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April 11, 1996 Page 2 Site History A Unocal service station was operated on the property from approximately 1921 through 1965. The original Unocal service station included three 550-gallon underground fuel storage tanks, located in the northern portion of the site adjacent to Eleventh Street (Figure 1). Available information suggests that the two eastern-most tanks were used to store regular gasoline. The western-most tank apparently contained "ethyl' gasoline. At some point prior to 1950, the westernmost of the original fuel storage tanks had been replaced with a larger tank of 1,000-gallon capacity. A single product dispenser island with two dispensers was located between the station building and Eleventh Street. In approximately 1950, three new underground fuel storage tanks were installed in a common excavation in the west-central portion of the site. The underground fuel storage tanks in the northern portion of the site appear to have been left in place. These fuel tanks were of 2,600-gallon, 4,000-gallon, and 6,000-gallon capacities. A waste oil tank, of unknown capacity, was also installed adjacent to the southeast corner of the service station building. The original product island remained in service. A second product island with two dispensers'was also installed above the new storage tanks, in the western portion of the site. In approximately 1956, the original product island was upgraded, and fitted with two dual dispensers. The second product island, which had overlain the second generation of fuel storage tanks, was removed. The service station was closed and demolished in 1965. Previous Investigations In 1994, Environmental assessment activities were initiated by L.M. Swift and Associates (LMS), on behalf of Wells Fargo. Subsequent investigations have been performed by Enviros, Inc. (Enviros), PACIFIC, and MPDS Services, Inc. (MPDS), on behalf of Unocal. Field activities have included the drilling of fourteen exploratory soil borings, designated B-I through B-4, UB-1, U-A through U-H, and U-G*, aqd the installation of three groundwater monitoring wells, designated U-I through U-3 (Figure 1). Cumulative soil analytical data are presented in Tables 1 through 3. Groundwater elevation.and analytical data are presented within a quarterly data report prepared by MPDS (Attachment B). Additional field activities have been performed to determine whether any of the underground storage tank`s remain in place beneath the site. These activities have included a magnetometer survey, and three exploratory excavations, designated TP-I through TP-3. In combination with the exploratory borings drilled at the site, these 3100971B\TANKWP.DOC