SITE INFORMATION AND CORRESPONDENCE

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January 4, 1993 Page 2 v, On August 23, 1988, three underground fuel storage tanks containing leaded gaso- line, unleaded gasoline, and diesel were removed from the GWSP site. A ground- water sample collected from the open excavation contained 110,000 parts per billion (ppb) total petroleum hydrocarbons calculated as diesel (TPH-diesel), 130 ppb xylenes, and 42 ppb benzene. Additional investigation was required by the R WQCB. On October 23 and 24, 1989, three groundwater monitoring wells, designated MW-1, MW-2, and MW-3, were installed at the GWSP site. Soil samples collected from the borings were analyzed for the presence of total petroleum hydrocarbons calculated as gasoline (TPH-gasoline), TPH-diesel, benzene, toluene, ethylben- zene, and xylenes (BTEX compounds). None of the soil samples contained detectable concentrations of any of these analytes. A fourth groundwater moni- toring well, MW-4, was installed on May 22, 1992. A soil sample collected from the boring for MW-4 contained 2.5 parts per million (ppm) TPH-diesel, 0.0058 ppm benzene, 0.0067 ppm ethylbenzene, and 0.0076 ppm xylenes. Quarterly groundwater monitoring and sampling have been conducted at the GWSP site since October 25, 1989. Groundwater has occurred at depths ranging from 6 to 9 feet below grade, with a consistent northwesterly flow direction. Groundwater samples collected from GWSP Wells MW-1 through MW-4 have contained maximum concentrations of 1,000 ppb TPH-diesel, 8.0 ppb benzene, 4.0 ppb toluene, 4.1 ppb ethylbenzene, and 14.0 ppb xylenes. The extent of hydro- carbons in groundwater beneath the GWSP site is not considered defined. SOUTHERN PACIFIC TRANSPORTATION COMPANY The Southern Pacific Transportation Company (SP) railyard, located approxi- mately 1,400 feet to the west-southwest of the site, is also the subject of an active environmental investigation (Figure 1). The SP site is located in the hydraulic crossgradient to upgradient direction from the Unocal site. According to data currently available to PACIFIC, a series of environmental inves- tigations have been conducted at the SP facility, beginning in approximately 1988. There are currently 30 groundwater monitoring wells in use for the SP investiga- tion, including 25 on-site wells and 5 off-site wells. The monitoring wells range in depth from approximately 15 to 90 feet below grade, and are installed in three distinct aquifer horizons. Groundwater in the SP shallow aquifer monitoring wells generally occurs at depths of approximately 6 to 11 feet below grade, with a northeasterly flow direction. Groundwater samples collected from on- and off-site SP wells have contained 3100103/FILERF-V