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,rlllr� <br /> f >>, Interim Corrective Action Plan—Tosco(76)Service Station No. 11195,Lathrop,California <br /> August 28,2002 <br /> As previously stated in this Interim CAP,it does not appear that the hydrocarbons that <br /> are present at the subject site threaten any surface water or wetlands in the vicinity of the <br /> site that have a current or potential beneficial use. However, the groundwater in the <br /> vicinity of the site has been classified by the RWQCB as an area of current and/or <br /> potential beneficial use. Therefore, GR recommends installation of an ozone <br /> microsparge system to remediate the impacted groundwater beneath the site. <br /> The existing groundwater monitoring wells are currently monitored and sampled quarterly. This <br /> program will be continued and modified,as appropriate,to provide verification monitoring of corrective <br /> action effectiveness and progress towards cleanup levels. <br /> 3.3. Cleanup Levels <br /> Cleanup levels for ground or surface waters, affected or threatened by the unauthorized release, shall <br /> meet the following requirements: <br /> (i) For waters with current or potential beneficial uses for which numerical objectives <br /> have been designated in water quality control plans, the responsible party shall <br /> propose at least two alternatives to achieve these numerical objectives. <br /> r (ii) For waters with current or potential beneficial uses for which no numerical objectives <br /> have been designated in water quality control plans, the responsible party shall <br /> recommend target cleanup levels for long-term corrective actions to the regulatory <br /> agency for concurrence. <br /> Final cleanup level goals for hydrocarbon constituents are proposed to be the California Department of <br /> Health Services Maximum Contaminant Levels (MCLS), which are 13 ppb for MtBE, 1.0 ppb for <br /> benzene, 150 ppb for toluene, 700 ppb for ethylbenzene, and 1,750 ppb for xylenes. If these levels are <br /> not achievable,then Tosco will work with the PHS-EHD to determine acceptable final cleanup goals. <br /> 3.4 Remedial Action Plan <br /> Based on the information provided, a review of the remedial progress at a nearby former Unocal site <br /> and the various remedial alternatives evaluated in this updated Interim CAP, GR recommends the <br /> installation of an ozone microsparge system,presented as Option#5 in the Feasibility Study above. The <br /> sparge points will target the shallow groundwater zone, and be placed at depths of approximately 25 <br /> feet bgs. A detailed description of the ozone system and sparge point locations will be presented in <br /> GR's forthcoming Work Plan for Additional Delineation,proposed to be submitted to the PHS-EHD by <br /> September 20, 2002. <br /> 140193.13 11 <br />