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CLEARWATER <br />' G R O U P <br /> • Environmental Services <br />' Contaminant Adopted Maximum Suggested Concentrations to Other Action Minimum <br /> Contaminant Level meet adopted Secondary Level Levels <br />' (MCL) MCL of 3 odor units <br /> Benzene 1 (primary) 1 <br /> Toluene 150(primary) 42 42 <br />' Eth lbenzene 700(primary)_ 29 29 <br /> Xylene 1,750(primary) 17 17 <br /> Total Petroleum 100 100 100 <br /> Hydrocarbons(gas) <br /> Total Petroleum 100 100 t00 <br /> Hydrocarbons (diesel) <br /> I Na thalene 20 20 <br /> Odor 3 units(secondary) 3 units <br /> Lead (elemental) 15 (primary) 15 <br /> Methyl tert-butyl ether 13 5 35 5 <br />' (MTBE) <br />' Although similar clean-up goals for soil have not been published by the CVRWQCB, it is clear <br /> any remediation to bring groundwater within the goals noted above will also necessitate <br /> remediation of soil to mitigate the potential of continued partitioning of contaminants from <br /> sorbed-phase to aqueous-phase within the saturated zone over time In fact, experience suggests <br /> that remediation of sorbed-phase contamination will often have a greater effect on dissolved- <br /> phase contaminant concentrations than attempts at direct groundwater remediation alone The <br /> California Regional Water Quality Control Board, San Francisco Bay Region (SFRWQCB) is <br />' currently evaluating Interim Risk-Based Screening Levels (RBSLs) for application as soil and <br /> groundwater cleanup levels in a variety of site and hydrogeologic settings The RSBLs are in the <br />' form of look-up tables based on Tier 1 RBCA models for 4 different combinations of soil, <br /> groundwater, and land-use characteristics The RBSLs were calculated using MCLs, cancer risk <br /> estimates, contact/inhalation hazards, aquatic life threat, and other risk factors Athough the <br />' RBSLs have not been adopted as formal cleanup levels, they are currently under evaluation as <br /> such by the SFRWQCB and a number of other regulatory agencies in California, and offer a <br />' reasonable approximation of a site-specific Tier 1 RBCA The RBSLs, as applicable to the <br /> subject site, are summarized as follows (from SFRWQCB Application of Risk-Based Screening <br />' Levels and Decision Making to Site with Impacted Soil and Groundwater, Interim Final Volume <br /> I Summary Tier I Lookup Tables, December, 2001) <br /> I <br /> I <br /> ZB178C RAP 17 May 18,2004 <br /> I <br />