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L U L ' (bgs); Pliocene-Pleistocene age Laguna Formation extending from 100 feet to approximately 1000 feet bgs; and the Oligocene age Mehrten Formation extending from approximately 1000 feet to 1600 feet bgs. The alluvium consists of interbedded lenses and layers of sand, gravel, silt,and clay. The ModestoNictor Formation contain discontinuous units of sand and gravel with local clay layers particularly within the Manteca City area. The Laguna Formation contains similar lithologic units as the ModestoNictor Formations which includes lenses and layers of gravel, sand, and clay. The Mehrten Formation consists of andesitic sand and sandstone (CDWR, 1967). Adjacent property soils were observed in a planter located between the subject site and the Dairy Queen Restaurant! The sur6ciai soils consisted of silty sand and sand. Soils encountered onsite during drilling included sandy 611 in the upper 3-5 feet; and alternating silts,clays and sands below this depth(see boring logs,Appendix B). i3 The closest active faults include the Vernelis Fault located approximately 7 miles to the southwest,the March Creek-Greenville Fault Zone is located approximately 30 miles to the southwest, and the Las Positas Fault located approximately 35 miles to the west, the Hayward Fault located approximately 54 miles to the southwest-west, and the San Andreas Fault Zone located 74 miles to the southwest (CDMG, 1994). 2.4 GROUNDWATER CONDITIONS The subject property is located within the San Joaquin Basin Hydrologic Study Area,Eastern San Joaquin County Groundwater Basin (CDWR, 1980). The Eastern San Joaquin County Groundwater Basin has for many years experienced an overdraft condition, causing saline water from the Delta area to migrate eastward, thereby significantly impacting the basin's groundwater quality. The Stockton area located to the na'rth of the subject site, has been the location of extensive groundwater pumping, and thereby having undergone considerable land subsidence. In addition, the regional groundwater flow direction to the west towards the San Joaquin River, has been influenced by the pumping in the Stockton area,which has redirected the Manteca area's regional flow direction to the northwest. �i t Depth to first encountered groundwater is approximately 2S feet bgs with a northwest flow . direction beneath the subject property (Manteca City Water Department, August 1996, personal communications). Historic water levels beneath the subject property are 8 feet bgs in the fall of 1950 and 11 feet bgs in the fall of 1964 based on groundwater elevation contour maps (CDWR, 1967). The depth of the well screen intervals used to in the CDWR contour maps is not known, therefore the contour elevations may represent accumulative piezometric heads from more than one aquifer. The first encountered groundwater is unconfined as perched water, located within the alluvial deposits. Groundwater wells within the Manteca area are screen below 100 feet bgs,obtaining water from the Victor and Laguna Formations. Local groundwater is used for municipal,agricultural,and industrial purposed. Five Manteca City Water Department groundwater wells, one up/cross gradient and four downgradient from the site, are located within a one mile radius of the site. These wells have been found to contain slightly elevated concentrations levels of a component of a pesticide(DBCP), and solvents (PCE)and Dichloroethane (1,2-DCA). The one uplcrossgradient well contained 0.2 L IN 40907-097-01 dec-96\arcm[eu.eca 2-2 s a