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d Frontier Transportation B23502.01A January 2, 1996 Page 3 First encountered groundwater in the site vicinity occurs under unconfined (water table) conditions. According to the San Joaquin County Flood Control District (SJCFCD), the expected seasonal high groundwater in the vicinity of the site corresponds to a depth of approximately 20 feet below site grade (BSG) (SJCFCD, 1988). Local groundwater elevation and flow direction may be influenced by pumping of water wells and recharge from various sources. The effect of these influences on groundwater beneath the site is beyond the scope of this investigation. 3.3 Project History: On. July 21, 1995 three gasoline and three diesel USTs were removed from the project site. Twining personnel were present during the removal of the gasoline USTs; however, the diesel USTs had been removed prior to the arrival of the Twining technician. The contents of the tanks and tank capacity are summarized in Table _ 1. TABLE 1 UNDERGROUND STORAGE <TANK (UST) CONTENTS AND CAPACITY UST UST Contents Diameter LengthVolume Depth s Dumber (1)_ feet feet gallons (2) . .fee'f (3) 39-2257-01 Gasoline 4 15 15413 6 39-2257-02 Gasoline 4 7 659 6 39-2257-03 Gasoline 4 7 659 6 39-2257-04 Diesel - Unknown Unknown 12,000 10 39-2257-05 Diesel Unknown Unknown 12,000 10 39-2257-06 Diesel Unknown Unknown 12,000 10 USP = Underground Storage Tank (1) = SJCPHS tank identification number as stated in November 7, 1995 correspondence (2) = Approximate (3) = Depth of bottom of tank below site grade Note = Diesel USP data based on information provided by K.S. Dunbar and Associates personnel Following tank removal, four soil samples were collected from approximately 3 feet below the bottom of the gasoline USTs (S- 1-W, S4-E, S2, and S3) and twelve soil samples were collected from approximately 3 feet below the bottom of the diesel USTs (T44 through T4- 4, T54 through T5-4, and T6- 1 through T6-4). The samples were submitted to the laboratory for chemical analyses of selected PPCs. Soil sample analytical results are summarized in Table 2. Drawing 3 illustrates the locations of the former USTs, the associated piping, and the soil sample locations.