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document titled Screening for Environmental Concerns at Sites With Contaminated Soil and Groundwater, July 2003. • The U.S. Environmental Protection Agency's Preliminary Remediation Goal (PRG) for MTBE in tap water is 11 ug/L. Concentrations exceed the PRGs at the north end of the site and several off-site wells. None of the groundwater concentrations measured during the June 2006 groundwater sampling event exceed the ESL for MTBE(Figure 4). 5.0 INTERIM REMEDIATION APPROACH The interim remediation approach for this site was selected to mitigate further downgradient migration of MTBE in groundwater. Based on the results of the pump test data collected by SECOR, groundwater extraction is a viable option for interim action. ERG will make use of existing wells and pump test data to optimize the interim remedial approach. 5.1 Interim Well Selection ERG recommends utilizing two of the three wells from the pump test(MWO-1X and MW-3) in order to prevent further migration of the MTBE plume. These wells were selected because they are located along the property boundary in the direction of groundwater flow. The wells are located within the 127 foot zone of capture established by SECOR during the pump test and, therefore, will create a barrier for contaminant migration off site. In addition,these wells are located near the area of highest MTBE concentration,thereby allowing for the greatest mass removal. MW-3 is screened in Sand A to total depths of 20 feet bgs. MWO-1X is screened in Sand B to a total depth of 30 feet bgs. Pumping from one well in Sand A(MW-3) and one well in Sand B (MWO-1X)will also provide a vertical barrier to off-site migration. The results of SECOR's pump test indicate that Sand A and Sand B are interconnected. Therefore, MW-2 will not be used for groundwater extraction due to redundancy. MW-2 and MW-10 will be monitored closely for drawdown effects. If no influence is observed, these wells may also be added as extraction wells. 5.2 Interim Extraction Rates Based on the results of the pump test,ERG recommends a target pump rate of 5.0 gallons per minute(gpm). This pumping rate was sustained in MW-3 during the pump test and was shown to contribute to a zone of capture of approximately 127 feet. The distance between the extraction wells is approximately 130 feet, indicating that a sufficient barrier will be created by this pumping rate. Groundwater will be extracted using a down-hole pump capable of up to 10 gpm. Since steady-state conditions were achieved during the pilot test in 10-30 minutes, adjustments to the system can be made quickly and will be used to optimize the efficiency of the interim action. ERG,0406 Page 4 IRAP