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MOUNTAIN HOUSE NEIGHBORHOODS KAND L INITIAL STUDY 5.ENVIRONMENTAL CHECKLIST 6, GEOLOGY AND SOILS s Table 5.6-1 ACTIVE AND POTENTIALLY ACTIVE FAULTS IN THE VICINITY OF THE SPECIFIC PLAN II AREA Estimated Estimated Maximum Peak i Distance to Earthquake Horizontal Project Area (Moment Acceleration Fault Status (Miles) Magnitude)' (%g)b Great Valley Thrust Active 4 6.7 0.59 (Segment 7) Greenville Potentially Active 8 6.6 0.27 Concord-Green Valley Active 25 6.2 0.12 Calaveras Potentially Active 21 6.8 0.13 Hayward Active 26 6.4 0.13 San Andreas Active 46 7.9 0.13 ~ a The moment magnitude is related to the physical size of fault rupture,the movement across the fault,and the strength of the rock that is faulted.Earthquakes with magnitudes of 6 or greater are capable of causing widespread damage. b Peak horizontal acceleration is defined as the speed at which the ground moves with respect to the force of gravity(g). An upward vertical ground acceleration of 1.0 g would throw loose objects into the air. 1 Source: Condor,2002. F1 Site Soils Linder the San Joaquin County Development Title and Chapter 4 Article 7 of the California Subdivision Act,the project applicant is required to prepare preliminary soils reports(i.e., geotechnical studies) prior to the submittal of each Tentative Subdivision Map area within the Mountain House community. Geotechnical engineering studies were conducted in March 2007 for Neighborhood K and in _y September 2010 for Neighborhood L and included subsurface explorations and laboratory soil testing(Engeo,2007b and 2010).The purpose of the completed } studies was to characterize geotechnical conditions that might affect design or L construction of proposed development and to provide geotechnical recommendations and design criteria to mitigate any identified impacts. A separate geotechnical study was completed for the potential fire house location I r within Neighborhood K(Engeo,2007a). Subsurface explorations were conducted throughout Neighborhoods K and L to depths ranging to 26.5 feet below the ground surface (bgs).The explorations indicate that the neighborhoods are underlain by medium stiff to hard silty clay F and sandy clay with occasional thin layers of soft silty clay and medium dense to dense silty and clayey sand to a depth of 26.5 feet. Soil Expansion l Soil expansion is a phenomenon in which clayey soils expand in volume as a N result of an increase in moisture content,and shrink in volume upon drying. Changes in soil volume as a result of changes in moisture content can cause F;I (snr„) 5-75 a