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Home My WebLink AboutADU Geotech Report 1^�T Ph 253-896-1011 Fix 253-896-2633 Signature Custom Homes 10407 8th St E Edgewood, WA 98372 Attn: Mr. Bill Hines (253) 606-3228 GeoResources, LLC 5007 Pacific Hwy E., Ste. 16 Fife, Washington 98424 January 14, 2016 Rev. March 31, 2017 Updated Geotechnical Engineering Report - Stormwater Feasibility Proposed Residential Development 1715 Morris Avenue S Renton, WA PN: 7222000334, 7222000342 Doc ID: Signatu reCustom Homes. MorrisAve. L INTRODUCTION This revise report summarizes our site evaluation, provides our opinion regarding the feasibility of the site soils to support onsite infiltration of stormwater, and addresses the current proposed project to be constructed at 1715 Morris Avenue. Our original report dated January 14, 2016 was prepared Brookstone Homes for both 1715 and 1723 Morris Avenue South in Renton, Washington. We understand that Signature Custom Home is now building the residence at 1715 Morris Avenue. The approximate site location is shown on the Site Location Map, Figure 1. Our understanding of the projects are based on discussions with you, our January 8, 2016 site visit, our understanding of the 2009 King County Stormwater Management Manual, a review of published geologic and soil literature, and our past experience in the area. Our original report was to provide soil logs in order to confirm subsurface conditions to determine the feasibility of stormwater infiltration at the site. The proposed development will include the construction a new single family residence with an additional dwelling until. The main house's roof will cover about 2624 square feet (sf), the ADU will cover about 1071 sq, and the driveway and walkways will cover about 1,400 sf. Site Conditions The sites and surrounding parcels are located In an area of established residential development. The parcel Is generally rectangular in shape, measuring about 160 feet deep (east to west) by 50 feet wide (north to south) and encompass about 8,050 square feet, or 0.18 acres each. The sites are bounded by residential developments and Morris Avenue S and are currently vacant. The sites generally slope down to the east. Total topographic relief is on the order of 5 feet on both sites. The site Is currently vegetated with residential landscaping. A site plan showing topography is included as Figure 2. Site Soils The USDA Natural Resources Conservation Service maps the site as being underlain by Beausite Gravelly Sandy Loam (BeC) soils. The Beausite soils are derived from till over residuum from sandstone and are Included in hydrologic soils group C1D. Sign atu reCustom Homes. MorrisAve.L March 31, 2017 Page 2 The BeC soils form on slopes of 6 to 15 percent and have a "moderate" erosion hazard when exposed. An excerpt from the USDA map is attached as Figure 3. Site Geology Geologlc Map of the Renton Quadrangle, King County, Washington, by D.R. Mullineaux (1965) maps the site as being underlain by Renton Formation jr). No areas of landslides or landslide debris are mapped on or within the vicinity of the site. An excerpt of the above referenced map is included as Figure 4. Subsurface Explorations On December 9, 2015, a GeoResources representative was on site and monitored the excavation of one hand auger exploration at 1715 Morris Avenue S and one hand auger exploration at 1723 Morris Avenue S to depths of 7 feet below the existing grade. The locations of the hand augers were selected by the contractor personnel in the field based on discussions regarding the proposed development. Prior to our arrival Brookstone Homes, LLC had excavated a test pit on each site to depths of approximately 5 feet. We monitored the hand augers the remaining 2 feet from the bottom of the test pits, maintained logs of the subsurface conditions encountered, obtained representative soil samples, and observed pertinent site features. Representative soil samples obtained from the explorations were placed in sealed plastic bags and taken to a laboratory for further examination and testing as deemed necessary. The hand augers excavated and reviewed as part of this evaluation Indicate the subsurface conditions at specific locations only, as actual subsurface conditions can vary across the site. Furthermore, the nature and extent of such variation would not become evident until additional explorations are performed or until construction activities have begun. Based on our experience in the area, it is our opinion that the soils encountered in the hand augers are generally representative of the soils at the site. The approximate locations of the hand augers are indicated on the attached Site and Exploration Plan as Figure 2. Subsurface Conditions Our explorations encountered relatively uniform conditions at the sites. Our hand auger explorations generally encountered approximately 10 inches of topsoil mantling brown gravelly sand with silt, organics, and mottling in a medium dense, moist condition. We Interpret these surficlal soils as fill associated with prior grading activities at the site. Below the surficlal soils and fill, our hand augers encountered tan to light brown sand with silt and gravel in a medium dense to dense, moist condition, which we interpret as weathered till mantling undisturbed glacial till. Dense till was encountered at a depth of approximately 5.5 feet. Detailed logs of the hand augers can be found in Figure 6 with lab results included as Figure 7 and Figure 8. Groundwater Groundwater seepage was not encountered in our hand augers at the time of excavation. We interpret the observed mottling in the explorations to be indicative of seasonal perched groundwater conditions. Perched groundwater develops when the vertical infiltration rate of precipitation through a more permeable soil is slowed at depth by a deeper, less permeable soil type. We expect that perched groundwater may develop seasonally atop the deeper and denser older fine-grained glacial deposits at the site. We anticipate fluctuations in the local groundwater levels likely will occur in response to precipitation patterns, off site construction activities, and site utilization. SlgnatureCustom Hom es. M orrisAve.L March 31, 2017 Page 3 CONCLUSIONS Based on our site observations, subsurface explorations and review of the King County Stormwater Manual (2009), it is our opinion that the site soils consist of fill over weathered till and till. Onsite infiltration will be limited to shallow systems (less than 3') and would likely be long trenches. Alternatively, stormwater can be collected and conveyed to an appropriate discharge point, such as a dispersion system or the roadway. Based on our review of the provided site plan, portions of the site's stormwater could be mitigated through a combination of downspout dispersion and/or sheet flow dispersion. Downspout dispersion systems should be designed and constructed in accordance with Volume V, Chapter 5.3.1 of the SWMWW 2012, BMP T5.10B. Sheet flow dispersion systems should be constructed in accordance with BMP T5.12 of the same reference. Alternatively, low -impact development (LID) methods, such as pervious pavement or rain gardens may also be considered provided the onsite soils meet site suitability criteria for treatment capacity. These additional tests can be performed at your request for an additional fee. LIMITATIONS We have prepared this report for Signature Custom Homes for use in evaluating a portion of this project. Our report, conclusions and interpretations are based on data from our limited subsurface explorations and reconnaissance, and should not be construed as a warranty of the subsurface conditions. Variations in subsurface conditions are possible between the explorations and may also occur with time. A contingency for unanticipated conditions should be included in the budget and schedule. Sufficient monitoring, testing and consultation should be provided by our firm during construction to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes should the conditions revealed during the work differ from those anticipated, and to evaluate whether Installation activities comply with contract plans and specifications. Our recommendations are not intended to direct the contractor's methods, techniques, sequences or procedures, except as specifically described in our report for consideration in design. If there are any changes in the configurations or type of facilities to be constructed, the conclusions and recommendations presented in this report may not be fully applicable. If such changes are made, we should be given the opportunity to review our recommendations and provide written modifications or verifications, as appropriate. r3KM Sign atureC ustom Homes. Morri sAve. L March 31, 2017 Page 4 We trust this is sufficient for your current needs. Should you have any questions, or require additional information, please contact us at your earliest convenience. Respectfully submitted, GeoResources, LLC stin Ta for El Y Staff Engineer Brad Biggerstaff, LHG Principal SPB:DCB:stm:drt DocID: SignalureCustomHomes.MorrisAve.L Attachments: Figure 1: Site Location Map Figure 2a: Site and Exploration Plan Figure 2b: Proposed Site Plan Figure 3: NRCS SCS Soils Map Figure 4: USGS Geologic Map Figure 5: Unified Soil Classification System Figure 6: Hand Auger Excavations Dana C. Biggerstaff, PE Senior Geotechnical Engineer 5 1611) 5f 5 17th St M) Pack S 20th °t 5 A Approximate Site Locations (Map created from King County Public GIS http://gismaps.kingcounty.gov/iMap/) GeoResources, LLC 5007 Pacific Highway East, Suite 16 Fife, Washington 98424 Phone: 253.896-1011 Fax: 253-896-2633 Site Location Map Proposed Single Family Residence 1715 Morris Ave S Renton, Washington Doc ID: SignatureCustomHomes.Mo(risAVe.F March 2017 I Figure 1 7 G J VJ :. `\l.C. S t6! Q to ro `l/ 41 U '- Approximate Site Locations (Map created from King County Public GIS http://gismaps.kingcounty.gov/iMap/) GeoResources, LLC 5007 Pacific Highway East, Suite 16 Fife, Washington 98424 Phone: 253.896-1011 Fax: 253-896-2633 Site Location Map Proposed Single Family Residence 1715 Morris Ave S Renton, Washington Doc ID: SignatureCustomHomes.Mo(risAVe.F March 2017 I Figure 1 Approximate Site Locations (Map created from King County Public GIS http://gismaps.kingcounty.gov/iMap/) GeoResources, LLC 5007 Pacific Highway East, Suite 16 Fife, Washington 98424 Phone: 253-896-1011 Fax: 253-896-2633 Site and Exploration Plan Proposed Single Family Residence 1715 Morris Ave S Renton, Washington (i) (i> C)JI �....�.�..,. Of $'Jrt3 nl v Site Plan created by Group Architected dated 2/3/2017 GeoResources, LLC 5007 Pacific Highway East, Suite 16 Fife, Washington 98424 Phone: 253.896-1011 Fax: 253.896-2633 Not to Scale I Site Pian Proposed Single Family Residence 1715 Morris Ave S Renton, Washington Doc ID: SignatureCustomHomes.MordsAVe.F March 2017 Figure 2b Approximate Site Locations (map created from the USDA Natural Resource Conservation Service Web Soil Survey) Soil Soil Name Parent Material Slopes Erosion Hazard Hydrologic Type Soils Group BeC Beausite Gravelly Till over residuum from 6-15 Moderate C Sandy Loam sandstone GeoResources, LLC 5007 Pacific Highway East, Suite 16 Fife, Washington 98424 Phone: 253-896-1011 Fax: 253-896-2633 NRCS SCS Sons Map Proposed Single Family Residence 1715 Morris Ave S Renton, Washington r \'j, i�#t� '� .l� t`° � i � i' f ,� 1 *a l � _••� 1 �;' �, '�-ti'`#= Qac 1 Qaw �t V51, VAI "n s � �'� , •—fr��f i jam/ � �� p i '. lly"•. o i 5 # ik �� ( 1 ;( i r ,'_'L Qaw 1 L , �. �r---j 7Q '6 a V r 3 01 4w, Approximate Site Location Geologic Map of the Renton Quadrangle, King County, Washington, by D.R. Mullineaux (1965) Tr I Renton Formation GeoResources, LLC 5007 Pacific Highway East, Suite 16 Fife, Washington 98424 Phone: 253-896-1011 Fax: 253-896-2633 USGS Geologic Map Proposed Single Family Residence 1715 Morris Ave S Renton, Washington SOIL CLASSIFICATION SYSTEM MAJOR DIVISIONS GROUP SYMBOL GROUP NAME GRAVEL CLEAN GW WELL -GRADED GRAVEL, FINE TO COARSE GRAVEL GRAVEL GP POORLY -GRADED GRAVEL COARSE GRAINED More than 50% GRAVEL WITH FINES GM SILTY GRAVEL SOILS Of Coarse Fraction Retained on No. 4 Sieve GC CLAYEY GRAVEL More than 50% SAND CLEAN SAND SW WELL -GRADED SAND, FINE TO COARSE SAND Retained on No. 200 Sieve SP POORLY -GRADED SAND More than 50% Of Coarse Fraction SAND SM SILTY SAND Passes WITH FINES No. 4 Steve SC CLAYEY SAND SILT AND CLAY INORGANIC ML SILT FINE GRAINED CL CLAY SOILS Liquid Limit Less than 50 ORGANIC OL ORGANIC SILT, ORGANIC CLAY SILTAND CLAY INORGANIC MH SILT OF HIGH PLASTICITY, ELASTIC SILT More than 50% Passes CH CLAY OF HIGH PLASTICITY, FAT CLAY No. 200 Sieve Liquid Limit 50 or more ORGANIC OH ORGANIC CLAY, ORGANIC SILT HIGHLY ORGANIC SOILS PT PEAT NOTES: 1. Field classification Is based on visual examination of sell In general accordance with ASTM D2488-90. 2. Solt classification using laboratory tests is based on ASTM D2487-90. 3. Description of soil density or consistency are based on Interpretation of blow count data, visual appearance of sells, and or test data. GeoResources, LLC 5007 Pacific Highway East, Suite 16 Fife, Washington 98424 Phone: 253-896-1011 Fax: 253-896-2633 SOIL MOISTURE MODIFIERS: Dry- Absence of moisture, dry to the touch Molal- Damp, but no visible water Wet- Visible free water or saturated, usually soil Is obtained from below water table Soil Classification System Proposed Residential Development 1715 Morris Ave S Renton, WA Hand Auger HA -1 Location: Middle of 1715 Morris Ave S Depth (feet) Soil Tvoe Soil Descriotion 0 - 0.8 Topsoil 0.8 - 1.3 SM Brown/tan gravelly SAND with silt, organics, and mottling (medium dense, moist) 1.3 - 4.0 SM Tan gravelly SAND with silt, organics, and mottling (medium dense, moist) 4.0 - 4.5 SM Tan/light brown mottled SAND with silt and gravel (medium dense, moist) 4.5 - 7.0 SM Tan/light brown SAND with silt, gravel, and some mottling (dense, moist, glacial till) No caving observed. No groundwater seepage observed. Logged by: DIRT GeoResources, LLC 5007 Pacific Highway East, Suite 16 Fife, Washington 98424 Phone: 253-896-1011 Fax: 253-896-2633 Excavated on: January 8, 2016 Hand Auger Excavations Proposed Residential Development 1715 Morris Ave S Renton, WA Wednesday, August 30, 2017 at 3:01:18 PM Pacific Daylight Time Subject: FW: City of Renton Date: Wednesday, August 30, 2017 at 2:17:33 PM Pacific Daylight Time From: Dustin Taylor To: Mike Clow CC: Keith Schembs From: Dustin Taylor Sent: Tuesday, August 29, 2017 3:16 PM To:'bill.hines@me.com' <bill.hines@me.com> Subject: RE: City of Renton Checkout this detail of the perforated stubout option. Let me know! Thanks!! From: Dustin Taylor Sent: Thursday, August 24, 2017 3:55 PM To: 'bill.hines@me.com'<bill.h!nes@me.com> Subject: City of Renton I finally got to have a conversation with Ann with the City of Renton. She said following the Appendix C for the BMPs is an option. I recommended to her a combination of splashblocks, limited infiltration, with overflow to city line across the street. She didn't think capacity would be an issue on the city line. For the overflow, a 2' by 10' infiltration trench is required first then that is tied into city line. So finding room for that may be tricky, but it seems there are options becoming available. Respectfully, Dustin Taylor, E.I.T. /Staff Engineer GeoResources, LLC 5007 Pacific Highway East, #16 Fife, Washington 98424 (253) 896-1011 office (253) 896-2633 fax (206) 390-6450 mobile www.georesou rces. rocks dustin@georesaurces.uS amu. —0010 77v GGEORESaURCES Sc7GlU'&gBoled�nicblc�gineL�ing jp Be green - think before you print Page 1 of 1