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Subject: Notification of Remediation System Shutdown <br /> ' Date: 11/18/2005 <br /> Page 3 of 4 <br /> SUMMARY AND CONCLUSIONS <br /> The analytical data for groundwater and soil vapor give preliminary indications that the s <br /> remediation system has effectively removed TPH-gasoline from the subsurface. Concentrations <br /> of TPH-gasoline and BTEX in groundwater have decreased by two to three orders of magnitude <br /> '• since operation of the AS/SVE system began. Petroleum hydrocarbons have not been detected in <br /> groundwater samples collected from wells MW-1, MW-3, and MW-4 since January 2003. <br /> Concentrations and removal rates for TPH-gasoline in soil vapor appear to be reaching low <br /> asymptotic levels. Based on these data, operation of the AS/SVE system appears unnecessary at <br /> this time and should be discontinued. <br /> � I <br /> + RECOMMENDATIONS <br /> Based on our evaluation of the remediation performed to date, we offer the following <br /> recommendations: <br /> i <br /> • Discontinue operation of the remediation system; <br /> • Retain the system onsite, in the event that further remediation is warranted in the future; <br /> • Continue quarterly groundwater monitoring to assess the effectiveness of remediation and <br /> to evaluate the potential for contaminant concentrations to "rebound"; <br /> Quarterly groundwater monitoring will be performed during January, April, July, and <br /> October; <br /> • The depth to groundwater and free product thickness (if present) will be measured on a <br /> quarterly basis in all four monitoring wells (MW-1 through MW-4); <br /> . The .total depth of each well will be measured annually, during the first quarter of each <br /> year(January); <br /> • Groundwater samples will be collected from all four monitoring wells on a quarterly <br /> basis. A duplicate groundwater sample will be collected from one well for quality <br /> assurance purposes. A travel blank will be prepared by the analytical laboratory and will <br /> accompany the groundwater samples. The groundwater samples and travel blank will be <br /> analyzed for TPH-gasoline, BTEX, and fuel oxygenates (DIPE, ETBE, MTBE, TAME, <br /> 1 and TBA) by EPA Method 8260B; and <br /> l <br /> • Collect soil samples in the vicinity of the former underground tank. Analyze the samples <br /> for TPH-gasoline, BTEX, and fuel oxygenates by EPA Method 8260B to evaluate the <br /> { progress of soil remediation. A work plan for soil testing will be prepared and submitted <br /> separately. <br /> PSC ENVIRONMENTAL SERVICES <br /> j210 West Sand Bank Road,Columbia,IL 62236 <br /> (618)281-1543 (800)733-7173 Fax(618)281-7020 <br /> e <br />