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June 30, 1992 Unocal Station No 6981, Stockton, California 1.3 Observe drilling of one 12-inch-diameter soil boring onsite to approximately 75 feet below surface grade and construction of a 6-inch-diameter pumping- test well the boring The proposed location of the boring is shown ojV 1.4 Develop the four monitoring wells and one pumping-test well 15 Analyze soil samples from the borings, as necessary, for TPHg using EPA Method 8015 with EPA extraction Method 5030 and for BTEX using EPA Method 8020 in a laboratory certified by the State of California. 16 Contract with a licensed surveyor to survey the four monitoring wells and pumping-test well with respect to mean sea level. This data will be used to evaluate the ground-water flow direction and gradient beneath the site TASK-2; Evaluation of Aquifer Characteristics 21 Perform a step-drawdown pumping test to evaluate a pumping rate and well efficiency for the 24-hour pumping test Conduct a 24-hour pumping test with 6-hour recovery at the site using the 6-inch-diameter well as the pumping well Collect three water samples from the pumping test well for laboratory analyses 22 Submit three water samples from the pumping test well for analyses for TPHg using EPA Method 8015 with EPA extraction Method 5030 and for BTEX using EPA Method 602. In addition, three water samples will be analyzed for total dissolved solids, common ions and cations, alkalinity, and bacteria. 23 Interpret pumping-test data and other hydrogeological data to evaluate the transmissivity and storativnty of the water-table aquifer, and estimate the theoretical capture radius and long-term pumping rate. We will discuss our interpretation of the data with Unocal and make recommendations TASK 3: Preparation of Problem Assessment Report 3.1 Prepare a PAR after the lateral extent of residual gasoline hydrocarbons in ground water has been delineated The PAR will include the results of the pumping test. W32- 3so3z-il 7 6