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� _ 'r/A.LSA■ { WEISS ASSOCIATES I I() ■ Richard O. Norona 2 May 16, 1989 TASK 1 - DETERMINE DEPTH-TO-WATER According to California Regional Water Quality Control Board (CWQCB) guidance documents, one or the criteria for determining soil clean up levels is the distance between the lower-most contaminated soil samples and the historic high ground water elevation. Since no ground water monitoring wells arc on the DWG site, the depth to ground water at the site is not precisely known. However, four municipal supply wells are located on the perimeter of the property (Figure 1). Since the depth to water in the municipal wells may approximate the ground water depth beneath the site, we will determine the depth to water and the construction characteristics of these wells. To indicate the historic high ground water level in the site vicinity, we will also research available historic ground water level fluctuation data in the municipal wells and in other nearby wells. In addition, as part of Task 2, one of the vertical borings from Tank 8 will be drilled forty to fifty ft below the deepest contaminated soil samples, to a total depth of eighty ft or to ground water, whichever is shallowest. Subsurface materials will be described from soil samples collected from the boring. If ground water is encountered in the boring, the measured depth to ground water will be compared to the ground water depths in the municipal wells to determine whether the water depths in the municipal wells accurately approximate the ground water depths in the vicinity of the tanks. TASK 2 - SOIL BORING AND CHEMICAL ANALYSIS To further define the vertical extent of chemicals found beneath Tanks 1, 6 and 8, we will drill one angled soil boring beneath each tank. Proposed borings and soil samples arc approximately located on Figures 2.a. through 2.17. The precise location of the borings will be based on the locations of the tanks with respect to underground utilities and other structures. The precise sample depths will be based on field observations and measurements, and portable photoionization detector (PID) readings. Soil samples collected from the borings will be analyzed for the chemicals formerly and presently contained in the tanks to indicate the vertical extent of the released chemicals.