9506 7TH AVE SE 2025-04-08 - Laserfiche WebLink

Pacific Ridge — DRH, LLC ES-8528.01 July 18, 2022 Page 3 Topsoil Topsoil was encountered generally within the upper 3 to 16 inches of existing grades at the test pit locations. Deeper pockets of topsoil may be present in localized areas across the site. The topsoil was characterized by the dark brown color, presence of fine organic material, and small root intrusions. Fill Fill was encountered within six of seven test pits excavated during our May 2022 exploration. The fill was generally characterized as brown and gray silty sand in a medium dense to dense, moist to wet condition. At four of seven test locations, relic topsoil horizons and/or buried organic deposits were observed underlying the fill — the buried organic soil horizons ranged in thickness between roughly one to two feet. Where observed, the fill and buried organic sections extended no deeper than about five feet bgs. Slight caving was noted at one test pit location within the observed fill soil. Native Soil Underlying the topsoil and fill, native soil consisting primarily of silty sand with gravel were observed (USCS: SM, GM), consistent with the typical make-up of glacial till deposits. Nearest the surface, the native soil was generally in a relatively weathered (brown), loose to medium dense condition, transitioning into very dense, weakly cemented, and unweathered (gray) glacial till beginning at roughly one to eight feet bgs. At some locations, the weathered glacial till soil was mostly or completely missing from the soil profile, indicating historic grade cuts and removal of the upper weathered soil. Glacial till deposits were observed extending to the maximum exploration depth of each respective test pit. Geologic Setting Local geologic mapping indicates the site is underlain by Vashon glacial till (Qvt) deposits. As reported on the geologic map, Vashon glacial till consists primarily of a non-sorted mixture of silt, sand, and sub-rounded to well-rounded gravels, commonly referred to as "hardpan." The till was deposited directly from the glacier as it advanced over bedrock and older Quaternary sediment. The online Web Soil Survey identifies Alderwood-urban land complex as the primary soil unit underlying the subject site. Alderwood series soils formed over glacial deposits beneath conifer trees. Urban land is described as areas that are covered by streets, buildings, parking lots, and other structures that obscure or alter the soils so that identification is not possible; classification as urban land also suggests that man-made modifications to the natural landscape have occurred in the past, including grade cuts or fills. Alderwood-urban land complex soils are characterized by the USDA with slow stormwater runoff and slight hazard of water erosion. In our opinion, based on our subsurface observations, the native soils are generally consistent with the geologic and soil mapping resources outlined in this section. Earth Solutions NW, LLC