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HYORDQWLOGIC ASSESSMENT RESULTS AND QUARTERLY GROUNDWATER MMM)FING REPORT 4445 Pershing Avenue Stockton Calsfornla Aegis has collected quarterly groundwater samples since the wells were installed in July 1990 Depth-to-groundwater measurements were collected by Aegis on a monthly basis from July 1990 through July 1991 Subsequent depth-to-groundwater measurements are collected on a quarterly basis coincident with analytical sampling Prior sampling events were conducted in October 1990 and January, April, July, and October 1991 In January 1992, Emcon was retained by Shell to collect measurements of depths to and groundwater samples from the four wells on site The data, including the laboratory analytical reports, were then provided to Aegis for inclusion in this report (Appendices B and C) 2.3 Adjacent Land Uses Several businesses surround the site To the north, across Rose Marie Lane, are Jamco, 7-Eleven, and a veterinary hospital West of the site is a coin operated car wash, to the south is a beauty college, and on the northeast corner of the intersection are several light commercial businesses A vacant lot to the east, across Pershing Avenue, is the location of an abandoned Exxon Company, U S A , service station 2.4 Generalized Geology and H dro eolo The site lies within the northern section of the San Joaquin Valley, within the southern portion of the Great Valley Province The San Joaquin Valley is a structural trough extending south from the Sacramento-San Joaquin Delta to the Tehachapi Mountains The San Joaquin Valley is bounded by the Sierra Nevada to the east and the Coast ' Ranges to the west Cretaceous sandstones and shales overlie pre-Cretaceous, ultra-basic igneous rocks, granitic rocks, and metamorphosed sedimentary and volcanic rocks Sediments originating from the Sierra Nevada and the Coast Ranges were deposited in a marine ' environment during the Cretaceous to the Tertiary Interruptions in the pre-Pleistocene sedimentary depositional cycle occurred several times as the volcanic activity, uplift, faulting and/or folding altered the region (DWR 1967) On the basis of monthly depth-to-groundwater measurements from July 1990 through July 1991 and quarterly depth-to-groundwater measurements from August 1991 through 1 January 1992, the estimated depth to groundwater and direction of flow is approximately 30 feet below surface and to the northeast, respectively 89-016A QMR 3