ARCHIVED REPORTS_XR0009348 - Laserfiche WebLink

Home Browse Search

GEQMATRIX Road G and about 300 feet west of Fort Road 14 (Figure 1) The site formerly contained two 12,000-gallon underground storage tanks (USTs) that were used to store unleaded gasoline The tanks were removed in 1988 by the Stockton Service Station Equipment Co , Inc , approximately 180 cubic yards of soil were excavated with the tanks to a depth of about 11 feet below ground surface (bgs) (B&R, 1998) Currently, the area over the former tanks and excavation is covered with concrete and surrounded by industrial activities associated with the production, storage, and transport of liquid ammonia A survey conducted in 1999 indicated that no municipal or drinking water supply wells were identified within a 2,000-foot radius of the site (Ross, 1999) 2.2 HYDROGEOLOGIC SETTING The site is located on the delta of the San Joaquin River, approximately 2 rrules east of the confluence of the San Joaquin and Calaveras rivers The subsurface geology consists of a thick sequence of alluvial deposits of late Tertiary to Holocene age, overlying sedimentary rocks of Cretaceous to Tertiary age, which in turn overlie crystalline basement rocks (Bartow and Nilsen, 1990) Data from nearby studies within the Port area indicate a soil profile to a depth of about 20 feet bgs consisting of interbedded sands and clays, mostly under reduced conditions (SPGC, 1994) Data from nearby studies indicate that the depth to water measured in monitoring wells in the vicinity ranged from about 5 to 10 feet bgs (SPGC, 1998, EMCON, 1998) Seasonal fluctuations in the water table ranged from about 3 to 5 feet, with some as much as 6 to 9 feet Tank removal inspection records for Port sites (dating back to 1987) indicate that no groundwater was encountered during excavation or soil sampling to a depth of as much as 16 feet bgs Water levels in this area have risen as much as 8 feet since 1994, 2 to 3 feet of which appear to be attributable to the heavy and prolonged El Nino rainfalls during the winter ' of 1997/98 Water levels measured in the three initial bonngs at Site No 3 on August 7, 1998, ranged from about 9 5 to 12 feet bgs Based on nearby studies (SPGC, 1998, EMCON, 1998), groundwater flow directions in the vicinity appear to be variable, ranging from west-northwest to east-southeast Flow direction changes may be due to tidal influences produced by the ' deep-water channel to the north and the San Joaquin River to the west and southwest of the Port complex 1 1 11PR01EC{VOON16437 00016437-06 doc 2