SITE INFORMATION AND CORRESPONDENCE_FILE 1

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• Ethylbenzene = 0.5 ppb • Xylenes = 0.5 ppb • TPH-g = 50 ppb Experience gained from remediation at similar sites suggests the water quality goals listed above may not be achieved given current technological and economic limitations. Less strin- gent water quality goals may be appropriate at some point during the remediation process. More reasonable water quality goals are associated with restoring the relevant beneficial water use that protects all other uses. To identify numeric goals, the relevant beneficial water use with the most stringent set of numeric water quality goals is identified. Resolution 88-63 is a logical starting point. Resolution 88-63 specifies that all groundwater is suitable for municipal supply, unless condi- tions preclude municipal supply use. Since groundwater conditions beneath the site may be suitable for municipal supply use, numeric water quality goals associated with restoring municipal supply pertain. This is because municipal supply is the relevant beneficial use with the most stringent set of water quality goals. Reasonable secondary waterguWjIy goals are: • Benzene= 1.0 ppb (California Primary Maximum Contaminant Levels) • Toluene=42 ppb (Taste and Odor Threshold) • Ethylbenzene=29 ppb (Taste and Odor Threshold) • Xylenes = 17 ppb (Taste and Odor Threshold) • TPH-g = 1,000 ppb (Taste and Odor Threshold; Reasonable Detection Limit) Existing water quality has been degraded by an upgradient chlorinated plume which has migrated onto Chevron property. The chlorinated impact currently precludes the use of shallow occurring groundwater for municipal supply. Use of groundwater in the vicinity of the site will necessitate water treatment regardless of petroleum hydrocarbon impact. Soil concentrations must also be considered in developing numeric goals that restore benefi- cial water uses. Petroleum hydrocarbon concentrations in soil that do not pose a threat to site water quality goals will constitute numerical cleanup goals for soil. Acceptable soil concen- trations, were determined by using the method proposed in The Designated Level Methodology for Waste Classification and Cleanup Level Determination(Marshack, 1989). These clean up goals are proposed in the case that hydrocarbon affected soils occur at the site. To date significant hydrocarbon impact in soil has not been identified. In addition, current site conditions indicate that further hydrocarbon impact to groundwater beneath the site via 3201357B/CAPREV 1 7 June 29, 1995