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1 ' 1444 MARIPOSA ROAD . WKA No 2307 02 December 4, 1992 ' Page 2 ' building An empty shed is located approximately 40 feet south of the vacant building and an Enactive well is located immediately south of the shed. Maintenance records for the well indicate that the total depth of the well is 191 feet, the last water level measurement was taken in 1990 when the depth to ' water was approximately 73 feet below site grade The remainder of the site is an asphalt-paved parking lot formerly used for customer parking and equipment storage ' The subject site and surrounding areas are relatively flat, surface elevation on site is approximately 26 feet above sea level Charter Way bounds the site to the north, beyond which is commercial ' development, and a vacant lot bounds the property to the east Learned Avenue bounds the property to the south, beyond which is residential development, and Mariposa Road bounds the property to the west, beyond which is commercial development PHYSIOGRAPHIC AND HYDROGEOLOGIC SETTING The site is located in the central portion of the Great Valley geomorphic province of California The I ' Great Valley is bounded by the mountains and foothills of the Sierra Nevada Range to the east and the California Coast Ranges to the west The geologic formations of the Great Valley are typified by thick sequences of alluvial sediments deposited during the filling of a large ancient basin Alternating layers ' of silty clay and clayey silt ranging from one to five feet in thickness were observed in the tank excavation during overexcavation operations ' The site lies within the San Joaquin River Ground Water Basin (California Department of Water Resources, 1986) Ground water was encountered at a depth of approximately 73 feet below grade during the last pump maintenance event in 1990 ' PREVIOUS WORK BY WKA On October 29 and September 2 and 9, 1992, our firm observed the excavation of a total of ' approximately 1500 cubic yards of soil from the vicinity of the former underground storage tanks Eleven sort samples were obtained from the sidewalls and bottom of the excavation, sample locations ' and depths are shown on Plate 2 Laboratory test results for the sidewall samples, EX4-22' through EX10-22', revealed non-detectable concentrations of Total Petroleum Hydrocarbons (TPH)`as gasoline, diesel, and motor oil and non-detectable concentrations of Benzene, Toluene, Ethylbenzene, and Total Xylenes (BTEX). Results for the bottom samples, EX1-30', EX2-30', and EX3-27', revealed TPH as • gasoline concentrations ranging from non-detectable concentrations to 25,000 mg/kg (diesel and motor oil range hydrocarbons were not detected in the samples), benzene concentrations ranging from 0 046 o `�W Recycled paper Er ASSOCIATES INC