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Home My WebLink AboutRS_TIR_Preliminary_Varma_Short_Plat_210326_v1.pdf Western Washington Division Eastern Washington Division 165 NE Juniper St., Ste 201, Issaquah, WA 98027 407 Swiftwater Blvd, Cle Elum, WA 98922 Phone: (425) 392-0250 Fax: (425) 391-3055 Phone: (509) 674-7433 Fax: (509) 674-7419 www.EncompassES.net PRELIMINARY TECHNICAL INFORMATION REPORT For Varma Short Plat 13016 156th Ave SE Renton, WA 98059 March 22, 2021 3/22/2021 Prepared by: Ian Dahl Encompass Engineering Job No. 20544 Prepared For: Kushal Varma 4159 NW Woodgate Avenue Portland, OR 97229 Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | i Table of Contents I. PROJECT OVERVIEW ................................................................................................................ 1 II. CONDITIONS AND REQUIREMENTS SUMMARY ...................................................................... 8 III. OFFSITE ANALYSIS .................................................................................................................. 13 IV. FLOW CONTROL, LOW IMPACT DEVELOPMENT AND WATER QUALITY FACILITY ANALYSIS AND DESIGN ........................................................................................................................... 28 V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN ..................................................................... 32 VI. SPECIAL REPORTS AND STUDIES ............................................................................................ 32 VII. OTHER PERMITS ..................................................................................................................... 32 VIII. CSWPP ANALYSIS AND DESIGN .............................................................................................. 32 IX. BOND QUANTITIES, FACILITY SUMMARIES AND DECLARATION of COVENANT ................... 32 X. OPERATION AND MAINTENANCE MANUAL .......................................................................... 32 List of Figures Figure 1 – TIR Worksheet Figure 2 – Vicinity Map Figure 3 – Soils Map and Legend Figure 4 – Existing Conditions Map Figure 5 – Developed Conditions Map Figure 6 – Drainage Review Flow Chart Figure 7 – East Basin Downstream Map 1 Figure 8 – East Basin Downstream Map 2 Figure 9 – West Basin Downstream Map 1 Figure 10 – West Basin Downstream Map 2 Appendix A Wetland and Stream Reconnaissance for 13016- 156th Ave. SE Renton WA by Altmann Oliver Associates, LLC, dated January 29, 2020. Appendix B Geotechnical Engineering Report by The Riley Group, Inc. dated September 16, 2020 Appendix C WWHM Output CITY OF RENTON SURFACE WATER DESIGN MANUAL 2017 City of Renton Surface Water Design Manual 12/12/2016 8-A-1 REFERENCE 8-A TECHNICAL INFORMATION REPORT (TIR) WORKSHEET Part 1 PROJECT OWNER AND PROJECT ENGINEER Part 2 PROJECT LOCATION AND DESCRIPTION Project Owner _____________________________ Phone ___________________________________ Address __________________________________ _________________________________________ Project Engineer ___________________________ Company _________________________________ Phone ___________________________________ Project Name __________________________ CED Permit # ________________________ Location Township ________________ Range __________________ Section _________________ Site Address __________________________ _____________________________________ Part 3 TYPE OF PERMIT APPLICATION Part 4 OTHER REVIEWS AND PERMITS  Land Use (e.g., Subdivision / Short Subd.)  Building (e.g., M/F / Commercial / SFR)  Grading  Right-of-Way Use  Other _______________________  DFW HPA  COE 404  DOE 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) Type of Drainage Review (check one): Date (include revision dates): Date of Final:  Full  Targeted  Simplified  Large Project  Directed __________________ __________________ __________________ Plan Type (check one): Date (include revision dates): Date of Final:  Full  Modified  Simplified __________________ __________________ __________________ REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 12/12/2016 2017 City of Renton Surface Water Design Manual 8-A-2 Part 6 SWDM ADJUSTMENT APPROVALS Type (circle one): Standard / Blanket Description: (include conditions in TIR Section 2) ____________________________________________________________________________________ ____________________________________________________________________________________ ____________________________________________________________________________________ Approved Adjustment No. ______________________ Date of Approval: _______________________ Part 7 MONITORING REQUIREMENTS Monitoring Required: Yes / No Start Date: _______________________ Completion Date: _______________________ Describe: _________________________________ _________________________________________ _________________________________________ Re: SWDM Adjustment No. ________________ Part 8 SITE COMMUNITY AND DRAINAGE BASIN Community Plan: ____________________________________________________________________ Special District Overlays: ______________________________________________________________ Drainage Basin: _____________________________________________________________________ Stormwater Requirements: _____________________________________________________________ Part 9 ONSITE AND ADJACENT SENSITIVE AREAS  River/Stream ________________________  Lake ______________________________  Wetlands ____________________________  Closed Depression ____________________  Floodplain ___________________________  Other _______________________________ _______________________________  Steep Slope __________________________  Erosion Hazard _______________________  Landslide Hazard ______________________  Coal Mine Hazard ______________________  Seismic Hazard _______________________  Habitat Protection ______________________  _____________________________________ REFERENCE 8-A: TECHNICAL INFORMATION REPORT (TIR) WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 2017 City of Renton Surface Water Design Manual 12/12/2016 Ref 8-A-3 Part 10 SOILS Soil Type ______________________ ______________________ ______________________ ______________________ Slopes ________________________ ________________________ ________________________ ________________________ Erosion Potential _________________________ _________________________ _________________________ _________________________  High Groundwater Table (within 5 feet)  Other ________________________________  Sole Source Aquifer  Seeps/Springs  Additional Sheets Attached Part 11 DRAINAGE DESIGN LIMITATIONS REFERENCE  Core 2 – Offsite Analysis_________________  Sensitive/Critical Areas__________________  SEPA________________________________  LID Infeasibility________________________  Other________________________________  _____________________________________ LIMITATION / SITE CONSTRAINT _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________  Additional Sheets Attached 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:__________________ Flow Control (include facility summary sheet) Standard: _______________________________ or Exemption Number: ____________ On-site BMPs: _______________________________ Conveyance System Spill containment located at: _____________________________ Erosion and Sediment Control / Construction Stormwater Pollution Prevention CSWPP/CESCL/ESC Site Supervisor: _____________________ Contact Phone: _________________________ After Hours Phone: _________________________ REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 12/12/2016 2017 City of Renton Surface Water Design Manual 8-A-4 Part 12 TIR SUMMARY SHEET (provide one TIR Summary Sheet per Threshold Discharge Area) Maintenance and Operation Responsibility (circle one): Private / Public If Private, Maintenance Log Required: Yes / No Financial Guarantees and Liability Provided: Yes / No Water Quality (include facility summary sheet) Type (circle one): Basic / Sens. Lake / Enhanced Basic / Bog or Exemption No. _______________________ Special Requirements (as applicable): Area Specific Drainage Requirements Type: SDO / MDP / BP / Shared Fac. / None Name: ________________________ Floodplain/Floodway Delineation Type (circle one): Major / Minor / Exemption / None 100-year Base Flood Elevation (or range): _______________ Datum: Flood Protection Facilities Describe: Source Control (commercial / industrial land use) Describe land use: Describe any structural controls: Oil Control High-Use Site: Yes / No Treatment BMP: _________________________________ Maintenance Agreement: Yes / No with whom? _____________________________________ Other Drainage Structures Describe: REFERENCE 8-A: TECHNICAL INFORMATION REPORT (TIR) WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 2017 City of Renton Surface Water Design Manual 12/12/2016 Ref 8-A-5 Part 13 EROSION AND SEDIMENT CONTROL REQUIREMENTS MINIMUM ESC REQUIREMENTS DURING CONSTRUCTION  Clearing Limits  Cover Measures  Perimeter Protection  Traffic Area Stabilization  Sediment Retention  Surface Water Collection  Dewatering Control  Dust Control  Flow Control  Control Pollutants  Protect Existing and Proposed BMPs/Facilities  Maintain Protective BMPs / Manage Project MINIMUM ESC REQUIREMENTS AFTER CONSTRUCTION  Stabilize exposed surfaces  Remove and restore Temporary ESC Facilities  Clean and remove all silt and debris, ensure operation of Permanent BMPs/Facilities, restore operation of BMPs/Facilities as necessary  Flag limits of sensitive areas and open space preservation areas  Other _______________________ 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  On-site BMPs  Other ________________ ________________ ________________ ________________ ________________ ________________  Vegetated Flowpath  Wetpool  Filtration  Oil Control  Spill Control  On-site BMPs  Other ________________ ________________ ________________ ________________ ________________ ________________ ________________ Part 15 EASEMENTS/TRACTS Part 16 STRUCTURAL ANALYSIS  Drainage Easement  Covenant  Native Growth Protection Covenant  Tract  Other ____________________________  Cast in Place Vault  Retaining Wall  Rockery > 4′ High  Structural on Steep Slope  Other _______________________________ REFERENCE 8: PLAN REVIEW FORMS AND WORKSHEET TECHNICAL INFORMATION REPORT (TIR) WORKSHEET 12/12/2016 2017 City of Renton Surface Water Design Manual 8-A-6 Part 17 SIGNATURE OF PROFESSIONAL ENGINEER 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 Information Report. To the best of my knowledge the information provided here is accurate. ____________________________________________________________________________________ Signed/Date Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 1 I. PROJECT OVERVIEW Project: Varma Short Plat Site Address: 13016 156th Ave SE Renton, WA 98059 (See Vicinity Map) Tax Parcel #: 366450-0205 & 366450-0185 Zoning District: R-4, Residential Site Area: 140,421 SF (3.22 Acres) Site Location: The site is in the City of Renton within the NE quarter of Section 14, Township 23 North, Range 5 East, W.M, King County, Washington. The site is located on the east side of 156th Ave SE, approximately 250 feet north of the intersection of SE 132nd St and 156th Ave SE. Figure 2: Vicinity Map Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 2 Pre-developed Site Conditions The project site is located in the City of Renton, consisting of two adjacent parcels totaling 140,421 SF (3.22 Acres) that are zoned R-4 (Residential). The west side of the site is accessed from 156th Ave SE, approximately 250 feet north of the intersection of SE 132nd St and 156th Ave SE. The east side of the site is accessed on 158th Ave SE, approximately 450 feet north of the intersection of SE 2nd Pl and 158th Ave SE. The site is bordered to the north and south by single- family residences, to the west by City of Renton ROW, and to the east by King County ROW. The site is currently developed with a single-family residence on the far west side of parcel 366450-0205 accessed from a gravel driveway on the east side of 156th Ave SE. North of the residence, the area encompassing parcel 366450-0185 has been cleared and consists of open grass and a few stockpiles of sand and gravel. To the east of the residence, the remainder of site is undeveloped and consists of a mixed upland forest and brush patches. The site is gently sloped to the south and southeast at slopes of 0-2%. The property is located within the Lower Cedar River drainage basin, however it has two separate discharge areas. Runoff from the eastern portion of the site sheet flows south and east into a roadside ditch on the west side of 158th Ave SE and flows south through a series of ditches and culverts. Runoff from the western portion of the site sheet flows south and west into a roadside ditch on the east side of 156th Ave SE and also flows south through a series of ditches and culverts. These two flow paths do not converge within a ¼ of a mile; therefore, the two separate Natural Discharge Areas have been described and modeled as two separate Threshold Discharge Areas. See full downstream analysis in Section III of this Technical Information Report (TIR). An Existing Conditions Map is included as Figure 4 at the end of this Section. Critical Areas According to COR Maps, and the Wetland and Stream Reconnaissance dated January 29, 2020, no critical areas are located on the project site. Soils Per the US Department of Agriculture (USDA), Natural Resources Conservation Service (NR CS) Web Soil Survey (WSS) information, the entire project site is underlain with Alderwood gravelly sandy loam, 8 to 15 percent slopes (See Figure 3 on the following page). Soils encountered in on- site investigations include medium dense silty sand with gravel over very dense glacial till per the Geotechnical Engineering Report prepared by The Riley Group, Inc. (Appendix B). Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 3 Figure 3: Soil Map and Legend Developed Site Conditions The project proposes the development of nine (9) single-family lots within the 140,421 SF (3.22 Acres) parcel, as well as a 5.5-foot right-of-way dedication with frontage improvements along 156th Ave SE. A residential access street will traverse east to west across the site giving access to each lot via paved driveways. Frontage improvements along 156th Ave SE and 158th Ave SE will include the addition of a 5-foot sidewalk, 8-foot planter strip, as well as curb and gutter along the edge of asphalt roadway. On the west side of the site, the residential access street will include a 5-foot sidewalk, 8-foot planter strip as well as curb and gutter on both side of the street. On the east side of the site, a 5-foot sidewalk, 8-foot planter strip as well as curb and gutter will only be present on the south side of the street. The parcel is zoned R-4, which allows for a maximum building coverage of 35% and a maximum impervious surface coverage of 50%. The final site layout of each Lot has not been determined Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 4 at this stage; therefore, this report assumes that the future impervious surfaces required to construct the residences on all lots will use the maximum coverages stated above. The maximum allowable building/impervious surface for each lot is discussed below: • Lot 1: The maximum allowable building coverage for Lot 1 is 16,333 SF*0.35 = 5,717 SF, and the maximum impervious surface coverage is 16,333 SF*0.50 = 8,167 SF. • Lot 2: The maximum allowable building coverage for Lot 2 is 12,284 SF*0.35 = 4,299 SF, and the maximum impervious surface coverage is 12,284 SF*0.50 = 6,142 SF. • Lot 3: The maximum allowable building coverage for Lot 3 is 12,550 SF*0.35 = 4,393 SF, and the maximum impervious surface coverage is 12,550 SF*0.50 = 6,275 SF. • Lot 4: The maximum allowable building coverage for Lot 4 is 9,909 SF*0.35 = 3,468 SF, and the maximum impervious surface coverage is 9,909 SF*0.50 = 4,955 SF. • Lot 5: The maximum allowable building coverage for Lot 5 is 10,185 SF*0.35 = 3,565 SF, and the maximum impervious surface coverage is 10,185 SF*0.50 = 5,093 SF. • Lot 6: The maximum allowable building coverage for Lot 6 is 10,179 SF*0.35 = 3,563 SF, and the maximum impervious surface coverage is 10,179 SF*0.50 = 5,090 SF. • Lot 7: The maximum allowable building coverage for Lot 7 is 10,174 SF*0.35 = 3,561 SF, and the maximum impervious surface coverage is 10,174 SF*0.50 = 5,087 SF. • Lot 8: The maximum allowable building coverage for Lot 8 is 10,168 SF*0.35 = 3,559 SF, and the maximum impervious surface coverage is 10,168 SF*0.50 = 5,084 SF. • Lot 9: The maximum allowable building coverage for Lot 9 is 10,162 SF*0.35 = 3,557 SF, and the maximum impervious surface coverage is 10,162 SF*0.50 = 5,081 SF. Stormwater runoff from the proposed development of Lots 1-9 as well as the proposed road improvements on 156th Ave SE, 158th Ave SE, and the Residential Access street will be managed as follows: • Lots 1-9: Stormwater from impervious areas including rooftop and driveways on Lots 1 and 4 will be conveyed to Tract A, and into a wet vault followed by three detention tanks before it is conveyed south and eventually released into the roadside ditch along the east side of 156th Ave SE. Stormwater from impervious areas including rooftop and driveways on Lots 2, 3, and 5-9 will be conveyed to Tract B, and into a combination wetvault/detention vault before entering a new storm conveyance system on 158th Ave SE, and eventually released into the ditch on the west side of 158th Ave SE. Where feasible, BMP’s satisfying Core Requirement #9 will be used to the maximum extent feasible to mitigate other new runoff Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 5 created by the proposed single-family residence and other impervious surfaces on-site. Basic dispersion will be used on some residences to mitigate stormwater from rooftop areas. • Residential Access Street: Stormwater from roadway improvements on the Residential Access Street will be conveyed through the on-site storm system to the wetvault/detention vault on Tract B. • 156th Ave SE: Stormwater from the improved roadway north of the intersection of 156th Ave SE and the Residential Access Street will flow into a series of 3 catch basins on the east side of 156th Ave SE which convey the stormwater to a wet vault and detention tank facility on Tract A. South of this intersection, stormwater will follow existing drainage patterns and sheet flow into the ditch on the east side of 156th Ave SE. • 158th Ave SE: Stormwater on 158th Ave SE will enter a series of catch basins and flow south down the center of 158th Ave SE. At the intersection of 158th Ave SE and NE 2nd Pl, the stormwater will enter the existing ditch on the west side of the road and follow existing drainage patterns to the south. Please refer to Core Requirement # 9 in Section II and Section IV of this TIR for additional discussion on stormwater BMPs. A Developed Conditions Map is provided as Figure 5 at this end of this Section. 03/22/2021 03/22/2021 Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 8 II. CONDITIONS AND REQUIREMENTS SUMMARY The 2017 City of Renton Surface Water Design Manual (RSWDM) was utilized to determine and address all core and special requirements. Based on the criteria specified in Figure 1.1.2.A of the RSWDM, the project falls under Full Drainage Review. Per Section 1.1.2.4 of the RSWDM, the project must meet all nine (9) core and all six (6) special requirements. See Figure 6 below for more information on how the type of drainage review was determined. Figure 6: Drainage Review Flow Chart Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 9 Core Requirements Core Requirement #1: Discharge at the Natural Location The proposed development will follow existing drainage patterns in which runoff flows south in roadside ditches on 156th Ave SE and 158th Ave SE. Stormwater from frontage improvements on 156th Ave SE will be detained and treated on Tract A before being released into the roadside ditch on the east side of 156th Ave SE south of the project site. Stormwater from the remainder of the project will be detained and treated on Tract B and conveyed 400-feet south in a new conveyance pipe system before being released into the roadside ditch on the west side of 158th Ave SE. Refer to the Level 1 Downstream Analysis in Section III of this TIR for a complete description of the existing drainage paths. Core Requirement #2: Downstream Analysis A Level 1 Downstream analysis has been completed for the site and no existing or potential problems have been identified. This analysis is included in Section III of this TIR. Core Requirement #3: Flow Control Facilities Based on the City of Renton’s flow control application map, the project site is located within the Flow Control Duration Standard (Forested Conditions). Flow control facilities are required to match the flow duration of pre-developed rates for forested (historical) site conditions over the range of flows extending from 50% of 2-year up to the full 50- year flow and matches the peaks for the 2- and 10- year return periods. The proposed detention facilities result in matching the flow duration of pre-developed rates from 50% of 2-year to 50-year as well as matching developed peak discharge rates to predeveloped peak discharge rates for the 2- and 10-year return periods. This meets the requirements of Flow Control Duration Standard (Forested Conditions) per Section 1.2.3.1.B of the RSWDM. Please refer to Appendix B for a copy of the full WWHM data output. Core Requirement #4: Conveyance System Conveyance in compliance with the requirements detailed in Section 1.2.4.1 of the City of Renton 2017 SWDM will be provided with final engineering. Core Requirement #5: Construction Stormwater Pollution Prevention A temporary erosion and sediment control (TESC) plan providing details on best management practices (BMPs) to be implemented during construction is included in the engineering plan set. A Construction Stormwater Pollution Prevention Plan (CSWPPP) will be provided with final engineering. Core Requirement #6: Maintenance and Operations An Operation and Maintenance Manual will be provided with final engineering. Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 10 Core Requirement #7: Financial Guarantees and Liability The owner will arrange for any financial guarantees and liabilities required by the permit. Core Requirement #8: Water Quality Facilities Water quality facilities have been designed according to Section 1.2.8 of the RSWDM and KCSWDM and will be located on Tract A & B. Refer to Section IV of this TIR for Water Quality Analysis and Design. Core Requirement #9: Flow Control BMPs This project is classified as a subdivision; therefore, it is subject to the Subdivision and Road Improvement Projects BMP Requirements detailed in Section 1.2.9.3 in the RSWDM. Although implementation of individual lot BMPs is not required until building permit application, BMPs have been considered for the future improvements on Lots 1-9 based on Section 1.2.9.2 and of the RSWDM. See Section IV of this TIR for further discussion and flow control analysis. Impervious Surface BMPs Full Dispersion: Infeasible. The space required for an 100-foot native vegetated flowpath segment is not available on the proposed lots. Full Infiltration: Infeasible. The Geotechnical Engineering Report prepared by The Riley Group, Inc. dated September 16, 2020 dated August 20, 2020 (Appendix B) states that infiltration is infeasible at the site due to underlain glacial till and confirmed by an in-situ infiltration test. Limited Infiltration: Infeasible. BMP’s relying on infiltration are not feasible as described above. Rain Gardens/Bioretention: Infeasible. BMP’s relying on infiltration are not feasible as described above. Permeable Pavement: Infeasible. The Infiltration Assessment prepared by The Riley Group, Inc. dated September 2, 2020 (Appendix B) states that permeable pavement is infeasible due to the shallow depth of lodgment till on the project site. Basic Dispersion: Feasible. 50-foot Basic Dispersion trenches with notched board and 25- foot native vegetated flowpaths are proposed for Lots 1-9. The maximum area of 3,500 SF will be conveyed to these trenches from the rooftops of the residences. Reduced Impervious Surface Credit: Infeasible. The maximum impervious surfaces per zoning were assumed for Lots 1-9 and exceed the threshold of 4,000 SF, which is required for eligibility for a reduced impervious surface credit. Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 11 Native Growth Retention Credit: Infeasible. The necessary area to allow for 3.5 SF of native vegetated surface for every SF of impervious surface is not available on lots 1-9. Tree Retention Credit: Feasible. At least 30% of significant trees will be retained per Department of Community and Economic Development notes in the Pre -Application Meeting. Soil Amendment: Feasible. All disturbed, pervious areas of the project will meet soil amendment requirements as detailed in Section C.2.13 of the RSWDM. Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 12 Special Requirements Special Requirement #1: Other Adopted Area-Specific Requirements Master Drainage Plans– N/A Basin Plan – N/A Salmon Conservation Plans- N/A Lake Management Plans – N/A Hazard Mitigation Plan- N/A Shared Facility Drainage Plans – N/A Special Requirement #2: Flood Hazard Area Delineation The limits of this project do not lie within a delineated FEMA 100-year floodplain. Special Requirement #3: Flood Protection Facilities This project does not rely on or propose to modify/construct a new flo od protection facility. Special Requirement #4: Source controls The project is not a commercial building or development; therefore, this requirement is not applicable. Special Requirement #5: Oil Control This project is not considered high-use in need of oil control. Special Requirement #6: Aquifer Protection Area The site is not located within an Aquifer Protection Area. Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 13 III. DOWNSTREAM ANALYSIS A Level 1 Downstream analysis has been conducted per the requirements in Section 1.2.2.1 of the RSWDM. As two Threshold Discharge Areas exist, two separate analysis were completed. Please see Tasks 1 through 4 below for a summary of the results for the east basin, followed by the west basin. East Basin Task 1: Define and Map the Study Area A Level 1 Offsite Analysis has been performed for the project site per Section 1.2.2.1 of the 2017 City of Renton Surface Water Design Manual. The project site is comprised of a two adjacent tax parcels; 366450-0205 & 366450-0185. The northern property (366450-0185) is currently undeveloped, and has been partially cleared by previous development to the north. The southern property (366450-0205) is currently developed with a single-family residence, a gravel driveway access, and several outbuildings. The majority of the site is covered with trees and vegetation. The site is contained within a single drainage basin, the Lower Cedar River, but discharges from two separate locations. The two flowpaths do not converge within ¼ mile downstream of the site, and therefore two Level 1 downstream analyses are required for this proj ect. The Eastern Drainage basin, detailed in this Analysis, is approximately 2.36 acres in size. Slopes range from 1-10% across the site. The study area for this analysis extends downstream for approximately one quarter mile and includes no upstream offsite drainage area tributary to the project site. The neighboring property to the north, while located at a higher elevation, has been previously developed and does not direct significant stormwater runoff to the subject property. A map showing the study area is included in Figures 7 & 8 Below. Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 14 Figure 7: East Basin Downstream Map 1 Figure 8: East Basin Downstream Map 2 Task 2: Review All Available Information on the Study Area Encompass has reviewed the site and the applicable resources for both listed and potential problems. The receiving waterbody, Lower Cedar River, is impaired at a Category 5 – 303d level for pH, Temperature, and Dissolved Oxygen per the Washington Depa rtment of Ecology Water Quality Atlas. No other critical areas or critical area buffers were located on the site per King County iMap, the City of Renton GIS maps, FEMA maps, or the CED Wetlands Inventory. Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 15 Task 3: Field Inspect the Study Area A Level 1 Downstream Analysis was performed by Encompass Engineering & Surveyin g on Wednesday June 10, 2020. The analysis was performed at approximately 3:30 PM with a temperature of about 75°. Soil conditions were observed to be saturated. The tributary basin detailed in Task 1 was confirmed during the site visit. Information collec ted during this study is included in the Task 4 system description. Task 4: Describe the Drainage System The site is divided into two drainage basins. An approximate “basin line” has been added to the downstream map to reflect this information. The easter n basin directs stormwater runoff south and east towards the 158th Avenue SE system as detailed below. Stormwater runoff from the eastern basin sheet flows (Map Element: A) to the sou th and east across the property line where it enters a stormwater ditch (B) along the west side of 158th Ave SE. This ditch conveys flows south along 158 th Ave SE through a series of culverts for driveway access (Elements C, D, E, F, G, H, and I). Runoff is then directed into sections of 12” Polyethylene culverts (J, K, L, and M) which convey stormwater under NE 1st St. The 158th Ave SE system collects runoff via catch basins within the public right-of-way as well as tie-ins from other residential development. The 12” Polyethylene pipe (M) discharges to a series of stormwater d itches (N, P, R, and T) which are interrupted by 12” Polyethylene (O, Q) culverts and a 12” Concrete culvert (S) for conveyance under driveway accesses. Element T directs stormwater into the SE 2nd Pl system which ultimately discharges runoff into the Lower Cedar River and the Lake Washington watershed. This Analysis was ended at a point over ¼ mile downstream of the site discharge location within Element T. Element B: Stormwater ditch along west side of 158th Ave SE Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 16 Element C: 12” Concrete culvert Element E: 12” Concrete Culvert Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 17 Element F: 12” CPP Culvert Element H: 12” Concrete Culvert Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 18 Element B: Stormwater ditch continued Element J: 12” Polyethylene culvert connecting to elements K, L, and M under 158 th Ave SE Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 19 Elements M and N: Outlet from 12” Polyethylene culvert into Stormwater ditch #2 Elements N, O, P, and Q: Along 158th Ave SE Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 20 West Basin Task 1: Define and Map the Study Area A Level 1 Offsite Analysis has been performed for the project site per Section 1.2.2.1 of the 2017 City of Renton Surface Water Design Manual. The project site is comprised of a two adjacent tax parcels; 366450-0205 & 366450-0185. The northern property (366450-0185) is currently undeveloped, and has been partially cleared by previous develop ment to the north. The southern property (366450-0205) is currently developed with a single-family residence, a gravel driveway access, and several outbuildings. The majority of the site is covered with trees and vegetation. The site is contained within a single drainage basin, the Lower Cedar River, but discharges from two separate locations. The two flowpaths do not converge within ¼ mile downstream of the site, and therefore two Level 1 downstream analyses are required for this project. The Western Drainage basin, detailed in this Analysis, is approximately 0.86 acres in size. Slopes range from 1-10% across the site. The study area for this analysis extends downstream for approximately one quarter mile and includes no upstream offsite drainage area trib utary to the project site. The neighboring property to the north, while located at a higher elevation, has been previously developed and does not direct significant stormwater runoff to the subject property. A map showing the study area is included in Figures 9 & 10. Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 21 Figure 9: West Basin Downstream Map 1 Figure 10: West Basin Downstream Map 2 Task 2: Review All Available Information on the Study Area Encompass has reviewed the site and the applicable resources for both listed and potent ial problems. The receiving waterbody, Lower Cedar River, is impaired at a Category 5 – 303d level for pH, Temperature, and Dissolved Oxygen per the Washington Department of Ecology Water Quality Atlas. No other critical areas or critical area buffers were located on the site per King County iMap, the City of Renton GIS maps, FEMA maps, or the CED Wetlands Inventory. Task 3: Field Inspect the Study Area A Level 1 Downstream Analysis was performed by Encompass Engineering & Surveying on Wednesday June 10, 2020. The analysis was performed at approximately 3:30 PM with a temperature of about 75°. Soil conditions were observed to be saturated. The tributary basin detailed in Task 1 was confirmed during the site visit. Information collected during this study is included in the Task 4 system description. Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 22 Task 4: Describe the Drainage System The site is divided into two drainage basins. An approximate “basin line” has been added to the downstream map to reflect this information. The western basin directs stormwate r runoff west towards the 156th Avenue SE system as detailed below. Stormwater runoff from the western basin sheet flows (Map Element: A) to the south and west across the property line where it enters a stormwater ditch (B) along the east side of 156 th Ave SE. This ditch conveys flows south along 156 th Ave SE through a series of culverts for driveway access (Elements C, D, E, F, G, H, and I). Runoff is then directed into a 12” Concrete culvert (J) which marks the beginning of the 156th Ave SE closed conveyance system. Element J continues to direct flows south into a section of 12” Ductile Iron pipe (K) which transitions to 12” Polyethylene pipe (Elements L, M, N, and O). This system collects runoff via catch basins within the public right-of-way as well as tie-ins from other residential development. The 12” Polyethylene pipe (O) continues to convey stormwater south, and ultimately discharges runoff into the Lower Cedar River and the Lake Washington watershed. This Analysis was ended at a point over ¼ mile downstream of the site discharge location within Element O. See Figure X: Downstream Map and the photos on the following pages for more info rmation. Existing residence and site access from 156th Ave SE Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 23 Element B: Stormwater ditch along east side of 156th Ave SE Element C: Obstructed culvert at property driveway access Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 24 Element D: 12” CPP Culvert Element E: 12” CPP Culvert Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 25 Element F: 12” Concrete Culvert Element H: 12” Concrete Culvert Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 26 Element J: 12” Concrete Culvert Elements K, L, and M: 12” Polyethylene pipe continues south under 156 th Ave SE Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 27 Element O: 12” Polyethylene pipe continues south under 156th Ave SE Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 28 IV. FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN Part A: Existing Site Hydrology The 140,421 SF (3.22 AC) site is currently developed with a single-family residence on the far west side of parcel 366450-0205 accessed from a gravel driveway om the east side of 156th Ave SE. North of the residence, the area encompassing parcel 366450-0185 has been cleared and consists of open grass and a few stockpiles of sand and gravel. To the east of the residence, the remainder of site is undeveloped and consists of a mixed upland forest and brush patches. The site is gently sloped to the south and southeast at slopes of 0-2%. The property is located within the Lower Cedar River drainage basin, however it has two separate discharge areas. Runoff from the eastern portion of the site sheet flows south and east into a roadside ditch on the west side of 158 th Ave SE and flows south through a series of ditches and culverts. Runoff from the western portion of the site sheet flows south and west into a roadside ditch on the east side of 156th Ave SE and also flows south through a series of ditches and culverts. These two flow paths do not converge within a ¼ of a mile; therefore, the two separate Natural Discharge Areas ha ve been described and modeled as two separate Threshold Discharge Areas (TDAs). See full downstream analysis in Section III of this Technical Information Report (TIR). Per the US Department of Agriculture (USDA), Natural Resources Conservation Service (NRCS) Web Soil Survey (WSS) information, the entire project site is underlain with Alderwood gravelly sandy loam, 8 to 15 percent slopes (See Figure 3 on the following page). Soils encountered in on- site investigations include medium dense silty sand with gravel over very dense glacial till per the Geotechnical Engineering Report prepared by The Riley Group, Inc. (Appendix B). WWHM 2012 was used to model the 150,469 SF (3.45 AC) limits of disturbance using the forested condition. Part B: Developed Site Hydrology Using WWHM, a wet vault and detention tank has been sized for the west basin, and a combination wetvault/detention vault has been sized for the east basin. This program automatically sized the tanks as level 3 flow control facilities. The predeveloped basin areas were modeled as forest. This analysis assumes the maximum impervious per lots 1-9 in the developed condition as described in Section I of this TIR. This limit will be recorded on the face of the final short plat. The West TDA includes Tract A, frontage and half-street improvements on 156th Ave SE, portions of Lots 1 & 4, as well as a portion of the Residential Access Street and associated frontage. The East TDA includes the remaining portions of Lots 1 & 4, Lots 2, 3, 5-9, Tract B, the frontage and half street improvements on 158th Ave SE, as well as the remaining portion of the Residential Access Street and associated frontage. All developed pervious are modeled as pasture due to the use of soil amendment BMPs as outlined in the 2017 Renton SWDM Appendix C, Section C.2.13.1. The results of this analysis are shown on the following page. See Stream Protection Duration Graphs and Existing and Developed Conditions Maps on at the end of this section. Full WWHM output is included in Appendix C. Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 29 West TDA Predeveloped Mitigated The Tank for the North TDA was sized with a storage volume of 0.149 Acre-Ft or 6,504 CU-FT. The water quality volume for the North Vault is 0.0503 Acre-Ft or 2,191 CU-FT. East TDA Predeveloped Mitigated The vault for the South TDA was sized with a storage volume of 0.8007 Acre-FT or 34,880 CU- FT. The water quality volume for the South Vault is 0.2426 Acre-FT or 10,568 CU-FT. Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 30 West Vault Stream Protection Duration Graph East Vault Stream Protection Duration Graph Part C: Performance Standards Based on the City of Renton’s flow control map, the project site is located within the Flow Control Duration Standard (Forested Conditions). Flow control facilities are required to match the flow duration of pre-developed rates for forested (historical) site conditions over the range of flows extending from 50% of 2-year up to the full 50-year flow and matches the peaks for the 2- and 10- year return periods. Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 31 In addition, this project is classified as a subdivision; therefore, it is subject to the Subdivision and Road Improvement Projects BMP Requirements detailed in Section 1.2.9.3 in the RSWDM. The site falls within a Basic Water Quality treatment area in accordance with Section 1.2.8.1.A of the RSWDM. Part D: Flow Control System As shown in the tables below, the proposed detention facilities result in matching the developed peak discharge rates to predeveloped peak discharge rates for the 2- and 10-year return periods. This meets the requirements of Flow Control Duration Standard (Forested Conditions) per Section 1.2.3.1.B of the RSWDM. Please refer to Appendix B for a copy of the full WWHM data output. West TDA East TDA Part E: Water Quality System Water Quality has been provided for both TDAs treating runoff from the target surfaces in accordance with Section 1.2.8.1.A of the RSWDM. A volume of 0.149 Acre-Ft or 6,504 CU-FT has been provided for the West TDA in the form of a wet vault, and a volume of 0.8007 Acre-FT or 34,880 CU-FT has been provided for the East TDA in the form of an combination wetvault/detention vault. Varma Short Plat Preliminary Technical Information Report 3/22/2021 P a g e | 32 V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN A conveyance system analysis will be provided with final engineering VI. SPECIAL REPORTS AND STUDIES • Geotechnical Engineering Report by The Riley Group, Inc. dated September 16, 2020 • Infiltration Assessment by The Riley Group, Inc. dated September 2, 2020 • Wetland and Stream Reconnaissance for 13016- 156th Ave. SE Renton WA by Altmann Oliver Associates, LLC, dated January 29, 2020. VII. OTHER PERMITS • Civil Construction Permit • Final Short Plat • Building Permits • Right-of-Way Use Permit VIII. CSWPP ANALYSIS AND DESIGN A CSWPPP will be provided with final engineering. IX. BOND QUANTITIES, FACILITY SUMMARIES AND DECLARATION of COVENANT Bond Quantities, Facility Summary and Declaration of Covenant to be provided with Final Engineering. X. OPERATION AND MAINTENANCE MANUAL An Operation and Maintenance Manual to be provided with Final Engineering. Varma Short Plat Preliminary Technical Information Report Appendix A Wetland and Stream Reconnaissance for 13016- 156th Ave. SE Renton WA by Altmann Oliver Associates, LLC, dated January 29, 2020. January 29, 2020 AOA-6125 Dan Finkbeiner danfinkbeiner@comcast.net SUBJECT: Wetland and Stream Reconnaissance for 13016 – 156th Ave. SE Renton, WA (Parcels 366450-0185 an -0205) Dear Dan: On January 21, 2020 I conducted a wetland and stream reconnaissance on the subject property utilizing the methodology outlined in the May 2010 Regional Supplement to the Corps of Engineers Wetland Delineation Manual: Western Mountains, Valleys, and Coast Region (Version 2.0). No wetlands or streams were identified on or adjacent to the property during the field investigation. The western portion of the site on Parcel 366450-0205 is currently developed with a single-family residence and associated yard. The remainder of this parcel is undeveloped and consisted of a mixed upland forest and brush patches that included Douglas fir (Pseudotsuga menziesii), western red cedar (Thuja plicata), Himalayan blackberry (Rubus armeniacus), English holly (Ilex aquilinum), sword fern (Polystichum munitum), and English ivy (Hedera helix). Parcel 366450-0185 consisted primarily of upland pasture and fill areas. Common plant species were generally typical of disturbed more mesic environments and included a variety of grasses, cats ear (Hypochaeris radicata), English plantain (Plantago lanceolata), and oxeye daisy (Chrysanthemum leucanthemum). No hydrophytic plant communities were observed on or adjacent to the property. Borings taken throughout the site revealed high chroma non-hydric soils and there was no evidence of ponding or prolonged soil saturation anywhere in the vicinity of the property. Dan Finkbeiner January 29, 2020 Page 2 Conclusion No wetlands or streams were identified on or immediately adjacent the site. This determination is based on a field investigation during which no hydrophytic plant communities, hydric soils, or evidence of wetland hydrology or channels were observed. If you have any questions regarding the reconnaissance, please give me a call. Sincerely, ALTMANN OLIVER ASSOCIATES, LLC John Altmann Ecologist P icto m etr y, Ki ng C oun ty, Ki ng Coun ty King C ou nty iMap Date: 1 /29 /20 20 Notes: Th e infor matio n in clu de d on t his map has been comp ile d b y Kin g Count y staf f from a variety of source s an d is su bject to cha ng ewithout n otice. Kin g Co unt y makes no re present ations o r wa rra nties, exp re ss o r im plied , a s to accu ra cy, complet en ess, t ime lin ess,or rig hts to the use of such informa tion . This d ocu me nt is not intended for u se as a survey pr od uct. King Cou nty shall n ot be lia blefor a ny g en er al, sp ecial, indirect, incide ntal, o r conse qu en tial damag es including , but not limited to , lost revenu es or lo st profitsresulting from th e use or m isu se of t he info rmat ion cont aine d on this map . An y sale of this map or in formation o n t his map isprohibited except by written p er mission of King County.± Varma Short Plat Preliminary Technical Information Report Appendix B Geotechnical Engineering Report by The Riley Group, Inc. dated September 16, 2020 Corporate Office 17522 Bothell Way Northeast Bothell, Washington 98011 Phone 425.415.0551 ♦ Fax 425.415.0311 www.riley-group.com GEOTECHNICAL ENGINEERING REPORT PREPARED BY: THE RILEY GROUP, INC. 17522 BOTHELL WAY NORTHEAST BOTHELL, WASHINGTON 98011 PREPARED FOR: KUSHAL VARMA 4159 NORTHWEST WOODGATE AVENUE PORTLAND, OREGON 97229 RGI PROJECT NO. 2020-317-1 VARMA SHORT PLAT 13016 156TH AVENUE SOUTHEAST RENTON, WASHINGTON SEPTEMBER 16, 2020 Geotechnical Engineering Report i September 16, 2020 Varma Short Plat, Renton, Washington RGI Project No. 2020-317-1 TABLE OF CONTENTS 1.0 INTRODUCTION ............................................................................................................................... 1 2.0 PROJECT DESCRIPTION ............................................................................................................... 1 3.0 FIELD EXPLORATION AND LABORATORY TESTING .......................................................... 1 3.1 FIELD EXPLORATION ................................................................................................................................... 1 3.2 LABORATORY TESTING ................................................................................................................................ 2 4.0 SITE CONDITIONS ........................................................................................................................... 2 4.1 SURFACE .................................................................................................................................................. 2 4.2 GEOLOGY ................................................................................................................................................. 2 4.3 SOILS ....................................................................................................................................................... 2 4.4 GROUNDWATER ........................................................................................................................................ 3 4.5 SEISMIC CONSIDERATIONS ........................................................................................................................... 3 4.6 GEOLOGIC HAZARD AREAS .......................................................................................................................... 4 5.0 DISCUSSION AND RECOMMENDATIONS ................................................................................. 4 5.1 GEOTECHNICAL CONSIDERATIONS ................................................................................................................. 4 5.2 EARTHWORK ............................................................................................................................................. 4 5.2.1 Erosion and Sediment Control ..................................................................................................... 4 5.2.2 Stripping and Subgrade Preparation ............................................................................................ 5 5.2.3 Excavations................................................................................................................................... 6 5.2.4 Structural Fill ................................................................................................................................ 6 5.2.5 Wet Weather Construction Considerations ................................................................................. 8 5.3 FOUNDATIONS .......................................................................................................................................... 8 5.4 RETAINING WALLS ..................................................................................................................................... 9 5.5 SLAB-ON-GRADE CONSTRUCTION ................................................................................................................. 9 5.6 DRAINAGE .............................................................................................................................................. 10 5.6.1 Surface ....................................................................................................................................... 10 5.6.2 Subsurface .................................................................................................................................. 10 5.6.3 Infiltration .................................................................................................................................. 10 5.7 UTILITIES ................................................................................................................................................ 10 6.0 ADDITIONAL SERVICES .............................................................................................................. 11 7.0 LIMITATIONS ................................................................................................................................. 11 LIST OF FIGURES AND APPENDICES Figure 1 ..................................................................................................................... Site Vicinity Map Figure 2 ............................................................................................... Geotechnical Exploration Plan Figure 3 ............................................................................................... Retaining Wall Drainage Detail Figure 4 ....................................................................................................Typical Footing Drain Detail Appendix A .......................................................................... Field Exploration and Laboratory Testing Geotechnical Engineering Report ii September 16, 2020 Varma Short Plat, Renton, Washington RGI Project No. 2020-317-1 Executive Summary This Executive Summary should be used in conjunction with the entire Geotechnical Engineering Report (GER) for design and/or construction purposes. It should be recognized that specific details were not included or fully developed in this section, and the GER must be read in its entirety for a comprehensive understanding of the items contained herein. Section 7.0 should be read for an understanding of limitations. RGI’s geotechnical scope of work included the advancement of 4 test pits and 2 hand augers to approximate depths of 4.5 feet below existing site grades. Based on the information obtained from our subsurface exploration, the site is suitable for development of the proposed project. The following geotechnical considerations were identified: Soil Conditions: The soils encountered during field exploration include medium dense silty sand with gravel over very dense glacial till. Groundwater: No groundwater seepage was encountered during our subsurface exploration. Foundations: Foundations for the proposed residences may be supported on conventional spread footings bearing on medium dense to dense native soil or structural fill. Slab-on-grade: Slab-on-grade floors and slabs for the proposed residences can be supported on medium dense to dense native soil or structural fill. Geotechnical Engineering Report 1 September 16, 2020 Varma Short Plat, Renton, Washington RGI Project No. 2020-317-1 1.0 Introduction This Geotechnical Engineering Report (GER) presents the results of the geotechnical engineering services provided for the Varma Short Plat in Renton, Washington. The purpose of this evaluation is to assess subsurface conditions and provide geotechnical recommendations for the construction of a single family residence. Our scope of services included field explorations, laboratory testing, engineering analyses, and preparation of this GER. The recommendations in the following sections of this GER are based upon our current understanding of the proposed site development as outlined below. If actual features vary or changes are made, RGI should review them in order to modify our recommendations as required. In addition, RGI requests to review the site grading plan, final design drawings and specifications when available to verify that our project understanding is correct and that our recommendations have been properly interpreted and incorporated into the project design and construction. 2.0 Project description The project site is located at 13016 156th Avenue Southeast in Renton, Washington. The approximate location of the site is shown on Figure 1. The site is currently occupied by a single-family residence. RGI understands that a short plat with 9 single-family residences will be constructed on the site. At the time of preparing this GER, building plans were not available for our review. Based on our experience with similar construction, RGI anticipates that the proposed building will be supported on perimeter walls with bearing loads of two to six kips per linear foot, and a series of columns with a maximum load up to 30 kips. Slab-on-grade floor loading of 250 pounds per square foot (psf) are expected. 3.0 Field Exploration and Laboratory Testing 3.1 FIELD EXPLORATION On August 24, 2020, RGI observed the excavation of 4 test pits and 2 hand augers. The approximate exploration locations are shown on Figure 2. Field logs of each exploration were prepared by the geologist that continuously observed the excavations. These logs included visual classifications of the materials encountered during excavation as well as our interpretation of the subsurface conditions between samples. The test pits and hand augers logs included in Appendix A represent an interpretation of the field logs and include modifications based on laboratory observation and analysis of the samples. Geotechnical Engineering Report 2 September 16, 2020 Varma Short Plat, Renton, Washington RGI Project No. 2020-317-1 3.2 LABORATORY TESTING During the field exploration, a representative portion of each recovered sample was sealed in containers and transported to our laboratory for further visual and laboratory examination. Selected samples retrieved from the test pits and hand augers were tested for moisture content and grain size analysis to aid in soil classification and provide input for the recommendations provided in this GER. The results and descriptions of the laboratory tests are enclosed in Appendix A. 4.0 Site Conditions 4.1 SURFACE The subject site is irregular-shaped, consisting of two parcels of land (King County Tax Parcel numbers 3664500205 and 3664500185), totaling approximately 3.2 acres in size. The site is bound to the north and south by residential properties, to the east by 158th Avenue Southeast and a residential property, and to the west by 156th Avenue Southeast. The existing site is occupied by a single-family residence and land covered by trees and other vegetation. The site is relatively flat with an overall elevation difference of approximately 10 feet. 4.2 GEOLOGY Review of the Geologic map of the Renton quadrangle, King County, Washington by Mullineaux, 1965 indicates that the soil in the project vicinity is mapped as Vashon-age lodgment till (Qvt). Lodgment till consists of a non-sorted mixture of silt, sand, gravel, cobbles, and boulders which looks like concrete mix. Till is very dense from compaction of glacial ice and is considered a restrictive layer in stormwater planning. Drainage does occur in the upper several feet of the till deposits, but water ponds and moves laterally along the underlying unweathered till surface. These descriptions are generally similar to our observations in the field. 4.3 SOILS The soils encountered during field exploration include medium dense silty sand with gravel over very dense glacial till. More detailed descriptions of the subsurface conditions encountered are presented in the test pits and hand augers included in Appendix A. Sieve analysis was performed on two selected soil samples. Grain size distribution curves are included in Appendix A. Geotechnical Engineering Report 3 September 16, 2020 Varma Short Plat, Renton, Washington RGI Project No. 2020-317-1 4.4 GROUNDWATER No groundwater seepage was encountered during our subsurface exploration. Evidence of high groundwater (mottling) was observed in the silty sand overlying the lodgment till in some of the explorations. It should be recognized that fluctuations of the groundwater table will occur due to seasonal variations in the amount of rainfall, runoff, and other factors not evident at the time the explorations were performed. In addition, perched water can develop within seams and layers contained in fill soils or higher permeability soils overlying less permeable soils following periods of heavy or prolonged precipitation. Therefore, groundwater levels during construction or at other times in the future may be higher or lower than the levels indicated on the logs. 4.5 SEISMIC CONSIDERATIONS Based on the International Building Code (IBC), RGI recommends the follow seismic parameters for design. Table 1 IBC Parameter 2015 Value 2018 Value Site Soil Class1 C2 Site Latitude 47.4854123 Site Longitude -122.1320619 Short Period Spectral Response Acceleration, SS (g) 1.373 1.372 1-Second Period Spectral Response Acceleration, S1 (g) 0.515 0.470 Adjusted Short Period Spectral Response Acceleration, SMS (g) 1.373 1.647 Adjusted 1-Sec Period Spectral Response Acceleration, SM1 (g) 0.669 0.704 Numeric seismic design value at 0.2 second; SDS(g) 0.915 1.098 Numeric seismic design value at 1.0 second; SM1(g) 0.446 0.470 1. Note: In general accordance with Chapter 20 of ASCE 7-10. The Site Class is based on the average characteristics of the upper 100 feet of the subsurface profile. 2. Note: The 2015 IBC and ASCE 7-10 require a site soil profile determination extending to a depth of 100 feet for seismic site classification. The current scope of our services does not include the required 100 foot soil profile determination. Test pits and hand augers extended to a maximum depth of 4.5 feet, and this seismic site class definition considers that similar soil continues below the maximum depth of the subsurface exploration. Additional exploration to deeper depths would be required to confirm the conditions below the current depth of exploration. Liquefaction is a phenomenon where there is a reduction or complete loss of soil strength due to an increase in water pressure induced by vibrations from a seismic event. Liquefaction mainly affects geologically recent deposits of fine-grained sands that are below the groundwater table. Soils of this nature derive their strength from intergranular Geotechnical Engineering Report 4 September 16, 2020 Varma Short Plat, Renton, Washington RGI Project No. 2020-317-1 friction. The generated water pressure or pore pressure essentially separates the soil grains and eliminates this intergranular friction, thus reducing or eliminating the soil’s strength. RGI reviewed the results of the field and laboratory testing and assessed the potential for liquefaction of the site’s soil during an earthquake. Since the site is underlain by glacial till, RGI considers that the possibility of liquefaction during an earthquake is minimal. 4.6 GEOLOGIC HAZARD AREAS Regulated geologically hazardous areas include erosion, landslide, earthquake, or other geological hazards. Based on the definition in the Renton Municipal Code, the site does not contain geologically hazardous areas. 5.0 Discussion and Recommendations 5.1 GEOTECHNICAL CONSIDERATIONS Based on our study, the site is suitable for the proposed construction from a geotechnical standpoint. Foundations for the proposed building can be supported on conventional spread footings bearing on competent native soil or structural fill. Slab-on-grade floors can be similarly supported. Detailed recommendations regarding the above issues and other geotechnical design considerations are provided in the following sections. These recommendations should be incorporated into the final design drawings and construction specifications. 5.2 EARTHWORK The earthwork is expected to include excavating and backfilling the building foundations and preparing slab subgrades. 5.2.1 EROSION AND SEDIMENT CONTROL Potential sources or causes of erosion and sedimentation depend on construction methods, slope length and gradient, amount of soil exposed and/or disturbed, soil type, construction sequencing and weather. The impacts on erosion-prone areas can be reduced by implementing an erosion and sedimentation control plan. The plan should be designed in accordance with applicable city and/or county standards. RGI recommends the following erosion control Best Management Practices (BMPs):  Scheduling site preparation and grading for the drier summer and early fall months and undertaking activities that expose soil during periods of little or no rainfall  Retaining existing vegetation whenever feasible  Establishing a quarry spall construction entrance Geotechnical Engineering Report 5 September 16, 2020 Varma Short Plat, Renton, Washington RGI Project No. 2020-317-1  Installing siltation control fencing or anchored straw or coir wattles on the downhill side of work areas  Covering soil stockpiles with anchored plastic sheeting  Revegetating or mulching exposed soils with a minimum 3-inch thickness of straw if surfaces will be left undisturbed for more than one day during wet weather or one week in dry weather  Directing runoff away from exposed soils and slopes  Minimizing the length and steepness of slopes with exposed soils and cover excavation surfaces with anchored plastic sheeting  Decreasing runoff velocities with check dams, straw bales or coir wattles  Confining sediment to the project site  Inspecting and maintaining erosion and sediment control measures frequently (The contractor should be aware that inspection and maintenance of erosion control BMPs is critical toward their satisfactory performance. Repair and/or replacement of dysfunctional erosion control elements should be anticipated.) Permanent erosion protection should be provided by reestablishing vegetation using hydroseeding and/or landscape planting. Until the permanent erosion protection is established, site monitoring should be performed by qualified personnel to evaluate the effectiveness of the erosion control measures. Provisions for modifications to the erosion control system based on monitoring observations should be included in the erosion and sedimentation control plan. 5.2.2 STRIPPING AND SUBGRADE PREPARATION Stripping efforts should include removal of pavements, vegetation, organic materials, and deleterious debris from areas slated for building, pavement, and utility construction. Minimal ground cover/mulch was observed in the test pit and hand auger locations, however, deeper areas of stripping may be required in forested or heavily vegetated areas of the site. Subgrade soils that become disturbed due to elevated moisture conditions should be overexcavated to reveal firm, non-yielding, non-organic soils and backfilled with compacted structural fill. In order to maximize utilization of site soils as structural fill, RGI recommends that the earthwork portion of this project be completed during extended periods of warm and dry weather if possible. If earthwork is completed during the wet season (typically November through May) it will be necessary to take extra precautionary measures to protect subgrade soils. Wet season earthwork will require additional mitigative measures beyond that which would be expected during the drier summer and fall months. Geotechnical Engineering Report 6 September 16, 2020 Varma Short Plat, Renton, Washington RGI Project No. 2020-317-1 5.2.3 EXCAVATIONS All temporary cut slopes associated with the site and utility excavations should be adequately inclined to prevent sloughing and collapse. The site soils consist of medium dense silty sand with gravel over very dense glacial till. Accordingly, for excavations more than 4 feet but less than 20 feet in depth, the temporary side slopes should be laid back with a minimum slope inclination of 1H:1V (Horizontal:Vertical). For open cuts at the site, RGI recommends:  No traffic, construction equipment, stockpiles or building supplies are allowed at the top of cut slopes within a distance of at least five feet from the top of the cut  Exposed soil along the slope is protected from surface erosion using waterproof tarps and/or plastic sheeting  Construction activities are scheduled so that the length of time the temporary cut is left open is minimized  Surface water is diverted away from the excavation  The general condition of slopes should be observed periodically by a geotechnical engineer to confirm adequate stability and erosion control measures In all cases, however, appropriate inclinations will depend on the actual soil and groundwater conditions encountered during earthwork. Ultimately, the site contractor must be responsible for maintaining safe excavation slopes that comply with applicable OSHA or WISHA guidelines. 5.2.4 STRUCTURAL FILL RGI recommends fill below the foundation and floor slab, behind retaining walls, and below pavement and hardscape surfaces be placed in accordance with the following recommendations for structural fill. The suitability of excavated site soils and import soils for compacted structural fill use will depend on the gradation and moisture content of the soil when it is placed. As the amount of fines (that portion passing the U.S. No. 200 sieve) increases, soil becomes increasingly sensitive to small changes in moisture content and adequate compaction becomes more difficult or impossible to achieve. Soils containing more than about 5 percent fines cannot be consistently compacted to a dense, non-yielding condition when the moisture content is more than 2 percent above or below optimum. Optimum moisture content is that moisture that results in the greatest compacted dry density with a specified compactive effort. Non-organic site soils are only considered suitable for structural fill provided that their moisture content is within about two percent of the optimum moisture level as determined by American Society of Testing and Materials D1557-09 Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Modified Effort (ASTM D1557). Geotechnical Engineering Report 7 September 16, 2020 Varma Short Plat, Renton, Washington RGI Project No. 2020-317-1 Excavated site soils may not be suitable for re-use as structural fill depending on the moisture content and weather conditions at the time of construction. If soils are stockpiled for future reuse and wet weather is anticipated, the stockpile should be protected with plastic sheeting that is securely anchored. Even during dry weather, moisture conditioning (such as, windrowing and drying) of site soils to be reused as structural fill may be required. The site soils are moisture sensitive and may require moisture conditioning prior to use as structural fill. If on-site soils are or become unusable, it may become necessary to import clean, granular soils to complete site work that meet the grading requirements listed in Table 2 to be used as structural fill. Table 2 Structural Fill Gradation U.S. Sieve Size Percent Passing 4 inches 100 No. 4 sieve 22 to 100 No. 200 sieve 0 to 5* *Based on minus 3/4 inch fraction. Prior to use, an RGI representative should observe and test all materials imported to the site for use as structural fill. Structural fill materials should be placed in uniform loose layers not exceeding 12 inches and compacted as specified in Table 3. The soil’s maximum density and optimum moisture should be determined by ASTM D1557. Table 3 Structural Fill Compaction ASTM D1557 Location Material Type Minimum Compaction Percentage Moisture Content Range Foundations On-site granular or approved imported fill soils: 95 +2 -2 Retaining Wall Backfill On-site granular or approved imported fill soils: 92 +2 -2 Slab-on-grade On-site granular or approved imported fill soils: 95 +2 -2 General Fill (non- structural areas) On-site soils or approved imported fill soils: 90 +3 -2 Geotechnical Engineering Report 8 September 16, 2020 Varma Short Plat, Renton, Washington RGI Project No. 2020-317-1 Placement and compaction of structural fill should be observed by RGI. A representative number of in-place density tests should be performed as the fill is being placed to confirm that the recommended level of compaction is achieved. 5.2.5 WET WEATHER CONSTRUCTION CONSIDERATIONS RGI recommends that preparation for site grading and construction include procedures intended to drain ponded water, control surface water runoff, and to collect shallow subsurface seepage zones in excavations where encountered. It will not be possible to successfully compact the subgrade or utilize on-site soils as structural fill if accumulated water is not drained prior to grading or if drainage is not controlled during construction. Attempting to grade the site without adequate drainage control measures will reduce the amount of on-site soil effectively available for use, increase the amount of select import fill materials required, and ultimately increase the cost of the earthwork phases of the project. Free water should not be allowed to pond on the subgrade soils. RGI anticipates that the use of berms and shallow drainage ditches, with sumps and pumps in utility trenches, will be required for surface water control during wet weather and/or wet site conditions. 5.3 FOUNDATIONS Following site preparation and grading, the proposed building foundation can be supported on conventional spread footings bearing on competent native soil or structural fill. Loose, organic, or other unsuitable soils may be encountered in the proposed building footprint. If unsuitable soils are encountered, they should be overexcavated and backfilled with structural fill. If loose soils are encountered, the soils should be moisture conditioned and compacted to a firm and unyielding condition. The foundation design value assumes the foundation is supported on at least two feet of medium dense native soil or structural fill. Table 4 Foundation Design Design Parameter Value Allowable Bearing Capacity 2,000 psf1 Friction Coefficient 0.30 Passive pressure (equivalent fluid pressure) 250 pcf2 Minimum foundation dimensions Columns: 24 inches Walls: 16 inches 1. psf = pounds per square foot 2. pcf = pounds per cubic foot The allowable foundation bearing pressures apply to dead loads plus design live load conditions. For short-term loads, such as wind and seismic, a 1/3 increase in this allowable capacity may be used. At perimeter locations, RGI recommends not including the upper 12 Geotechnical Engineering Report 9 September 16, 2020 Varma Short Plat, Renton, Washington RGI Project No. 2020-317-1 inches of soil in the computation of passive pressures because they can be affected by weather or disturbed by future grading activity. The passive pressure value assumes the foundation will be constructed neat against competent soil or backfilled with structural fill as described in Section 5.2.4. The recommended base friction and passive resistance value includes a safety factor of about 1.5. Perimeter foundations exposed to weather should be at a minimum depth of 18 inches below final exterior grades. Interior foundations can be constructed at any convenient depth below the floor slab. Finished grade is defined as the lowest adjacent grade within 5 feet of the foundation for perimeter (or exterior) footings and finished floor level for interior footings. With spread footing foundations designed in accordance with the recommendations in this section, maximum total and differential post-construction settlements of 1 inch and 1/2 inch, respectively, should be expected. 5.4 RETAINING WALLS If retaining walls are needed in the building area, RGI recommends cast-in-place concrete walls be used. The magnitude of earth pressure development on retaining walls will partly depend on the quality of the wall backfill. RGI recommends placing and compacting wall backfill as structural fill. Wall drainage will be needed behind the wall face. A typical retaining wall drainage detail is shown in Figure 3. With wall backfill placed and compacted as recommended, and drainage properly installed, RGI recommends using the values in the following table for design. Table 5 Retaining Wall Design Design Parameter Value Allowable Bearing Capacity 2,000 psf Active Earth Pressure (unrestrained walls) 35 pcf At-rest Earth Pressure (restrained walls) 50 pcf For seismic design, an additional uniform load of 7 times the wall height (H) for unrestrained walls and 14H in psf for restrained walls should be applied to the wall surface. Friction at the base of foundations and passive earth pressure will provide resistance to these lateral loads. Values for these parameters are provided in Section 5.3. 5.5 SLAB-ON-GRADE CONSTRUCTION Once site preparation has been completed as described in Section 5.2, suitable support for slab-on-grade construction should be provided. RGI recommends that the concrete slab be Geotechnical Engineering Report 10 September 16, 2020 Varma Short Plat, Renton, Washington RGI Project No. 2020-317-1 placed on top of medium dense native soil or structural fill. Immediately below the floor slab, RGI recommends placing a four-inch thick capillary break layer of clean, free-draining sand or gravel that has less than five percent passing the U.S. No. 200 sieve. This material will reduce the potential for upward capillary movement of water through the underlying soil and subsequent wetting of the floor slab. Where moisture by vapor transmission is undesirable, an 8- to 10-millimeter thick plastic membrane should be placed on a 4-inch thick layer of clean gravel. For the anticipated floor slab loading, we estimate post-construction floor settlements of 1/4- to 1/2-inch. 5.6 DRAINAGE 5.6.1 SURFACE Final exterior grades should promote free and positive drainage away from the building area. Water must not be allowed to pond or collect adjacent to foundations or within the immediate building area. For non-pavement locations, RGI recommends providing a minimum drainage gradient of 3 percent for a minimum distance of 10 feet from the building perimeter. In paved locations, a minimum gradient of 1 percent should be provided unless provisions are included for collection and disposal of surface water adjacent to the structure. 5.6.2 SUBSURFACE RGI recommends installing perimeter foundation drains. A typical footing drain detail is shown on Figure 4. The foundation drains and roof downspouts should be tightlined separately to an approved discharge facility. Subsurface drains must be laid with a gradient sufficient to promote positive flow to a controlled point of approved discharge. 5.6.3 INFILTRATION The site is underlain by very dense glacial till, commonly referred to as “hardpan.” This material does not allow for infiltration. Our infiltration evaluation was provided under separate cover. 5.7 UTILITIES Utility pipes should be bedded and backfilled in accordance with American Public Works Association (APWA) specifications. For site utilities located within the right-of-ways, bedding and backfill should be completed in accordance with City of Renton specifications. At a minimum, trench backfill should be placed and compacted as structural fill, as described in Section 5.2.4. Where utilities occur below unimproved areas, the degree of compaction can be reduced to a minimum of 90 percent of the soil’s maximum density as determined by the referenced ASTM D1557. As noted, soils excavated on site will not be Geotechnical Engineering Report 11 September 16, 2020 Varma Short Plat, Renton, Washington RGI Project No. 2020-317-1 suitable for use as backfill material. Imported structural fill meeting the gradation provided in Table 2 should be used for trench backfill. 6.0 Additional Services RGI is available to provide further geotechnical consultation throughout the design phase of the project. RGI should review the final design and specifications in order to verify that earthwork and foundation recommendations have been properly interpreted and incorporated into project design and construction. RGI is also available to provide geotechnical engineering and construction monitoring services during construction. The integrity of the earthwork and construction depends on proper site preparation and procedures. In addition, engineering decisions may arise in the field in the event that variations in subsurface conditions become apparent. Construction monitoring services are not part of this scope of work. If these services are desired, please let us know and we will prepare a cost proposal. 7.0 Limitations This GER is the property of RGI, Kushal Varma, and its designated agents. Within the limits of the scope and budget, this GER was prepared in accordance with generally accepted geotechnical engineering practices in the area at the time this GER was issued. This GER is intended for specific application to the Varma Short Plat project in Renton, Washington, and for the exclusive use of Kushal Varma and its authorized representatives. No other warranty, expressed or implied, is made. Site safety, excavation support, and dewatering requirements are the responsibility of others. The scope of services for this project does not include either specifically or by implication any environmental or biological (for example, mold, fungi, bacteria) assessment of the site or identification or prevention of pollutants, hazardous materials or conditions. If the owner is concerned about the potential for such contamination or pollution, we can provide a proposal for these services. The analyses and recommendations presented in this GER are based upon data obtained from the explorations performed on site. Variations in soil conditions can occur, the nature and extent of which may not become evident until construction. If variations appear evident, RGI should be requested to reevaluate the recommendations in this GER prior to proceeding with construction. It is the client’s responsibility to see that all parties to the project, including the designers, contractors, subcontractors, are made aware of this GER in its entirety. The use of information contained in this GER for bidding purposes should be done at the contractor’s option and risk. USGS, 2020, Renton, Washington USGS, 2020, Maple Valley, Washington 7.5-Minute Quadrangle Approximate Scale: 1"=1000' 0 500 1000 2000 N Site Vicinity Map Figure 1 09/2020 Corporate Office 17522 Bothell Way Northeast Bothell, Washington 98011 Phone: 425.415.0551 Fax: 425.415.0311 Varma Short Plat RGI Project Number: 2020-317-1 Date Drawn: Address: 13016 156th Avenue Southeast, Renton, Washington 98059 SITE TP-1TP-2TP-3TP-4HA-1HA-209/2020Corporate Office17522 Bothell Way NortheastBothell, Washington 98011Phone: 425.415.0551Fax: 425.415.0311Varma Short PlatRGI Project Number:2020-317-1Date Drawn:Address: 13016 156th Avenue Southeast, Renton, Washington 98059Figure 2Approximate Scale: 1"=80'04080160N= Test pit by RGI, 08/24/20= Hand auger by RGI, 08/24/20= Site boundaryGeotechnical Exploration Plan Incliniations) 12" Over the Pipe 3" Below the Pipe Perforated Pipe 4" Diameter PVC Compacted Structural Backfill (Native or Import) 12" min. Filter Fabric Material 12" Minimum Wide Free-Draining Gravel Slope to Drain (See Report for Appropriate Excavated Slope 09/2020 Corporate Office 17522 Bothell Way Northeast Bothell, Washington 98011 Phone: 425.415.0551 Fax: 425.415.0311 Varma Short Plat RGI Project Number: 2020-317-1 Date Drawn: Address: 13016 156th Avenue Southeast, Renton, Washington 98059 Retaining Wall Drainage Detail Figure 3 Not to Scale 3/4" Washed Rock or Pea Gravel 4" Perforated Pipe Building Slab Structural Backfill Compacted Filter Fabric 09/2020 Corporate Office 17522 Bothell Way Northeast Bothell, Washington 98011 Phone: 425.415.0551 Fax: 425.415.0311 Varma Short Plat RGI Project Number: 2020-317-1 Date Drawn: Address: 13016 156th Avenue Southeast, Renton, Washington 98059 Typical Footing Drain Detail Figure 4 Not to Scale Geotechnical Engineering Report September 16, 2020 Varma Short Plat, Renton, Washington RGI Project No. 2020-317-1 APPENDIX A FIELD EXPLORATION AND LABORATORY TESTING On August 24, 2020, RGI performed field explorations using a trackhoe and hand auger. We explored subsurface soil conditions at the site by observing the excavation of four test pits and two hand augers to a maximum depth of 4.5 feet below existing grade. The test pits and hand augers locations are shown on Figure 2. The test pits and hand augers locations were approximately determined by measurements from existing property lines and paved roads. A geologist from our office conducted the field exploration and classified the soil conditions encountered, maintained a log of each test exploration, obtained representative soil samples, and observed pertinent site features. All soil samples were visually classified in accordance with the Unified Soil Classification System (USCS). Representative soil samples obtained from the explorations were placed in closed containers and taken to our laboratory for further examination and testing. As a part of the laboratory testing program, the soil samples were classified in our in house laboratory based on visual observation, texture, plasticity, and the limited laboratory testing described below. Moisture Content Determinations Moisture content determinations were performed in accordance with ASTM D2216-10 Standard Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass (ASTM D2216) on representative samples obtained from the exploration in order to aid in identification and correlation of soil types. The moisture content of typical sample was measured and is reported on the test pits and hand augers logs. Grain Size Analysis A grain size analysis indicates the range in diameter of soil particles included in a particular sample. Grain size analyses was determined using D6913-04(2009) Standard Test Methods for Particle-Size Distribution (Gradation) of Soils Using Sieve Analysis (ASTM D6913) on two of the samples. Project Name:Varma Short Plat Project Number:2020-317-1 Client:Kushal Varma Test Pit No.: TP-1 Date(s) Excavated:08/24/20 Excavation Method: Excavator Type: Groundwater Level:Not encountered Test Pit Backfill:Native Soil Logged By LC Bucket Size:n/a Excavating Contractor:Client Provided Sampling Method(s)Grab Location 13016 156th Avenue Southeast, Renton, Washington 98059 Surface Conditions:Mulch Total Depth of Excavation:4 feet bgs Approximate Surface Elevation n/a Compaction Method n/a USCS SymbolSM SM REMARKS AND OTHER TESTSGraphic LogMATERIAL DESCRIPTION Brown, silty SAND with debris (fill), medium dense, moist Brown, silty SAND with gravel (till), very dense, moist Test pit excavated to 4 feet bgs No groundwater encounteredDepth (feet)0 5 10 Sample NumberSample TypeElevation (feet)Sheet 1 of 1 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 Project Name:Varma Short Plat Project Number:2020-317-1 Client:Kushal Varma Test Pit No.: TP-2 Date(s) Excavated:08/24/20 Excavation Method: Excavator Type: Groundwater Level:Not encountered Test Pit Backfill:Native Soil Logged By LC Bucket Size:n/a Excavating Contractor:Client Provided Sampling Method(s)Grab Location 13016 156th Avenue Southeast, Renton, Washington 98059 Surface Conditions:Mulch Total Depth of Excavation:4 feet bgs Approximate Surface Elevation n/a Compaction Method n/a USCS SymbolSM SM REMARKS AND OTHER TESTSGraphic LogMATERIAL DESCRIPTION Brown, silty SAND with gravel, medium dense, moist Gray, silty SAND with gravel (till), very dense, moist Test pit excavated to 4 feet bgs No groundwater encounteredDepth (feet)0 5 10 Sample NumberSample TypeElevation (feet)Sheet 1 of 1 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 Project Name:Varma Short Plat Project Number:2020-317-1 Client:Kushal Varma Test Pit No.: TP-3 Date(s) Excavated:08/24/20 Excavation Method: Excavator Type: Groundwater Level:Not encountered Test Pit Backfill:Native Soil Logged By LC Bucket Size:n/a Excavating Contractor:Client Provided Sampling Method(s)Grab Location 13016 156th Avenue Southeast, Renton, Washington 98059 Surface Conditions:Mulch Total Depth of Excavation:4.5 feet bgs Approximate Surface Elevation n/a Compaction Method n/a USCS SymbolSM SM REMARKS AND OTHER TESTSGraphic LogMATERIAL DESCRIPTION Brown, silty SAND with some gravel, medium dense, moist Gray, silty SAND with gravel (till), very dense, moist Test pit excavated to 4.5 feet bgs No groundwater encounteredDepth (feet)0 5 10 Sample NumberSample TypeElevation (feet)Sheet 1 of 1 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 Project Name:Varma Short Plat Project Number:2020-317-1 Client:Kushal Varma Test Pit No.: TP-4 Date(s) Excavated:08/24/20 Excavation Method: Excavator Type: Groundwater Level:Not encountered Test Pit Backfill:Native Soil Logged By LC Bucket Size:n/a Excavating Contractor:Client Provided Sampling Method(s)Grab Location 13016 156th Avenue Southeast, Renton, Washington 98059 Surface Conditions:Mulch Total Depth of Excavation:4.5 feet bgs Approximate Surface Elevation n/a Compaction Method n/a USCS SymbolSM SM REMARKS AND OTHER TESTSGraphic LogMATERIAL DESCRIPTION Brown, silty SAND with gravel, medium dense, moist Gray, silty SAND with gravel (till), very dense, moist Test pit excavated to 4.5 feet bgs No groundwater encounteredDepth (feet)0 5 10 Sample NumberSample TypeElevation (feet)Sheet 1 of 1 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 Project Name:Varma Short Plat Project Number:2020-317-1 Client:Kushal Varma Key to Logs USCS SymbolREMARKS AND OTHER TESTSGraphic LogMATERIAL DESCRIPTIONDepth (feet)Sample NumberSample TypeElevation (feet)1 2 3 4 5 6 7 8 COLUMN DESCRIPTIONS 1 Elevation (feet): Elevation (MSL, feet). 2 Depth (feet): Depth in feet below the ground surface. 3 Sample Type: Type of soil sample collected at the depth interval shown. 4 Sample Number: Sample identification number. 5 USCS Symbol: USCS symbol of the subsurface material. 6 Graphic Log: Graphic depiction of the subsurface material encountered. 7 MATERIAL DESCRIPTION: Description of material encountered. May include consistency, moisture, color, and other descriptive text. 8 REMARKS AND OTHER TESTS: Comments and observations regarding drilling or sampling made by driller or field personnel. FIELD AND LABORATORY TEST ABBREVIATIONS CHEM: Chemical tests to assess corrosivity COMP: Compaction test CONS: One-dimensional consolidation test LL: Liquid Limit, percent PI: Plasticity Index, percent SA: Sieve analysis (percent passing No. 200 Sieve) UC: Unconfined compressive strength test, Qu, in ksf WA: Wash sieve (percent passing No. 200 Sieve) MATERIAL GRAPHIC SYMBOLS Silty SAND (SM) TYPICAL SAMPLER GRAPHIC SYMBOLS Auger sampler Bulk Sample 3-inch-OD California w/ brass rings CME Sampler Grab Sample 2.5-inch-OD Modified California w/ brass liners Pitcher Sample 2-inch-OD unlined split spoon (SPT) Shelby Tube (Thin-walled, fixed head) OTHER GRAPHIC SYMBOLS Water level (at time of drilling, ATD) Water level (after waiting) Minor change in material properties within a stratum Inferred/gradational contact between strata ?Queried contact between strata GENERAL NOTES 1: Soil classifications are based on the Unified Soil Classification System. Descriptions and stratum lines are interpretive, and actual lithologic changes may be gradual. Field descriptions may have been modified to reflect results of lab tests. 2: Descriptions on these logs apply only at the specific boring locations and at the time the borings were advanced. They are not warranted to be representative of subsurface conditions at other locations or times. Sheet 1 of 1 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 Project Name:Varma Short Plat Project Number:2020-317-1 Client:Kushal Varma Hand Auger:HA-1 Date(s) Drilled:08/24/20 Drilling Method(s): Drill Rig Type: Groundwater Level:Not encountered Borehole Backfill:Native Soil Logged By:LC Drill Bit Size/Type:n/a Drilling Contractor:Client Provided Sampling Method(s):Grab Location:13016 156th Avenue Southeast, Renton, Washington 98059 Surface Conditions:Mulch Total Depth of Borehole:2.5 feet bgs Approximate Surface Elevation:n/a Hammer Data :n/a USCS SymbolSM SM Graphic LogWater Content, %MATERIAL DESCRIPTION Brown, silty SAND with gravel, medium dense, moist Gray, silty SAND with gravel (till), very dense, moist Hand auger bored to 2.5 feet bgs No groundwater encounteredGW DepthDepth (feet)0 5 10Sample IDSample TypeSampling Resistance, blows/ftSheet 1 of 1 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 Project Name:Varma Short Plat Project Number:2020-317-1 Client:Kushal Varma Hand Auger:HA-2 Date(s) Drilled:08/24/20 Drilling Method(s): Drill Rig Type: Groundwater Level:Not encountered Borehole Backfill:Native Soil Logged By:LC Drill Bit Size/Type:n/a Drilling Contractor:Client Provided Sampling Method(s):Grab Location:13016 156th Avenue Southeast, Renton, Washington 98059 Surface Conditions:Mulch Total Depth of Borehole:3 feet bgs Approximate Surface Elevation:n/a Hammer Data :n/a USCS SymbolSM SM Graphic LogWater Content, %MATERIAL DESCRIPTION Brown, silty SAND with some gravel, medium dense, moist Gray, silty SAND with gravel (till), very dense, moist Hand auger bored to 3 feet bgs No groundwater encounteredGW DepthDepth (feet)0 5 10Sample IDSample TypeSampling Resistance, blows/ftSheet 1 of 1 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 Project Name:Varma Short Plat Project Number:2020-317-1 Client:Kushal Varma Boring Log Key USCS SymbolGraphic LogWater Content, %MATERIAL DESCRIPTIONGW DepthDepth (feet)Sample IDSample TypeSampling Resistance, blows/ft1 2 3 4 5 6 7 8 9 COLUMN DESCRIPTIONS 1 Water Content, %: Water content of the soil sample, expressed as percentage of dry weight of sample. 2 Sample ID: Sample identification number. 3 Sample Type: Type of soil sample collected at the depth interval shown. 4 Sampling Resistance, blows/ft: Number of blows to advance driven sampler one foot (or distance shown) beyond seating interval using the hammer identified on the boring log. 5 GW Depth: Groundwater depth in feet below the ground surface. 6 Depth (feet): Depth in feet below the ground surface. 7 MATERIAL DESCRIPTION: Description of material encountered. May include consistency, moisture, color, and other descriptive text. 8 USCS Symbol: USCS symbol of the subsurface material. 9 Graphic Log: Graphic depiction of the subsurface material encountered. FIELD AND LABORATORY TEST ABBREVIATIONS CHEM: Chemical tests to assess corrosivity COMP: Compaction test CONS: One-dimensional consolidation test LL: Liquid Limit, percent PI: Plasticity Index, percent SA: Sieve analysis (percent passing No. 200 Sieve) UC: Unconfined compressive strength test, Qu, in ksf WA: Wash sieve (percent passing No. 200 Sieve) MATERIAL GRAPHIC SYMBOLS Silty SAND (SM) TYPICAL SAMPLER GRAPHIC SYMBOLS Auger sampler Bulk Sample 3-inch-OD California w/ brass rings CME Sampler Grab Sample 2.5-inch-OD Modified California w/ brass liners Pitcher Sample 2-inch-OD unlined split spoon (SPT) Shelby Tube (Thin-walled, fixed head) OTHER GRAPHIC SYMBOLS Water level (at time of drilling, ATD) Water level (after waiting) Minor change in material properties within a stratum Inferred/gradational contact between strata ?Queried contact between strata GENERAL NOTES 1: Soil classifications are based on the Unified Soil Classification System. Descriptions and stratum lines are interpretive, and actual lithologic changes may be gradual. Field descriptions may have been modified to reflect results of lab tests. 2: Descriptions on these logs apply only at the specific boring locations and at the time the borings were advanced. They are not warranted to be representative of subsurface conditions at other locations or times. Sheet 1 of 1 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 THE RILEY GROUP, INC. 17522 Bothell Way NE Bothell, WA 98011 PHONE: (425) 415-0551 FAX: (425) 415-0311 GRAIN SIZE ANALYSIS ASTM D421, D422, D1140, D2487, D6913 PROJECT TITLE Varma Short Plat SAMPLE ID/TYPE HA-2 PROJECT NO.2020-317-1 SAMPLE DEPTH 2' TECH/TEST DATE EW 9/14/2020 DATE RECEIVED 9/14/2020 WATER CONTENT (Delivered Moisture) Total Weight Of Sample Used For Sieve Corrected For Hygroscopic Moisture Wt Wet Soil & Tare (gm) (w1)381.7 Weight Of Sample (gm)363.5 Wt Dry Soil & Tare (gm) (w2)363.5 Tare Weight (gm) 16.0 Weight of Tare (gm) (w3)16.0 (W6) Total Dry Weight (gm) 347.5 Weight of Water (gm) (w4=w1-w2) 18.2 SIEVE ANALYSIS Weight of Dry Soil (gm) (w5=w2-w3) 347.5 Cumulative Moisture Content (%) (w4/w5)*100 5 Wt Ret (Wt-Tare) (%Retained)% PASS +Tare {(wt ret/w6)*100}(100-%ret) % COBBLES 0.0 12.0"16.0 0.00 0.00 100.00 cobbles % C GRAVEL 0.0 3.0"16.0 0.00 0.00 100.00 coarse gravel % F GRAVEL 21.7 2.5" coarse gravel % C SAND 7.9 2.0" coarse gravel % M SAND 16.5 1.5"16.0 0.00 0.00 100.00 coarse gravel % F SAND 31.9 1.0" coarse gravel % FINES 22.0 0.75"16.0 0.00 0.00 100.00 fine gravel % TOTAL 100.0 0.50" fine gravel 0.375"70.4 54.40 15.65 84.35 fine gravel D10 (mm)#4 91.3 75.30 21.67 78.33 coarse sand D30 (mm)#10 118.8 102.80 29.58 70.42 medium sand D60 (mm)#20 medium sand Cu #40 176.1 160.10 46.07 53.93 fine sand Cc #60 fine sand #100 252.5 236.50 68.06 31.94 fine sand #200 286.9 270.90 77.96 22.04 fines PAN 363.5 347.50 100.00 0.00 silt/clay 322 DESCRIPTION Silty SAND with some gravel USCS SM Prepared For:Reviewed By: Kushal Varma KMW 0 10 20 30 40 50 60 70 80 90 100 0.0010.010.11101001000 % P A S S I N G Grain size in millimeters 12"3" 2" 1".75" .375" #4 #10 #20 #40 #60 #100 #200 THE RILEY GROUP, INC. 17522 Bothell Way NE Bothell, WA 98011 PHONE: (425) 415-0551 FAX: (425) 415-0311 GRAIN SIZE ANALYSIS ASTM D421, D422, D1140, D2487, D6913 PROJECT TITLE Varma Short Plat SAMPLE ID/TYPE TP-3 PROJECT NO.2020-317-1 SAMPLE DEPTH 4' TECH/TEST DATE EW 9/14/2020 DATE RECEIVED 9/14/2020 WATER CONTENT (Delivered Moisture) Total Weight Of Sample Used For Sieve Corrected For Hygroscopic Moisture Wt Wet Soil & Tare (gm) (w1)531.0 Weight Of Sample (gm)502.6 Wt Dry Soil & Tare (gm) (w2)502.6 Tare Weight (gm) 16.1 Weight of Tare (gm) (w3)16.1 (W6) Total Dry Weight (gm) 486.5 Weight of Water (gm) (w4=w1-w2) 28.4 SIEVE ANALYSIS Weight of Dry Soil (gm) (w5=w2-w3) 486.5 Cumulative Moisture Content (%) (w4/w5)*100 6 Wt Ret (Wt-Tare) (%Retained)% PASS +Tare {(wt ret/w6)*100}(100-%ret) % COBBLES 0.0 12.0"16.1 0.00 0.00 100.00 cobbles % C GRAVEL 18.0 3.0"16.1 0.00 0.00 100.00 coarse gravel % F GRAVEL 21.2 2.5" coarse gravel % C SAND 6.3 2.0" coarse gravel % M SAND 19.2 1.5"16.1 0.00 0.00 100.00 coarse gravel % F SAND 19.8 1.0" coarse gravel % FINES 15.6 0.75"103.7 87.60 18.01 81.99 fine gravel % TOTAL 100.0 0.50" fine gravel 0.375"173.8 157.70 32.42 67.58 fine gravel D10 (mm)#4 206.9 190.80 39.22 60.78 coarse sand D30 (mm)#10 237.4 221.30 45.49 54.51 medium sand D60 (mm)#20 medium sand Cu #40 330.6 314.50 64.65 35.35 fine sand Cc #60 fine sand #100 406.3 390.20 80.21 19.79 fine sand #200 426.8 410.70 84.42 15.58 fines PAN 502.6 486.50 100.00 0.00 silt/clay 322 DESCRIPTION Silty gravelly SAND USCS SM Prepared For:Reviewed By: Kushal Varma KMW 0 10 20 30 40 50 60 70 80 90 100 0.0010.010.11101001000 % P A S S I N G Grain size in millimeters 12"3" 2" 1".75" .375" #4 #10 #20 #40 #60 #100 #200 Varma Short Plat Preliminary Technical Information Report Appendix C WWHM Output WWHM2012 PROJECT REPORT 20544 Preliminary WWHM 12/1/2020 3:36:19 PM Page 2 General Model Information Project Name:20544 Preliminary WWHM Site Name: Site Address: City: Report Date:12/1/2020 Gage:Seatac Data Start:1948/10/01 Data End:2009/09/30 Timestep:15 Minute Precip Scale:1.167 Version Date:2018/10/10 Version:4.2.16 POC Thresholds Low Flow Threshold for POC1:50 Percent of the 2 Year High Flow Threshold for POC1:50 Year Low Flow Threshold for POC2:50 Percent of the 2 Year High Flow Threshold for POC2:50 Year 20544 Preliminary WWHM 12/1/2020 3:36:19 PM Page 3 Landuse Basin Data Predeveloped Land Use Basin 1 (West) Bypass:No GroundWater:No Pervious Land Use acre C, Forest, Flat 0.611 Pervious Total 0.611 Impervious Land Use acre Impervious Total 0 Basin Total 0.611 Element Flows To: Surface Interflow Groundwater 20544 Preliminary WWHM 12/1/2020 3:36:19 PM Page 4 Basin 2 (East) Bypass:No GroundWater:No Pervious Land Use acre C, Forest, Flat 2.843 Pervious Total 2.843 Impervious Land Use acre Impervious Total 0 Basin Total 2.843 Element Flows To: Surface Interflow Groundwater 20544 Preliminary WWHM 12/1/2020 3:36:19 PM Page 5 Mitigated Land Use Basin 1 Bypass:No GroundWater:No Pervious Land Use acre C, Pasture, Flat 0.3289 Pervious Total 0.3289 Impervious Land Use acre ROADS FLAT 0.1515 ROOF TOPS FLAT 0.0555 SIDEWALKS FLAT 0.0751 Impervious Total 0.2821 Basin Total 0.611 Element Flows To: Surface Interflow Groundwater Tank 1 Tank 1 20544 Preliminary WWHM 12/1/2020 3:36:19 PM Page 6 Basin 2 Bypass:No GroundWater:No Pervious Land Use acre C, Pasture, Flat 1.4375 Pervious Total 1.4375 Impervious Land Use acre ROADS FLAT 0.2835 ROOF TOPS FLAT 0.726 DRIVEWAYS FLAT 0.3112 SIDEWALKS FLAT 0.0848 Impervious Total 1.4055 Basin Total 2.843 Element Flows To: Surface Interflow Groundwater Vault 2 Vault 2 20544 Preliminary WWHM 12/1/2020 3:36:19 PM Page 7 Routing Elements Predeveloped Routing 20544 Preliminary WWHM 12/1/2020 3:36:19 PM Page 8 Mitigated Routing Vault 2 Width:40 ft. Length:109 ft. Depth:8 ft. Discharge Structure Riser Height:7 ft. Riser Diameter:18 in. Orifice 1 Diameter:1.05 in.Elevation:0 ft. Orifice 2 Diameter:1.79 in.Elevation:4.625 ft. Orifice 3 Diameter:1.13 in.Elevation:6.1 ft. Element Flows To: Outlet 1 Outlet 2 Vault Hydraulic Table Stage(feet)Area(ac.)Volume(ac-ft.)Discharge(cfs)Infilt(cfs) 0.0000 0.100 0.000 0.000 0.000 0.0889 0.100 0.008 0.008 0.000 0.1778 0.100 0.017 0.012 0.000 0.2667 0.100 0.026 0.015 0.000 0.3556 0.100 0.035 0.017 0.000 0.4444 0.100 0.044 0.019 0.000 0.5333 0.100 0.053 0.021 0.000 0.6222 0.100 0.062 0.023 0.000 0.7111 0.100 0.071 0.025 0.000 0.8000 0.100 0.080 0.026 0.000 0.8889 0.100 0.089 0.028 0.000 0.9778 0.100 0.097 0.029 0.000 1.0667 0.100 0.106 0.030 0.000 1.1556 0.100 0.115 0.032 0.000 1.2444 0.100 0.124 0.033 0.000 1.3333 0.100 0.133 0.034 0.000 1.4222 0.100 0.142 0.035 0.000 1.5111 0.100 0.151 0.036 0.000 1.6000 0.100 0.160 0.037 0.000 1.6889 0.100 0.169 0.038 0.000 1.7778 0.100 0.177 0.039 0.000 1.8667 0.100 0.186 0.040 0.000 1.9556 0.100 0.195 0.041 0.000 2.0444 0.100 0.204 0.042 0.000 2.1333 0.100 0.213 0.043 0.000 2.2222 0.100 0.222 0.044 0.000 2.3111 0.100 0.231 0.045 0.000 2.4000 0.100 0.240 0.046 0.000 2.4889 0.100 0.249 0.047 0.000 2.5778 0.100 0.258 0.048 0.000 2.6667 0.100 0.266 0.048 0.000 2.7556 0.100 0.275 0.049 0.000 2.8444 0.100 0.284 0.050 0.000 2.9333 0.100 0.293 0.051 0.000 3.0222 0.100 0.302 0.052 0.000 3.1111 0.100 0.311 0.052 0.000 3.2000 0.100 0.320 0.053 0.000 3.2889 0.100 0.329 0.054 0.000 20544 Preliminary WWHM 12/1/2020 3:36:19 PM Page 9 3.3778 0.100 0.338 0.055 0.000 3.4667 0.100 0.347 0.055 0.000 3.5556 0.100 0.355 0.056 0.000 3.6444 0.100 0.364 0.057 0.000 3.7333 0.100 0.373 0.057 0.000 3.8222 0.100 0.382 0.058 0.000 3.9111 0.100 0.391 0.059 0.000 4.0000 0.100 0.400 0.059 0.000 4.0889 0.100 0.409 0.060 0.000 4.1778 0.100 0.418 0.061 0.000 4.2667 0.100 0.427 0.061 0.000 4.3556 0.100 0.436 0.062 0.000 4.4444 0.100 0.444 0.063 0.000 4.5333 0.100 0.453 0.063 0.000 4.6222 0.100 0.462 0.064 0.000 4.7111 0.100 0.471 0.090 0.000 4.8000 0.100 0.480 0.101 0.000 4.8889 0.100 0.489 0.110 0.000 4.9778 0.100 0.498 0.118 0.000 5.0667 0.100 0.507 0.125 0.000 5.1556 0.100 0.516 0.131 0.000 5.2444 0.100 0.524 0.136 0.000 5.3333 0.100 0.533 0.142 0.000 5.4222 0.100 0.542 0.147 0.000 5.5111 0.100 0.551 0.152 0.000 5.6000 0.100 0.560 0.156 0.000 5.6889 0.100 0.569 0.161 0.000 5.7778 0.100 0.578 0.165 0.000 5.8667 0.100 0.587 0.169 0.000 5.9556 0.100 0.596 0.173 0.000 6.0444 0.100 0.605 0.177 0.000 6.1333 0.100 0.613 0.187 0.000 6.2222 0.100 0.622 0.196 0.000 6.3111 0.100 0.631 0.204 0.000 6.4000 0.100 0.640 0.210 0.000 6.4889 0.100 0.649 0.216 0.000 6.5778 0.100 0.658 0.222 0.000 6.6667 0.100 0.667 0.227 0.000 6.7556 0.100 0.676 0.232 0.000 6.8444 0.100 0.685 0.237 0.000 6.9333 0.100 0.694 0.242 0.000 7.0222 0.100 0.702 0.299 0.000 7.1111 0.100 0.711 0.839 0.000 7.2000 0.100 0.720 1.660 0.000 7.2889 0.100 0.729 2.635 0.000 7.3778 0.100 0.738 3.651 0.000 7.4667 0.100 0.747 4.594 0.000 7.5556 0.100 0.756 5.370 0.000 7.6444 0.100 0.765 5.926 0.000 7.7333 0.100 0.774 6.294 0.000 7.8222 0.100 0.782 6.710 0.000 7.9111 0.100 0.791 7.052 0.000 8.0000 0.100 0.800 7.378 0.000 8.0889 0.100 0.809 7.690 0.000 8.1778 0.000 0.000 7.990 0.000 20544 Preliminary WWHM 12/1/2020 3:36:19 PM Page 10 Tank 1 Dimensions Depth:7 ft. Tank Type:Circular Diameter:7 ft. Length:169 ft. Discharge Structure Riser Height:6 ft. Riser Diameter:24 in. Orifice 1 Diameter:0.4844 in.Elevation:0 ft. Orifice 2 Diameter:0.8594 in.Elevation:4 ft. Orifice 3 Diameter:0.5469 in.Elevation:5.2 ft. Element Flows To: Outlet 1 Outlet 2 Tank Hydraulic Table Stage(feet)Area(ac.)Volume(ac-ft.)Discharge(cfs)Infilt(cfs) 0.0000 0.000 0.000 0.000 0.000 0.0778 0.005 0.000 0.001 0.000 0.1556 0.008 0.000 0.002 0.000 0.2333 0.009 0.001 0.003 0.000 0.3111 0.011 0.002 0.003 0.000 0.3889 0.012 0.003 0.004 0.000 0.4667 0.013 0.004 0.004 0.000 0.5444 0.014 0.005 0.004 0.000 0.6222 0.015 0.006 0.005 0.000 0.7000 0.016 0.007 0.005 0.000 0.7778 0.017 0.009 0.005 0.000 0.8556 0.017 0.010 0.005 0.000 0.9333 0.018 0.011 0.006 0.000 1.0111 0.019 0.013 0.006 0.000 1.0889 0.019 0.014 0.006 0.000 1.1667 0.020 0.016 0.006 0.000 1.2444 0.020 0.018 0.007 0.000 1.3222 0.021 0.019 0.007 0.000 1.4000 0.021 0.021 0.007 0.000 1.4778 0.022 0.023 0.007 0.000 1.5556 0.022 0.024 0.007 0.000 1.6333 0.023 0.026 0.008 0.000 1.7111 0.023 0.028 0.008 0.000 1.7889 0.023 0.030 0.008 0.000 1.8667 0.024 0.032 0.008 0.000 1.9444 0.024 0.033 0.008 0.000 2.0222 0.024 0.035 0.009 0.000 2.1000 0.024 0.037 0.009 0.000 2.1778 0.025 0.039 0.009 0.000 2.2556 0.025 0.041 0.009 0.000 2.3333 0.025 0.043 0.009 0.000 2.4111 0.025 0.045 0.009 0.000 2.4889 0.026 0.047 0.010 0.000 2.5667 0.026 0.049 0.010 0.000 2.6444 0.026 0.051 0.010 0.000 2.7222 0.026 0.053 0.010 0.000 2.8000 0.026 0.055 0.010 0.000 2.8778 0.026 0.057 0.010 0.000 20544 Preliminary WWHM 12/1/2020 3:36:19 PM Page 11 2.9556 0.026 0.059 0.010 0.000 3.0333 0.026 0.062 0.011 0.000 3.1111 0.027 0.064 0.011 0.000 3.1889 0.027 0.066 0.011 0.000 3.2667 0.027 0.068 0.011 0.000 3.3444 0.027 0.070 0.011 0.000 3.4222 0.027 0.072 0.011 0.000 3.5000 0.027 0.074 0.011 0.000 3.5778 0.027 0.076 0.012 0.000 3.6556 0.027 0.078 0.012 0.000 3.7333 0.027 0.081 0.012 0.000 3.8111 0.027 0.083 0.012 0.000 3.8889 0.027 0.085 0.012 0.000 3.9667 0.026 0.087 0.012 0.000 4.0444 0.026 0.089 0.017 0.000 4.1222 0.026 0.091 0.019 0.000 4.2000 0.026 0.093 0.022 0.000 4.2778 0.026 0.095 0.023 0.000 4.3556 0.026 0.097 0.025 0.000 4.4333 0.026 0.099 0.026 0.000 4.5111 0.026 0.101 0.027 0.000 4.5889 0.025 0.103 0.029 0.000 4.6667 0.025 0.105 0.030 0.000 4.7444 0.025 0.107 0.031 0.000 4.8222 0.025 0.109 0.032 0.000 4.9000 0.024 0.111 0.033 0.000 4.9778 0.024 0.113 0.034 0.000 5.0556 0.024 0.115 0.034 0.000 5.1333 0.024 0.117 0.035 0.000 5.2111 0.023 0.119 0.037 0.000 5.2889 0.023 0.121 0.039 0.000 5.3667 0.023 0.122 0.041 0.000 5.4444 0.022 0.124 0.043 0.000 5.5222 0.022 0.126 0.044 0.000 5.6000 0.021 0.128 0.045 0.000 5.6778 0.021 0.129 0.046 0.000 5.7556 0.020 0.131 0.047 0.000 5.8333 0.020 0.133 0.049 0.000 5.9111 0.019 0.134 0.050 0.000 5.9889 0.019 0.136 0.051 0.000 6.0667 0.018 0.137 0.417 0.000 6.1444 0.017 0.138 1.214 0.000 6.2222 0.017 0.140 2.259 0.000 6.3000 0.016 0.141 3.476 0.000 6.3778 0.015 0.142 4.801 0.000 6.4556 0.014 0.143 6.169 0.000 6.5333 0.013 0.145 7.513 0.000 6.6111 0.012 0.146 8.770 0.000 6.6889 0.011 0.147 9.882 0.000 6.7667 0.009 0.147 10.81 0.000 6.8444 0.008 0.148 11.54 0.000 6.9222 0.005 0.149 12.09 0.000 7.0000 0.000 0.149 12.52 0.000 7.0778 0.000 0.000 13.14 0.000 20544 Preliminary WWHM 12/1/2020 3:36:19 PM Page 12 Analysis Results POC 1 + Predeveloped x Mitigated Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.611 Total Impervious Area:0 Mitigated Landuse Totals for POC #1 Total Pervious Area:0.3289 Total Impervious Area:0.2821 Flow Frequency Method:Log Pearson Type III 17B Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.023869 5 year 0.039352 10 year 0.051105 25 year 0.067531 50 year 0.080852 100 year 0.095064 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.014838 5 year 0.024671 10 year 0.033277 25 year 0.047001 50 year 0.059617 100 year 0.074577 Annual Peaks Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.029 0.010 1950 0.034 0.016 1951 0.049 0.047 1952 0.016 0.010 1953 0.014 0.011 1954 0.020 0.012 1955 0.031 0.012 1956 0.025 0.025 1957 0.023 0.012 1958 0.023 0.012 20544 Preliminary WWHM 12/1/2020 3:36:52 PM Page 13 1959 0.020 0.011 1960 0.038 0.036 1961 0.019 0.012 1962 0.013 0.009 1963 0.019 0.012 1964 0.023 0.011 1965 0.017 0.017 1966 0.015 0.011 1967 0.036 0.012 1968 0.021 0.011 1969 0.020 0.010 1970 0.017 0.011 1971 0.022 0.012 1972 0.037 0.031 1973 0.018 0.014 1974 0.020 0.012 1975 0.028 0.012 1976 0.020 0.012 1977 0.007 0.009 1978 0.017 0.012 1979 0.011 0.009 1980 0.053 0.033 1981 0.016 0.011 1982 0.037 0.029 1983 0.025 0.012 1984 0.016 0.010 1985 0.009 0.010 1986 0.040 0.024 1987 0.037 0.032 1988 0.016 0.010 1989 0.010 0.009 1990 0.102 0.038 1991 0.046 0.038 1992 0.019 0.012 1993 0.019 0.010 1994 0.008 0.009 1995 0.025 0.013 1996 0.058 0.046 1997 0.046 0.039 1998 0.016 0.010 1999 0.064 0.029 2000 0.018 0.012 2001 0.005 0.009 2002 0.025 0.026 2003 0.034 0.010 2004 0.039 0.043 2005 0.026 0.012 2006 0.027 0.013 2007 0.076 0.076 2008 0.080 0.049 2009 0.036 0.024 Ranked Annual Peaks Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.1022 0.0759 2 0.0804 0.0486 3 0.0756 0.0467 20544 Preliminary WWHM 12/1/2020 3:36:52 PM Page 14 4 0.0637 0.0462 5 0.0583 0.0427 6 0.0534 0.0388 7 0.0491 0.0384 8 0.0461 0.0382 9 0.0460 0.0363 10 0.0399 0.0325 11 0.0394 0.0316 12 0.0381 0.0306 13 0.0375 0.0295 14 0.0371 0.0292 15 0.0367 0.0261 16 0.0363 0.0247 17 0.0362 0.0244 18 0.0341 0.0243 19 0.0340 0.0169 20 0.0310 0.0165 21 0.0292 0.0141 22 0.0284 0.0127 23 0.0268 0.0125 24 0.0259 0.0124 25 0.0255 0.0124 26 0.0252 0.0124 27 0.0248 0.0123 28 0.0248 0.0123 29 0.0234 0.0121 30 0.0231 0.0121 31 0.0228 0.0121 32 0.0218 0.0121 33 0.0212 0.0120 34 0.0205 0.0120 35 0.0202 0.0119 36 0.0201 0.0118 37 0.0199 0.0117 38 0.0196 0.0116 39 0.0192 0.0116 40 0.0190 0.0111 41 0.0186 0.0109 42 0.0186 0.0109 43 0.0178 0.0108 44 0.0177 0.0107 45 0.0174 0.0107 46 0.0172 0.0107 47 0.0170 0.0105 48 0.0164 0.0103 49 0.0164 0.0103 50 0.0161 0.0102 51 0.0158 0.0102 52 0.0156 0.0101 53 0.0155 0.0100 54 0.0139 0.0100 55 0.0129 0.0095 56 0.0106 0.0092 57 0.0099 0.0091 58 0.0094 0.0090 59 0.0076 0.0089 60 0.0070 0.0087 61 0.0046 0.0085 20544 Preliminary WWHM 12/1/2020 3:36:53 PM Page 15 20544 Preliminary WWHM 12/1/2020 3:36:53 PM Page 16 Duration Flows The Facility PASSED Flow(cfs)Predev Mit Percentage Pass/Fail 0.0119 18454 12316 66 Pass 0.0126 16091 5388 33 Pass 0.0133 14326 4697 32 Pass 0.0140 12694 4519 35 Pass 0.0147 11197 4361 38 Pass 0.0154 9890 4209 42 Pass 0.0161 8814 4055 46 Pass 0.0168 7848 3923 49 Pass 0.0175 7007 3724 53 Pass 0.0182 6299 3568 56 Pass 0.0189 5679 3424 60 Pass 0.0196 5168 3275 63 Pass 0.0203 4701 3123 66 Pass 0.0210 4278 2982 69 Pass 0.0217 3903 2851 73 Pass 0.0224 3527 2733 77 Pass 0.0231 3183 2573 80 Pass 0.0238 2864 2447 85 Pass 0.0245 2594 2278 87 Pass 0.0252 2353 2129 90 Pass 0.0259 2141 1991 92 Pass 0.0266 1951 1826 93 Pass 0.0272 1797 1700 94 Pass 0.0279 1669 1560 93 Pass 0.0286 1514 1455 96 Pass 0.0293 1344 1338 99 Pass 0.0300 1223 1231 100 Pass 0.0307 1123 1131 100 Pass 0.0314 1042 1035 99 Pass 0.0321 969 923 95 Pass 0.0328 910 828 90 Pass 0.0335 838 741 88 Pass 0.0342 766 638 83 Pass 0.0349 704 549 77 Pass 0.0356 633 456 72 Pass 0.0363 571 406 71 Pass 0.0370 488 372 76 Pass 0.0377 425 335 78 Pass 0.0384 376 286 76 Pass 0.0391 341 264 77 Pass 0.0398 307 254 82 Pass 0.0405 271 237 87 Pass 0.0412 235 223 94 Pass 0.0419 196 201 102 Pass 0.0426 171 174 101 Pass 0.0433 145 149 102 Pass 0.0440 125 124 99 Pass 0.0447 107 110 102 Pass 0.0453 95 97 102 Pass 0.0460 84 81 96 Pass 0.0467 71 60 84 Pass 0.0474 61 51 83 Pass 0.0481 55 40 72 Pass 20544 Preliminary WWHM 12/1/2020 3:36:53 PM Page 17 0.0488 45 25 55 Pass 0.0495 40 21 52 Pass 0.0502 37 17 45 Pass 0.0509 35 9 25 Pass 0.0516 29 6 20 Pass 0.0523 25 6 24 Pass 0.0530 22 5 22 Pass 0.0537 17 5 29 Pass 0.0544 15 5 33 Pass 0.0551 11 5 45 Pass 0.0558 9 5 55 Pass 0.0565 8 4 50 Pass 0.0572 8 4 50 Pass 0.0579 8 4 50 Pass 0.0586 7 4 57 Pass 0.0593 7 4 57 Pass 0.0600 7 4 57 Pass 0.0607 7 4 57 Pass 0.0614 7 4 57 Pass 0.0621 7 4 57 Pass 0.0628 7 4 57 Pass 0.0634 6 4 66 Pass 0.0641 5 2 40 Pass 0.0648 5 2 40 Pass 0.0655 5 2 40 Pass 0.0662 4 2 50 Pass 0.0669 4 2 50 Pass 0.0676 4 2 50 Pass 0.0683 4 2 50 Pass 0.0690 4 2 50 Pass 0.0697 4 2 50 Pass 0.0704 4 2 50 Pass 0.0711 4 2 50 Pass 0.0718 4 2 50 Pass 0.0725 4 1 25 Pass 0.0732 3 1 33 Pass 0.0739 3 1 33 Pass 0.0746 3 1 33 Pass 0.0753 3 1 33 Pass 0.0760 2 0 0 Pass 0.0767 2 0 0 Pass 0.0774 2 0 0 Pass 0.0781 2 0 0 Pass 0.0788 2 0 0 Pass 0.0795 2 0 0 Pass 0.0802 2 0 0 Pass 0.0809 1 0 0 Pass 20544 Preliminary WWHM 12/1/2020 3:36:53 PM Page 18 Water Quality Water Quality BMP Flow and Volume for POC #1 On-line facility volume:0.0503 acre-feet On-line facility target flow:0.0531 cfs. Adjusted for 15 min:0.0531 cfs. Off-line facility target flow:0.0295 cfs. Adjusted for 15 min:0.0295 cfs. 20544 Preliminary WWHM 12/1/2020 3:36:53 PM Page 19 LID Report 20544 Preliminary WWHM 12/1/2020 3:37:39 PM Page 20 POC 2 + Predeveloped x Mitigated Predeveloped Landuse Totals for POC #2 Total Pervious Area:2.843 Total Impervious Area:0 Mitigated Landuse Totals for POC #2 Total Pervious Area:1.4375 Total Impervious Area:1.4055 Flow Frequency Method:Log Pearson Type III 17B Flow Frequency Return Periods for Predeveloped. POC #2 Return Period Flow(cfs) 2 year 0.111063 5 year 0.183106 10 year 0.237795 25 year 0.314223 50 year 0.376205 100 year 0.442338 Flow Frequency Return Periods for Mitigated. POC #2 Return Period Flow(cfs) 2 year 0.069964 5 year 0.114221 10 year 0.15241 25 year 0.212603 50 year 0.267368 100 year 0.331774 Annual Peaks Annual Peaks for Predeveloped and Mitigated. POC #2 Year Predeveloped Mitigated 1949 0.136 0.048 1950 0.159 0.064 1951 0.228 0.219 1952 0.077 0.044 1953 0.064 0.052 1954 0.093 0.058 1955 0.144 0.059 1956 0.117 0.110 1957 0.106 0.057 1958 0.108 0.060 1959 0.091 0.051 20544 Preliminary WWHM 12/1/2020 3:38:12 PM Page 21 1960 0.177 0.173 1961 0.089 0.060 1962 0.060 0.040 1963 0.087 0.057 1964 0.109 0.054 1965 0.081 0.064 1966 0.072 0.052 1967 0.169 0.060 1968 0.099 0.054 1969 0.095 0.049 1970 0.080 0.051 1971 0.101 0.060 1972 0.174 0.147 1973 0.082 0.063 1974 0.093 0.060 1975 0.132 0.056 1976 0.094 0.059 1977 0.032 0.043 1978 0.079 0.060 1979 0.049 0.042 1980 0.249 0.158 1981 0.072 0.053 1982 0.173 0.136 1983 0.119 0.059 1984 0.075 0.047 1985 0.044 0.046 1986 0.186 0.113 1987 0.171 0.156 1988 0.073 0.048 1989 0.046 0.044 1990 0.476 0.177 1991 0.214 0.174 1992 0.089 0.061 1993 0.086 0.049 1994 0.035 0.040 1995 0.115 0.062 1996 0.271 0.216 1997 0.214 0.174 1998 0.076 0.049 1999 0.296 0.142 2000 0.083 0.057 2001 0.022 0.040 2002 0.115 0.122 2003 0.158 0.049 2004 0.183 0.200 2005 0.120 0.060 2006 0.125 0.062 2007 0.352 0.261 2008 0.374 0.225 2009 0.168 0.116 Ranked Annual Peaks Ranked Annual Peaks for Predeveloped and Mitigated. POC #2 Rank Predeveloped Mitigated 1 0.4757 0.2606 2 0.3739 0.2252 3 0.3518 0.2188 4 0.2963 0.2156 20544 Preliminary WWHM 12/1/2020 3:38:12 PM Page 22 5 0.2712 0.2002 6 0.2485 0.1775 7 0.2283 0.1740 8 0.2144 0.1737 9 0.2141 0.1735 10 0.1857 0.1577 11 0.1833 0.1557 12 0.1773 0.1469 13 0.1744 0.1424 14 0.1725 0.1362 15 0.1706 0.1217 16 0.1688 0.1157 17 0.1683 0.1135 18 0.1587 0.1100 19 0.1581 0.0636 20 0.1441 0.0635 21 0.1359 0.0626 22 0.1323 0.0622 23 0.1248 0.0618 24 0.1204 0.0609 25 0.1185 0.0604 26 0.1174 0.0603 27 0.1154 0.0602 28 0.1153 0.0601 29 0.1088 0.0599 30 0.1076 0.0597 31 0.1061 0.0595 32 0.1012 0.0591 33 0.0986 0.0590 34 0.0952 0.0588 35 0.0941 0.0582 36 0.0934 0.0573 37 0.0928 0.0573 38 0.0914 0.0571 39 0.0895 0.0559 40 0.0886 0.0541 41 0.0868 0.0535 42 0.0865 0.0530 43 0.0827 0.0525 44 0.0824 0.0523 45 0.0810 0.0515 46 0.0799 0.0513 47 0.0790 0.0494 48 0.0765 0.0491 49 0.0764 0.0490 50 0.0749 0.0487 51 0.0734 0.0482 52 0.0724 0.0482 53 0.0719 0.0472 54 0.0645 0.0462 55 0.0601 0.0440 56 0.0492 0.0436 57 0.0459 0.0433 58 0.0438 0.0417 59 0.0353 0.0403 60 0.0324 0.0398 61 0.0215 0.0397 20544 Preliminary WWHM 12/1/2020 3:38:12 PM Page 23 20544 Preliminary WWHM 12/1/2020 3:38:12 PM Page 24 Duration Flows The Facility PASSED Flow(cfs)Predev Mit Percentage Pass/Fail 0.0555 18871 18486 97 Pass 0.0588 16600 12628 76 Pass 0.0620 14322 6421 44 Pass 0.0652 12791 3720 29 Pass 0.0685 11383 3593 31 Pass 0.0717 10170 3506 34 Pass 0.0750 9135 3431 37 Pass 0.0782 7901 3330 42 Pass 0.0814 7122 3258 45 Pass 0.0847 6429 3195 49 Pass 0.0879 5835 3123 53 Pass 0.0912 5197 3031 58 Pass 0.0944 4746 2920 61 Pass 0.0976 4357 2817 64 Pass 0.1009 4002 2708 67 Pass 0.1041 3533 2567 72 Pass 0.1074 3221 2436 75 Pass 0.1106 2920 2316 79 Pass 0.1138 2665 2197 82 Pass 0.1171 2357 2052 87 Pass 0.1203 2156 1961 90 Pass 0.1236 1986 1860 93 Pass 0.1268 1827 1740 95 Pass 0.1300 1669 1576 94 Pass 0.1333 1528 1498 98 Pass 0.1365 1365 1416 103 Pass 0.1397 1247 1336 107 Pass 0.1430 1159 1225 105 Pass 0.1462 1047 1103 105 Pass 0.1495 977 1020 104 Pass 0.1527 920 927 100 Pass 0.1559 859 831 96 Pass 0.1592 769 705 91 Pass 0.1624 713 626 87 Pass 0.1657 647 568 87 Pass 0.1689 591 509 86 Pass 0.1721 490 410 83 Pass 0.1754 432 340 78 Pass 0.1786 383 279 72 Pass 0.1819 347 265 76 Pass 0.1851 309 248 80 Pass 0.1883 271 237 87 Pass 0.1916 244 224 91 Pass 0.1948 206 207 100 Pass 0.1981 171 179 104 Pass 0.2013 146 149 102 Pass 0.2045 125 133 106 Pass 0.2078 112 121 108 Pass 0.2110 95 103 108 Pass 0.2142 85 89 104 Pass 0.2175 73 73 100 Pass 0.2207 62 59 95 Pass 0.2240 56 50 89 Pass 20544 Preliminary WWHM 12/1/2020 3:38:12 PM Page 25 0.2272 45 37 82 Pass 0.2304 41 32 78 Pass 0.2337 37 25 67 Pass 0.2369 35 21 60 Pass 0.2402 29 16 55 Pass 0.2434 25 9 36 Pass 0.2466 23 8 34 Pass 0.2499 19 6 31 Pass 0.2531 15 3 20 Pass 0.2564 12 3 25 Pass 0.2596 9 1 11 Pass 0.2628 9 0 0 Pass 0.2661 8 0 0 Pass 0.2693 8 0 0 Pass 0.2726 7 0 0 Pass 0.2758 7 0 0 Pass 0.2790 7 0 0 Pass 0.2823 7 0 0 Pass 0.2855 7 0 0 Pass 0.2887 7 0 0 Pass 0.2920 7 0 0 Pass 0.2952 6 0 0 Pass 0.2985 5 0 0 Pass 0.3017 5 0 0 Pass 0.3049 5 0 0 Pass 0.3082 4 0 0 Pass 0.3114 4 0 0 Pass 0.3147 4 0 0 Pass 0.3179 4 0 0 Pass 0.3211 4 0 0 Pass 0.3244 4 0 0 Pass 0.3276 4 0 0 Pass 0.3309 4 0 0 Pass 0.3341 4 0 0 Pass 0.3373 4 0 0 Pass 0.3406 4 0 0 Pass 0.3438 3 0 0 Pass 0.3471 3 0 0 Pass 0.3503 3 0 0 Pass 0.3535 2 0 0 Pass 0.3568 2 0 0 Pass 0.3600 2 0 0 Pass 0.3632 2 0 0 Pass 0.3665 2 0 0 Pass 0.3697 2 0 0 Pass 0.3730 2 0 0 Pass 0.3762 1 0 0 Pass 20544 Preliminary WWHM 12/1/2020 3:38:12 PM Page 26 Water Quality Water Quality BMP Flow and Volume for POC #2 On-line facility volume:0.2426 acre-feet On-line facility target flow:0.264 cfs. Adjusted for 15 min:0.264 cfs. Off-line facility target flow:0.1469 cfs. Adjusted for 15 min:0.1469 cfs. 20544 Preliminary WWHM 12/1/2020 3:38:12 PM Page 27 LID Report 20544 Preliminary WWHM 12/1/2020 3:38:13 PM Page 28 Model Default Modifications Total of 0 changes have been made. PERLND Changes No PERLND changes have been made. IMPLND Changes No IMPLND changes have been made. 20544 Preliminary WWHM 12/1/2020 3:38:13 PM Page 29 Appendix Predeveloped Schematic 20544 Preliminary WWHM 12/1/2020 3:38:15 PM Page 30 Mitigated Schematic