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L PRELN ZIY REPORT AND TANK CLOSURE REPORT Tracy Boulevard Shelf 3725 Tracy Boulevard,Tracy,California Delta Project No.49-89-912 Page 3 On May 31,1990,during station reconstruction activities,a concrete vault of unknown origin was discovered at the site(Figure 3). The vault,a'flow-through"type tank,was 16.5 feet long,6 feet wide,and 4 feet deep. a On dune 4, 1990,thirteen 55-gallon barrels of sludge were pumped from the vault. The vault was dismantled and removed from the ground on June 5, 1990. 4 2.2 Previous Subsurface[nvestative Activlties i.� Prior to tank replacement activities in 1985,Shell contracted J.H.Kleinfelder&Associates(Meinfelder) .x to drill four test soil borings in the vicinity of the underground storage tank;. The soil borings were drilled to a depth ranging from 11.5 to 16.5 fent below the ground surface;approximate locations are illustrated in :.z the Kleinfelder report presented in Appendix A. In the course of their investigation,Meinfelder collected soil samples for classification and screening with a trace gas analyzer(believed to be an OVA). In general, Meinfelder characterized the natural soils at the site as sand and silt. Water was encountered in boring B-1 at a depth of approximately 11.5 feet. Gasoline hydrocarhnng fnr(<umed)were detected using a trace gas analyzer in borings B4,B-2,and B-1 at a depth of approximately 10 feet or roughly corresponding to the bottom of the tanks and just above the detected water level. Samples collected from greater depths (i.e., ry below the water table) did not contain petroleum hydrocarbon constituents. Petroleum hydrocarbon constituents were not found in any of the soil samples screened tz_lt boring B-3. m Following removal of the steel underground tanks in 1985,soil samples were collected by Canonie Engineers, Inc., from beneath the three tanks. in addition, water samples were collected from the bottom of the excavation. The results are included in the analytical report prepared by Canonie Engineers(Appendix B). Samples were analyzed for total extractable hydrocarbons, benzene, toluene,xylenes, ethylene dibromide (EDB),and organic lead. In summary,TPH concentrations ranged from less than the laboratory analytical method detention limits to 40 parts per million(ppm)in soils and 0.7 ppm in water. Organic lead,ethylene dibromide,benzene,and toluene were below detectable levels in all soil samples analyzed. Xylenes were detected in the water sample at a concentration of 66 parts per Milion (ppb) and in one soil sample at a concentration of 1.2 ppb. The depth represented by these same;,�s is not known. 2.3 Prevlous Delta Re its O!t December 4, 1989,Delta submitted a Pretank Closure Site Assessment Report to the County,dated November 22, 1989,presenting the results of our soil and ground water assessment. At the requejt of the County,this report was submitted to the Califernia Regional Water Quality Control Board,Central Valley Region(Regional Board),on February 20, 1990.