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Mr.Mahmoud Parvar �,, Page 2 r/ January 26,2000 Modesto Formation in this area is reported by Atwater (1982) to be composed of fluvial (river) �.. deposits of silt and sand, eolian(wind blown)deposits of loose sand,and compact silt and very fine sand(see Appendix Plate 11).' The site is located in UBC Seismic Zone 32 and there are no known faults that cross the site. The two closest active, potentially active, or capable faults to the site are the Great Valley Fault Zone, located 13 miles west-southwest and the Foothills Fault System, located 33 miles east- northeast.3 Due to the relative proximity of these faults to the site there is a reasonable possibility that the site will be subjected to a moderate amount of shaking from a seismic event during the life of the structure. The California Division of Mines and Geology assigns a probabilistic (10% probability of accedence in 50 years)peak horizontal ground acceleration for the Lathrop area near the subject site of 0.2 to 0.3g.' The ground water depth, elevation, and flow direction at the site can be determined from ground-water contour maps produced by the San Joaquin County Flood Control and Water Conservation District. The two most recent ground water depth and elevation contour maps indicate the levels for the fall 1997 and spring 1998 seasons. Table I summarizes all the available ground water information collected for the site. TABLE 1,SUMMARY OF GROUND WATER DEPTH INFORMATION Date,Source Groundwater Depth Notes August 8 and 8,1996,four deep soil borings excavated by Ground water encountered Total depth of borings is about 49 feet. Neil O.Anderson&Associates,Inc. in all 4 borings ranging in depth between 14.5 to 21.0 feet. Spring 1998,San Joaquin County Ground-Water Map. Less then 10 feet in depth. Gradient about 6 feet/mile just east of the site, Plates 12 and 13. direction of flow is generally northwest, slightly variable. Fall 1997, San Joaquin County Ground-Water Map. Between 10 to 20 feet in Gradient about 6 feet/mile just east of the site, Plates 14 and 15. depth. Probably closer to direction of flow is generally northwest, 10. 1 slightly variable. 1 Atwater, B.F., 1982, Geologic Maps of the Sacramento - San Joaquin Delta, California. USGS Miscellaneous File Report MF-1401. 2 Uniform Building Code, 1994 Edition,International Conference of Building Officials,Whittier,CA. 3 Jennings,C.W.,(1994),Fault Activity Map of California and Adjacent Areas with Locations and Ages of Recent Volcanic Eruptions,California Department of Mines and Geology,Sacramento,CA. ' California Division of Mines and Geology[CDMG], 1999,Seismic Shaking Hazard Maps of California, Map Sheet 48. **Aw �pE RS N 1 1 '• o � �srot�