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• The groundwater in the vicinity of the site is unconfined Groundwater flow direction at the site has generally been to the east, varying from due north through south, but never within the northwestern or southwestern quadrants Groundwater elevation at the site has ranged from a current high of 25 feet bgs to a minimum of 72 to 77 feet bgs The gradient has ranged from 0 003 to 0 03 feet/linear feet SITE HISTORY The property previously contained one 500 gallon gasoline Underground Storage Tank (UST), that was used to store leaded and unleaded gasoline from the late 1950's or early 1960's through 1987 (Figure 3) The UST, product dispenser, and associated underground piping were removed from the site in 1987 Three groundwater-monitoring wells (MW1-MW3) were installed at the site in July 1995 Soil samples collected from the three monitor well boreholes showed concentrations of TPH-G and BTEX above laboratory detection limits beginning at approximately 20 feet bgs and extending to the last point sampled (35 5 feet bgs) in each of the three boreholes The highest TPH-G and BTEX concentrations were found between 25and 32 feet bgs The TPH-G and BTEX concentrations found in the deepest samples collected were at orjust above the laboratory detection limits • Groundwater samples have been collected from the three monitor wells on a quarterly basis since their installation in July 1995 All three monitor wells have shown concentrations of TPH-G ranging from a maximum of 24 mg/l of TPH-G at MW1 to a minimum of 1 8 mg/1 at MW3 Benzene concentrations have ranged from a maximum of 8700 ug/l at MW1 to less than the laboratory detection limits at MW2 MTBE concentrations have ranged from a maximum of 110 ug/l at MW 1 to less than the laboratory detection limits at MW1 and MW2 Concentrations of the remaining four fuel oxygenants have been less than laboratory detection limits at all three wells with the exception of TAME which has shown a maximum concentration of 28 ug/1 at MW2 At the request of the SJCEHD, WEGE reviewed current and historical water well records maintained by the California Division of Water Resources, the San Joaquin County Flood Control District, the City of Stockton, and California Water Services in order to locate potential sensitive receptors in the site vicinity and to determine the historically lowest groundwater elevation at the site between 1965 and the present Groundwater elevation at the site has ranged from a current high of 25 feet bgs to a minimum of 72 to 77 feet bgs during the historical low period of September 15 through October 15 1977 The groundwater flow direction for this period was to the northeast at a gradient of approximately 0 006 feet/linear foot This information was presented in WEGE's October-December 1998 Quarterly Groundwater Monitoring Report dated March 26, 1999 • 2 ARC PUMP -WKPLN- 9/28/99