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' effectivelyrem ° <br /> removed m excess of 95/o of the petroleum mass Impacting the unsaturated soil underlying <br />' this site This petroleum mass removal confirms that the source of gasohne and aromatic constituents <br /> affecting groundwater has been effectively remediated <br />' 10 0) CLOSURE OF VAPOR EXTRACTION AND AIR SPARGING OPERATIONS <br /> Soil vapor extraction operations were discontinued during December 1998 pending submittal of dus <br />' request for No Further Remedial Action based on data collected from soil sample results, <br /> groundwater sample results, and effluent sample results of the vapor extraction unit <br />' 11.0) RECOMMENDATIONS FOR NO FURTHER REMEDIAL ACTION <br /> It is recommended that no further remedial action be implemented at this site based upon enhanced <br />' and intrinsic removal of greater than 97% of the Total Petroleum Hydrocarbons as gasoline and <br /> greater than 99% of the dissolved benzene The total EAC from all biodegradation processes was <br /> calculated as 13 238 mg/L, while the maximum BTEX concentration identified at the site was only <br />' 1 332 mg/L Based on the biodegradation indicator testing, the subsurface groundwater beneath the <br /> site supports the sustainability of anaerobic biodegradation to bioattenuate the remammg residual <br /> dissolved petroleum hydrocarbon mass <br /> Closure of SVE operation is requested since effective petroleum removal rates occurred in that <br /> period from 1990 to 1994 Removal rates resulting from SVE operation from 1994 to 1997 <br /> approached asymptotic levels in all momtonng wells tested, supporting that continued system <br /> operation would be unnecessary and ineffective Both TPH-g and benzene concentrations in <br /> groundwater have decreased significantly in all monitoring wells from 1988 to 1994 <br /> Concentrations have remained asymptotic or less than detectable in all on site monitoring wells <br /> from 1994 to 1998 <br /> 21 <br />