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July 2, 2012 <br /> Job No. 1806.101A <br /> Page 2 <br /> SUBSURFACE CONDITIONS <br /> We excavated eleven test pits (TP-1 to TP-11) up to 9 feet deep on September 16, 2010 and <br /> October 13, 2011 to explore the subsurface conditions at the locations shown on Plate 2, Site <br /> Plan. Soils encountered were generally silty to sandy clays and clayey silts overlying the <br /> Livermore Gravels formation. Siltstone was encountered in TP-9 at a depth of 4 feet below <br /> existing ground surface and was highly weathered, friable, and moderately to highly fractured. <br /> The test pit logs are contained on Plates 3 and 4. <br /> GROUNDWATER <br /> Groundwater was not encountered in the test pits. <br /> GEOLOGIC HAZARDS <br /> LANDSLIDES <br /> Mapped landslides at the site were not found in the geologic literature in our files and we did not <br /> find evidence of landslides during our field exploration. <br /> EARTHQUAKES <br /> The site is not located within a designated State of California Earthquake Fault Zone for active <br /> faults . We did not observe signs of active faults during our field exploration Hence, the <br /> potential for surface fault rupture'at the site is low. The subject site is located at approximately <br /> 37.6623 degrees north latitude and 121.8369 degrees west longitude. The peak ground <br /> acceleration (PGA) with a 10% chance of exceedance in 50 years (475 year return period) is <br /> 0.53g according to the United States Geologic Survey (USGS) Deaggregation website with an <br /> assumed shear wave velocity of 270 m/s. <br /> LIQUEFACTION AND DYNAMIC COMPACTION <br /> Liquefaction is the temporary transformation of saturated, loose cohesionless soils into a viscous <br /> liquid during strong ground shaking from a major earthquake. The site is underlain by silty to <br /> sandy clays and clayey silts which are underlain by the Livermore Gravel formation. Therefore, <br /> the risk of liquefaction at the site is believed to be low. Dynamic compaction is the densification <br /> of dry, loose sandy soil above the water table. Loose, relatively clean sandy soil was not <br /> encountered in the test pits,hence, the potential for dynamic compaction is considered to be low. <br /> CONCLUSIONS AND RECOMMENDATIONS <br /> GENERAL <br /> From a geotechnical engineering standpoint, the proposed home sites appear to be feasible at the <br /> site, provided the conclusions and recommendations contained in this report are followed as <br /> project planning advances. <br /> BERLOGAR STEVENS&ASSOCIATES <br />