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APPROVED STM RESUB 2-BLD2023-1083+Storm_Drainage_Report+7.29.2024_3.25.02_PM+4408059C � ENGINEERING 250 4th Ave S Ste 200 Edmonds, WA 98020 Phone: (425) 778-8500 Fax: (425) 778-5536 civil & structural engineering & planning BLD2023-1083 RESUB Jul 30 2024 CITY OF EDMONDS DEVELOPMENT SERVICES DEPARTMENT DRAINAGE REPORT Hopper Residence 1005 Olympic Ave Edmonds, WA 98020 Applicant/Contact: Daren & Kari Hopper 11924 42nd Drive SE, Everett, WA 98208 425.425.5434 dhopper@seamountain.com Contractor: TBD Project Engineer: Greg Guillen, PE 250 4th Ave S, Suite 200, Edmonds WA, 98020 425.778.8500 grego@cgengineering.com Submittal Date: 07129124 CG Project No.: 22372.20 COMPLIES WITH APPLICABLE CITY STORMWATER CODE 08/15/2024 Contents SectionI — Project Site Maps.......................................................................................................... 3 Section II — Project Overview.......................................................................................................... 7 SectionIII — Off -Site Analysis...................................................................................................... 15 Section IV — Permanent Stormwater Control Plan....................................................................... 21 Section V —Construction Stormwater Pollution Prevention Plan ................................................ 27 Section VI — Special Reports and/or Studies................................................................................. 31 Section VII — Other Permits........................................................................................................... 32 Section VIII — Bond Quantities, Declaration of Covenant, & Operation and Maintenance Manual ....................................................................................................................................................... 33 Appendix A —Attached Reports.................................................................................................... 42 Appendix B — Maintenance Covenant.......................................................................................... 79 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ENGINEERING Z ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Hopper Residence - CG #22372.20 Drainage Report July 29, 2024 Section I, Page 1 Section I — Project Site Maps Please see below for the attached project site maps. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 C CM ph.425.778.8500 1 f.425.778.5536 ENGINEERING 3 www.cgengineering.com City of Edmonds Map Title 0 63.15 126.3 Feet 1,128 94.0 This map is a user generated static output from an Internet mapping site and is for 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 00 53 . Legend Storm Catch Basins o Edmonds p Private ■ Infiltration Storm Manholes p Edmonds p Private Infiltration • Detention Facilities Culvert <all other values> Yes o Facility Feature Creeks Storm Line — <all other values> No, BNSF; No, COUNTY; No, LYNI MOUNTLAKE TERRACE; No, POF SHORELINE; No, STATE; No, WO, — Yes, EDMONDS; Yes, PRIVATE; 1 Facility Lines Storm Ditch Hydrants « Edmonds a Other L► PRV VaIVPC Notes TOTAL PROJECT AREA: 0.312 ACRES *TOTAL HARD SURFACE: 5,999 SF PROPOSED PGIS: 1,037 SF PROPOSED PGPS: 0 SF EXISTING UNMANAGED HARD SURFACE: 0 SF TOTAL DISTURBED AREA: 0.312 ACRES AVERAGE SLOPE: 10% NRCS SOIL GROUP: EVERETT VERY GRAVELLY SANDYLOAM - 55 - - - - 55 _ F9UN0 SyEB *ALL AREAS EXCEPT THE OFFSITE DRIVEWAY APRON, WALKWAY, AND THE PAVEMENT PATCHING u �i (103 SF TOTAL) WILL BE ROUTED TO THE DETENTION N8808165001) NE 1 /4, SECTION 24, TOWNSHIP 27 NORTH, RANGE 3 EAST, W.M. o I s.( pI I`� a HOUSE I I ---0_ O 8 ,�c_ O .. O CS �SttS�_ CONCRETE a -SS - -_-SS}- 55 •I ( NEW EASEMENTAND PROPERTY \' BOUNDARIES UNDER BLA, TO BE ` RECORDED. PREVIOUS EASEMENT TO BE VACATED 55�-55 `SS SS ^-94.04'- - 55 . . .1114. �� . • 7 A • .. - MMEME■EM■E■ _ _■■ ■■IIIM■■■■■■�!Ir■IE�I�!!'!■■■■■■■L,ii ■■■■M ■■■11/I■■■■■■■iMMOr■■■■■■■■■ MEMO ■■■■IIIM■■■■■■■■■■■■■■■■■■EMIR ■■■■ISM■'/.M■■■■■■■■■■■■ME■■I■■■■� ••. .: ► ■■■■ MEN ■■■■■■ HOM■M! SEi�il�I i 4l M■ �� ME III■ I■■■■■OII E I■ MI■■M� EMEN 1 III ■■■ MEE OEM • • �j, 4 I/t7////////////// ////�i. ,�KM ou _ 1r 1 -- 0 - -G G - 197 - G 58944'S3"E G G G _• G G ` x 20LIF ^'12"DI@0.5%MINA - ---I'- 7 G - - - ADD CLEANOUTS TO PIPE PER - - -4 TOTALING 54 LF W/ (2) 3 LF CONNECTORS�'%108.20�VS (2) ROWS OF 36' N-12 DETENTION PIPEDETENTION COE STD SD-619 BETWEEN(60 LF TOTAL) OILAME 5.13 OFS PER BMP T5.13 OF 4 EX C.B. ---------------------- ' 101- GRADING AND DRA ANI GE PLAN 5' Priva 'l Rd THESWMMWW C3. q---WA---WA-l- --- A--- A---W'A-_(_WA---WA---WA---WA-L-WA---WA---WA---W'A-y EX C.B. SLOPE ALL UNCOVERED RIM= i 04.32 I.E.=f02.22 1"N HARD SURFACES AWAY ') I.E=f02.42 BN / FROM BUILDING `\ , SCALE: 1" = 10' GRADING AND DRAINAGE PLAN NOTES: 1. Sol LS REPORT REPORT NUMBER: 1406422 PREPARED BY: NELSON GEOTECHNICAL ASSOCIATES, INC. DATED: 12/15/2022 2. AMINIMUM OF 3' HORIZONTAL SEPARATION AND I'VERTICALSEPARATION IS REQUIRED BETWEEN DRY UTILITIES(POWER, GAS, PHONE, CABLE, ETC) AND SEWER, WATER AND STORM, AND A MINIMUM OF 5' HORIZONTAL SEPARATION AND V VERTICAL SEPARATION FROM ANY CITY OW NED LINES. 3. NEW/REPLACED IMPERVIOUS SURFACE(INCLUDING ROW): 5,999 SF NEBUILDING: 4,527 SF ROOF AREA. RUNOFF ROUTED TO AN ONSITE DETENTION PIPE THROUGH ROOF DRAINS AND CATCH BASINS. THE RUNOFF WI LL OUTLET TO THE PRIVATE STORM MAIN. NEW WALKWAYS: 435 SF RUNOFF INTERCEPTED BY AREA DRAINS, YARD DRAINS, AND CATCH BASINS AND ROUTED TO AN ONSITE DETENTION PIPE. THE RUNOFF WILL OUTLET OT HE PRIVATE STORM MAIN. NEW DRIVEWAY: 934 SF. RUNOFF INTERCEPTED BY CATCH BASIN AND ROUTED TO AN ONSITE DETENTION PIPE. THE RUNOFF WILL OUTLET TO THE PRIVATE STORM MAIN. OFFSITE DRIVEWAY: 47 SF. RUNOFF COLLECTED BY PRIVATE DRIVE CATCH BASIN. OFFSITE PAVEMENT PATCHING: 56 SF. RUNOFF COLLECTED BY PRIVATE DRIVE CATCH BASIN. `CONCEPT PATIO: 1,110 SF. PATIO WILL NOT BE INSTALLED DURING THIS PROJECT. THE PATIO AREA HAS BEEN INCLUDED IN DETENTION SIZING FOR FUTURE INSTALLATION. EXCLUDED FROM OVERALL HARDSCAPE CALCULATIONS. - 'CONCEPT POOL: 290 SF. POOL WILL NOT BE INSTALLED DURING THIS PROJECT. THE POOL AREA HAS BEEN INCLUDED IN DETENTION SIZING FOR FUTURE INSTALLATION. EXCLUDED FROM OVERALL HARDSCAPE CALCULATIONS. 4. ALL DISTURBED AREAS TO BE COMPOST AMENDED PER 2019 SW MM W W BMP T5.13. 5. ALL DISTURBED AREAS ON AND OFF- SITE SHALL BE COMPOST- AMENDED PER THE REQUIREMENTS OF THE BMP T5.13 IN THE STORMWATER MANUAL VOLUME V, CHAPTER 5. 6. TOW AND BOW REFER TO FINISHED GRADE AT THE TOP AND BOTTOM OF THE WALLS, RESPECTIVELY. 7. AMINIMUM OF 2'OF COVER IS REQUIRED FOR ALL PIPES LOCATED UNDER DRIVABLE SURFACES AND VOF COVER UNDER LANDSCAPE SURFACES. DUCTILE IRON PIPES WILL BE USED IN AREAS THAT THIS STANDARD CANNOT BE MET. 8. PRIOR TO PLACING ANY SURFACING MATERIAL ON THE DRIVEWAY, IT WILL BE THE RESPONSIBILITY OF THE DEVELOPER/CONTRACTOR TO PROVIDE DENSITY TEST REPORTS CERTIFIED BY A PROFESSIONAL ENGINEER REQUIRED IN THE STATE OF WASHINGTON. 9. A TYPE II MANHOLE IS REQUIRED WHEREVER RIM TO INVERT EXCEEDS 5' 9. DRIVEWAY SLOPES SHALL NOT EXCEED 14% GRADE PER ECDC 18. 80.060. q�d GRADING QUANTITIES TOTAL EXCAVATION (CUT) - 300 CU YDS TOTAL EMBANKMENT(FILL)- 225 CU YDS TOTAL 525 CU YDS THE QUANTITIES SHOWN ABOVE ARE FOR THE PERMIT PROCESS ONLY. THESE VALUES ARE APPROXIMATE. DO NOT USE FOR BIDDING, PAYMENT, OR ESTIMATING PURPOSES. ASPHALT CONCRETE WEARING COURSE HMA CLASS 1/2" PG 64-22 (WSDOT STD SPEC 5-04.1) CRUSHED SURFACING BASE COURSE(WSDOT STD SPEC 9-03.9(3)) SUITABLE NATIVE MATERIAL FILL; TOP 12" COMPACTED TO A MINIMUM OF 95%RELATIVE COMPACTION USING AASHTO T-180(ASTM D1557). UNSUITABLE NATIVE MATERIAL SHALL BE REPLACED TYPICAL PAVEMENT SECTION ECO-BLOCK RE.. WALL -EXISTING SSCO IE (4" E): 111.59 APPROX. PER AS BUILT UNDER BLD2022-0497) CONTRACTOR TO VERIFY SEWER LOCATION, SIZE, MATERIAL, AND DEPTH PRIOR TO CONSTRUCTION 114.39 NEW DRIVEWAY ANDTURNAROUND 114.39 INSTALL 6" ROLLED CURB ON WEST AND SOUTH SIDE OF PROPOSED DRIVEWAY RUNOFF TO PROPOSED CB T PT PP ,T T PT P- T_ P P� L 3 E E E CONCRETE SECTION �� PROTECT EXISTING ASPHALT EDGE ROPOSED PAVEMENT WITHIN PRIVATE - WA= ROAD (249 SF). PROTECT EXISTING ASPHALT EDGE INSTALL 6" ROLLED CURB ON W ESfAND SOUTH SIDE OF PROPOSED DRIVEWAY RUNOFF TO PROPOSEDSB n CATCH BASIN SCHEDULE MARK TYPE RIM ELEV INV ELEV NOTES TYPE 111.0 (6"NW): 108.50 1 C3. 2 C3. 3 C3. q) 12" AREA 115.90 (6" S): 110.95 4 DRAIN 12" AREA 115.80 IV N): 110.90 1 2 3 \3� DRAIN IV SW): 110.80 C3. C3. C3. (6" E): 108.07 1 2 3 (4� - TYPE 110.39 (6" NE): 108.07 C3. C3. C3. (6" NW): 107.97 TYPE 104.93 IV E): 103.18 (6" N): 103.18 1 2 3 IV S): 103.08 C3. C3.2 C3. (36" E): 99.93 06 /� 60"O TYPE II 104.93 (12" SW): 99.93 (we (4" NE): 300.03 O TYPE I 102.0 (12" NEI: 99.71 1 2 3 (12" S): 99.61 (12"N): 99.51 CONTRACTOR TO VERIFY TYPE 101.17 (12" W): ^'99.41 EXIST 12" CRP MAIN 1 2 3 (12" E): ^991 LOCATION, DEPTH, & SLOPE PRIOR TO CONSTRUCTION 4" DIA PERFORATED PVC PIPE WITH 6" OF 1" MINUS GRAVEL ALL AROUND, WRAPPED IN 8" MIN FROM WOOD. NON -WOVEN GEOTEXTILE SEE STRUCTURAL DRAWINGS FABRIC, SLOPE AT 0.5% MIN. TURN DOWN PERFORATIONS AS SHOWN 6" DOWNSPOUT TIGHTLINE FINISHED GRADE I - TO CONVEYANCE SYSTEM @ - 0.5%MIN. PLACE NEXTTO FOOTING DRAIN OR AS SHOWN ON GRADING & _ _ -1 I- III DRAINAGE PLAN (CONTRACTOR MAY LOCATE ON EITHER SIDE OF O O FOOTING DRAIN) 00 O a O e OO a 0 O° , O a LINE OF MAX EXCAVATION. o O -d IF SOIL IS OVEREXCAVATED, O O OOP °O REPLACE WITH LEAN MIX o CONCRETE FOOTING 1 1 FOOTING AND ROOF DRAIN SECTION � SCALE: NTS 14" 12" BLDXXXX-XXXX APPROVED FOR CONSTRUCTION NOTES: i. WEIGHT 360LBS. CITY OF EDMONDS 2. (1) 6" KNOCKOUT PROVIDED FOR PIPE ENTRY. 3. FOR USE WITH 14" CAST DATE: IRON GRATE. 4. AREA TO HAVE SOLID BOTTOM. BY: 12" AREA DRAIN CITY ENGINEERING DIVISION U C CMI ENGINEERING 250 4TH AVE. S., SUITE 200 EDMONDS, WASHINGTON 98020 PHONE (425) 778-8500 FAX (425) 778-5536 FOR REPORT USE ONLY City of Edmonds Map Title 0 63.15 126.3 Feet 94.0 This ma is a user generated static output from an Internet mapping site and is for ���2$ P� 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 53 . Legend Storm Catch Basins o Edmonds p Private ■ Infiltration Storm Manholes 0 Edmonds p Private Infiltration • Detention Facilities Culvert <all other values> Yes o Facility Feature Creeks Storm Line — <all other values> No, BNSF; No, COUNTY; No, LYNI MOUNTLAKE TERRACE; No, POF SHORELINE; No, STATE; No, WO, — Yes, EDMONDS; Yes, PRIVATE; 1 Facility Lines Storm Ditch Contour Lines 10 50; 100 ArcSDE.GIS.STREET CENTERLINE' <all other values> Notes Hopper Residence - CG #22372.20 July 29, 2024 Drainage Report Section II, Page 1 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 residence project on a 0.33 acre lot. The development will take place on the majority of the lot with a total disturbance area of 0.312 acres. The subject parcel is undeveloped and contains two onsite retaining walls. The western most retaining wall will be removed. Site topography descends from east to west. Lot Address: 1005 Olympic Ave, Edmonds, WA 98020 Parcel Number: 00766100001000 Zoning: RS-12 Watershed: Hindley Watershed The new single-family residence will consist of a house, driveway, and walkways/patio areas. The house will have roof coverage of approximately 4,527 sf (0.104 ac). The project's right-of-way (ROW) improvements include approximately 305 sf of new driveway, walkway, and private drive pavement. The total of new/replaced hard surface areas for the project is approximately 5,999 sf (0.138 ac). Since the project will add between 5,000 and 10,000 sf of new hard surfaces, the project is classified as Category 2 per the Edmonds Community Development Code (herein referred to as ECDC) Chapter 18.30.060.C.1.b and the June 2022 Addendum to Edmonds Community Development Code Chapter 18.30 (herein referred to as the Edmonds Stormwater Addendum), Chapter 3.1.3.1. Category 2 projects are required to comply with Minimum Requirements #1-9 from ECDC 18.30.060.E and Chapter 5 of the Edmonds Stormwater Addendum. Existing Condition The site is currently undeveloped and contains two onsite retaining walls with grass covering the remainder of the subject parcel. The subject parcel is an irregular shape and is approximately 14,250 sf (0.327 ac). The parcel is moderate sloping from east to west with an average slope of 8%. Due to high groundwater and depth of densic materials per the Geotechnical report, infiltration is infeasible. The Geotechnical Engineer recommends that "all runoff generated within this site should be directed to an approved discharge point most likely located in the adjacent streets". The project will not received hardscape runoff from adjacent properties. 250 4th Avenue South, Suite 200 C CM ph. WA 98020 ph.425.778.8500 1 f.425.778.5536 ENGINEERING 7 www.cgengineering.com Hopper Residence - CG #22372.20 July 29, 2024 Drainage Report Section II, Page 2 The geotechnical report, by Nelson Geotechnical Associates, can be found in Section V of this report. Nelson visited the site on December 01, 2022 and they dug three test pits and one infiltration test pit. According to the report, surficial topsoil/undocumented fill was generally encountered in the 1 ft to 3 ft depths of the geotechnical explorations. Beneath the surficial topsoil in all test pits, they encountered outwash soils and native glacial till. Groundwater was encountered between 1-3 feet in all of the test pits, therefore, infiltration is not feasible on the site. The subject parcel is bordered by other single-family residences to the north, east, and west. A private road lies along the south boundary line of the site. The site does not appear to take on significant upstream runoff from the neighbors to the east, north, or anywhere else. Stormwater from the property to the east is to be intercepted by the installed drainage facilities within that site prior to the subject property. Sanitary sewer is proposed to be provided by the existing manhole located northwest of the site. There is a sewer line on site that serves the property to the east. This line is proposed to be rerouted into the new sewer easement. The existing water main was not identified on the survey however, with the use of adjacent property as builts and GIS mapping, the water main was found to be within Olympic Ave to the east of the site. A new water meter is to be installed and directional boreing is proposed to route the new water line beneath the private drive to the site. The existing main shown on the plans is based on Edmonds GIS Map and notes have been added directing the contractor to pothole and verify the existing water main. Per the survey, there is an existing stormdrain conveyance system within the private road just south of the site. The project has proposed to direct discharge the site's stormwater to the catch basin on the north side of the private road. A new catch basin will be installed at this connection. The existing site area was considered as follows: Lawn: 14,250 sf (0.33 ad Total: 14,250 sf (0.33 ac) Developed Condition The project is classified as New Development and will occur on a mostly undeveloped lot. The proposed develompent is the construction of a new single-family residence that consists of a 2-story house with a driveway, and walkways. The total of the new plus replaced hard surface areas on -site and in the ROW are 5,999 sf (0.138 ac). Land disturbance will be to the extents of the clearing limits and will be approximately 13,571 sf (see civil plans for more). The site will utilize area drains, catch basins, and yard drains to collect the proposed hardscape runoff. The runoff will then be routed to a detention pipe with a flow control structure to comply with Minimum Requirement #5: On -Site Stormwater Management. The detention pipe was designed using the sizing equations from Chapter 6.3.1 of the 2017 Edmonds Stormwater Addendum and will not consist of CMP material per the 2022 Edmonds Stormwater Addendum. All runoff from hard surface areas as a party of the project site will be directed into a proposed catch basins and area drains and will be routed to the 250 4th Avenue South, Suite 200 C CM ph. WA 98020 ph.425.778.8500 1 f.425.778.5536 ENGINEERING 8 www.cgengineering.com Hopper Residence - CG #22372.20 Drainage Report July 29, 2024 Section II, Page 3 proposed detention pipe with the flow control structure that will discharge southwest into an existing storm main per survey. Offsite hardscape not a part of the project and not included in the below calculations are not proposed to flow into the designed detention system and onsite catch basins and area drains. See the civil plans and Section III for more on the Permanent Stormwater Control Plan. The proposed hard surface areas were considered as follows: Hard Surface Areas Roof: 4,527 sf (0.104 ac) Driveway Pavement (on -site): 742 sf (0.017 ac) Walkways (on -site): 425 sf (0.010 ac) Driveway (in Private Drive): 239 sf (0.006 ac) Walkway (in Private Drive): 10 sf (0.000 ac) Pavement Patching (in Private Drive): 56 sf (0.001 ac) Total: 5,999 sf (0.138 ac) An additional 0.032 acres is added to the mitigated flow control model as sidewalk and pool to account for potential future areas. While only 0.138 ac is being installed, 0.170 acres will be used in flow control calculations. The proposed pollution -generating hard surface areas were considered as follows: Pollution -generating Impervious Areas Driveway: 1,037 sf (0.024 ad Total: 1,037 sf (0.024 ac) 250 4th Avenue South, Suite 200 C CM ph. WA 98020 ph.425.778.8500 1 f.425.778.5536 ENGINEERING 9 www.cgengineering.com Hopper Residence - CG #22372.20 Drainage Report July 29, 2024 Section 11, Page 4 Q4et Dr et Way Grace Lutheran Church 19 ndley Ln n z Brookmete St at§�• 9� 7' t m z Mountain Ln x• __]18-342 � IT vlyinNw Vl�— v�si 524 Edmonds Elementary School 9 Total Lot Area: 0.33 ac Total New Hard Surface Area: 0.138 ac PGHS: 0.024 ac Total disturbed area: 0.31 ac Average slope in development area: 8% NRCS Parent Material: Glacial Outwash NRCS Hydro. Soil Group: C Viewland Way 0 R D 0 D t m Z Argonaut Diving Argonaut Diving - Scuba School • Puge.- Vista way Vista PI 0 D Figure 1-1: Vicinity map (from Google Maps) 1005 1001 PROJECT SITE Viewland '99m St SW 3 w H3-111 96 PSI Figure 1-2: Map showing existing utilities near site. (from City of Edmonds GIS map 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph.425.778.8500 1 f.425.778.5536 ENGINEERING 10 www.cgengineering.com Hopper Residence - CG #22372.20 July 29, 2024 Drainage Report Section II, Page 5 oob _E r ��� -- 4V Figure 1-3: Aerial image of site. (from City of Edmonds GIS map) i The project must comply with ECDC 18.30 — Stormwater Management Code, the 2019 Stormwater Management Manual of Western Washington (DOE Manual), and the 2022 Edmonds Stormwater Addendum (Stormwater Addendum). It is classified as a Category 2 project per ECDC 18.30 and must meet Minimum Requirements #1-9 because the amount of new plus replaced impervious surfaces total over 5,000 sf. 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 I 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 V and the civil drawings. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph.425.778.8500 1 f.425.778.5536 ENGINEERING 11 www.cgengineering.com Hopper Residence - CG #22372.20 July 29, 2024 Drainage Report Section II, Page 6 Minimum Requirement #3: Source Control of Pollution: All known, available and reasonable source control BMPs are required for all projects approved by the city. All single-family residential projects shall, at a minimum, incorporate required BMPs from SWMMWW Volume IV, S411— BMPs for Landscaping and Lawn/Vegetation Management. The Operation & Maintenance Manual found in Section VII addresses Lawn/Vegetation management. Minimum Requirement #4: Preservation of Natural Drainage Systems and Outfalls: Natural drainage patterns shall be maintained, and discharges from the project site shall occur at the natural location, to the maximum extent practicable. The manner by which runoff is discharged from the project site must not cause a significant adverse impact to downstream receiving waters and down -gradient properties. All projects shall submit an off -site qualitative analysis. A qualitative analysis of the upstream and downstream system entering the site is presented in Section III. Minimum Requirement #5: On -Site Stormwater Management: The proposed project discharges into the private storm system and ultimately into Hindley Creek. Per ECDC 18.30, it must implement BMP T5.13 Post -Construction Soil Quality and Depth and evaluate BMPs T5.10A Downspout Full Infiltration Systems, T5.1013 Downspout Dispersion Systems, T5.10C Perforated Stub -out Connections, T5.11 Concentrated Flow Dispersion, and T5.12 Sheet Flow Dispersion. The majority of on -site Stormwater BMPs were found to be infeasible for all hard surfaces due to the high groundwater and densic soils. See Section IV. Minimum Requirement #6: Runoff Treatment: This requirement applies to the new plus replaced hard surfaces and the converted vegetation areas. The following require construction of stormwater treatment facilities: i.) Projects in which the total of pollution -generating hard surface (PGHS) is 5,000 square feet or more in a threshold discharge area of the project, or ii.) projects in which the total of pollution -generating pervious surfaces (PGPS) — not including permeable pavements is 0.75 acres or more in a threshold discharge area, and from which there will be a surface discharge in a natural or man-made conveyance system from the site. The project's total amount of PGHS is less than 5,000 square feet and the amount of PGPS is less than 0.75 ac. Runoff treatment is not required. Roof materials will be non -pollution generating. Minimum Requirement #7: Flow Control: Projects must provide flow control to reduce the impacts of stormwater runoff from hard surfaces and land cover conversions. The requirement below applies to projects that discharge stormwater directly, or indirectly through a conveyance system, into a fresh waterbody. The following circumstances require achievement of the standard flow control requirement for western Washington: i.) Projects in which the total of effective impervious surfaces is 10,000 square feet or more in a threshold discharge area, or ii.) projects that convert 0.75 acres or more of vegetation to lawn or landscape, or iii.) projects that through a combination of hard surfaces and converted vegetation areas cause a 0.15 cubic feet per second (cfs) increase or greater in the 100-year flow frequency from a threshold discharge area as estimated using the Western Washington Hydrology Model or other approved model and 15-minute time steps. The total target effective new/replaced hard surfaces in the site threshold discharge area is 5,999 sf, there is no vegetation to be converted to lawn/landscape, 250 4th Avenue South, Suite 200 C CM ph. WA 98020 ph.425.778.8500 1 f.425.778.5536 ENGINEERING 12 www.cgengineering.com Hopper Residence - CG #22372.20 Drainage Report July 29, 2024 Section 11, Page 7 and the difference between predeveloped and mitigated flows is less than 0.15 cfs. Therefore, the project does not require flow control. The WWHM report for the flow increase check can be found in Section III. Minimum Requirement #8: Wetlands Protection: This requirement applies only to projects whose stormwater discharges into a wetland, either directly or indirectly through a conveyance system. This project site's stormwater does not discharge into a wetland and does not require wetland protection. Minimum Requirement #9: Operation and Maintenance: An operation and maintenance manual that is consistent with the provisions in Volume I and Volume V of the SWMMWW is required for proposed Stormwater Treatment and Flow Control BMPs/facilities. The party (or parties) responsible for maintenance and operation shall be identified in the operation and maintenance manual. For private facilities approved by the City, a copy of the operation and maintenance manual shall be retained on - site or within reasonable access to the site and shall be transferred with the property to the new owner. For public facilities, a copy of the operation and maintenance manual shall be retained in the appropriate department. A log of maintenance activity that indicates what actions were taken shall be kept and be available for inspection. See Section VIII. 250 4th Avenue South, Suite 200 C CM ph. WA 98020 ph.425.778.8500 1 f.425.778.5536 ENGINEERING 13 www.cgengineering.com Hopper Residence - CG #22372.20 Drainage Report July 29, 2024 Section II, Page 8 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? Yes No Nlminuun Requirements No. 1 through 5 apply I Minimum Requirement No. 2 applies Next 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? Yes No Is this a road related project? I Minimum Requirements apply to the new and replaced hard surfaces and converted vegetation areas. All Minimum Requirements apply to the new hard surfaces and converted vegetation areas. Yea 1Z67 Yes Does the project add 5,000 square feet or No 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 additional requirements. Figure 1-4: Flow Chart for Determining Minimum Requirements for Development. (Figure 3.1 in the Edmonds Stormwater Addendum) C CM ENGINEERING 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph.425.778.8500 1 f.425.778.5536 14 www.cgengineering.com Hopper Residence - CG #22372.20 Drainage Report July 29, 2024 Section III, Page 1 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 6.2.1 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. The runoff sheet flows in a westerly direction across adjacent parcels to the west for approximately 0.02 miles. The runoff then enters Hindley Creek. Hindley Creek is about 0.02 mi downstream from the site. Per city GIS and site recon there are no no known detention facilities within the downstream flowpath. The downstream flowpath is outlined below in Figure II-1 from the City GIS map. 1008 1006 Ln 1021 1011 p PROJECT SITE /HINDLEY CREEK 1 002 0,02 mi 0 1 1001 1005 923 925 927 9� Figure II-1: Map showing approximate stormwater flow path and distance from site to outfall (from City of Edmonds GIS map. 250 4th Avenue South, Suite 200 C Edmonds, WA 98020 CM ph.425.778.8500 1 f.425.778.5536 ENGINEERING 15 www.cgengineering.com Hopper Residence - CG #22372.20 July 29, 2024 Drainage Report Section III, Page 2 Task 2 — Review all available information on the study area Existing stormwater improvements were determined from the survey and the City GIS map. There is an existing catch basin south of the property, which starts a private stormwater conveyance system that is note shown on the COE GIS mapping. This catch basin is where the proposed runoff will discharge. The conveyance system continues beneath the private road to the souths side of the road. The runoff is then redirected in a westerly direction for approximately 170 feet until it daylights into Hindley Creek. See the II-2 below for approximate located of private conveyance. The existing property sheet flows in a westerly direction across adjacent parcels to the west for approximately 0.02 miles. The runoff then enters Hindley Creek. Hindley Creek is about 0.02 mi downstream from the site. Per the survey and City GIS map, the site appears to contain no critical areas (see Figure II-3 below). The geotechnical report found high groundwater in all test pit locations which makes most stormwater BMPs infeasible and/or not recommended in this area. Figure II-2: City of Edmonds GIS Map with stormwater and contour layers active. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 CM ph.425.778.8500 1 f.425.778.5536 ENGINEERING 16 www.cgengineering.com Hopper Residence - CG #22372.20 Drainage Report July 29, 2024 Section III, Page 3 r 1006 1021 to o 1004 �'u � FZ 1001 � 925 927 929 Figure II-3: Landslide and Erosion Hazard area map. (from City of Edmonds GIS map) 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph.425.778.8500 1 f.425.778.5536 ENGINEERING 17 www.cgengineering.com Hopper Residence - CG #22372.20 Drainage Report July 29, 2024 Section I11, Page 4 Task 3 — Field inspect the study area The site was visited on the morning of November 16, 2022. The weather was clear and there was no rain. From evaluating surrounding conditions, the site does not appear to take on any significant upstream runoff. There was nothing remarkable found from the site visit or the downstream walk. Site conditions were as expected based on the survey and catch basins were free of debris and appeared that they would function normally during rain events. The following figures show pictures that were taken on the site visit that show the existing site and pictures of the downstream walk from the site. Figure II-4: From west boundary line of site. 250 4th Avenue South, Suite 200 C Edmonds, WA 98020 CM ph.425.778.8500 1 f.425.778.5536 ENGINEERING 18 www.cgengineering.com Hopper Residence - CG #22372.20 Drainage Report July 29, 2024 Section III, Page 5 Figure II-5: Facing westerly from the same location as the previous photo. J PRIVATE CONVEYANCE SYSTEM. DISCHARGE POINT. Figure II-6: From the south boundary line of the site, facing south. r4i 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph.425.778.8500 1 f.425.778.5536 ENGINEERING 19 www.cgengineering.com Hopper Residence - CG #22372.20 Drainage Report July 29, 2024 Section III, Page 6 Figure II-7: Offsite at the end of the private drive, facing westerly. Task 4 — Describe the drainage system, and its existing and predicted problems Existing stormwater improvements were determined from the survey and the City GIS map. The site's existing topography descends to the west towards other properties and Hindley Creek to the west. It is believed that stormwater runoff currently sheet flows across adjacent parcles into Hindley Creek. The proposed point of connection for the site's stormwater will be through a discharge pipe from onsite conveyance into the private stowater system within the private road to the south. This conveyance system guides the runoff westerly and daylights into Hindley Creek. The project proposes to route all runoff from new and replaced hard surfaces of the site to various area drains, yard drains, and catch basins which will discharge into an offsite catch basin, to meet the on -site stormwater management requirements (see Section III). There are no anticipated problems associated with the development from this project. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 C CM ph.425.778.8500 1 f.425.778.5536 ENGINEERING 20 www.cgengineering.com Hopper Residence - CG #22372.20 Drainage Report July 29, 2024 Section IV Page 1 Section IV — Permanent Stormwater Control Plan Section III Summa Narrative Feasibility Review Narrative 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. The total onsite area to be amended per BMP T5.13 is 7,572 sf of disturbed area. Please see civil plans. 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 infeasible because there is not at least 1 foot or more of permeable soil from the proposed bottom of the infiltration system to the seasonal high groundwater table or other impermeable layer. 3. Bioretention in accordance with BMP T7.30 and Bioretention in accordance with Chapter 7 are infeasible because of the presence of high groundwater per the geotechnical report. 4. Downspout Dispersion Systems in accordance with BMP T5.1013 are infeasible/not recomended because the majority of the site does not allow for the required flowpath for splash blocks and does not provide the space for the required dispersion trench length while being parallel to the contours. Additionally, it is recommended by the Geotech that the onsite stormwater be collected and discharged to an approved discharge location. 5. Detention vaults or pipes in accordance with the Edmonds Stormwater Addendum are feasible and a detention pipe system will be used to manage runoff for the proposed other hard surfaces on -site. 6. A Perforated Stub -Out Connection in accordance with BMP T5.10C is infeasible because there is not at least 1 foot of permeable soil from the proposed bottom of the perforated stub -out connection trench to the highest estimated groundwater table or other impermeable layer. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 C CM ph.425.778.8500 1 f.425.778.5536 ENGINEERING 21 www.cgengineering.com Hopper Residence - CG #22372.20 July 29, 2024 Drainage Report Section IV Page 2 The proposed roof runoff will be collected via roof downspouts and perimeter drains, and will be conveyed to the offsite private stormwater conveyance system located south of the site. Other Hard Surfaces: 1. Full Dispersion in accordance with BMP T5.30 is infeasible because a 65 to 10 ratio of forested or native vegetation area to impervious area cannot be achieved. 2. Full Infiltration in accordance with BMP T5.10A and/or Permeable Pavement in accordance with BMP T 5.15 are infeasible because there is not at least 1 foot or more of permeable soil from the proposed bottom of the infiltration system to the seasonal high groundwater table or other impermeable layer. 3. Bioretention in accordance with BMP T7.30 and Bioretention in accordance with Chapter 7 are infeasible because of the presence of high groundwater per the geotechnical report. 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/not recomended because the majority of the site does not allow for the required flowpath for splash blocks and does not provide the space for the required dispersion trench length while being parallel to the contours. Additionally, it is recommended by the Geotech that the onsite stormwater be collected and discharged to an approved discharge location. 5. Detention vaults or pipes in accordance with the Edmonds Stormwater Addendum are feasible and a detention pipe system will be used to manage runoff for the proposed other hard surfaces on -site. The proposed driveway, walkway, and patio runoff will be collected via area drains, yard drains, and catch basins, and will be conveyed to the proposed onsite 36" 0 60 LF detention pipe. The pipe is to overflow to the offsite private stormwater conveyance system located south of the site. Calculations Per the 2017 Edmonds Stormwater Addendum 6.3.1, a detention pipe was sized for length. A 36"- diameter pipe was sized using the equation L = 0.008*A, where L is length of pipe (ft) and A is contributing surface area (sf). Per the clients request, the detentions pipe has been sized using concept sizing for a pool and patio area for possible future installation. See civil plans and note below. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 C CM ph.425.778.8500 1 f.425.778.5536 ENGINEERING 22 www.cgengineering.com Hopper Residence - CG #22372.20 Drainage Report July 29, 2024 Section IV Page 5 The proposed hard surface areas were considered as follows: Hard Surface Areas Roof: 4,527 sf (0.104 ac) Driveway Pavement (on -site): 742 sf (0.017 ac) Walkways (on -site): 425 sf (0.010 ac) Driveway (in Private Drive): 239 sf (0.006 ac) Walkway (in Private Drive): 10 sf (0.000 ac) Pavement Patching (in Private Drive): 56 sf (0.001 ad Total: 5,999 sf (0.138 ac) *Concept Future Hard Surfaces Patio: 1,110 sf (0.026 ac) Pool: 290 sf (0.007 ac) Total: 1,400 sf (0.032 ac) *Note that the concept areas are only used to size the detention system for a possibility of installing those areas in the future after obtaining the proper permits. Not to be installed as a part of this project. L = 0.008*(7,399 sf) = 59.19 ft. Therefore, a total of 60 lineal feet of 36"-diameter detention pipe (including connector pipes between) was designed to meet the on -site stormwater management requirement for this project. See civil plans for more. Flow Control Check Please see the map snips below, found using USGS EROS aerial maps, of the site prior to July 6th, 1977. The site existed as grass/lawn prior to July 6th, 1977 and is modelled as pasture areas to be conservative in our 0.15 cfs check. This shows that even with conservative assumptions, the 0.15 cfs increase requirement is met. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 C CM ph.425.778.8500 1 f.425.778.5536 ENGINEERING 23 www.cgengineering.com Hopper Residence - CG #22372.20 Drainage Report July 29, 2024 Section IV Page 5 ,11 P*EESI� 1 �� Ili, IF ilp Figure IV-1. July 13t'', 1974, aerial photo. WWHM2012 PROJECT REPORT Project Name: Hopper Flow Control Check Site Name: Site Address: City Report Date: 7/25/2024 MGS Regoin Puget East Data Start 1901/10/1 Data End : 2058/09/30 DOT Data Number: 03 Version Date: 2021/08/18 Version : 4.2.18 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 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph.425.778.8500 I f.425.778.5536 ENGINEERING 24 www.cgengineering.com Hopper Residence - CG #22372.20 Drainage Report July 29, 2024 Section IV Page 5 GroundWater: No Pervious Land Use acre C, Pasture, Flat .335 Pervious Total 0.335 Impervious Land Use acre Impervious Total 0 Basin Total 0.335 Element Flows To: Surface Interflow MITIGATED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Pasture, Flat .013 C. Pasture, Mod .151 Pervious Total 0.164 Groundwater Impervious Land Use acre ROADS FLAT 0.023 ROADS MOD 0.001 ROOF TOPS FLAT 0.104 SIDEWALKS FLAT 0.036 POND 0.007 Impervious Total 0.171 (actual 0.138 ac, extra area included for future pool) Basin Total 0.335 Element Flows To: Surface Interflow ANALYSIS RESULTS Stream Protection Duration Groundwater 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph.425.778.8500 1 f.425.778.5536 ENGINEERING 25 www.cgengineering.com Hopper Residence - CG #22372.20 Drainage Report July 29, 2024 Section IV Page 5 Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.335 Total Impervious Area:O Mitigated Landuse Totals for POC #1 Total Pervious Area:0.164 Total Impervious Area:0.171 Flow Frequency Return Periods for Predeveloped Return Period Flow(cfs) 2 year 0.007089 5 year 0.011017 10 year 0.013596 25 year 0.016764 50 year 0.019042 100 year 0.021244 Flow Frequency Return Periods for Mitigated Return Period Flow(cfs) 2 year 0.053096 5 year 0.07216 10 year 0.086437 25 year 0.106457 50 year 0.122878 100 year 0.140649 0.1406 - 0.0212 = 0.1194 < 0.15 cfs POC #1 POC #1 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph.425.778.8500 I f.425.778.5536 ENGINEERING 26 www.cgengineering.com Hopper Residence - CG #22372.20 July 29, 2024 Drainage Report Section V, Page 1 Section V— Construction Stormwater Pollution Prevention Plan Section IV Summary: Narrative Construction SWPPP Elements Source Controls 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. A Construction SWPPP is not required by the Department of Ecology because the site is under one acre (the land -disturbing activity threshold which requires the completion of their SWPPP document and Construction Stormwater General Permit). Construction SWPPP Elements The elements for construction pollution prevention are discussed as follows: Element 1: Mark Clearing Limits To protect adjacent properties and to reduce the area of soil exposed to construction, the limits of construction will be clearly marked before land -disturbing activities begin. Clearing limits will be to the extents of necessary land disturbance for the new house and associated driveway, walkways and utilities. 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 installed per the following BMP: Stabilized Construction Entrance (BMP C105) Element 3: Control Flow Rates The site development area is small and flat enough that concentrated flow rates are not expected to occur within the construction activity area of this site and a silt fence that will be used for Element 4 and the use of BMP C235, straw wattles, is expected to be sufficient to control flow rates on -site. See civil plans and geotechnical report. 250 4th Avenue South, Suite 200 C Edmonds, WA 98020 CM ph.425.778.8500 1 f.425.778.5536 ENGINEERING 27 www.cgengineering.com Hopper Residence - CG #22372.20 July 29, 2024 Drainage Report Section V, Page 2 Element 4: Install Sediment Controls All stormwater runoff from disturbed areas shall pass through an appropriate sediment removal BMP before leaving the construction site or prior to being discharged. Silt 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 Exposed slopes shall be stabilized with BMPs found in Element 5. Element 7: Protect Drain Inlets Drain inlets along the private road and those as made operable on -site must be protected from sedimentation. Stormwater must not enter the conveyance system without first being filtered or treated to remove sediment. Inlet protection devices must 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 There are no existing or proposed conveyance channels on -site. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph.425.778.8500 1 f.425.778.5536 ENGINEERING 28 www.cgengineering.com Hopper Residence - CG #22372.20 Drainage Report July 29, 2024 Section V, Page 3 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 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. Element 11: Maintain BMPs All temporary and permanent erosion and sediment control BMPs must 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 take into account seasonal work limits. • Inspection and monitoring— Inspect, maintain, and repair all BMPs as needed to assure continued performance of their intended function. Conduct site inspections and monitoring in accordance with the Construction Stormwater General Permit or local plan approval authority. • Maintain an Updated Construction SWPPP - This SWPPP shall be retained on -site or within reasonable access to the site. - The SWPPP shall be modified whenever there is a change in the design, construction, operation, or maintenance at the construction site that has, or could have, a significant effect on the discharge of pollutants to waters of the state. - The SWPPP shall be modified if, during inspections or investigations conducted by the owner/operator, or the applicable local or state regulatory authority, it is determined that the SWPPP is ineffective in eliminating or significantly minimizing pollutants in stormwater discharges from the site. The SWPPP shall be modified as necessary to include additional or modified BMPs designed to correct problems identified. Revisions to the SWPPP shall be completed within seven (7) days following the inspection. Element 13: Protect Low Impact Development BMPs There are no LID BMPs proposed that will need protection. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph.425.778.8500 1 f.425.778.5536 ENGINEERING 29 www.cgengineering.com Hopper Residence - CG #22372.20 Drainage Report July 29, 2024 Section V, Page 4 Source Controls 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. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 C CM ph.425.778.8500 1 f.425.778.5536 ENGINEERING 30 www.cgengineering.com Hopper Residence - CG #22372.20 Drainage Report July 29, 2024 Section VI, Page 1 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 December 15, 2022. 2. Soil Resource Report from the USDA and NRCS Web Soil Survey dated June 16, 2023. C 4CM ENGINEERING 31 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Hopper Residence - CG #22372.20 Drainage Report July 29, 2024 Section VII, Page 1 Section VII — Other Permits Section VI Summary: Narrative Other permits are not anticipated beyond those required by the City of Edmonds. C 4M ENGINEERING 32 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Hopper Residence - CG #22372.20 Drainage Report July 29, 2024 Section VIII, Page 1 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 Hopper 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. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 O ph.425.778.8500 1 f.425.778.5536 ENGINEERING 33 www.cgengineering.com Hopper Residence - CG #22372.20 Drainage Report July 29, 2024 Section VIII, Page 2 Hopper Residence 1005 Olympic Ave Edmonds, WA 98020 OPERATION AND MAINTENANCE MANUAL Date: July 2024 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph.425.778.8500 1 f.425.778.5536 ENGINEERING 34 www.cgengineering.com Hopper Residence - CG #22372.20 July 29, 2024 Drainage Report Section VIII, Page 3 Operation and Maintenance Manual This Operation and Maintenance Manual has been created for the Hopper Residence: a 4,527 sf single- family residence project on a 0.33-acre lot. The proposed storm system consists of routing a area drains, yard drains, and roof drains to a offsite catch basin within the privite road to the south. 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. Catch Basins: Concrete structures with steel grates that collect stormwater runoff from the site and act as junctions for storm conveyance pipes. See "No. 5" for maintenance. Control Structures: Control structures are catch basins or manholes with a restrictor device for controlling outflow from a facility to meet the desired performance. See "No. 4" for maintenance. Closed Detention Systems (Detention Pipes/Tanks): Underground storage facilities typically constructed with large diameter corrugated metal or plastic pipe. See "No. 3" for maintenance. Vegetation Management: Landscaping can include grading, soil transfer, vegetation removal, pesticide and fertilizer applications, and watering. Stormwater contaminants include toxic organic compounds, heavy metals, oils, total suspended solids, coliform bacteria, fertilizers, and pesticides. Facilities shall be inspected for defects listed in the following facility sheets. Most maintenance tasks are generally reactionary to a defect being found, rather than a matter of constant upkeep. It is generally expected that few to none of these defects will be present upon the yearly inspection of each facility. The facility sheets list the potential conditions warranting maintenance and the expected result following any maintenance. Several engineer's notes for specific tasks are provided within the facility sheets. Unless otherwise noted on the facility sheets the maintenance tasks should be performed on an "as needed" basis: (a) when the described defect is visible to whomever performs the yearly inspection, or (b) should any defect become apparent between inspections. 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph.425.778.8500 1 f.425.778.5536 ENGINEERING 35 www.cgengineering.com Hopper Residence - CG #22372.20 July 29, 2024 Drainage Report Section VIII, Page 4 Figure VII-1: Aerial image of project area. (from City of Edmonds GIS Map) C CM ENGINEERING 36 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Hopper Residence - CG #22372.20 Drainage Report July 29, 2024 Section VIII, Page 5 SAMPLE ACTIVITY LOG DATE FACILITY MAINTENANCE PERFORMED RESULTS/ NOTES C � ENGINEERING 37 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com NE 1 /4, SECTION 24, TOWNSHIP 27 NORTH, RANGE 3 EAST, W.M. zo, HOUSE EXISTING SSCO � \ ���PN eQ Q � RIM-97.98 �' p �/' - _- - -_ o _Q o a -e o a� �- o,.-c2 O a 0 0 o a o O CT 1 E_BAA, TYP. CONCRETE -5 5 - , NEW EASEMENT AND PROPERTY - - BOUNDARIES UNDER BLA, TO BE RECORDED. PREVIOUS EASEMENT TO BE VACATED 10' (AFN8808165001) - ss ss � S5 ss ^'94.04' I ECO-BLOCK RET. WALL RO OVERHANG LINEL - ----_THE R OTI-- A------1 .96F F T F � F ROOF AND FO NG � �kg $ryas / F A DRAIN LINES ARE TO BE INSTALLED OUTSIDE OF THE I / LOWER PATIO ENTRIES: II' - UTILITY EASEMENT 104.93 FUTUREPOOLCONCEPT / pLL COVERED DECK FFE: 115.98 FUTURE PATIO CONCEPT / / LOT 1 o PROPOSED SFR �' J FFE: %115.98 L NEW GARAGE FFE: 115;41 T / r-L -=_ MAIN FLOOR ENTRY FFE: 115,98 / ' 5LF "'6"PVC@0.5%) ' i ROOF AND FOOTING DRAIN �� ��I I 20.00' I CONNECT FOOTING DRAIN 5 2 I FROM HOUSE TO OVERFLOW "" CONVEYANCE AFTER FLOW / 42 LF ^' 6" PVC @ 12.8%MIN '. x 20' UTILITY l EASEMENT CONTROL STRUCTURE _____ �__ _ _ _ ________ �_-r_______________ _ �'_____i-_ _� _ _ rT� 11t-l--F l S® I EXISTING SSCO CATCH BASIN SCHEDULE MARK TYPE RIM ELEV INV ELEV NOTES (1> TYPE1 111.0 I6"NW): 108.50 1 2 C3. C3. U 12" AREA 115.90 IS" S): 111.18 4 DRAIN ( 12" AREA 115.80 IV N): 111.0 4 \3� DRAIN IS" SW): 110.90 IS" E): 108.39 1 2 (4� - TYPE 110.39 IS" NE): 108.39 C3. C3. IV NW): 108.29 IV E): 102.13 1 2 /� \ TYPE 1 104.93 (6" N): 102.93 C3. C3. (6" S): 102.83 60"� TYPE II 104.93 (36" E): 99.93 5 1 (12" SW): 99.93 C3. C3.3 O TYPE 1 102.0 (12" NEI: 99.71 1 2 (12" S): 99.51 C3. C3. (12"N): 99.41 CONTRACTOR TO VERIFY TYPE 101.17 (12"W): 99.41 LOCATIONCRP I&SLOPE (12" E): 99.41 DEPTH, C3. C3. PRIORTO CONSTRUCTION (AFN 88081650001) II dLL F R R F R -F It OF.R _ IE (4" E): 111.59 TIE ROOF DRAIN LINE r APPROX.PER AS BUILT TO CATCH BASIN ) l v I UNDER BLD2022-0497) VERIFY - - - I ' - -;, CONTRACTOR TO VERIFY F F F 'F F F � 114.14 11, SEWER LOCATION, SIZE, Zx II , ---_- -R RF - R- -R -- R Q Q a - 'R�-R - p--J - I`SE MATERIAL, AND DEPTH n . F F il' PRIOR TO CONSTRUCTION o i L�4LF "'6'PVC@163% " L--R-- R- 41'i� �E .Iv 114.39 WICIA TH F1"MIINUP RAVEL =x ■ d 1 ', °' i 3a=p - 1 a.'. j WIT LL AROUND, WRAPPED GRAVEL \\ IE: 102.18 I � - .z� E I NEW DRIVEWAY ALL AROUND, WRAPPED IN 8" MIN FROM WOOD. ANDTURNAROUND NO GEOTEXTILE SEE STRUCTURAL DRAWINGS 9LF ^'6 PVC @2.0% N FABRIC, SLOPE AT 0.5%MIN. '"� ' '' tf I v v 1 - 11439 TU RNDOWNPERFORATIONS SEE DETAIL 3/C3.3 1 - _ .3 ( t va 4 ¢ba' a PRO LED v AS SHOWN FOR STORM PROFILE / d - F 8 LF'6' PVC @ �0 ` GAS 71 Q INSTALL 6 ROLLED CURB _ / 4 - PROPOSED ON WEST AND SOUTH SIDE 6" DOWNSPOUT TIGHTLINE FINISHED GRADE ■ tE/ �� 'WAFER71E pF PROPOSED DRIVEWAY TO CONVEYANCE SYSTEM@ L I Iff 29 24.85 v �� TO DIRECT RUNOFF TO05%MIN. PLACE NEXT TO44 LF ^ 12' DI @ 0.5% PIT T7 _ PV7,PROPOSED CB FOOTING DRAIN OR ASSHOWN ON GRADING & G - - - - - - DRAINAGE PLAN -III- ( G G C. zlc G (CONTRACTOR MAY LOCATE 20 LF ^'12"DI@0.5%MIN G- - - - - - - - - - _ w,>wnW Awn _wA ON EITHER SIDE OF ° Op° ° d T f ADD DIAGONAL ASPHALT BERM FOR - FOOTING DRAIN O O ADD CLEANOUTS TO , (2) ROWS OF 36" Q N-12 DETENTION PIPE 5 108.20 32.29' ) O Q O O FLOW TO CBpl, 3" MAX HEIGHT IE: 99.47 / DETENTION PIPE PER TOTALING 54 LF W/ (2J 3 LF CONNECTORS C3. SOIL AMENDMENTS O ° ° OO a a - PVMT 101.05 COE STD SD-619 BETWEEN (fi0 LF TOTAL) C CONCRETE SECTION 0 O a PER BMP T5.13 OF ° 0 -' COVER:7 THESWMMWW C3. LINE OF MAX EXCAVATION. 00 O Qa EX C.B. �j p y D PROTECT EXISTING ASPHALT EDGEa' c w - - _ _✓_I ! �VQ I !`� IF SOIL 15 OVEREXCAVATED O O ° O o - a , w ti �1^^ o , , ' - +�i WA- - WA- - WA- ' lUA 1>T - WA- _�_ W'A- - - -- - - -- - - WA- - WA- - - WA- - - WA- - - W'A- y - A- - - V RIM=103.98 A - T -_- O ( " EX C.B. { ROPOSED PAVEMENT WITHIN PRIVATE - WA- - WA= _ - REPLACE WI H LEAN MI% O O O ° 12" CRP I.E.=f 02.68 - E SLOPE HARD S ALL UNCOVERED ROAD (249 SF). PROTECT EXISTING T CONCRETE 0 _-____-__-________ _______________ _ ___ _ __ RIM-f04.32 1 = _ E-f02.22 12"W % SURFACES AWAY ASPHALT EDGE / I.E.-102.42 8"N i FROM BUILDING / , \ SOUTHL6" ROLLED IDF OF POSED DRIVEWAY � /� FOOTING \ - - - - --'UNOFFO PROPOSED CB DTRIVEWIVEWAY EXISTING EDGE OF,PAVEMENT ,0K No lid �1 GRADING AND DRAINAGE PLAN GRADING AND DRAINAGE PLAN NOTES: 1. Sol IS REPORT REPORT NUMBER: 1406422 PREPARED BY: NELSON GEOTECHNICAL ASSOCIATES, INC. DATED: 12/15/2022 2. AMINIMUM OF 3' HORIZONTAL SEPARATION AND I'VERTICALSEPARATION IS REQUIRED BETWEEN DRY UTILITIES(POWER, GAS, PHONE,CABLE, ETC)AND SEWER, WATER AND STORM, AND A MINIMUM OF 5' HORIZONTAL SEPARATION AND V VERTICAL SEPARATION FROM ANY CITY OW NEE LINES. 3. NEW/REPLACED IMPERVIOUS SURFACE(INCLUDING ROW): 5,9995F NEW BUILDING: 4,527 SF ROOF AREA. RUNOFF ROUTED TO AN ONSITE DETENTION PIPE THROUGH ROOF DRAINS AND CATCH BASINS. THE RUNOFF WI ILL OUTLET TO THE PRIVATE STORM MAIN. NEW WALKWAYS: 435 SF RUNOFF INTERCEPTED BY AREA DRAINS, YARD DRAINS, AND CATCH BASINS AND ROUTED TO AN ONSITE DETENTION PIPE. THE RUNOFF WILL OUTLET OT HE PRIVATE STORM MAIN. NEW DRIVEWAY: 934 SF. RUNOFF INTERCEPTED BY CATCH BASIN AND ROUTED TO AN ONSITE DETENTION PIPE. THE RUNOFF WILL OUTLET TO THE PRIVATE STORM MAIN. OFFSITE DRIVEWAY: 47 SF. RUNOFF COLLECTED BY PRIVATE DRIVE CATCH BASIN. Co TE PAVEMENT PATCHING: 56 SF. RUNOFF COLLECTED BY PRIVATE DRIVE CATCH BASIN. 'CONCEPT PATIO: 1,110 SF. PATIO WILL NOT BE INSTALLED DURING THIS PROJECT. THE PATIO AREA HAS BEEN INCLUDED IN DETENTION SIZING FOR FUTURE INSTALLATION. EXCLUDED FROM OVERALL HARDSCAPE CALCULATIONS. - 'CONCEPT POOL: 290 SF. POOL WILL NOT BE INSTALLED DURING THIS PROJECT. THE POOL AREA HAS BEEN INCLUDED IN DETENTION SIZING FOR FUTURE INSTALLATION. EXCLUDED FROM OVERALL HARDSCAPE CALCULATIONS. 4. ALL DISTURBED AREAS TO BE COMPOST AMENDED PER 2019 SW MM W W BMP T5.13. 5. ALL DISTURBED AREAS ON AND OFF- SITE SHALL BE COMPOST- AMENDED PER THE REQUIREMENTS OF THE BMP T5.131N THE STORMWATER MANUAL VOLUME V, CHAPTER 5. 6. TOW AND BOW REFER TO FINISHED GRADE AT THE TOP AND BOTTOM OF THE WALLS, RESPECTIVELY. 7. AMINIMUM OF 2'OF COVER IS REQUIRED FOR ALL PIPES LOCATED UNDER DRIVABLE SURFACES AND VOF COVER UNDER LANDSCAPE SURFACES. DUCTILE IRON PIPES WILL BE USED IN AREAS THAT THIS STANDARD CANNOT BE MET. 8. PRIOR TO PLACING ANY SURFACING MATERIAL ON THE DRIVEWAY, IT WILL BE THE RESPONSIBILITY OF THE DEVELOPER/CONTRACTOR TO PROVIDE DENSITY TEST REPORTS CERTIFIED BY A PROFESSIONAL ENGINEER REQUIRED IN THE STATE OF WASHINGTON. 9. A TYPE II MANHOLE IS REQUIRED WHEREVER RIM TO INVERT EXCEEDS 5' 9. DRIVEWAY SLOPES SHALL NOT EXCEED 14% GRADE PER ECDC 18.80.060. GRADING QUANTITIES TOTAL EXCAVATION (CUT) - 300 CU YDS TOTAL EMBANKMENT(FILL)- 225 CU YDS TOTAL 525 CU VDS THE QUANTITIES SHOWN ABOVE ARE FOR THE PERMIT PROCESS ONLY. THESE VALUES ARE APPROXIMATE. DO NOT USE FOR BIDDING, PAYMENT, OR ESTIMATING PURPOSES. ASPHALT CONCRETE WEARING COURSE HMA CLASS 1/2" PG 64-22 - (WSDOT STD SPEC 5-04.1) CRUSHED SURFACING o� o,o BASE COURSE(WSDOT �p o� - obo n� ° STD SPEC 9-03.9(3)) cbo -III-III-III-III-III- SUITABLE NATIVE MATERIAL III III III III III III III FILL; TOP 12"COMPACTEDTOA III III III III MI NIMUMOF95%RELATIVE III III COMPACTION USING AASHTO =III=III=III=III=III= T-180 (ASTM D1557). UNSUITABLE NATIVE MATERIAL SHALL BE REPLACED TYPICAL PAVEMENT SECTION © FOOTING AND ROOF DRAIN SECTION UG SCALE: NTS 14" 12" NOTES: 1. WEIGHT 360 LBS. 2. (1) 6" KNOCKOUT PROVIDED FOR PIPE ENTRY. 3. FOR USE WITH 14" CAST IRON GRATE. 4. AREA TO HAVE SOLID BOTTOM. 12" AREA DRAIN BLDXXOC-HOC APPROVED FOR CONSTRUCTION CITY OF EDMONDS DATE: BY: CITY ENGINEERING DIVISION C 4m ENGINEERING 250 4TH AVE. S., SUITE 200 EDMONDS, WASHINGTON 98020 PHONE (425) 778-8500 FAX (425) 778-5536 u 07/29/24 iu ul[ulC-iC-i O DESIGN: NAT DRAWN: ATE) CHECK: GAG JOB NO: 22372.20 DATE: 08/17/23 Ld 0 Q Q V) J coO Q LJ W wLd a a> 0 0 Q L) QLLJ D � - J N V Z Q 0 0 LLJ Z Q Z a- CD :2Q Q 0 O 0 = - W 0 E y SHEET C3.1 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.3: Maintenance Standards - Closed Detention Systems (Tanks[Vaults) (continued) Maintenance Defect Conditions When Maintenance is Needed Results Expected When Maintenance is Per - Component formed Cover Not in Place Cover is missing oronly partially in place. Any open manhole requires maintenance. Manhole is closed. Manhole Mechanism cannot be opened by one maintenance person with proper tools. Bolts into frame have less than 1/2 inch of Locking Mechanism Not Working thread (may not apply to self-locking lids). Mechanism opens with proper tools. Cover Difficult to Remove One maintenance person cannot remove lid after applying normal lifting pressure. I ntent is to keep cover from sealing off Cover can be removed and reinstalled by one access to maintenance. maintenance person. Ladder Rungs Unsafe Ladder is unsafe due to missing rungs, misalignment, not securely attached to structure wall, rust, or cracks. Ladder meets design standards. Allows main- tenance person safe access. Catch Basins See Table V-A.5: Maintenance Standards - Catch See Table V-A.5: Maintenance Standards - Catch Basins See Table V-A.S: Maintenance Standards - Basins Catch Basins Table V-A.4: Maintenance Standards - Control Structure/Flow Restrictor Maintenance Com- Defect Condition When Maintenance is Needed Results Expected When Maintenance is Performed ponent Trash and Debris (Includes Sediment) Material exceeds 25 % of sump depth or 1 foot below orifice plate. Control structure orifice is not blocked. All trash and debris removed. Structure is not securely attached to manhole wall. Structure securely attached to wall and outlet pipe. General o Structure is not in upright position (allow up to 10 /o from plumb). Structure in correct position. Structural Damage Connections to outlet pipe are not watertight and show signs of rust. Connections to outlet pipe are water tight; structure repaired or replaced and works as designed. Any holes - other than designed holes - in the structure. Structure has no holes other than designed holes. Cleanout gate is not watertight or is missing. Gate is watertight and works as designed. Gate cannot be moved up and down by one maintenance person. Gate moves up and down easily and is watertight. Cleanout Gate Damaged or Missing Chain/rod leading to gate is missing or damaged. Chain is in place and works as designed. Gate is rusted over 50% of its surface area. Gate is repaired or replaced to meet design standards. Orifice Plate Damaged or Missing Control device is not working properly due to missing, out of place, or Plate is in place and works as designed. bent orifice plate. Obstructions Any trash, debris, sediment, or vegetation blocking the plate. Plate is free of all obstructions and works as designed. Overflow Pipe Obstructions Any trash or debris blocking (or having the potential of blocking) the Pipe is free of all obstructions and works as designed. overflow pipe. Manhole See Table V-A.3: Maintenance Standards - Closed Detention Systems See Table V-A.3: Maintenance Standards - Closed Detention Systems See Table V-A.3: Maintenance Standards - Closed Detention Systems (Tank- s/Vaults (Tanks/Vaults) (Tanks/Vaults) Catch Basin See Table V-A.S: Maintenance Standards - Catch Basins See Table V-A.S: Maintenance Standards - Catch Basins See Table V-A.5: Maintenance Standards -Catch Basins 2019 Stormwater Management Manual for Western Washington Volume V - Appendix A - Page 1008 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 Hopper Residence - CG #22372.20 Drainage Report July 29, 2024 Appendix A, Page 1 Appendix A —Attached Reports 250 4th Avenue South, Suite 200 Edmonds, WA 98020 ph.425.778.8500 1 f.425.778.5536 ENGINEERING 42 www.cgengineering.com 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 16, 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 Custom Soil Resource Report Soil Map 547652 547659 547666 547673 5476M 547687 547694 47° 49'6"N M_ N 47° 49' 5" N 547659 547666 547673 547680 547687 Map Scale: 1:324 if printed on A landscape (11" x 8.5") sheet. Meters N 0 4 9 18 27 Feet 0 15 30 60 90 Map projection: Web Mercator Comer coordinates: WGS84 Edge tics: UTM Zone 1ON WGS84 9 547701 547708 547715 547694 547701 547708 547715 547722 47° 49'6" N 1 R 47° 49' S" N 547722 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 31.3% 2 to 8 percent slopes Alderwood-Urban land complex, 0.2 68.7% 8 to 15 percent slopes Totals for Area of Interest 0.3 100.0% Map Unit Descriptions The map units delineated on the detailed soil maps in a soil survey represent the soils or miscellaneous areas in the survey area. The map unit descriptions, along with the maps, can be used to determine the composition and properties of a unit. A map unit delineation on a soil map represents an area dominated by one or more major kinds of soil or miscellaneous areas. A map unit is identified and named according to the taxonomic classification of the dominant soils. Within a taxonomic class there are precisely defined limits for the properties of the soils. On the landscape, however, the soils are natural phenomena, and they have the characteristic variability of all natural phenomena. Thus, the range of some observed properties may extend beyond the limits defined for a taxonomic class. Areas of soils of a single taxonomic class rarely, if ever, can be mapped without including areas of other taxonomic classes. Consequently, every map unit is made up of the soils or miscellaneous areas for which it is named and some minor components that belong to taxonomic classes other than those of the major soils. Most minor soils have properties similar to those of the dominant soil or soils in the map unit, and thus they do not affect use and management. These are called noncontrasting, or similar, components. They may or may not be mentioned in a particular map unit description. Other minor components, however, have properties and behavioral characteristics divergent enough to affect use or to require different management. These are called contrasting, or dissimilar, components. They generally are in small areas and could not be mapped separately because of the scale used. Some small areas of strongly contrasting soils or miscellaneous areas are identified by a special symbol on the maps. If included in the database for a given area, the contrasting minor components are identified in the map unit descriptions along with some characteristics of each. A few areas of minor components may not have been observed, and consequently they are not mentioned in the descriptions, especially where the pattern was so complex that it was impractical to make enough observations to identify all the soils and miscellaneous areas on the landscape. The presence of minor components in a map unit in no way diminishes the usefulness or accuracy of the data. The objective of mapping is not to delineate pure taxonomic classes but rather to separate the landscape into landforms or landform segments that have similar use and management requirements. The delineation of such segments on the map provides sufficient information for the development of resource plans. If intensive use of small areas is planned, however, 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 NELSON GEOTECHNICAL ASSOCIATES. INC. December 15, 2022 Darren Hopper c/o: Jacob Strobl Strobl Design, LLC VIA Email: Jacob@strobldesign.com Geotechnical Engineering Evaluation Hopper Residence Development 1005 Olympic Avenue Edmonds, Washington NGA File No. 1406422 17311-1351" Ave. N.E. Suite A-500 Woodinville, WA 98072 (425) 486-1669 www.nelsongeotech.com Dear Darren: NELSON GEOTECHNICAL ASSOCIATES, INC. (NGA) is pleased to submit this letter for a subsurface geotechnical and infiltration evaluation for the Hopper Residence Development project located at 1005 Olympic Avenue in Edmonds, Washington, as shown on the Vicinity Map in Figure 1. Our services were completed in general accordance with the proposal signed by you on October 30, 2022. INTRODUCTION The property is irregular in shape and covers approximately 0.31 acres in area. It is currently vacant and covered with grass. The property is bordered by a private access drive to the south, by single-family residence to the east and west, and a vacant lot and single-family residence to the north. Topographically, the site slopes gently to the west. We understand that the plans for development include the construction of a single-family residence with associated driveway and utilities. We have been requested to provide this letter for determination of geological hazards affecting the site, as well as development considerations for the proposed residence. For our use in preparing this letter we were provided with Architectural plans titled "Hopper Residence," dated August 8, 2022, and prepared by Strobl Design. Specific grading and stormwater plans have not been developed, but we understand that stormwater may be directed to on -site infiltration systems, if feasible. Geotechnical Engineering Evaluation NGA File No. 1406422 Hopper Residence Development December 15, 2022 Edmonds, Washington Page 2 We have been requested to evaluate the infiltration capacity of the site soils. We will collect samples and determine the infiltration rate based on the Department of Ecology's 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW), utilized by the City of Edmonds. According to this manual, we understand that 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). SCOPE The purpose of this study is to explore and characterize the site surface and subsurface conditions and provide general recommendations for site development. Specifically, our scope of services included the following: 1. Reviewing available soil and geologic maps of the area. 2. Exploring the subsurface soil and groundwater conditions within the site using trackhoe- excavated test pits. Excavation services were subcontracted by NGA. 3. Providing long-term design infiltration rates based on on -site Small Pilot Infiltration Testing (PIT) per the 2019 SWMMWW, if feasible. 4. Performing laboratory grain -size sieve analysis on soil samples, as necessary. 5. Determining the presence of Geologically Hazardous Areas in accordance with the City of Edmonds Code, as warranted. 6. Providing recommendations for mitigation or reduction of risk from present geologic hazards, as warranted. 7. Providing recommendations for earthwork and foundation support. 8. Providing recommendations for retaining walls. 9. Providing recommendations for temporary and permanent slopes. 10. Providing recommendations for subsurface utilities and pavement subgrade preparation. 11. Providing our opinion on stormwater infiltration feasibility. SITE CONDITIONS Surface Conditions The property is irregular in shape and covers approximately 0.31 acres in area. It is currently vacant and covered with grass. The property is bordered by a private access drive to the south, by single-family residences to the east and west, and a vacant lot and single-family residence to the north. Topographically, the site slopes gently to the west. There is a 2-foot-tall rockery on the west portion of the site that runs north to south. We did not observe standing water within the property during our site visit on December 1, 2022. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1406422 Hopper Residence Development December 15, 2022 Edmonds, Washington Page 3 Subsurface Conditions Geology: The geologic units for this area are shown on Geologic Map of the Edmonds East and Part of the Edmonds West Quadrangles, Washington, by James P. Minard (1983). The site is mapped as Advance Outwash (Qva). Advance Outwash underlies the till. The outwash typically is a thick section of mostly clean, gray, pebbly sand with increasing amounts of gravel higher in the section. Our explorations generally encountered surficial undocumented fill and topsoil underlain by silty fine to coarse sand with gravel which fits the description of the mapped Advance Outwash glacial soil. Explorations: We visited the site on December 1, 2022, to explore the subsurface conditions within the site by excavating four test pit explorations through the site, one which was used for infiltration testing. The approximate locations of our explorations are shown on the Schematic Site Plan in Figure 2. An engineer from Nelson Geotechnical Associates, Inc. (NGA) completed the explorations, examined the soils and geologic conditions encountered, and maintained logs of the explorations. The soils were visually classified in general accordance with the Unified Soil Classification System, presented in Figure 3. The logs of our explorations are presented as Figure 4. The following paragraph contains a brief description of the subsurface conditions encountered in the explorations. For a detailed description of the subsurface conditions, the hand auger logs should be reviewed. Topsoil/ Undocumented Fill: At the surface of Infiltration Test Pit One, Test Pit One, and Test Pit Two we encountered a 1.0-to-1.5-foot layer of topsoil. In Test Pit Three, which was located above the 2-foot-tall rockery, we encountered dark brown, silty, fine to medium sand with gravel and trace roots in a loose condition that we interpreted as undocumented fill soils. Advanced Outwash: Underlying the topsoil/undocumented fill soils in all our explorations at depth anywhere between 1 and 3 feet below existing grade we generally encountered silty, fine to coarse sand with gravel in a medium dense to dense condition which we interpreted as native advanced outwash soils. Test Pits One, Two, Three, and Infiltration Test Pit One terminated in the native glacial soils at depths of 5.0, 7.0, 8.0, and 6.0 feet below existing grade, respectively. Hydrogeologic Conditions Groundwater seepage was encountered in all explorations. We interpret encountered seepage to be perched water and not a regional groundwater table. Perched water occurs when surface water infiltrates through less dense, more permeable soils and accumulates on top of underlying, less permeable soils. Perched water does not represent a regional groundwater "table" within the upper soil horizons. Perched water tends to vary spatially and is dependent upon the amount of rainfall. We would expect the amount of perched water to decrease during drier times of the year and increase during wetter periods. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Hopper Residence Development Edmonds, Washington SENSITIVE AREA EVALUATION Seismic Hazard NGA File No. 1406422 December 15, 2022 Page 4 We reviewed the 2018 International Building Code (IBC) for seismic site classification for this project. Since competent glacial soils were encountered at depth at the subject site, the site conditions best fit the IBC description for Site Class D. Table 1 below provides seismic design parameters for the site that are in conformance with the ASCE 7-16, which specifies a design earthquake having a two percent probability of occurrence in 50 years (return interval of 2,475 years), and the 2008 USGS seismic hazard maps. Table 1— ASCE 7-16 Seismic Design Parameters Site Class Spectral Acceleration Spectral Acceleration Site Coefficients Design Spectral at 0.2 sec. (g) at 1.0 sec. (g) Response SS S1 Parameters Fa Fv SDs SD1 rC 1.291 0.455 1.0 - null 0.861 null The spectral response accelerations were obtained from the OSHPD Seismic Design Maps website for the project latitude and longitude. The site is located within the South Whidbey Island Fault Zone (SWIFZ): an active, shallow region of seismicity within central Puget Sound stretching from the Strait of Juan de Fuca to North Bend. Information published in 2013 by the Washington State Department of Natural Resources suggests the SWIFZ last ruptured less than 2,700 years ago, and that the fault zone can produce a M7.5 earthquake. The nearest mapped fault strand is located on the eastern property line and was constrained by the USGS based on subsurface geophysical techniques, not surface mapping. It is our opinion that the risk of surface rupture at the site is low, based on available information. Hazards associated with seismic activity include liquefaction potential and amplification of ground motion. Liquefaction is caused by a rise in pore pressures in a loose, fine sand deposit beneath the groundwater table. It is our opinion that the dense, generally fine-grained glacial deposits interpreted to underlie the site have a low potential for liquefaction or amplification of ground motion. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1406422 Hopper Residence Development December 15, 2022 Edmonds, Washington Page 5 Erosion Hazard The criteria used for determination of the erosion hazard for affected areas include soil type, slope gradient, vegetation cover, and groundwater conditions. The erosion sensitivity is related to vegetative cover and the specific surface soil types, which are related to the underlying geologic soil units. The Soil Survey of the Snohomish County Area, Washington, by the Natural Resource Conservation Service (NRCS), has classified the east half of the site as Alderwood-Urban land complex, 8 to 15 percent slopes and the west half Alderwood-Urban land complex, 2 to 8 percent slopes. The erosion hazard for these soils is listed as moderate. On the City of Edmonds GIS map there is a small area on the east half of the site mapped as Erosion Hazard Areas 15 to 40 percent. Based on our experience in the area and our observations in the field, the native soils at the site present a slight to moderate erosion hazard for areas where the soils are exposed. It is our opinion that the erosion hazard for site soils should be low in areas where vegetation is not disturbed. CONCLUSIONS AND RECOMMENDATIONS General It is our opinion from a geotechnical standpoint that the planned single-family residence is feasible, provided the recommendations provided in this letter are followed. In general, the medium dense or better native soils interpreted to underlie the site at depth should provide adequate support for the planned structure. If structures are to be located in areas of loose soils or undocumented fill, foundations will need to extend through this material and rest on the underlying medium dense or better native soils or placed within reworked and engineered structural fill. The proposed structure should be founded on shallow spread footings extending down to the medium dense or better native soils. Such soils should be encountered approximately 1 to 3 feet below the existing ground surface. We recommend that the foundations for the planned structure extend through any loose or undocumented fill soils and bear wholly on the underlying native soils or approved structural fill. All foundations should generally be placed on subgrade soils or structural fill of the same type and density to reduce potential differential settlement. More information can be found in the Foundations and Structural Fill subsections of this report. Due to the presence of groundwater seepage in our explorations, it is our opinion that traditional stormwater infiltration is infeasible within this site. All runoff generated within this site should be directed to an approved discharge point most likely located in the adjacent streets. More detailed drainage recommendations are provided in the Site Drainage subsection of this report. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Hopper Residence Development Edmonds, Washington NGA File No. 1406422 December 15, 2022 Page 6 Some of the soil encountered on this site is considered very moisture -sensitive and may disturb easily when wet. We recommend that construction take place during the drier summer months, if possible. If construction is to take place during wet weather, the soils may disturb, and additional expenses and delays may be expected due to the wet conditions. Additional expenses could include the need for placing a blanket of rock spalls to protect exposed subgrades and construction traffic areas, and erecting silt fences and straw bales to prevent muddy water from leaving the site. Erosion Control The erosion hazard for the on -site soils is interpreted to be slight to moderate for exposed soils, but actual erosion potential will be dependent on how water is allowed to concentrate. Best Management Practices (BMPs) should be used to control erosion. Areas disturbed during construction should be protected from erosion. Erosion control measures may include diverting surface water away from disturbed areas. Silt fences and straw wattles should be erected to prevent muddy water from leaving the site. Disturbed areas and stockpiles should be covered as soon as practical. Erosion potential of areas not stripped should be low. Site Preparation and Grading After erosion control measures are implemented, site preparation should consist of removing loose soils, topsoil, and any undocumented fill from foundations, slab, and pavement areas, to expose medium or better native bearing soils at depth. The stripped soil should be removed from the site. Based on our observations, we anticipate native, medium dense or better soil to be encountered at approximately one to three feet throughout explored areas of the site. We should note that additional deeper areas of unsuitable soils and/or undocumented fill could be encountered in unexplored areas of the site. This condition, if encountered, would require deeper excavations in foundation, slab, and pavement areas to remove the unsuitable soils. After site preparation, if the exposed subgrade is deemed loose, it should be compacted to a non -yielding condition and then proof -rolled with a heavy, rubber -tired piece of equipment. Areas observed to pump or weave during the proof -roll test should be reworked to structural fill specifications or over -excavated and replaced with properly compacted structural fill or rock spalls. If loose soils are encountered in the foundation areas, the loose soils should be removed and replaced with rock spalls. If significant surface water flow is encountered during construction, this flow should be diverted around work areas, and exposed subgrades should be maintained in a semi -dry condition. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Hopper Residence Development Edmonds, Washington NGA File No. 1406422 December 15, 2022 Page 7 If wet conditions are encountered, which is likely on this site, alternative site grading techniques might be necessary. These could include using large excavators equipped with wide tracks and a smooth bucket to complete site grading and covering exposed subgrade with a layer of crushed rock for protection. If wet conditions are encountered or construction is attempted in wet weather, the subgrade should not be compacted, as this could cause further subgrade disturbance. In wet conditions, it may be necessary to cover the exposed subgrade with a layer of crushed rock as soon as it is exposed to protect the moisture sensitive soils from disturbance by machine or foot traffic during construction. The prepared subgrade should be protected from construction traffic and surface water should be diverted around areas of prepared subgrade. Temporary and Permanent Slopes Cuts and fills should be used only where necessary and minimized in final grading plans for the development of the site. Temporary cut slope stability is a function of many factors, including the type and consistency of soils, depth of the cut, surcharge loads adjacent to the excavation, length of time a cut remains open, and the presence of surface or groundwater. It is exceedingly difficult under these variable conditions to estimate a stable, temporary, cut slope angle. Therefore, it should be the responsibility of the contractor to maintain safe slope configurations at all times as indicated in OSHA guidelines for cut slopes. The following information is provided solely for the benefit of the owner and other design consultants and should not be construed to imply that Nelson Geotechnical Associates, Inc. assumes responsibility for job site safety. Job site safety is the sole responsibility of the project contractor. For planning purposes, we recommend that temporary cuts in the site soils be no steeper than 1.5 Horizontal to 1 Vertical (1.51-1:1V). If significant groundwater seepage or surface water flow were encountered, we would expect that flatter inclinations would be necessary. We recommend that cut slopes be protected from erosion, as necessary. The slope protection measures may include covering cut slopes with plastic sheeting and diverting surface runoff away from the top of cut slopes, if such potential exists. We do not recommend vertical slopes for cuts deeper than four feet, if worker access is necessary. We recommend that cut slope heights and inclinations conform to appropriate OSHA/WISHA regulations. Permanent cut and fill slopes should be no steeper than 2H:1V. However, flatter inclinations may be required in areas where loose soils are encountered. Permanent slopes should be vegetated, and the vegetative cover maintained until established. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1406422 Hopper Residence Development December 15, 2022 Edmonds, Washington Page 8 Foundations Foundations should be designed in accordance with the 2018 IBC. Footing widths should be based on the anticipated loads and allowable soil bearing pressure. We recommend an allowable design bearing pressure of not more than 2,000 pounds per square foot (psf) be used to evaluate the design of footings founded on the medium dense or better native, bearing soils exposed at depths of 1.0 to 3.0 feet in our explorations. We should be retained during construction to observe and evaluate foundation subgrade. If higher bearing pressures are needed, current IBC guidelines should be used when considering increased allowable bearing pressure for short-term transitory wind or seismic loads. Potential foundation settlement using the recommended allowable bearing pressure is estimated to be less than 1-inch total and %-inch differential between adjacent footings or across a distance of about 20 feet, based on our experience with similar projects. Lateral loads may be resisted by friction on the base of the footing and passive resistance against the subsurface portions of the foundation. A coefficient of friction of 0.35 may be used to calculate the base friction and should be applied to the vertical dead load only. Passive resistance may be calculated as a triangular equivalent fluid pressure distribution. An equivalent fluid density of 200 pounds per cubic foot (pcf) should be used for passive resistance design for a level ground surface adjacent to the footing. This level surface should extend a distance equal to at least three times the footing depth. These recommended values incorporate safety factors of 1.5 and 2.0 applied to the estimated ultimate values for frictional and passive resistance, respectively. To achieve this value of passive resistance, the foundations should be poured "neat" against the soils or compacted fill should have been used as backfill against the front of the footing. We recommend that the upper one foot of soil be neglected when calculating passive resistance. Retaining Walls Plans have not been finalized for the new single-family residence but retaining walls may be incorporated into the design. The lateral pressure acting on subsurface retaining walls is dependent on the nature and density of the soil behind the wall, the amount of lateral wall movement which can occur as backfill is placed, wall drainage conditions, and the inclination of the backfill. For walls that are free to yield at the top at least one thousandth of the height of the wall (active condition), soil pressures will be less than if movement is limited by such factors as wall stiffness or bracing (at -rest condition). We recommend that walls supporting horizontal backfill and not subjected to hydrostatic forces be designed using a triangular earth pressure distribution equivalent to that exerted by a fluid with a density of 40 pcf for yielding (active condition) walls, and 60 pcf for non -yielding (at -rest condition) walls. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Hopper Residence Development Edmonds, Washington NGA File No. 1406422 December 15, 2022 Page 9 These recommended lateral earth pressures are for a drained granular backfill and are based on the assumption of a horizontal ground surface behind the wall for a distance of at least the height of the wall, and do not account for surcharge loads. Additional lateral earth pressures should be considered for surcharge loads acting adjacent to walls and within a distance equal to the subsurface height of the wall. This would include the effects of surcharges such as floor slab loads or other surface loads. We could consult with the structural engineer regarding additional loads on retaining walls during final design, if needed. The lateral pressures on walls may be resisted by friction between the foundation and subgrade soil, and by passive resistance acting on the below -grade portion of the foundation. Recommendations for frictional and passive resistance to lateral loads are presented in the Foundations subsection of this report. All wall backfill should be well compacted as outlined in the Structural Fill subsection of this report. Care should be taken to prevent the buildup of excess lateral soil pressures due to over -compaction of the wall backfill. This can be accomplished by placing wall backfill in 8-inch loose lifts and compacting the backfill with small, hand -operated compactors within a distance behind the wall equal to at least one-half the height of the wall. The thickness of the loose lifts should be reduced to accommodate the lower compactive energy of the hand -operated equipment. The recommended level of compaction should still be maintained. Permanent drainage systems should be installed for retaining walls. Recommendations for these systems are found in the Subsurface Drainage subsection of this report. We recommend that we be retained to evaluate the proposed wall drain backfill material and observe installation of the drainage systems. Erosion Control The erosion hazard for the on -site soils is interpreted to be slight to moderate for exposed soils, but actual erosion potential will be dependent on how water is allowed to concentrate. Best Management Practices (BMPs) should be used to control erosion. Areas disturbed during construction should be protected from erosion. Erosion control measures may include diverting surface water away from disturbed areas. Silt fences and straw wattles should be erected to prevent muddy water from leaving the site. Disturbed areas and stockpiles should be covered as soon as practical. Erosion potential of areas not stripped should be low. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1406422 Hopper Residence Development December 15, 2022 Edmonds, Washington Page 10 Structural Fill General: Fill placed beneath foundations, pavement, or other settlement -sensitive structures should be placed as structural fill. Structural fill, by definition, is placed in accordance with prescribed methods and standards, and is monitored by an experienced geotechnical professional or soils technician. Field monitoring procedures would include the performance of a representative number of in -place density tests to document the attainment of the desired degree of relative compaction. The area to receive the fill should be suitably prepared as described in the Site Preparation and Grading subsection prior to beginning fill placement. Sloping areas to receive fill should be benched using a minimum 8-foot-wide horizontal benches into competent soils. Materials: Structural fill should consist of good quality, granular soil, free of organics and other deleterious material, and be well graded to a maximum size of about three inches. All-weather fill should contain no more than five -percent fines (soil finer than U.S. No. 200 sieve, based on that fraction passing the U.S. 3/4-inch sieve). Some of the more granular on -site soils may be suitable for use as structural fill; however, this will be highly dependent on the moisture content of the soil during construction. The use of the on - site soils as structural fill during wet weather will be very difficult, if not impossible. We should be retained to evaluate all proposed structural fill material prior to placement. Fill Placement: Following subgrade preparation, placement of structural fill may proceed. All filling should be accomplished in uniform lifts up to eight inches thick. Each lift should be spread evenly and be thoroughly compacted prior to placement of subsequent lifts. All structural fill underlying building areas and pavement subgrade should be compacted to a minimum of 95 percent of its maximum dry density. Maximum dry density, in this letter, refers to that density as determined by the ASTM D-1557 Compaction Test procedure. The moisture content of the soils to be compacted should be within about two percent of optimum so that a readily compactable condition exists. It may be necessary to over -excavate and remove wet soils in cases where drying to a compactable condition is not feasible. All compaction should be accomplished by equipment of a type and size sufficient to attain the desired degree of compaction and should be tested. Slab -on -Grade We recommend that all floor slabs be underlain by at least six inches of free -draining material with less than three percent by weight of the material passing Sieve #200 for use as a capillary break. We recommend that the capillary break be hydraulically connected to the footing drain system to allow free drainage from under the slab. A suitable vapor barrier, such as heavy plastic sheeting (6-mil minimum), should be placed over the capillary break material. An additional 2-inch-thick moist sand layer may be NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1406422 Hopper Residence Development December 15, 2022 Edmonds, Washington Page 11 used to cover the vapor barrier. This sand layer is optional and is intended to be used to protect the vapor barrier membrane and to aid in curing the concrete. Pavements The pavement subgrade should be prepared as recommended in the Site Preparation and Grading and Structural Fill subsections of this report, including proof -rolling the subgrade with a loaded dump truck and repairing areas observed to pump or weave during the proof -roll test. Also, all fill placed within the pavement areas, including utility trench backfill, should be compacted to 95 percent of the Maximum Dry Density (Modified Proctor). We should be retained to observe the proof -roll test. Any areas observed to pump or weave under the wheels of the loaded dump truck should be over -excavated and replaced with crushed rock. Utilities We recommend that underground utilities be bedded with a minimum six inches of pea gravel prior to backfilling the trench with on -site or imported material. Trenches within settlement sensitive areas should be compacted to 95% of the modified proctor as described in the Structural Fill subsection of this report. Trenches located in non-structural areas should be compacted to a minimum 90% of the maximum dry density. The trench backfill compaction should be tested. Stormwater Infiltration Small-scale pilot infiltration tests were performed within Infiltration Test Pit 1(ITP1) on December 1, 2022. ITP1 measured approximately 4.0-feet long by 3.0-feet wide by 6.0-feet deep. During the presoak period, the water level was unable to be maintained at 12 inches. The sides of the excavation were caving and perched water was filling the hole faster than it was infiltrating. It is our opinion that onsite infiltration is not an option for this site. Site Drainage Surface Drainage: The finished ground surface should be graded such that stormwater is directed to an approved stormwater collection system. Water should not be allowed to stand in any areas where footings, slabs, or pavements are to be constructed. Final site grades should allow for drainage away from the structures, if possible. We suggest that the finished ground be sloped at a minimum gradient of three percent, for a distance of at least 10 feet away from the structures. Surface water should be collected by permanent catch basins and drain lines and be discharged into an approved discharge system. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation NGA File No. 1406422 Hopper Residence Development December 15, 2022 Edmonds, Washington Page 12 Subsurface Drainage: Groundwater seepage was observed as shallow as 2.0-feet below the existing ground surface in our explorations. If groundwater is encountered during construction, we recommend that the contractor slope the bottom of the excavation and collect the water into ditches and small sump pits where the water can be pumped out and routed into an approved location. We recommend the use of footing drains around the structure. Footing drains should be installed at least one foot below planned finished floor elevation. The drains should consist of a minimum 4-inch-diameter, rigid, slotted or perforated, PVC pipe surrounded by free -draining material wrapped in a filter fabric. We recommend that the free -draining material consist of an 18-inch-wide zone of clean (less than three -percent fines), granular material placed along the back of walls. Pea gravel is an acceptable drain material. The free - draining material should extend up the wall to one foot below the finished surface. The top foot of backfill should consist of impermeable soil placed over plastic sheeting or building paper to minimize surface water or fines migration into the footing drain. Footing drains should discharge into tightlines leading to an approved collection and discharge point with convenient cleanouts to prolong the useful life of the drains. Roof drains should not be connected to wall or footing drains. USE OF THIS LETTER NGA has prepared this letter for Darren Hopper and associated agents, for use in the planning and design of the development on this site only. The scope of our work does not include services related to construction safety precautions and our recommendations are not intended to direct the contractors' methods, techniques, sequences, or procedures, except as specifically described in our report for consideration in design. There are possible variations in subsurface conditions between the explorations and also with time. Our letter, conclusions, and interpretations should not be construed as a warranty of subsurface conditions. A contingency for unanticipated conditions should be included in the budget and schedule. We recommend that NGA be retained to provide monitoring and consultation services during construction to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes should the conditions revealed during the work differ from those anticipated, and to evaluate whether or not earthwork and foundation installation activities comply with contract plans and specifications. We should be contacted a minimum of one week prior to construction activities and could attend pre -construction meetings if requested. NELSON GEOTECHNICAL ASSOCIATES, INC. Geotechnical Engineering Evaluation Hopper Residence Development Edmonds, Washington NGA File No. 1406422 December 15, 2022 Page 13 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. Geotechnical Engineering Evaluation Hopper Residence Development Edmonds, Washington NGA File No. 1406422 December 15, 2022 Page 14 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. Jonathan D. Klevan, PE Project Engineer � 7 J!9 Nr. s�i `i tic, i x 35215 S�CISTE4�g �FVt �NNAL Khaled M. Shawish, PE Principal JDK:KMS:dy Four Figures Attached 12.15.2022 NELSON GEOTECHNICAL ASSOCIATES, INC. rk a m U a D o " PUg0 a IDS Project Q Site `.,nnSt 6OK'bOrq W ey VICINITY MAP Not to Scale D -- O ♦ � ii 176th St SW D Seaview Park J\or Q��` Lynnwood . � Costco BusinesswQenter Recreation Center 9 Fred Meyer sza Lynnwood 24 V p. D � 208th St SW -AN �G F� 1 N 212th St SW :' 212th St SW 71?th cr cw r WinCo Foods Edmonds, WA go n lake Terrace High School Project Number Hopper Residence � mson GEOTEnnim No. Date Revision By cK 1406422 Development ASSOCIATES, inc 11 1 12/1/22 Original FKS JDK Figure 1 Vicinity Map Wo°dinvIIIeOffce Wenatchee Office ` 17311-135th Ave. NE, A-500 105 Palouse St. Wood-ille, WA 98072 Wenatchee, WA 98801 www.nelsongeotech.com (425) 486-1669 / Fax. 481-2510 (509) 665-7696 / Fax: 665-7692 C o� CD z N 3 CT CD 2 0 -°v U! CD CD N CD -0-0 CD ET CD CDD Q CD CD 3 M o�o � a_a � a O O o O m —I cn M C7 c- T��� n i— 1 � 1 '* INF-1—�— TP-2 I TP-1 i I � n Reference: Site tl LEGEND Property line TP-1 —�— Number and approximate location of test pit TP-3 Site Plan N a r t � INF-1 —�— Number and approximate location of infiltration test pit based on field measurements. observations. and aerial mao review. 0 50 100 Scale: 1 inch = 50 feet Al "AO 1< c>' D CD v c CD 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 GEOTEnninl_ No. Date Revision By cK Hopper Residence �. 1406422 Development ASSOCIATES, inc , 1 12/1/22 Original FKS JDK Figure 3 Soil Classification Chart ui " 135th,"'°e CA Wenatchee Office 17311-1351h Ave. ffi A-500 105 Palouse St. Woodinville, WA 98072 Wenatchee, WA 98801 www.nelsongeoiech.com (425) 486-1669 / Fax 481-2510 (509) 665-7696 / Fax: 665-7692 LOG OF EXPLORATION DEPTH (FEET) USCS SOIL DESCRIPTION INFILTRATION TEST PIT ONE 0.0 — 1.0 TOPSOIL / FILL 1.0 — 6.0 SM BROWN, SILTY, FINE TO COARSE SAND WITH GRAVEL (MEDIUM DENSE TO DENSE, MOIST TO WET) (OUTWASH) SAMPLES WERE NOT COLLECTED GROUNDWATER SEEPAGE WAS ENCOUNTERED AT 2.0 FEET TEST PIT CAVING WAS NOT ENCOUNTERED TEST PIT WAS COMPLETED AT 6.0 FEET ON 12/01/2022 0.0 — 1.5 TOPSOIL / FILL 1.5-3.0 SM GRAY BROWN, SILTY, FINE TO MEDIUM SAND WITH GRAVEL AND IRON -OXIDE STAINING (MEDIUM DENSE TO DENSE, MOIST TO WET) (OUTWASH) 2.0 — 5.0 SM BLUE -GRAY, SILTY, FINE TO COARSE SAND WITH GRAVEL (MEDIUM DENSE TO DENSE, MOIST TO WET) (OUTWASH) SAMPLE WAS COLLECTED AT 4.0 FEET GROUNDWATER SEEPAGE WAS ENCOUNTERED AT 1.5 FEET TEST PIT CAVING WAS ENCOUNTERED TEST PIT WAS COMPLETED AT 5.0 FEET ON 12/01/2022 TEST PIT TWO 11111m l llo1:'iol l lwm y llIq 1.0 — 4.5 SP LIGHT BROWN, GRAVELLY, FINE TO COARSE SAND WITH TRACE SILT (MEDIUM DENSE TO DENSE, MOIST TO WET) (OUTWASH) 4.5 — 7.0 SM BROWN, SILTY, FINE TO COARSE SAND WITH TRACE GRAVEL (MEDIUM DENSE TO DENSE, MOIST TO WET) (OUTWASH) SAMPLES WERE COLLECTED AT 3.0 AND 5.0 FEET GROUNDWATER SEEPAGE WAS ENCOUNTERED AT 1.5 FEET TEST PIT CAVING WAS ENCOUNTERED TEST PIT WAS COMPLETED AT 7.0 FEET ON 12/01/2022 TEST PIT THREE 0.0 — 3.0 DARK BROWN, SILTY, FINE TO MEDIUM SAND WITH GRAVEL AND TRACE ROOTS (LOOSE, MOIST TO WET) (FILL) 3.0-4.0 SM LIGHT BROWN, SILTY, FINE TO COARSE SAND WITH TRACE GRAVEL, AND IRON -OXIDE STAINNING (MEDIUM DENSE, MOIST TO WET) (OUTWASH) 4.0 — 8.0 SM BROWN TO GRAY BROWN, SILTY, FINE TO COARSE SAND WITH GRAVEL, (MEDIUM DENSE TO DENSE, MOIST TO WET) (OUTWASH) SAMPLE WAS COLLECTED AT 6.0 FEET GROUNDWATER SEEPAGE WAS ENCOUNTERED AT 3.0 FEET TEST PIT CAVING WAS ENCOUNTERED TEST PIT WAS COMPLETED AT 8.0 FEET ON 12/01/2022 FKS:JDK NELSON GEOTECHNICAL ASSOCIATES, INC. FILE NO 1406422 FIGURE 4 Hopper Residence - CG #22372.20 Drainage Report July 29, 2024 Appendix B, Page 1 endix B — Maintenance Covenant 250 4th Avenue South, Suite 200 Edmonds, WA 98020 C CM ph.425.778.8500 1 f.425.778.5536 ENGINEERING 79 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) Hopper, Daren Grantee: City of Edmonds Legal Description (abbreviated form; i.e., lot, plat or section, township, range, quarter/quarter) LOT 10, SEA MOUNTAIN ESTATES, ACCORDING TO THE PLAT THEREOF RECORDED IN VOLUME 48 OF PLATS, PAGES 208-210, RECORDS OF SNOHOMISH COUNTY, WASHINGTON. SITUATE IN THE COUNTY OF SNOHOMISH, STATE OF WASHINGTON. Assessor's Property Tax Parcel/Account Number at the Time of Recording: 00766100001000 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 x❑ 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: 1005 OLYMPIC AVE 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 LOT 10, SEA MOUNTAIN ESTATES, ACCORDING TO THE PLAT THEREOF RECORDED IN VOLUME 48 OF PLATS, PAGES 208-210, RECORDS OF SNOHOMISH COUNTY, WASHINGTON. SITUATE IN THE COUNTY OF SNOHOMISH, STATE OF WASHINGTON. S01°34'11"W 69.01' S89°34'28"E 16.96' o c ° o a ROOF AND FOOTING DRAIN 00 19.12' r° g LINES 94.04' � 0o I g o CATCH BASIN 0 L PROPOSED RESIDENCE AREA DRAIN :. CATCH BASIN I oco m a� a f a LL I a DETENTION PIPE ° FLOW CONTROL STRUCTURE t Li_ I I ----- CATCH BASIN ` I I I N49'14'02"E 82.28' L CATCH BASIN. CONNECT 589'44 53 E 20.0 STORM DRAIN INTO EXISTING 12" CRP MAIN N00°11'38"W 37.0' S89°44'53"E 191.30'