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r. S ECOR r w 5.0 SITE REMEDIATION Between April 6 and June 29, 2000, interim remediation consisting of weekly pumping of water from well EX -1 was conducted by G -R. During weekly well pumping activities, approximately 2,635 gallons of water were removed from the site. Concentrations of MtBE in groundwater samples from well EX -1, collected on April 6 and June 29, 2000, decreased from 720,000 µg11 to 325,000 µg/l. On July 3, 2000, operation of interim soil vapor extraction (SVE) and groundwater extraction (GWE) remediation was initiated at the site. The interim SVE system consists of four SVE wells (VE -1 through VE -4) and a 100 cubic foot per minute (cfm) catalytic oxidizer. SVE system historical data is presented in Tables 5 and 6. The interim GWE system initially consisted of one extraction well (EX -1) and three 2,000 pound carbon vessels in series. A submersible pump and the necessary piping (to the existing GWE system) were installed to begin groundwater extraction at MW -14. Well MW -14 was converted to an extraction well, and renamed EW -2, to increase groundwater extraction and establish capture of the plume. Groundwater extraction from EX -2 was initiated on September 22, 2000. A third extraction well (EX -3) was installed, and GWE from EX -3 began on November 28, 2000. GWE historical data is presented in Table 7. On August 20, 2003 the SVE system was discontinued following approval of the RWQCB in their letter dated August 18, 2003 and has remained offline. The primary reason for this is as follows: (1) the hydrocarbon removal rates were very low and reached asymptotic levels, (2) the groundwater analytical data showed a decrease in hydrocarbon concentrations, and (3) the plume appeared to be stabilized. On April 18, 2005 groundwater extraction was discontinued to evaluate rebound of chemical constituents. Rebound of chemical constituents was not observed and the GWE system has remained offline. The primary sources of contamination have been removed and MtBE contamination at the site is mainly isolated in the A -Zone near the former USTs. Therefore, without any additional source the plume is expected to decrease with time by natural attenuation and/or biodegradation prior to reaching any down gradient groundwater wells or City of Lodi Municipal wells. In addition, due to the depth at which the City wells are screened (between 210 and approximately 490 feet bgs), it is unlikely that the City of Lodi wells would be impacted. Typical applications of Best Available Technology (SATs) to similar plumes include oxidation of the plume, enhanced biological treatment, or thermal treatment. Concentrations have been reduced to the point that the incremental cost for further mass removal exceeds the incremental benefit. 95775 NFAR REPORT Final.doc 11 SECOR Intemational Incorporated