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File: 218267 November 30, 2018 CONCLUSIONS AND RECOMMENDATIONS General Based upon our investigation, we believe that the proposed improvements can be safely constructed. Geotechnical development of the site is controlled by the presence of expansive soils. Expansive soils derive their name from their propensity to change volume in response to changes in moisture content. When they are dry,they shrink; when they become wet,they swell. The pressures these soils can exert as they expand can be sufficiently high to move conventional residential foundations. The foundation movement induced by the soil shifting can cause wall coverings to crack, doors and windows to stick, and floors to slope, pools to crack and tilt. Seasonal movements of expansive soils have caused such distress to countless pools and houses in the Bay Area. To combat seasonal expansive soil movements, it is necessary to utilize a foundation system which derives its support from the deeper, more stable soils. Typically, a drilled, cast-in-place pier foundation system is used to reach the more stable materials. Therefore, we have recommended that such foundation system be utilized at this site for the at-grade foundations,while the deeper basement may have a mat slab foundation. The recommendations in this report should be incorporated into the design and construction of the proposed new residence and associated improvements. Seismicity The greater San Francisco Bay Area is recognized by Geologists and Seismologists as one of the most active seismic regions in the United States. Several major fault zones pass through the Bay Area in a northwest direction which have produced approximately 12 earthquakes per century strong enough to cause structural damage. The faults causing such earthquakes are part of the San Andreas Fault System, a major rift in the earth's crust that extends for at least 700 miles along western California. The San Andreas Fault System includes the San Andreas, San Gregorio, Hayward, Calaveras Fault Zones, and other faults. During 1990,the U.S. Geological Survey cited a 67 percent probability that an earthquake of Richter magnitude 7, similar to the 1989 Loma Prieta Earthquake, would occur on one of the active faults in the San Francisco Bay Region in the following 30 years. Recently, this probability was increased to 70 percent, as a result of studies in the vicinity of the Hayward Fault. A 23 percent probability is still attributed specifically to the potential for a magnitude 7 earthquake to occur along the San Andreas Fault by the year 2020. Ground Rupture-The lack of mapped active fault traces through the site, suggests that the potential for primary rupture due to fault offset on the property is low. S