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. ALISTO ENGINEERING GROUP 4/0 RJ\J� February 21, 1995 Mr. Scott Hooton BP Oil Company JUS Environmental Resources Management 1995 295 S.W. 41st Street �1vVj Building 13, Suite N ��5 HyCl H - -t�4401 Renton, Washington 98055 Subject: Baildown Test Results BP Oil Company Service Station No. 11193 3202 West Hammer Lane Stockton, California Dear Mr. Hooton: In accordance with BP Oil Company Contract Release No. G489719, Alisto Engineering Group performed baildown testing at BP Oil Company Service Station No. 11193, 3202 West Hammer Lane, Stockton, California on February 16, 1995. The testing involved extracting groundwater using a submersible pump until a portion of the available drawdown in the well was depleted. Pumping was discontinued and the drawdown of the water column in the wells was then allowed to recover to a minimum of 90 percent of the initial water column. Recovery of drawdown in the wells was recorded using pressure-sensitive transducers and a data logger. The test data were then used in an analytical computer program (Agtesoly, Geraghty and Miller, 1991) to estimate the hydraulic conductivity (K) of the shallow water-bearing zone using techniques developed by Bower-Rice (1976). The estimates of hydrogeologic properties are summarized in Table 1. The transmissivity (T) was calculated using the equation T=Kb, where b is the saturated thickness of the water-bearing zone. For purposes of this calculation, the measured water column in each well was assumed to be the saturated thickness of the water-bearing zone. The graphical analysis for each well from the baildown test is included for reference. Based on review of the boring logs, the predominant soil types of the water-bearing zone are silt and silty sand underlain by fine to medium sand, which generally have K values ranging from approximately 1 to 1 x 105 cm/s (Freeze and Cherry, 1979). The values of the aquifer parameters calculated from the baildown tests are comparable and consistent with the characteristics of subsurface soils encountered at the site. The submersible pump was only capable of drawing down 1.5 feet of groundwater in MW-1 at a maximum pumping rate of 6 gallons per iinute. The rapid recovery is consistent with. the silty sand and sand encountered in the well's water-bearing zone. 1777 OAKLAND BOULEVARD, SUITE 200 •WALNUT CREEK. CA 94596 • (510) 295=1650 • FAX (510) 295-1823 CONTRACTORS LICENSE NO. A-652544