LEVEL OF EXPANSION JOINT CONCRETE SURROUND TO BE APPROX 1/8" ABOVE INSTALL ACO DRAIN TOP OF CHANNEL EDGE MODEL K1005 OR EQUAL SURFACING PER d CIVIL DRAWINGS CONCRETE 3000 PSI MIN BEDDING LAYER "-IIt IFIT' iir 6I 6 TRENCH DRAIN (IN CONCRETE) 3 SCALE: 1" = V-0" ASPHALT CONCRETE WEARING COURSE HMA CLASS 1/2" PG 64-22 (WSDOT STD SPEC 5-04.1) ul Z �.°° l- CRUSHED SURFACING BASE COURSE (WSDOT STD SPEC 9-03.9(3)) Cyo ° -III-III-III-III-III-III SUITABLE NATIVE MATERIAL FILL; - TOP 12"COMPACTED TO III -III -III -III -III -III MINIMUMOF95%RELATIVE -III-III-III- -IF COMPACTION USING AASHTO T-180 III -III -III -III -III -III- (ASTM D1557). UNSUITABLE NATIVE MATERIAL SHALL BE REPLACED TYPICAL PAVEMENT SECTION BLD2023-0799 & BLD2023-0811 APPROVED FOR CONSTRUCTION CITY OF EDMONDS DATE: BY: CITY ENGINEERING DIVISION W 0 Q LJ Q J LJ a N U Q a- O oo L-I--I Ld Y U 0 � Q 0 � � � Z zLdvi ZQ a0 Z Q Z Q Q U C) 0 00 LLJ 0 E SHEET C3.1 Table V-A.1: Maintenance Standards - Detention Ponds (continued) Maintenance Com- Defect Conditions When Maintenance Is Needed Results Expected When Maintenance Is Performed ponent Liner (if Applic- able) Liner is visible and has more than three 1/4-inch holes in it. Liner repaired or replaced. Liner is fully covered. Any part of berm which has settled 4 inches lower than the design elevation If settlement is apparent, measure berm to determine amount of settlement Settlements Settling can be an indication of more severe problems with the berm or outlet works. A Dike is built back to the design elevation. licensed engineer in the state of Washington should be consulted to determine the source of Ponds Berms (Dikes) the settlement. Discernable water flow through pond berm. Ongoing erosion with potential for erosion to con- tinue. Piping Piping eliminated. Erosion potential resolved. (Recommend a Gcethechnical engineer be called in to inspect and evaluate condition and recommend repair of condition. Tree growth on emergency spillways creates blockage problems and may cause failure of the bens due to uncontrolled overtopping. Trees should be removed. If root system is small (base less than 4 inches) the root system may be left in Tree Growth place. Otherwise the roots should be removed and the berm restored. A licensed engineer in the state of Emergency Overflow/ Tree growth on berms over 4 feet in height may lead to piping through the berm which could Washington should be consulted for proper berm/spillway restoration. Spillway Berms lead to failure of the berm. and over 4 feet in height Discernable waterflow through pond berm. Ongoing erosion with potential for erosion to con- tinue. Piping Piping eliminated. Erosion potential resolved. (Recommend a Geotechnical engineer be called in to inspect and evaluate condition and recommend repair of condition. Only one layer of rock exists above native soil in area five square feet or larger, or any expos - Emergency Over- Emergency Over- ure of native soil at the top of out flow path of spillway. Rocks and pad depth are restored to design standards. flow/Spillway flow/Spillway (Rip -rap on inside slopes need not be replaced.) Erosion See "Side Slopes of Pond" Table V-A.2: Maintenance Standards - Infiltration Maintenance Component Defect Conditions When Maintenance Is Needed Results Expected When Maintenance Is Per- formed See Table V-A.1: Maintenance Standards - Deten- Trash & Debris See Table V-A.1: Maintenance Standards - Detention Ponds tion Ponds Poisonous/Noxious See Table V-A.1: Maintenance Standards - Deten- See Table V-A. Maintenance Standards - Detention Ponds General Vegetation tion Ponds Contaminants and Pol- See Table V-A.1: Maintenance Standards - Deten- See Table V-A. Maintenance Standards - Detention Ponds lution tion Ponds See Table V-A.1: Maintenance Standards - Deten- Rodent Holes See Table V-A.1: Maintenance Standards - Detention Ponds tion Ponds Water ponding in infiltration pond after rainfall ceases and appropriate time allowed for infiltration. Treatment basins should infiltrate Sediment is removed and/or facility is cleaned so Storage Area Sediment Water Quality Design Storm Volume within 48 hours, and empty within 24 hours after cessation of most rain events. that infiltration system works according to design. 2019 Stormwater Management Manual for Western Washington Volume V - Appendix A - Page 1006 Table V-A.2: Maintenance Standards - Infiltration (continued) Maintenance Component Defect Conditions When Maintenance Is Needed Results Expected When Maintenance Is Per- formed (A percolation test pit ortest of facility indicates facility is only working at 90 % of its designed capabilities. Test every 2 to 5 years. If two inches or more sediment is present, remove). Filled with Sediment and Filter Bags if a licable 9( applicable) Debris Sediment and debris fill bagmore than 112 full. Filter bag is replaced ors stem is redesigned. 9y 9 Rock Filters Sediment and Debris By visual inspection, little or no water flows through filter during heavy rain storms. Gravel in rock filter is replaced. Side Slopes of Pond Erosion See Table V-A.1: Maintenance Standards - Detention Ponds See Table V-A.1: Maintenance Standards - Deten- tion Ponds Tree Growth See Table V-A.1: Maintenance Standards - Detention Ponds See Table V-A.1: Maintenance Standards - Deten- Emergency Overflow Spillway tion Ponds and Berms over feet in height. See Table V-A. Maintenance Standards - Deten- Piping See Table V-A.1: Maintenance Standards -Detention Ponds tion Ponds Rock Missing See Table V-A.1: Maintenance Standards - Detention Ponds See Table V-A.1: Maintenance Standards - Deten- Emergency Overflow Spillway tion Ponds Erosion See Table V-A.1: Maintenance Standards - Detention Ponds See Table V-A.1: Maintenance Standards - Deten- tion Ponds Facility or sump filled Pre -settling Ponds and Vaults with Sediment and/or 6" or designed sediment trap depth of sediment. Sediment is removed. debris Table V-A.3: Maintenance Standards - Closed Detention Systems (TanksiVaults) Maintenance Defect Conditions When Maintenance is Needed Results Expected When Maintenance is Per - Component formed Plugged Air Vents One-half of the cross section of a vent is blocked at any point orthe vent is damaged. Vents open and functioning. Accumulated sediment depth exceeds 10% of the diameter of the storage area for 1/2 length of storage vault or any point Debris and Sediment depth exceeds 15 % of diameter. All sediment and debris removed from storage (Example: 72-inch storage tank would require cleaning when sediment reaches depth of 7 inches for more than 1/2 length of area. Storage Area tank.) Any openings or voids allowing material to be transported into facility. Joints Between Tank/Pipe Section All joint between tank/pipe sections are sealed. (Will require engineering analysis to determine structural stability). Tank Pipe Bent Out of Shape Any part of tank/pipe is bent out of shape more than 10% of its design shape. (Review required by engineerto determine Tank/pipe repaired or replaced to design. structural stability). Cracks wider than 1/2-inch and any evidence of soil particles entering the structure through the cracks, or main- Vault replaced or repaired to design spe- Vault Structure Includes Cracks in Wall, Bottom, tenance/inspection personnel determines that the vault is not structurally sound. cifications and is structurally sound. Damage to Frame and/or Top Slab Cracks wider than 1/2-inch at the joint of any inlet/outlet pipe or any evidence of soil particles entering the vault through the No cracks more than 1/4-inch wide at thejoint of walls. the inlet/outlet pipe. 2019 Stormwater Management Manual for Western Washington Volume V - Appendix A - Page 1007 Table V-A.S: Maintenance Standards - Catch Basins Maintenance Defect Conditions When Maintenance is Needed Results Expected When Maintenance is per - Component formed Trash or debris which is located immediately in front of the catch basin opening or is blocking inletting capacity of the basin by more than 10 % . No Trash or debris located immediately in front of Trash or debris (in the basin) that exceeds 60 percent of the sump depth as measured from the bottom of basin to invert of the lowest pipe into or out of the catch basin or on grate opening. basin, but in no case less than a minimum of six inches clearance from the debris surface to the invert of the lowest pipe. No trash or debris in the catch basin. Trash & Debris Trash or debris in an inlet or outlet i blocking more than 1/3 of its height. Y pipe 9 9 Inlet and outlet pipes free of trash or debris. Dead animals or vegetation that could generate odors that could cause complaints or dangerous gases (e.g., methane). No dead animals or vegetation present within the catch basin. Sediment (in the basin) that exceeds 60 percent of the sump depth as measured from the bottom of basin to invert of the lowest pipe into or out of the Sediment basin, but in no case less than a minimum of 6 inches clearance from the sediment surface to the invert of the lowest pipe. No sediment in the catch basin General Structure Damage to To slab has holes larger than 2 square inches or cracks wider than 1/4 inch. Intent is to make sure no material is running into basin P r9 q ( 9 )� Top slab is free of holes and cracks. Frame and/or Top Slab Frame not sitting flush on top slab, i.e., separation of more than 3/4 inch of the frame from the top slab. Frame not securely attached Frame is sitting flush on the riser rings or top slab and firmly attached. Fractures or Cracks in Maintenance person judges that structure is unsound. Basin replaced or repaired to design standards. Basin Walls/ Bottom Grout fillet has separated orcracked widerthan 1/2 inch and longerthan 1 foot at thejoint of any inlet/outlet pipe or any evidence of soil particles entering Pipe is regrouted and secure at basin wall. catch basin through cracks. Settlement/ Mis- alignment If failure of basin has created a safety, function, or design problem. Basin replaced or repaired to design standards. Vegetation growing across and blocking more than 10% of the basin opening. No vegetation blocking opening to basin. Vegetation Vegetation growing in inlet/outlet pipe joints that is more than six inches tall and less than six inches apart. No vegetation or root growth present. Contamination and Pol- See Table V-A.1: Maintenance Standards - Detention Ponds No pollution present. lution Cover Not in Place Cover is missing oronly partially in place. Any open catch basin requires maintenance. Cover/grate is in place, meets design standards, and is secured Catch Basin Locking Mechanism Not Working Mechanism cannot be opened by one maintenance person with proper tools. Bolts into frame have less than 1/2 inch of thread. Mechanism opens with proper tools. Cover Cover Difficult to One maintenance person cannot remove lid after applying normal lifting pressure. Cover can be removed by one maintenance per - Remove (Intent is keep coverfrom sealing off access to maintenance.) son. Ladder Ladder Rungs Unsafe Ladder is unsafe due to missing rungs, not securely attached to basin wall, misalignment, rust, cracks, or sharp edges. Ladder meets design standards and allows main- tenance person safe access. Grate opening Unsafe Grate with opening wider than 7/8 inch. Grate opening meets design standards. Metal Grates Trash and Debris Trash and debris that is blocking more than 20% of grate surface inletting capacity. Grate free of trash and debris. (If Applicable) Damaged or Missing. Grate missing or broken member(s) of the grate. Grate is in place, meets the design standards, and is installed and aligned with the flow path. 2019 Stormwater Management Manual for Western Washington Volume V - Appendix A - Page 1009 Table V-A.17: Maintenance Standards - Coalescing Plate Oil/Water Separators Maintenance Component Defect Condition When Maintenance is Needed Results Expected When Maintenance is Performed Monitoring Inspection of discharge waterforobvious signs of poor water quality. Effluent discharge from vault should be clearwith no thick visible sheen. Sediment Accumulation Sediment depth in bottom of vault exceeds 6-inches in depth and/or visible signs of sediment on No sediment deposits on vault bottom and plate media, which would impede flow plates. through the vault and reduce separation efficiency. Trash and Debris Accumulation Trash and debris accumulated in vault, or pipe inlet/outlet, floatables and non-floatables. Trash and debris removed from vault, and inlet/outlet piping. Oil Accumulation Oil accumulation that exceeds 1-inch at the watersurface. Oil is extracted from vault using vactoring methods. Coalescing plates are cleaned by thoroughly rinsing and flushing. Should be no visible oil depth on water. Damaged Coalescing Plates Plate media broken, deformed, cracked and/or showing signs of failure. A portion of the media pack or the entire plate pack is replaced depending on sever- ity of failure. General Damaged Pipes Inlet or outlet piping damaged or broken and in need of repair. Pipe repaired and or replaced. Baffles Baffles corroding, cracking, warping and/or showing signs of failure as determined by main- Baffles repaired or replaced to specifications. tenance/inspection person. Cracks widerthan 1/2-inch or evidence of soil particles entering the structure through the cracks, Vault replaced or repairs made so that vault meets design specifications and is Vault Structure Damage - Includes Cracks in or maintenance/inspection personnel determine that the vault is not structurally sound. structurally sound. Walls, Bottom, Damage to Frame and/or Top Slab Cracks widerthan 1/2-inch at thejoint of any inlet/outlet pipe or evidence of soil particles enter- Vault repaired so that no cracks exist wider than 1/4-inch at the joint of the ing through the cracks. inlet/outlet pipe. Access Ladder Damaged Ladder is corroded or deteriorated, not functioning properly, not securely attached to structure Ladder replaced or repaired and meets specifications, and is safe to use as determ- wall, missing rungs, cracks, and misaligned. ined by inspection personnel. Table V-A.18: Maintenance Standards - Catch Basin Inserts Maintenance Component Defect Conditions When Maintenance is Needed Results Expected When Maintenance is Performed Sediment Accumulation When sediment forms a cap over the insert media of the insert and/or unit. No sediment cap on the insert media and its unit. Trash and Debris Accumulation Trash and debris accumulates on insert unit creating a blockage/restriction. Trash and debris removed from insert unit. Runoff freely flows into catch basin. Media Insert Not Removing Oil Effluent waterfrom media insert has a visible sheen. Effluent waterfrom media insert is free of oils and has no visible sheen. General Media Insert Water Saturated Catch basin insert is saturated with water and no longer has the capacity to absorb. Remove and replace media insert Media Insert -Oil Saturated Media oil saturated due to petroleum spill that drains into catch basin. Remove and replace media insert. Media Insert Use Beyond Product Life Media has been used beyond the typical average life of media insert product. Remove and replace media at regular intervals, depending on insert product. Table V-A.19: Maintenance Standards - Media Filter Drain (MFD) Maintenance Component Defect Conditions When Maintenance is Needed Results Expected When Maintenance is Performed Sediment accumulation Remove sediment deposits on grass treatment area of the embankment. When finished, embank - on grass filter Sediment depth exceeds 2 inches or creates uneven grading that interferes with sheet flow. ment should be level from side to side and drain freely toward the toe of the embankment slope. General strip There should be no areas of standing water once inflow has ceased. No -vegetation Flow spreader is uneven or clogged so that flows are not uniformly distributed over entire embankment width. Level the spreader and clean to spread flows evenly over entire embankment width. 2019 Stormwater Management Manual for Western Washington Volume V - Appendix A - Page 1017 Cochran Residence - CG #23038.20 August 23, 2024 Drainage Report Section VIII, Page 42 Figure VIII-1. Map of project area (from Edmonds GIS). 250 4th Avenue South, Suite 200 Edmonds, WA 98020 42 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com Cochran Residence - CG #23038.20 Drainage Report August 23, 2024 Section VIII, Page 43 SAMPLE ACTIVITY LOG DATE FACILITY MAINTENANCE PERFORMED RESULTS / NOTES C GM ENGINEERING 43 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Cochran Residence - CG #23038.20 Drainage Report August 23, 2024 Appendix A, Page 44 Appendix A —Attached Reports 250 4th Avenue South, Suite 200 CM Edmonds, WA 98020 43 ph.425.778.8500 1 f.425.778.5536 ENGINEERING www.cgengineering.com Main Office 17311 — 1351 Ave NE, A-500 Woodinville, WA 98072 (425) 486-1669 - FAX (425) 481-2510 February 2, 2018 Mr. Reed Johnson 8498 Talbot Road Edmonds, WA 98026 Stormwater Infiltration Letter Reed Johnson Short Plat 8498 Talbot Road Edmonds, Washington NGA Job No. 1021818 Dear Mr. Johnson: NELSON E T NI AL AssociATEs, INC. GEOT'ECHNICAL ENGINEERS & GEOLOGIST'S Engineering -Geology Branch 5526 Industry Lane, ##2 East Wenatchee, WA 98802 (509) 665-7696 � FAX (509) 665-7692 This letter documents our explorations and provides our opinions and recommendations for the feasibility of stormwater infiltration at the property located at 8498 Talbot Road in Edmonds, Washington, as shown on the Vicinity Map in Figure 1. INTRODUCTION The subject site consists of an irregular -shaped parcel that is currently occupied by a single-family residence and a detached garage within the northern and central portions of the property, respectively. We understand that the proposed development will consist of subdividing the property into two separate northern and southern parcels. The existing residence and garage will remain in the northern parcel while the southern parcel will likely be developed with a new single-family residence. We understand that stormwater generated within the property may be directed to onsite infiltration systems, if feasible. We have been requested to evaluate the infiltration capacity of the site soils within the property. The City of Edmonds utilizes the 2014 Department of Ecology (DOE) Stormwater Management in Western Washington, manual to determine the design of infiltration or detention facilities. According to this manual, long-term design infiltration rates for this site are to be determined by performing on -site infiltration testing consisting of the Small Pilot Infiltration Test (PIT). For our use in preparing this letter, we were provided with a preliminary site plan titled "Reed Johnson Short Plat," dated July 31, 2017, prepared by CSP Engineering, showing the existing and proposed site conditions. Stormwater Infiltration Letter NGA File No. 1021818 Reed Johnson Short Plat February 2, 2018 Edmonds, Washington Page 2 Specifically, our scope of set -vices included the following: 1. A review of available soil and geologic maps of the area. 2. Exploring the subsurface soil and groundwater conditions within the site with backhoe excavated test pits. The bacidioe was provided by the client. 3. Performing grain -size sieve analysis on selected soil samples, as needed. 4. Determining feasibility of on -site storinwater infiltration. 5. Providing long-term design infiltration rates based on one on -site Small Scale Pilot Infiltration Test (PIT) per the 2014 DOE Stornwater Manual. Location and depth of tests to be determined by civil engineer. Water for the test to be secured by client. 6. Providing recommendations for infiltration system installation. 7. Documenting the results of our findings, conclusions, and recommendations in a written geotechnical letter. SITE CONDITIONS Surface Conditions The subject site consists of a irregular -shaped lot covering approximately 0.92-acres. The ground surface within the proposed development area within the the central and northern portion of the property slopes gently from the east to the west. An existing single-family residence is located within the northern portion of the property. The property is mostly vegetated with grass yard areas and scattered landscaping plants, as well as mature coniferous trees throughout the southern portion of the property. We did not observe surface water within the site during our visit on January 17, 2018. Subsurface Conditions: The geologic units for this area are shown on the Geologic Map of the Edmonds East and part of the Edmonds West Quadrangles, Washington, by James P. Minard (USGS, 1983). The site is mapped Qvt (Glacial Till) deposits with Qva (Advance Outwash) mapped nearby. Till is described as a non -sorted mixture of clay, silt, sand, pebbles, cobbles, and boulders. The advance outwash is described as mostly clean gray pebbly sand. The soils generally encountered in our explorations consisted of fine to medium sand with varying amounts of silt and gravel consistent with the description of advance outwash deposits at depth. Explorations: The subsurface conditions within the site were explored on January 17, 2018 by observing the soil and groundwater conditions with three bacldioe excavated test pits and one hand auger exploration. The approximate locations of the explorations are shown on the Site Plan in Figure 2. A geologist from NGA was present during the explorations, examined the soils and geologic conditions encountered, obtained samples of the different soil types, and maintained logs of the explorations. NELSON GEOTECHNICAL ASSOCIATES, INC. Stormwater Infiltration Letter NGA File No. 1021818 Reed Johnson Short Plat February 2, 2018 Edmonds, Washington Page 3 The soils were visually classified in general accordance with the Unified Soil Classification System, presented in Figure 3. The logs of our explorations are attached to this letter and are presented in Figures 4 and 5. We present a brief summary of the subsurface conditions in the following paragraph. For a detailed description of the subsurface conditions, the exploration logs should be reviewed. Hand Auger 1 and Test Pit 2 encountered surficial fill composed of light gray, silt and fine to medium sand with roots and fine gravel within the top 0.4 feet of soil, and were underlain by 1.3 to 1.7 feet of red - brown, silty fine to medium sand with gravel in a loose to medium dense condition. Test Pit 1 and Infiltration Pit 1 encountered surficial topsoil to depths of 0.1 and 0.9 feet, underlain by red -brown to brown, silty fine to medium sand with gravel to depths of 1.5 and 2.0 feet, respectively. Underlying this material in all explorations, we encountered yellow -gray to gray, fine to medium sand with varying amounts of silt and fine gravel that we interpreted as native advance outwash soils. All of our explorations were terminated within the native advance outwash soils at a depth of 5.0 to 9.5 feet below the existing ground surface. Hydrogeologic Conditions Moderate groundwater seepage was encountered within our deepest exploration, Test Pit 1, at a depth of 8.7 feet below the existing ground surface. If groundwater is encountered during construction we would interpret this water to be perched. Perched water occurs when surface water infiltrates through less dense, more permeable soils, such as topsoil and the weathered horizon, and accumulates on top of a less permeable soil. Perched water does not represent a regional groundwater "table" within the upper soil horizons. Perched water tends to vary spatially and is dependent upon the amount of rainfall. We would expect the amount of groundwater to decrease during drier times of the year and increase during wetter periods. Stormwater Infiltration The subsurface soils generally consisted of topsoil and/or fill underlain by fine to coarse sand with varying amounts of silt and gravel to the depths explored within the proposed infiltration areas. We conducted on -site infiltration testing in accordance with the 2014 Department of Ecology DOE Stormwater ManalZement in Western Washington, to determine the long term design infiltration rate of the site soils. On -site testing consisted of a Small Pilot Infiltration Test (Small PIT) to determine the long-term design infiltration rates. NELSON GEOTECHNICAL ASSOCIATES, INC. Stormwater Infiltration Letter NGA File No. 1021818 Reed Johnson Short Plat February 2, 2018 Edmonds, Washington Page 4 We conducted a Small PIT within Infiltration Pit 1, located as shown on the attached Schematic Site Plan in Figure 2. The test was conducted within a pit that measured 5.2-feet long by 2.7-feet wide by 3.5-feet deep. We attempted to fill the pit with 12-inches of water at the beginning of the day and were able to reach a head of 11.50 inches within the soaking period of the PIT for approximately 6 hours. At this time, the water flow rate into the hole was monitored with a Great Plains Industries (GPI) TM 075 water flow meter for the pre-soak period. After the 6-hour soaking period was completed, the water level was maintained at approximately 11.50- inches for one hour for the steady-state period. The flow rate for Infiltration Pit 1 stabilized at 4.70 gallons per minute (282 gallons per hour). This equated to an approximate infiltration rate of 32.22 inches per hour. The water was shut off after the steady-state period and monitored at least every 15 minutes. After 19 minutes, the water level within the pit dropped the entire 11.50-inches, resulting in an infiltration rate of 36.71 inches per hour. In accordance with the Table 3.5 of the Department of Ecology 2014 Stormwater Management Manual for Western Washington, correction factors of 0.8, 0.5, and 0.9 for CF,,, CFt, CF,,,, respectively were applied to the field measured infiltration rate of 36.71 inches per hour, obtained from the falling -head portion of the testing. A total correction factor of 0.36 was applied to the measured field infiltration rate obtained from the falling head portion of the test to determine the long-term design infiltration rate. Using the above correction factor, we calculated a long-term design infiltration rate of approximately 13.22 inches per hour. In our opinion, a long-term design infiltration rate of 10 inches per hour could be utilized to design the on -site infiltration systems within the native, fine to medium sand with gravel and varying amounts of silt found on this site at depth. CONCLUSIONS It is our opinion that stormwater infiltration within the site is feasible. We recommend that the base of any on -site infiltration systems be terminated within the granular glacial outwash soils encountered at depth within the site. We recommend these systems be sized and designed in accordance with the 2014 Stormwater Management Manual for Western Washington. The infiltration systems should be sized and designed utilizing a long-term infiltration rate of 10 inches per hour. NGA must be retained to observe the bottom of any infiltration systems to confirm the above rate applies. This is due to the large swing in silt content from within the site soils. We encountered perched groundwater at a depth of approximately 8.7 feet below the existing ground surface in Test Pit 1. The 2014 Stormwater Management Manual for Western Washington gton requires that a minimum five foot separation and the base of the proposed infiltration system be maintained. As a result, NELSON GEOTECHNICAL ASSOCIATES, INC. Stormwater Infiltration Letter NGA File No. 1021818 Reed Johnson Short Plat February 2, 2018 Edmonds, Washington Page 5 we recommend that the base of the proposed infiltration system be founded no deeper than 3.5 feet below the existing ground surface to maintain the separation from the bottom of the proposed infiltration and the observed perched groundwater encountered at depth. We recommend that any proposed infiltration systems be placed as to not negatively impact any proposed or existing nearby structures and also meet all required setbacks from existing property lines, structures, and sensitive areas as discussed in the drainage manual. In general, infiltration systems should not be located within proposed fill areas within the site associated with site grading or retaining wall backfill as such condition could lead to failures of the placed fills and/or retaining structures. We should be retained to evaluate the infiltration system design and installation during construction. USE OF THIS LETTER This letter was prepared for Mr. Reed Johnson and his agents, for use in planning and budgeting the above -referenced project only. Our services included an evaluation of the infiltration capability of the site soils at specific locations and should not be considered as an in-depth geotechnical study of the site or an evaluation of the overall site stability. This letter may be used for bidding and estimating purposes, but our letter, conclusions, and interpretations should not be construed as a warranty of the subsurface conditions. The subsurface conditions between explorations may vary. A contingency for varying conditions should be incorporated into the project plans. We recommend that NGA be retained to review the design and provide monitoring and consultation services during construction to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes should the conditions revealed during the work differ from those anticipated, and to evaluate whether or not earthwork activities comply with contract plans and specifications. We should be contacted a minimum of one week prior to construction activities and could attend pre -construction meetings if requested. Within the limitations of scope, schedule, and budget, our services have been performed in accordance with generally accepted geotechnical engineering practices in effect in this area at the time this report was prepared. No other warranty, expressed or implied, is made. Our observations, findings, and opinions are a means to identify and reduce the inherent risks to the owner. NELSON GEOTECHNICAL ASSOCIATES, INC. Stormwater Infiltration Letter Reed Johnson Short Plat Edmonds, Washington NGA File No. 1021818 February 2, 2018 Page 6 We appreciate the opportunity to provide service to you on this project. If you have any questions or require further information, please call. Sincerely, NELSON GEOTECHNICAL ASSOCIATES, INC. Carston T. Curd, GIT Staff Geologist 2883 I LEE S. BELLAH Lee S. Bellah, LG Project Geologist Khaled M. Shawish, PE Principal CTC:LSB:KMS:dy Five Figures Attached NELSON GEOTECHNICAL ASSOCIATES, INC. VICINITY MAP Not to Scale Project Site t- N "74 Pt,r�. tMadoNda,e g aer� � 0 V pQ P QO %at St SW v 12'..'1 Sl sil' .t P 1%LJSt Sl1' G O. 5 `D` `1yJ.S+SIY 175th S1 SVI T �i 176th St Sri A J a6 Southwest 7.b County Park D 9 180thSit SW � 1 oyinplc View D1 z N g rJ `j D 6 p� 1820d St SW 181 3 a o 9 3 C y s• t3 > P136eY1u1 � J � m 184thStSW SeaVie d D o . ��. a o Dlmlpic View Dr c 1951h PI SPi V .. o Hutt Park IBfithSiSW 5 Y ) c V187th St SW D 187111 St SW 0 J D P E R R I N V I L L E ;- o leeu,stsw a c _. Seaview �• L•ynndale Park o O d d Edmonds, WA Project Number Johnson Short Plat NELSON GEOTECHNICAL INC. No. Date Revision By I CK m 1021818 (� ASSOCIATES, N A 1 1/26/18 Original DPN LSB Infiltration GEOTECHNICAL ENGINEERS & GEOLOGISTS a Figure 1 Vicinity Map WaudinNlle Office East Wenatchee Office 17311-135th Ave NE, A-500 5526Indus Lane, #2 E Woodinville, WA98072 East Wenatchee, WA 98802 (425)486-1669/Fax:481-2510 ,w.nelsongeotech— (509)66576961Fax:665-7692 t Rd — ----�" --°'— Talbot _ r �I Existing Residence —�„ -� = ? I' Existing Garage ; ( `, LEGEND Property line PROPOSED LOT t {�_ � '�JNIUNE 9-R k DRIt£wAY NOTE 1 r LOCATRW AND Caf"ATION OF FUME 9R AND I I =. PROP03D LINE R SEPARATE POUT APMD ATT APPROLED UNDER SEPARATE PFRle1 APft1CARON I PROPOSED HA-1 III INF-1 LOT TP-2 I 1 ■- 2117 RO(f'AREA I.. I Proposed STOWWATER DANAfi1m/T SY U NOTE, ��.L F117W&NaE FAMLY REMMC TO Residence PROYIDE STORUWATER WANAfilENT . SYSTEW (INFURAIKW AND/OR DETENTION)- .. FOR ALL NEW ARERNWS RWACES - - : - 1,079 SF ORVEWAY (SEE I O1, 97E NA W MTM7 R1W-OF-rY W FURK DRVEWAY NOTEr TCMTY FOR CWPVNME MIH STOROWATER TP-1 1 sTgNNAMR STAWARDS W FORCE A 1F!€-D�F= • � 1 (sEE No) MUM PERar suSwnA / MAX DRnEwAr SLOPE Tu [ " OCm smLOCAATOR TTW (SERE NoTE F ) Y/ wA7ER I ASRM¢ FE40LE 1REE lO A[CgWCOAIE ') / NNRE 9R INfRASTRUCIURE (TIP) — — �. _ - - 74 _ - '�--� ;•S- -- � ME 94AADER TO PRO Fredrick 11/O(a® PALfl471T EDOE� —. -22' TOTAL PA1 WNT K .�-",- _- � _ rowvr�micrvw awnawn mo --.- - � Number and approximate location of infiltration test pit Number and approximate location of test pit 0 50 100 � 11• 11• � Scale: 1 inch = 50 feet M__ Number and approximate i location of hand auger Reference: Site Plan based on a plan dated July 31, 2017 titled "Reed Johnson Short Plat," prepared by CSP Engineering. Project Number Johnson Short Plat NELSON GEOTECHNICAL, No. Date Revision By CK 1021818 NGA ASSOCIATES, INC. 1 1126118 Original DON LSB Infiltration GEOTECHNICAL ENGINEERS & GEOLOGISTS Site P I a n Wood1 Wlle Office East Wenatchee OfficeFigure 2 17311-135th Ave, NE, A-500 5526 IndustryLena, W2 Woodlm'ie, WA 98072 East Wenalhee, WA 98802 (425)486-1669/Fax: 481-2510 w..w.nelsongeotah.can (509) 665-76961 Fax: 665-7692 UNIFIED SOIL CLASSIFICATION SYSTEM GROUP MAJOR DIVISIONS GROUP NAME SYMBOL CLEAN GW WELL -GRADED, FINE TO COARSE GRAVEL COARSE- GRAVEL GRAVEL GP POORLY -GRADED GRAVEL GRAINED MORE THAN 50 % GRAVEL GM SILTY GRAVEL OF COARSE FRACTION RETAINED ON SOILS NO.4 SIEVE WITH FINES GC CLAYEY GRAVEL SAND CLEAN SW WELL -GRADED SAND, FINE TO COARSE SAND SAND SP POORLY GRADED SAND MORE THAN 50 % RETAINED ON MORE THAN 50 % NO. 200 SIEVE OF COARSE FRACTION SAND SM SILTY SAND PASSES NO. 4 SIEVE WITH FINES Sc CLAYEY SAND FINE - SILT AND CLAY ML SILT INORGANIC GRAINED LIQUID LIMIT CL CLAY LESS THAN 50 % SOILS ORGANIC OL ORGANIC SILT, ORGANIC CLAY SILT AND CLAY MH SILT OF HIGH PLASTICITY, ELASTIC SILT INORGANIC MORE THAN 50 % PASSES LIQUID LIMIT CH CLAY OF HIGH PLASTICITY, FAT CLAY NO. 200 SIEVE 50 % OR MORE ORGANIC OH ORGANIC CLAY, ORGANIC SILT HIGHLY ORGANIC SOILS PT PEAT NOTES: 1) Field classification is based on visual SOIL MOISTURE MODIFIERS: examination of soil in general accordance with ASTM D 2488-93. Dry - Absence of moisture, dusty, dry to the touch 2) Soil classification using laboratory tests is based on ASTM D 2488-93. Moist -Damp, but no visible water. 3) Descriptions of soil density or Wet - Visible free water or saturated, consistency are based on usually soil is obtained from interpretation of blowcount data, below water table visual appearance of soils, and/or test data. Project Number NELSON GEOTECHNICAL No. Date Revision By CK 1021818 Johnson Short Plat �� ASSOCIATES, INC. NC7A Infiltration GEOTECHNICAL ENGINEERS & GEOLOGISTS 1 1/26/18 Original DPN LSB F I g u re 7 Soil Classification Chart Woed1nv11le Office East Wenatchee office 17311-1351h Ave. NE, A-500 5526 Industry Lane, 42 - WoodinvIle, WA 98072 East Wenatchee, WA 98802 (425) 486-16691 Fax:481-2510 ww.nels gaelech. (509) 665-76961 Fax: 665.7692 LOG OF EXPLORATION DEPTH (FEET) TEST PIT ONE 0.0 - 0.1 0.1 - 1.5 1.5 - 2.3 2.3 - 7.1 7.1 - 8.0 8.0 - 9.5 TEST PIT TWO 0.0 - 0.4 0.4 - 1.7 1.7 - 3.8 3.8 - 9.0 HAND AUGER ONE 0.0 - 0.3 0.3 - 2.0 2.0 - 3.6 3.6 - 5.0 CTC: USC SOIL DESCRIPTION TOPSOIL SM BROWN SILTY FINE TO MEDIUM SAND WITH ROOTS AND TRACE IRON OXIDATION STAINING (LOOSE, DRY) SP-SM LIGHT YELLOW -TAN FINE TO COARSE SAND WITH SILT (MEDIUM DENSE, DRY -MOIST) SP-SM LIGHT GRAY -TAN FINE TO MEDIUM SAND WITH SILT AND TRACE FINE GRAVEL AND IRON OXIDATION STAINING (DENSE, MOIST) SM BROWN SILTY FINE TO MEDIUM SAND WITH TRACE COARSE SAND AND IRON OXIDATION STAINING (MEDIUM DENSE, MOIST) SM GRAY SILTY FINE TO COARSE SAND WITH IRON OXIDATION STAINING (DENSE, WET) SAMPLES WERE COLLECTED AT 3.5, 4.5, 7.3, 7.5, AND 8.2 FEET MODERATE GROUNDWATER SEEPAGE WAS ENCOUNTERED AT 8.7 FEET TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 9.5 FEET ON 1/17/18 LIGHT GRAY SILT AND FINE TO MEDIUM SAND WITH ROOTS AND FINE GRAVEL (LOOSE, DRY -MOIST) (FILL) SM RED -BROWN SILTY FINE TO MEDIUM SAND WITH GRAVEL AND TRACE ROOTS (LOOSE -MEDIUM DENSE, MOIST) SM YELLOW -GRAY SILTY FINE TO MEDIUM SAND WITH TRACE FINE GRAVEL (DENSE, MOIST) SM GRAY SILTY FINE TO MEDIUM SAND WITH TRACE IRON OXIDATION STAINING (DENSE, MOIST) SAMPLES WERE COLLECTED AT 1.5, 3.0, AND 9.0 FEET GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 9.0 FEET ON 1/17/18 LIGHT GRAY SILT AND FINE TO MEDIUM SAND WITH ROOTS AND ORGANIC AND ANTHROPOGENIC DEBRIS (LOOSE, DRY) (FILL) SM RED -BROWN SILTY FINE TO MEDIUM SAND WITH GRAVEL AND TRACE ROOTS (LOOSE -MEDIUM DENSE, MOIST) SM YELLOW -GRAY SILTY FINE TO MEDIUM SAND WITH TRACE FINE GRAVEL (DENSE, MOIST) SM GRAY SILTY FINE TO MEDIUM SAND WITH TRACE IRON OXIDATION STAINING (DENSE, MOIST) NO SAMPLES WERE COLLECTED GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED TEST PIT CAVING WAS NOT ENCOUNTERED HAND AUGER WAS TERMINATED AT 5.0 FEET ON 1/17/18 NELSON GEOTECHNICAL ASSOCIATES, INC. FILE NO 1021818 FIGURE 4 LOG OF EXPLORATION DEPTH (FEET) USC SOIL DESCRIPTION INFILTRATION PIT ONE 0.0-0.9 DARK BROWN SILTY FINE TO MEDIUM SAND WITH TRACE FINE GRAVEL AND ROOTS (LOOSE, MOIST) (TOPSOIL) 0.9-2.0 SM RED -BROWN SILTY FINE TO MEDIUM SAND WITH GRAVEL AND TRACE ROOTS (LOOSE - MEDIUM DENSE, MOIST) 2.0 - 5.0 SM YELLOW -GRAY SILTY FINE TO MEDIUM SAND WITH TRACE FINE GRAVEL (DENSE, MOIST) SAMPLES WERE COLLECTED AT 0.5 AND 2.5 FEET GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED TEST PIT CAVING WAS NOT ENCOUNTERED INFILTRATION TEST PIT WAS TERMINATED AT 5.0 AT DEPTH ON 1/17/2018 CTC: NELSON GEOTECHNICAL ASSOCIATES, INC. FILE NO 1021818 FIGURE 5 NELSON GEOTECHNICAL ASSOCIATES. INC. May 2, 2024 Ryan and Sydney Cochran Via Email: ryanrcochran@gmail.com Geotechnical Comment Response Letter Cochran Residence Development Infiltration 8475 Frederick Place Edmonds, Washington NGA File No. 102181323 Dear Mr. and Mrs. Cochran: 17311-1351" Ave. N.E. Suite A-500 Woodinville, WA 98072 (425)486-1669 www.nelsongeotech.com This letter presents our geotechnical engineering comment response regarding the proposed residence development project located at 8475 Frederick Place in Edmonds, Washington. INTRODUCTION We understand that the proposed development for the property will include the construction of a new single-family residence and pool. We previously prepared a stormwater infiltration evaluation for the property for the previous owner dated February 2, 2018 and have since provided an updated memo dated February 21, 2023. We also provided a supplemental comment response letter dated March 1, 2024. We understand that the City of Edmonds has requested additional information regarding the geotechnical aspects of this project in a letter dated April 2, 2024. For our use in preparing this plan review letter, we have been provided with the following documents: • Civil plan set titled "Cochran Residence," dated February 23, 2024, prepared by CG Engineering. In the following section, we summarize the City's comments and our responses. Geotechnical Comment Response Letter Cochran Residence Development Infiltration Edmonds, Washington NGA File No. 10218623 May 2, 2024 Page 2 CITY OF EDMONDS STORMWATER REVIEW COMMENT AND OUR RESPONSE Comment 6: Per the Geotech report, the base of the infiltration trench shall be terminated within the granular glacial outwash soils. The Geotech report does not state the depth of the granular glacial outwash soils. Please provide a Geotech memo confirming the depth and update the trench dimensions if necessary. Our Response 6: Our previous explorations performed within the site generally encountered approximately 0.1 to 1.0 feet of surficial topsoil and/or undocumented fill underlain by red -brown to gray, fine to medium sand with varying amounts of silt and gravel, which we interpreted as native granular advance outwash soils to the depths explored. All of our explorations were terminated within the native granular advance outwash soils at depths in the range of 5.0 to 9.5 feet below the existing ground surface. Based on our explorations performed within the site, the native granular glacial outwash soils exist at depths in the range of 1.0 and 9.5 feet below the existing ground surface. Review of the provided plans indicates that the base of the infiltration trench will be approximately 7.7 feet below the existing ground surface. In our opinion, it appears that the proposed infiltration trench will be fully founded within the native granular advance outwash soils interpreted to underlie this site. We recommend that NGA be retained to observe the base of the infiltration trench during construction to confirm soil conditions will support the design infiltration rate. CLOSURE We recommend that NGA be retained to provide monitoring and consultation services during construction to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes should the conditions revealed during the work differ from those anticipated, and to evaluate whether or not earthwork activities comply with contract plans and specifications. ... NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Comment Response Letter Cochran Residence Development Infiltration Edmonds, Washington NGA File No. 10218623 May 2, 2024 Page 3 We appreciate the opportunity to provide service to you on this project. Please contact us if you have any questions regarding this letter or require further information. Sincerely, NELSON GEOTECHNICAL ASSOCIATES, INC. Lee S. Bellah, LG Senior Geologist 02.2024 Khaled M. Shawish, PE Principal LSB:KMS:dy NELSON GEOTECHNICAL ASSOCIATES, INC. NELSON GEOTECHNICAL ASSOCIATES. INC. March 1, 2024 Ryan and Sydney Cochran Via Email: ryanrcochran@gmail.com Geotechnical Comment Response Letter Cochran Residence Development Supplemental Infiltration 8475 Frederick Place Edmonds, Washington NGA File No. 10218623 Dear Mr. and Mrs. Cochran: 17311-135' Ave. N.E. Suite A-500 Woodinville, WA 98072 (425)486-1669 www.nelsongeotech.com This letter presents our geotechnical engineering comment response regarding the proposed residence development project located at 8475 Frederick Place in Edmonds, Washington. INTRODUCTION We understand that the proposed development for the property will include the construction of a new single-family residence and pool. We previously prepared a stormwater infiltration evaluation for the property for the previous owner dated February 2, 2018 and have since provided an updated memo dated February 21, 2023. We understand that the City of Edmonds has requested additional information regarding the geotechnical aspects of this project in a letter dated August 11, 2023. For our use in preparing this plan review letter, we have been provided with the following documents: • Civil plan set titled "Cochran Residence," dated February 23, 2024, prepared by CG Engineering. In the following section, we summarize the City's comments and our responses. Geotechnical Comment Response Letter Cochran Residence Development Infiltration Edmonds, Washington NGA File No. 10218623 March 1, 2024 Page 2 CITY OF EDMONDS STORMWATER REVIEW COMMENTS AND OUR RESPONSES Comment 11: Please provide a geotechnical memo addressing the retaining wall drainage and update the drainage plans accordingly. Our Response 11: Based on review of the plans it appears that all site retaining walls will have wall footing drains that will discharge into the proposed on -site infiltration system and on -site drywells. The residence retaining walls will be backed with a Miradrain mat tightlined to the footing drain and backfilled with free -draining backfill. The other site retaining walls will be backfilled within free -draining backfill surrounding the foundation footing drain. Comment 15: Edmonds GIS shows landslide and erosion hazards on site. Please provide a geotechnical memo supporting the placement of the proposed infiltration trench, building, pool, and other hardscapes in relation to the steep slopes on site. Additionally, please provide the Geotech with an updated proposed development footprint as the previous geotechnical memo shows that the Geotech did not have the updated proposed development footprint. Our Response 15: Please see the attached updated Site Plan in Figure 1 showing the most recent residence location footprint. Comment 24: The geotechnical report was completed using the 2014 DOE SWMMWW. Please submit a memo from Geotech that states that it is in compliance with the 2019 DOE SWMMWW. Our Response 24: In our opinion, our previous stormwater infiltration testing consisting of the small-scale PIT test was performed in compliance with the updated 2019 DOE SWMMWW. Comment 25: Please provide a memo from Geotech providing all of the information listed in Checklist 2, Lines 111 and Our Response 25: An itemized list of the items within Lines 111 and 112 of Checklist 2 have been included below. Our response to each item is followed in bold. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Comment Response Letter Cochran Residence Development Infiltration Edmonds, Washington LINE 111 List: Soils Report includes the following: • Topography within 500 feet of the proposed facility NGA File No. 10218623 March 1, 2024 Page 3 - Topography within 500 feet of the subject development generally slopes gently down toward the property from the east, south and west and gently away and down from the property to the north. Please see attached Figure 4 showing topographic contours within a 500 foot radius of the proposed development. • Depth to hydraulic restriction layer - A hydraulic restrictive layer was not encountered in our previous explorations. Please review attached exploration logs in Figures 2 and 3. • Detailed soil logs (see below) - Please review attached exploration logs in Figures 2 and 3. • Visual grain size analysis - This has been included in the exploration logs. Please review attached exploration logs in Figures 2 and 3. • Grain -size distribution (required if using the grain size analysis method to estimate infiltration rates) - This is not applicable as infiltration rates were based on on -site infiltration testing. • Textural class - This has been included in the exploration logs. Please review attached exploration logs in Figures 2 and 3. • Percent clay content (include type of clay, if known) - Clay soils were not encountered within our explorations so this is not applicable. • Cation exchange capacity - Cation exchange capacity testing was not performed on soil samples as the proposed infiltration facilities are not being utilized for groundwater quality treatment. • Color/ mottling - This has been included in the exploration logs. Please review attached exploration logs in Figures 2 and 3. • Variations and nature of stratification - This has been included in the exploration logs. Please review attached exploration logs in Figures 2 and 3. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Comment Response Letter Cochran Residence Development Infiltration Edmonds, Washington LINE 112 List: NGA File No. 10218623 March 1, 2024 Page 4 Detailed logs for each test pit or hole were prepared, along with a map showing the locations of the test pits or holes. Logs include: • Depth of log - This has been included in the exploration logs. Please review attached exploration logs in Figures 2 and 3. • Soil description - This has been included in the exploration logs. Please review attached exploration logs in Figures 2 and 3. • Depth to groundwater - This has been included in the exploration logs. Please review attached exploration logs in Figures 2 and 3. • Evidence of seasonal high groundwater elevation - This has been included in the exploration logs. Please review attached exploration logs in Figures 2 and 3. • Existing ground surface elevation - This has been included in the exploration logs. Please review attached exploration logs in Figures 2 and 3. • Proposed basin bottom elevation - Based on review of the most recent civil plans, it appears that the base of the proposed infiltration trench is at elevation 38.30 feet. • Presence of stratification that may impact the infiltration design - We did not encounter any stratification that may impact the infiltration design within our soil explorations. CLOSURE We recommend that NGA be retained to provide monitoring and consultation services during construction to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes should the conditions revealed during the work differ from those anticipated, and to evaluate whether or not earthwork activities comply with contract plans and specifications. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Comment Response Letter Cochran Residence Development Infiltration Edmonds, Washington NGA File No. 10218623 March 1, 2024 Page 5 We appreciate the opportunity to provide service to you on this project. Please contact us if you have any questions regarding this letter or require further information. Sincerely, NELSON GEOTECHNICAL ASSOCIATES, INC. Lee S. Bellah, LG Senior Geologist 3.01.2024 Khaled M. Shawish, PE Principal LSB:KMS:dy Four Figures Attached NELSON GEOTECHNICAL ASSOCIATES, INC. Site Plan LEGEND — • — Property line INF-1 Number and approximate location I of previous infiltration test pit TP-1 0 30 60 Number and approximate location of previous test pit HA-1 HA-101 Scale: finch - 30 feet Number and approximate _�_ Number and approximate location of previous hand auger I location of recent hand auger Reference: Site Plan based the civil plan set titled "Cochran Residence," dated February 23, 2024, prepared by CG Engineering Project Number Cochran Residence nELson GEOTECHnICAL No. Date Revision By cK 102181323 Development Infiltration , ASSOCIATES, inn 1 2/29/24 Original LSB LSB Figure 1 Site Plan / W. di -ill. Moe Wenatchee."lce , 7311-, 95th Ave. NF, A-500 105 Palouse St. Woodinville, WA 98072 Wenatchee, WA 98801 songeotech-com (425) 486-1669 / Fax: 481-2510 (509) 665-7696 / Fax: 665-7692 LOG OF EXPLORATION DEPTH (FEET) TEST PIT ONE (ELEV:46 FEET) 0.0 - 0.1 0.1 - 1.5 1.5 - 2.3 2.3 - 7.1 7.1 - 8.0 8.0 - 9.5 TEST PIT TWO (ELEV:57 FEET) 0.0 - 0.4 0.4 - 1.7 1.7 - 3.8 3.8 - 9.0 HAND AUGER ONE (ELEV:53 FEET) 0.0 - 0.3 0.3 - 2.0 2.0 - 3.6 3.6 - 5.0 LSB:KMS USC SOIL DESCRIPTION TOPSOIL SM BROWN SILTY FINE TO MEDIUM SAND WITH ROOTS AND TRACE IRON OXIDATION STAINING (LOOSE, DRY) SP-SM LIGHT YELLOW -TAN FINE TO COARSE SAND WITH SILT (MEDIUM DENSE, DRY -MOIST) SP-SM LIGHT GRAY -TAN FINE TO MEDIUM SAND WITH SILT AND TRACE FINE GRAVEL AND IRON OXIDATION STAINING (DENSE, MOIST) SM BROWN SILTY FINE TO MEDIUM SAND WITH TRACE COARSE SAND AND IRON OXIDATION STAINING (MEDIUM DENSE, MOIST) SM GRAY SILTY FINE TO COARSE SAND WITH IRON OXIDATION STAINING (DENSE, WET) SAMPLES WERE COLLECTED AT 3.5, 4.5, 7.3, 7.5, AND 8.2 FEET MODERATE GROUNDWATER SEEPAGE WAS ENCOUNTERED AT 8.7 FEET TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 9.5 FEET ON 1/17/18 LIGHT GRAY SILT AND FINE TO MEDIUM SAND WITH ROOTS AND FINE GRAVEL (LOOSE, DRY -MOIST) (FILL) SM RED -BROWN SILTY FINE TO MEDIUM SAND WITH GRAVEL AND TRACE ROOTS (LOOSE -MEDIUM DENSE, MOIST) SM YELLOW -GRAY SILTY FINE TO MEDIUM SAND WITH TRACE FINE GRAVEL (DENSE, MOIST) SM GRAY SILTY FINE TO MEDIUM SAND WITH TRACE IRON OXIDATION STAINING (DENSE, MOIST) SAMPLES WERE COLLECTED AT 1.5, 3.0, AND 9.0 FEET GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 9.0 FEET ON 1/17/18 LIGHT GRAY SILT AND FINE TO MEDIUM SAND WITH ROOTS AND ORGANIC AND ANTHROPOGENIC DEBRIS (LOOSE, DRY) (FILL) SM RED -BROWN SILTY FINE TO MEDIUM SAND WITH GRAVEL AND TRACE ROOTS (LOOSE -MEDIUM DENSE, MOIST) SM YELLOW -GRAY SILTY FINE TO MEDIUM SAND WITH TRACE FINE GRAVEL (DENSE, MOIST) SM GRAY SILTY FINE TO MEDIUM SAND WITH TRACE IRON OXIDATION STAINING (DENSE, MOIST) NO SAMPLES WERE COLLECTED GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED TEST PIT CAVING WAS NOT ENCOUNTERED HAND AUGER WAS TERMINATED AT 5.0 FEET ON 1/17/18 NELSON GEOTECHNICAL ASSOCIATES, INC. FILE NO 102181323 FIGURE 2 LOG OF EXPLORATION DEPTH (FEET) USC SOIL DESCRIPTION INFILTRATION PIT ONE (ELEV:46 FEET) 0.0 - 0.9 DARK BROWN SILTY FINE TO MEDIUM SAND WITH TRACE FINE GRAVEL AND ROOTS (LOOSE, MOIST) (TOPSOIL) 0.9-2.0 SM RED -BROWN SILTY FINE TO MEDIUM SAND WITH GRAVEL AND TRACE ROOTS (LOOSE - MEDIUM DENSE, MOIST) 2.0 - 5.0 SM YELLOW -GRAY SILTY FINE TO MEDIUM SAND WITH TRACE FINE GRAVEL (DENSE, MOIST) SAMPLES WERE COLLECTED AT 0.5 AND 2.5 FEET GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED TEST PIT CAVING WAS NOT ENCOUNTERED INFILTRATION TEST PIT WAS TERMINATED AT 5.0 AT DEPTH ON 1/17/2018 HAND AUGER 101 (ELEV:48 FEET) 0.0 - 1.0 DARK BROWN SILTY FINE TO MEDIUM SAND WITH TRACE FINE GRAVEL AND ROOTS (LOOSE, MOIST) (TOPSOIL) 1.0 - 2.0 SM RED -BROWN SILTY FINE TO MEDIUM SAND WITH GRAVEL AND TRACE ROOTS (LOOSE -MEDIUM DENSE, MOIST) 2.0 - 9.0 SM GRAY SILTY FINE TO MEDIUM SAND WITH TRACE IRON OXIDATION STAINING (DENSE, MOIST) SAMPLES WERE NOT COLLECTED GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED HAND AUGER CAVING WAS NOT ENCOUNTERED HAND AUGER WAS COMPLETED AT 9.0 FEET ON 2/8/23 HAND AUGER 102 (ELEV:48 FEET) 0.0 - 1.0 DARK BROWN SILTY FINE TO MEDIUM SAND WITH TRACE FINE GRAVEL AND ROOTS (LOOSE, MOIST) (TOPSOIL) 1.0 - 3.0 SM RED -BROWN SILTY FINE TO MEDIUM SAND WITH GRAVEL AND TRACE ROOTS (LOOSE -MEDIUM DENSE, MOIST) 3.0 - 9.0 SM GRAY SILTY FINE TO MEDIUM SAND WITH TRACE IRON OXIDATION STAINING (DENSE, MOIST) SAMPLES WERE NOT COLLECTED GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED HAND AUGER CAVING WAS NOT ENCOUNTERED HAND AUGER WAS COMPLETED AT 9.0 FEET ON 2/8/23 LSB:KMS NELSON GEOTECHNICAL ASSOCIATES, INC. 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Site Plan wnelson9eotech.com (425 Woodinville 8fi i1669IF z948125,0 (509 6657696;F z96657692 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 June 12, 2023 Preface Soil surveys contain information that affects land use planning in survey areas. They highlight soil limitations that affect various land uses and provide information about the properties of the soils in the survey areas. Soil surveys are designed for many different users, including farmers, ranchers, foresters, agronomists, urban planners, community officials, engineers, developers, builders, and home buyers. Also, conservationists, teachers, students, and specialists in recreation, waste disposal, and pollution control can use the surveys to help them understand, protect, or enhance the environment. Various land use regulations of Federal, State, and local governments may impose special restrictions on land use or land treatment. Soil surveys identify soil properties that are used in making various land use or land treatment decisions. The information is intended to help the land users identify and reduce the effects of soil limitations on various land uses. The landowner or user is responsible for identifying and complying with existing laws and regulations. Although soil survey information can be used for general farm, local, and wider area planning, onsite investigation is needed to supplement this information in some cases. Examples include soil quality assessments (http://www.nres.usda.gov/wps/ portal/nres/main/soils/health/) and certain conservation and engineering applications. For more detailed information, contact your local USDA Service Center (https://offices.sc.egov.usda.gov/locator/app?agency=nres) or your NRCS State Soil Scientist (http://www.nres.usda.gov/wps/portal/nres/detail/soils/contactus/? cid=nres142p2_053951). Great differences in soil properties can occur within short distances. Some soils are seasonally wet or subject to flooding. Some are too unstable to be used as a foundation for buildings or roads. Clayey or wet soils are poorly suited to use as septic tank absorption fields. A high water table makes a soil poorly suited to basements or underground installations. The National Cooperative Soil Survey is a joint effort of the United States Department of Agriculture and other Federal agencies, State agencies including the Agricultural Experiment Stations, and local agencies. The Natural Resources Conservation Service (NRCS) has leadership for the Federal part of the National Cooperative Soil Survey. Information about soils is updated periodically. Updated information is available through the NRCS Web Soil Survey, the site for official soil survey information. The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, age, disability, and where applicable, sex, marital status, familial status, parental status, religion, sexual orientation, genetic information, political beliefs, reprisal, or because all or a part of an individual's income is derived from any public assistance program. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA's TARGET Center at (202) 720-2600 (voice and TDD). To file a complaint of discrimination, write to USDA, Director, Office of Civil Rights, 1400 Independence Avenue, S.W., Washington, D.C. 20250-9410 or call (800) 795-3272 (voice) or (202) 720-6382 (TDD). USDA is an equal opportunity provider and employer. 3 Contents Preface.................................................................................................................... 2 How Soil Surveys Are Made..................................................................................5 SoilMap.................................................................................................................. 8 SoilMap................................................................................................................9 Legend................................................................................................................10 MapUnit Legend................................................................................................ 11 MapUnit Descriptions.........................................................................................11 Snohomish County Area, Washington............................................................ 13 5—Alderwood-Urban land complex, 2 to 8 percent slopes ......................... 13 6—Alderwood-Urban land complex, 8 to 15 percent slopes ....................... 14 References............................................................................................................16 How Soil Surveys Are Made Soil surveys are made to provide information about the soils and miscellaneous areas in a specific area. They include a description of the soils and miscellaneous areas and their location on the landscape and tables that show soil properties and limitations affecting various uses. Soil scientists observed the steepness, length, and shape of the slopes; the general pattern of drainage; the kinds of crops and native plants; and the kinds of bedrock. They observed and described many soil profiles. A soil profile is the sequence of natural layers, or horizons, in a soil. The profile extends from the surface down into the unconsolidated material in which the soil formed or from the surface down to bedrock. The unconsolidated material is devoid of roots and other living organisms and has not been changed by other biological activity. Currently, soils are mapped according to the boundaries of major land resource areas (MLRAs). MLRAs are geographically associated land resource units that share common characteristics related to physiography, geology, climate, water resources, soils, biological resources, and land uses (USDA, 2006). Soil survey areas typically consist of parts of one or more MLRA. The soils and miscellaneous areas in a survey area occur in an orderly pattern that is related to the geology, landforms, relief, climate, and natural vegetation of the area. Each kind of soil and miscellaneous area is associated with a particular kind of landform or with a segment of the landform. By observing the soils and miscellaneous areas in the survey area and relating their position to specific segments of the landform, a soil scientist develops a concept, or model, of how they were formed. Thus, during mapping, this model enables the soil scientist to predict with a considerable degree of accuracy the kind of soil or miscellaneous area at a specific location on the landscape. Commonly, individual soils on the landscape merge into one another as their characteristics gradually change. To construct an accurate soil map, however, soil scientists must determine the boundaries between the soils. They can observe only a limited number of soil profiles. Nevertheless, these observations, supplemented by an understanding of the soil -vegetation -landscape relationship, are sufficient to verify predictions of the kinds of soil in an area and to determine the boundaries. Soil scientists recorded the characteristics of the soil profiles that they studied. They noted soil color, texture, size and shape of soil aggregates, kind and amount of rock fragments, distribution of plant roots, reaction, and other features that enable them to identify soils. After describing the soils in the survey area and determining their properties, the soil scientists assigned the soils to taxonomic classes (units). Taxonomic classes are concepts. Each taxonomic class has a set of soil characteristics with precisely defined limits. The classes are used as a basis for comparison to classify soils systematically. Soil taxonomy, the system of taxonomic classification used in the United States, is based mainly on the kind and character of soil properties and the arrangement of horizons within the profile. After the soil 5 Custom Soil Resource Report scientists classified and named the soils in the survey area, they compared the individual soils with similar soils in the same taxonomic class in other areas so that they could confirm data and assemble additional data based on experience and research. The objective of soil mapping is not to delineate pure map unit components; the objective is to separate the landscape into landforms or landform segments that have similar use and management requirements. Each map unit is defined by a unique combination of soil components and/or miscellaneous areas in predictable proportions. Some components may be highly contrasting to the other components of the map unit. The presence of minor components in a map unit in no way diminishes the usefulness or accuracy of the data. The delineation of such landforms and landform segments on the map provides sufficient information for the development of resource plans. If intensive use of small areas is planned, onsite investigation is needed to define and locate the soils and miscellaneous areas. Soil scientists make many field observations in the process of producing a soil map. The frequency of observation is dependent upon several factors, including scale of mapping, intensity of mapping, design of map units, complexity of the landscape, and experience of the soil scientist. Observations are made to test and refine the soil -landscape model and predictions and to verify the classification of the soils at specific locations. Once the soil -landscape model is refined, a significantly smaller number of measurements of individual soil properties are made and recorded. These measurements may include field measurements, such as those for color, depth to bedrock, and texture, and laboratory measurements, such as those for content of sand, silt, clay, salt, and other components. Properties of each soil typically vary from one point to another across the landscape. Observations for map unit components are aggregated to develop ranges of characteristics for the components. The aggregated values are presented. Direct measurements do not exist for every property presented for every map unit component. Values for some properties are estimated from combinations of other properties. While a soil survey is in progress, samples of some of the soils in the area generally are collected for laboratory analyses and for engineering tests. Soil scientists interpret the data from these analyses and tests as well as the field -observed characteristics and the soil properties to determine the expected behavior of the soils under different uses. Interpretations for all of the soils are field tested through observation of the soils in different uses and under different levels of management. Some interpretations are modified to fit local conditions, and some new interpretations are developed to meet local needs. Data are assembled from other sources, such as research information, production records, and field experience of specialists. For example, data on crop yields under defined levels of management are assembled from farm records and from field or plot experiments on the same kinds of soil. Predictions about soil behavior are based not only on soil properties but also on such variables as climate and biological activity. Soil conditions are predictable over long periods of time, but they are not predictable from year to year. For example, soil scientists can predict with a fairly high degree of accuracy that a given soil will have a high water table within certain depths in most years, but they cannot predict that a high water table will always be at a specific level in the soil on a specific date. After soil scientists located and identified the significant natural bodies of soil in the survey area, they drew the boundaries of these bodies on aerial photographs and I. Custom Soil Resource Report identified each as a specific map unit. Aerial photographs show trees, buildings, fields, roads, and rivers, all of which help in locating boundaries accurately. 7 Soil Map The soil map section includes the soil map for the defined area of interest, a list of soil map units on the map and extent of each map unit, and cartographic symbols displayed on the map. Also presented are various metadata about data used to produce the map, and a description of each soil map unit. N. 3 0 N N 548756 47' 50' 25' N 47° 50' 24" N Custom Soil Resource Report Soil Map 548764 54 m W780 548788 5487% 548804 548756 548764 548772 548780 54878E 548796 3 o Map Scale: 1:368 if printed on A landscape (11" x 8.5') sheet. Meters N 0 5 10 20 30 Feet 0 15 30 60 90 Map projection: Web Mercator Comer coordinates: WGS84 Edge tics: UTM Zone 1ON WGS84 9 548812 548820 548828 548804 548812 548820 548828 3 0 N 47° 50' 25" N i� N m 47° 50' 24" N 548836 ti MAP LEGEND Area of Interest (AOI) Area of Interest (AOI) Soils 0 Soil Map Unit Polygons ^/ Soil Map Unit Lines 0 Soil Map Unit Points Special Point Features V Blowout ® Borrow Pit Clay Spot 0 Closed Depression Gravel Pit Gravelly Spot O Landfill ALava Flow 46 Marsh or swamp �i Mine or Quarry OMiscellaneous Water OPerennial Water V Rock Outcrop + Saline Spot Sandy Spot Severely Eroded Spot O Sinkhole Slide or Slip 0o Sodic Spot Custom Soil Resource Report ,--y Spoil Area Q Stony Spot Very Stony Spot Wet Spot Other Special Line Features Water Features Streams and Canals Transportation Rails N Interstate Highways US Routes Major Roads Local Roads Background W Aerial Photography MAP INFORMATION The soil surveys that comprise your AOI were mapped at 1:24,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the 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 24, Sep 8, 2022 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Jul 31, 2022—Aug 8, 2022 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. 10 Custom Soil Resource Report Map Unit Legend Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI Alderwood-Urban land complex, 0.1 23.8% 2 to 8 percent slopes Alderwood-Urban land complex, 0.4 76.2% 8 to 15 percent slopes Totals for Area of Interest 0.6 100.0% 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, 11 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. 12 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 supply, 0 to 60 inches: Low (about 3.0 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 4s Hydrologic Soil Group: B Ecological site: F002XA004WA - Puget Lowlands Forest 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: Depressions Other vegetative classification: Wet Soils (G002XN102WA) Hydric soil rating: Yes 13 Custom Soil Resource Report Terric medisaprists, 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 supply, 0 to 60 inches: Low (about 3.0 inches) 14 Custom Soil Resource Report Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 4s Hydrologic Soil Group: B Ecological site: F002XA004WA - Puget Lowlands Forest 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 15 References American Association of State Highway and Transportation Officials (AASHTO). 2004. Standard specifications for transportation materials and methods of sampling and testing. 24th edition. American Society for Testing and Materials (ASTM). 2005. Standard classification of soils for engineering purposes. ASTM Standard D2487-00. Cowardin, L.M., V. Carter, F.C. Golet, and E.T. LaRoe. 1979. Classification of wetlands and deep -water habitats of the United States. U.S. Fish and Wildlife Service FWS/OBS-79/31. Federal Register. July 13, 1994. Changes in hydric soils of the United States. Federal Register. September 18, 2002. Hydric soils of the United States. Hurt, G.W., and L.M. Vasilas, editors. Version 6.0, 2006. Field indicators of hydric soils in the United States. National Research Council. 1995. Wetlands: Characteristics and boundaries. Soil Survey Division Staff. 1993. Soil survey manual. Soil Conservation Service. U.S. Department of Agriculture Handbook 18. http://www.nres.usda.gov/wps/portal/ nres/detail/national/soils/?cid=nres142p2_054262 Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making and interpreting soil surveys. 2nd edition. Natural Resources Conservation Service, U.S. Department of Agriculture Handbook 436. http:// www.nres.usda.gov/wps/portal/nres/detail/national/soils/?cid=nres142p2_053577 Soil Survey Staff. 2010. Keys to soil taxonomy. 11th edition. U.S. Department of Agriculture, Natural Resources Conservation Service. http:// www.nres.usda.gov/wps/portal/nres/detail/national/soils/?cid=nres142p2_053580 Tiner, R.W., Jr. 1985. Wetlands of Delaware. U.S. Fish and Wildlife Service and Delaware Department of Natural Resources and Environmental Control, Wetlands Section. United States Army Corps of Engineers, Environmental Laboratory. 1987. Corps of Engineers wetlands delineation manual. Waterways Experiment Station Technical Report Y-87-1. United States Department of Agriculture, Natural Resources Conservation Service. National forestry manual. http://www.nres.usda.gov/wps/portal/nres/detail/soils/ home/?cid=nres142p2_053374 United States Department of Agriculture, Natural Resources Conservation Service. National range and pasture handbook. http://www.nres.usda.gov/wps/portal/nres/ detail/national/landuse/rangepasture/?cid=stelprdb1043084 09 Custom Soil Resource Report United States Department of Agriculture, Natural Resources Conservation Service. National soil survey handbook, title 430-VI. http://www.nres.usda.gov/wps/portal/ nres/deta il/soils/scientists/?cid=nres142p2_054242 United States Department of Agriculture, Natural Resources Conservation Service. 2006. Land resource regions and major land resource areas of the United States, the Caribbean, and the Pacific Basin. U.S. Department of Agriculture Handbook 296. http://www.nres.usda.gov/wps/portal/nres/detail/national/soils/? cid=nres142p2_053624 United States Department of Agriculture, Soil Conservation Service. 1961. Land capability classification. U.S. Department of Agriculture Handbook 210. http:// www.nrcs.usda.gov/lnternet/FSE—DOCUMENTS/nrcsl42p2_052290.pdf 17 Cochran Residence - CG #23038.20 Drainage Report August 23, 2024 Appendix B, Page 45 Appendix B — Maintenance Covenant 250 4th Avenue South, Suite 200 Edmonds, WA 98020 44 ph.425.778.8500 1 f.425.778.5536 ENGINEERING 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 BMP Reference Number(s) of Related Documents City of Edmonds (permit number) Grantor(s) (Last, First and Middle Initial) Cochran, Ryan Cochran, Sidney Grantee: City of Edmonds Legal Description (abbreviated form; i.e., lot, plat or section, township, range, quarter/quarter) Section 07 Township 27 Range 04 Quarter SW TALBOT PARK BLK 000 D-02 LOT 2 OF CITY OF ED SP NO PLN-2017-0020 REC UND AFN 201908265001 BEING A PTN OF LOTS 63 & 64 SD PLAT Assessor's Property Tax Parcel/Account Number at the Time of Recording: 0059-4400-006-402 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 BMP WHEREAS, the undersigned Declarant(s) have installed one or more stormwater facilities under Edmonds Community Development Code (ECDC) Chapter 18.30 known as "stormwater best management practices (BMP)" as selected below: ❑ Permeable Pavement © Infiltration Trench/Gallery/Drywell ❑ Detention Pipe/Tank/Vault ❑ Concentrated Flow Dispersion ❑ Other: ❑ Infiltration Tank/Vault ❑ Sheet Flow Dispersion ❑ Reduced Impervious Footprint ❑ Rain Garden / Bioretention Cell WHEREAS, the City of Edmonds has allowed installation of the 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: 8475 FREDERICK PLACE 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: 1. Declarant(s) warrant that he/she/they/it is/are the owner(s) 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 agree that the Property contains one or more stormwater management facilities referred to as a '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. a. For infiltration -based BMPs, the BMP shall include all pretreatment devices upstream, the infiltration facility, and a minimum of 3-feet of soil beneath the infiltration contact layer, defined as the elevation at which runoff enters native soils. b. For bio-retention or rain garden BMPs, the BMP shall include all pretreatment devices upstream, the retention facility, the vegetation within the retention facility, and a minimum of 3-feet of soil beneath the infiltration contact layer, defined as the elevation at which runoff enters native soils. While specific plants are not necessarily required, a quantitative amount of vegetation coverage is required and may be subject to maintenance requests per Section 5. c. For dispersion based BMPs, the BMP shall include all pretreatment devices upstream, the dispersion mechanism/device, and all elements of the downstream vegetated flow path, including restrictions on slopes and surface materials, as required by ECDC 18.30. d. For detention BMPs, the BMP shall include all pretreatment devices upstream, the detention device, and the control structure device. e. For reduced impervious footprints, the BMP shall include all areas which are used as mitigation credits, including a full ten foot (10') driveway width when using wheel strip driveways. 3. The Owners shall maintain the size, placement, and design of the BMP as depicted on the approved site plan, Exhibit B, attached hereto and incorporated herein by this reference as if set forth in full, 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 a BMP is located. All costs of maintenance and repair shall be the sole responsibility of the Owners. 4. The Owners shall inspect 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 BMPs so they function 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 BMP facility. If, as the result of any such inspection, the City of Edmonds determines that the BMP is in disrepair, requires maintenance or repair, or is otherwise not functioning as provided in the site plan, the City Engineer or his designee shall have the right, but not the obligation, to order the Owners to maintain or repair the same. The Owners agree to maintain reasonable one-man access to all portions of the BMP and shall avoid permanent or lockable obstructions from blocking a reasonable path of access by City inspectors. Such obstruction may be the sole cause for the City to request maintenance as noted above. 6. If the City of Edmonds determines that the 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 Owners 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, 8. Dated: damages, judgments, attorneys' fees and/or costs of any kind whatsoever, arising out of or in any way resulting from the approval of the BMP(s), the installation and presence of the BMP(s), and the acts or omissions of the Owners, their officers, employees, contractors, and agents relating to the construction, operation and maintenance of the BMP(s) 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 BMP(s). This covenant shall run with the land and be binding upon the Owners. DECLARANT(S): (Signature) (Print Name) (Signature) (Print Name) State of Washington M County of Snohomish APPROVED: CITY OF EDMONDS (Signature) (Print Name) (Title) On this day personally appeared before me {Declarant(s)I 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/it signed the same as his/her/their/its free and voluntary act and deed, for the uses and purposes therein mentioned. SUBSCRIBED AND SWORN before me this day of (Signature) 20 . (Name legibly printed or stamped) Notary Public in and for the State of Washington. Residing at: My commission expires Exhibit A Legal description Section 07 Township 27 Range 04 Quarter SW TALBOT PARK BLK 000 D-02 LOT 2 OF CITY OF ED SP NO PLN-2017-0020 REC UND AFN 201908265001 BEING A PTN OF LOTS 63 & 64 SD PLAT. SITUATE IN THE COUNTY OF SNOHOMISH, STATE OF WASHINGTON. LOT 1 (ON AREA DRAIN PLN-2017-0020 .l 18.00' N I g5°09'00" E 2 �� (all — — ROOF AND — i \ PROPOSED FOOTING /\ \ POOL DRAIN LINES I INFILTRATION \ DRYWELL O AREA DRAIN I I� PROPOSED HOUSE / i I O AREA DRAIN g4 FFE:51.80' _ O p I I / UPPER FLOOR FFE: 62.10' i s O \\ LOWER FLOOR FFE: 42.40' I V a 'I TRENCH INFILTRATION \/ AREA DRAIN I a °\Q ® �I DRAIN X 4< CDDRYWELL T 1_ Al O � O / I— I Wq a / PROPOSED p —� r I DRIVEWAY INFILTRATION r''I I �P I 56 TRENCH CATC BASIN AREA DRAIN 14 s — - - E 182.00 I — — N 85°09' 00 z / o v, IW W d FREDERICKIPL \\ — S SS SS�S �S —�—� C —S� \ _cnSn P -SS —SS— GRADING AND DRAINAGE PLAN 1 SCALE: 1" = 30' �� 30 0 15 30 60