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V Extended Investigation of Groundwater Quality - 152 East 1 lth Street, Tracy Page 3 Directly north of the subject property (i a 152 East 11th Street), and across 11th Street, there is a Beacon station located at 153 East l lth Street The station is owned by Ultramar Inc of Hanford, California In connection with investigations of a release of hydrocarbon fuels at the Beacon station, a total of nine ground water monitoring wells have been installed on and around that property The locations of these wells are also shown on Figure 2 where they are designated as ULT 1 through ULT 9 The Ultramar monitoring wells were installed subsequent to installation of new tanks at the Beacon Station in October 1986 Components of fuel hydrocarbons were detected in the pit excavated to accomplish the tank replacement project and the pit was over-excavated to remove approximately 1,155 tons of affected sod which was disposed off-site at a permitted facility Some 52,000 gallons of affected groundwater was pumped from the excavation and similarly disposed by shipment off-site for treatment at a permitted facility The over-excavated pit, which was backfilled with clean material, had plan dimensions of 42f1 by 40ft and was 15ft deep Its location is indicated on Figure 2 GEOLOGY AND HYDROGEOLOGY The subject property and the surrounding area are situated on level terrain on the distal, northern slope of an alluvial fan The underlaying all vW sediments are of Quaternary to Recent age Logs of the monitoring well boreing indicate that the soils beneath the site includes clays, silty clays, sandy clays, clays with gravel, sands, silty sands and sands with gravel These clastic materials are distributed in a complex lenticular structure Areas beneath the streets adjacent to the property have been extensively excavated and backfilled for installation of sewers and other utilities The depth to groundwater is in the range 7 to 9ft and vanes seasonally The general direction of the groundwater gradient is northwest across the 152 East 11th Street property but may vary seasonally The slope of the groundwater gradient is typically about 0 003 ft/f} INSTALLATION OF ADDITIONAL MONITORING WELLS On February 26th 1993, on behalf of the Navarras, The San Joaquin Company submitted a W—o-ftlan firYpr1her Sod And Cagundwater Califoima to the SJCPHS The workplan called for installation of four additional groundwater wells to further asses the extent to which sod and groundwater has been affected by the release of gasoline from the tanks formerly located on the property The workplan was approved by the SJCPHS Encroachment Permit No 93 150 was obtained from the City of Tracy to permit installation of three of the new wells in the sidewalks of East 11th Street Permit No 93-1177 for construction of the wells was issued by the SJCPHS