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24-100334-Preliminary TIR-01.31.24TECHNICAL INFORMATION REPORT FOR SAAD 2951h SHORT PLAT CLIENT: Emerald Real Estate Investments LLC 6208 S 300th St Phone: (253) 394-6346 PREPARED BY: Daley-Morrow-Poblete, Inc. 726 Auburn Way North Auburn, WA 98002 Phone: (253) 333-2200 PROJECT No. 23-440 DATE: Jan. 8, 2024 4� o � OS 2 52 �OG I S 1 N 1 STAMP NOT VALID UNLESS SIGNED & DATED TABLE OF CONTENTS DESCRIPTION PAGE SECTION I — PROJECT OVERVIEW Project Overview 1 Figure 1 - TIR Worksheet 2-6 Figure 2 - Vicinity Map 7 Figure 3 — Basin Map 8 Figure 4 - Soils Map 9 - 10 SECTION II — CONDITIONS AND REQUIREMENTS SUMMARY Core Requirements 1-2 SECTION III — OFF -SITE ANALYSIS Off -Site Analysis 1 —3 SECTION IV — FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN Existing Site Hydrology 1 Developed Site Hydrology 1 Performance Standards 1 Flow Control System 1-2 Water Quality System 2 Peale Flow Analysis 3 - 4 SECTION V — CONVEYANCE SYSTEM ANALYSIS AND DESIGN N/A SECTION VI — SPECIAL REPORTS AND STUDIES Geotechnical Evaluation 1 - 16 SECTION VII — OTHER PERMITS N/A SECTION VIII — C.S.W.P.P. PLAN ANALYSIS AND DESIGN T.E.S.C. 1 SECTION IX — BOND QUANTITIES, FACILITY SUMMARIES AND DECLARATION OF COVENANT Bond Quantities Worksheet To be added if required Storm Facility Summary Sheet N/A Declaration of Covenant To be added if required SECTION X — OPERATIONS AND MAINTENANCE MANUAL Operation and Maintenance 1-3 SECTION I PROJECT OVERVIEW PROJECT OVERVIEW The project site, with Tax parcel 515180-0035 is within the northeast quarter of Section 5, Township 21 North, Range 4 East, Willamette Meridian, King County, Washington. The property is on the south side of S 295th Place and is approximately 450 feet east of the intersection of S 295th Place SE and 9th Place S. The site address is 1013 S 295th Place, Federal Way, WA 98003. The 0.55-acre property is zoned RS9.6 and is surrounded by single-family homes. The irregularly -shaped project site is presently developed with a single-family home with landscaping and a wooded area in the south side of the lot. The site slopes to the northwest and southwest. Site soils are classified as Arents, Alderwood material (AmC) by the USDA Natural Resources Conservation Services. However, the Geotechnical Evaluation in Section VI indicates that the site is underlain by Vashon Recessional Outwash and is suitable for infiltration. It is proposed to subdivide the property into 2 lots, with the existing home remaining in Lot 1. Utility services will be provided to the proposed Lot 2. Flow Control BMPs will be provided to the proposed impervious surfaces. We believe that with implementation of the Flow Control BMPs, this project should not have any adverse effects on the downstream properties. KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 1 PROJECT OWNER AND PROJECT ENGINEER Project Owner 04CX41.0 AC4,e I11,9-Y "CIV 7S I. L C Phone K?-513),2 Y!g— 43 �14 Address 2,o 5 3 0o lW AIddemd, WA 9 001 Project Engineer XZ I-K 190 Company 1/11/f , Phone 2. 3) 3.3.3- Z Z00 Part 3 TYPE OF PERMIT APPLICATION U Land use (e.g.,Subdivision Short Sub / UPD) ❑ Building (e.g.,M/F / Commercial / SFR) ❑ Clearing and Grading ❑ Right -of -Way Use ❑ Other Part 2 PROJECT LOCATION AND DESCRIPTION Project Name .S AA 0 2 ?5 7-11 DLS-Permitting Permit # Location Township 2/ /t/ NE Range Section Site Address /0/3 , jo 2!?(rrl'l FG,9F-/�A e- WAY Part 4 OTHER REVIEWS AND PERMITS' I ❑ DFW HPA ❑ COE CWA 404 ❑ ECY Dam Safety ❑ FEMA Floodplain ❑ COE Wetlands ❑ Other ❑ Shoreline Management ❑ Structural Rockery/Vault/ ❑ ESA Section 7 Part 5 PLAN AND REPORT INFORMATION Technical Information Report Site Improvement Plan (Engr. Plans) Full Type of Drainage Review ❑ Targeted Plan Type (check ❑ ❑ Full (check one): ❑ Simplified one): Modified ❑ Large Project ❑ Simplified Date (include revision dates): ❑ Directed JAAh ria 20 0 y Date (include revision dates): Date of Final: Date of Final: Part 6 SWDM ADJUSTMENT APPROVALS Type (circle one): Standard / Experimental / Blanket Description: (include conditions in TIR Section 2) Approved Adjustment No. Date of Approval: DFW: WA State Dept. of Fish and Wildlife. HPA: hydraulic project approval. COE: (Army) Corps of Engineers. CWA: Clean Water Act. ECY: WA State Dept. of Ecology. FEMA: Federal Emergency Management Agency. ESA: Endangered Species Act. 2021 Surface Water Design Manual 1 Last revised 7/23/2021 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 7 MONITORING REQUIREMENTS Monitoring Required: Yes No Start Date: Completion Date: Describe: Re: KCSWDM Adjustment No. Part 8 SITE COMMUNITY AND DRAINAGE BASIN Community Plan DC,�,4 G41,4 Special District Overlays: ItIoA/ Drainage Basin: WA Stormwater Requirements: eoAjsc,Q t/47,-/o/L/ 5g-o ' e-- 41isu-, wArez a bA61 Part 9 ONSITE AND ADJACENT SENSITIVE AREAS ❑ River/Stream ❑ Steep Slope ❑ Lake ❑ Erosion Hazard ❑ Wetlands ❑ Landslide Hazard ❑ Closed Depression ❑ Coal Mine Hazard ❑ Floodplain ❑ Seismic Hazard ❑ Other ❑ Habitat Protection Lj Part 10 SOILS Soil Type Slopes ❑ High Groundwater Table (within 5 feet) ❑ Other ❑ Additional Sheets Attached ❑ Sole Source Aquifer ❑ Seeps/Springs Erosion Potential 2021 Surface Water Design Manual 2 Last revised 7/23/2021 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 11 DRAINAGE DESIGN LIMITATIONS REFERENCE ❑ Core 2 — Offsite Analysis ❑ Sensitive/Critical Areas ❑ SEPA ❑ LID Infeasibility ❑ Other n I ❑ Additional Sheets Attached LIMITATION / SITE CONSTRAINT Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Threshold Discharge Area: (name or description) Core Requirements (all 8 apply): Discharge at Natural Location Number of Natural Discharge Locations: Offsite Analysis Level: 1 / 2 / 3 dated: /fZ-Z 9123 Flow Control (include facility Level: 1 / 2 / 3 or Exemption Number summary sheet) Flow Control BMPs Conveyance System Spill containment located at: Erosion and Sediment Control / CSWPP/CESCL/ESC Site Supervisor: ]-o Sc p/Lv t,1/1) Construction Stormwater Contact Phone: '4/opa T9 t aLPzVc�n` `� Pollution Prevention After Hours Phone: Maintenance and Operation Responsibility (circle one): Private / Public If Private, Maintenance Log Required: Yes / No Financial Guarantees and Provided: Yes / No % e-" 1 VI A Liability /le6Qul /'c Water Quality (include facility Type (circle one): Basic / Sens. Lake / Enhanced Basic / Bog summary sheet) or Exemption No. Landscape Management Plan: Yes / o For Entire Project: Total Replaced Impervious surfaces on the site O % of Target Impervious that had a Total New Pervious Surfaces on the site feasible FCBMP a implemented 00 / ReDI. Imp. on site mitigated w/flow control facility D Repl. Imp. on site mitigated w/water quality facility D Repl. Imp. on site mitigated with FCBMP D 2021 Surface Water Design Manual 3 Last revised 7/23/2021 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Special Requirements (as applicable): Area Specific Drainage Type: CDA / SDO / MDP / BP / LMP / Shared Fac. Non Requirements Name: Floodplain/Floodway Delineation Type (circle one): Major / Minor / Exemption / None 100-_near Base Flood Elevation (or range): Datum: Flood Protection Facilities Describe: IV11 Source Control Describe land use: (commercial / industrial land use) Describe any structural controls: Oil Control High -use Site: Yes / o Treatment BMP:` Maintenance Agreement: Yes /f No with whom? Other Drainage Structures Describe: Part 13 EROSION AND SEDIMENT CONTROL REQUIREMENTS MINIMUM ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION AFTER CONSTRUCTION Clearing Limits Stabilize exposed surfaces Cover Measures emove and restore Temporary ESC Facilities Ld Perimeter Protection Yclean and remove all silt and debris, ensure Ef Traffic Area Stabilization operation of Permanent Facilities, restore operation of Flow Control BMP Facilities as Sediment Retention necessary ❑ Surface Water Collection ❑ Flag limits of SAO and open space preservation Dewatering Control areas ,-❑,( ❑ Other LI Dust Control Flow Control ,❑ iJ Protection of Flow Control BMP Facilities (existing and proposed) Maintain BMPs / Manage Project 2021 Surface Water Design Manual 4 Last revised 7/23/2021 KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 14 STORMWATER FACILITY DESCRIPTIONS (Note: Include Facility Summary and Sketch) Flow Control Type/Description Water Quality Type/Description ❑ Detention ❑ Infiltration ❑ Regional Facility ❑ Shared Facility ❑ Flow Control BMPs ❑ Other ❑ Vegetated Flowpath ❑ Wetpool ❑ Filtration ❑ Oil Control ❑ Spill Control ❑ Flow Control BMPs ❑ Other I?A5—IL hzii4 - G Part 15 EASEMENTS/TRACTS Part 16 STRUCTURAL ANALYSIS ❑ Drainage Easement ❑ Cast in Place Vault ❑ Covenant Retaining Wall ❑ Native Growth Protection Covenant ❑ Rockery > 4' High ❑ Tract ❑ Structural on Steep Slope ❑ Other ❑ Other I Part 17 SIGNATURE OF PROFESSIONAL ENGINEER I I, or a civil engineer under my supervision, have visited the site. Actual site conditions as observed were incorporated into this worksheet and the attached Technical Inform ion Report. To the best of my knowledge the information provided here is accurate. �,i' 6- a/1 8/24 Z, 2021 Surface Water Design Manual Last revised 7/23/2021 . _ - r ,, _ The information included on this map has been compiled by King County staff from a variety of sources and is subject to change wihout notice. King County makes no representations orwarranties, express or implied, as to accuracy,complateness, burst has a, or rights to the use of such nfonnation.This document is not!ntended r� ,m� 'r I I f / 014. E 2- N A lor use as a survey pmduct. King County shal not be liable for any general, special, indirect incidental or ' wnsequential damagesindudng, but not fmlted to, lostrewnues or Istprofitsmsulting from the use or misuse of the information contained on this map. Any sale of this map or nfonnationon this map is prohibited except by 5 R �y \ j,� / ti F (* 'kf1 'F p.�i t..� VICINITY N A written permissionof King County. ¢ 4 ,j'' 4 f I , / -yam King County Date: 11/29/2023 Notes: /`0 ®5 ��' `'�� a�x�' ��xI" m�✓��`''rTx,�`� `�"��""��c � 1.414'``(�� aJ; i -�- ° f ` - p' BSBOL / r ONCE % r' t CONC.s � II _BAR DECK 11 f l 0.3' �` t 4\ I _RLY 17.7 16•g' Ro9F EXISTING 2 STORtY HOUSE \� 0.4' 20.3, BLDG � nR �` i 101J SOUTH 295ACTH PL0.3' 7.3' ROOF moe t / Q 15.a' STAIRS �. ROOF LINE „\ \ I D � 10 e 1 � t. 20.0 DEC -ECK s. '- RR 11E �'9 20.9 ! Po - WALL 04 :" _ :SFE co .10t z 40 ;� 7.:............ ........................ ... ...-- ,mot =:::::::n.:::::::::::::::: ��dc r':::: .....:..s.\:::::::::::.::. 40 0 ...................-::.:. - 2• 0' 4 To %/A //2 Ga 1 140 6- AX ROOF 4o2"s f f - 16qel 40 1 HE�GN7 `4,9 39g . 39 � 39s 5FFE:0430g6 p J 394 Sc � r! C i d° !i=0 d �� 1 \ BFE' 96 + w 0 y 0. g`'�"•j ...j \'� \ t 394' t ,396' -o:8i - 3 Soil Map —King County Area, Washington N (SOILS MAP) 470 20' 18" N 470 2Y 14° N 551250 5512.0 551270 551280 551290 551300 551310 551320 Map Scale: 1:679 ff printed on A portra t (8.5' x I V) sheet. Meters N 0 10 20 40 60 �et o so so 120 ,ao Map projection: Web Mercator Comer coordinates: WGS84 Edge tics: UTM Zone 10N WGS84 USDA Natural Resources Web Soil Survey Conservation Service National Cooperative Soil Survey 47o 2918' N 0 N N� N 47o 2U 14' N 55133f) 55134U 55135U 3 11/27/2023 Page 1 of 3 Soil Map —King County Area, Washington Map Unit Legend SOILS MAP Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI AmC Arents, Alderwood material, 6 to 15 percent slopes 1.4 100.0% Totals for Area of Interest 1.4 100.0% USDA Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11 /27/2023 Page 3 of 3 01 SECTION II CONDITIONS AND REQUIREMENTS SUMMARY CORE REQUIREMENT #1: DISCHARGE AT THE NATURAL LOCATION Discharge from the proposed development will be infiltrated. Any release from the site will discharge to the natural location. CORE REQUIREMENT #2: OFFSITE ANALYSIS See Section III. CORE REQUIREMENT #3: FLOW CONTROL FACILITIES This project proposes subdividing the property into 2 lots. The existing home will remain in Lot 1. Lot 2 will contain a new home. It was assumed that the house will have a roof area of approximately 3,419 sf, while approximately 1,644 sf of new driveway will be added. New target surfaces will be the additional driveway, new house and landscaped areas within Lot 2. A comparison of the pre and post -development 100-yr peak flow rate in Section IV shows that the increase will be less than 0.15 cfs; therefore, this project is has met Exception 2 and does not need to have a flow control facility. CORE REQUIREMENT #4: CONVEYANCE SYSTEM There are no conveyance facilities being proposed. CORE REQUIREMENT #5: CONSTRUCTION STORMWATER POLLUTION PREVENTION Silt fencing, stabilized construction entrance and site stabilization will be provided consistent with developments this size. Less than 1-acre of disturbance will be created; therefore, this project is exempt from the NPDES permit requirement. A Residential TESC plan will be included with the building permit for Lot 2. CORE REQUIREMENT #6: MAINTENANCE AND OPERATIONS On -site facilities will be privately maintained. See Section X for the maintenance guidelines. CORE REQUIREMENT #7: FINANCIAL GUARANTEES AND LIABILITY Will be provided if required by the City. CORE REQUIREMENT #8: WATER QUALITY It is projected that no more than 5,000 sf of new and replaced pollution generating impervious surfaces (PGIS) may be created on this lot. This project is therefore exempt from this requirement. Furthermore, either basic dispersion or permeable pavement will be used for the PGIS, which provides water quality treatment. 6 CORE REQUIREMENT #9: FLOW CONTROL BMPs The property falls under the Small Lot BMP requirements. The following BMPs were considered for this project: Full Dispersion - Full dispersion is not feasible due to lack of available native vegetated flowpath. Full Infiltration —Medium sands may be used for this project per paragraph 5 on page 8 of the Geotechnical Evaluation in Section VI; therefore, this BMP is feasible. A drywell will be used for the roof runoff. Limited Infiltration — Full infiltration is already being used for the roof runoff. Bioretention — There is no safe overflow pathway to a municipal or private storm system. Therefore, this BMP is infeasible. Permeable Pavement — Since most of the proposed pavement will be in fill and if is on the upstream side of the proposed house, water that infiltrates would threaten the below grade floors, this BMP is not feasible. Basic Dispersion — Most of the proposed pavement will be dispersed, except for the new pavement at the entrance since there is no sufficient area to disperse. Lot 2 will be bigger than 11,000 sf. Per Section C.1.3.1 of the 2021 KCSWDM, if is required to provide BMPs to 20% of the lot size. With a lot size of 14,162 sf, it is required to provide BMPs to 2,833s£ It is proposed to provide BMPS to 5,063 (3,419 sf roof+ 1,644 sf driveway). Therefore, this project meets this requirement. SPECIAL REQUIREMENT #1: OTHER ADOPTED AREA -SPECIFIC REQUIREMENTS. N/A SPECIAL REQUIREMENT #2: FLOOD HAZARD AREA DELINEATION N/A SPECIAL REQUIREMENT #3: FLOOD PROTECTION FACILITIES N/A SPECIAL REQUIREMENT #4: SOURCE CONTROL N/A SPECIAL REQUIREMENT #5: OIL CONTROL This project is not a "High Use Site". Eel SECTION III OFF -SITE ANALYSIS OFF -SITE ANALYSIS As previously stated, there are two drainage points for the site. Approximately half of the existing house and the area north of it drains to the northwest, while the other half of the house and the area south of it drains to the southwest. Any runoff leaving the proposed improvements will drain to the southwest. Runoff from the southwest will sheet flow across private property, while runoff to the northwest drains to S 295'h Place. Both flows combine at the intersection of S 295'h Place SE and 9'h Place S, which is approximately 450 feet west of the site. Since the flows combine within a quarter mile, there is only one threshold discharge area. There is approximately 1.5 acre upstream of the site that potentially contributes runoff through the site. However, since said area is partially wooded and the soils in the area have infiltrative capacity, we believe that very little runoff will actually enter the site. Any runoff that does enter the site, will do so near the southeast corner of the site and exit near the southwest corner. No sensitive areas were identified. As previously mentioned, flows to the southwest initially enter private property; therefore, we are not able to inspect the flow path. Since both flows recombined within a quarter mile, this analysis will therefore begin at the northwest corner of the site. Runoff from the northwest corner of the site drains to S 295'h Place and flows along the south side of S 295'h Place for a distance of approximately 210'feet to a catch basin. A 12" pipe conveys water across the street for a distance of approximately 28 feet to another catch basin. From said catch basin, a 12" pipe carries water for approximately 220 feet to a catch basin on the northwest corner of the intersection of S 295'h Place and 9'h Place S. Water then travels for a distance of approximately 30 feet through a 12" pipe across 9'h Place S to another catch basin. From said catch basin, water flows north for approximately 360 feet to a catch basin at the intersection of 9'h Place S and S 294'h Place. From said catch basin, water is conveyed north by a 12" pipe for approximately 155 feet to another catch basin. Water then travels north for a distance of approximately 230 feet to a catch basin at the southwest corner of the intersection of 9'h Place S and S 293rd Street. Water then travels west along the south side of S 293rd Street within a 15" pipe for a distance of approximately 350 feet to a catch basin at the southwest corner of the intersection of S 293rd Street and 8'h Avenue S. Said catch basin being 1,583 feet or more than a quarter mile downstream from the site. Water then continues north and eventually drains into the Puget Sound. The downstream path is shown on the attached map. INS King County Map t, r��'�: ��l;.�r`�--�a�� f ,�! .;5.r'' 1�' � � � _ ` � �I ++-' � ;T'�-.-,c�`"��w�s , ''� a""""��r :, ,"1 ��%� S�irl�k"w I� °� I`�Ill�fill�',@9��I�;I� King County '4� > The information included on this map has been compiled by King County staff from a variety of sources and is subject to change without notice. King County makes no representations orwarranfies, express or implied, as to accuracy, Date: 11/29/2023 N completeness, timeliness, or rights to the use of such information. This documentis not intended for use asasurvey product. King County shall not be liable for any general, special, indirect, incidental, or consequential damages including, LIZ but not limited to, lost revenues or lost profits resulting from the use or misuse of the information contained on this map. Notes: A Any sale of this map or information on this map is prohibited except by written permission of King County. IV7--G King County I I NAIIVA-irne- NAF OFF -SITE ANALYSIS DRAINAGE SYSTEM TABLE KING COUNTY SURFACE WATER DESIGN MANUAL, CORE REQUIREMENT #2 P4�� sOiT� Subbasin Subbasin Date `%oZ Name: Number: Symbol Drainage Component Type, Name, and Size Drainage Component Description Slope Distance from site discharge Existing Problems Potential Problems Observations of field inspector, resource reviewer, or resident see map Type: sheet flow, swale, stream, channel, pipe, pond, flow control/wq BMP; Size: diameter, surface area drainage basin, vegetation, cover, depth, type of sensitive area, volume % '/4 ml = 1,320 ft. constrictions, under capacity, ponding, overtopping, flooding, habitat or organism destruction, scouring, bank sloughing, sedimentation, incision, other erosion tributary area, likelihood of problem, overflow pathways, potential impacts G UT7C-12 0 mac- ti ,� ® - 210 ILJO N 5 oVOA16 29�r � � Al � r/ �� c ass e � �-� ��. _ ,� 2 7. �(2 f ,/per/,f� C,6 TO ,�z,6�� mo /�:.� ✓ .! l2 �� -r3c�oG M 3TH b� �733- 2021 Draft Surface Water Design Manual Last revised 4/24/2016 H SECTION IV QUALITY FACILITY ANALYSIS AND DESIGN EXISTING SITE HYDROLOGY (PART A) As previously stated, there are two drainage points for the site. Approximately half of the existing house and the area north of it drains to the northwest, while the other half of the house and the area south of it drains to the southwest. Any runoff leaving the proposed improvements will drain to the southwest. Runoff from the southwest will sheet flow across private property, while runoff to the northwest drains to S 295"' Place. Both flows combine at the intersection of S 295"' Place SE and 91h Place S, which is approximately 450 feet west of the site. Since the flows combine within a quarter mile, there is only one threshold discharge area. DEVELOPED SITE HYDROLOGY (PART B) Runoff from the site will be dispersed or fully infiltrated. Any release from the site will continue to discharge to its natural drainage path after construction of the house and associated driveway. PERFORMANCE STANDARDS (PART C) The project site is within the Conservation Flow Control/Level,2 Flow Control and the Basic Water Quality Treatment Area. FLOW CONTROL SYSTEM (PART D) This project proposes the construction of a single-family home with a roof area of approximately 3,419 sf and additional driveway of approximately 1,644 sf. A comparison of the 100-yr pre and post -development peak flow rates in this Section shows that the increase is less than 0.15 cfs; therefore, this project is exempt from this requirement. The following BMPs are sized as follows (See Basin Map in Section I for tributary Areas): Drywell: Tributary roof area = 3,419 sf Required gravel volume for medium sands for drywells = 90 cy per 1,000sf Required gravel volume (V) = 3,419 x 90 / 1,000 = 307.7 Drywell height (H) = 4 ft Required drywell radius (R) = (V / (71 x H))A o.s = (307.7 / (n x 4))A0.5 = 4.95 ft, say 5 ft Required drywell diameter (D) = R x 2 =5x2 = 10, EO Dispersion trench Tributary Area = 1,644 sf (266 sf at the entrance will not be treated due to location) Required dispersion trench per Section C.2.4.4 = 10 if per 700 Length Required = 1,644 x 10 / 700 = 23.5 ft, use 24 ft WATER QUALITY SYSTEM (PART E) A total of 1,644 sf of pollution generating impervious surface will be created (PGIS). Since the PGIS is less than 5,000 sf, this project is exempt from this requirement. Furthermore, basic dispersion will be used for most of the new PGIS, which provide water quality treatment. ■ l'otAl Ld / IVAL Y5-15 WWHM2012 PROJECT REPORT Project Name: BASIN Site Name: SAAD 295th Site Address: 1013 S 295th Pl City : Federal Way Report Date: 1/24/2024 Gage : Seatac Data Start : 1948/10/01 Data End : 2009/09/30 Precip Scale: 1.00 Version Date: 2023/01/27 Version : 4.2.19 PREDEVELOPED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Forest, Steep .29 Pervious Total 0.29 Impervious Land Use acre DRIVEWAYS STEEP 0. 03 '&yt- WA y ToAC"AIAI Impervious Total 0.03 AV11/11- -11R n n a Basin Total 0.32 MITIGATED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Lawn, Steep .18 Pervious Total 0.18 Impervious Land Use acre ROOF TOPS FLAT 0.08 DRIVEWAYS STEEP 0.06 1--- Aj`t) o cam'`° "f ` , Impervious Total 0.14 Basin Total 0.32 H Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.29 Total Impervious Area:0.03 Mitigated Landuse Totals for POC #1 Total Pervious Area:0.18 Total Impervious Area:0.14 Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.023558 5 year 0.033126 10 year 0.040035 25 year 0.049426 50 year 0.056908 100 year 0.064812 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.076652 5 year 0.103958 10 year 0.123553 25 year 0.150086 50 year 0.171174 100 year 0.193423 6,13 - 0,an U, o+. ®l,� - Ain IJC-, r rf PAJ F4 e-!"/ Q SECTION V CONVEYANCE SYSTEM ANALYSIS AND DESIGN SECTION VI SPECIAL REPORTS AND STUDIES E � COBALT GEOSCIENCES November 9, 2023 Muhammad Saad Mohyuddin saadmohi(&googlemail.com RE: Geotechnical Evaluation Proposed Residence 1013 S. 295th Place Federal Way, Washington Cobalt Geosciences, LLC P.O. Box 1792 North Bend, WA 98045 In accordance with your authorization, Cobalt Geosciences, LLC has prepared this letter to discuss the results of our geotechnical evaluation at the referenced site. The purpose of our evaluation was to determine the feasibility of utilizing infiltration devices for stormwater runoff management along with providing recommendations for foundation and retaining wall design. Site and Project Description The site is located at 1013 S. 295th Place in Federal Way, Washington. The site consists of one nearly rectangular shaped parcel (No. 5151800O35) with a total area of about 23,753 square feet. The northern portion of the property is developed with a single family residence with partial basement and driveway. The remainder of the property is undeveloped and vegetated with grasses, bushes, ferns, ivy, and spares trees. The developed portion of the site is nearly level to slightly sloping downward to the northwest and southwest with low relief. The southern half of the site slopes downward to the north and south into a shallow ravine -like feature. Slope areas have been previously graded and have magnitudes of about 15 to 50 percent and local relief of io feet within the property. There is a taller slope that is locally faced with walls south of the subject parcel sloping downward to the north into the ravine. The ravine is very shallow and does not have evidence of seasonal streams or surface waters. The property is bordered to the east, west, and south by residential properties and to the north by S. 295th Place. The project includes subdivision of the parcel and construction of a residence in the southern half of the site. A driveway will extend to the area along the west property line. Figure 1 shows the current conditions and planned layout. Grading could include cuts of 8 feet or less if a daylight basement is utilized, and foundation loads will generally be light. Stormwater management may include dispersion, detention, or infiltration facilities depending on feasibility. We should be provided with the plans when they become available so that we may determine if additional recommendations are warranted. www.cobaltgeo.com (2o6) 331-1097 November 9, 2023 Page 2 of 11 Geotechnical Evaluation Area Geology The Geologic Map of the Poverty Bay Quadrangle, indicates that the site is underlain by Vashon Glacial Till and near the contacts with Vashon Advance Outwash. Vashon Glacial Till consists of dense mixtures of silt, sand, clay, and gravel. These deposits are typically impermeable below a weathered zone. Vashon Advance Outwash includes fine to medium grained sand trace gravel with local interbeds of silt and clay. These deposits become denser below a weathered zone. The till and outwash can locally be overlain by Vashon Recessional Outwash. These deposits include normally consolidated sand and gravel with lesser silt and clay. These deposits can be highly permeable. Soil & Groundwater Conditions As part of our evaluation, we excavated two test pits within the property to determine the shallow soil and groundwater conditions, where accessible. The test pits encountered about 6 inches of topsoil and grass underlain by approximately 2.5 to 3 feet of loose to medium dense, silty -fine to fine grained sand trace to with gravel (Weathered Recessional Outwash). This layer was underlain by medium to locally dense, fine to medium grained sand with gravel trace cobbles (Recessional Outwash?), which continued to the termination depths of the explorations. Groundwater was not observed in the test pits during our evaluation. Based on the soil conditions, it appears that perched groundwater would likely be 8 or more feet below grade during later winter and spring months. A review of available well logs (from the DOE well log site) within 2,000 feet of the site indicates groundwater at more than 77 feet below grade. 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. Steep Slope Hazard Most critical area ordinances designate slopes with magnitudes greater than about 40 percent and vertical relief of at least 10 feet as potentially geologically hazardous (steep slope/landslide hazards). The developed portion of the site is nearly level to slightly sloping downward to the northwest and southwest with low relief. The southern half of the site slopes downward to the north and south into a shallow ravine -like feature. Slope areas have been previously graded and have magnitudes of about 15 to 50 percent and local relief of 10 feet within the property. There is a taller slope that is locally faced with walls south of the subject parcel sloping downward to the north into the ravine. The ravine is very shallow and does not have evidence of seasonal streams or surface waters. Slope areas to the south are well vegetated. It is our opinion that the modified and natural slopes with.magnitudes over 40 percent within and near the properly are stable at this time. We did not observe evidence of erosion, landslide activity or soil creep. These areas are not consistent with landslide hazard areas. www.cobalt eg o.com (2o6) 331-1097 0 November 9, 2023 Page 3 of 11 Geotechnical Evaluation Provided all stormwater runoff during construction is fully managed, and stormwater is infiltrated or dispersed in areas with magnitudes of about 20 percent or more, the proposed development should not increase the risk of soil movements on the subject property and adjacent areas. Any new foundation systems should be embedded an adequate depth in order to create a minimum 7 foot effective setback from adjacent slope systems (downslope areas) where slope magnitudes are 30 percent or more. This is the horizontal distance from the lower outside face of the footing to the face of the adjacent slope. Erosion Hazard The Natural Resources Conservation Services (NRCS) maps for King County indicate that the site is underlain by Arents, Alderwood material (6 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 ist. Erosion control measures should be in place before the onset of wet weather. Seismic Parameters The overall subsurface profile corresponds to a Site Class D as defined by Table 1613.5.2 of the International Building Code (IBC). A Site Class D applies to an overall profile consisting of medium dense to very dense soils within the upper loo feet. We referenced the U.S. Geological Survey (USGS) Earthquake Hazards Program Website to obtain values for Ss, S1, Fa, and F,,. The USGS website includes the most updated published data on seismic conditions. The following tables provide seismic parameters from the USGS web site with referenced parameters from ASCE 7-10 and 7-16. Seismic Design Parameters (ASCE 7-16) Site Spectral Spectral Site Design Spectral Design Class Acceleration Acceleration Coefficients Response Parameters PGA at 0.2 sec. (g) at 1.o sec. (g) Fa K SDs SM D 1.343 0.461 1.0 Null o.895 Null 0.568 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 site has a low likelihood of liquefaction. "Null' indicates see Section 11.4.8 of the ASCE. www.cobaltgeo.com (2o6) 331-1097 November 9, 2023 Page 4 of 11 Geotechnical Evaluation Conclusions and Recommendations General The site is underlain by sand and gravel generally consistent with Vashon Recessional Outwash. The proposed residence may be supported on a shallow foundation system bearing on medium dense or firmer native soils or on structural fill placed on the native soils. Local overexcavation or recompaction of loose weathered native soils may be necessary depending on the proposed elevations and location of the new residence. Any new foundation systems should be embedded an adequate depth in order to create a minimum 7 foot effective setback from adjacent slope systems (downslope areas) where slope magnitudes are 30 percent or more. This is the horizontal distance from the lower outside face of the footing to the face of the adjacent slope. Infiltration is generally feasible in the soils consistent with the coarser outwash soils at depth. Trenches or drywells should be located in areas with slope magnitudes of 20 percent or less. Dispersion devices and permeable pavements are also generally feasible depending on their elevations and locations. We can provide additional recommendations once a site plan has been prepared. 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 where root systems can extend to greater depths, in areas of existing foundation systems, and in any areas underlain by undocumented fill. The native soils consist of silty -sand with gravel and poorly graded sand/gravel with silt and sand. Most of the native 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. Temporary Excavations Based on our understanding of the project, we anticipate that the grading could include local cuts on the order of approximately 8 feet or less for foundation and utility placement. Any deeper temporary excavations should be sloped no steeper than 1.5H:iV (Horizontal:Vertical) in loose native soils and fill and 1H:1V in medium dense, native soils. If an excavation is subject to heavy vibration or surcharge loads, we recommend that the excavations be sloped no steeper than 2H:1V, where room permits. www.cobaltgeo.com (2o6) 331-1097 O November 9, 2023 Page 5 of it Geotechnical Evaluation 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 10 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. Foundation Design The proposed residence 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. Any undocumented fill should be removed and replaced with structural fill below foundation elements. Structural fill below footings should consist of clean angular rock 5/8 to 2 inches in size. 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 1,500 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 25400t 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 www.cobaltgeo.com (2o6) 331-1097 0 November 9, 2023 Page 6 of ii Geotechnical Evaluation 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 0.4o 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 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. Concrete Retaining Walls The following table, titled Wall Design Criteria, presents the recommended soil related design parameters for retaining walls with a level backslope. Contact Cobalt if an alternate retaining wall system is used. This has been included if any concrete walls are proposed in yard areas. Wall Design Criteria "At -rest" Conditions (Lateral Earth Pressure — EFD+) 55 pef (Equivalent Fluid Density) "Active" Conditions (Lateral Earth Pressure — EFD+) 35 pcf (Equivalent Fluid Density) Seismic Increase for "At -rest" Conditions (Lateral Earth Pressure) 14H* (Uniform Distribution) 1 in 500 year event Seismic Increase for "Active" Conditions (Lateral Earth Pressure) 7H* (Uniform Distribution) Passive Earth Pressure on Low Side of Wall (Allowable, includes F.S. =1.5) Neglect upper 2 feet, then 250 pcf EFD+ Soil -Footing Coefficient of Sliding Friction (Allowable; includes F.S. =1.5) 0.40 *H is the height of the wall; Increase based on one in 500 year seismic event (io percent probability of being exceeded in 50 years), +EFD — Equivalent Fluid Density The stated lateral earth pressures do not include the effects of hydrostatic pressure generated by water accumulation behind the retaining walls. Uniform horizontal lateral active and at -rest pressures on the retaining walls from vertical surcharges behind the wall may be calculated using active and at -rest lateral earth pressure coefficients of 0.3 and 0.5, respectively. A soil unit weight Of 125 pcf may be used to calculate vertical earth surcharges. To reduce the potential for the buildup of water pressure against the walls, continuous footing drains (with cleanouts) should be provided at the bases of the walls. The footing drains should www.cobaltgeo.com (2o6) 331-1097 O November 9, 2023 Page 7 of 11 Geotechnical Evaluation consist of a minimum 4-inch diameter perforated pipe, sloped to drain, with perforations placed down and enveloped by a minimum 6 inches of pea gravel in all directions. The backfill adjacent to and extending a lateral distance behind the walls at least 2 feet should consist of free -draining granular material. All free draining backfill should contain less than 3 percent fines (passing the U.S. Standard No. 200 Sieve) based upon the fraction passing the U.S. Standard No. 4 Sieve with at least 30 percent of the material being retained on the U.S. Standard No. 4 Sieve. The primary purpose of the free -draining material is the reduction of hydrostatic pressure. Some potential for the moisture to contact the back face of the wall may exist, even with treatment, which may require that more extensive waterproofing be specified for walls, which require interior moisture sensitive finishes. We recommend that the backfill be compacted to at least 90 percent of the maximum dry density based on ASTM Test Method D1557• In place density tests should be performed to verify adequate compaction. Soil compactors place transient surcharges on the backfill. Consequently, only light hand operated equipment is recommended within 3 feet of walls so that excessive stress is not imposed on the walls. Slab -on -Grade We recommend that the upper 18 inches of the existing native soils within slab areas be re - compacted to at least 95 percent of the modified proctor (ASTM D1557 Test Method). Any fill should be fully removed and replaced with imported fill. 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. Slabs on grade may be designed using a coefficient of subgrade reaction of 150 pounds per cubic inch (pci) assuming the slab -on -grade base course is underlain by structural fill placed and compacted as outlined above. A minimum 4 inch thick capillary break should be placed over the prepared subgrade. These materials should consist of 5/8 inch clean angular rock or pea gravel. 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. www.cobaltgeo.com (2o6) 331-1097 0 November 9, 2023 Page 8 of 1i Geotechnical Evaluation Stormwater Management Feasibility The site is underlain by Vashon Recessional Outwash. Infiltration is suitable in these soil deposits. Groundwater was not encountered in the explorations. Groundwater is likely more than 8 and possibly more than 50 feet below site elevations based on a review of nearby boring logs. Because the recessional deposits have not been overridden by glacial ice, this soil unit is considered normally -consolidated. The Washington State Department of Ecology Stormwater Management Manual for Western Washington allows determination of infiltration rates of this soil unit by Soil Particle Size Distribution testing. This method involves using a logarithmic equation and grain size values along with correction factors for testing type, soil homogeneity, and influent control. The equation in conjunction with sieve analysis results yields design infiltration rates of between 2.5 to 3.5 inches per hour at depths of 3 to 6 feet below grade. These rates reflect application of correction factors for variability (0.6 used), influent control (0.9), and testing analysis type (0.4). We also performed an infiltration test in TP-1 at 4 feet below grade. Following saturation, testing, and application of the correction factors noted above, the design rate was determined to be 2.5 inches per hour. We recommend using this rate for system design. We note that the subsurface soils vary from Medium Sand to Coarse Sand/Gravel if sizing is determined using the Textural Triangle information in the King County Surface. Water Design Manual (SWDM). We recommend using Medium Sand for any systems. Infiltration systems should have a depth of at least 3 feet below existing grades and located at least 10 feet apart. Any fine grained soils or interbeds of fine grained soils must be removed prior to rock placement. 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. We should observe the soil conditions in infiltration systems during construction to confirm soils are consistent with our investigation. 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. ww,v.cobaltgeo.com (206) 331-1097 November 9, 2023 Page 9 of ii Geotechnical Evaluation • 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. 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, sandy and gravelly 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. 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 ■ Monitor subgrade preparation of roadways ■ Observe excavation stability ■ Verify soil conditions at any stormwater management systems 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. www.cobaltgeo.com (2o6) 331-1097 November 9, 2023 Page io of ii Geotechnical Evaluation CLOSURE This report was prepared for the exclusive use of Muhammad Saad Mohyuddin 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 Muhammad Saad Mohyuddin 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. Sincerely, Cobalt Geosciences, LLC NY 4 5d896 !: r31 NA6 11/9/2023 Phil Haberman, PE, LG, LEG Principal www.cobaltgeo.com (2o6) 331-1097 101 November 9, 2023 Page ii of ii Geotechnical Evaluation 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. www.cobaltgeo.com (2o6) 331-1097 Y 1 t t wes t It acs 3 1 _ t --8- 1tt 1 Provided figures TP-1 Approximate Test Pit Location Cobalt Geosciences, LLC Proposed Residence SITE PI AN P.O. Box 1792 North Bend, WA 98045 COBALT 1013 S. 295th Place (206) 331-1097 GEOSCIENCES Federal Way, Washington FIGURE 1 wcvw•cobaltgeo.com phil(&cobaltgeo.com Unified Soil Classification System (USCS) MAJOR DIVISIONS TYPICAL DESCRIPTION Clean Gravels JBOL 0w 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 ;t- 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% retained on Clean Sands :•, sw Well -graded sands, gravelly sands, little or no fines No. 200 sieve) Sands (less than 5% SP (5o% or more fines) Poorly graded sand, gravelly sands, little or no fines of coarse fraction Sands with sit Silty sands, sand -silt mixtures passes the No. 4 sieve) 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 Inorganic cL Inorganic clays of low to medium plasticity, gravelly clays, sandy clays (liquid limit less silty clays, lean clays FINE GRAINED than 50) OL SOILS Organic Organic silts and organic silty clays of low plasticity (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 50 or Inorganic C4'1 Inorganic clays of medium to high plasticity, sandy fat clay, more) or gravelly fat clay Organic oxOrganic 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 5o 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 o 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/Fr Consistency 0-4 Very loose Under 2 Very soft 4 - 10 Loose 2-4 Soft 10 - 30 Medium dense 4-8 Medium stiff 30 - 50 Dense 8 -15 Stiff Over 50 Very dense 15 - 30 Very stiff Over 3o Hard Cobalt Geosciences, LLC P.O. Box 82243 Kenmore, WA 98o28 (2o6) 331-1097 www.cobaltzeo.com cobaltgeo(@gmail.com Grain Size Definitions Description Sieve Number and/or Size Fines <#200 (o.o8 nun) Sand -Fine #200 to #40 (0.08 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 Dry Absence of moisture, dusty, dry to the touch Moist Damp but no visible water Wet Visible free water, from below water table Soil Classification Chart Figure C1 Test Pit TP-1 Date: October 2023 Depth: 8' Groundwater: None Contractor: Jim Elevation: Logged By: PH Checked By: SC o> O o Moisture Content (%) Plastic 1 I Liquid � U N Limit Limit Q a Material Description a)? o DCP Equivalent N-Value O 0 10 20 30 40 50 ------ ---- -- Topsoil/Grass --------------------------------------------- 1 SM Loose to medium dense, silty -fine to medium grained sand with gravel SP yellowish brown, moist. (Weathered Recessional Outwash) 2 T .' --------------------------------------------------- SP Medium dense to locally dense, fine to medium grained sand trace 4 gravel to gravel with sand, grayish brown, moist. '% (RecessionalOutwash?) ;..; Local caving limits test pit depth b t 7 ti End of Test Pit 8' 9 10 Cobalt Geosciences, LLC Proposed Residence P.O. Box 82243 Test Pit Kenmore, WA 98028 COBALT1013 S. 295th Place (2o6) 331-1097 • Federal Way, Washington Logs 6v%%�v.cobaItgeo.com �� cobaltgeo(@gmail.com Test Pit TP-2 Date: October 2023 Depth: 8' Groundwater: None Contractor: Jim Elevation: Logged By: PH Checked By: SC 0) O o Moisture Content (%) Plastic I Liquid U T 3 Limit Q o � Material Description o O ? 'o DCP Equivalent N Value O 0 10 20 30 40 50 ---- -- Topsoil/Grass --------------------------------------------- ------ 1 SM Loose to medium dense, silty -fine to medium grained sand with gravel SP yellowish brown, moist. (Weathered Recessional Outwash) 2 + ~ i Local yard waste at ground surface 3 ; ,• ------ 4 ---- -} ; :,'::: SP --------------------------------------------- Medium dense to locally dense, fine to medium grained sand trace gravel to gravel with sand, grayish brown, moist. 5::i:: (RecessionalOutwash?) L•i 11 6 ; �` i�• ti• Local caving limits test pit depth 7 1 y End of Test Pit 8' 9 10 Proposed Residence 1013 S. 295th Place Federal Way, Washington Cobalt Geosciences, LLC P.O. Box 82243 Test Pit Kenmore, WA 98028 (2o6) 331-1097 Logs lb -,%,i%-%v.cobaltgeo.com cobalteeo(@gmail.com SECTION VII SECTION VIII T.E.S.C. Silt fencing, stabilized construction entrance and site stabilization will be provided consistent with developments this size. Less than 1-acre of disturbance will be created, therefore, this project is exempt from the NPDES permit requirement. A Residential TESC plan is included with the submittal. SECTION IX BOND QUANTITIES, FACILITY SUMMARIES AND DECLARATION OF COVENANT a wa SECTION X OPEIaATIONS AND MAINTENANCE MANUAL OPERATIONS AND MAINTENANCE Maintenance of the different BMPs proposed for this project is the responsibility of the property owner. The following pages include the maintenance guidelines for the gravel fill trench and drywell. EO NO.25 - DRYWELL BMP Maintenance Defect or Problem Conditions When Maintenance is Needed Results Expected When Component Maintenance is Performed Preventative Plugging, obstructions Any cause limiting flow into drywell. Drywell able to receive full flow prior to and during wet season. Site Trash and debris Trash or debris that could end up in the drywell is No trash or debris that could get into evident. the drywell can be found. Pipes Inlet is plugged The entrance to the pipe is restricted due to The entrance to the pipe is not sediment, trash, or debris. restricted. Vegetation/roots Vegetation/roots that reduce free movement of Water flows freely through pipes. water through pipes. Plugged Sediment or other material prevents free flow of Water flows freely through pipes. water through the pipe. Broken or joint leaks. Damage to the pipe or pipe joints allowing water Pipe does not allow water to exit to seep out. other than at the outlet. Structure Basin leaks Holes or breaks in the basin allow water to leave Basin is sealed and allows water to the basin at locations other than per design. exit only where designed. Filter Media Filter media plugged Filter media plugged. Flow through filter media is normal. Inspection Frequency Annually and prior to and following significant Inspect drywell system for any storms. defects of deficiencies. ■ NO. 27 - GRAVEL FILLED DISPERSION TRENCHBMP Maintenance Defect or Problem Conditions When Maintenance is Needed Results Expected When Component Maintenance is Performed Preventative Blocking, obstructions Debris or trash limiting flow to dispersion trench Dispersion trench able to receive full or preventing spreader function. flow prior to and during wet season. Site Trash and debris Trash or debris that could end up in the No trash or debris that could get into dispersion trench is evident. the dispersion trench can be found. Pipes Inlet is plugged The entrance to the pipe is restricted due to The entrance to the pipe is not sediment, trash, or debris. restricted. Vegetation/roots Vegetation/roots that reduce free movement of Water flows freely through pipes. water through pipes. Plugged Sediment or other material prevents free flow of Water flows freely through pipes. water through the pipe. Broken joint or joint Damage to the pipe or pipe joints allowing water Pipe does not allow water to exit leaks. to seep out. other than at the outlet to the trench. Cleanout caps Cleanout caps are broken, missing, or buried. Cleanout caps are accessible and intact. Structure Flow not reaching Flows are not getting into the trench as designed. Water enters and exits trench as trench designed. Perforated pipe Flow not able to enter or properly exit from Water freely enters and exits plugged perforated pipe. perforated pipe. Flow not spreading Outlet flows channelizing or not spreading evenly Sheet flow occurs at the outlet of the evenly at outlet of from trench. trench. trench Cleanout/inspection The cleanout/inspection access is not available. Cleanout/inspection access is access does not allow available. cleaning or inspection of perforated pipe Filter Media Filter media plugged Filter media plugged. Flow through filter media is normal. Inspection Inspection -? Frequency Annually and prior to and following significant Inspect dispersion trench system for storms. any defects of deficiencies. U