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If the fate and transport model and the risk assessment indicate there is a risk to <br /> human health, or the plume is not stable, a feasibility study to determine the most <br /> cost effective methodology to remediate the plume will be required. If the model and <br /> the risk assessment indicate that there is no risk to human health, and the plume is <br /> stable, the plume may be monitored (historic quarterly groundwater monitoring data <br /> may be sufficient) to verify that the model is accurate. <br /> Gathering data required to model intrinsic bioremediation (natural attenuation) is <br /> useful in determining the risk posed by the site. Intrinsic bioremediation will cause a <br /> plume to reach stability and degrade without implementing active remediation. If the <br /> feasibility study indicates that intrinsic bioremediation is a cost effective methodology <br /> then active remediation may not be necessary. <br /> Parameters used to determine closure of a site usually involve a combination of <br /> source removal, fate and transport modeling, risk assessment, plume stability and the <br /> feasibility of utilizing active remediation. All parameters must indicate that the plume <br /> is stable and degrading and will not adversely affect human health or the environment <br /> for closure to be issued. <br /> PHSIEHD recommends that you submit an amended workplan to complete the site <br /> assessment and which will describe a methodology to obtain data for modeling fate <br /> and transport, risk assessment and natural attenuation at this site. The report that <br /> will be generated from this data should include a well survey and feasibility study. <br /> The workplan should provide adequate data in one or two mobilizations, to save time <br /> and money, and maintain the progress you have made towards closure of your site. <br /> For additional information, please contact Steven Sasson at (209) 468-3459. <br /> Donna Heran, RENS, Director <br /> Environmental Health Division <br /> S J ;y� <br /> /ell <br /> �4 <br /> Steven Sasson, Senior RENS Margare Lagorio, REHS <br /> Site Mitigation Unit Supervisor <br /> SS <br /> cc: Elizabeth Thayer, CVRWQCB <br /> Mel Jacobo, SWRCB <br />