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4 t ` Ms Mary Meays Page 3 < March 2, 3994 nature of the ground water was confirmed after construction and S development of monitoring wells at both sites indicated that stabilized water levels tended to be higher than initial water levels In general, the ground water potentiometric surface at the site is at a depth of approximately 4 to b feet bgs Potentiometric surface maps prepared individually for Sites 1 and 2 have consistently shown ground water flow directions to be toward the south- southwest The predominant flow direction appears to be away from the Stockton Deep Water Channel, which lies immediately north of the property line Tidally induced water level fluctuations in the channel appear to be the cause of slight-to-moderate variations in the ground water flow gradient Ground water wells are a common source of potable water in the Great Valley geomorphic province However, no water supply wells are located within a 2,000-foot radius of the West Weber sites PREVIOUS INVESTIGATIONS A brief summary of the investigation and tank closure activities previously conducted at Saes 1 and 2 is provided below (for additional details, see the Preliminary Assessment Report prepared by ERM-West in May 1993) The evidence of a possible cherrucal release was found at both Sites 1 and 2 The individual sites are discussed separately below Site 1 A release of petroleum products to soil and ground water from a 2,000-gallon underground fuel storage tank formerly located at Site 1 was documented Subsequent investigations conducted at the site defined the extent of the release The lateral and vertical extent of Total Petroleum Hydrocarbons (TPH) and Benzene, Toluene, Ethylbenzene and Xylene (BTEX) in soil at Site 1 was limited to a localized area in the vicinity of the former tank, in a zone between approximately b and 11 feet bgs Based on data obtained during the investigation, the volume of soils containing TPH as gasoline in excess of 100 mg/kg (ppm) at Site 1 was estimated to be approximately 200 to 300 cubic yards The extent of TPH and BTEX in ground water was also limited to a localized area in the vicinity of the former tank The results of quarterly ground water samples collected from the five site monitoring wells between April 1991 and April 1993 showed a steady decline in the concentrations of TPH as gasoline and benzene in ground water All monitoring wells at Site 1 (except for well MW-5) have been non-detect for these compounds since December 1992