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Home My WebLink AboutRS_Geotechnical_Report_250728_v1INNOVATIVE GEO-SERVICES, LLC ENGINEERING GEOLOGY SERVICES ENGGEOLOGIST.COM 253 279-4205 17903 82nd ST E, Bonney Lake, WA 98391 rex@enggeologist.com Van Vuong December 20, 2022 14349 SE 92nd ST Newcastle, WA 98059 Soil Characterization and Infiltration Letter Address 12820 156th AV SE Renton, WA Parcel No. 3664500165 Site Visit Performed 12/09/2022 INTRODUCTION It is the intent of this evaluation to describe the surface and subsurface conditions observed on the residential lot located at 12820 156th AV SE in Renton, WA. Site observations are related to surface water runoff and storm water control planning. The parcel is a developed 46,575 sf lot (1.07 acre) with access from 156th AV SE which extends across the west property line. The parcel contains a single-family structure on the western third of the lot with a paved driveway entering the lot at the northwest corner. Development plans call for creating a three-lot plat with the existing home on 123 ft wide western most lot and two new 83 ft wide lots to the east. Access to the three-lot plat will be via a new road extending east across the south property line. This report is for the exclusive use of Van Vuong, his consultants and contractors for the intended purpose described. Site observations and exploration methods applied and described in this study represent the standard of practices for the industry. Sources of information cited are uniformly accepted resources when utilized in conjunction with field reconnaissance as confirmation. Opinions are based on using these standardized practices to adequately characterize the local surficial geology and general conditions at the site. SITE AND PROJECT DESCRIPTION The 1.07-acre parcel is a rectangular lot extending east from 156th AV SE approximately 289 ft. and is nearly 161 ft wide. The parcel will be divided into three lots with the existing home on the western 123 ft lot and two 83 ft wide lots to the east. Access to the three lots will be provided by a new road across the south property line. The parcel is located in an established residential neighborhood with direct access from 156th AV SE. Surface grades across the parcel are predominantly gentle, rising gently across the parcel to the north and northeast. The new residential plat will be served by municipal water, sewer and private storm water control systems. Sewer service will be extended east from 156th AV SE near the southwest corner of the parcel and water service will be extended from the northwest corner. Surface water runoff currently flows to the south and southwest across the grassy areas surrounding the home. Vuong Soil and Infiltration Study 12820 156th AV SE, Renton December 20, 2022 Page 2 253 279-4205 17903 82nd ST E, Bonney Lake, WA 98391 rex@enggeologist.com Site plan Topography and Aerial Photo obtained from King County GIS EVALUATION METHODS We Observed surface and subsurface conditions at the project site on December 9th, 2022. Our evaluation involved a review of available public mapping and information, three exploration soil pits and conducted two EPA Falling Head Perk tests. SITE SOILS The Natural Resources Conservation Service (NRCS) describes the soil across the parcels as Alderwood gravelly sandy loam. This silty, sand and gravel were derived from glacial deposits from the advance and retreat of the Frasier Ice sheet across the region. IGS Soil Pit and Perk Test IGS Soil Pit and Perk Test Vuong Soil and Infiltration Study 12820 156th AV SE, Renton December 20, 2022 Page 3 253 279-4205 17903 82nd ST E, Bonney Lake, WA 98391 rex@enggeologist.com Alderwood AgC – Alderwood gravelly sandy loam, 8 – 15 percent slopes This rolling Alderwood soil is moderately well drained. It formed in glacial till on broad uplands. Vegetation is hardwoods and conifers. Elevation ranges from 200 to 800 feet. The mean annual precipitation is about 35 inches, mean annual air temperature is about 50 degrees F, and the frost- free season averages about 180 days. Individual soil areas average about 125 acres in size. Most slopes average about 8 percent. Granite boulders and stones are strewn across some slopes. Included with this soil in mapping are small areas of better drained Indianola loamy sand on the side slopes and poorer drained Norma sandy loam or Dupont muck in troughs. In addition, some areas of Alderwood gravelly sandy loam and Kapowsin gravelly loam, zero to six percent slopes, are included. In a typical soil profile, a mat of undecomposed needles and wood fragments rests upon a 1 ½ inch thick very dark grayish brown gravelly sandy loam surface layer. The subsoil and the upper part of the substratum, to a depth of 38 inches, are dark yellowish brown, brown, and dark grayish brown gravelly VUONG PROPERTY (APPROX. LOCATION) Vuong Soil and Infiltration Study 12820 156th AV SE, Renton December 20, 2022 Page 4 253 279-4205 17903 82nd ST E, Bonney Lake, WA 98391 rex@enggeologist.com sandy loam. The lower parrot of the substratum, to a depth of more than 60 inches, is weakly cemented compact glacial till. Reaction is medium acid. The water table is perched above the very slowly permeable, weakly cemented and compact part of the substratum during periods of heavy rainfall. However, the perched water table is of short duration because the water flows laterally above this layer to seeps at the bottom of slopes. Very few roots penetrate this dense substratum. The available water capacity is low. Surface runoff is medium, and the erosion hazard is moderate. Because of its proximity to urban centers, this Alderwood soil is subject to urbanization pressure. The soil has an inherent ability to support a large load. Soil slope and the weakly cemented, compact substratum are its limiting features. In areas of moderate to high population density, onsite sewage disposal systems often fail or do not function properly during periods of rainfall in winter. Excavation for basements and utility lines is difficult to cover excavated soil material. SITE GEOLOGY According to maps from the Washington Division of Geology and Earth Resources, this region of King County lies in the glacial lowland area of multiple glacial advance and recessional periods. The surface deposits are described as glacial till consisting of well compacted, fine to medium grain, poorly sorted sand with gravel and cobbles. Geology of the Renton Quadrangle, WA, (Excerpt) Mapping prepared by D.R. Mullineaux, 1965 Findings / Infiltration Feasibility On December 9th, 2022, IGS visually inspected the parcel and observed the excavation of three exploratory soil pits. Two soil pits were excavated near the southwest and southeast portions of the parcel. Infiltration testing was conducted in each hole at a depth of 18 in. to 24 in. Raw infiltration rates were observed in the two shallow soil pits using the EPA Falling Head guidelines. Following each test the exploratory soil pit was excavated to a depth of 5 ft. to confirm soil textures below the test elevation. The native soil is described as silty, gravelly sand consistent with the NRCS classification of Alderwood gravelly sandy loam. No groundwater or indications of seasonal groundwater were observed in the soil pits. VUONG PROPERTY Vuong Soil and Infiltration Study 12820 156th AV SE, Renton December 20, 2022 Page 5 253 279-4205 17903 82nd ST E, Bonney Lake, WA 98391 rex@enggeologist.com Infiltration testing in TP 1 indicates a raw infiltration rate of 5 in/hr. at 18 in and 7 in/hr. in TP 2 at 24 in. Testing was conducted in tan silty sand with small gravel and rocks. We recommend using an infiltration rate of 4 in/hr. for storm water infiltration or dispersion planning. Vegetative ground cover consisting of grasses with landscape shrubs and a few conifer trees. Glacial Till (restrictive layer) was encountered at a depth of 60 in. across the south side of the parcel and 48 in. in the north. Site observations indicate the soil is consistent across the property. CLOSURE Our conclusions and recommendations are professional opinions derived in accordance with current standards of practice within the scope of our services and within budget and time constraints. No warranty is expressed or implied. We appreciate the opportunity to be of service on this project. If you have any questions regarding this letter or any aspects of the project, please feel free to contact our office. Respectfully submitted, Innovative GEO-Services, LLC Rex Humphrey, L.E.G. Principal Engineering Geologist Attached: Soil Test Pits TP 1, 2 and 3 12/20/2022 Vuong Soil and Infiltration Study 12820 156th AV SE, Renton December 20, 2022 Page 6 253 279-4205 17903 82nd ST E, Bonney Lake, WA 98391 rex@enggeologist.com Vuong Soil and Infiltration Study 12820 156th AV SE, Renton December 20, 2022 Page 7 253 279-4205 17903 82nd ST E, Bonney Lake, WA 98391 rex@enggeologist.com Vuong Soil and Infiltration Study 12820 156th AV SE, Renton December 20, 2022 Page 8 253 279-4205 17903 82nd ST E, Bonney Lake, WA 98391 rex@enggeologist.com