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RS_TIR_SapphireOnTalbot_181101_v1.pdf
Sapphire on Talbot Technical Information Report 10/29/2018 Page i Table of Contents I. PROJECT OVERVIEW ................................................................................................................ 1 II. CONDITIONS AND REQUIREMENTS SUMMARY ...................................................................... 6 III. OFF-SITE ANALYSIS .................................................................................................................. 8 IV. FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN ........................... 12 V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN ..................................................................... 13 VI. SPECIAL REPORTS AND STUDIES ............................................................................................ 13 VII. OTHER PERMITS ..................................................................................................................... 13 VIII. CSWPPP ANALYSIS AND DESIGN............................................................................................ 13 IX. BOND QUANTITIES and DECLARATION of COVENANT .......................................................... 13 X. OPERATION AND MAINTENANCE MANUAL .......................................................................... 13 Appendix Geotechnical Engineering Report by Migizi Group Revised 10/11/2017. WWHM Output Sapphire on Talbot Technical Information Report 10/29/2018 Page 1 I. PROJECT OVERVIEW Site Address: 4827 TALBOT RD S; Renton, WA 98055 (See Vicinity Map) King County Tax Parcel: 312305-9022 Vicinity Map This project involves platting a 1.69-acre plat into 20 lots. Frontage improvements increase the project area to approximately 1.75 acres and decrease the onsite area to 1.59 acres through Right-of-Way dedication. The site is zoned R-14. Existing Site Conditions: The site is currently developed with an existing single-family residence, detached garage and out buildings and an asphalt driveway. The site is vegetated with grasses with trees and shrubs around the boundaries of the property. There are a few scattered small gardens on the eastern half of the property. The site slopes to the west at 5-8%. Please see the Existing Conditions Exhibit. The USDA Web Soil Survey maps the soil on the site as Alderwood gravelly sandy loam at 8-15% slopes (See Soils Map on Following Page). The site is underlain with Alderwood soil, generally glacial till over outwash sandy, gravelly soil at a depth of about 8’ as presented in the Geotechnical Engineering Report prepared by Migizi Group dated October 11, 2017 and Revised August 30, 2018. The Migizi Group also indicated that stormwater infiltration is feasible at lower depths—see Appendix A. SITE Sapphire on Talbot Technical Information Report 10/29/2018 Page 2 Soils Map Sapphire on Talbot Technical Information Report 10/29/2018 Page 4 Developed Site Conditions: Twenty lots will be created. Fee simple homes will be constructed in duplex and triplex configurations. Two roadways will be constructed onsite. S 48th St will be a public right of way varying from 20 – 26 feet in width and will have a landscape strip and sidewalks along the length of it. Tracts B and C will contain a private access alley for the residences along that route. The residences will have single or shared driveways. An open space tract is also being preserved. 10.5’ of right of way is being dedicated with road widening, new curb, gutter and sidewalk and a planter strip. Area Swap: A portion of the frontage improvements is hydraulically dislocated from available water collection, flow control and water quality facilities. The PGIS for this area is 742 square feet, total impervious area is 2,132 square feet and the landscape strip is 1,132 square feet. Mitigation for this area is being provided by collecting approximately 2,106 square feet of existing asphalt from the half street of Talbot Road South. While the area isn’t exactly the same as the impervious area, the flow from the site will still meet flow control requirements due to the fact that we are proposing a full infiltration system onsite. Water quality treatment area will exceed what is required for the swap. Please see the developed conditions exhibit on the following page. Sapphire on Talbot Technical Information Report 10/29/2018 Page 6 II. CONDITIONS AND REQUIREMENTS SUMMARY The 2017 City of Renton Surface Water Design Manual along with the 2016 King County Surface Water Design Manual was utilized for this report per the City of Renton requirements. Core Requirements Core Requirement #1: Discharge at the Natural Location The proposed development runoff will follow existing drainage patterns and will be routed to same discharge points as existing condition. Refer to the Downstream Analysis in Section III for a complete description of the existing drainage path. Core Requirement #2: Offsite Analysis A Level 1 Downstream analysis has been prepared and is included in Section III of this TIR. Core Requirement #3: Flow Control Facilities Flow control facilities have been designed to utilize the infiltration potential of lower soil lenses with an infiltration rate of 1.25 inches per hour. This is accomplished by using an infiltration vault in the south west portion of the site that has been set aside for open space. The infiltration vault will be equipped with an outlet structure that will mimic predeveloped flow rates for larger storms, while infiltrating 100% of most storm events. In the event the soils encountered onsite during construction do not actually provide infiltration, a strict detention vault will become necessary. A detention vault has been preliminarily designed to ensure the site can contain such a structure. The resulting vault would be approximately 76-feet square. This size vault does fit within the provided open space without significantly altering the site design. See Section IV of this TIR for a detailed breakdown of areas used for modeling. Core Requirement #4: Conveyance System Design and analysis of on and off-site conveyance systems will be submitted with final engineering. Core Requirement #5: Erosion and Sediment Control A temporary erosion and sediment control (TESC) plan provides BMPs to be implemented during construction. This plan and included BMPs will be provided during final engineering. Core Requirement #6: Maintenance and Operations See Section X – Operation and Maintenance Manual Core Requirement #7: Financial Guarantees and Liability The owner will arrange for any financial guarantees and liabilities required by the permit. Sapphire on Talbot Technical Information Report 10/29/2018 Page 7 Core Requirement #8: Water Quality Facilities Consistent with the designed infiltration facilities, a presettling basin has been designed as 25% of the water quality volume that would be necessary for a basic water quality pond / vault (0.1605 AC-ft = 6,991 cft x 0.25 = 1,748 cft required.) In the event that soils encountered onsite during construction do not support infiltration and a larger detention vault becomes necessary, basic water quality will be achieved by adding a wetpool depth of 3-4 feet (the minimum) throughout the vault . Core Requirement #9: Flow Control BMPs Full infiltration is proposed for flow control for the site, therefore additional, onsite BMP’s are not required. In the event the infiltration rates projected by the geotechnical engineer are not found during construction and a detention facility must be used, additional onsite BMP’s would be required. Infiltration facilities would not be feasible, nor would full dispersion due to the 15% native vegetation retention requirement. Therefore, basic dispersion BMP’s would be implemented. The site design allows for 14 downspout splashblocks with 50’ flow paths and one 50’ dispersion trench in the open space tract. These facilities would serve 6,300 square feet of impervious surfaces. The credit allotted for these converts 630 square feet of impervious surface to be modelled as grass. Special Requirements Special Requirement #1: Other Adopted Area-Specific Requirements Critical Drainage Area – N/A Master Drainage Plan – N/A Basin Plan – May Creek & Lower Cedar River Drainage Basin Lake management 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 a 100-year floodplain Special Requirement #3: Flood Protection Facilities This special requirement is for Class 1 or 2 streams with an existing flood protection facility. The site does not contain any streams and is therefore not applicable. Special Requirement #4: Source controls Source control is not required for this single family residential plat. Special Requirement #5: Oil Control This project is not considered high-use in need of oil control. Sapphire on Talbot Technical Information Report 10/29/2018 Page 8 III. OFF-SITE ANALYSIS . The site mostly sheet flows (A) west into a wooded tract, part of the adjacent Ashburn Condominium project. There is an existing flow splitting structure that routes most drainage from the existing site to one of two flow paths. The majority of the flow from this structure is designed to flow through a level spreader (B) to an onsite wetland. (outlet IE 134.2) while the overflow to the bypass system doesn’t begin until the water depth within the structure reaches elevation 135.62. See below. That portion of runoff from the site (A) that doesn’t drain into the bypass pipe mentioned above drains past the existing level spreader (B) into a wooded area south of the site, then into an inlet pipe (D), about 200’ west of the site. The flows drain though the 12” Ashburn pipe system about ¼ mile before discharging into a large underground detention vault (E). The vault discharges into an overgrown bioswale F) draining south, then west towards the SR-167 storm system (G), a distance of greater than ¼ mile downstream from the site. The remainder of the site runoff is routed into a 12” pipe system in Ashburn that directs flows around the detention vault constructed for the Ashburn project (E). This bypass pipe (C) discharges into a wooded ravine (H) about 350’ downstream from the site. Flows from the ravine cross under on the Ashburn streets through a 12” pipe (I), continuing west through more wooded ravine (J) then into the SR-167 storm system (G), about ¼ mile downstream from the site. Per King county resources, there have been no significant drainage complaints. There were no apparent downstream drainage issues Sapphire on Talbot Technical Information Report 10/29/2018 Page 9 Site (A) Ashburn Stormwater Vault (E) Sapphire on Talbot Technical Information Report 10/29/2018 Page 10 Ashburn Bioswale (F) Wooded Ravine (J) Sapphire on Talbot Technical Information Report 10/29/2018 Page 11 Sapphire on Talbot Technical Information Report 10/29/2018 Page 12 IV. FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN Area Breakdown for Modelling Total Predeveloped Area 1.7514 Acres Developed Conditions Breakdown Maximum Impervious onsite (houses, driveways, walks, etc.) 80% 0.5789 Acres Sidewalk Area 0.103 Acres Roadway Area 0.3177 Acres Driveway Area 0.1465 Acres Pervious Total 0.5902 Acres Basin maps are included on the following pages. Full WWHM output is included in the Appendix of this TIR Sapphire on Talbot Technical Information Report 10/29/2018 Page 13 V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN Conveyance system analysis and design will be provided with final engineering. VI. SPECIAL REPORTS AND STUDIES Geotechnical Engineering Report Dated 7/14/17 Revised 9/28/17. VII. OTHER PERMITS Building Permits will be required. VIII. CSWPPP ANALYSIS AND DESIGN CSWPPP Analysis and Design will be provided with final engineering. IX. BOND QUANTITIES and DECLARATION of COVENANT Bond Quantities and 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. Sapphire on Talbot Technical Information Report 10/29/2018 Page 14 Appendix Geotechnical Report and WWHM Output ` Geotechnical Engineering Report Proposed Talbot Gardens Short Plat 4827 Talbot Rd S Renton, Washington 98055 P/N 3123059022 October 11, 2017 Revised August 30, 2018 prepared for: Sapphire Homes Attention: Troy Schmeil 16834 SE 43rd St Bellevue, Washington 98006 prepared by: Migizi Group, Inc. PO Box 44840 Tacoma, Washington 98448 (253) 537-9400 MGI Project P1389-T18 i TABLE OF CONTENTS Page No. 1.0 SITE AND PROJECT DESCRIPTION............................................................................................... 1 2.0 EXPLORATORY METHODS ............................................................................................................. 2 2.1 Test Pit Procedures ................................................................................................................ 3 3.0 SITE CONDITIONS ............................................................................................................................ 3 3.1 Surface Conditions ................................................................................................................. 3 3.2 Soil Conditions ....................................................................................................................... 3 3.3 Groundwater Conditions ...................................................................................................... 4 3.4 Infiltration Conditions and Infiltration Rate ...................................................................... 4 3.5 Seismic Conditions ................................................................................................................. 6 3.6 Liquefaction Potential ............................................................................................................ 6 4.0 CONCLUSIONS AND RECOMMENDATIONS ............................................................................ 7 4.1 Site Preparation ...................................................................................................................... 8 4.2 Spread Footings .................................................................................................................... 10 4.3 Slab-On-Grade-Floors .......................................................................................................... 11 4.4 Asphalt Pavement ................................................................................................................ 12 4.5 Structural Fill ........................................................................................................................ 13 5.0 RECOMMENDED ADDITIONAL SERVICES .............................................................................. 14 6.0 CLOSURE ........................................................................................................................................... 14 List of Tables Table 1. Approximate Locations and Depths of Explorations ............................................................................. 2 Table 2. Laboratory Test Results for Non-Organic Onsite Soils .......................................................................... 5 List of Figures Figure 1. Topographic and Location Map Figure 2. Site and Exploration Plan APPENDIX A Soil Classification Chart and Key to Test Data .................................................................................................. A-1 Logs of Test Pits TP-1 through TP-5 .......................................................................................................... A-2…A-6 MIGIZI GROUP, INC. PO Box 44840 PHONE (253) 537-9400 Tacoma, Washington 98448 FAX (253) 537-9401 October 11, 2017 Revised August 30, 2018 Sapphire Homes 16834 SE 43rd St Bellevue, Washington 98006 Attention: Troy Schmeil Subject: Revised Geotechnical Engineering Report Proposed Talbot Gardens Short Plat 4827 Talbot Rd S Renton, Washington 98055 P/N 3123059022 MGI Project P1389-T18 Dear Mr. Schmeil: Migizi Group, Inc. (MGI) is pleased to submit this revised report describing the results of our geotechnical engineering evaluation of the proposed residential development in Renton, Washington. It is our understanding that since our initial iteration of this report, the subject property has changed hands, and that a new design scheme is being implemented. Additional soils information is needed in order to execute the new design. This report has been prepared for the exclusive use of Sapphire Homes, and their consultants, for specific application to this project, in accordance with generally accepted geotechnical engineering practice. 1.0 SITE AND PROJECT DESCRIPTION The project site consists of a 1.67-acre, residential parcel located immediately southwest of the intersection between S 48th St and Talbot Rd S in Renton, Washington, as shown on the enclosed Topographic and Location Map (Figure 1). The subject property is situated in a densely populated residential area located towards the south end of the city limits of Renton. A single-family residence, originally constructed in 1936, and accompanying detached garage and shed building occupy the central portion of the site, with the northeast corner of the project area containing extensive paved surfaces for overflow parking. The remainder of the parcel is occupied by tall grasses, and various forms of vegetation. Page 1 of 14 Sapphire Homes – Talbot Gardens Short Plat, Renton, WA October 11, 2017 / Revised August 30, 2018 Revised Geotechnical Engineering Report P1389-T18 Migizi Group, Inc. Page 2 of 14 Improvement plans involve the clearing/stripping of the property, demolition of the existing structures, and development of the site for residential purposes. The proposed development will result in approximately 20 buildable lots and contain a primary access road which travels east-west across the length of the property, following the general course of the existing driveway. A supplemental alleyway will also be introduced as part of the proposed development, traveling south from S 48th Street, spanning the full length of the property along this orientation. The southwest corner of the subject property will be utilized as an Open Space / Tree Retention Tract, and will also house stormwater retention facilities, if feasible. 2.0 EXPLORATORY METHODS We explored surface and subsurface conditions at the project site on September 5, 2017 and July 24, 2018. Our exploration and evaluation program comprised the following elements: • Surface reconnaissance of the site; • Five test pit explorations (designated TP-1 through TP-5) advanced on September 5, 2017 and July 24, 2018; • Two grain-size analyses performed on soil samples collected from our subsurface explorations; and • A review of published geologic and seismologic maps and literature. Table 1 summarizes the approximate functional locations and termination depths of our subsurface explorations, and Figure 2 depicts their approximate relative locations. The following sections describe the procedures used for excavation of the test pits. TABLE 1 APPROXIMATE LOCATIONS AND DEPTHS OF EXPLORATIONS Exploration Functional Location Termination Depth (feet) TP-1 TP-2 TP-3 TP-4 TP-5 Northwest corner of the project area West of the existing residence Southeast corner of the project area Southwest corner of the project area, in proposed stormwater retention area Immediately northeast of test pit exploration TP-4 10 10 10 15 15 The specific number and locations of our explorations were selected in relation to the existing site features, under the constraints of surface access, underground utility conflicts, and budget considerations. It should be realized that the explorations performed and utilized for this evaluation reveal subsurface conditions only at discrete locations across the project site and that actual conditions in other areas could vary. Furthermore, the nature and extent of any such variations would not become evident until additional explorations are performed or until construction activities have begun. If significant variations are observed at that time, we may need to modify our conclusions and recommendations contained in this report to reflect the actual site conditions. Sapphire Homes – Talbot Gardens Short Plat, Renton, WA October 11, 2017 / Revised August 30, 2018 Revised Geotechnical Engineering Report P1389-T18 Migizi Group, Inc. Page 3 of 14 2.1 Test Pit Procedures Our exploratory test pits were excavated with a rubber-tracked mini-excavator operated by an excavation contractor under subcontract to MGI. An engineering geologist from our firm observed the test pit excavations, collected soil samples, and logged the subsurface conditions. The enclosed test pit logs indicate the vertical sequence of soils and materials encountered in our test pits, based on our field classifications. Where a soil contact was observed to be gradational or undulating, our logs indicate the average contact depth. We estimated the relative density and consistency of the in-situ soils by means of the excavation characteristics and the stability of the test pit sidewalls. Our logs also indicate the approximate depths of any sidewall caving or groundwater seepage observed in the test pits. The soils were classified visually in general accordance with the system described in Figure A-1, which includes a key to our exploration logs. Summary logs of our explorations are included as Figures A-2 through A-6. 3.0 SITE CONDITIONS The following sections present our observations, measurements, findings, and interpretations regarding surface, soil, groundwater, and infiltration conditions. 3.1 Surface Conditions As previously indicated, the project site consists of a fully developed, 1.67-acre residential parcel located immediately southwest of the intersection between S 48th St and Talbot Rd S in Renton, Washington. The project area is roughly square-shaped, spanning approximately 270 feet along its primary boundaries. The central portion of the site is occupied by an existing single-family residence and accompanying detached garage and shed building. Expanded asphalt pavements occupy the northeast corner of the subject property. The primary driveway enters the site from the east along Talbot Rd S, looping to the north to access the aforementioned expanded parking area. Vegetation consists primarily of lawn grass immediately east and west of the existing structures. A thick growth of alder and fir trees are located towards the southern and western margins of the project area, containing a dense understory of fern, blackberry bushes, and other brush. Topographically, the subject property is gently sloped, generally descending from east to west at gradients of less than 10 percent; with a total elevation change of ± 25 feet being observed over the extent of the parcel. The subject parcel is situated along the eastern valley wall of the Duwamish Valley. No hydrologic features were observed on site, such as seeps, springs, ponds and streams. 3.2 Soil Conditions Our test pit explorations revealed relatively consistent subgrade conditions across the project area, generally consisting of a surface mantle of sod/topsoil, underlain by native, Vashon-aged glacial soils. Renton, and the larger Puget Sound area in general, has been glaciated a number of times over the last 2.4 million years. The most recent of these glacial events, the Vashon Stade of the Fraser Sapphire Homes – Talbot Gardens Short Plat, Renton, WA October 11, 2017 / Revised August 30, 2018 Revised Geotechnical Engineering Report P1389-T18 Migizi Group, Inc. Page 4 of 14 Glaciation, receded from this region approximately 13,500 years ago. The majority of near surface soils encountered within the Renton area are either directly associated with, or have been physically altered by the Vashon glacial event. Glacial till is typically described as being a compact, coherent mixture of gravel, silt, clay and sand-sized clasts deposited along the base of glacial ice during a period of localized advancement. This material is generally encountered in a compact relative consistency given the fact that it was overridden by the ice mass shortly after deposition, and is commonly underlain by advance outwash soils. Advance outwash is resultant of pro-glacial rivers and streams which carried sediment ahead of the advancing ice mass. In general, our test pit explorations encountered glacial till soils within 12 inches of existing grade. This material was continuous through a depth of approximately 8 feet below existing grade, being comprised of silty sand with some gravel, to gravelly silty sand. As encountered on site, glacial till soils were highly weathered and heavily mottled; indicating poor surface drainage. From a depth of 8 feet to 10 feet below existing grade, the termination depth of three of our subsurface explorations, we encountered advance outwash deposits. Advance outwash is typically comprised of densely consolidated, relatively clean, sands and gravel. However, on site, this soil group was largely comprised of alternating lenses of fine sand and silty sand; with an average relative fines content (percent silt and clay) between 25 to 30 percent. This soil group was found to extend to a depth of ± 13 feet below existing grade; transitioning to a more homogenous, relatively impervious, dense, silty sand with some gravel. In the Geologic Map of the Renton Quadrangle, King County, Washington, as prepared by the Department of the Interior United States Geological Survey (USGS) (1965), the project site is mapped as containing Qvt, or Vashon-aged glacial till. Our subsurface explorations generally correspond with the geologic mapping prepared by the USGS. The enclosed exploration logs (Appendix A) provide a detailed description of the soil strata encountered in our subsurface explorations. 3.3 Groundwater Conditions We did not encounter groundwater in any of our subsurface explorations, which extended to a depth upwards of 15 feet below existing grade. Given the fact that our explorations were performed outside of what is generally considered the rainy season (November 1 to March 31), groundwater could rise higher than that which we observed. However, given the geologic/topographic setting of the project area, we do not anticipate that groundwater will rise high enough to adversely affect the proposed development. Seasonally perched groundwater will likely be encountered on site at relatively shallow depths during periods of extended precipitation, given the presence of low permeability till soils along the subsurface. 3.4 Infiltration Conditions and Infiltration Rate As indicated in the Soil Conditions section of the report, the site is underlain by low permeability glacial till soils at shallow depths, extending upwards of 8 feet below existing grade. The extensive soil mottling encountered in this soil group is indicative of poor surface drainage. Encountered at a depth of 8 feet, extending through a depth of ± 13 feet, we encountered advance outwash. As Sapphire Homes – Talbot Gardens Short Plat, Renton, WA October 11, 2017 / Revised August 30, 2018 Revised Geotechnical Engineering Report P1389-T18 Migizi Group, Inc. Page 5 of 14 observed in our explorations, this soil group was largely comprised of alternating lenses of fine sand and silty sand. Though not ideal for stormwater retention, it is our opinion that this soil group could support limited infiltration. Additionally, we are of the opinion that groundwater levels are at a sufficient depth so as to not adversely affect stormwater retention. Our grain-size analysis indicates that the advance outwash contains an average relative fines (percent silt/clay) content between 27 to 30 percent. The results of our soil grain size analyses are presented below, and the attached Soil Gradation Graphs (Appendix B) display the grain-size distribution of the samples tested. TABLE 2 LABORATORY TEST RESULTS FOR NON-ORGANIC ONSITE SOILS Soil Sample, Depth % Coarse Gravel % Fine Gravel % Coarse Sand % Medium Sand % Fine Sand % Fines D10 TP-1, S-3, 9 feet TP-2, S-2, 9 feet TP-4, S-1, 10 feet TP-5, S-1, 9 feet 19.3 3.3 0.0 0.0 5.7 9.2 3.8 4.5 2.6 4.2 3.5 2.6 7.3 13.3 14.2 12.7 33.8 43.1 52.3 50.0 31.3 26.9 26.1 30.3 - - - - Design Infiltration Rate We determined a design infiltration rate for the advance soils on site, by utilizing Section 3.3.6 of Volume III of the 2014 Stormwater Management Manual for Western Washington (SMWW). This section determines a design infiltration rate by taking gradational information from sieve analyses, and inputting this data into equation 1: log10(Ksat) = -1.57 + 1.90D10 + 0.015D60 – 0.013D90 – 2.08Ffines Where D10, D60, and D90 are the grain sizes in mm for which 10 percent, 60 percent and 90 percent of the sample is more fine and Fines is the fraction of the soil (by weight) that passes the #200 sieve. Ksat is in cm/s, though we, for ease of use, have converted this value to inches per hour. We recommend that an uncorrected Ksat initial value of 7.1 in/hr be utilized by the design engineer, for retention facilities utilizing the native advance outwash as the primary infiltrative unit. The value acquired above is an initial rate. It is recommended that this initial rate be reduced through correction factors that are appropriate for the design situation to produce a design infiltration rate. As per the same section of the SMWW, the Total Correction Factor (CFT): CFT = CFv x CFt x CFm Where CFv accounts for site variability and number of locations tested, CFt accounts for errors associated with the test method, and CFm accounts for potential siltation and biofouling. Utilizing a Sapphire Homes – Talbot Gardens Short Plat, Renton, WA October 11, 2017 / Revised August 30, 2018 Revised Geotechnical Engineering Report P1389-T18 Migizi Group, Inc. Page 6 of 14 value of 0.5 for CFv, 0.40 for CFt, and 0.9 for CFm, our recommended CFT = 0.18. Ksat design = Ksat initial x CFT We recommend that a Ksat design value of 1.25 in/hr be utilized by the engineer in charge of design of retention facilities associated with this project. This value is for the native advance outwash soils which underlie the project area. Retention facility should have an invert elevation of at least 8 feet below existing grade. A more homogeneous restrictive layer is encountered at a depth of 13 feet in the proposed stormwater retention area. The presence of this restrictive layer should be evaluated by the Civil Engineer of Record for this project to determine whether it will adversely affect any proposed designs. Generally, in the City of Renton, field infiltration tests are performed in order to determine design infiltration rates for native soils. However, given the relative depth to the only potential soil group to support stormwater retention onsite, we are of the opinion that the grain size analysis method is appropriate. 3.5 Seismic Conditions Based on our analysis of subsurface exploration logs and our review of published geologic maps, we interpret the onsite soil conditions to generally correspond with site class D, as defined by Table 30.2-1 in ASCE 7, per the 2015 International Building Code (IBC). Using 2015 IBC information on the USGS Design Summary Report website, Risk Category I/II/III seismic parameters for the site are as follows: Ss = 1.394 g SMS = 1.394 g SDS = 0.929 g S1 = 0.520 g SM1 = 0.780 g SD1 = 0.520 g Using the 2015 IBC information, MCER Response Spectrum Graph on the USGS Design Summary Report website, Risk Category I/II/III, Sa at a period of 0.2 seconds is 1.39 g and Sa at a period of 1.0 seconds is 0.78 g. The Design Response Spectrum Graph from the same website, using the same IBC information and Risk Category, Sa at a period of 0.2 seconds is 0.93 g and Sa at a period of 1.0 seconds is 0.52 g. 3.6 Liquefaction Potential Liquefaction is a sudden increase in pore water pressure and a sudden loss of soil shear strength caused by shear strains, as could result from an earthquake. Research has shown that saturated, loose, fine to medium sands with a fines (silt and clay) content less than about 20 percent are most susceptible to liquefaction. Our explorations did not encounter any saturated, or potentially saturated granular soils, and we interpret the site as having a low potential for soil liquefaction during a large-scale seismic event. Sapphire Homes – Talbot Gardens Short Plat, Renton, WA October 11, 2017 / Revised August 30, 2018 Revised Geotechnical Engineering Report P1389-T18 Migizi Group, Inc. Page 7 of 14 4.0 CONCLUSIONS AND RECOMMENDATIONS Improvement plans involve the clearing/stripping of the property, demolition of the existing structures, and development of the site for residential purposes. The proposed development will result in approximately 20 buildable lots and contain a primary access road which travels east-west across the length of the property, following the general course of the existing driveway. A supplemental alleyway will also be introduced as part of the proposed development, traveling south from S 48th Street, spanning the full length of the property along this orientation. The southwest corner of the subject property will be utilized as an Open Space / Tree Retention Tract, and will also house stormwater retention facilities, if feasible. We offer these recommendations: • Feasibility: Based on our field explorations, research and analyses, the proposed structures appear feasible from a geotechnical standpoint. • Foundation Options: Foundation elements for the proposed residences should be constructed on medium dense or denser undisturbed native soils, or on structural fill bearing pads extending down to these soils. We anticipate that adequate bearing soils will be encountered within two to three feet of existing grade. Recommendations for Spread Footings are provided in Section 4.2. • Floor Options: Floor sections for the proposed residences should bear on medium dense or denser native soils or on properly compacted structural fill extending down to these soils. We anticipate that adequate bearing soils will be encountered within two to three feet of existing grade. Recommendations for slab-on-grade floors are included in Section 4.3. Fill underlying floor slabs should be compacted to 95 percent (ASTM:D-1557). • Pavement Sections: Native, in-situ soil conditions are amenable to the use of soil- supported pavements. We recommend a conventional pavement section comprised of an asphalt concrete pavement over a crushed rock base course over a properly prepared (compacted) subgrade or a granular subbase, depending on subgrade conditions during pavement subgrade preparation. All soil subgrades should be thoroughly compacted, then proof-rolled with a loaded dump truck or heavy compactor. Any localized zones of yielding subgrade disclosed during this proof-rolling operation should be over-excavated to a depth of 12 inches and replaced with a suitable structural fill material. • Infiltration Conditions: Given the geological conditions encountered on site, we do not foresee full-infiltration as being feasible for this project. However, limited infiltration utilizing a system of trenches, likely can be implemented on site, utilizing the advance outwash soils for stormwater retention. We recommend utilizing a design infiltration rate of 1.25 inches per hour for this soil group. Invert elevations for retention facilities should be located at least 8 feet below existing grade. A more homogeneous restrictive layer is encountered at a depth of 13 feet in the proposed stormwater retention area. The presence of this restrictive layer should be evaluated by the Civil Engineer of Record for this project to determine whether it will adversely affect any proposed designs. Shallower glacial till soils, should be considered impermeable for design purposes. Sapphire Homes – Talbot Gardens Short Plat, Renton, WA October 11, 2017 / Revised August 30, 2018 Revised Geotechnical Engineering Report P1389-T18 Migizi Group, Inc. Page 8 of 14 • Geologic Hazards: During our site reconnaissance, advancement of subsurface explorations, and general evaluation of the proposed development, we did not observe any erosional, landslide, seismic, settlement, or other forms of geologic hazards within the subject property. Given this fact, we recommend that no buffers, setbacks, or other forms of site restraints be implemented to address these potential hazards. The following sections of this report present our specific geotechnical conclusions and recommendations concerning site preparation, spread footings, slab-on-grade floors, asphalt pavement, and structural fill. The Washington State Department of Transportation (WSDOT) Standard Specifications and Standard Plans cited herein refer to WSDOT publications M41-10, Standard Specifications for Road, Bridge, and Municipal Construction, and M21-01, Standard Plans for Road, Bridge, and Municipal Construction, respectively. 4.1 Site Preparation Preparation of the project site should involve erosion control, temporary drainage, clearing, stripping, excavations, cutting, subgrade compaction, and filling. Erosion Control: Before new construction begins, an appropriate erosion control system should be installed. This system should collect and filter all surface water runoff through silt fencing. We anticipate a system of berms and drainage ditches around construction areas will provide an adequate collection system. Silt fencing fabric should meet the requirements of WSDOT Standard Specification 9-33.2 Table 3. In addition, silt fencing should embed a minimum of 6 inches below existing grade. An erosion control system requires occasional observation and maintenance. Specifically, holes in the filter and areas where the filter has shifted above ground surface should be replaced or repaired as soon as they are identified. Temporary Drainage: We recommend intercepting and diverting any potential sources of surface or near-surface water within the construction zones before stripping begins. Because the selection of an appropriate drainage system will depend on the water quantity, season, weather conditions, construction sequence, and contractor's methods, final decisions regarding drainage systems are best made in the field at the time of construction. Based on our current understanding of the construction plans, surface and subsurface conditions, we anticipate that curbs, berms, or ditches placed around the work areas will adequately intercept surface water runoff. Clearing and Stripping: After surface and near-surface water sources have been controlled, sod, topsoil, and root-rich soil should be stripped from the site. Our subsurface explorations indicate that the organic horizon can reach thicknesses of up to 14 inches. Stripping is best performed during a period of dry weather. Site Excavations: Based on our explorations, we expect deeper site excavations will predominately encounter densely consolidated glacial till soils. This soil group can be readily excavated utilizing standard excavation equipment, though special teeth, or “rippers”, may need to be utilized in order to rapidly excavate glacial till soils. Shallower excavations will encounter highly weathered, loosely consolidated soils which can be readily excavated using standard excavation equipment. Sapphire Homes – Talbot Gardens Short Plat, Renton, WA October 11, 2017 / Revised August 30, 2018 Revised Geotechnical Engineering Report P1389-T18 Migizi Group, Inc. Page 9 of 14 Dewatering: We did not encounter groundwater seepage in any of subsurface explorations, which extended a maximum depth of 15 feet below existing grade. We do not anticipate that groundwater levels will rise high enough to adversely affect the proposed development; however, seasonally perched groundwater will likely be encountered at relatively shallow depths across the project area during extended precipitation given the presence of low permeability till soils across the subsurface. If groundwater is encountered, we anticipate that an internal system of ditches, sump holes, and pumps will be adequate to temporarily dewater excavations. Temporary Cut Slopes: All temporary soil slopes associated with site cutting or excavations should be adequately inclined to prevent sloughing and collapse. Temporary cut slopes in site soils should be no steeper than 1½H:1V, and should conform to Washington Industrial Safety and Health Act (WISHA) regulations. Subgrade Compaction: Exposed subgrades for the foundation of the proposed residence should be compacted to a firm, unyielding state before new concrete or fill soils are placed. Any localized zones of looser granular soils observed within a subgrade should be compacted to a density commensurate with the surrounding soils. In contrast, any organic, soft, or pumping soils observed within a subgrade should be overexcavated and replaced with a suitable structural fill material. Site Filling: Our conclusions regarding the reuse of onsite soils and our comments regarding wet- weather filling are presented subsequently. Regardless of soil type, all fill should be placed and compacted according to our recommendations presented in the Structural Fill section of this report. Specifically, building pad fill soil should be compacted to a uniform density of at least 95 percent (based on ASTM:D-1557). Onsite Soils: We offer the following evaluation of these onsite soils in relation to potential use as structural fill: • Surficial Organic Soil and Organic-Rich Fill Soils: Where encountered, surficial organic soils like duff, topsoil, root-rich soil, and organic-rich fill soils are not suitable for use as structural fill under any circumstances, due to high organic content. Consequently, this material can be used only for non-structural purposes, such as in landscaping areas. • Glacial Till: Underlying a surface mantle of sod and topsoil, native glacial till soils were encountered; generally consisting of dense, gravelly silty sand. These soils are moderately moisture sensitive and will be difficult, if not impossible, to reuse during wet weather conditions. If reuse is planned, care should be taken while stockpiling in order to avoid saturation/over-saturation of the material, and moisture conditioning should be expected. Permanent Slopes: All permanent cut slopes and fill slopes should be adequately inclined to reduce long-term raveling, sloughing, and erosion. We generally recommend that no permanent slopes be steeper than 2H:1V. For all soil types, the use of flatter slopes (such as 2½H:1V) would further reduce long-term erosion and facilitate revegetation. Sapphire Homes – Talbot Gardens Short Plat, Renton, WA October 11, 2017 / Revised August 30, 2018 Revised Geotechnical Engineering Report P1389-T18 Migizi Group, Inc. Page 10 of 14 Slope Protection: We recommend that a permanent berm, swale, or curb be constructed along the top edge of all permanent slopes to intercept surface flow. Also, a hardy vegetative groundcover should be established as soon as feasible, to further protect the slopes from runoff water erosion. Alternatively, permanent slopes could be armored with quarry spalls or a geosynthetic erosion mat. 4.2 Spread Footings In our opinion, conventional spread footings will provide adequate support for the proposed residences if the subgrade is properly prepared. We offer the following comments and recommendations for spread footing design. Footing Depths and Widths: For frost and erosion protection, the bases of all exterior footings should bear at least 18 inches below adjacent outside grades, whereas the bases of interior footings need bear only 12 inches below the surrounding slab surface level. To reduce post-construction settlements, continuous (wall) and isolated (column) footings should be at least 16 and 24 inches wide, respectively. Bearing Subgrades: Footings should bear on medium dense or denser, undisturbed native soils which have been stripped of surficial organic soils and vigorously surface compacted, or on properly compacted structural fill bearing pads which extend down to soils described above. We anticipate that adequate bearing subgrades will be encountered within 1 to 2 feet of existing grade, within glacial till soils. In general, before footing concrete is placed, any localized zones of loose soils exposed across the footing subgrades should be compacted to a firm, unyielding condition, and any localized zones of soft, organic, or debris-laden soils should be over-excavated and replaced with suitable structural fill. Lateral Overexcavations: Because foundation stresses are transferred outward as well as downward into the bearing soils, all structural fill placed under footings, should extend horizontally outward from the edge of each footing. This horizontal distance should be equal to the depth of placed fill. Therefore, placed fill that extends 3 feet below the footing base should also extend 3 feet outward from the footing edges. Subgrade Observation: All footing subgrades should consist of firm, unyielding, native soils, or structural fill materials that have been compacted to a density of at least 95 percent (based on ASTM:D-1557). Footings should never be cast atop loose, soft, or frozen soil, slough, debris, existing uncontrolled fill, or surfaces covered by standing water. Bearing Pressures: In our opinion, for static loading, footings that bear on medium dense or denser, native, glacial soils can be designed for a maximum allowable soil bearing pressure of 2,000 psf. A one-third increase in allowable soil bearing capacity may be used for short-term loads created by seismic or wind related activities. Sapphire Homes – Talbot Gardens Short Plat, Renton, WA October 11, 2017 / Revised August 30, 2018 Revised Geotechnical Engineering Report P1389-T18 Migizi Group, Inc. Page 11 of 14 Footing Settlements: Assuming that structural fill soils are compacted to a medium dense or denser state, we estimate that total post-construction settlements of properly designed footings bearing on properly prepared subgrades will not exceed 1 inch. Differential settlements for comparably loaded elements may approach one-half of the actual total settlement over horizontal distances of approximately 50 feet. Footing Backfill: To provide erosion protection and lateral load resistance, we recommend that all footing excavations be backfilled on both sides of the footings and stemwalls after the concrete has cured. Either imported structural fill or non-organic onsite soils can be used for this purpose, contingent on suitable moisture content at the time of placement. Regardless of soil type, all footing backfill soil should be compacted to a density of at least 90 percent (based on ASTM:D-1557). Lateral Resistance: Footings that have been properly backfilled as recommended above will resist lateral movements by means of passive earth pressure and base friction. We recommend using an allowable passive earth pressure of 225 psf and an allowable base friction coefficient of 0.35 for site soils. 4.3 Slab-On-Grade Floors In our opinion, soil-supported slab-on-grade floors can be used in the proposed residences if the subgrades are properly prepared. Floor sections for the proposed structures should bear on medium dense or denser native soils or on properly compacted structural fill which extends down to soils described above. We anticipate that adequate bearing soils will be encountered within 1 to 2 feet of existing grade. We offer the following comments and recommendations concerning slab- on-grade floors. Floor Subbase: Surface compaction of all slab subgrades is recommended. If a subbase is required, it should be compacted to a density of at least 95 percent (based on ASTM:D-1557). Capillary Break and Vapor Barrier: To retard the upward wicking of moisture beneath the floor slab, we recommend that a capillary break be placed over the subgrade. Ideally, this capillary break would consist of a 4-inch-thick layer of pea gravel or other clean, uniform, well-rounded gravel, such as “Gravel Backfill for Drains” per WSDOT Standard Specification 9-03.12(4), but clean angular gravel can be used if it adequately prevents capillary wicking. In addition, a layer of plastic sheeting (such as Crosstuff, Visqueen, or Moistop) should be placed over the capillary break to serve as a vapor barrier. During subsequent casting of the concrete slab, the contractor should exercise care to avoid puncturing this vapor barrier. Vertical Deflections: Due to elastic compression of subgrades, soil-supported slab-on-grade floors can deflect downwards when vertical loads are applied. In our opinion, a subgrade reaction modulus of 250 pounds per cubic inch can be used to estimate such deflections. Sapphire Homes – Talbot Gardens Short Plat, Renton, WA October 11, 2017 / Revised August 30, 2018 Revised Geotechnical Engineering Report P1389-T18 Migizi Group, Inc. Page 12 of 14 4.4 Asphalt Pavement Since asphalt pavements will also be used for the proposed communal driveway system, we offer the following comments and recommendations for pavement design and construction. Subgrade Preparation: All soil subgrades should be thoroughly compacted, then proof-rolled with a loaded dump truck or heavy compactor. Any localized zones of yielding subgrade disclosed during this proof-rolling operation should be over excavated to a maximum depth of 12 inches and replaced with a suitable structural fill material. All structural fill should be compacted according to our recommendations given in the Structural Fill section. Specifically, the upper 2 feet of soils underlying pavement section should be compacted to at least 95 percent (based on ASTM D-1557), and all soils below 2 feet should be compacted to at least 90 percent. Pavement Materials: For the base course, we recommend using imported washed crushed rock, such as "Crushed Surfacing Base Course” per WSDOT Standard Specification 9-03.9(3) but with a fines content of less than 5 percent passing the No. 200 Sieve. Although our explorations do not indicate a need for a pavement subbase, if a subbase course is needed, we recommend using imported, clean, well-graded sand and gravel such as “Ballast” or “Gravel Borrow” per WSDOT Standard Specifications 9-03.9(1) and 9-03.14, respectively. Conventional Asphalt Sections: A conventional pavement section typically comprises an asphalt concrete pavement over a crushed rock base course. We recommend using the following conventional pavement sections: Minimum Thickness Pavement Course Parking Areas High Traffic Driveways and Private Access Roads Asphalt Concrete Pavement 2 inches 4 inches Crushed Rock Base 4 inches 8 inches Granular Fill Subbase (if needed) 6 inches 12 inches Compaction and Observation: All subbase and base course material should be compacted to at least 95 percent of the Modified Proctor maximum dry density (ASTM D-1557), and all asphalt concrete should be compacted to at least 92 percent of the Rice value (ASTM D-2041). We recommend that an MGI representative be retained to observe the compaction of each course before any overlying layer is placed. For the subbase and pavement course, compaction is best observed by means of frequent density testing. For the base course, methodology observations and hand-probing are more appropriate than density testing. Pavement Life and Maintenance: No asphalt pavement is maintenance-free. The above described pavement sections present our minimum recommendations for an average level of performance during a 20-year design life; therefore, an average level of maintenance will likely be required. Furthermore, a 20-year pavement life typically assumes that an overlay will be placed after about 10 years. Thicker asphalt and/or thicker base and subbase courses would offer better long-term performance, but would cost more initially; thinner courses would be more susceptible to “alligator” cracking and other failure modes. As such, pavement design can be considered a Sapphire Homes – Talbot Gardens Short Plat, Renton, WA October 11, 2017 / Revised August 30, 2018 Revised Geotechnical Engineering Report P1389-T18 Migizi Group, Inc. Page 13 of 14 compromise between a high initial cost and low maintenance costs versus a low initial cost and higher maintenance costs. 4.5 Structural Fill The term "structural fill" refers to any material placed under foundations, retaining walls, slab-on- grade floors, sidewalks, pavements, and other structures. Our comments, conclusions, and recommendations concerning structural fill are presented in the following paragraphs. Materials: Typical structural fill materials include clean sand, gravel, pea gravel, washed rock, crushed rock, well-graded mixtures of sand and gravel (commonly called "gravel borrow" or "pit- run"), and miscellaneous mixtures of silt, sand, and gravel. Recycled asphalt, concrete, and glass, which are derived from pulverizing the parent materials, are also potentially useful as structural fill in certain applications. Soils used for structural fill should not contain any organic matter or debris, nor any individual particles greater than about 6 inches in diameter. Fill Placement: Clean sand, gravel, crushed rock, soil mixtures, and recycled materials should be placed in horizontal lifts not exceeding 8 inches in loose thickness, and each lift should be thoroughly compacted with a mechanical compactor. Compaction Criteria: Using the Modified Proctor test (ASTM:D-1557) as a standard, we recommend that structural fill used for various onsite applications be compacted to the following minimum densities: Fill Application Minimum Compaction Footing subgrade and bearing pad Foundation backfill Asphalt pavement base Asphalt pavement subgrade (upper 2 feet) Asphalt pavement subgrade (below 2 feet) 95 percent 90 percent 95 percent 95 percent 90 percent Subgrade Observation and Compaction Testing: Regardless of material or location, all structural fill should be placed over firm, unyielding subgrades prepared in accordance with the Site Preparation section of this report. The condition of all subgrades should be observed by geotechnical personnel before filling or construction begins. Also, fill soil compaction should be verified by means of in-place density tests performed during fill placement so that adequacy of soil compaction efforts may be evaluated as earthwork progresses. Soil Moisture Considerations: The suitability of soils used for structural fill depends primarily on their grain-size distribution and moisture content when they are placed. As the "fines" content (that soil fraction passing the U.S. No. 200 Sieve) increases, soils become more sensitive to small changes in moisture content. Soils containing more than about 5 percent fines (by weight) cannot be consistently compacted to a firm, unyielding condition when the moisture content is more than 2 percentage points above or below optimum. For fill placement during wet-weather site work, we recommend using "clean" fill, which refers to soils that have a fines content of 5 percent or less (by weight) based on the soil fraction passing the U.S. No. 4 Sieve. APPROXIMATE SITE LOCATION P.O. Box 44840 Tacoma, WA 98448 Location Job Number Figure DateTitle 4827 Talbot Rd S Renton, WA P/N 3123059022 Topographic and Location Map 1 08/28/18 P1389-T18 APPENDIX A SOIL CLASSIFICATION CHART AND KEY TO TEST DATA LOGS OF TEST PITS CLAYEY GRAVELS, POORLY GRADED GRAVEL-SAND-CLAY MIXTURES SILTS AND CLAYSCOARSE GRAINED SOILSMore than Half > #200 sieveLIQUID LIMIT LESS THAN 50 LIQUID LIMIT GREATER THAN 50 CLEAN GRAVELS WITH LITTLE OR NO FINES GRAVELS WITH OVER 15% FINES CLEAN SANDS WITH LITTLE OR NO FINES MORE THAN HALF COARSE FRACTION IS SMALLER THAN NO. 4 SIEVE MORE THAN HALF COARSE FRACTION IS LARGER THAN NO. 4 SIEVE INORGANIC SILTS, MICACEOUS OR DIATOMACIOUS FINE SANDY OR SILTY SOILS, ELASTIC SILTS ORGANIC CLAYS AND ORGANIC SILTY CLAYS OF LOW PLASTICITY OH INORGANIC SILTS AND VERY FINE SANDS, ROCK FLOUR, SILTY OR CLAYEY FINE SANDS, OR CLAYEY SILTS WITH SLIGHT PLASTICITY CH SILTY GRAVELS, POORLY GRADED GRAVEL-SAND-SILT MIXTURES SANDS SILTS AND CLAYS Figure A-1 INORGANIC CLAYS OF LOW TO MEDIUM PLASTICITY, GRAVELLY CLAYS, SANDY CLAYS, SILTY CLAYS, LEAN CLAYS R-Value Sieve Analysis Swell Test Cyclic Triaxial Unconsolidated Undrained Triaxial Torvane Shear Unconfined Compression (Shear Strength, ksf) Wash Analysis (with % Passing No. 200 Sieve) Water Level at Time of Drilling Water Level after Drilling(with date measured) RV SA SW TC TX TV UC (1.2) WA (20) Modified California Split Spoon Pushed Shelby Tube Auger Cuttings Grab Sample Sample Attempt with No Recovery Chemical Analysis Consolidation Compaction Direct Shear Permeability Pocket Penetrometer CA CN CP DS PM PP PtHIGHLY ORGANIC SOILS TYPICAL NAMES GRAVELS ORGANIC CLAYS OF MEDIUM TO HIGH PLASTICITY, ORGANIC SILTS WELL GRADED GRAVELS, GRAVEL-SAND MIXTURES MAJOR DIVISIONS PEAT AND OTHER HIGHLY ORGANIC SOILS WELL GRADED SANDS, GRAVELLY SANDS POORLY GRADED SANDS, GRAVELLY SANDS SILTY SANDS, POORLY GRADED SAND-SILT MIXTURES CLAYEY SANDS, POORLY GRADED SAND-CLAY MIXTURES POORLY GRADED GRAVELS, GRAVEL-SAND MIXTURES SOIL CLASSIFICATION CHART AND KEY TO TEST DATA GW GP GM GC SW SP SM SC ML FINE GRAINED SOILSMore than Half < #200 sieveLGD A NNNN02 GINT US LAB.GPJ 11/4/05INORGANIC CLAYS OF HIGH PLASTICITY, FAT CLAYS CL OL MH SANDS WITH OVER 15% FINES SM SM SM SM 0.6 1.5 5.0 8.0 10.0 Sod and topsoil (SM) Gray fine silty sand (medium dense, damp) (Weathered Glacial Till) (SM) Light brown mottled silty sand with gravel (dense, damp) (Weathered Glacial Till) (SM) Gray/brown silty sand with gravel (very dense, moist) (Unweathered Glacial Till) (SM) Brown silty sand with gravel and intermittent lenses of fine sand (medium dense, moist) (Advanced Outwash) No caving observed No groundwater seepage observed The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to 0.5 foot. Bottom of test pit at 10.0 feet. NOTES LOGGED BY ZLL EXCAVATION METHOD Rubber Tracked Mini Excavator EXCAVATION CONTRACTOR Paulman GROUND WATER LEVELS: CHECKED BY JEB DATE STARTED 9/5/17 COMPLETED 9/5/17 AT TIME OF EXCAVATION --- AT END OF EXCAVATION --- AFTER EXCAVATION --- TEST PIT SIZEGROUND ELEVATION SAMPLE TYPENUMBERDEPTH(ft)0.0 2.5 5.0 7.5 10.0 PAGE 1 OF 1 Figure A-2 TEST PIT NUMBER TP-1 CLIENT Monsef Donogh Design Group PROJECT NUMBER P1056-T17 PROJECT NAME Proposed Talbot Gardens Short Plat PROJECT LOCATION 4827 Talbot Rd S, Renton, WA 98055 COPY OF GENERAL BH / TP LOGS - FIGURE.GDT - 10/11/17 10:17 - C:\USERS\JESSICA\DESKTOP\TEST PITS AND BORINGS - GINT\P1056-T17\P1056-T17 TEST PITS.GPJMigizi Group, Inc. PO Box 44840 Tacoma, WA 98448 Telephone: 253-537-9400 Fax: 253-537-9401 U.S.C.S.GRAPHICLOGMATERIAL DESCRIPTION ML SM SM SM 0.6 2.5 5.0 8.0 10.0 Sod and topsoil (ML) Gray/brown mottled sandy silt (medium stiff, damp) (Recessional Outwash) (SM) Gray fine silty sand (medium dense, damp) (Weathered Glacial Till) (SM) Gray/brown silty sand with gravel (dense, moist) (Unweathered Glacial Till) (SM) Brown silty sand with some gravel and intermittent lenses of fine sand (medium dense, moist) (Advanced Outwash) No caving observed No groundwater seepage observed The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to 0.5 foot. Bottom of test pit at 10.0 feet. NOTES LOGGED BY ZLL EXCAVATION METHOD Rubber Tracked Mini Excavator EXCAVATION CONTRACTOR Paulman GROUND WATER LEVELS: CHECKED BY JEB DATE STARTED 9/5/17 COMPLETED 9/5/17 AT TIME OF EXCAVATION --- AT END OF EXCAVATION --- AFTER EXCAVATION --- TEST PIT SIZEGROUND ELEVATION SAMPLE TYPENUMBERDEPTH(ft)0.0 2.5 5.0 7.5 10.0 PAGE 1 OF 1 Figure A-3 TEST PIT NUMBER TP-2 CLIENT Monsef Donogh Design Group PROJECT NUMBER P1056-T17 PROJECT NAME Proposed Talbot Gardens Short Plat PROJECT LOCATION 4827 Talbot Rd S, Renton, WA 98055 COPY OF GENERAL BH / TP LOGS - FIGURE.GDT - 10/11/17 10:17 - C:\USERS\JESSICA\DESKTOP\TEST PITS AND BORINGS - GINT\P1056-T17\P1056-T17 TEST PITS.GPJMigizi Group, Inc. PO Box 44840 Tacoma, WA 98448 Telephone: 253-537-9400 Fax: 253-537-9401 U.S.C.S.GRAPHICLOGMATERIAL DESCRIPTION SM SM SM SM 1.2 3.0 7.0 8.0 10.0 Sod and topsoil with small roots (SM) Gray fine silty sand (medium dense, damp) (Weathered Glacial Till) (SM) Light brown mottled silty sand with some gravel (medium dense, damp) (Weathered Glacial Till) (SM) Gray/brown silty sand with some gravel (dense, damp) (Unweathered Glacial Till) (SM) Brown silty sand with some gravel and intermittent lenses of fine sand (dense, moist) (Advanced Outwash) No caving observed No groundwater seepage observed The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to 0.5 foot. Bottom of test pit at 10.0 feet. NOTES LOGGED BY ZLL EXCAVATION METHOD Rubber Tracked Mini Excavator EXCAVATION CONTRACTOR Paulman GROUND WATER LEVELS: CHECKED BY JEB DATE STARTED 9/5/17 COMPLETED 9/5/17 AT TIME OF EXCAVATION --- AT END OF EXCAVATION --- AFTER EXCAVATION --- TEST PIT SIZEGROUND ELEVATION SAMPLE TYPENUMBERDEPTH(ft)0.0 2.5 5.0 7.5 10.0 PAGE 1 OF 1 Figure A-4 TEST PIT NUMBER TP-3 CLIENT Monsef Donogh Design Group PROJECT NUMBER P1056-T17 PROJECT NAME Proposed Talbot Gardens Short Plat PROJECT LOCATION 4827 Talbot Rd S, Renton, WA 98055 COPY OF GENERAL BH / TP LOGS - FIGURE.GDT - 10/11/17 10:17 - C:\USERS\JESSICA\DESKTOP\TEST PITS AND BORINGS - GINT\P1056-T17\P1056-T17 TEST PITS.GPJMigizi Group, Inc. PO Box 44840 Tacoma, WA 98448 Telephone: 253-537-9400 Fax: 253-537-9401 U.S.C.S.GRAPHICLOGMATERIAL DESCRIPTION GB S-1 SM SM SM SM 0.8 2.5 8.0 13.0 15.0 Sod and topsoil (SM) Gray/brown fine silty sand (medium dense, damp) (Weathered Glacial Till) (SM) Orange/brown mottled fine silty sand with some gravel (dense, moist) (Unweathered Glacial Till) (SM) Light brown silty sand with some gravel and intermittent lenses of fine sand (medium dense, moist) (Advanced Outwash) (SM) Gray fine silty sand with gravel (dense, moist) No caving observed No groundwater seepage observed The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to 0.5 foot. Bottom of test pit at 15.0 feet. NOTES LOGGED BY ZLL EXCAVATION METHOD Steel Tracked Excavator EXCAVATION CONTRACTOR Dreamline Construction GROUND WATER LEVELS: CHECKED BY JEB DATE STARTED 7/24/18 COMPLETED 7/24/18 AT TIME OF EXCAVATION --- AT END OF EXCAVATION --- AFTER EXCAVATION --- TEST PIT SIZEGROUND ELEVATION SAMPLE TYPENUMBERDEPTH(ft)0.0 2.5 5.0 7.5 10.0 12.5 15.0 PAGE 1 OF 1 Figure A-5 TEST PIT NUMBER TP-4 CLIENT Sapphire Homes PROJECT NUMBER P1389-T18 PROJECT NAME Proposed Talbot Gardens Short Plat PROJECT LOCATION 4827 Talbot Rd S, Renton, WA COPY OF GENERAL BH / TP LOGS - FIGURE.GDT - 8/28/18 17:10 - C:\USERS\JESSICA\DESKTOP\TEST PITS AND BORINGS - GINT\P1389-T18\P1389-T18 TEST PITS.GPJMigizi Group, Inc. PO Box 44840 Tacoma, WA 98448 Telephone: 253-537-9400 Fax: 253-537-9401 U.S.C.S.GRAPHICLOGMATERIAL DESCRIPTION GB S-1 SM SM SM SM 1.0 3.0 8.5 13.0 15.0 Sod and topsoil (SM) Gray/brown fine silty sand (loose, damp) (Weathered Glacial Till) (SM) Orange/brown mottled fine silty sand (dense, moist) (Unweathered Glacial Till) (SM) Light brown silty sand with some gravel and intermittent lenses of fine sand (medium dense, moist) (Advanced Outwash) (SM) Gray fine silty sand with gravel (dense, moist) No caving observed No groundwater seepage observed The depths on the test pit logs are based on an average of measurements across the test pit and should be considered accurate to 0.5 foot. Bottom of test pit at 15.0 feet. NOTES LOGGED BY ZLL EXCAVATION METHOD Steel Tracked Excavator EXCAVATION CONTRACTOR Dreamline Construction GROUND WATER LEVELS: CHECKED BY JEB DATE STARTED 7/24/18 COMPLETED 7/24/18 AT TIME OF EXCAVATION --- AT END OF EXCAVATION --- AFTER EXCAVATION --- TEST PIT SIZEGROUND ELEVATION SAMPLE TYPENUMBERDEPTH(ft)0.0 2.5 5.0 7.5 10.0 12.5 15.0 PAGE 1 OF 1 Figure A-6 TEST PIT NUMBER TP-5 CLIENT Sapphire Homes PROJECT NUMBER P1389-T18 PROJECT NAME Proposed Talbot Gardens Short Plat PROJECT LOCATION 4827 Talbot Rd S, Renton, WA COPY OF GENERAL BH / TP LOGS - FIGURE.GDT - 8/28/18 17:10 - C:\USERS\JESSICA\DESKTOP\TEST PITS AND BORINGS - GINT\P1389-T18\P1389-T18 TEST PITS.GPJMigizi Group, Inc. PO Box 44840 Tacoma, WA 98448 Telephone: 253-537-9400 Fax: 253-537-9401 U.S.C.S.GRAPHICLOGMATERIAL DESCRIPTION WWHM2012 PROJECT REPORT Talbot infiltration 5.5 10/30/2018 10:24:45 AM Page 2 General Model Information Project Name:Talbot infiltration 5.5 Site Name:Talbot Site Address: City: Report Date:10/30/2018 Gage:Seatac Data Start:1948/10/01 Data End:2009/09/30 Timestep:15 Minute Precip Scale:1.000 Version Date:2017/04/14 Version:4.2.13 POC Thresholds Low Flow Threshold for POC1:50 Percent of the 2 Year High Flow Threshold for POC1:50 Year Talbot infiltration 5.5 10/30/2018 10:24:45 AM Page 3 Landuse Basin Data Predeveloped Land Use Talbot Bypass:No GroundWater:No Pervious Land Use acre C, Forest, Mod 1.7515 Pervious Total 1.7515 Impervious Land Use acre Impervious Total 0 Basin Total 1.7515 Element Flows To: Surface Interflow Groundwater Talbot infiltration 5.5 10/30/2018 10:24:45 AM Page 4 Mitigated Land Use Basin 1 Bypass:No GroundWater:No Pervious Land Use acre C, Lawn, Mod 0.5098 C, Lawn, Flat 0.0804 Pervious Total 0.5902 Impervious Land Use acre ROADS FLAT 0.0546 ROADS MOD 0.2631 ROOF TOPS FLAT 0.594 DRIVEWAYS FLAT 0.1465 SIDEWALKS FLAT 0.0485 SIDEWALKS MOD 0.0545 Impervious Total 1.1612 Basin Total 1.7514 Element Flows To: Surface Interflow Groundwater Vault 1 Vault 1 Talbot infiltration 5.5 10/30/2018 10:24:45 AM Page 5 Routing Elements Predeveloped Routing Talbot infiltration 5.5 10/30/2018 10:24:45 AM Page 6 Mitigated Routing Vault 1 Width:44 ft. Length:42 ft. Depth:10 ft. Infiltration On Infiltration rate:1.25 Infiltration safety factor:1 Total Volume Infiltrated (ac-ft.):227.67 Total Volume Through Riser (ac-ft.):2.435 Total Volume Through Facility (ac-ft.):230.105 Percent Infiltrated:98.94 Total Precip Applied to Facility:0 Total Evap From Facility:0 Discharge Structure Riser Height:9 ft. Riser Diameter:12 in. Notch Type:Rectangular Notch Width:0.090 ft. Notch Height:0.600 ft. Orifice 1 Diameter:0.893 in.Elevation:3.5 ft. Element Flows To: Outlet 1 Outlet 2 Vault Hydraulic Table Stage(feet)Area(ac.)Volume(ac-ft.)Discharge(cfs)Infilt(cfs) 0.0000 0.042 0.000 0.000 0.000 0.1111 0.042 0.004 0.000 0.053 0.2222 0.042 0.009 0.000 0.053 0.3333 0.042 0.014 0.000 0.053 0.4444 0.042 0.018 0.000 0.053 0.5556 0.042 0.023 0.000 0.053 0.6667 0.042 0.028 0.000 0.053 0.7778 0.042 0.033 0.000 0.053 0.8889 0.042 0.037 0.000 0.053 1.0000 0.042 0.042 0.000 0.053 1.1111 0.042 0.047 0.000 0.053 1.2222 0.042 0.051 0.000 0.053 1.3333 0.042 0.056 0.000 0.053 1.4444 0.042 0.061 0.000 0.053 1.5556 0.042 0.066 0.000 0.053 1.6667 0.042 0.070 0.000 0.053 1.7778 0.042 0.075 0.000 0.053 1.8889 0.042 0.080 0.000 0.053 2.0000 0.042 0.084 0.000 0.053 2.1111 0.042 0.089 0.000 0.053 2.2222 0.042 0.094 0.000 0.053 2.3333 0.042 0.099 0.000 0.053 2.4444 0.042 0.103 0.000 0.053 2.5556 0.042 0.108 0.000 0.053 2.6667 0.042 0.113 0.000 0.053 2.7778 0.042 0.117 0.000 0.053 2.8889 0.042 0.122 0.000 0.053 3.0000 0.042 0.127 0.000 0.053 Talbot infiltration 5.5 10/30/2018 10:24:45 AM Page 9 Analysis Results POC 1 + Predeveloped x Mitigated Predeveloped Landuse Totals for POC #1 Total Pervious Area:1.7515 Total Impervious Area:0 Mitigated Landuse Totals for POC #1 Total Pervious Area:0.5902 Total Impervious Area:1.1612 Flow Frequency Method:Log Pearson Type III 17B Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.052151 5 year 0.085454 10 year 0.106868 25 year 0.13234 50 year 0.149983 100 year 0.166463 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.234765 5 year 0.482216 10 year 0.649953 25 year 0.84725 50 year 0.978859 100 year 1.096284 Annual Peaks Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.060 0.000 1950 0.071 0.007 1951 0.114 0.039 1952 0.036 0.000 1953 0.029 0.000 1954 0.044 0.000 1955 0.071 0.017 1956 0.057 0.013 1957 0.046 0.000 1958 0.051 0.000 Talbot infiltration 5.5 10/30/2018 10:25:26 AM Page 15 Water Quality Water Quality BMP Flow and Volume for POC #1 On-line facility volume:0.1619 acre-feet On-line facility target flow:0.1743 cfs. Adjusted for 15 min:0.1893 cfs. Off-line facility target flow:0.0986 cfs. Adjusted for 15 min:0.1071 cfs. Talbot infiltration 5.5 10/30/2018 10:25:26 AM Page 16 LID Report Talbot infiltration 5.5 10/30/2018 10:31:55 AM Page 18 Appendix Predeveloped Schematic Talbot infiltration 5.5 10/30/2018 10:31:55 AM Page 19 Mitigated Schematic Talbot infiltration 5.5 10/30/2018 10:31:56 AM Page 24 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. 2005-2018; 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 WWHM2012 PROJECT REPORT Talbot Detention Only 10/30/2018 10:41:20 AM Page 2 General Model Information Project Name:Talbot Detention Only Site Name:Talbot Site Address: City: Report Date:10/30/2018 Gage:Seatac Data Start:1948/10/01 Data End:2009/09/30 Timestep:15 Minute Precip Scale:1.000 Version Date:2017/04/14 Version:4.2.13 POC Thresholds Low Flow Threshold for POC1:50 Percent of the 2 Year High Flow Threshold for POC1:50 Year Talbot Detention Only 10/30/2018 10:41:20 AM Page 3 Landuse Basin Data Predeveloped Land Use Talbot Bypass:No GroundWater:No Pervious Land Use acre C, Forest, Mod 1.7515 Pervious Total 1.7515 Impervious Land Use acre Impervious Total 0 Basin Total 1.7515 Element Flows To: Surface Interflow Groundwater Talbot Detention Only 10/30/2018 10:41:20 AM Page 4 Mitigated Land Use Basin 1 Bypass:No GroundWater:No Pervious Land Use acre C, Lawn, Mod 0.5098 C, Lawn, Flat 0.0949 Pervious Total 0.6047 Impervious Land Use acre ROADS FLAT 0.0546 ROADS MOD 0.2631 ROOF TOPS FLAT 0.58 DRIVEWAYS FLAT 0.1465 SIDEWALKS FLAT 0.0485 SIDEWALKS MOD 0.0545 Impervious Total 1.1472 Basin Total 1.7519 Element Flows To: Surface Interflow Groundwater Vault 1 Vault 1 Talbot Detention Only 10/30/2018 10:41:20 AM Page 5 Routing Elements Predeveloped Routing Talbot Detention Only 10/30/2018 10:41:20 AM Page 6 Mitigated Routing Vault 1 Width:75.9350127494339 ft. Length:75.9350127494339 ft. Depth:6.5 ft. Discharge Structure Riser Height:5.5 ft. Riser Diameter:18 in. Orifice 1 Diameter:0.57 in.Elevation:0 ft. Orifice 2 Diameter:0.97 in.Elevation:3.5585 ft. Orifice 3 Diameter:1.2 in.Elevation:4.015 ft. Element Flows To: Outlet 1 Outlet 2 Vault Hydraulic Table Stage(feet)Area(ac.)Volume(ac-ft.)Discharge(cfs)Infilt(cfs) 0.0000 0.132 0.000 0.000 0.000 0.0722 0.132 0.009 0.002 0.000 0.1444 0.132 0.019 0.003 0.000 0.2167 0.132 0.028 0.004 0.000 0.2889 0.132 0.038 0.004 0.000 0.3611 0.132 0.047 0.005 0.000 0.4333 0.132 0.057 0.005 0.000 0.5056 0.132 0.066 0.006 0.000 0.5778 0.132 0.076 0.006 0.000 0.6500 0.132 0.086 0.007 0.000 0.7222 0.132 0.095 0.007 0.000 0.7944 0.132 0.105 0.007 0.000 0.8667 0.132 0.114 0.008 0.000 0.9389 0.132 0.124 0.008 0.000 1.0111 0.132 0.133 0.008 0.000 1.0833 0.132 0.143 0.009 0.000 1.1556 0.132 0.153 0.009 0.000 1.2278 0.132 0.162 0.009 0.000 1.3000 0.132 0.172 0.010 0.000 1.3722 0.132 0.181 0.010 0.000 1.4444 0.132 0.191 0.010 0.000 1.5167 0.132 0.200 0.010 0.000 1.5889 0.132 0.210 0.011 0.000 1.6611 0.132 0.219 0.011 0.000 1.7333 0.132 0.229 0.011 0.000 1.8056 0.132 0.239 0.011 0.000 1.8778 0.132 0.248 0.012 0.000 1.9500 0.132 0.258 0.012 0.000 2.0222 0.132 0.267 0.012 0.000 2.0944 0.132 0.277 0.012 0.000 2.1667 0.132 0.286 0.013 0.000 2.2389 0.132 0.296 0.013 0.000 2.3111 0.132 0.305 0.013 0.000 2.3833 0.132 0.315 0.013 0.000 2.4556 0.132 0.325 0.013 0.000 2.5278 0.132 0.334 0.014 0.000 2.6000 0.132 0.344 0.014 0.000 2.6722 0.132 0.353 0.014 0.000 Talbot Detention Only 10/30/2018 10:41:20 AM Page 8 Analysis Results POC 1 + Predeveloped x Mitigated Predeveloped Landuse Totals for POC #1 Total Pervious Area:1.7515 Total Impervious Area:0 Mitigated Landuse Totals for POC #1 Total Pervious Area:0.6047 Total Impervious Area:1.1472 Flow Frequency Method:Log Pearson Type III 17B Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.052151 5 year 0.085454 10 year 0.106868 25 year 0.13234 50 year 0.149983 100 year 0.166463 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.029581 5 year 0.054612 10 year 0.076273 25 year 0.110055 50 year 0.140275 100 year 0.175166 Annual Peaks Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.060 0.015 1950 0.071 0.049 1951 0.114 0.155 1952 0.036 0.013 1953 0.029 0.042 1954 0.044 0.025 1955 0.071 0.015 1956 0.057 0.069 1957 0.046 0.016 1958 0.051 0.024 Talbot Detention Only 10/30/2018 10:42:19 AM Page 15 LID Report Talbot Detention Only 10/30/2018 10:48:13 AM Page 17 Appendix Predeveloped Schematic Talbot Detention Only 10/30/2018 10:48:44 AM Page 18 Mitigated Schematic Talbot Detention Only 10/30/2018 10:48:45 AM Page 23 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. 2005-2018; 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