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Mr.Harlin Knoll, SJCEHD April 7,2006 Work Plan for Confirmation Soil Borings Project No. 2007-0065-01 USA Station No. 65, Lodi,California Page 3 Stratus oversaw the construction and installation of a Soil Vapor Extraction System (SVES) in July and August 2000. Simultaneous air sparging was completed in conjunction with vapor extraction. Since the start-up in August 2000, the SVES has removed and abated approximately 4,138 pounds of total petroleum hydrocarbons as gasoline (TPHG). Influent soil vapor concentrations to the SVES are currently below laboratory detection limits. Depth to groundwater beneath the site has fluctuated between approximately 35 and 54 feet below ground surface (bgs) since monitoring was initiated in October 1987. Groundwater elevations have decreased approximately 7 feet since 2000 (approximately 39 to 46 feet bgs), concurrently with operation of the SVES. The groundwater flow direction has consistently been calculated to be towards the south-southeast at low gradients (0.001 to 0.015 ft/ft). At the time of the most recent groundwater sampling event (first quarter 2006), petroleum hydrocarbon and fuel additive concentrations in each well sample were reported below laboratory detection limits. PROJECT APPROACH Historical soil analytical data are summarized on Figure 3 and Figure 4. The available soil analytical data indicate that the highest concentrations of petroleum hydrocarbons in soil were reported beneath, and immediately surrounding, the UST cavity. Petroleum hydrocarbons were also detected beneath the fuel dispenser islands. Concentrations of petroleum hydrocarbons beneath the northern fuel dispenser islands (closest to the UST complex) are generally higher than the concentrations near the southern fuel pump area. Boring CB-1 will be advanced adjacent to the northeastern portion of the UST complex, where TPHG and benzene were reported at maximum concentrations of 7,200 milligrams per kilogram (mg/Kg) and 6.1 mg/Kg, respectively (samples 1-EXC and 14-EXC). Boring CB-2 will be completed near the southeastern portion of the UST pit and north of the fuel dispenser islands, near previously identified petroleum hydrocarbon impact. Boring CB-3 will be advanced west of the UST complex, approximately 10 feet from well boring VW-1. TPHG was reported at concentrations ranging from 620 mg/Kg to 990 mg/Kg at boring VW-1 between approximately 25 and 35 feet bgs. Completion of soil borings at these locations should enable an adequate evaluation of current petroleum hydrocarbon concentrations in soil. The borings will be advanced, using hollow stem augers, to approximately 55 feet bgs, near the lowest historical depth to groundwater level and approximately 9 feet below the current water table interface. In the March 29, 2006 letter, SJCEHD requested downgradient groundwater confirmation sampling near the area where dissolved petroleum hydrocarbons have recently been reported in groundwater (near well MW-3). Stratus will advance borings CPT-1 and KAUSA Gasoline100651Workplanslusa65-boring-cpt-workplan.doc 5TRATU5