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Stockton Scavenger Association Facility <br /> November, 1997 <br /> Page 9 <br /> 6 0 CONCLUSIONS AND RECOMMENDATIONS <br /> As shown on Figures 7 and 8, the concentration of TPHg in MW-2 has trended downward since <br />' February 1995 The concentration of benzene in MW-2 has trended downward since July 1994 <br /> Benzene is the only analyte that remains above the MCl_ during the latest monitoring event <br /> Continued operation of the groundwater pump and treat system would result in monthly removals <br /> of 0 2 percent of the TPHg and 0 4 percent of the benzene mass removed to date by the pump and <br /> treat system Continued operation of the pump and treat system is not cost effective to remove the <br /> minor amount of petroleum hydrocarbons remaining Overexcavation and operation of an in situ <br />' vapor extraction/injection system in 1993 removed petroleum hydrocarbons in soil <br /> On the basis of a review of historical information and the latest groundwater monitoring event, <br />' ENSR recommends the following for this site <br /> • Additional groundwater remediation is not warranted The groundwater pump and treat <br /> system should be dismantled after receiving concurrence from EHD <br /> • Allow natural attenuation to complete remediation of the site Biodegradation is indicated <br /> by the dissolved oxygen concentration measurement collected during the latest monitoring <br /> event <br /> G Review files at EHD and complete a water supply well survey <br /> 1 <br /> 1 <br /> 1 <br /> 5027002 ART <br />