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MOUNTAIN HOUSE NEIGHBORHOOD'T'PROJECT INITIAL STUDY I. GEOLOGY AND SOILS The project site is located within the Great Valley Geomorphic Province of Central California and is underlain by non-marine sediments. The majority of near-surface sediments consists of silt and clay. Groundwater has been encountered at depths varying from 5 to 16 feet below the ground surface. The entire area of the Mountain House New Community slopes at about one percent to the northeast from an elevation of 165 feet at Interstate 205 to near sea level near Old River at the north. This project site is in the center of the New Community on fairly level terrain. A Geotechnical Engineering Study for Neighborhood"F"was completed by the applicant in January 1999 (Condor Earth Technologies, Inc.). This study addressed site conditions(including subsurface soils and groundwater conditions), seismic considerations, grading and earthwork, foundations, retaining walls, pavements, and site drainage. Many of the recommendations identified in the Geotechnical Engineering Study would mitigate potential impacts created by the project. These recommendations would be conditions for the project, enforced by the County Building Department. An additional report, entitled Mountain House Farm Irrigation Drainage Report for Neighborhood F (Condor Earth Technologies, Inc., 2000), addressed the need to remove subsurface drains currently present at the site to accommodate new development. A Geotechnical Report was also completed for the Bethany Elementary School (Condor Earth Technologies, Inc., 1997)and this was reviewed for preparation of this Initial Study. As per the recommendation in the Master Plan EIR, the County's 1998 Plan for Community Engineering Planning and Preparedness Development addresses earthquake preparedness. Environmental Checklist Potentially Significant Potentia0v Unless Less Than Significant Mitigation Significant No Impact Incorporated Impact Impact GEOLOGY AND SOILS. Would the project.- a) roject:a) Expose people or structures to potential substantial adverse effects,including the risk of loss, injury, or death involving: i) Rupture of a known earthquake fault, as delineated on the 71 O 71 0 most recent Alquist-Priolo Earthquake Fault Zoning Map issued by the State Geologist for the area or based on other substantial evidence of a known fault? Refer to Division of Mines and Geology Special Publication 42. ii) Strong seismic ground shaking? E iii) Seismic-related ground failure,including liquefaction? 0 71 iv) Landslides? 71 0 b) Result in substantial soil erosion or the loss of topsoil? 0 O C:UOBSMO M77AL 9NDYJPMAL1NMAL9I1UDY-PARn.D0C(720/00) 87 V.I. GEOLOGY AND SOILS