917 112TH ST SE Geotech Report 2022-10-25

Habitat for Humanity of Snolsh County ES-5168 April 26, 2017 Page 3 Subsurface An ESNW representative observed, logged, and sampled four test pits, excavated at accessible locations within the property boundaries, on March 29, 2017 using a mini trackhoe and operator retained by our firm. The test pits were completed for purposes of assessment and classification of site soils as well as characterization of groundwater conditions within accessible areas of the site. The approximate locations of the test pits are depicted on Plate 2 (Test Pit Location Plan). Please refer to the test pit logs provided in Appendix A for a more detailed description of subsurface conditions. Representative soil samples collected at the test pit locations were evaluated in accordance with Unified Soil Classification System (USCS) and United States Department of Agriculture (USDA) methods and procedures. Topsoil and Fill Topsoil was encountered generally in the upper one to four inches of existing grades at the test pit locations. The topsoil was characterized by dark brown color, the presence of fine organic material, and small root intrusions. Based on our field observations, we estimate topsoil will be encountered with an average thickness of two to four inches across the site. Deeper pockets of topsoil, however, may be encountered locally across the site. Fill was encountered at test pit locations TP-1 and TP-4 extending to depths of approximately one to two feet below the existing ground surface (bgs). The fill was characterized primarily as medium dense silty sand with gravel in a moist condition. Elsewhere across the site, fill may be encountered in proximity to and underlying existing structural improvements. ESNW can evaluate in-situ fill deposits where encountered during construction, as needed. Native Soil Underlying topsoil and the isolated fill areas, native soils were encountered primarily as silty sand with gravel (USCS: SM), generally consistent with glacial till deposits. The upper, medium dense deposits may be characterized as "weathered", and the lower, dense to very dense deposits may be characterized as "unweathered". The unweathered glacial till was observed to be weakly cemented in some areas. Native soils were primarily observed in a moist condition and extended to the maximum exploration depth of approximately nine feet bgs. Geologic Setting The referenced geologic map resource identifies Vashon till (Qvt) across the site and surrounding areas. According to the geologic map resource, Vashon till is chiefly a non-sorted mixture of clay, silt, sand, pebbles, cobbles, and boulders in variable amounts. Vashon till is primarily compact and is commonly referred to as "hardpan". The referenced WSS resource identifies Alderwood-Urban land complex (Map Unit Symbol: 5) across the site and surrounding areas. The Alderwood series was formed in glacial till plains, and, with respect to urban development, may have been modified by human activities in some areas. Based on our field observations, native soils likely to be exposed during grading activities will be consistent with the geologic setting outlined in this section. Earth Solutions NW,LLC