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Ex09_Preliminary_Technical_Information_Report
Western Washington Division Eastern Washington Division 165 NE Juniper St., Ste 201, Issaquah, WA 98027 108 East 2nd Street, 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 CITY OF RENTON For VEK on Aberdeen 957 Aberdeen Avenue Northeast Renton, WA 98056 December 11, 2020 12/11/2020 Prepared By: Briana Bennington Encompass Engineering Job No. 19510 Prepared For: Century Construction, LLC 13220 42nd Avenue East Tacoma, WA 98446 EXHIBIT 9 PLANNING DIVISION AWEIHS 03/04/2021 RECEIVED DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 VEK on Aberdeen Preliminary Technical Information Report 12/11/2020 Page i TABLE OF CONTENTS I. PROJECT OVERVIEW ............................................................................................................ 1 II. CONDITIONS AND REQUIREMENTS SUMMARY .................................................................. 6 III. OFFSITE ANALYSIS ............................................................................................................... 9 IV. FLOW CONTROL, LOW IMPACT DEVELOPMENT (LID) AND WATER QUALITY FACILITY ANALYSIS AND DESIGN ..................................................................................................... 20 V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN ................................................................ 24 VI. SPECIAL REPORTS AND STUDIES ....................................................................................... 24 VII. OTHER PERMITS ................................................................................................................ 24 VIII. CSWPPP ANALYSIS AND DESIGN ....................................................................................... 24 IX. BOND QUANTITIES AND DECLARATION OF COVENANT ................................................... 24 X. OPERATION AND MAINTENANCE MANUAL ..................................................................... 24 LIST OF FIGURES 1. TIR Worksheet 2. Site Location 3. Soils Map and Legend 4. Existing Conditions Map 5. Developed Conditions Map 6. Downstream Map 1 7. Downstream Map 2 8. Flow Frequency Return Periods 9. Oldcastle Biopod Sizing Chart APPENDIX A Revised Geotechnical Engineering Report by The Riley Group, Inc. dated September 2, 2020 APPENDIX B WWHM2012 Output APPENDIX C Oldcastle Infrastructure Biopod Submittal Package DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 957 Aberdeen Avenue NE Renton, WA 98056 VEK On Aberdeen NE-8 Century Construction LLC (206) 612-8647 13220 42nd Avenue East Tacoma, WA 98446 Chad Allen Encompass Engineering & Surveying (425) 392-0250 TBD 23 5 4 4 10/31/2019 12/11/2020 4 10/31/2019 12/11/2020 4 02/28/2020 02/28/2020 4 4 4 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 TBD TBD Newcastle N/A East Lake Washington - Renton None Yes Flow Control Duration Turbidity Monitoring 4 Stream 4 Steep Slopes present 4 Low and High EH areas 4 High Landslide Hazard DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Detention Tank Ragnar-Indianola As. (RdC, RdE)0-25%Medium/High East Lake Washington - Renton 1 1 03/05/19 Peak Rate Flow Control Standard Contractor Staging Area T.B.D. Low Erosion Hazard, High Erosion Hazard, High Landslide Hazard4 Alderwood and Kitsap (AkF)15-45%Medium/High DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Private No Yes Enhanced Basic None None None N/A No Oldcastle Biopod Biofilter Underground DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Detention Tank 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 BioPod 4 4 4 4 4 4 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Chad Allen 12/11/2020 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 VEK on Aberdeen Preliminary Technical Information Report 12/11/2020 1 I. PROJECT OVERVIEW Project Name: VEK on Aberdeen Tax Parcel #: 311990-0066 Site Address: 957 Aberdeen Avenue NE, Renton, WA 98056 Site Area: The tax parcel area is 54,057 SF (1.24 Acres) Legal Description: HARRIES GARDEN HOME TRS N 37.50 FT OF TRACT 11 TGW S 1/2 OF TRACT 12, Plat Lot: 11-12 Zoning: RM-F Figure 2: Site Location Predeveloped Site Conditions: The site is currently developed as a single-family residence. The parcel contains an existing residence with associated out buildings and a gravel driveway. The remainder of the site is vegetated with grass, trees, and shrubs. The site slopes to the western property border at 2% to 30%. Stormwater runoff from the existing site drains to a low point in the form of a natural stream which discharges at the western property border. A full Level 1 Downstream Analysis has been prepared for the project site and is included in Section III of thi s report. See Figure 4 for a map of the existing site conditions and drainage characteristics. Critical Areas: The Geotechnical Engineering Report prepared by The Riley Group, Inc., dated November 27, 2018, identifies two erosion hazard areas on-site. The eastern portion of the site meets the criteria for a Low Erosion Hazard (EL) and the western portion of the site meets the criteria of a High Erosion Hazard (EH). The report also identifies that the western portion of the site meets the criteria of High Landslide Hazards (LH). A Type NS Stream is located on the project site and requires a 50-foot buffer with an additional 15-foot BSBL. Per King County iMap, this site DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 VEK on Aberdeen Preliminary Technical Information Report 12/11/2020 2 is not located within a Critical Aquifer Recharge Area or any other mapped critical areas. The full Geotechnical Engineering Report is included in Appendix A of this report. Soils: Per the US Department of Agriculture, Natural Resources Conservation Service (NCRS) Web Soil Survey information, the project site is generally underlain with Ragnar-Indianola association (RdC, RdE), with smaller areas of Alderwood and Kitsap soils (AkF), and Urban Land (Ur). Per the Geotechnical Engineering Report, the site is underlain with “loose to medium dense silty sand with varying amounts of gravel, becoming dense at depths of three to six feet, over very stiff silt.” Test-Pit 2, located near the proposed stormwater tank location, encountered no groundwater seepage to the maximum testing depth of 8.5 feet. A field infiltration test was performed for this Geotech report and soils were found to be non-conductive to infiltration. Portions of both the neighboring properties to the north and south drain into the natural stream located on the western area of the parcel. Soils downstream of the site discharge location are classified as “Urban Land” per the NRCS mapping. Figure 3: Soils Map and Legend DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 VEK on Aberdeen Preliminary Technical Information Report 12/11/2020 4 Developed Site Conditions: The project proposes demolition of the existing onsite structures, and the clearing and grading of approximately 0.58 Acres on the 1.24 Acre site to accommodate the construction of two multi-family residential buildings and the platting of twelve individual multi-family parcels. An additional 0.02 Acres of offsite area will be improved by the project in the form of frontage redevelopment along Aberdeen Ave NE. Twelve unit-homes, designed by Monsef Design Studio, will be constructed in townhouse configuration s. A private unit lot driveway connecting to Aberdeen Avenue NE will be constructed to access the site development. Other amenities such as sidewalks and common space areas will be included in the site development. Stormwater runoff from the developed site will ultimately be routed to the predeveloped natural discharge location. The combination of a stormwater detention tank and an Oldcastle Biopod filtration device will comprise the on-site stormwater system for the project development. An above-ground tightline system will be utilized for the conveyance of mitigated flows from the system outlet over the on-site critical areas. DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 VEK on Aberdeen Preliminary Technical Information Report 12/11/2020 6 II. CONDITIONS AND REQUIREMENTS SUMMARY The 2017 City of Renton Surface Water Design Manual (RSWDM) along with the 2016 King County Surface Water Design Manual (KCSWDM) have been utilized for the preparation of this report and stormwater design per the City of Renton requirements. This project is a multi-family redevelopment and will result in more than 2,000 SF of new plus replaced impervious surface, but is not subject to Large Project Drainage Review. Therefore, the project is subject to a Full Drainage Review per Section 1.1.2.4 of the 2017 RSWDM and must comply with all 9 core requirements and all 5 special requirements. Core Requirements Core Requirement #1: Discharge at the Natural Location The existing site drains to a low point in the form of a vegetated drainage channel which discharges to the western edge of the property and it is conveyed off-site under Highway 405. The project proposes to emulate the existing site drainage patterns for the developed stormwater runoff. An above-ground tightline system, designed to convey stormwater runoff from the developed portion of the site over the onsite steep slopes, High Landslide Hazard, Low Erosion Hazard, and High Erosion Hazard areas is proposed to meet this requirement. Per the City of Renton’s comments, the tightline system will discharge flows at a location nearby John’s Creek and outside of the 15% sloped areas. See Sections IV and V of this report for further stormwater analysis. Core Requirement #2: Offsite Analysis A full Level 1 Downstream Analysis per Section 1.2.2.1 of the RSWDM has been prepared for the project and is included in Section III of this report. Core Requirement #3: Flow Control Facilities Per the City of Renton “On Hold” Notice dated January 10, 2020, this project site is within the “Flood Problem Flow Control Standard” area. In this area, flow control facilities are required to match the Flow Duration of pre-developed rates for Existing Site Conditions from 50% of the 2-year up to the full 50-year flow, and match Existing Site Conditions for the 2-, 10-, and 100-year peaks. A stormwater detention tank, designed per Section 5.1.2 of the RSWDM, will be utilized to mitigate all developed onsite flows for the project. The WWHM2012 program has been utilized for stormwater modeling calculations. After modeling the proposed system and applying the Flow Control BMP credits for soil amendment, per Table 1.2.9.A of the RSWDM, the WWHM output displayed that the developed conditions meet these standards. Therefore, no further flow control facilities are required. See Section IV for a full discussion of the flow control facilities, Figure 5 for a map of the developed site conditions, and Appendix B for the full WWHM2012 Output. DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 VEK on Aberdeen Preliminary Technical Information Report 12/11/2020 7 Core Requirement #4: Conveyance System The design and analysis of the proposed conveyance systems will be submitted with final engineering. The systems will be designed to meet the Conveyance Requirements for New Systems per Section 1.2.4.1 of the RSWDM. Core Requirement #5: Construction Stormwater Pollution Prevention A temporary erosion and sediment control (ESC) plan will provide BMPs to be implemented during construction for the project development. A Construction Stormwater Pollution Prevention (CSWPP) plan will be prepared for the site and included with final engineering. Core Requirement #6: Maintenance and Operations See Section X – Operation and Maintenance Manual of this report for details. 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 The project proposes the construction of approximately 6,875 SF of new and replaced pollution-generating impervious surfaces (PGIS). This is greater than the threshold of 5,000 SF of new PGIS, and more than 50% of the runoff that drains to the proposed water quality facility is from multifamily land use. Therefore, Enhanced Basic Water Quality treatment is required for this project per Section 1.2.8.1.A. Water quality requirements are proposed to be met using an Oldcastle Biopod filtration device. The biofiltration device has been sized to provide enhanced water quality treatment to all target surfaces on-site downstream of detention. See Section IV of this report for full discussion of water quality facilities and Appendix C for the Biopod submittal package. Core Requirement #9: On-Site BMPs The proposed development is considered by the City of Renton to be in order with the “Large Lot” project type. However, the City of Renton “On Hold” Notice, dated January 10, 2020 states: “Due to steep slopes, landslide and erosion hazard areas being located onsite, full dispersion, full infiltration, limited dispersion, limited infiltration, bioretention and permeable pavement are all infeasible. Specifically, Section 1.2.9.2.2 (5) of the 2017 RSWDM states: ‘The buildable portion of the site/lot is the total area of the site/lot minus any critical areas and minus a 200-foot buffer from a steep slope hazard, landslide hazard, or erosion hazard.’ For the applicability of BMP’s, the 200-foot buffer encompasses the entire site, therefore, per definition, there are no onsite buildable areas subject to BMP’s and the project is exempt from meeting Core Requirement #9.” DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 VEK on Aberdeen Preliminary Technical Information Report 12/11/2020 8 Special Requirements Special Requirement #1: Other Adopted Area-Specific Requirements Master Drainage Plan – N/A Basin Plan – N/A Salmon Conservation Plan – N/A Lake Management Plan – N/A Hazard Mitigation Plan – N/A Shared Facility Drainage Plan – N/A Special Requirement #2: Flood Hazard Area Delineation The limits of this project do not lie in the FEMA 100-year floodplain and do not contain and are not adjacent to a flood hazard area. Special Requirement #3: Flood Protection Facilities The site does not rely on any existing flood protection facilities and does not propose to modify or construct a new flood protection facility. Special Requirement #4: Source controls The project is not a commercial site and source controls are therefore not required. Special Requirement #5: Oil Control This project is not considered high-use or in need of oil control. Special Requirement #6: Aquifer Protection Area Per the City of Renton GIS maps, the project is not located within Zones 1 or 2 of an Aquifer Protection Area. DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 VEK on Aberdeen Preliminary Technical Information Report 12/11/2020 9 III. OFFSITE ANALYSIS A Level 1 downstream analysis per Section 1.2.2 of the RSWDM has been prepared for the site and is included in this section. The field inspection portion of the analysis was performed by Encompass Engineering & Surveying on Tuesday March 5, 2019. The analysis was performed at approximately 11:00 AM with a temperature of about 50°. The site is currently forested with one single-family residence. Access to the site is and will be provided by Aberdeen Ave NE. The site is contained entirely within the Cedar River Drainage Basin which discharges to the Lake Washington Watershed per King County iMap. The USGS Web Soil Survey has mapped the soils on site as Ragnar-Indianola association and an area of Alderwood and Kitsap soils. It is difficult to get photos or perform reconnaissance on-site due to dense vegetation and fences along most of the property boundaries, especially so for the area of the site in proximity to Hwy 405. The resources reviewed for this analysis include documents either previously developed by Encompass Engineering & Surveying for neighboring developments, obtained from City of Renton record drawings, or from the City of Renton GIS mapping. Stormwater runoff from the existing site sheet flows from the residential portion of the site down the steep slopes to the west and collects into a section of open channel flow (Map Element A) in the form of a vegetated drainage channel. This vegetated channel conveys flows west off the parcel toward Highway 405. Runoff from this element is collected by Catch Basins #1 and #2 (B) along the eastern edge of Hwy 405 East. Flows are then transported through a series of 36” Concrete and 36” Corrugated Metal Pipe (CMP) culverts (B) located underneath Hwy 405. This system connects to a Type 2 Storm Drain Manhole (SDMH #1, D). Element D drains via a series of 36” CMP culverts (E) along the east side of Houser Way N. The 36” CMP culverts extends to the south and collects stormwater runoff from Houser Way N via a series of Storm Drain Manholes (Elements F, G, H, and I) and associated catch basins. SDMH #5 (I) outlets to a section of 36” Concrete culvert (J) located under the Houser Way N right -of-way. This section of pipe also collects runoff from Houser Way N via two further Storm Drain Manholes (Elements K and L). This Level 1 Downstream Analysis was completed at the point (L) ¼ mile downstream of the site discharge location within the Houser Way N drainage system. Stormwater runoff associated with the frontage along Aberdeen Ave NE, or the “Bypass” area, flows north along the Aberdeen Ave NE gutter system. Flows enter the private “Aberdeen Townhomes” stormwater system via a type 1 catch basin (Facility ID No. 134561). Runoff from the private system (Facility ID No. 159573) is treated and discharged to John’s Creek. John’s Creek flows southwest onto the project site where the two drainage areas converge at the site’s point of compliance, less than ¼ mile downstream. See Figures 6 and 7 for further details. Neither King County iMap nor the City of Renton GIS maps show any drainage complaints within this downstream path. Based on this analysis no existing downstream problems were observed and no potential problems are anticipated to occur from the site development. DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 VEK on Aberdeen Preliminary Technical Information Report 12/11/2020 10 Figure 6: Downstream Map 1 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 VEK on Aberdeen Preliminary Technical Information Report 12/11/2020 11 Figure 7: Downstream Map 2 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 VEK on Aberdeen Preliminary Technical Information Report 12/11/2020 12 TABLE 1: OFF-SITE ANALYSIS DRAINAGE SYSTEM TABLE Basin: East Lake Washington - Renton Subbasin Name: Subbasin Number: Symbol Drainage Component Type, Name, and Size Drainage Component Description Slope Distance from site discharge Existing Problems Potential Problems Observations of field inspector, resource reviewer, or resident see map Type: sheet flow, swale, stream, channel, pipe, pond; Size: diameter, surface area drainage basin, vegetation, cover, depth, type of sensitive area, volume % ¼ ml = 1,320 ft. constrictions, under capacity, ponding, overtopping, flooding, habitat or organism destruction, scouring, bank sloughing, sedimentation, incision, other erosion tributary area, likelihood of problem, overflow pathways, potential impacts A SHEET FLOW / OPEN CHANNEL FLOW VEGETATED COVER, SEASONAL DRAINAGE CHANNEL 2- 30% POINT OF DISCHARGE – 400’ NONE SEDIMENT ATION, EROSION COLLECTS DRAINAGE FROM SITE AND PORTION OF NEIGHBORING PROPERTIES B CATCH BASIN #1 AND CATCH BASIN #2, BOTH TYPE 1 COLLECTION OF SITE RUNOFF ALONG EAST SIDE OF HWY 405 N/A 400’ NONE SEDIMENT ATION INFORMATION FROM CITY OF RENTON GIS MAPS C 36” CONCRETE CULVERT, 36” CMP COLLECTS RUNOFF FROM EXISTING HWY 405 SYSTEM 2 – 15% 400 – 600’ NONE SEDIMENT ATION CONVEYANCE WEST UNDER HWY 405 D SDMH #1, CB TYPE 2 COLLECTS RUNOFF FROM EXISTING HOUSER WAY N SYSTEM N/A 600’ NONE NONE ALONG EAST SIDE OF HOUSER WAY N E 36” CMP CONVEYANCE SOUTH ALONG HOUSER WAY N 0.5% 600 – 925’ NONE NONE F SDMH #2, CB TYPE 2 72” DIAMETER, COLLECTS RUNOFF FROM EXISTING HOUSER WAY N SYSTEM N/A 670’ NONE NONE DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 VEK on Aberdeen Preliminary Technical Information Report 12/11/2020 13 G SDMH #3, CB TYPE 2 COLLECTS RUNOFF FROM EXISTING HOUSER WAY N SYSTEM N/A 835’ NONE NONE H SDMH #4, CB TYPE 2 N/A 900’ NONE NONE I SDMH #5, CB TYPE 2 72” DIAMETER, COLLECTS RUNOFF FROM EXISTING HOUSER WAY N SYSTEM N/A 925’ NONE NONE LOCATED IN HOUSER WAY N RIGHT-OF-WAY J 36” CONCRETE CULVERT REINFORCED PIPE, CONVEYANCE SOUTH UNDER HOUSER WAY N 0.5% 925 – 1375’ NONE NONE K SDMH #6, CB TYPE 2 72” DIAMETER, COLLECTS RUNOFF FROM EXISTING HOUSER WAY N SYSTEM N/A 1150’ NONE NONE LOCATED IN HOUSER WAY N RIGHT-OF-WAY L SDMH #7, CB TYPE 2 84” DIAMETER, COLLECTS OUTFALL FROM HOUSER WAY N WETLAND AREAS N/A 1375’ NONE NONE CONNECTS TO NE 8TH STREET SYSTEM DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 VEK on Aberdeen Preliminary Technical Information Report 12/11/2020 14 Site Access off Aberdeen Ave NE Existing Lawn Area DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 VEK on Aberdeen Preliminary Technical Information Report 12/11/2020 15 Lower Portion of Existing Lawn Area Element A: Open Channel Flow at Western Portion of Site DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 VEK on Aberdeen Preliminary Technical Information Report 12/11/2020 16 Element A: Open Channel Flow at Western Portion of Site Edge of Property Marker DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 VEK on Aberdeen Preliminary Technical Information Report 12/11/2020 17 Elements C and D: 36” CMP under Hwy 405 and SDMH #1 Catch Basin along Houser Way N, Tributary to Element D DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 VEK on Aberdeen Preliminary Technical Information Report 12/11/2020 18 Element F: SDMH #2 along Houser Way N Element G: SDMH #3 along Houser Way N DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 VEK on Aberdeen Preliminary Technical Information Report 12/11/2020 19 Element H: SDMH #4 along Houser Way N Element I: SDMH #5 and Catch Basin along Houser Way N DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 VEK on Aberdeen Preliminary Technical Information Report 12/11/2020 20 IV. FLOW CONTROL, LOW IMPACT DEVELOPMENT (LID) AND WATER QUALITY FACILITY ANALYSIS AND DESIGN Part A: Existing Site Hydrology The site is currently developed as a single-family residence. The parcel contains an existing residence with associated out buildings and a gravel driveway. The remainder of the site is vegetated with grass, trees, and shrubs. Per the Geotechnical Engineering Report, the site is underlain with loose to medium dense silty sand with varying amounts of gravel, over very stiff silt. The site slopes to the western property border at slopes up to 120 percent. Stormwater runoff from the existing site drains to the low poi nt in the form of a vegetated drainage channel which drains to the western property edge. Stormwater runoff associated with the frontage along Aberdeen Ave NE, or the “Bypass” area, flows north along the Aberdeen Ave NE gutter system. Flows enter the private “Aberdeen Townhomes” stormwater system, is treated and then discharged to John’s Creek. A full Level 1 Downstream Analysis has been prepared for the project site and is included in Section III of this report. Table 2 on the following page shows the measured and modeled surface condition areas for both the existing and developed site conditions. See Figure 4 for a map of the existing site conditions. Part B: Developed Site Hydrology This project proposes the clearing and grading of approximately 0.58 Acres on the 1.24 Acre site to accommodate the construction of two multi-family residential buildings and the platting of twelve individual multi-family parcels. An additional 0.02 Acres of offsite area will be improved by the project in the form of frontage redevelopment along Aberdeen Ave NE. All developed stormwater runoff flows are designed to be discharged to the natural location identified in the Offsite Analysis. Table 2 on the following page shows the measured and modeled surface condition areas for both the existing and developed site conditions. See Figure 5 for a map of the developed site conditions. The 28,793 SF (0.66 AC) Tract F Critical Area proposed for the site has not been included in the stormwater models for the project as the existing conditions will be preserved by the development. The steep forested areas on the western portion of the site will be included in this tract and will not require mitigation of flows at the point of compliance. The Soil Amendment BMP per Appendix C.2.13 of the RSWDM will be used to stabilized all on- and off-site landscaped areas. Where available, naturally occurring soil and vegetation will be preserved. Areas disturbed by construction activities and designated to remain as pervious surfaces will be amended to a minimum soil quality and depth per the BMP requirements. The 6,342 SF (0.145 AC) of on- and off-site areas will be re-stabilized using this BMP and have been credited as “pasture” per Table 1.2.9.A of the RSWDM. DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 VEK on Aberdeen Preliminary Technical Information Report 12/11/2020 21 Table 2: WWHM Area Breakdown Predeveloped Mitigated Condition Measured Modeled Measured Modeled Lawn, Mod: 19,627 SF (0.450 AC) 19,627 SF (0.450 AC) Pasture, Mod: 6,342 SF (0.145 AC) 6,342 SF (0.145 AC) Roofs, Flat: 3,398 SF (0.078 AC) 3,398 SF (0.078 AC) 10,461 SF (0.240 AC) 10,461 SF (0.240 AC) Roads/Sidewalks/Driveways, Flat 3,267 SF (0.075 AC) 3,267 SF (0.075 AC) 9,489 SF (0.218 AC) 9,489 SF (0.218 AC) Total Area: 26,292 SF (0.603 AC) 26,292 SF (0.603 AC) 26,292 SF (0.603 AC) 26,292 SF (0.603 AC) A stormwater detention tank, designed per Section 5.1.2 of the RSWDM and sized using WWHM, will be utilized to mitigate the developed flows. A circular tank with a diameter of 10-feet and a length of 37-feet was designed in WWHM to meet the applicable flow control requirements for the project. See Appendix B for the full WWHM output. Part C: Performance Standards Per the City of Renton “On Hold” Notice, dated January 10, 2020, this project site is within the “Flood Problem Flow Control Standard” area. In this area, flow control facilities are required to match the Flow Duration of pre-developed rates for Existing Site Conditions from 50% of the 2 - year up to the full 50-year flow, and match Existing Site Conditions for the 2 -, 10-, and 100-year peaks. The City of Renton “On Hold” Notice, dated January 10, 2020 states: “Due to steep slopes, landslide and erosion hazard areas being located onsite, full dispersion, full infiltration, limited dispersion, limited infiltration, bioretention and permeable pavement are all infeasible. Specifically, Section 1.2.9.2.2 (5) of the 2017 RSWDM states: ‘The buildable portion of the site/lot is the total area of the site/lot minus any critical areas and minus 200 ft. buffer areas from a steep slope hazard, landslide hazard, or erosion hazard are ’. For the applicability of BMP’s, the 200 ft. buffer encompasses the entire site, therefore, per definition, there are no onsite buildable areas subject to BMP’s and the project is exempt from meeting Core Requirement #9.” The stormwater system will be designed to meet the Conveyance Requirements for New Systems per Section 1.2.4.1 of the RSWDM. The project proposes the construction of approximately 6,875 SF of new and replaced pollution- generating impervious surfaces (PGIS). This is greater than the threshold of 5,000 SF of new PGIS, and more than 50% of the runoff that drains to the proposed water quality facility is from multifamily land use. Therefore, Enhanced Basic Water Quality treatment is required for this project per Section 1.2.8.1.A. Source and Oil controls are not required for the project development. DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 VEK on Aberdeen Preliminary Technical Information Report 12/11/2020 22 Part D: Flow Control System A circular stormwater detention tank, designed per Section 5.1.2 of the RSWDM and sized using WWHM, will be utilized to mitigate the developed flows. This tank will provide the treatment necessary to meet the applicable “Flood Problem Flow Control Standard” requirements for the development. See the engineering plan set for the full system details and Appendix B for the full WWHM output. The mitigated flows will be conveyed to a riprap-lined outfall location via a tightline system comprised of 8” HDPE above-ground piping. This system will convey stormwater runoff from the tank outlet over onsite steep slopes, High Landslide Hazard, Low Erosion Hazard, and High Erosion Hazard areas. Per the City of Renton’s comments, the tightline system will discharge flows at a location nearby John’s Creek and outside of the 15% sloped areas. The design flow out of the Detention system for the 100-year storm is 0.1549 CFS. As shown in the Figure below, an 8” HDPE pipe sloped at approximately 28% will convey the design flow at a velocity of 8.21 FPS. With a design discharge velocity of 8.21 FPS, the outlet will require riprap protection per Table 4.2.2.A of the SWDM. DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 VEK on Aberdeen Preliminary Technical Information Report 12/11/2020 23 Figure 8: Flow Frequency Return Periods Per the WWHM output (Figure 8), the developed conditions meet the applicable flow control standards. Therefore, the use of further flow control facilities or BMPs is not required. Part E: Water Quality System Stormwater runoff from the onsite PGIS will be treated to the “Enhanced basic” water quality level per the RSWDM. This project proposes to meet this requirement by utilizing a Biopod filtration device, manufactured by Oldcastle Infrastructure, downstream of detention. This device is considered to be a proprietary facility and has been designed to meet all requirements listed in Section 6.7. Per Section 6.2.1 of the 2017 RSWDM, the Biopod was sized using the WWHM based on the full 2-year release rate from the detention facility. Per Figure 8 above, the 2-year release rate is 0.0485 CFS. As required in Section 6.2.1 of the 2017 RSWDM, the flow rate must be corrected in accordance with Table 6.2.1.A of the 2017 RSWDM. Based on the 2-Year 24-hour isopluvial map for western Washington, the 2-year 24-hour precipitation is approximately 1.95 inches. The 6- month 24-hour precipitation is 1.95-inches x 72% = 1.40-inches. Per the equation provided in Table 6.2.1.A of the 2017 RSWDM: 𝑘=1.4366(𝑃6−𝑚𝑚𝑚𝑡ℎ)−0.1369 = 1.4366(1.40)−0.1369 =1.88 Therefore, the corrected design water quality flow rate is (0.0 485)(1.88) = 0.0912 cfs. This is the flow rate that was used to size the water quality treatment system for the project. For these conditions, the Oldcastle BPU-412IB Underground Biopod configuration with a maximum treatment flowrate equal to 0.143 CFS has been selected using Oldcastle’s sizing chart (Figure 9) and is proposed for the development. The Biopod device has received General Use Level Designation (GULD) for Basic, Enhanced, and Phosphorus Treatment from the Washington State Department of Ecology. The device will be installed and maintained per the Department of Ecology’s Conditions of Use, detailed in Appendix C of this report. This design has been approved per an email from Jonathan Chavez, P.E. for the City of Renton. See Figure 10 for Biopod details, Appendix B for the full WWHM output, and Appendix C for the complete Biopod Submittal package. DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 VEK on Aberdeen Preliminary Technical Information Report 12/11/2020 24 Figure 9: Oldcastle Biopod Sizing Chart V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN Conveyance system analysis and design will be prepared for the project and provided with final engineering. VI. SPECIAL REPORTS AND STUDIES Revised Geotechnical Engineering Report Aberdeen Townhomes, prepared by The Riley Group, Inc., dated September 2, 2020. VII. OTHER PERMITS Building Permits, Land Use, Right-of-way Use, and Grading permits will be required for the project. VIII. CSWPPP ANALYSIS AND DESIGN A Construction Stormwater Pollution Prevention Plan (CSWPPP) will be prepared for the project and provided with final engineering. IX. BOND QUANTITIES AND DECLARATION OF COVENANT Bond Quantities and a Declaration of Covenant will be provided with final engineering. X. OPERATION AND MAINTENANCE MANUAL An Operation and Maintenance Manual will be provided with final engineering. DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 VEK on Aberdeen Preliminary Technical Information Report Appendix A Revised Geotechnical Engineering Report Aberdeen Townhomes 957 Aberdeen Avenue Northeast Renton, Washington By The Riley Group, Inc. Dated September 2, 2020 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Corporate Office 17522 Bothell Way Northeast Bothell, Washington 98011 Phone 425.415.0551 ♦ Fax 425.415.0311 www.riley-group.com REVISED GEOTECHNICAL ENGINEERING REPORT PREPARED BY: THE RILEY GROUP, INC. 17522 BOTHELL WAY NORTHEAST BOTHELL, WASHINGTON 98011 PREPARED FOR: CENTURY CONSTRUCTION, LLC 13220 42ND AVENUE EAST TACOMA, WASHINGTON 98446 RGI PROJECT NO. 2018-223 ABERDEEN TOWNHOMES 957 ABERDEEN AVENUE NORTHEAST RENTON, WASHINGTON SEPTEMBER 2, 2020 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Geotechnical Engineering Report i September 2, 2020 Aberdeen Townhomes, Renton, Washington RGI Project No. 2018-223 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 ....................................................................................................................................................... 3 4.4 GROUNDWATER ........................................................................................................................................ 3 4.5 SEISMIC CONSIDERATIONS ........................................................................................................................... 3 4.6 GEOLOGIC HAZARD AREAS .......................................................................................................................... 4 4.6.1 Steep Slopes ................................................................................................................................. 5 4.6.2 Landslide Hazards ........................................................................................................................ 5 4.6.3 Erosion Hazards ............................................................................................................................ 5 4.6.4 Seismic Hazards ............................................................................................................................ 5 4.6.5 Other Hazards .............................................................................................................................. 5 4.6.6 Slope Setbacks ............................................................................................................................. 5 5.0 DISCUSSION AND RECOMMENDATIONS ................................................................................. 6 5.1 GEOTECHNICAL CONSIDERATIONS ................................................................................................................. 6 5.2 EARTHWORK ............................................................................................................................................. 6 5.2.1 Erosion and Sediment Control ..................................................................................................... 7 5.2.2 Stripping ....................................................................................................................................... 8 5.2.3 Excavations................................................................................................................................... 8 5.2.4 Site Preparation ........................................................................................................................... 8 5.2.5 Structural Fill ................................................................................................................................ 9 5.2.6 Cut and Fill Slopes ...................................................................................................................... 11 5.2.7 Wet Weather Construction Considerations ............................................................................... 11 5.3 FOUNDATIONS ........................................................................................................................................ 12 5.4 RETAINING WALLS ................................................................................................................................... 13 5.5 SLAB-ON-GRADE CONSTRUCTION ............................................................................................................... 13 5.6 DRAINAGE .............................................................................................................................................. 14 5.6.1 Surface ....................................................................................................................................... 14 5.6.2 Subsurface .................................................................................................................................. 14 5.6.3 Infiltration .................................................................................................................................. 14 5.7 UTILITIES ................................................................................................................................................ 14 5.8 PAVEMENTS ............................................................................................................................................ 14 6.0 ADDITIONAL SERVICES .............................................................................................................. 15 7.0 LIMITATIONS ................................................................................................................................. 16 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Geotechnical Engineering Report ii September 2, 2020 Aberdeen Townhomes, Renton, Washington RGI Project No. 2018-223 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 Appendix B .................................................................................................................... Slope Stability DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Geotechnical Engineering Report iii September 2, 2020 Aberdeen Townhomes, Renton, Washington RGI Project No. 2018-223 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 three test pits to approximate depths of 9 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 loose to medium dense silty sand with varying amounts of gravel, becoming dense at depths of three to six feet, over very stiff silt. Groundwater: Groundwater seepage was encountered at 5.5 to 6.5 feet at TP-1 during our subsurface exploration. Foundations: Foundations for the proposed buildings 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 buildings can be supported on medium dense to dense native soil or structural fill. Pavements: The following pavement sections are recommended: For heavy truck traffic areas: 3 inches of Hot Mix Asphalt (HMA) over 6 inches of crushed rock base (CRB) For general parking areas: 2 inches of HMA over 4 inches of CRB For concrete pavement areas: 5 inches of concrete over 4 inches of CRB DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Geotechnical Engineering Report 1 September 2, 2020 Aberdeen Townhomes, Renton, Washington RGI Project No. 2018-223 1.0 Introduction This Geotechnical Engineering Report (GER) presents the results of the geotechnical engineering services provided for the Aberdeen Townhomes in Renton, Washington. The purpose of this evaluation is to assess subsurface conditions and provide geotechnical recommendations for the construction of townhomes on the site. 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 957 Aberdeen Avenue Northeast in Renton, Washington. The approximate location of the site is shown on Figure 1. Based on the plan provided, the existing residence and parking will be demolished and the site redeveloped with 12 townhomes, parking and utilities including stormwater control. The proposed townhomes have been designed to step down with the existing topography and minimize the site grading necessary. At the time of preparing this GER, building plans for the townhomes were not available for our review. Based on our experience with similar construction, RGI anticipates that the proposed buildings 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 November 13, 2018, RGI observed the excavation of three test pits. The approximate exploration locations are shown on Figure 2. Field logs of each exploration were prepared by the geologist that continuously observed the excavation. 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 logs included in Appendix A represent an interpretation of the field DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Geotechnical Engineering Report 2 September 2, 2020 Aberdeen Townhomes, Renton, Washington RGI Project No. 2018-223 logs and include modifications based on laboratory observation and analysis of the samples. 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 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 a rectangular-shaped parcel of land approximately 1.24 acres in size. The site is bound to the north and south by residential property, to the east by Aberdeen Avenue Northeast, and to the west by Puget Sound Energy undeveloped land and Interstate 405. The eastern portion of the site is occupied by a single family residence with attached shed, a shed, and a barn. The western portion of the site is occupied by a drainage feature that descends west to John Creek near the western property line. The eastern portion of the property descends generally west with an elevation change of about 28 feet over a horizontal distance of 290 feet. The area is vegetated with grass, decorative plants and shrubs, a garden, fruit trees, and scattered medium- to large- diameter trees. The western portion of the property descends generally west with an elevation change of about 84 feet over a horizontal distance of 300 feet. Slope gradients range from about 40 percent to over 120 percent. The area is vegetated with medium- to large-diameter trees with an undergrowth of ferns, mixed brush, and blackberry brambles. 4.2 GEOLOGY Review of the Geologic Map of the Renton Quadrangle, King County, Washington, by D. R. Mullineaux (1965) indicates that the soil through most of the site is mapped as Ground morain deposits (Map Unit Qgt), which is thin ablation till over lodgement till comprised of a nonsorted, nonstratified mixture of clay, silt, sand, and gravel. The soils in the westernmost portion of the site are mapped as Undifferentiated deposits (Qu) which include till, glaciofluvial sand and gravel, glaciolacustrine clay and sand, and non-glacial DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Geotechnical Engineering Report 3 September 2, 2020 Aberdeen Townhomes, Renton, Washington RGI Project No. 2018-223 deposits of clay, sand, and peat. These descriptions are generally similar to the findings in our field explorations. 4.3 SOILS The soils encountered during field exploration include loose to medium dense silty sand with varying amounts of gravel, becoming dense at depths of three to six feet, over very stiff silt. More detailed descriptions of the subsurface conditions encountered are presented in the test pits logs included in Appendix A. Sieve analysis was performed on four selected soil samples. Grain size distribution curves are included in Appendix A. 4.4 GROUNDWATER Groundwater seepage was encountered at 5.5 to 6.5 feet at TP-1 during our subsurface exploration. Surface seepage was observed near TP-1 and adjacent to and within the small stream channel extending east through the western portion of the site, and in John Creek extending south through the site near the western property line. 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. 4.5 SEISMIC CONSIDERATIONS Based on the 2015 International Building Code (IBC), RGI recommends the follow seismic parameters for design. Table 1 2012/2015 IBC Parameter Value Site Soil Class1 D2 Site Latitude 47.498842o N Site Longitude 122.191919o W Short Period Spectral Response Acceleration, SS (g) 1.438 1-Second Period Spectral Response Acceleration, S1 (g) 0.540 Adjusted Short Period Spectral Response Acceleration, SMS (g) 1.438 Adjusted 1-Second Period Spectral Response Acceleration, SM1 (g) 0.810 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. DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Geotechnical Engineering Report 4 September 2, 2020 Aberdeen Townhomes, Renton, Washington RGI Project No. 2018-223 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 extended to a maximum depth of 9 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 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 glacially consolidated deposits, 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 mapping on the City of Renton GIS, the site contains geologically hazardous areas including erosion and high landslide hazard areas. The slope on the west side of the site also contains sensitive and protected slope areas. To assess the stability of the slopes in the western portion of the site, a slope reconnaissance was performed on November 13, 2018. The western portion of the site is occupied by a drainage that descends west to John Creek near the western property line. The drainage originates on the property to the north, and the head of the drainage is occupied by a detention tank overflow comprised of a 12 inch Drisco pipe and spillway constructed of gabion cages and quarry spalls. The drainage appears to have intermittent flow, with native, glacially consolidated soils exposed along the channel and lower slope areas. Soils are generally silty sand in the upper drainage, with silt occupying the channel around the 135-foot elevation. Light seepage was observed along the sand/silt contact in the southern bank of the channel, consistent with seasonal perched groundwater collecting above the generally impermeable silt. Trees with curved trucks were observed that are indicative of surficial creep, however, the slopes are well vegetated with trees that do not appear to be effected by large-scale movements. Exposed soils at and near the base of the drainage are indicative of moderate erosion at the toe of slope during the wetter winter months. DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Geotechnical Engineering Report 5 September 2, 2020 Aberdeen Townhomes, Renton, Washington RGI Project No. 2018-223 4.6.1 STEEP SLOPES The site slopes have gradients in the range of about 40 percent to over 120 percent, and meet the criteria of Protected Slopes. 4.6.2 LANDSLIDE HAZARDS The site is mapped as a high landslide hazard area with slopes greater than forty percent in the western portion of the site. The area also appears to be underlain by silt deposits. The slopes in the western portion of the site meet the criteria of High Landslide Hazards (LH). 4.6.3 EROSION HAZARDS Review of the Soil Survey, King County Area, Washington by the USDA Soil Conservation Service (1973) indicates the eastern portion of the site is underlain by Ragnar-Indianola association, sloping (RdC) and the western portion of the site is underlain by Ragnar- Indianola association, moderately steep (RdE). The eastern portion of the site meets the criteria for a Low Erosion Hazard (EL) and the western portion of the site meets the criteria of a High Erosion Hazard (EH). The area of the site that is mapped as a high erosion hazard will not be developed. The portion of the site that will be developed should have erosion control measure as outlined in section 5.2.1 of this GER. 4.6.4 SEISMIC HAZARDS The site is not mapped as a seismic hazard area. The site is underlain by glacially consolidated deposits and seismic induced settlements are not expected. 4.6.5 OTHER HAZARDS There are no coal mine hazards, volcanic hazards or shoreline areas mapped on the site or within 150 feet of the site. 4.6.6 SLOPE SETBACKS The slope stability was revised in response to The City of Renton letter dated January 10, 2020 and was provided to the City under separate cover. The analysis has been incorporated into this updated report. RGI completed a stability analysis for the currently proposed conditions as shown on the plans and included the proposed drainage facilities. Per our recommendation, the retaining wall that was previously shown on the top of the slope has been removed and the grade changes will be accomplished with grading and the wall is not necessary except for the southwest corner and the wall is at the setback line. Based on the stability analysis of the proposed conditions, a buffer is not necessary for most of the slope. We have shown a small area near the center where the slope is the DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Geotechnical Engineering Report 6 September 2, 2020 Aberdeen Townhomes, Renton, Washington RGI Project No. 2018-223 steepest that does require a small buffer. The buffer area may be graded as shown on the plans and should be revegetated as part of the open space area for the project. The setback and buffer areas are shown on the attached Figure 2 and on the referenced plan in addition to the sections analyzed in the stability analysis which is also attached. Based on the results of our subsurface explorations and slope stability analysis, the proposal will not increase the threat of the geological hazard to adjacent or abutting properties beyond predevelopment conditions; and will not adversely impact other critical areas; and the proposed development can be safely accommodated on the site. The storm tight-line has been updated to avoid crossing the stream and the installation of storm drainage piping in a geologic hazard area is an exempt activity in accordance with RMC 4-3-050C3.iv. The storm pipe is an HDPE above ground pipe anchored on the surface that does not required modification of the slope. The stability analysis of the slope indicates stable conditions and the pipe installation should have no impact on the stability of the slopes. No mitigation for the pipe is necessary as the installation is not proposed to modify the slope conditions that currently exist. The pipe installation should take place in the drier summer months from June 30 through October 1 and any slope areas disturbed during installation should have erosion control measures consisting of a double sided straw or coir fiber erosion control blanket installed upon completion of the work. 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 buildings can be supported on conventional spread footings bearing on medium dense to dense native soil or structural fill. Slab-on- grade floors and pavements 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 We expect the earth work will consist of excavating the townhome foundations, installing underground utilities and preparing roadway and slab subgrades. The road grading and the townhomes slope and step down with the existing topography. We expect shallow cuts and fill to establish the proposed grades. DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Geotechnical Engineering Report 7 September 2, 2020 Aberdeen Townhomes, Renton, Washington RGI Project No. 2018-223 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 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 (Graded and disturbed slopes should be tracked in place with the equipment running perpendicular to the slope contours so that the track marks provide a texture to help resist erosion and channeling. Some sloughing and raveling of slopes with exposed or disturbed soil should be expected.) 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. DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Geotechnical Engineering Report 8 September 2, 2020 Aberdeen Townhomes, Renton, Washington RGI Project No. 2018-223 5.2.2 STRIPPING Stripping efforts should include removal of pavements, vegetation, organic materials, and deleterious debris from areas slated for building, pavement, and utility construction. The test pits encountered 6 to 18 inches of topsoil and rootmass. Deeper areas of stripping may be required in forested or heavily vegetated areas of the site. 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 loose to dense silty sand with varying amounts of gravel over very stiff silt. 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). If there is insufficient room to complete the excavations in this manner, or excavations greater than 20 feet in depth are planned, using temporary shoring to support the excavations should be considered. 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 SITE PREPARATION RGI anticipates that some areas of loose or soft soil will be exposed upon completion of stripping and grubbing. Proofrolling and subgrade verification should be considered an essential step in site preparation. After stripping, grubbing, and prior to placement of structural fill, RGI recommends proofrolling building and pavement subgrades and areas to receive structural fill. These areas should moisture conditioned and compacted to a firm and unyielding condition in order to achieve a minimum compaction level of 95 percent of the modified proctor maximum dry density as determined by the American Society of DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Geotechnical Engineering Report 9 September 2, 2020 Aberdeen Townhomes, Renton, Washington RGI Project No. 2018-223 Testing and Materials D1557-09 Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Modified Effort (ASTM D1557). Proofrolling and adequate subgrade compaction can only be achieved when the soils are within approximately ± 2 percent moisture content of the optimum moisture content. Soils which appear firm after stripping and grubbing may be proofrolled with a heavy compactor, loaded double-axle dump truck, or other heavy equipment under the observation of an RGI representative. This observer will assess the subgrade conditions prior to filling. The need for or advisability of proofrolling due to soil moisture conditions should be determined at the time of construction. In wet areas it may be necessary to hand probe the exposed subgrades in lieu of proofrolling with mechanical equipment. If fill is placed in areas of the site where existing slopes are steeper than 5:1 (Horizontal:Vertical), the area should be benched to reduce the potential for slippage between existing slopes and fills. Benches should be wide enough to accommodate compaction and earth moving equipment, and to allow placement of horizontal lifts of fill. 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. 5.2.5 STRUCTURAL FILL Once stripping, clearing and other preparing operations are complete, cuts and fills can be made to establish desired building grades. Prior to placing fill, RGI recommends proof- rolling as described above. 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 structural fill should be placed after completion of site preparation procedures as described above. 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 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Geotechnical Engineering Report 10 September 2, 2020 Aberdeen Townhomes, Renton, Washington RGI Project No. 2018-223 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 ASTM D1557. 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. Even during the summer, delays in grading can occur due to excessively high moisture conditions of the soils or due to precipitation. If wet weather occurs, the upper wetted portion of the site soils may need to be scarified and allowed to dry prior to further earthwork, or may need to be wasted from the site. 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. DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Geotechnical Engineering Report 11 September 2, 2020 Aberdeen Townhomes, Renton, Washington RGI Project No. 2018-223 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 Pavement – Subgrade and Base Course On-site granular or approved imported fill soils: 95 +2 -2 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. 5.2.6 CUT AND FILL SLOPES All permanent cut and fill slopes should be graded with a finished inclination no greater than 2H:1V. Upon completion of construction, the slope face should be trackwalked, compacted and vegetated, or provided with other physical means to guard against erosion. All fill placed for slope construction should meet the structural fill requirements as described in Section 5.2.5. Final grades at the top of the slopes must promote surface drainage away from the slope crest. Water must not be allowed to flow in an uncontrolled fashion over the slope face. If it is necessary to direct surface runoff towards the slope, it should be controlled at the top of the slope, piped in a closed conduit installed on the slope face, and taken to an appropriate point of discharge beyond the toe of the slope. 5.2.7 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. DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Geotechnical Engineering Report 12 September 2, 2020 Aberdeen Townhomes, Renton, Washington RGI Project No. 2018-223 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 foundations can be supported on conventional spread footings bearing on medium dense native soil or structural fill. Loose, organic, or other unsuitable soils may be encountered in the proposed building footprints. If unsuitable soils are encountered, they should be overexcavated and backfilled with structural fill. 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. Table 4 Foundation Design Design Parameter Value Allowable Bearing Capacity 2,500 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 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 5.2.5. The recommended base friction and passive resistance value includes a safety factor of about 1.5. 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. DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Geotechnical Engineering Report 13 September 2, 2020 Aberdeen Townhomes, Renton, Washington RGI Project No. 2018-223 5.4 RETAINING WALLS If retaining walls are needed in the building area, RGI recommends cast-in-place concrete walls be used. Grade changes outside of the building areas may be completed with slopes or modular block retaining walls. The magnitude of earth pressure development on cast-in place 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 2,500 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 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. DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Geotechnical Engineering Report 14 September 2, 2020 Aberdeen Townhomes, Renton, Washington RGI Project No. 2018-223 5.6 DRAINAGE 5.6.1 SURFACE Final exterior grades should promote free and positive drainage away from the building areas. Water must not be allowed to pond or collect adjacent to foundations or within the immediate building areas. 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 soils are not conducive to infiltration. We do not recommend infiltration on the site due to the relatively impermeable soils and the slopes on the west side of the site. 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 5.2.5. 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 onsite should be suitable for use as backfill material provided to soils can be moisture conditioned. Imported structural fill meeting the gradation provided in Table 2 may be necessary for trench backfill if the native soils cannot be moisture conditioned. 5.8 PAVEMENTS Pavement subgrades should be prepared as described in Section 5.2 and as discussed below. Regardless of the relative compaction achieved, the subgrade must be firm and relatively unyielding before paving. The subgrade should be proof-rolled with heavy construction equipment to verify this condition. DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Geotechnical Engineering Report 15 September 2, 2020 Aberdeen Townhomes, Renton, Washington RGI Project No. 2018-223 5.8.1 FLEXIBLE PAVEMENTS With the pavement subgrade prepared as described above, RGI recommends the following pavement sections for parking and drive areas paved with flexible asphalt concrete surfacing. For drive areas: 3 inches of Hot Mix Asphalt (HMA) over 6 inches of crushed rock base (CRB) For general parking areas: 2 inches of HMA over 4 inches of CRB 5.8.2 CONCRETE PAVEMENTS With the pavement subgrade prepared as described above, RGI recommends the following pavement sections for parking and drive areas paved with concrete surfacing. For concrete pavement areas: 5 inches of concrete over 4 inches of CRB The paving materials used should conform to the WSDOT specifications for HMA, concrete paving, CRB surfacing (9-03.9(3) Crushed Surfacing), and gravel base (9-03.10 Aggregate for Gravel Base). Long-term pavement performance will depend on surface drainage. A poorly-drained pavement section will be subject to premature failure as a result of surface water infiltrating into the subgrade soils and reducing their supporting capability. For optimum pavement performance, surface drainage gradients of no less than 2 percent are recommended. Also, some degree of longitudinal and transverse cracking of the pavement surface should be expected over time. Regular maintenance should be planned to seal cracks when they occur. 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. DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Geotechnical Engineering Report 16 September 2, 2020 Aberdeen Townhomes, Renton, Washington RGI Project No. 2018-223 7.0 Limitations This GER is the property of RGI, Century Construction, LLC, 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 Aberdeen Townhomes project in Renton, Washington, and for the exclusive use of Century Construction, LLC 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. DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 USGS, 2014, Mercer Island, Washington USGS, 2014, Renton, 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 Aberdeen Townhomes RGI Project Number 2018-223 Date Drawn: Address: 957 Aberdeen Avenue Northeast, Renton, Washington 98056 SITE DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 B'AA'CC'TP-2TP1TP-3B09/2020Corporate Office17522 Bothell Way NortheastBothell, Washington 98011Phone: 425.415.0551Fax: 425.415.0311Aberdeen TownhomesRGI Project Number2018-223Date Drawn:Address: 957 Aberdeen Avenue Northeast, Renton, Washington 98056Geotechnical Exploration PlanFigure 2Approximate Scale: 1"=80'04080160N= Slope stability cross section= Test pit by RGI, 11/13/18= Site boundaryDocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 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 Aberdeen Townhomes RGI Project Number 2018-223 Date Drawn: Address: 957 Aberdeen Avenue Northeast, Renton, Washington 98056 Retaining Wall Drainage Detail Figure 3 Not to Scale DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 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 Aberdeen Townhomes RGI Project Number 2018-223 Date Drawn: Address: 957 Aberdeen Avenue Northeast, Renton, Washington 98056 Typical Footing Drain Detail Figure 4 Not to Scale DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Geotechnical Engineering Report September 2, 2020 Aberdeen Townhomes, Renton, Washington RGI Project No. 2018-223 APPENDIX A FIELD EXPLORATION AND LABORATORY TESTING On November 13, 2018, RGI performed field explorations using mini excavator. We explored subsurface soil conditions at the site by observing the excavation of three test pits to a maximum depth of 9 feet below existing grade. The test pits locations are shown on Figure 2. The test pits 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 sam1ples 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 pit 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 four of the samples. DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Project Name:Aberdeen Townhomes Project Number:2018-223 Client:Century Construction, LLC Test Pit No.: TP-1 Date(s) Excavated:11/13/2018 Excavation Method:Test Pit Excavator Type:Mini Excavator Groundwater Level:Seepage from 5.5 to 6.5' Test Pit Backfill:Cuttings Logged By ELW Bucket Size:N/A Excavating Contractor:Kelly's Excavating Sampling Method(s)Grab Location 957 Aberdeen Avenue Northeast, Renton, Washington Surface Conditions:Mixed Brush Total Depth of Excavation:9 feet bgs Approximate Surface Elevation 182 Compaction Method Bucket USCS SymbolTPSL SM SM ML REMARKS AND OTHER TESTS 23% moisture 22% moisture 21% moisture 17% moisture, 33% fines 17% moisture 19% moisture 23% moisture 18% moistureGraphic LogMATERIAL DESCRIPTION 18" topsoil Reddish brown silty SAND, loose to medium dense, moist to wet Tan silty SAND with trace gravel, medium dense, wet Becomes mottled Light to moderate groundwater seepage at 5.5 to 6.5 feet Becomes dense, moist Gray SILT, very stiff, moist Contains pockets of sand with iron oxide staining Test Pit terminated at 9'Depth (feet)0 5 10 Sample NumberSample TypeElevation (feet)182 177 172 Sheet 1 of 1 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Project Name:Aberdeen Townhomes Project Number:2018-223 Client:Century Construction, LLC Test Pit No.: TP-2 Date(s) Excavated:11/13/2018 Excavation Method:Test Pit Excavator Type:Mini Excavator Groundwater Level:Not Encountered Test Pit Backfill:Cuttings Logged By ELW Bucket Size:N/A Excavating Contractor:Kelly's Excavating Sampling Method(s)Grab Location 957 Aberdeen Avenue Northeast, Renton, Washington Surface Conditions:Grass Total Depth of Excavation:8.5 feet bgs Approximate Surface Elevation 182 Compaction Method Bucket USCS SymbolTPSL SM SM REMARKS AND OTHER TESTS 13% moisture 16% moisture 8% moisture 6% moisture, 29% fines 10% moisture 8% moistureGraphic LogMATERIAL DESCRIPTION 6" topsoil Brown silty SAND, loose, moist Tan silty SAND with some gravel, loose to medium dense, moist to wet Becomes medium dense, dry to moist Becomes dense, dry Becomes moist, lightly cemented Trace iron oxide staining Test Pit terminated at 8.5'Depth (feet)0 5 10 Sample NumberSample TypeElevation (feet)182 177 172 Sheet 1 of 1 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Project Name:Aberdeen Townhomes Project Number:2018-223 Client:Century Construction, LLC Test Pit No.: TP-3 Date(s) Excavated:11/13/2018 Excavation Method:Test Pit Excavator Type:Mini Excavator Groundwater Level:Not Encountered Test Pit Backfill:Cuttings Logged By ELW Bucket Size:N/A Excavating Contractor:Kelly's Excavating Sampling Method(s)Grab Location 957 Aberdeen Avenue Northeast, Renton, Washington Surface Conditions:Grass Total Depth of Excavation:9 feet bgs Approximate Surface Elevation 188 Compaction Method Bucket USCS SymbolTPSL SM REMARKS AND OTHER TESTS 15% moisture 15% moisture, 29% fines 9% moisture 7% moisture 19% moisture 8% moistureGraphic LogMATERIAL DESCRIPTION 10" topsoil Reddish brown silty SAND with trace gravel, loose, moist Becomes tan, mottled Becomes dense, dry to moist Lightly cemented Trace iron oxide staining Contains sand and silt interbeds iron oxide staining in sand beds Test Pit terminated at 9'Depth (feet)0 5 10 Sample NumberSample TypeElevation (feet)188 183 178 Sheet 1 of 1 The Riley Group, Inc. 17522 Bothell Way NE, Bothell, WA 98011 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Project Name:Aberdeen Townhomes Project Number:2018-223 Client:Century Construction, LLC 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 SILT, SILT w/SAND, SANDY SILT (ML)Silty SAND (SM) Topsoil 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 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 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 Aberdeen Townhomes SAMPLE ID/TYPE Outcrop PROJECT NO.2018‐223 SAMPLE DEPTH Surface TECH/TEST DATE EW 11/14/2018 DATE RECEIVED 11/14/2018 WATER CONTENT (Delivered Moisture) Total Weight Of Sample Used For Sieve Corrected For Hygroscopic Moisture Wt Wet Soil & Tare (gm) (w1)340.1 Weight Of Sample (gm)301.0 Wt Dry Soil & Tare (gm) (w2)301.0 Tare Weight (gm) 16.0 Weight of Tare (gm) (w3)16.0 (W6) Total Dry Weight (gm) 285.0 Weight of Water (gm) (w4=w1‐w2) 39.1 SIEVE ANALYSIS Weight of Dry Soil (gm) (w5=w2‐w3) 285.0 Cumulative Moisture Content (%) (w4/w5)*100 14 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 0.4 2.5" coarse gravel % C SAND 0.5 2.0" coarse gravel % M SAND 1.3 1.5"16.0 0.00 0.00 100.00 coarse gravel % F SAND 9.6 1.0" coarse gravel % FINES 88.2 0.75"16.0 0.00 0.00 100.00 fine gravel % TOTAL 100.0 0.50" fine gravel 0.375"16.0 0.00 0.00 100.00 fine gravel D10 (mm)#4 17.0 1.00 0.35 99.65 coarse sand D30 (mm)#10 18.5 2.50 0.88 99.12 medium sand D60 (mm)#20 medium sand Cu #40 22.2 6.20 2.18 97.82 fine sand Cc #60 fine sand #100 31.9 15.90 5.58 94.42 fine sand #200 49.5 33.50 11.75 88.25 fines PAN 301.0 285.00 100.00 0.00 silt/clay 322 DESCRIPTION SILT with trace sand USCS ML Prepared For: Reviewed By: Century Construction, LLC 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 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 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 Aberdeen Townhomes SAMPLE ID/TYPE TP‐1 PROJECT NO.2018‐223 SAMPLE DEPTH 5' TECH/TEST DATE EW 11/14/2018 DATE RECEIVED 11/14/2018 WATER CONTENT (Delivered Moisture) Total Weight Of Sample Used For Sieve Corrected For Hygroscopic Moisture Wt Wet Soil & Tare (gm) (w1)279.1 Weight Of Sample (gm)241.6 Wt Dry Soil & Tare (gm) (w2)241.6 Tare Weight (gm) 15.9 Weight of Tare (gm) (w3)15.9 (W6) Total Dry Weight (gm) 225.7 Weight of Water (gm) (w4=w1‐w2) 37.5 SIEVE ANALYSIS Weight of Dry Soil (gm) (w5=w2‐w3) 225.7 Cumulative Moisture Content (%) (w4/w5)*100 17 Wt Ret (Wt‐Tare) (%Retained)% PASS +Tare {(wt ret/w6)*100}(100‐%ret) % COBBLES 0.0 12.0"15.9 0.00 0.00 100.00 cobbles % C GRAVEL 0.0 3.0"15.9 0.00 0.00 100.00 coarse gravel % F GRAVEL 5.3 2.5" coarse gravel % C SAND 3.8 2.0" coarse gravel % M SAND 12.0 1.5"15.9 0.00 0.00 100.00 coarse gravel % F SAND 46.5 1.0" coarse gravel % FINES 32.5 0.75"15.9 0.00 0.00 100.00 fine gravel % TOTAL 100.0 0.50" fine gravel 0.375"18.0 2.10 0.93 99.07 fine gravel D10 (mm)#4 27.8 11.90 5.27 94.73 coarse sand D30 (mm)#10 36.4 20.50 9.08 90.92 medium sand D60 (mm)#20 medium sand Cu #40 63.4 47.50 21.05 78.95 fine sand Cc #60 fine sand #100 136.7 120.80 53.52 46.48 fine sand #200 168.3 152.40 67.52 32.48 fines PAN 241.6 225.70 100.00 0.00 silt/clay 322 DESCRIPTION Silty SAND with trace gravel USCS SM Prepared For: Reviewed By: Century Construction, LLC 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 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 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 Aberdeen Townhomes SAMPLE ID/TYPE TP‐2 PROJECT NO.2018‐223 SAMPLE DEPTH 4.5' TECH/TEST DATE EW 11/14/2018 DATE RECEIVED 11/14/2018 WATER CONTENT (Delivered Moisture) Total Weight Of Sample Used For Sieve Corrected For Hygroscopic Moisture Wt Wet Soil & Tare (gm) (w1)556.1 Weight Of Sample (gm)527.2 Wt Dry Soil & Tare (gm) (w2)527.2 Tare Weight (gm) 15.9 Weight of Tare (gm) (w3)15.9 (W6) Total Dry Weight (gm) 511.3 Weight of Water (gm) (w4=w1‐w2) 28.9 SIEVE ANALYSIS Weight of Dry Soil (gm) (w5=w2‐w3) 511.3 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"15.9 0.00 0.00 100.00 cobbles % C GRAVEL 13.7 3.0"15.9 0.00 0.00 100.00 coarse gravel % F GRAVEL 6.3 2.5" coarse gravel % C SAND 3.9 2.0" coarse gravel % M SAND 10.1 1.5"15.9 0.00 0.00 100.00 coarse gravel % F SAND 37.6 1.0" coarse gravel % FINES 28.5 0.75"85.9 70.00 13.69 86.31 fine gravel % TOTAL 100.0 0.50" fine gravel 0.375"95.4 79.50 15.55 84.45 fine gravel D10 (mm)#4 117.9 102.00 19.95 80.05 coarse sand D30 (mm)#10 137.6 121.70 23.80 76.20 medium sand D60 (mm)#20 medium sand Cu #40 189.1 173.20 33.87 66.13 fine sand Cc #60 fine sand #100 340.0 324.10 63.39 36.61 fine sand #200 381.5 365.60 71.50 28.50 fines PAN 527.2 511.30 100.00 0.00 silt/clay 322 DESCRIPTION Silty SAND with some gravel USCS SM Prepared For: Reviewed By: Century Construction, LLC 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 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 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 Aberdeen Townhomes SAMPLE ID/TYPE TP‐3 PROJECT NO.2018‐223 SAMPLE DEPTH 2' TECH/TEST DATE EW 11/14/2018 DATE RECEIVED 11/14/2018 WATER CONTENT (Delivered Moisture) Total Weight Of Sample Used For Sieve Corrected For Hygroscopic Moisture Wt Wet Soil & Tare (gm) (w1)355.6 Weight Of Sample (gm)311.7 Wt Dry Soil & Tare (gm) (w2)311.7 Tare Weight (gm) 15.9 Weight of Tare (gm) (w3)15.9 (W6) Total Dry Weight (gm) 295.8 Weight of Water (gm) (w4=w1‐w2) 43.9 SIEVE ANALYSIS Weight of Dry Soil (gm) (w5=w2‐w3) 295.8 Cumulative Moisture Content (%) (w4/w5)*100 15 Wt Ret (Wt‐Tare) (%Retained)% PASS +Tare {(wt ret/w6)*100}(100‐%ret) % COBBLES 0.0 12.0"15.9 0.00 0.00 100.00 cobbles % C GRAVEL 0.0 3.0"15.9 0.00 0.00 100.00 coarse gravel % F GRAVEL 7.4 2.5" coarse gravel % C SAND 5.3 2.0" coarse gravel % M SAND 16.7 1.5"15.9 0.00 0.00 100.00 coarse gravel % F SAND 41.4 1.0" coarse gravel % FINES 29.1 0.75"15.9 0.00 0.00 100.00 fine gravel % TOTAL 100.0 0.50" fine gravel 0.375"27.6 11.70 3.96 96.04 fine gravel D10 (mm)#4 37.9 22.00 7.44 92.56 coarse sand D30 (mm)#10 53.7 37.80 12.78 87.22 medium sand D60 (mm)#20 medium sand Cu #40 103.1 87.20 29.48 70.52 fine sand Cc #60 fine sand #100 191.6 175.70 59.40 40.60 fine sand #200 225.5 209.60 70.86 29.14 fines PAN 311.7 295.80 100.00 0.00 silt/clay 322 DESCRIPTION Silty SAND with trace gravel USCS SM Prepared For: Reviewed By: Century Construction, LLC 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 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 Geotechnical Engineering Report September 2, 2020 Aberdeen Townhomes, Renton, Washington RGI Project No. 2018-223 APPENDIX B SLOPE STABILITY RGI performed the slope stability analysis by using a computer program, Slide version 6.0, which was developed by Rocscience. The safety factor for the critical surfaces was calculated by the Bishop Method. The analyses were performed for the existing conditions under static and seismic loading condition, as well as the proposed conditions. DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 1.1171.11711 150.00 lbs/ft21.1171.117Material NameColorUnit WeightlStrength TypeCoheionlPhiWater SurfaceRuSilty sand125Mohr-Coulomb20036Piezometric Line 1Silt110Mohr-Coulomb40034None0 0.2Safety Factor0.0000.2500.5000.7501.0001.2501.5001.7502.0002.2502.5002.7503.0003.2503.5003.7504.0004.2504.5004.7505.0005.2505.5005.7506.000+275250225200175150125-50-250255075100125150175200Analysis DescriptionProposed Seismic A-A'CompanyRiley Group, Inc.Scale1:310Drawn ByELWFile NameProposed Seismic A-A'.slimDate11/20/2018, 10:14:49 AMProjectAberdeen TownhomesSLIDEINTERPRET 6.009DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 1.1731.1731 150.00 lbs/ft21.1731.173Material NameColorUnit WeightlStrength TypeCoheionlPhiWater SurfaceRuSilty sand125Mohr-Coulomb20036Piezometric Line 1Silt110Mohr-Coulomb40034None0Fill125Mohr-Coulomb036None0 0.2Safety Factor0.0000.2500.5000.7501.0001.2501.5001.7502.0002.2502.5002.7503.0003.2503.5003.7504.0004.2504.5004.7505.0005.2505.5005.7506.000+260240220200180160140-40-20020406080100120140160180Analysis DescriptionProposed Seismic - B-B'CompanyRiley Group, Inc.Scale1:281Drawn ByELWFile NameProposed Seismic B-B'.slimDate11/20/2018, 10:14:49 AMProjectAberdeen TownhomesSLIDEINTERPRET 6.009DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 1.3681.3681 150.00 lbs/ft21.3681.368Material NameColorUnit WeightlStrength TypeCoheionlPhiWater SurfaceRuSilty sand125Mohr-Coulomb20036Piezometric Line 1Silt110Mohr-Coulomb40034None0 0.2Safety Factor0.0000.2500.5000.7501.0001.2501.5001.7502.0002.2502.5002.7503.0003.2503.5003.7504.0004.2504.5004.7505.0005.2505.5005.7506.000+300250200150-50-250255075100125150175200225Analysis DescriptionProposed Seismic - C-C'CompanyRiley Group, Inc.Scale1:374Drawn ByELWFile NameProposed Seismic C-C'.slimDate11/20/2018, 10:14:49 AMProjectAberdeen TownhomesSLIDEINTERPRET 6.009DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 1.6001.60011 150.00 lbs/ft21.6001.600Material NameColorUnit WeightlStrength TypeCoheionlPhiWater SurfaceRuSilty sand125Mohr-Coulomb20036Piezometric Line 1Silt110Mohr-Coulomb40034None0Fill125Mohr-Coulomb036None0Safety Factor0.0000.2500.5000.7501.0001.2501.5001.7502.0002.2502.5002.7503.0003.2503.5003.7504.0004.2504.5004.7505.0005.2505.5005.7506.000+275250225200175150125-50-250255075100125150175200Analysis DescriptionProposed Static A-A'CompanyRiley Group, Inc.Scale1:311Drawn ByELWFile NameProposed Static.slimDate11/20/2018, 10:14:49 AMProjectAberdeen TownhomesSLIDEINTERPRET 6.009DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 1.6641.6641 150.00 lbs/ft21.6641.664Material NameColorUnit WeightlStrength TypeCoheionlPhiWater SurfaceRuSilty sand125Mohr-Coulomb20036Piezometric Line 1Silt110Mohr-Coulomb40034None0Fill125Mohr-Coulomb036None0Safety Factor0.0000.2500.5000.7501.0001.2501.5001.7502.0002.2502.5002.7503.0003.2503.5003.7504.0004.2504.5004.7505.0005.2505.5005.7506.000+275250225200175150-60-40-20020406080100120140160180Analysis DescriptionProposed Static - B-B'CompanyRiley Group, Inc.Scale1:290Drawn ByELWFile NameProposed Static B-B'.slimDate11/20/2018, 10:14:49 AMProjectAberdeen TownhomesSLIDEINTERPRET 6.009DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 2.0402.0401 150.00 lbs/ft22.0402.040Material NameColorUnit WeightlStrength TypeCoheionlPhiWaterSurfaceRuSilty sand125Mohr-Coulomb20036PiezometricLine 1Silt110Mohr-Coulomb40034None0Safety Factor0.0000.2500.5000.7501.0001.2501.5001.7502.0002.2502.5002.7503.0003.2503.5003.7504.0004.2504.5004.7505.0005.2505.5005.7506.000+300250200150-75-50-250255075100125150175200225Analysis DescriptionProposed Static - C-C'CompanyRiley Group, Inc.Scale1:374Drawn ByELWFile NameProposed Static C-C'.slimDate11/20/2018, 10:14:49 AMProjectAberdeen TownhomesSLIDEINTERPRET 6.009DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 VEK on Aberdeen Preliminary Technical Information Report Appendix B WWHM2012 Output DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 WWHM2012 PROJECT REPORT DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 19510 - WWHM Analysis 12/9/2020 1:26:52 PM Page 2 General Model Information Project Name:19510 - WWHM Analysis Site Name: Site Address: City: Report Date:12/9/2020 Gage:Seatac Data Start:1948/10/01 Data End:2009/09/30 Timestep:15 Minute Precip Scale:0.000 (adjusted) Version Date:2019/09/13 Version:4.2.17 POC Thresholds Low Flow Threshold for POC1:50 Percent of the 2 Year High Flow Threshold for POC1:50 Year DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 19510 - WWHM Analysis 12/9/2020 1:26:52 PM Page 3 Landuse Basin Data Predeveloped Land Use Basin 1 Bypass:No GroundWater:No Pervious Land Use acre C, Lawn, Mod 0.45 Pervious Total 0.45 Impervious Land Use acre ROADS MOD 0.075 ROOF TOPS FLAT 0.078 Impervious Total 0.153 Basin Total 0.603 Element Flows To: Surface Interflow Groundwater DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 19510 - WWHM Analysis 12/9/2020 1:26:52 PM Page 4 Mitigated Land Use Basin 1 Bypass:No GroundWater:No Pervious Land Use acre C, Pasture, Mod 0.145 Pervious Total 0.145 Impervious Land Use acre ROADS MOD 0.218 ROOF TOPS FLAT 0.24 Impervious Total 0.458 Basin Total 0.603 Element Flows To: Surface Interflow Groundwater Tank 1 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 19510 - WWHM Analysis 12/9/2020 1:26:52 PM Page 6 Mitigated Routing Tank 1 Dimensions Depth:10 ft. Tank Type:Circular Diameter:10 ft. Length:37 ft. Discharge Structure Riser Height:9 ft. Riser Diameter:12 in. Notch Type:Rectangular Notch Width:0.005 ft. Notch Height:2.500 ft. Orifice 1 Diameter:0.625 in.Elevation:0 ft. Orifice 2 Diameter:0.75 in.Elevation:2.5 ft. Element Flows To: Outlet 1 Outlet 2 Tank Hydraulic Table Stage(feet)Area(ac.)Volume(ac-ft.)Discharge(cfs)Infilt(cfs) 0.5000 0.000 0.000 0.000 0.000 0.6111 0.001 0.000 0.003 0.000 0.7222 0.002 0.000 0.005 0.000 0.8333 0.003 0.000 0.006 0.000 0.9444 0.003 0.001 0.007 0.000 1.0556 0.003 0.001 0.007 0.000 1.1667 0.004 0.001 0.008 0.000 1.2778 0.004 0.002 0.009 0.000 1.3889 0.004 0.002 0.010 0.000 1.5000 0.005 0.003 0.010 0.000 1.6111 0.005 0.004 0.011 0.000 1.7222 0.005 0.004 0.011 0.000 1.8333 0.005 0.005 0.012 0.000 1.9444 0.006 0.005 0.012 0.000 2.0556 0.006 0.006 0.013 0.000 2.1667 0.006 0.007 0.013 0.000 2.2778 0.006 0.008 0.014 0.000 2.3889 0.006 0.008 0.014 0.000 2.5000 0.006 0.009 0.015 0.000 2.6111 0.006 0.010 0.015 0.000 2.7222 0.007 0.011 0.015 0.000 2.8333 0.007 0.011 0.016 0.000 2.9444 0.007 0.012 0.016 0.000 3.0556 0.007 0.013 0.020 0.000 3.1667 0.007 0.014 0.023 0.000 3.2778 0.007 0.015 0.025 0.000 3.3889 0.007 0.016 0.027 0.000 3.5000 0.007 0.016 0.029 0.000 3.6111 0.007 0.017 0.030 0.000 3.7222 0.007 0.018 0.032 0.000 3.8333 0.008 0.019 0.033 0.000 3.9444 0.008 0.020 0.034 0.000 4.0556 0.008 0.021 0.035 0.000 4.1667 0.008 0.022 0.036 0.000 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 19510 - WWHM Analysis 12/9/2020 1:26:52 PM Page 7 4.2778 0.008 0.023 0.037 0.000 4.3889 0.008 0.024 0.038 0.000 4.5000 0.008 0.024 0.039 0.000 4.6111 0.008 0.025 0.040 0.000 4.7222 0.008 0.026 0.041 0.000 4.8333 0.008 0.027 0.042 0.000 4.9444 0.008 0.028 0.043 0.000 5.0556 0.008 0.029 0.044 0.000 5.1667 0.008 0.030 0.045 0.000 5.2778 0.008 0.031 0.046 0.000 5.3889 0.008 0.032 0.047 0.000 5.5000 0.008 0.033 0.047 0.000 5.6111 0.008 0.034 0.048 0.000 5.7222 0.008 0.035 0.049 0.000 5.8333 0.008 0.036 0.050 0.000 5.9444 0.008 0.037 0.050 0.000 6.0556 0.008 0.038 0.051 0.000 6.1667 0.008 0.039 0.052 0.000 6.2778 0.008 0.039 0.053 0.000 6.3889 0.008 0.040 0.053 0.000 6.5000 0.008 0.041 0.054 0.000 6.6111 0.008 0.042 0.055 0.000 6.7222 0.008 0.043 0.055 0.000 6.8333 0.008 0.044 0.056 0.000 6.9444 0.008 0.045 0.057 0.000 7.0556 0.008 0.046 0.058 0.000 7.1667 0.008 0.047 0.059 0.000 7.2778 0.007 0.048 0.061 0.000 7.3889 0.007 0.049 0.063 0.000 7.5000 0.007 0.049 0.065 0.000 7.6111 0.007 0.050 0.068 0.000 7.7222 0.007 0.051 0.070 0.000 7.8333 0.007 0.052 0.073 0.000 7.9444 0.007 0.053 0.075 0.000 8.0556 0.007 0.054 0.078 0.000 8.1667 0.007 0.054 0.081 0.000 8.2778 0.007 0.055 0.084 0.000 8.3889 0.006 0.056 0.087 0.000 8.5000 0.006 0.057 0.099 0.000 8.6111 0.006 0.058 0.103 0.000 8.7222 0.006 0.058 0.108 0.000 8.8333 0.006 0.059 0.112 0.000 8.9444 0.006 0.060 0.117 0.000 9.0556 0.006 0.060 0.122 0.000 9.1667 0.005 0.061 0.127 0.000 9.2778 0.005 0.062 0.132 0.000 9.3889 0.005 0.062 0.137 0.000 9.5000 0.005 0.063 0.143 0.000 9.6111 0.004 0.063 0.533 0.000 9.7222 0.004 0.064 1.190 0.000 9.8333 0.004 0.064 1.828 0.000 9.9444 0.003 0.065 2.233 0.000 10.056 0.003 0.065 2.493 0.000 10.167 0.003 0.066 2.717 0.000 10.278 0.002 0.066 2.924 0.000 10.389 0.001 0.066 3.116 0.000 10.500 0.000 0.066 3.297 0.000 10.611 0.000 0.000 3.468 0.000 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 19510 - WWHM Analysis 12/9/2020 1:26:52 PM Page 9 Analysis Results POC 1 + Predeveloped x Mitigated Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.45 Total Impervious Area:0.153 Mitigated Landuse Totals for POC #1 Total Pervious Area:0.145 Total Impervious Area:0.458 Flow Frequency Method:Log Pearson Type III 17B Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.101457 5 year 0.146794 10 year 0.180248 25 year 0.22649 50 year 0.263872 100 year 0.303817 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.048503 5 year 0.068852 10 year 0.085266 25 year 0.109735 50 year 0.130941 100 year 0.154939 Annual Peaks Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.164 0.048 1950 0.160 0.048 1951 0.095 0.059 1952 0.057 0.040 1953 0.056 0.041 1954 0.081 0.037 1955 0.087 0.058 1956 0.087 0.049 1957 0.114 0.052 1958 0.072 0.045 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 19510 - WWHM Analysis 12/9/2020 1:27:23 PM Page 10 1959 0.061 0.045 1960 0.103 0.058 1961 0.086 0.043 1962 0.058 0.034 1963 0.093 0.039 1964 0.081 0.037 1965 0.120 0.044 1966 0.065 0.039 1967 0.157 0.053 1968 0.144 0.042 1969 0.108 0.047 1970 0.093 0.045 1971 0.114 0.041 1972 0.148 0.056 1973 0.052 0.041 1974 0.117 0.037 1975 0.119 0.055 1976 0.088 0.043 1977 0.081 0.037 1978 0.101 0.047 1979 0.102 0.037 1980 0.198 0.052 1981 0.095 0.046 1982 0.175 0.082 1983 0.104 0.047 1984 0.069 0.040 1985 0.094 0.045 1986 0.094 0.071 1987 0.102 0.071 1988 0.052 0.039 1989 0.077 0.030 1990 0.292 0.123 1991 0.211 0.097 1992 0.076 0.044 1993 0.054 0.041 1994 0.047 0.028 1995 0.082 0.045 1996 0.148 0.063 1997 0.110 0.081 1998 0.093 0.044 1999 0.241 0.055 2000 0.102 0.046 2001 0.082 0.040 2002 0.150 0.072 2003 0.137 0.038 2004 0.218 0.221 2005 0.091 0.055 2006 0.090 0.047 2007 0.270 0.134 2008 0.201 0.165 2009 0.122 0.057 Ranked Annual Peaks Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.2921 0.2211 2 0.2699 0.1647 3 0.2407 0.1343 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 19510 - WWHM Analysis 12/9/2020 1:27:23 PM Page 11 4 0.2179 0.1231 5 0.2107 0.0969 6 0.2008 0.0815 7 0.1979 0.0810 8 0.1746 0.0719 9 0.1639 0.0709 10 0.1598 0.0708 11 0.1565 0.0634 12 0.1498 0.0594 13 0.1479 0.0577 14 0.1479 0.0576 15 0.1443 0.0570 16 0.1369 0.0556 17 0.1222 0.0555 18 0.1196 0.0552 19 0.1186 0.0547 20 0.1169 0.0534 21 0.1140 0.0524 22 0.1138 0.0521 23 0.1098 0.0489 24 0.1079 0.0479 25 0.1041 0.0478 26 0.1027 0.0473 27 0.1024 0.0471 28 0.1018 0.0469 29 0.1018 0.0468 30 0.1012 0.0460 31 0.0950 0.0456 32 0.0946 0.0454 33 0.0940 0.0453 34 0.0939 0.0451 35 0.0932 0.0449 36 0.0928 0.0449 37 0.0926 0.0438 38 0.0911 0.0436 39 0.0897 0.0436 40 0.0880 0.0432 41 0.0867 0.0429 42 0.0867 0.0424 43 0.0862 0.0409 44 0.0822 0.0408 45 0.0821 0.0407 46 0.0812 0.0406 47 0.0808 0.0405 48 0.0807 0.0403 49 0.0766 0.0399 50 0.0762 0.0392 51 0.0718 0.0388 52 0.0688 0.0387 53 0.0650 0.0378 54 0.0606 0.0372 55 0.0582 0.0372 56 0.0575 0.0368 57 0.0557 0.0368 58 0.0538 0.0368 59 0.0524 0.0343 60 0.0517 0.0298 61 0.0469 0.0282 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 19510 - WWHM Analysis 12/9/2020 1:27:23 PM Page 13 Duration Flows The Facility PASSED Flow(cfs)Predev Mit Percentage Pass/Fail 0.0507 1058 1048 99 Pass 0.0529 927 789 85 Pass 0.0550 822 581 70 Pass 0.0572 720 413 57 Pass 0.0593 639 333 52 Pass 0.0615 570 297 52 Pass 0.0636 520 274 52 Pass 0.0658 468 249 53 Pass 0.0680 430 207 48 Pass 0.0701 388 175 45 Pass 0.0723 350 154 44 Pass 0.0744 321 141 43 Pass 0.0766 295 123 41 Pass 0.0787 275 115 41 Pass 0.0809 251 102 40 Pass 0.0830 234 96 41 Pass 0.0852 217 91 41 Pass 0.0873 194 84 43 Pass 0.0895 183 84 45 Pass 0.0916 172 83 48 Pass 0.0938 156 79 50 Pass 0.0959 143 76 53 Pass 0.0981 133 74 55 Pass 0.1002 122 73 59 Pass 0.1024 114 72 63 Pass 0.1046 108 72 66 Pass 0.1067 99 69 69 Pass 0.1089 96 66 68 Pass 0.1110 92 66 71 Pass 0.1132 88 63 71 Pass 0.1153 85 59 69 Pass 0.1175 78 55 70 Pass 0.1196 76 46 60 Pass 0.1218 72 43 59 Pass 0.1239 66 39 59 Pass 0.1261 63 37 58 Pass 0.1282 60 34 56 Pass 0.1304 57 27 47 Pass 0.1325 53 24 45 Pass 0.1347 51 20 39 Pass 0.1368 48 19 39 Pass 0.1390 46 17 36 Pass 0.1412 45 16 35 Pass 0.1433 43 16 37 Pass 0.1455 41 15 36 Pass 0.1476 38 14 36 Pass 0.1498 36 14 38 Pass 0.1519 34 13 38 Pass 0.1541 32 13 40 Pass 0.1562 30 11 36 Pass 0.1584 27 10 37 Pass 0.1605 25 9 36 Pass 0.1627 25 8 32 Pass DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 19510 - WWHM Analysis 12/9/2020 1:27:23 PM Page 14 0.1648 23 7 30 Pass 0.1670 22 7 31 Pass 0.1691 21 7 33 Pass 0.1713 21 7 33 Pass 0.1734 20 7 35 Pass 0.1756 19 7 36 Pass 0.1778 18 7 38 Pass 0.1799 17 7 41 Pass 0.1821 17 7 41 Pass 0.1842 16 6 37 Pass 0.1864 15 6 40 Pass 0.1885 15 6 40 Pass 0.1907 14 6 42 Pass 0.1928 14 6 42 Pass 0.1950 14 6 42 Pass 0.1971 12 5 41 Pass 0.1993 11 5 45 Pass 0.2014 10 5 50 Pass 0.2036 10 5 50 Pass 0.2057 10 5 50 Pass 0.2079 9 5 55 Pass 0.2100 9 5 55 Pass 0.2122 8 5 62 Pass 0.2144 7 4 57 Pass 0.2165 7 4 57 Pass 0.2187 5 3 60 Pass 0.2208 5 1 20 Pass 0.2230 5 0 0 Pass 0.2251 4 0 0 Pass 0.2273 4 0 0 Pass 0.2294 4 0 0 Pass 0.2316 3 0 0 Pass 0.2337 3 0 0 Pass 0.2359 3 0 0 Pass 0.2380 3 0 0 Pass 0.2402 3 0 0 Pass 0.2423 2 0 0 Pass 0.2445 2 0 0 Pass 0.2466 2 0 0 Pass 0.2488 2 0 0 Pass 0.2510 2 0 0 Pass 0.2531 2 0 0 Pass 0.2553 2 0 0 Pass 0.2574 2 0 0 Pass 0.2596 2 0 0 Pass 0.2617 2 0 0 Pass 0.2639 2 0 0 Pass DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 19510 - WWHM Analysis 12/9/2020 1:27:23 PM Page 15 Water Quality Water Quality BMP Flow and Volume for POC #1 On-line facility volume:0.0466 acre-feet On-line facility target flow:0.033 cfs. Adjusted for 15 min:0.033 cfs. Off-line facility target flow:0.0172 cfs. Adjusted for 15 min:0.0172 cfs. DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 19510 - WWHM Analysis 12/9/2020 1:27:23 PM Page 16 LID Report DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 19510 - WWHM Analysis 12/9/2020 1:27:58 PM Page 18 Appendix Predeveloped Schematic DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 19510 - WWHM Analysis 12/9/2020 1:28:00 PM Page 19 Mitigated Schematic DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 19510 - WWHM Analysis 12/9/2020 1:28:02 PM Page 32 Disclaimer Legal Notice This program and accompanying documentation are provided 'as-is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc. and the governmental licensee or sublicensees disclaim all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions Inc. be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions Inc. or their authorized representatives have been advised of the possibility of such damages. Software Copyright © by : Clear Creek Solutions, Inc. 2005-2020; All Rights Reserved. Clear Creek Solutions, Inc. 6200 Capitol Blvd. Ste F Olympia, WA. 98501 Toll Free 1(866)943-0304 Local (360)943-0304 www.clearcreeksolutions.com DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 VEK on Aberdeen Preliminary Technical Information Report Appendix C Oldcastle Infrastructure Biopod Submittal Package DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 ISOMETRIC VIEW BPU-IB Bioretention/ Biofiltration B US Patents Pending THIS DOCUMENT IS THE PROPERTY OF OLDCASTLE INFRASTRUCTURE, INC. IT IS SUBMITTED FOR REFERENCE PURPOSES ONLY AND SHALL NOT BE USED IN ANY WAY INJURIOUS TO THE INTERESTS OF SAID COMPANY. COPYRIGHT © 2019 OLDCASTLE INFRASTRUCTURE, INC. ALL RIGHTS RESERVED. BioPod f Biofilter Underground Vault with Internal Bypass dOldcastle dOldcastle dOldcastle DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2 A PLAN VIEW A SECTION A-A BPU-IB Bioretention/ Biofiltration B US Patents PendingSAUDFI1325-0510USAXXXXTHIS DOCUMENT IS THE PROPERTY OF OLDCASTLE INFRASTRUCTURE, INC. IT IS SUBMITTED FOR REFERENCE PURPOSES ONLY AND SHALL NOT BE USED IN ANY WAY INJURIOUS TO THE INTERESTS OF SAID COMPANY. COPYRIGHT © 2019 OLDCASTLE INFRASTRUCTURE, INC. ALL RIGHTS RESERVED. MODEL VAULT SIZE 1 (ID) VAULT FOOTPRINT 1 (OD) TREATMENT FLOW CAPACITY (GPM/CFS) A DIM B DIM C DIM A1 DIM B1 DIM 1.6 GPM/SF (WA GULD2) 1.8 GPM/SF (NJCAT3) BPU-46IB 4'6'1.5'5'7'25.6 / 0.057 28.8 / 0.064 BPU-48IB 4'8'1.5'5'9'38.4 / 0.086 43.2 / 0.096 BPU-412IB 4'12'1.5'5'13'64.0 / 0.143 72.0 / 0.160 BPU-66IB 6'6'1.5'7'7'38.4 / 0.086 43.2 / 0.096 BPU-68IB 6'8'1.5'7'9'57.6 / 0.128 64.8 / 0.144 BPU-612IB 6'12'2'7'13'91.2 / 0.203 102.6 / 0.229 BPU-816IB 8'16'2'9'17'172.8 / 0.385 194.4 / 0.433 BioPod f Biofilter Underground Vault with Internal Bypass fFIDSAUXXXXUSADFI11540010FIDSAUXXXXUSADFI11540010 SITE SPECIFIC DATA Structure ID Model Size Orientation (Left or Right) Treatment Flow Rate (cfs) Peak Flow Rate (cfs) Rim Elevation Pipe Data Pipe Location (Front or Side)Pipe Size Pipe Type Invert Elevation Inlet Outlet Notes: 1 All Dimensions are nominal, ID=Inside Dimension, OD=Outside Dimension. 2 Treartment flow capacity at 1.6 gpm/sf media surface area based on an WA Ecology GULD Approval for Basic, Enhanced & Phosphorus. 3 Treatment flow capacity at 1.8 gpm/sf media surface area based on an NJCAT Verification & NJ DEP Certification. DocuSign Envelope ID: 69D0A746-C343-49C8-931A-17990D5283F2