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5 SECONDARY REMEDIAL ACTION PROCESS <br /> Petroleum hydrocarbon impacts on the fringe of the dissolved phase plume <br /> ' and residual impacts that may remain following the primary remedial actions <br /> will be addressed through monitored natural attenuation Degradation would <br /> continue to proceed through the same mechanisms as during active sparging, <br /> but through mineralization processes utilizing naturally occurring oxygen <br /> rather then sparged air Historical groundwater quality trends indicate that <br /> natural attenuation is currently occurring at the facility <br /> Soil samples were collected from a subsurface investigation performed in <br /> March 1994, and were evaluated for total heterotrophic plate count <br /> ' (microbial identification and characterization), and the respective microbes <br /> ability to degrade fuel hydrocarbons (Appendix E) Results of this analysis, <br /> contained in the April 25, 1994 Groundwater Monitoring Well Installation <br /> ' Report, identified naturally occurring microbes that digested petroleum <br /> hydrocarbons <br /> 1 Factors important to the natural attenuation process have been monitored at <br /> the facility (December, 1996 monitoring event) and found to be conducive to <br /> the natural degradation of the petroleum hydrocarbons on site Samples were <br /> analyzed for alkalinity, dissolved oxygen, oxidation-reduction (redox) <br /> potential,pH, specific conductance, temperature, nitrates, sulfate, and ferrous <br /> iron Analytical results were reported in the February 21, 1997 Quarterly <br />' Groundwater Monitoring and Natural Biodegradation Assessment Report <br /> and are summarized in the following Table 5 <br /> r <br /> Remedial Action Work Pian <br /> Prepared for THE EARTHGRAIN5 COMPANY Prepared by Philip Services Corp <br /> H 1ENV1624001451RAP61300 doe 16 8/31/00 <br />