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groundwater morutonng Since the source of contamination has been stopped with the removal <br /> of Tank A and benzene concentrations in groundwater are relatively low, the subject site would <br /> be a likely candidate for such a nsk-based closure strategy <br /> Additional environmental corrective action work will be required to achieve site closure To <br />' proceed with a risk-based closure strategy, IT recommends that the following tasks be <br /> performed <br /> I Begin a quarterly groundwater monitoring and sampling program to evaluate the <br />' stability and migration of the contaminant plume and to assess the rate of natural <br /> biodegradation Prior to any additional monitoring, the existing monitoring wells <br />' should be resurveyed to correct the wellhead elevation references. <br />' 2 Conduct a survey of potential sensitive receptors to impacted groundwater <br /> beneath the site This survey should include a review of all surface water bodies <br />' and groundwater wells within a % mule radius of the site <br /> 3 Using the quarterly groundwater monitoring data. existing soil data and the survey <br /> of possible sensitive receptors, perform a preliminary risk assessment using the <br /> American Society for Testing and Materials (ASTM) Risk-Based Corrective <br />' Action (RBCA) framework <br /> t4 Based on the results of the RBCA analysis, either continue groundwater <br /> monitoring or apply for site closure The site closure application should be in <br /> accordance with the Tri-Regional Board Staff Recommendations for Prelim ary <br /> Investigation and Evaluation of Underground Tank Sites, Appendix B <br />' wells ed at <br /> IT does not recommend that additional groundwater monitoring s be install this time. If <br /> groundwater monitoring results indicate that the contaminant plume is unstable and migrating, <br /> then additional wells downgradient of MW-3 should be considered <br /> _ 8 <br />