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I <br /> Baseline Intrinsic Bioremediation Data Evaluation <br /> A more sophisticated quarterly groundwater monitoring program to carefully evaluate then <br /> geochemistry intrinsic bioremediation will begin in June 1995. Annual reports will be " <br /> g tri' of in� .,.-:.., <br /> generated to describe geochemistry, groundwater gradients, degradation rates, and mass , <br /> removal calculations. Intrinsic remediation monitoring will be conducted in MW-DIS-2, 3, 9, <br /> and .10, and conventional groundwater monitoring will continue in MW-DIS-1, SS, and SD. <br /> ` The procedure and laboratory methods required for collecting and analyzing intrinsic <br /> bioremediation samples are presented in Appendix D. <br /> A contaminant fate and transport model will be developed and calibrated to historical data. <br /> Compliance monitoring points that are beyond the extent of migration potential, as <br /> determined by fate and transport modeling, will be identified. The gasoline plume is expected <br /> to be degraded most aggressively at the outer perimeter or directly within the air sparging <br /> system zone of influence, where oxygen is available as the electron acceptor for microbial <br /> degradation. An equilibrium is expected to be established where the slow outward migration <br /> of gasoline constituents is offset by the microbial utilization of gasoline constituents as a <br /> substrate. If fate and transport calculations indicate that existing monitoring well locations <br /> are not beyond the equilibrium extent of the plume, additional wells may be required.- Fate <br /> and transport analysis can begin when fourth quarter data are collected in June 1996. <br /> Progress Reporting <br /> ( By October 1996, final plume monitoring well locations and intrinsic bioremediation <br /> demonstration data will be presented to PHS/EHD in a progress report. The October 1996 <br /> progress report will also establish the criteria that will initiate contingency plan activity. The <br /> tentative contingency initiation criteria are (1) the plume migrates beyond the established <br /> compliance monitoring points, (2) constituent concentrations are not degrading at a <br /> satisfactory rate, or (3) the risk to human health increases significantly. The contingency plan <br /> will consist of aggressive remediation intervention that may require augmenting the natural <br /> rate of contaminant removal and/or creating an inward hydraulic gradient by pumping. <br /> Subsequent annual'progress reports will contain a summary of all data collected and a <br /> discussion of intrinsic bioremediation trends. <br /> Closure Investigation <br /> When groundwater quality data begin to consistently indicate that concentrations have <br /> i stabilized and no further remediation is occurring, a closure investigation plan will be <br /> submitted to PHS/EHD for review. The closure investigation plan will propose locations for <br /> confirmatory soil boring and Hydropunch sampling. Upon reaching a'consensus with <br /> ` PHS/EHD about the number and location of samples, Del Monte will collect confirmatory <br /> l samples and submit a closure request letter with laboratory documentation of analytical <br /> results. <br /> r� <br /> 10030984.DOC 5-2 <br />