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APPROVED STM RESUB1 BLD2024-0266+Storm_Drainage_Report+6.7.2024_4.06.06_PM+4309436RESUB BLD2024-0266 Jun 10 2024 CITY OF EDMONDS DEVELOPMENT SERVICES DEPARTMENT 648 Walnut Street Single Family Residence 648 Walnut Street Edmonds, WA 98020 BLD2024-0266 Stormwater Site Plan Report Prepared for: Select Homes Date: February 27, 2024 Revised: June 7, 2024 36508W \� EGISTEV,�� IONeT . 0/j /2024 Prepared by: Rob Long, PE RAM Fnginininring, Inr, 19109 3611 Ave W, Suite 103, Lynnwood WA 98036 (425) 678-6960 RAMengineeringinc.com COMPLIES WITH APPLICABLE CITY STORMWATER CODE 07/10/2024 Job No. 24-002 648 Walnut Street Single Family Residence Introduction: This summary report provides site design information for a single-family residence at 648 Walnut Street. This report includes stormwater analysis to support permit review and approval. The property is located on the south side of Walnut Street, in the southwest 1/4 of Section 24, Township 27N, Range 3E, W.M. Site Address: Applicant: 648 Walnut Street Select Homes Edmonds, WA 98020 8304 212t" St SW Edmonds WA 98026 Tax Parcel Number: Contact: Kayla Clark Nichols 00434209301500 (425) 742-6044 TABLE OF CONTENTS SECTION PAGES A. Project Overview.............................................................................................................................. 5 B. Existing Conditions Summary........................................................................................................... 1 C. Developed Site Hydrology................................................................................................................ 5 D. Soils Reports................................................................................................................................... 20 E. Construction SWPPPP Requirements................................................................................................ 2 F. Operation and Maintenance Guidelines............................................................................................ 5 RAMEngineering, Inc. RAM No. 24-002 648 Walnut Street SFR Stormwater Site Plan Report Page A. PROJECT OVERVIEW: This report provides engineering information for the proposed construction of a single family residence on a 0.19 acre parcel; the project is located on the south side of Walnut Street in the City of Edmonds. The applicant, Select Homes proposes to remove the existing residence and all existing hard surface to construct a new single family residence on the project site. This report provides the evaluation for the new single family residential development. Summary of Minimum Requirements for Category 1 Project: Minimum Requirement #1 — Preparation of Stormwater Site Plan. The proposed site development consists of disturbing the entire 0.19 acres site with the removal of all existing improvements onsite. The project will create/replace about 4,725 sf of hard surface area; thus, the project is classified as a Category 1 project per the City's classification system. Per ECDC 18.30, Category 1 projects must comply with Minimum Requirements No. 1 through No. 5. The civil site development plans and this report have been prepared to address the project's impacts. Minimum Requirement #2 — Construction Stormwater Pollution Prevention (SWPPP). A construction Stormwater Pollution Prevention Plan (SWPPP) has been incorporated into the site development plans. A summary of the site's erosion control measures that evaluates the typical 13 elements of a SWPPP are included in section E. The total site disturbance area (0.19 ac) of the project will not exceed one acre, thus a formal Notice of Intent application for NPDES coverage will not be made to the Department of Ecology. Minimum Requirement #3 —Source Control of Pollution. Specific source controls are not required for single family residential sites. General requirements for these sites include preventing the discharge of pollutants to the City's storm drainage system per Edmonds City Code Chapter 7.200 (Illicit Discharges). This includes common household items such as pesticides, herbicides, fertilizers, detergents and fluids from vehicle maintenance. Single family residences shall incorporate DOE's S411 BMPs for landscape and lawn vegetation management. Lawn and vegetation management can include control of objectionable weeds, insects, mold, bacteria, and other pests with pesticides. Examples include weed control on golf course lawns, access roads, and utility corridors and during landscaping; sap stain and insect control on lumber and logs; rooftop moss removal; killing nuisance rodents; fungicide application to patio decks, and residential lawn/plant care. It is possible to release toxic pesticides such as pentachlorophenol, carbamates, and organometallics to the environment by leaching and dripping from treated parts, container leaks, product misuse, and outside storage of pesticide contaminated materials and equipment. Poor management of the vegetation and poor application of pesticides or fertilizers can cause appreciable stormwater contamination. RAMEngineering, Inc. RAM No. 24-002 648 Walnut Street SFR Stormwater Site Plan Report Page A-3 Minimum Requirement #4 —Preservation of Natural Drainage Systems and Outfalls. The natural flow path and outfall of the site generally slopes northerly to the municipal separate storm sewer system (MS4) within Walnut Street. Stormwater runoff is collected along the south gutter line and the stormwater pipe and catch basin (MS4) along Walnut Street. The MS4 flows westerly down Walnut Street. The project will discharge to the existing MS4 within Walnut Street and therefore maintain the site's natural outfall. Additional discussion of the downstream path is included in Section C below. Minimum Requirement #5 — Onsite Stormwater Management. The proposed project is a category 1 project, thus is subject to the City's on -site stormwater management BMPs found in "List No. 1" in the City's code. A site -specific geotechnical evaluation of the site's soils and groundwater conditions demonstrates/recommends that infiltration is a not a viable option for stormwater management onsite. The project geotechnical evaluation recommends infiltration not be utilized due to relatively shallow groundwater conditions found onsite. Additionally, adequate flow length paths are not available for any dispersion type BMP. Only post construction soil amendment and BMP detention pipe are proposed for onsite stormwater BMP. A summary table of the project Stormwater Management BMPs are provided below. RAMEngineering, Inc. RAM No. 24-002 648 Walnut Street SFR Stormwater Site Plan Report Page A-4 MR#5 Stormwater Management BMP List No. 1 Evaluation Lawn and landscaped areas: BMP Viable Limitations / Infeasibility Criteria BMP T5.13: Post -Construction Soil Quality and Depth Limitation: Considered infeasible on slopes greater than 33 (Volume V, Chapter 11) Yes percent are present., BMP T5.13 shall be applied to the site post construction. Roofs: BMP T5.30: Full Dispersion Infeasibility: A viable vegetated flow path 50 or 100 feet (Volume V, Chapter 3) NO and less than 20% is not achievable onsite. BMP T5.10A: Downspout Full Infiltration Systems Infeasibility: The project geotechnical evaluation (Volume V, Chapter 4) No recommends infiltration not be used due to the relatively shall groundwater (moist soil) conditions and fill soils. BMP T5.14 Rain Gardens Infeasibility: The project geotechnical evaluation (Volume V, Chapter 11) or No recommends infiltration not be used due to the relatively BMP T7.30: Bioretention shall groundwater (moist soil) conditions and fill soils. (Volume V, Chapter 7) BMP T5.106: Downspout Dispersion Systems NO Infeasibility: A viable vegetated flow path 50 or 100 feet (Volume V, Chapter 4) and less than 20% is not achievable onsite. Detention Vaults or Pipes A detention vault/pipe is viable and proposed to meet (Edmonds Stormwater Addendum) Yes Minimum Requirement No. 5. BMP T5.10C: Perforated Stub -out Infeasibility: The project geotechnical evaluation (Volume V, Chapter 4) No recommends infiltration not be used due to the relatively shall groundwater (moist soil) conditions and fill soils. Other Hard Surfaces: BMP T5.30: Full Dispersion Infeasibility: A viable vegetated flow path 50 or 100 feet (Volume V, Chapter 3) NO and less than 20% is not achievable onsite. BMP T5.10A: Full Infiltration Infeasibility: The project geotechnical evaluation (Volume V, Chapter 4) No recommends infiltration not be used due to the relatively BMP T5.15: Permeable Pavement shall groundwater (moist soil) conditions and fill soils. (Volume V, Chapter 5) BMP T5.14 Rain Gardens Infeasibility: The project geotechnical evaluation (Volume V, Chapter 11) or No recommends infiltration not be used due to the relatively BMP T7.30: Bioretention shall groundwater (moist soil) conditions and fill soils. (Volume V, Chapter 7) BMP T5.12: Sheet Flow Dispersion Infeasibility: A viable vegetated flow path 50 or 100 feet (Volume V, Chapter 3) NO and less than 20% is not achievable onsite. Detention Vaults or Pipes A detention vault/pipe is viable and proposed to meet (Edmonds Stormwater Addendum) Yes Minimum Requirement No. 5. The project geotechnical report (attached below) includes two test pits that demonstrate the inadequate soils to implement infiltration based storm water BMPs including rain gardens and permeable pavements. Both test pits reveal the first 1.5 to 2.5 feet is fill and then the next soil horizon containing moist to wet weathered advance outwash soils (evidence of shallow/seasonal groundwater). It is noted that "moist to wet" soils were observed in July 2020, a summer month when typically lower seasonal ground water is present. Fill and "moist to wet" soils are not conducive to rain gardens and permeable pavements and are considered infeasible for design. RAMEngineering, Inc. RAM No. 24-002 648 Walnut Street SFR Stormwater Site Plan Report Page A-5 Parcel (Vicinity) Map: QUARTER I SECTION I TOWNSHIP N.W.B.L. I RANGE E.W.M. SW 24 27 3 Centerline Lot — Block — Section - City Limits Gov Lot Subd., — ROW — Quarter - Tax Am: I Inch 200feet Major Water Other Lot ------- Vac ROW - - - - 16th - Easement; Ap-dxd.f1h,+—S,'.�0K— h ..h—kh C-1y. W., Mg — Minor Water — Other Subdiv Vac Lot - - L- NW-24-27-03 77 1 4- 7 16 U2 2 to Isp 1 07 2-245 CREEKSIDE ALOHA 7rrg S 17 H 565 .26-81 6 05 Lo 9, 2_20. 2-219 2- 2-208 -209 2 18 GLEN- ST---. 2-219 j Z7 2-071 6 08, i ED ONtu �l . ...... 09 -2 2-251 DD 3 2 Sp �Sp 2-207 ASP 4)7-76 0 i4 i J 023 J.- -------- HIK DALEY- =N1 • 4" RhOR NOW RMIMIRPRI PRO .r fill 'IN r. RAN Engineering, Inc. RAM No. 24-002 NW-2&27-03 - - - - - - WAU 648 Walnut Street SFR Stormwater Site Plan Report Page A-6 Site Plan: CB 1 NEW STMNI MAIN WILL NEED )YPE 11-48' � TEyhA• q{y 11&6B' 0 W 7b lE PRESSURE TESTED AT SIX/O LOCX/NC L" 4 P9 FOR 15 ~ESN=28524B.72 E 126109B.J1 i .�� S,y/H WALNUT STREET I� PoM 119.4I 9 B' IE irl 8' RCR(E}Id.JJ % � I gEgp� CURB A5 NECESSARY PER CITY E 8' RCP(IYf-104.2J , I2' E I1S00 (OUT-1{� STD DAG NO TR-520 (SEE SHEET OT--01 K 6' RCP(S}IOI.JJ ,M1 I ti ! COYSIRUCIRX/ NOTE THIS SWEET) ---- - EX 8' SEM£R r----=-SS=-1=--=ss- =-S -- - — h g 11'0 "Pw200% LOCAT/OV O� E0 SEWER SS - O 2.00R !`l "WAL. �UIERAL (CONNACR/R 7D 4ERno / LOCATION PRIOR TO Cd/STRUCTILY/). SEE SIDE SEWER NOTES MS SI/EET..� COVC DRIVEWAY CN PER CITY CB 2 / N/NADTOR TD PoN 510 OMC NO iR-545 (SEE $4EEi DT-DI) �RY / I 3 LIN NED INSTALL TE MAILBOX PER VN=2982�JSA84 5' I !NOISY ENGINEER E COVFL/CT 3 Zf RE5/ORE E STING NN 1 EM5T5 OR AS / 119.SJ (EXAC� OCAT RON TO BE RI /262096.14 SS E i1S ]1 (IN-5) DfiERM/WED BY USPS) I20.JJ CUT FL SAW I..____ NECVEL AI`IE D NECESSARY AFTER DAY UTIIITY INSTALLATIDN B/MlE 1I555(OUT-1) __ - MISTALL 6' SANITARY SEWER CLEANCUT Ar THE 7' - AC EASEMENT LINE. pEANOUT SMALL NAPE A 12' I 17.0 407X GSr /RCVI LC MP COVER IWN I/2' NEX /i - /„ H .. - SSW CONpE1E / c- __ _- . — • . - - - — - BLX.1S A PICK HOLE AND A 1'X1' CQVCRf1E I WIB CITY STADAD DET RIM-ITOS DRIVEWAY -7 FC 1£ 1140#T2N EXIST WATER METER OMVEED I ,SAD SS-2C0pG49�51SENS-(SEE -SHEET { N8B152458.95 MO Y!E WATER ATER (TEOT-0) R IDRpNSINSIA ORYIIfl.L WIN { 111.3 FC - - AT PROPOSED- - 3/4' 1-1 2 ROCK J/4' TO J 4' PW O L OX MIN III LOL.ITIDIJ T IT l5 I DRAW FOR WALL DRAIN CONNEC7)OW NN) (3- N gEP 3• 1 CHAS Na AN PROP05FD i' WATER METER To LTE INSTALLED TO TO I / III OR APPROVED EWAL ITS PoCHT--CF-WAY SIDE OF WE PROPERTY IRK I (EX WATER METER MAY BE REUSED IF IT IS I) y� '�I (SEE O£TNC ON SHT OT-02) mg-E-116.23 I 4. PK I GROAN i m J5'-JB'HOPE OE1EN' ON SiS1EM (SEE DETAR, SWEET �T-01) 6 50 4' SS TOP-115I& I RGHRRE I 1228 FC I SEPARATION-I.Y I 01.ox N MN - - B 1-12 WA-E-I17ft 4• SS TCP-115.33 I A --- - 00y -:.- •- ,• SEPARA7tON-1.3' PoM 1220UTILITIES E lil.3t l \ CARA(E DEPN AND SPALYND SHALL PER PURVEKIRS REW/REMENTS - - - - _ 4' PIC SEVER SERN FF 11300 I UNDERGROUND HIRING O 1(LJX (20X MIN) 83 I1-49 I REWIREIENTS aF ECOC 1d05 M I22.p TYPE SCL/D ROUND LOCYMG L/D I SHALL LE FOILOWED. ALL UTILITY SERMCES SN- BE E 119.5f, i T RESIATO % I INSTALLED UNDERGROUND INSTALL 1-1/2' PE (160 p9) FROM WATER METER To E 1T6T087.B0 I TOM 12200 I 24• E 1K50 (!I ill 00434209301700 HOUSE (TRACER WWE ro� INSrAL ED WAN WATER L,,�Tur10.00 (IN-5) 4' E 111L00 (R4-NE) I CONGRE1E _-----_--_ J I I PATIO PROPOSED HOUSE PLAN JJAT - - 1-I AI i I i WAIN IF121.00 PARCEL A ---- --- --_ � �. ... No iI III i I i I f i I INSTALL 3i1 X� DPYMN1 WINIII N J/4'TO 1, DRW ROCK I Fm IN ). Ip'w) o 'II I /'1z b i 4'P£RF PPI; :IT'_-_J I I ----_ -i/ OUPAA O D FOOTING DRAIN Iil I I I ' ii O I.OR M/N I EU.lWNG -- i li I C `EAVES(TIP) I ` 00434209301701 DRAIN ICI IIWE I I O I.OR MIN ,_- -- '� I MAW DRYWELL TRENCH I I I I I �s + Oon It.) I N 4525- W ) 1.4� yh BSB • �CrrP) ,�! — ",1z4' I I i I yg I'------- In I - - - - --- W I 1 HV 10 __ -- N88f525W RAMEngineering, Inc. RAM No. 24-002 648 Walnut Street SFR Stormwater Site Plan Report Page A-7 B. EXISTING CONDITIONS SUMMARY Existing Conditions. The total site consists of 8,381 sf (0.19 acres) and is currently occupied by an existing single-family residence. The site's access is from Walnut Street along the north boundary of the subject site. The existing house is surrounded by grass lawn and landscape areas. The site is surrounded by single family residences to the west, south and east; and Walnut Street along the north boundary of the site (see aerial photo below). In accordance with the site's geotechnical report evaluation, the site slopes gently downward from southeast to northwest at magnitudes of less than 10 percent and relief of about 15 feet. There is a short steep slope area on properties south of the subject property. These slope areas are well vegetated and locally developed with walls/structures. The slope area has magnitudes of 50 to 80 percent and relief of about 20 feet. No defined drainage courses are found on -site, and stormwater runoff would sheet flow northerly towards Walnut Street; no stream or wetlands are located onsite. Additional discussion of the local drainage basin and downstream path is discussed in Section C of this report. Soils: In accordance with the project's site -specific geotechnical engineering evaluation by Cobalt Geosciences the on -site soils consist of poorly graded sand with gravel and silt (USCS: SM / SP) advance outwash deposits with some areas of fill. Groundwater was encountered approximately 3.5 to 4 feet below grade in the test pits, and it is anticipated that the seasonal high groundwater table may be within 3 feet of the ground surface during the wet season. The subject site is generally consistent with Alderwood-Urban land complex series soil. Full soils description is included in the project's site specific geotechnical engineering study by Cobalt Geosciences. Aerial Photo (City of Edmonds GIS, 2022 photo) RAMEngineering, Inc. RAM No. 24-002 648 Walnut Street SFR Stormwater Site Plan Report Page B-1 C. DEVELOPED SITE HYDROLOGY: Developed Conditions. The proposed project includes the construction of a single family residence with associated driveway and utilities. All existing structures and impervious (hard) surface onsite will be removed/replaced with the site development; landscaping and grass lawn around the new residence will stabilize the site upon building construction. The project proposes to create and/or replace 4,725 sf of hard surface with the complete site development, all existing hard surface will be removed with the project site development. The following is a summary of the proposed new/replaced hard surface areas: Total Hard Surface to Mitigated = 4,725 sf (0.108 ac) Roof Area = 2,680 sf Walkway/Patio Area = 225 sf Driveway Area = 880 sf Total Site = 3,785 sf Offsite Utility Tench Cuts/Replace Pavement = 940 sf Total Pervious Surface (Lawn/Landscape) = 4,661 sf (0.108 ac) In accordance with the Edmonds City Code (18.30) Category 1 projects shall meet MR#5 (see discussion in Section A above) and provide on -site stormwater management. To meet these criteria, the proposed hard surfaces of the site shall implement BMPs from "List No. 1" or meet the LID performance standard. As discussed above in the MR#5 evaluation above in Section A, and individual lot stormwater BMP detention pipe (Edmonds Storm water Addendum Section 6.3) will be utilized to manage the project's new/replaced hard surfaces. BMP T5.13: Post -Construction Soil Quality and Depth will be applied to the disturbed pervious areas of the site development. The total proposed new replaced hard surface of 4,725 sf will be mitigated with an individual lot detention pipe systems. The onsite detention pipe systems have been sized in accordance with the Edmonds Storm water Addendum simplified sizing approach, below is a summary of the system: Detention Pipe Sizing Calculations: ■ Hard Surface = 4,725 sf ■ Required 36" Detention Pipe = 37.8 ft (0.008 x 4,725 sf)1 ■ Provided 36" Detention Pipe = 38 ft 1. Per Edmonds Stormwater Addendum simplified sizing approach Section 6.3.1. RAMEngineering, Inc. RAM No. 24-002 648 Walnut Street SFR Stormwater Site Plan Report Page C-1 SOLID LOCKING LID EL. 122.Ot EMERGENCY P , OVERFLOW 119.67 1. n 6" PVC RESTRfCTOR .. I 6" PVC IE 116.40 PVC CAP ON BOTTOM WITH 0.5" ORIFICE (SEE FLOW CONTROL STRUCTURE DETAIL SD-301 ON THIS SHEET) 38 =36" HOPE ® 0.50% MIN DETENTION TANK r� 3'-12" HDPE STUB CONNECTION ® 0.5% 2 12" IE 116.50 CB 48" - TYPE !1 CB 3 - FLOW CONTROL STRUCTURE NOT TO SCALE DETENTION SYSTEM SIZING 36" DETEN770N PIPE REQUIRED 4,725 X 0.008 = 3780 LF REQ D (38 LF 36' PIPE PROPOSED) (PER EDMONDS STORMWA7FR ADDENDUM 6.3.1) Additionally, all disturbed pervious (lawn and landscape) areas will preserve or restore the health and water - holding capacity of the soils by compost -amending (Per DOE BMP T5.13: Post -Construction Soil Quality and Depth). See attached City of Edmonds Standard Detail SD-642 criteria for BMP T5.13: Post -Construction Soil Quality and Depth. RAMEngineering, Inc. RAM No. 24-002 648 Walnut Street SFR Stormwater Site Plan Report Page C-2 UNDISTURBED NATIVE VEGETATION UNDISTURBED NATIVE SOIL 2" ORGANIC MULCH 3" OF COMPOST INCORPORATED INTO 5" OF SITE SOIL (TOTAL AMENDED DEPTH OF 9.5", FOR A SETTLED DEPTH OF 8") SUBSOIL SCARIFIED 4" BELOW COMPOST AMENDED LAYER (12" BELOW SOIL SURFACE) 2" ORGANIC MULCH 6" IMPORTED TOPSOIL MIX (COMPACTED DEPTH) SUBSOIL IS SCARIFIED 6" BELOW IMPORTED TOPSOIL MIX UNDISTURBED PLANTS (SEE NOTE 1) UNDISTURBED TURF (LAWN) AREAS (SEE NOTE 1) m OPTION 1 — NO DISTURBANCE PLANTING BEDS TURF (LAWN) AREAS 11�LflJ�fl�I�fl�IIfl�Lh�I�fl��fl�I�fl� m 8" UNDISTURBED TURF/LAWN/LANDSCAPE UNDISTURBED NATIVE SOIL STEEP SLOPE NOTE: AMENDED SOILS SHOULD NOT BE INSTALLED ON FINISHED SLOPES EXCEEDING 33%. AREAS EXCEEDING 33% SHALL BE STABILIZED PER THE ENGINEER/GEOTECH OF RECORD. 3RASS: SEED OR SOD 1.75" OF COMPOST INCORPORATED INTO 6.25" OF SITE SOIL (TOTAL 4MENDED DEPTH OF 9.5", FOR A SETTLED DEPTH OF 8") SUBSOIL SCARIFIED 4" BELOW COMPOST AMENDED LAYER ,12" BELOW SOIL SURFACE) OPTION 2 — AMEND IN PLACE OR STOCKPILE AND AMEND GENERAL NOTES: PLANTING BEDS TURF (LAWN) AREAS 1. AREAS OF NO DISTURBANCE SHALL BE FENCED AND EXISTING GRASS: SEED VEGETATION AND SOIL SHALL BE OR SOD PROTECTED FROM CONSTRUCTION 1 I'1f1 �I1-1 I1 11-1 11 I IMPACTS. I L 11L 1 I 1=1 III I I I M III 11=1 11=1 11=1 11=1 I I I —I —I 1=1 I=1 I I—III=1 1=1 I IEl 11=1 11=1 11=1 11=1 I I III-1I I� �I I I —I �I I1=1 III —I I I� I1=1I I� I1=1I1=1I 2. TO MEASURE SETTLED DEPTH, II=11FI1 11=III—III—III—III II —III —III —III —III 6" IMPORTED WATER SOIL SUFFICIENTLY TO , TOPSOIL MIX FULLY SATURATE WITHOUT III II II —III —III II III II — III—;ITE III II COMPACTED CAUSING EROSION. III= �- I— �TEI III 111=1 I —I I I I I I III-1I DEPTH) III-III-II=III-11F111=1 6" III=111 I -11 =11 3. COMPOST SHALL MEET SPEC. III, _I- _� =1� VA'�-1-� II- 11 'm1 1=fj�j -I \ REQUIREMENTS IN THE 2017 IIFj�\�j_IIN '1-' SUBSOIL IS EDMONDS STORMWATER \j II SCARIFIED 6" ADDENDUM (CHECKLIST 7). BELOW 4. COMPACTION OF TOPSOIL (WHERE IMPORTED REQUIRED) TO BE TO 85% (MAX) 12' \ \/\ TOPSOIL MIX OF THE MAXIMUM DRY DENSITY OPTION 3 — IMPORT TOPSOIL PER MODIFIED PROCTOR TEST (ASTM D 1557). OF EDMONDS POST CONSTRUCTION SOIL QUALITY AND DEPTH REVISION DATE APRIL 2021 T PUBLIC WORKS STANDARD DEPARTMENT DETAIL Fs t �g9� APPROVED BY: R. ENGLISH S D - 642 R.4MEngineering, Inc. 648 Walnut Street SFR RAM No. 24-002 Stormwater Site Plan Report Page C-3 Offsite Basin Analysis. The site is located in the Shellabarger Creek watershed basin. The Shellabarger Creek basin is an urban basin that collects stormwater runoff from primarily residential areas in the City Edmonds and ultimately discharges flow westerly to Puget Sound (see attached watershed map). The subject site slopes north and sheet flows site runoff to the municipal separate storm sewer system (MS4) within Walnut Street. Stormwater runoff is collected along the south gutter line and the stormwater pipe and catch basin (MS4) along Walnut Street. The MS4 flows westerly down Walnut Street and then turns north at 6th Avenue S, about 500 feet from the site. The MS4 stormwater pipe system continues north along 6th Avenue S to Dayton Street, and then is directed westerly. At 3rd Avenue S the MSR turns south and discharges to the open channel of Shellabarger Shell Creek about 3,900 feet from the site. The Shellabarger Creek continues in a westerly direction and eventually discharges into the Puget Sound about 1.8 miles from the site near the City of Edmonds Marina Beach Park. See the Downstream Drainage Facility Map and Watershed Basin Map, delineating the downstream path attached below. Downstream Drainage Facility Map (City of Edmonds GIS) PUGETSOUND DISCHARGE 1.8 MILES ° FROM THE SITE R0 a d- OD� �• 0 •. o - ••` 0 0 0 0 0 13 0 ° 0 �g 8 0 ° D a Q, E U. RAMEngineering, Inc. RAM No. 24-002 o 0 o�❑ na° °" oB0 � � v � °pa ° oom�o a N J� c MAIN ST oa o y Rocramoo u D p D a O 4. a 0- 40 - '64-o- w- o O m m ° 13 COL ..u.....nn. 0 0 DISCHARGE TO SHELLABARGER CREEK 3,900 FEET pD FROM THE SITE Gnu m bF o �wQ 6 _g a 0 07 SITE o eo o B I O ° 69 ^� �= 0 a m o i 000 0o QJ 648 Walnut Street SFR Stormwater Site Plan Report Page C-4 Watershed Basin Map FIGURE B-1 CITY OF EDMON DS WATERSHEDS Deer Creek �Perrinville Edmonds Marsh - Puget Sound Edmonds Way Puget Sound Piped Fruitdale - Shell Creek Good Hope Pond ® Shellabarger Halls Creek - Southwest Edmonds A I_ Hindley Creek Southwest Edmonds 8 Lake Ballinger Stihhouse Creek Lund's Gulch _Talbot Park Meadowdale A Talbot Park B Meadowdale B Terrace Creek Northstrean Westgate Pond Outfall Creek Willow Creek 0 1.000 3,000 6,o00 61000 a 1 in = 2,000 ft No warranty of aN sort, including ac —q, fitness, or me —ability accompany this Prod — Mar& 30, 2010 A SITE Meadowdale A--- 3 1 Meadowdale B \- I'd�W ale Rtl `j\�I___________— ____� Outf�lll CreekStilthouse Creek , `. Terrace Creek !/ 41I)fF ` s vued`'�+ I k13` s !� Puge ound, a �JalhotPark ' o,� .Talb�t Park B -Li ,Fruitdale - 3 196th st sw L rrprthstream _ 20- St SW L Hindley i i mood Hope Pond - i Puget Sound Piped waom y Shell Creek Ielrabargew - �R vise 6t E_ RAN Engineering, Inc. RAM No. 24-002 i Westgate Pond Halls Creek ice___- ____- ______iiamsesW------3 'WillQwCreek 334tb St SW I � 3 ;Deer Creek W, � � 3 231st stSW Edmonds Way Southwest Edmonds A E Southwest Edmonds B L------ ------------- zoom st sw take Ballinger � Q 648 Walnut Street SFR Stormwater Site Plan Report Page C-5 D. SOILS REPORTS: 1. Geotechnical Evaluation Letter Prepared by: Cobalt Geosciences Date: August 2, 2020 Pages: 19 MAN =ngineering, Inc. RAM No. 24-002 648 Walnut Street SFR Stormwater Site Plan Report Page D-1 COBALT G E 0 S C I E N C E S Geotechnical Investigation Proposed Residential Development 648 Walnut Street Edmonds, Washington August 2, 2020 This document was created by an application that isn't licensed to use novaPDF. Purchase a license to generate PDF files without this notice. GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON Table of Contents i.o INTRODUCTION............................................................................................................. 1 2.0 PROJECT DESCRIPTION.............................................................................................. 1 3.0 SITE DESCRIPTION....................................................................................................... 1 4.o FIELD INVESTIGATION............................................................................................... 2 4.1.1 Site Investigation Program................................................................................... 2 5.o SOIL AND GROUNDWATER CONDITIONS.............................................................. 2 5.1.1 Area Geology........................................................................................................ 2 5.1.2 Groundwater........................................................................................................ 3 6.o GEOLOGIC HAZARDS................................................................................................... 3 6.1 Erosion Hazard.................................................................................................... 3 6.2 Seismic Hazard.................................................................................................... 3 7.o DISCUSSION................................................................................................................... 4 7.1.1 General.................................................................................................................4 8.o RECOMMENDATIONS.................................................................................................. 4 8.1.1 Site Preparation................................................................................................... 4 8.1.2 Temporary Excavations........................................................................................ 4 8.1.3 Erosion and Sediment Control.............................................................................. 5 8.1.4 Foundation Design............................................................................................... 6 8.1.5 Stormwater Management..................................................................................... 7 8.1.6 Slab-on-Grade...................................................................................................... 7 8.1.E Groundwater Influence on Construction.............................................................. 8 8.1.8 Utilities................................................................................................................ 8 9.o CONSTRUCTION FIELD REVIEWS............................................................................ 8 1o.o CLOSURE.................................................................................................................... 9 LIST OF APPENDICES Appendix A — Statement of General Conditions Appendix B — Figures Appendix C — Exploration Logs This document was created by an application that isn't licensed to use novaPDF. Purchase a license to generate PDF files without this notice. GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON August 2, 2020 1.o Introduction COBALT GEOSCIENCES In accordance with your authorization, Cobalt Geosciences, LLC (Cobalt) has completed a geotechnical investigation for the proposed residential development located at 648 Walnut Street in Edmonds, Washington (Figure 1). The purpose of the geotechnical investigation was to identify subsurface conditions and to provide geotechnical recommendations for foundation design, stormwater management, earthwork, soil compaction, and suitability of the on -site soils for use as fill. The scope of work for the geotechnical evaluation consisted of a site investigation followed by engineering analyses to prepare this report. Recommendations presented herein pertain to various geotechnical aspects of the proposed development, including foundation support of the new building and stormwater management. 2.o Project Description The project includes construction of a new single-family residence in the north -central portion of the property. Anticipated building loads are expected to be light to moderate and site grading will include cuts and fills on the order of 4 feet or less. Stormwater management will include infiltration devices, if feasible. We should be provided with the final plans when they become available. 3.0 Site Description The site is located at 648 Walnut Street in Edmonds, Washington (Figure 1). The property consists of two adjoining parcels (No.'s 00434209301500 & 27032500202600) with a total area of about 0.25 acres. The north -central portion of the property is developed with a residence. There is a joint -use driveway near the east property line on an adjacent property. The remainder of the property is undeveloped and vegetated with grasses, bushes, blackberry vines, ferns, ivy, and sparse trees. The site slopes gently downward from southeast to northwest at magnitudes of less than io percent and relief of about 15 feet. There is a short steep slope area on properties south of the subject property. These slope areas are well vegetated and locally developed with walls/structures. The slope area has magnitudes Of 50 to 8o percent and relief of about 20 feet. The toe of this slope is located at least 70 feet from the area of the proposed residence (closest point). The site is bordered to the east, west, and south by residential developments and to the north by Walnut Street. PO Box 82243 Kenmore, WA 98028 cobalt zeoCcpamail.com 206-331-1097 This document was created by an application that isn't licensed to use novaPDF. Purchase a license to generate PDF files without this notice. GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON August 2, 2020 4.o Field Investigation COBALT G E O S C I E N C E S 4.1.1 Site Investigation Program The geotechnical field investigation program was completed on July 16, 202o and included excavating and sampling two test pits within the property for subsurface analysis. The soils encountered were logged in the field and are described in accordance with the Unified Soil Classification System (USCS). A Cobalt Geosciences field representative conducted the explorations, collected disturbed soil samples, classified the encountered soils, kept a detailed log of the explorations, and observed and recorded pertinent site features. The results of the sampling are presented on the exploration logs enclosed in Appendix C. 5.0 Soil and Groundwater Conditions 5.1.1 Area Geology The site lies within the Puget Lowland. The lowland is part of a regional north -south trending trough that extends from southwestern British Columbia to near Eugene, Oregon. North of Olympia, Washington, this lowland is glacially carved, with a depositional and erosional history including at least four separate glacial advances/retreats. The Puget Lowland is bounded to the west by the Olympic Mountains and to the east by the Cascade Range. The lowland is filled with glacial and non -glacial sediments consisting of interbedded gravel, sand, silt, till, and peat lenses. The Geologic Map of Washington — Northwest Quadrant, indicates that the site is underlain by Vashon Advance Outwash. Vashon Advance Outwash consists of poorly graded sand and are typically permeable. These soils are typically medium dense to very dense and are often underlain by silt and clay of either Pre -Fraser Deposits, Pre -Olympia Deposits, or Transitional Beds. In this area, Transitional Beds underlie the outwash. Groundwater is common at or near this contact. Explorations The test pits encountered about 6 inches of grass and topsoil underlain by approximately 3 to 4 feet of loose to medium dense, silty -fine to medium grained sand with organics and gravel (Fill and Weathered Outwash). These materials were underlain by medium dense to very dense, fine to medium grained sand with gravel and silt (Advance Outwash), which continued to the termination depths of the test pits. 2 PO Box 82243 Kenmore, WA 98028 cobalt zeoCcpamail.com 2o6-331-1097 This document was created by an application that isn't licensed to use novaPDF. Purchase a license to generate PDF files without this notice. GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON August 2, 2020 5.1.2 Groundwater COBALT GEOSCIENCES�Z Groundwater was encountered approximately 3.5 to 4 feet below grade in the test pits. We anticipate that the seasonal high groundwater table may be within 3 feet of the ground surface during the wet season. Groundwater appears to be perched on the underlying Transitional Beds or a silt/clay interbed at the base of the outwash. Water table elevations often fluctuate over time. The groundwater level will depend on a variety of factors that may include seasonal precipitation, irrigation, land use, climatic conditions and soil permeability. Water levels at the time of the field investigation may be different from those encountered during the construction phase of the project. 6.o Geologic Hazards 6a Erosion Hazard The Natural Resources Conservation Services (NRCS) maps for Snohomish County indicate that the site is underlain by Alderwood-Urban land complex (8 to 15 percent slopes). These soils would have a slight to moderate erosion potential in a disturbed state, depending on the slope magnitude. It is our opinion that soil erosion potential at this project site can be reduced through landscaping and surface water runoff control. Typically erosion of exposed soils will be most noticeable during periods of rainfall and may be controlled by the use of normal temporary erosion control measures, such as silt fences, hay bales, mulching, control ditches and diversion trenches. The typical wet weather season, with regard to site grading, is from October 31st to April is'. Erosion control measures should be in place before the onset of wet weather. 6.2 Seismic Hazard The overall subsurface profile corresponds to a Site Class D as defined by Table 1613.5.2 of the 2015 International Building Code (2015 IBC). A Site Class D applies to an overall profile consisting of dense to very dense soils within the upper too feet. We referenced the U.S. Geological Survey (USGS) Earthquake Hazards Program Website to obtain values for Ss, S,, FQ. The USGS website includes the most updated published data on seismic conditions. The site specific seismic design parameters and adjusted maximum spectral response acceleration parameters are as follows: PGA (Peak Ground Acceleration, in percent of g) Ss 128.40% of g S, 45.20% of g FA 1.2 Additional seismic considerations include liquefaction potential and amplification of ground motions by soft/loose soil deposits. The liquefaction potential is highest for loose sand with a high groundwater table. The relatively dense soil deposits that underlie the site have a low liquefaction potential. 3 PO Box 82243 Kenmore, WA 98028 cobalt zeoCcpamail.com 2o6-331-1097 This document was created by an application that isn't licensed to use novaPDF. Purchase a license to generate PDF files without this notice. GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON August 2, 2020 7.o DISCUSSION 7.1.1 General COBALT G E O S C I E N C E S The site is underlain by areas of fill and at depth by weathered and unweathered advance outwash. The proposed residential structure may be supported on a shallow foundation system bearing on medium dense or firmer native soils and/or structural fill placed on suitable native soils. Local overexcavation of fill and/or loose soils may be necessary below proposed foundation elements. Infiltration of stormwater runoff is not feasible due to a shallow groundwater table. Rain gardens or permeable pavements could be considered, if necessary. We recommend direction connection to City infrastructure for a majority of the collected runoff. While there is a localized steep slope extending downward toward the south property line, the proposed structure will be setback at least 70 feet from the toe of this slope. Landslide run out, if sloughing were to occur in this area, would not affect the proposed building. 8.o Recommendations 8.m Site Preparation Trees, shrubs and other vegetation should be removed prior to stripping of surficial organic -rich soil and fill. Based on observations from the site investigation program, it is anticipated that the stripping depth will be 6 to 12 inches. Deeper excavations will be necessary below large trees and in any areas underlain by undocumented fill materials. The native soils consist of silty -sand with gravel and poorly graded sand with gravel. These soils may be used as structural fill provided they achieve compaction requirements and are within 3 percent of the optimum moisture. Some of these soils may only be suitable for use as fill during the summer months, as they will be above the optimum moisture levels in their current state. These soils are variably moisture sensitive and may degrade during periods of wet weather and under equipment traffic. Imported structural fill should consist of a sand and gravel mixture with a maximum grain size of 3 inches and less than 5 percent fines (material passing the U.S. Standard No. 200 Sieve). Structural fill should be placed in maximum lift thicknesses of 12 inches and should be compacted to a minimum of 95 percent of the modified proctor maximum dry density, as determined by the ASTM D 1557 test method. 8.1.2 Temporary Excavations Based on our understanding of the project, we anticipate that the grading could include local cuts on the order of approximately 4 feet or less for foundation and utility placement. Any deeper excavations should be sloped no steeper than 1.5H:1V in loose soils, 1H:1V in medium dense native soils and 3/4H:iV in dense to very dense native soils above the groundwater table. If an excavation is subject to heavy vibration or surcharge loads, we recommend that the excavations be sloped no steeper than 2H:iV, where room permits. 4 PO Box 82243 Kenmore, WA 98028 cobalt zeoCcpamail.com 2o6-331-1097 This document was created by an application that isn't licensed to use novaPDF. Purchase a license to generate PDF files without this notice. GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON August 2, 2020 COBALT G E O S C I E N C E S Temporary cuts should be in accordance with the Washington Administrative Code (WAC) Part N, Excavation, Trenching, and Shoring. Temporary slopes should be visually inspected daily by a qualified person during construction activities and the inspections should be documented in daily reports. The contractor is responsible for maintaining the stability of the temporary cut slopes and reducing slope erosion during construction. Temporary cut slopes should be covered with visqueen to help reduce erosion during wet weather, and the slopes should be closely monitored until the permanent retaining systems or slope configurations are complete. Materials should not be stored or equipment operated within io feet of the top of any temporary cut slope. Soil conditions may not be completely known from the geotechnical investigation. In the case of temporary cuts, the existing soil conditions may not be completely revealed until the excavation work exposes the soil. Typically, as excavation work progresses the maximum inclination of temporary slopes will need to be re-evaluated by the geotechnical engineer so that supplemental recommendations can be made. Soil and groundwater conditions can be highly variable. Scheduling for soil work will need to be adjustable, to deal with unanticipated conditions, so that the project can proceed and required deadlines can be met. If any variations or undesirable conditions are encountered during construction, we should be notified so that supplemental recommendations can be made. If room constraints or groundwater conditions do not permit temporary slopes to be cut to the maximum angles allowed by the WAC, temporary shoring systems may be required. The contractor should be responsible for developing temporary shoring systems, if needed. We recommend that Cobalt Geosciences and the project structural engineer review temporary shoring designs prior to installation, to verify the suitability of the proposed systems. 8.1.3 Erosion and Sediment Control Erosion and sediment control (ESC) is used to reduce the transportation of eroded sediment to wetlands, streams, lakes, drainage systems, and adjacent properties. Erosion and sediment control measures should be implemented and these measures should be in general accordance with local regulations. At a minimum, the following basic recommendations should be incorporated into the design of the erosion and sediment control features for the site: • Schedule the soil, foundation, utility, and other work requiring excavation or the disturbance of the site soils, to take place during the dry season (generally May through September). However, provided precautions are taken using Best Management Practices (BMP's), grading activities can be completed during the wet season (generally October through April). • All site work should be completed and stabilized as quickly as possible. • Additional perimeter erosion and sediment control features may be required to reduce the possibility of sediment entering the surface water. This may include additional silt fences, silt fences with a higher Apparent Opening Size (AOS), construction of a berm, or other filtration systems. • Any runoff generated by dewatering discharge should be treated through construction of a sediment trap if there is sufficient space. If space is limited other filtration methods will need to be incorporated. 5 PO Box 82243 Kenmore, WA 98028 cobalt zeoCcpamail.com 2o6-331-1097 This document was created by an application that isn't licensed to use novaPDF. Purchase a license to generate PDF files without this notice. GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON August 2, 2020 8.1.4 Foundation Design COBALT G E O S C I E N C E S The proposed residential building may be supported on a shallow spread footing foundation system bearing on undisturbed medium dense or firmer native soils or on properly compacted structural fill placed on the suitable native soils. If structural fill is used to support foundations, then the zone of structural fill should extend beyond the faces of the footing a lateral distance at least equal to the thickness of the structural fill. For shallow foundation support, we recommend widths of at least 16 and 24 inches, respectively, for continuous wall and isolated column footings supporting the proposed structure. Provided that the footings are supported as recommended above, a net allowable bearing pressure of 2,500 pounds per square foot (psf) may be used for design. A 1/3 increase in the above value may be used for short duration loads, such as those imposed by wind and seismic events. Structural fill placed on bearing, native subgrade should be compacted to at least 95 percent of the maximum dry density based on ASTM Test Method D1557. Footing excavations should be inspected to verify that the foundations will bear on suitable material. Exterior footings should have a minimum depth of 18 inches below pad subgrade (soil grade) or adjacent exterior grade, whichever is lower. Interior footings should have a minimum depth of 12 inches below pad subgrade (soil grade) or adjacent exterior grade, whichever is lower. If constructed as recommended, the total foundation settlement is not expected to exceed 1 inch. Differential settlement, along a 25-foot exterior wall footing, or between adjoining column footings, should be less than 1/2 inch. This translates to an angular distortion of 0.002. Most settlement is expected to occur during construction, as the loads are applied. However, additional post -construction settlement may occur if the foundation soils are flooded or saturated. All footing excavations should be observed by a qualified geotechnical consultant. Resistance to lateral footing displacement can be determined using an allowable friction factor of 0.40 acting between the base of foundations and the supporting subgrades. Lateral resistance for footings can also be developed using an allowable equivalent fluid passive pressure of 225 pounds per cubic foot (pcf) acting against the appropriate vertical footing faces (neglect the upper 12 inches below grade in exterior areas). The allowable friction factor and allowable equivalent fluid passive pressure values include a factor of safety of 1.5. The frictional and passive resistance of the soil may be combined without reduction in determining the total lateral resistance. Care should be taken to prevent wetting or drying of the bearing materials during construction. Any extremely wet or dry materials, or any loose or disturbed materials at the bottom of the footing excavations, should be removed prior to placing concrete. The potential for wetting or drying of the bearing materials can be reduced by pouring concrete as soon as possible after completing the footing excavation and evaluating the bearing surface by the geotechnical engineer or his representative. 0 PO Box 82243 Kenmore, WA 98028 cobalt zeoCcpamail.com 206-331-1097 This document was created by an application that isn't licensed to use novaPDF. Purchase a license to generate PDF files without this notice. GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON August 2, 2020 8.1.5 Stormwater Management COBALT GEOSCIENCES�Z The site is underlain by advance outwash. Groundwater was encountered in the test pits at shallow depths and there is inadequate clearance for infiltration systems above the groundwater table. It was not necessary to perform an infiltration test due to the lack of clearance above groundwater. Shallow systems such as rain gardens or permeable pavements could be considered, if necessary. Otherwise, we recommend direct connection of stormwater collection devices to be tightlined (via perforated connection) to City infrastructure in Walnut Street. We can provide additional recommendations once a civil plan has been prepared. We should be provided with final plans for review to determine if the intent of our recommendations has been incorporated or if additional modifications are needed. 8.1.6 Slab -on -Grade We recommend that the upper 18 inches of the existing fill and/or native soils within slab areas be re - compacted to at least 95 percent of the modified proctor (ASTM D1557 Test Method). Often, a vapor barrier is considered below concrete slab areas. However, the usage of a vapor barrier could result in curling of the concrete slab at joints. Floor covers sensitive to moisture typically requires the usage of a vapor barrier. A materials or structural engineer should be consulted regarding the detailing of the vapor barrier below concrete slabs. Exterior slabs typically do not utilize vapor barriers. The American Concrete Institutes ACI 36oR-o6 Design of Slabs on Grade and ACI 302.1R-04 Guide for Concrete Floor and Slab Construction are recommended references for vapor barrier selection and floor slab detailing. A minimum 4 inch thick capillary break should be placed over the prepared subgrade. This may consist of pea gravel or 5/8 inch clean angular rock. Slabs on grade may be designed using a coefficient of subgrade reaction of 18o pounds per cubic inch (pci) assuming the slab -on -grade base course is underlain by structural fill placed and compacted as outlined in Section 8.1. A 4 inch thick capillary break material should be placed over the prepared subgrade. This could include pea gravel or 5/8 inch clean angular rock. A perimeter drainage system is recommended unless interior slab areas are elevated a minimum of 12 inches above adjacent exterior grades. If installed, a perimeter drainage system should consist of a 4 inch diameter perforated drain pipe surrounded by a minimum 6 inches of drain rock wrapped in a non -woven geosynthetic filter fabric to reduce migration of soil particles into the drainage system. The perimeter drainage system should discharge by gravity flow to a suitable stormwater system. Exterior grades surrounding buildings should be sloped at a minimum of one percent to facilitate surface water flow away from the building and preferably with a relatively impermeable surface cover immediately adjacent to the building. N PO Box 82243 Kenmore, WA 98028 cobalt zeoCcpamail.com 2o6-331-1097 This document was created by an application that isn't licensed to use novaPDF. Purchase a license to generate PDF files without this notice. L�zCOBALT GEOTECHNICAL INVESTIGATION GEOSCIENCES EDMONDS, WASHINGTON August 2, 2020 8.1.7 Groundwater Influence on Construction Groundwater was encountered approximately 3.5 to 4 feet below grade in the test pits. We anticipate that the seasonal high groundwater table may be within 3 feet of the ground surface during the wet season. Groundwater appears to be perched on the underlying Transitional Beds or a silt/clay interbed at the base of the outwash. If groundwater is encountered, we anticipate that sump excavations and small diameter pumps systems will adequately de -water short-term excavations, if required. Any system should be designed by the contractor. We can provide additional recommendations upon request. 8.1.8 Utilities Utility trenches should be excavated according to accepted engineering practices following OSHA (Occupational Safety and Health Administration) standards, by a contractor experienced in such work. The contractor is responsible for the safety of open trenches. Traffic and vibration adjacent to trench walls should be reduced; cyclic wetting and drying of excavation side slopes should be avoided. Depending upon the location and depth of some utility trenches, groundwater flow into open excavations could be experienced, especially during or shortly following periods of precipitation. In general, silty and sandy soils were encountered at shallow depths in the explorations at this site. These soils have low cohesion and density and will have a tendency to cave or slough in excavations. Shoring or sloping back trench sidewalls is required within these soils in excavations greater than 4 feet deep. All utility trench backfill should consist of imported structural fill or suitable on site soils. Utility trench backfill placed in or adjacent to buildings and exterior slabs should be compacted to at least 95 percent of the maximum dry density based on ASTM Test Method D1557. The upper 5 feet of utility trench backfill placed in pavement areas should be compacted to at least 95 percent of the maximum dry density based on ASTM Test Method D1557. Below 5 feet, utility trench backfill in pavement areas should be compacted to at least 90 percent of the maximum dry density based on ASTM Test Method D1557. Pipe bedding should be in accordance with the pipe manufacturer's recommendations. The contractor is responsible for removing all water -sensitive soils from the trenches regardless of the backfill location and compaction requirements. Depending on the depth and location of the proposed utilities, we anticipate the need to re -compact existing fill soils below the utility structures and pipes. The contractor should use appropriate equipment and methods to avoid damage to the utilities and/or structures during fill placement and compaction procedures. 9.o Construction Field Reviews Cobalt Geosciences should be retained to provide part time field review during construction in order to verify that the soil conditions encountered are consistent with our design assumptions and that the intent of our recommendations is being met. This will require field and engineering review to: ■ Monitor and test structural fill placement and soil compaction ■ Observe bearing capacity at foundation locations ■ Observe slab -on -grade preparation 0 PO Box 82243 Kenmore, WA 98028 cobalt zeoCcpamail.com 2o6-331-1097 This document was created by an application that isn't licensed to use novaPDF. Purchase a license to generate PDF files without this notice. GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON August 2, 2020 ■ Verify foundation drains ■ Observe excavation stability COBALT G E O S C I E N C E S Geotechnical design services should also be anticipated during the subsequent final design phase to support the structural design and address specific issues arising during this phase. Field and engineering review services will also be required during the construction phase in order to provide a Final Letter for the project. m o Closure This report was prepared for the exclusive use of Rick Cuevas and his appointed consultants. Any use of this report or the material contained herein by third parties, or for other than the intended purpose, should first be approved in writing by Cobalt Geosciences, LLC. The recommendations contained in this report are based on assumed continuity of soils with those of our test holes, and assumed structural loads. Cobalt Geosciences should be provided with final architectural and civil drawings when they become available in order that we may review our design recommendations and advise of any revisions, if necessary. Use of this report is subject to the Statement of General Conditions provided in Appendix A. It is the responsibility of Rick Cuevas who is identified as "the Client" within the Statement of General Conditions, and its agents to review the conditions and to notify Cobalt Geosciences should any of these not be satisfied. Respectfully submitted, Cobalt Geosciences, LLC Original signed by: N 01 54896 AL Exp. 6/26/2020 Phil Haberman, PE, LG, LEG Principal PH/sc E:] PO Box 82243 Kenmore, WA 98028 cobalt zeoCcpamail.com 2o6-331-1097 This document was created by an application that isn't licensed to use novaPDF. Purchase a license to generate PDF files without this notice. I:1» pill, 113 Statement of General Conditions This document was created by an application that isn't licensed to use novaPDF. Purchase a license to generate PDF files without this notice. Statement of General Conditions USE OF THIS REPORT: This report has been prepared for the sole benefit of the Client or its agent and may not be used by any third party without the express written consent of Cobalt Geosciences and the Client. Any use which a third parry makes of this report is the responsibility of such third party. BASIS OF THE REPORT: The information, opinions, and/or recommendations made in this report are in accordance with Cobalt Geosciences present understanding of the site specific project as described by the Client. The applicability of these is restricted to the site conditions encountered at the time of the investigation or study. If the proposed site specific project differs or is modified from what is described in this report or if the site conditions are altered, this report is no longer valid unless Cobalt Geosciences is requested by the Client to review and revise the report to reflect the differing or modified project specifics and/or the altered site conditions. STANDARD OF CARE: Preparation of this report, and all associated work, was carried out in accordance with the normally accepted standard of care in the state of execution for the specific professional service provided to the Client. No other warranty is made. INTERPRETATION OF SITE CONDITIONS: Soil, rock, or other material descriptions, and statements regarding their condition, made in this report are based on site conditions encountered by Cobalt Geosciences at the time of the work and at the specific testing and/or sampling locations. Classifications and statements of condition have been made in accordance with normally accepted practices which are judgmental in nature; no specific description should be considered exact, but rather reflective of the anticipated material behavior. Extrapolation of in situ conditions can only be made to some limited extent beyond the sampling or test points. The extent depends on variability of the soil, rock and groundwater conditions as influenced by geological processes, construction activity, and site use. VARYING OR UNEXPECTED CONDITIONS: Should any site or subsurface conditions be encountered that are different from those described in this report or encountered at the test locations, Cobalt Geosciences must be notified immediately to assess if the varying or unexpected conditions are substantial and if reassessments of the report conclusions or recommendations are required. Cobalt Geosciences will not be responsible to any party for damages incurred as a result of failing to notify Cobalt Geosciences that differing site or sub -surface conditions are present upon becoming aware of such conditions. PLANNING, DESIGN, OR CONSTRUCTION: Development or design plans and specifications should be reviewed by Cobalt Geosciences, sufficiently ahead of initiating the next project stage (property acquisition, tender, construction, etc), to confirm that this report completely addresses the elaborated project specifics and that the contents of this report have been properly interpreted. Specialty quality assurance services (field observations and testing) during construction are a necessary part of the evaluation of sub -subsurface conditions and site preparation works. Site work relating to the recommendations included in this report should only be carried out in the presence of a qualified geotechnical engineer; Cobalt Geosciences cannot be responsible for site work carried out without being present. This document was created by an application that isn't licensed to use novaPDF. Purchase a license to generate PDF files without this notice. APPENDIX B Figures: Vicinity Map, Site Plan 10.2 PO Box 82243 Kenmore, WA 98028 cobaltgeo(q�gmail.com 2o6-331-1097 This document was created by an application that isn't licensed to use novaPDF. 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Box 82243 Proposed Residence VICINITY MAP Kenmore, WA 98028 (2o6) 331-1097 648 Walnut Street COBALTwww.cobaltgeo.com Edmonds, Washington FIGURE i cobaltgeoRgmail.com This document was created by an application that isn't licensed to use novaPDF. Purchase a license to generate PDF files without this notice. ab • �; � AW 6�4t_i AL 8 654 t: TP-i Approximate Test Pit N �- Location Not to scale Cobalt Geosciences, LLC Proposed Residence SITE PLAN P.O. Box 82243 Kenmore, WA 98028 COBALT648 Walnut Street (2o6) 331-1097 GEOSCIENCES Edmonds, Washington FIGURE 2 www.cobaltgeo.com cobaltgeoPgmail.com This document was created by an application that isn't licensed to use novaPDF. Purchase a license to generate PDF files without this notice. APPENDIX C Exploration Logs This document was created by an application that isn't licensed to use novaPDF. Purchase a license to generate PDF files without this notice. Unified Soil Classification System (USCS) MAJOR DIVISIONS SYMBOL TYPICAL DESCRIPTION Clean Gravels GW Well -graded gravels, gravels, gravel -sand mixtures, little or no fines Gravels (less than 5% GP (more than 50% fines) Poorly graded gravels, gravel -sand mixtures, little or no fines of coarse fraction GM retained on No. 4 Gravels with Silty gravels, gravel -sand -silt mixtures COARSE sieve) Fines GC Clayey gravels, gravel -sand -clay mixtures GRAINED (more than 12% fines) SOILS (more than 50% sw retained on Clean Sands Well -graded sands, gravelly sands, little or no fines No. 200 sieve) Sands (less than 5% sP (50% or more fines) Poorly graded sand, gravelly sands, little or no fines of coarse fraction passes the No. 4 sieve) Sands with sM Silty sands, sand -silt mixtures Fines sc (more than 12% fines) Clayey sands, sand -clay mixtures ML Inorganic silts of low to medium plasticity, sandy silts, gravelly silts, or clayey silts with slight plasticity Silts and Clays (liquid limit less Inorganic cL Inorganic clays of low to medium plasticity, gravelly clays, sandy clays FINE GRAINED than 50) silty clays, lean clays Organic oL Organic silts and organic silty clays of low plasticity SOILS (50% or more passes the MH Inorganic silts, micaceous or diatomaceous fine sands or silty soils, No. 200 sieve) elastic silt Silts and Clays (liquid limit 5o or Inorganic CH Inorganic clays of medium to high plasticity, sandy fat clay, more) or gravelly fat clay Organic OH Organic clays of medium to high plasticity, organic silts HIGHLY ORGANIC Primarily organic matter, dark in color, PT Peat, humus, swamp soils with high organic content (ASTM D4427) SOILS and organic odor Classification of Soil Constituents MAJOR constituents compose more than 50 percent, by weight, of the soil. Major constituents are capitalized (i.e., SAND). Minor constituents compose 12 to 50 percent of the soil and precede the major constituents (i.e., silty SAND). Minor constituents preceded by "slightly" compose 5 to 12 percent of the soil (i.e., slightly silty SAND). Trace constituents compose 0 to 5 percent of the soil (i.e., slightly silty SAND, trace gravel). Relative Density (Coarse Grained Soils) Consistency (Fine Grained Soils) N, SPT, Relative N, SPT, Relative Blows/FT Density Blows/FT Consistency 0-4 Very loose Under 2 Very soft 4 -10 Loose 2-4 Soft 10 - 3o Medium dense 4-8 Medium stiff 30 - 50 Dense 8 -15 Stiff Over 50 Very dense 15 - 3o Very stiff Over 3o Hard Grain Size Definitions Description Sieve Number and/or Size Fines <#200 (o.o8 mm) Sand -Fine #200 to #40 (o.o8 to 0.4 mm) -Medium #40 to #10 (0.4 to 2 mm) -Coarse #10 to #4 (2 to 5 mm) Gravel -Fine #4 to 3/4 inch (5 to 19 mm) -Coarse 3/4 to 3 inches (19 to 76 mm) Cobbles 3 to 12 inches (75 to 305 mm) Boulders >12 inches (305 mm) Moisture Content Definitions I Dry Absence of moisture, dusty, dry to the touch Moist Damp but no visible water Wet Visible free water, from below water table Cobalt Geosciences, LLC P.O. Box 82243 _ - Kenmore, WA 98028 (2o6) 331-1097 Soil Classification Chart Figure Ci COBALT www.cobalt eg o.com cobaltgeo(cpgmail.com This document was created by an application that isn't licensed to use novaPDF. Purchase a license to generate PDF files without this notice. Test Pit TP-1 Date: July 16, 2020 Depth: 8' Groundwater: 4' Contractor: Jim Elevation: Logged By: PH Checked By: SC — N (3) 0 o Q Moisture Content (%) Plastic I Liquid O U E 3 Limit �� Limit N Material Description C o ? o DCP Equivalent N Value O 0 10 20 30 40 50 — — — To soil/Grass 1 SM Loose to medium dense, silty -fine to medium grained sand with gravel dark yellowish brown, moist. (Fill) 2 ------ 3 — , -- SM --------------------------------------------- Loose to medium dense, silty -fine to medium grained sand with gravel :: SP reddish brown to yellowish brown, moist. 4 (Weathered Advance Outwash) _ ------ 5 ---- = . -- SM --------------------------------------------- Dense to very dense, silty -fine to medium grained sand with gravel, SP grayish brown, moist. (Advance Outwash) 6 7 N. c End of Test Pit 8' 9 10 Date: July 16, 2020 Depth: 6' Groundwater: 3.5' Contractor: Jim Elevation: Logged By: PH Checked By: SC 0 o 6 Moisture Content (%) N Q Plastic Liquid U E 3 Limit Limit 0-N Material Description � o 'c 0 ? o DCP Equivalent N-Value O 0 10 20 30 40 50 ------- 1 ------- ---- _ — `' -- SM -- TopsoilGross ---------------------------- Loose to medium dense, silty -fine to medium grained sand with gravel sJr;rl�yElls�risli�raeuitagravi^ch hrabcn�F�fJ�----------------- Loose to medium dense, silty -fine to medium grained sand with gravel 2 SP/ SM grayish brown, moist to wet. (Weathered Advance Outwash) 3-------------------------------------------------- �•, :... Z 4 : SP Medium dense, fine to medium grained sand with gravel trace silt, grayish brown, moist to wet. (Advance Outwash) 5...... : "' -Severe caving End of Test Pit 6' Refusal due to caving 7 8 9 10 Cobalt Geoscicnccs, LLC hi COBALT • Proposed Residence 648 Walnut Street Edmonds, Washington Test Pit Los g P.O. Box 82243 Kenmore, WA 98028 (2o6) 331-1097 www.cobaltgeo.com cobaltgeo(@gmail.com This document was created by an application that isn't licensed to use novaPDF. Purchase a license to generate PDF files without this notice. E. CONSTRUCTION SWPPP REQUIREMENTS: The project will require grading to construct the proposed building and utilities (including the stormwater control facilities). Standard erosion control measures are proposed to be used during construction. The primary erosion and sediment control BMP during construction will be proper soil stabilization methods. Exposed soils shall be stabilized by application of effective BMPs that protect the soil from the erosive forces of raindrops, flowing water, and wind. Applicable practices include, but not limited to, temporary and permanent seeding, sodding, mulching, plastic covering, erosion control fabrics, matting, the early application of gravel base on areas to be paved, and dust control. The contractor shall select a soil stabilization method best suited for the particular situation. Stockpiles must be stabilized and protected with sediment trapping measures. In addition, site containment of exposed soils shall be sustained by using silt fence barriers along the down -slope boundaries of the site's disturbance areas. See the site development plan for details. Construction Stormwater Pollution Prevention Plan (SWPPP): The following is a summary of the site's erosion control measures that evaluates the typical DOE 13 elements of a SWPPP: Element 1: Mark Clearing Limits: Clearing limits have been delineated on the engineering site development plans. BMP Recommended: Utilized: BMP C233: Silt Fence Element 2: Establish Construction Access: A construction access has been delineated on the engineering site development plans. BMP Recommended: BMP C105: Stabilized Construction Access Element 3: Control Flow Rates: Due to the relatively small size of the site's disturbance areas (less than 0.2 ac); it is recommended to maintain sheet flow dispersion (through downslope perimeter silt fencing) and not install collect swales and a sediment trap that would concentrate runoff flows. During construction silt fencing will provide attenuation of site runoff and upon project completion and stabilization (established lawns and landscape of exposed soils). BMP Recommended: No site specific BMP prescribed. Element 4: Install Sediment Controls: Filter fabric fence has been delineated and detailed on the engineering site development plans. At a minimum, silt fence will be installed along the down gradient perimeter of the disturbed area that will receive sediment -laden runoff. BMP Recommended: BMP C233: Silt Fence Element 5: Stabilize Soils: Soils will be stabilized per the TESC notes listed on the engineering site development plans. BMP Recommended: BMP C120: Temporary and Permanent Seeding and BMP C123: Plastic Covering Element 6: Protect Slopes: Exposed slopes shall be stabilized per the TESC notes listed on the engineering RAMEngineering, Inc. RAM No. 24-002 648 Walnut Street SFR Stormwater Site Plan Report Page E-1 site development plans. BMP Recommended: BMP C120: Temporary and Permanent Seeding and BMP C123: Plastic Covering Element 7: Protect Drain Inlets: Drain inlet protection will be installed on all catch basins that will receive sediment -laden runoff. See the engineering site development plans for locations and detail. BMP Recommended: BMP C220: Inlet Protection Element 8: Stabilize Channels and Outlets: This element is not applicable since there are no temporary channels or outlets proposed. BMP Recommended: BMP C209: Outlet Protection Element 9: Control Pollutants: Pollutants shall be managed as described in the TESC notes listed on the engineering site development plans. BMP Recommended: BMP C151: Concrete Handling Element 10: Control De -Watering: Highly turbid or contaminated de -watering water shall be handled separately from stormwater. The water from all de -watering systems for trenches and foundations shall be treated or disposed of prior to discharging from the site. BMP Recommended: No site specific BMP prescribed. Element 11: Maintain BMPs: BMPs shall be maintained and removed at the end of the project as follows: i. All temporary and permanent erosion and sediment control BMPs shall be inspected, maintained and repaired in accordance with the Drainage Manual or as approved or required by the City to assure continued performance of their intended function in accordance with BMP specifications. ii. The applicant may remove temporary BMPs when they are no longer needed. iii. All temporary erosion and sediment control BMPs shall be removed within 30 days after construction is completed and the City has determined that the site is stabilized. BMP Recommended: BMP C150: Materials on Hand Element 12: Manage the Project: The owner of the site is responsible for managing the installation and maintenance of the site BMPs. BMP Recommended: BMP C150: Materials on Hand and BMP C162: Scheduling. Element 13. Protect Low Impact Development BMPs: No LID stormwater BMPs are proposed. BMP Recommended: No site specific BMP prescribed. Conclusion: The total site disturbance area (0.19 ac.) of the project is less than one acre, thus a formal Notice of Intent application for NPDES coverage will not be made to the Department of Ecology. The final site development construction plans include specific grading and drainage improvement notes and details. With proper installation, maintenance and inspections of the proposed construction the project should have minimal impact to the surrounding environment. RAMEngineering, Inc. RAM No. 24-002 648 Walnut Street SFR Stormwater Site Plan Report Page E-2 F. OPERATION AND MAINTENANCE GUIDELINES: These guidelines are intended to provide operation and maintenance instructions for the project's storm drainage control facilities. The owner is responsible for maintenance of storm drainage facilities within the property (private property owner system); the owner is not responsible for maintenance within the public right-of-way (City system). Private property owner is responsible for properly maintaining the stormwater infrastructure on their property to ensure it operates as designed. The City has developed an inspection program to ensure private property owners are properly maintaining their stormwater systems. This manual is not comprehensive; although it explains the intended operation of the various components of the drainage system, and suggests a routine of inspection and maintenance, it cannot anticipate every problem. Once a historical record of maintenance is established, it may be prudent to alter the routine. It is recommended that maintenance records be kept, and that the records be reviewed periodically. The onsite detention tank system, control structure, junction catch basins, and onsite conveyance pipes are to be privately maintained by the project residence. Maintenance shall include the removal of sediment from the detention tank system, using a vactor truck or equally effective method. Regular inspections of the control structure within the catch basin shall be conducted to detect if non -routine maintenance is required due to sediment or debris blocking or clogging the fixed orifice or standpipe inlet. Regular sediment removal from the catch basins with a vactor truck or equally effective method shall be conducted as determined by regular inspections. Regular inspection and maintenance of the storm filter should occur according to the attached maintenance tables from the Washington State Department of Ecology Stormwater Manual (2019- Volume V). Semi-annual inspections shall be conducted to ensure proper operations of the drainage system. The inspections should occur prior to the winter rain season (Oct/Nov), leaving sufficient time to correct any detected maintenance problems, and at the end of the season (April/May) to determine the effect of the season's runoff. Once a historical basis is developed the frequency of inspection may be modified as necessary. Sediment can build up inside control structures and catch basins, blocking or restricting flow to the inlet. To prevent this problem, these structures should be routinely cleaned. Regular inspections of control structures should be conducted to detect the need for non -routine cleanout. MAINTENANCE REQUIREMENTS ECDC Section 18.30.090 requires privately -owned stormwater management facilities, such as LID BMPs be properly maintained. The owner of the property is the responsible party for such maintenance. The system must be kept in good working order. The entire system should be inspected once per year. An improperly maintained BMP may cause private property or street flooding. RAMEngineering, Inc. RAM No. 24-002 Contact the City Engineering Division for maintenance information. The City may make periodic inspections of BMPs to ensure they are operating properly. ECDC Section 18.30.100 contains the enforcement provisions the City can use to ensure the system is properly maintained. 648 Walnut Street SFR Stormwater Site Plan Report Page F-1 Appendix V-A: BMP Maintenance Tables Ecology intends the facility -specific maintenance standards contained in this section to be conditions for determining if maintenance actions are required as identified through inspection. Recognizing that Permittees have limited maintenance funds and time, Ecology does not require that a Permittee perform all these maintenance activities on all their stormwater BMPs. We leave the determination of importance of each maintenance activity and its priority within the stormwater program to the Permittee. We do expect, however, that sufficient maintenance will occur to ensure that the BMPs continue to operate as designed to protect ground and surface waters. Ecology doesn't intend that these measures identify the facility's required condition at all times between inspections. In other words, exceedance of these conditions at any time between inspections and/or maintenance does not automatically constitute a violation of these standards. However, based upon inspection observations, the Permittee shall adjust inspection and maintenance schedules to minimize the length of time that a facility is in a condition that requires a maintenance action. Table V-A.3: Maintenance Standards - Closed Detention Systems (Tanks/Vaults) Maintenance Results Expected Component Defect Conditions When Maintenance is Needed When Maintenance is Performed Plugged Air Vents One-half of the cross section of a vent is blocked at Vents open and any point or the vent is damaged. functioning. Accumulated sediment depth exceeds 10% of the diameter of the storage area for 1/2 length of storage vault or any point depth exceeds 15% of All sediment and debris Debris and Sediment diameter. removed from storage (Example: 72-inch storage tank would require area. cleaning when sediment reaches depth of 7 inches for more than 1/2 length of tank.) Storage Area Any openings or voids allowing material to be Joints Between transported into facility. All joint between Tank/Pipe Section (Will require engineering analysis to determine tank/pipe sections are sealed. structural stability). Tank Pipe Bent Out of Any part of tank/pipe is bent out of shape more than Tank/pipe repaired or Shape 10% of its design shape. (Review required by replaced to design. engineer to determine structural stability). Cracks wider than 1/2-inch and any evidence of soil Vault replaced or particles entering the structure through the cracks, repaired to design Vault Structure Includes or maintenance/inspection personnel determines specifications and is Cracks in Wall, Bottom, that the vault is not structurally sound. structurally sound. Damage to Frame and/or Top Slab Cracks wider than 1/2-inch at the joint of any No cracks more than inlet/outlet pipe or any evidence of soil particles 1/4-inch wide at the joint entering the vault through the walls. of the inlet/outlet pipe. RAMEngineering, Inc. RAM No. 24-002 648 Walnut Street SFR Stormwater Site Plan Report Page F-2 Table V-A.3: Maintenance Standards - Closed Detention Systems (Tanks/Vaults) Maintenance Results Expected Component Defect Conditions When Maintenance is Needed When Maintenance is Performed Cover Not in Place Cover is missing or only partially in place. Any open Manhole is closed. manhole requires maintenance. Mechanism cannot be opened by one maintenance Locking Mechanism Not person with proper tools. Bolts into frame have less Mechanism opens with Manhole Working than 1/2 inch of thread (may not apply to self-locking proper tools. lids). Cover Difficult to One maintenance person cannot remove lid after Cover can be removed Remove applying normal lifting pressure. Intent is to keep and reinstalled by one cover from sealing off access to maintenance. maintenance person. Ladder is unsafe due to missing rungs, Ladder meets design Ladder Rungs Unsafe misalignment, not securely attached to structure standards. Allows maintenance person wall, rust, or cracks. safe access. See Table V-A.5: See Table V-A.5: Maintenance Standards -Catch See Table V-A.5: Catch Basins Maintenance Standards Basins Maintenance Standards Catch Basins Catch Basins Table V-A.4: Maintenance Standards - Control Structure/Flow Restrictor Maintenance Defect Condition When Maintenance Results Expected When Component is Needed Maintenance is Performed Trash and Debris (Includes Material exceeds 25% of sump Control structure orifice is not Sediment) depth or 1 foot below orifice blocked. All trash and debris plate. removed. Structure is not securely attached to manhole wall. Structure securely attached to wall and outlet pipe. General Structure is not in upright position (allow up to 10% from Structure in correct position. plumb). Structural Damage Connections to outlet pipe are Connections to outlet pipe are watertight; structure repaired or not watertight and show signs of replaced and works as designed. rust. Structure has no holes other than Any holes - other than designed designed holes. holes - in the structure. Cleanout gate is not watertight Gate is watertight and works as or is missing. designed. Gate cannot be moved up and Gate moves up and down easily down by one maintenance and is watertight. Cleanout Gate Damaged or Missing person. Chain/rod leading to gate is Chain is in place and works as missing or damaged. designed. Gate is rusted over 50% of its Gate is repaired or replaced to surface area. meet design standards. Control device is not working Plate is in place and works as Orifice Plate Damaged or Missing properly due to missing, out of designed. place, or bent orifice plate. Obstructions Any trash, debris, sediment, or Plate is free of all obstructions and vegetation blocking the plate. works as designed. RAMEngineering, Inc. RAM No. 24-002 648 Walnut Street SFR Stormwater Site Plan Report Page F-3 Table V-A.4: Maintenance Standards - Control Structure/Flow Restrictor Maintenance Defect Condition When Maintenance Results Expected When Component is Needed Maintenance is Performed Any trash or debris blocking (or Pipe is free of all obstructions and Overflow Pipe Obstructions having the potential of blocking) the overflow pipe. works as designed. See Table V-A.3: Maintenance See Table V-A.3: Maintenance See Table V-A.3: Maintenance Manhole Standards - Closed Detention Standards - Closed Detention Standards - Closed Detention Systems (Tanks/Vaults) Systems (Tanks/Vaults) Systems (Tanks/Vaults) Catch Basin See Table V-A.5: Maintenance See Table V-A.5: Maintenance See Table V-A.5: Maintenance Standards - Catch Basins Standards - Catch Basins Standards - Catch Basins Table V-A.S: Maintenance Standards - Catch Basins Maintenance Results Expected When Component Defect Conditions When Maintenance is Needed Maintenance is performed 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 Trash or debris (in the basin) that exceeds 60 percent of front of catch basin or on the sump depth as measured from the bottom of basin grate opening. to invert of the lowest pipe into or out of the basin, but in no case less than a minimum of six inches clearance No trash or debris in the Trash & Debris from the debris surface to the invert of the lowest pipe. catch basin. Trash or debris in any inlet or outlet pipe blocking more Inlet and outlet pipes free than 1/3 of its height. of trash or debris. Dead animals or vegetation that could generate odors No dead animals or that could cause complaints or dangerous gases (e.g., vegetation present within methane). the catch basin. General Sediment (in the basin) that exceeds 60 percent of the sump depth as measured from the bottom of basin to invert of the lowest pipe into or out of the basin, but in no No sediment in the catch Sediment case less than a minimum of 6 inches clearance from basin the sediment surface to the invert of the lowest pipe. Top slab has holes larger than 2 square inches or Top slab is free of holes cracks wider than 1/4 inch. (Intent is to make sure no and cracks. Structure Damage material is running into basin). to Frame and/or Top Slab Frame not sitting flush on top slab, i.e., separation of Frame is sitting flush on more than 3/4 inch of the frame from the top slab. Frame the riser rings or top slab and firmly attached. not securely attached Maintenance person judges that structure is unsound. Basin replaced or Fractures or Grout fillet has separated or cracked wider than 1/2 inch repaired to design standards. Cracks in Basin and longer than 1 foot at the joint of any inlet/outlet pipe Walls/ Bottom or any evidence of soil particles entering catch basin Pipe is regrouted and through cracks. secure at basin wall. RAMEngineering, Inc. RAM No. 24-002 648 Walnut Street SFR Stormwater Site Plan Report Page F-4 Table V-A.S: Maintenance Standards - Catch Basins Maintenance Results Expected When Component Defect Conditions When Maintenance is Needed Maintenance is performed Settlement/ If failure of basin has created a safety, function, or Basin replaced or repaired to design Misalignment design problem. standards. Vegetation growing across and blocking more than 10% No vegetation blocking of the basin opening. opening to basin. Vegetation Vegetation growing in inlet/outlet pipe joints that is more No vegetation or root than six inches tall and less than six inches apart. growth present. Contamination and See Table V-A.1: Maintenance Standards -Detention No pollution present. Ponds Pollution Cover Not in Place Cover is missing or only partially in place. Any open Cover/grate is in place, meets design standards, catch basin requires maintenance. and is secured Locking Mechanism cannot be opened by one maintenance Mechanism opens with Catch Basin Mechanism Not person with proper tools. Bolts into frame have less than proper tools. Cover Working 1/2 inch of thread. One maintenance person cannot remove lid after Cover Difficult to applying normal lifting pressure. Cover can be removed by Remove (Intent is keep cover from sealing off access to one maintenance person. maintenance.) Ladder Rungs Ladder is unsafe due to missing rungs, not securely Ladder meets design standards and allows Ladder Unsafe attached to basin wall, misalignment, rust, cracks, or maintenance person safe sharp edges. access. Grate opening Grate with opening wider than 7/8 inch. Grate opening meets Unsafe design standards. Trash and Debris Trash and debris that is blocking more than 20% of Grate free of trash and Metal Grates (If grate surface inletting capacity. debris. Applicable) Grate is in place, meets Damaged or Grate missing or broken member(s) of the grate. the design standards, and Missing. is installed and aligned with the flow path. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 RAMEngineering, Inc. RAM No. 24-002 648 Walnut Street SFR Stormwater Site Plan Report Page F-5 ENGINEERING, INC. Civil Engineering /Land Planning