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_ t �., <br />Geotechnical Engineering Investigation � <br />Schwab Residence <br />� July 13, 2001 <br />NGA File No. 329401 <br />Page 4 <br />Subsurface Conditions <br />We encountered between 1.5 and 2.8 feet of loose suficial filUtopsoil in all of our explorations. <br />The majority of the fill was encountered within the upper portion of the site near the road; <br />however, some filUslope wash was encountered on the slope. The fill was encountered to the <br />extent explored in Hand Auger 1. <br />Below the fill and topsoil, we encountered grayish-brown, silty ftne to coarse sand with gravel in <br />Test Pits 1 and 2, and Hand Auger 2. We interpreted this material to be part of the till cap located <br />along the top of the slope. The till was encountered to the extent explored in Test Pit 2 and Hand <br />Auger 2, and to a depth of five feet in Test Pit 1. Below the till in Test Pit 1 and the topsoil in <br />Hand Auger 3, we encountered medium der�se to dense sand with varying amounts of silt. This <br />material was interpreted to be advance outwash. <br />Hydrologic Conditions <br />Ground water seepage was not observed in the explorations or on the slope during our site visit, <br />however, a perched ground water condition may develop above the glacial till found within the <br />upper portion of the site. <br />Perched water occurs when surface water infiltrates through less dense, more permeable soils and <br />accumulates on top of the underlying, less permeable soils. The more pertneable soils, in this <br />case, consist of topsoil and fill. The less permeable soils consist of the underlying unweathered <br />till. Perched water does not represent a regional ground water "table" within the upper soil <br />horizons. Perched water tends to vary spatially and is dependent upon the amount of rainfall. We <br />would expect the amount of ground water to decrease during drier times of the year and increase <br />during wetter periods. Also, g*ound water seepage could be observed on the face of the steep <br />slope within the advance outwash sand deposits. <br />SENSITIVE AREA EVALUATION <br />Seismic Hazard <br />The project is located within Zone 3 of the Seismic Zone Map shown as Figure 16-2 of the 1997 <br />Uniform Building Code (UBC). This corresponds to a Seismic Zone Factor, Z, of 030. Since <br />medium dense to very dense glacial soils were encountered at the site, the site conditions best fit <br />NELSOlV GEOTECHN/CAL ASSOC/ATES, /NC. ��9 <br />