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r„ GEoMATRIX . Mr Jeff Wong San Joaquin County Department of Public Health Services August 10, 2004 Page 4 Deeper monitoring well MW-7 was sampled for the first time in June 2004 and results indicated the presence of TPHd (520 µg/L) and toluene (0 63 pg/L) These results may be anomalous and also will be reevaluated in future monitoring events The vertical extent of TPH was previously based on reported analytical results from grab groundwater samples i collected at depths of up to approximately 50 feet bgs in boring SB 12 (Table 2) I SUMMARY OF RWQCB RECOMMENDATIONS FOR UST SITES The proposed road map for obtaining closure at the subject site, which will be developed in the CAP, is designed to follow recommendations developed by Region 5 RWQCB Staff for UST sites (RWQCB, 2004) The RWQCB allows for closure of UST sites when the site is shown to present no significant risk This allowance for closure is shown by RWQCB (2004) to include cases when chemical constituents or analytes, including TPH, are shown to remain in soil or groundwater beneath the site even at concentrations above RWQCB water quality objectives Site closure can thus be approved, based on the RWQCB guidelines, under these • conditions when the chemicals or analytes • are shown not to pose a threat to current or probable future beneficial uses of groundwater, • do not pose a threat to water supply wells or surface water, and • do not pose a threat to human health An important consideration for granting closure also includes the criterion that best available, cost-effective technology has been implemented, if warranted(i e , if the concentration of target analytes exceed WQOs), that the area of affected groundwater is stable with respect to areal migration and mass flux, and that groundwater is projected to meet water quality objectives within a reasonable period of time The specific requirements for a "No Further Action Required" (NFAR) case closure by the RWQCB are outlined in the April 2004 update to Appendix A of the Tri-Regional Board Staff Recommendations For Preliminary Investigations and Evaluation of Underground Tank Sites (Appendix A) PROPOSED CORRECTIVE ACTION PLAN The following paragraphs provide the proposed plan for developing the CAP for the subject site The CAP will be prepared for submittal to the PHS/EHD for approval The CAP will present a thorough summary of site conditions, including summary tables and figures, and the proposed future work at the site to conform to closure requirement guidelines The proposed work to develop the CAP will include completing the following tasks 1 1Project19000s199631CAP Work Plan doc