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January 9, 1992 � Z Unocal Station No 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 hydrocarbons remained in the soil Results of water 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, February 19, 1991, Report No 38032-3) PRESENT GROUND-WATER SAMPLING On September 30, 1991 and November 14, 1991, we visited the site to attempt to conduct quarterly monitoring of ground water at the site However, water was not present in the five monitoring wells (MW-1 through MW-5), probably due to the seasonal fluctuations and the lower than normal precipitation 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 ground water at the site, and a vapor-extraction test The work plan was submitted to San Joaquin County Public Health Services, Environmental Health Division, 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 January 1992, and will purge and sample the wells if possible I I 40 31104rsis 38032-b-6 2