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n TERRA VAC minimize risk of adverse human health effects. If future site usage changes significantly, this health risk assessment should be re-evaluated. 8.1 Reduction of Immediate Health Risk The GSI/RBCA models all indicate that benzene in soil and groundwater may pose a treat to human health via volatilization to indoor air. The models calculate the Site Specific Target Levels for benzene in soil and groundwater at 0.02 mg/kg and 0.054 mg/L, respectively. These levels represent the maximum benzene concentrations allowable for the protection of human health and ecological resources. To protect human health and ecological resources, the representative benzene concentrations in soil and groundwater should be reduced to these values. 8.2 Central Valley Regional Water Quality Control Board Objectives For Ground Waters The Central Valley Regional Water Quality Control Board (CVRWQCB) Basin Plan establishes water quality objectives for bacteria, chemical constituents, radioactivity, taste and odors, and toxicity. The basin plan water quality objectives are relevant to the protection of designated beneficial use waters, but do not require improvement over naturally occurring background concentrations. The ground water objectives contained in the basin plan are not required by the federal Clean Water Act. 8.2.1.1 Tastes/Odors and Toxicity Groundwater shall not contain taste- or odor-producing substances in concentrations that cause nuisance or adversely affect beneficial uses.'Groundwater shall be maintained free j of toxic substances in concentrations that produce detrimental physiological responses in human, plant, animal, or aquatic life associated with designated beneficial use(s). 8.3 Achievement of Water Quality Objectives The State of California assigned maximum contaminant level (MCL) for benzene in drinking water is 0.001 mg/L. The maximum Federal MCL for benzene in drinking water is 0.005 mg/L. The calculated Site Specific Target Level for benzene in groundwater is 0.054 mg/L. This SSTL is 54 times greater than the State of California MCL for benzene in drinking water. To achieve reasonable water quality, the representative benzene concentration should be reduced to the Site Specific Target Level of 0.054 mg/L. 9. REMEDIAL OPTIONS The RBCA model results set cleanup goals for benzene in the vadose zone soil and groundwater beneath the site at 0.02 mg/kg and 0.054 mg/L, respectively. The following is a summary of remedial technologies commonly used for source remediation at petroleum hydrocarbon impacted sites. The following can be used individually or in combination with any of the others. i 1. Intrinsic Bioremediation or Natural Attenuation Project 30-021 . 11 caalton130-02121caplrev5lcap-rev5.doc July 15, 1998