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'iWXMM '�_"B �ro September 16, 1991 Unocal Service Station 6981, Stockton, California During January and February 1990,five soil borings and five monitoring wells were installed at the site. The locations of the monitoring wells are shown on the Generalized Site Plan (Plate 2). Analytical results of soil samples indicated detectable concentrations of P, hydrocarbons remained in the soil. Results of water sample analyses indicated detectable concentrations of dissolved hydrocarbons,nitrate,and total and fecal coliform bacteria were in the ground water beneath the site. We recommended initiating a quarterly monitoring program, performing additional work to assess hydrocarbons in the soil, and conducting a vapor-extraction test to evaluate the feasibility of remediating the soil and water-bearing zone beneath the site (Applied GeoSystems, in progress, Report No. 38032-3). Present Quarterly Monitoring On July 18, 1991, we visited the site to attempt to conduct quarterly monitoring of ground water at the site. However, water was not present in four of the monitoring to through MW-4) and less than 1/3 foot in the fifth well (well MW-5), probably seasonal fluctuations and the lower than normal precipitation. We evaluated that there was insufficient water in the one well to collect a sample for chemical analyses. Results of subjective and laboratory analyses of ground water from previous work are summarized in Tables 1 through 3. Work In Progress At Unocal°s request, Applied GeoSystems has prepared a work plan for additional evaluation of soil and growid water at the site,and a vapor-extraction test. The work plan was submitted to SJCPHS on September 16, 1991. We recommend continued site visits on a quarterly schedule and monitoring of the ground water, if possible. We have scheduled the next site visit for the week of October 15, 1991, and will purge and sample the wells if possible. 5 0724rsis 38032-6 i'