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March 18, 1993' ` Page 5 00 Conceptual Site Model A fuel leak, documented by site personnel, occurred on a piping run located on site leading from fuel tanks to the loading rack. Additional releases may have occurred and contributed to hydrocarbon impact at the site though there may be no documentation to show it happened. Product release notification procedures are-relatively new mandates. It is also possible that petroleum hydrocarbons may have entered the subsurface environment via product transfer operations and minor leaks from equipment used in the early 1900s. There was no information disclosed to suggest there was any other significant release. Since loading and off-loading procedures have become more stringent, and technological advances have allowed for better equipment and product reconciliation tracking, PACIFIC suggests that there are no longer any primary sources of petroleum hydrocarbons at the site. The greatest hydrocarbon concentrations were detected in soils within the 5-to 6- 1/2-foot interval in Wells U-1 and U-2 and in the 7- to 8-1/2-foot interval in Boring U-C. To a lesser degree Well U-5 and Boring U-A were impacted. Thus the major impact area appears to be in the vicinity of the aboveground bulk tanks, loaders, and loading rack, above the piezometric surface. This supposition is supported by the detection of hydrocarbons in groundwater samples taken form Wells U-5 and U-6. Both of these wells are located downgradient from the assumed area of greatest hydrocarbon impact. Impacted soil beneath the site has been characterized primarily as clay, and stratig- raphy within the impact zone does not appear to be complex. The gradient beneath the site seems to be consistent with the regional flow direction; north to northwest. Geological cross-sections are presented as Figures 3 and 4. Of foremost health and environmental concern are BTEX compounds; constituents of gasoline. These compounds have been identified in groundwater beneath the site at concentrations exceeding primary and proposed secondary Maximum Contaminant Levels (MCLS) for drinking water per Title 26, Division 22, Section(644445) of the California Code of Regulations (CCR). As previously stated, groundwater beneath the site is considered a potential source of municipal and domestic drinking water supply. There are several water-supply wells within a 1/2-mile radius of the site. Two wells are located are within 1,000 feet of the site and WSW-1, discussed above, is located on site. 3100104/1RAP