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GEOMATRIX Mr. Robert Mihalovich Chevron Environmental Management Company April 3, 2002 Page 2 SUMMARY OF EXISTING DATA A Phase I site investigation was conducted in 1995 (Geologic Technics), and Phase II site assessment activities were conducted between 1994 and 1995 (Geological Technics) and in 1998 (Radian International LLC, Geomatrix). These investigative activities and pertinent results are summarized below; a more comprehensive description is provided in Geomatrix's February 1999 Site Investigation and Screening-Level Health Risk Assessment. Summary of Previous Investigations Phase II activities were initiated in 1995 and consisted of drilling two soil borings (SB-1 and SB-2) adjacent to the location of the former pipeline. Additional Phase II activities were con- ducted in July 1998 and included advancing six soil borings (SB-3 through SB-8) to delineate the lateral extent of the petroleum hydrocarbons encountered in SB-2 and the installation, develop- ment, and sampling of monitoring wells MW-1 through MW-4. In November 1998, Geomatrix sampled the four wells. The locations of borings and wells are shown on Figure 2. A summary of historical soil data is presented in Tables 1 through 3 and the groundwater data in Table 4. Boring logs for borings SB-3 through SB-8 and MW-1 through MW-4 are presented in Appendix A. Soil Conditions Petroleum hydrocarbons were reportedly observed soil borings SB-2 and SB-8 and the boring of monitoring well MW-1 at depths between 10 and 50 feet bgs. Petroleum-hydrocarbon affected soil was not observed in borings SB-1, SB-3 through SB-7, or in MW-2 through MW-4. A summary of analytical results is presented below. Soil samples collected between 11 and 32 feet bgs from SB-1 and SB-2 were analyzed for ben- zene, toluene, ethylbenzene, and xylenes (BTEX); TPHd, and/or total recoverable petroleum hy- drocarbons (TRPH). Soil samples from boring SB-1 did not contain BTEX, TPHd, or TRPH. Soil samples from boring SB-2 contained TPHd at concentrations ranging from 11,800 to 17,200 milligrams per kilogram (mg/kg) and TRPH at a concentration of 17,600 mg/kg. Boring SB-2 contained separate-phase petroleum coincident with the water table (approximately 33 feet bgs). A wipe sample of this material was collected and analyzed for BTEX and TPH quantified as various petroleum products. No benzene or ethylbenzene was detected; and con- centrations of toluene and xylenes were 37 and 42 micrograms per kilogram (µg/kg), respectively. Concentrations as great as 167,000 mg/kg for TPH quantified within the kerosene, diesel, dielec- tric and motor oil ranges and of 44,000 mg/kg of TRPH were reported.' In 1998, a total of 59 soil samples were collected from 10 soil/well borings and were analyzed for TPHd, TPH quantified as motor oil (TPHmo),TPH quantified as gasoline (TPHg), BTEX,poly- nuclear aromatic hydrocarbons (PAHs), and methyl tert butyl ether(MtBE, analyzed in 34 sam- ples only). Soil samples collected from boring locations MW-2, MW-3, MW-4, SB-3, SB-4, ' The sample of separate-phase petroleum reportedly was liquid,yet the laboratory reported concentration values as units of mass per mass,and no density calculations were provided in the laboratory report.