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1 <br /> IThe lodgement till is interpreted to be the result of deposition dirccdy at the sole of the advancing <br /> Vashon age ice s6eet. The mode of deposidon resulted in a highly consolidated seciirrient (froin <br /> � the weight of the ice) that possesses high strength, low compressibility and relatively low <br /> •� permeabiliry characterisdcs. <br /> � 4.4 Recent Alluvi �m nd Co11Lvi�m <br /> Recent alluvial and colluvial sediments were limited to the stream channels and steep ravine side <br /> I slopes. Alluvial sedimenu include the present-day stream channel system. Colluvial sedimenu <br /> form as the result of downslope movement of surficial soils by gravity. <br /> I4•5 Fill <br /> Fill �eposits (materials not ttaturally placed) were infened to exist along the sanitary sewer <br /> � easement that bisecu the parcel. Fill is also inferred to exist in the extreme southwestern cor�r <br /> of the property where improvemenu related to the n�site detendon facility for the East Fork of <br /> IPowder Mill Creek are located. <br /> , 5.0 HYDROGEOLOGY <br /> � <br /> 5.1 Surface Water <br /> 1 Surface water flow was observed in both drainages at the time of our field reconnaissance. The <br /> water in these draiaages was interpreted to be primarily from ground water sources. No surface <br /> ! water was noted on the upland portions of the site duriqg our field work. However, during rainy <br /> 1 periods it is likely that water will pond in localized riepressions on the upland surface. <br /> Iz.2 Ground Water ' <br /> I Based on the regional hydrogeologic setting and site-specific conditions, three dislinct ground <br /> water regimes aze interpreted to be present at the site. These include a shallow interIIow network <br /> developed in the soil horizon above the lodgement till, a shallow ground water zoa developed in <br /> Vashon advance sand and gravel, and a deeper regional aquifer developed in the undifferentiated <br /> foutwash deposits. <br /> I5.2.1 Interflow <br /> Interflow was not encountered in the explorarion pits at the time of our field study; however, <br /> I interflow is interpreted to form during ratny periods. Interflow develops where a relatively <br /> permeable layer of topsoil and/or weathered lodgement till or silt overlies a relaBvely impermeable <br /> unweathered substratum. Water that infiltrates the grouc►d surface cannot ieadily penetrau the <br /> � unweathered substratum and accumulates in the soil zone forming a very shallow "water table" <br /> perched atop the unweat�red parent material. Ground water within flvs surficial soil zo� moves <br /> � <br /> down stope, generally parallel to the land surface as interflow. Recharge to the intertlow is <br /> 5 <br /> � <br />