3321 52ND PL SW 2016-01-01 MF Import

-� C C � ' Geotechnical Engineering Investigation � Schwab Residence — July 13,20b1 NGA File No. 329401 Page 3 Geology Most of the Puget Sound region was affected by past intrusion of continental glaciation. The last period of glaciation, the Vashon Stade, ended approximately 10,000 to 1 I,000 years ago. Many of the geomorphic features seen today are a result of scouring and overriding by glacial ice. During the Vashon Stade, the Puget Sound region was overridden by over 3,000 feet of ice. Soil layers overridden by the ice sheet were compacted to a much greater extent than those that were not. A typical glacial sequence includes recessional ouhvash sand, overlying glacial till or drift, underlain by advance outwash. The geologic units for this area are shown on Distribution and Description of Geolog�Units in the Mukilteo Ouadrangle. Washin on, by James P. Minard (U.S.G.S., 1982). The site is mapped as glacial till (Qvt) and advance outwash sands (Qva). Glacial till is described as a dense to very dense, unsorted mixture of silt, sand, and gravel. The advance ouhvash sands consists of relatively clean sand with varying amounts of gravel. Our explorations encountered the glacial till and advance ouhvash deposits. Explorations The subsurface conditions within the site were explored on June 29, 2001 by excavating two test pits and three hand-augered holes. 'I'he test pits were excavated within th� planned residence footprint to depths of approximately 7 to 8 feet below the existing surface, while the hand- augered holes were exca�•ated on the face of the slope. The approximate locations of the explorations are shown on the Site Plan in Figure 2. A geologist from Nelson Geotechnical Associates, Inc., (NGA) was present during the explorations, examined _he soils and geologic conditions encountered, obtained samples of the different soil types, and maintained logs of the test pits. The soils were visually classified in general accordance with the Unified Soil Classification System, presented in Figure 4. The test pit and hand-augered hole logs are attached to this report and are presented as Figures 5 and 6. We present a brief summary of the subsurface conditions in the followin; section. For a detailed description of the subsurface conditions, the logs should be reviewed. NELSON GEOTECHN/CAL ASSOC/ATES, /NC. -s�q