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LAINE • FRICKE <br /> ENGINEERS.HVDROGEOLOGISTS&APPLIED SCIENTISTS <br /> table to inject air into the groundwater in order to volatilize detected Hazardous Substances. <br /> Sparged air/vapors would be recovered by applying a vacuum to wells screened in the vadose zone, <br /> to extract detected Hazardous Substances from subsurface soils. Extracted vapors would be <br /> conveyed to a centralized process area where they would be treated by adsorption onto granulated <br /> activated carbon, or by combustion using catalytic oxidation. <br /> At this time, Levine-Fricke believes groundwater extraction wells installed in the A-zone at the <br /> downgradient boundary of Lincoln Center would be appropriate to minimize off-site migration of <br /> groundwater containing relatively high concentrations of detected Hazardous Substances. <br /> Conceptually, these wells would be designed to intercept and extract the contaminated groundwater <br /> at the downgradient boundary of Lincoln Center, using low pumping rates to minimize the radius <br /> of influence and potential mobilization of DNAPLs. A-zone aquifer testing will need to be <br /> performed and a groundwater flow model will need to be developed prior to designing this "low- <br /> flow" groundwater extraction system. The results of the aquifer testing and the groundwater flow <br /> modeling will be used to evaluate appropriate well spacing and pumping rates. Additionally, the <br /> groundwater extraction system will need to be designed to minimize the potential commingling of <br /> plumes from the Chevron and/or Exxon service station sites. <br /> Based on our current conceptual understanding of the Site, Levine-Fricke anticipates that mass <br /> removal of detected Hazardous Substances at or near source areas could be accomplished using <br /> groundwater extraction and/or air sparging wells. These wells could be located, for example, in <br /> the vicinity of sanitary sewer lines and/or the former dry cleaning facilities, and would provide <br /> mass removal in the A-zone in groundwater "hot spot" areas. In order to select the appropriate <br /> locations for such wells, the existing data must be supplemented with data from the source <br /> investigation and aquifer testing to be performed as part of the upcoming RI. Additionally, vapor <br /> extraction testing and air sparging testing will need to be performed to evaluate the effectiveness of <br /> air sparging at the Site, if air sparging is a recommended IRA. These data will allow Levine-Fricke <br /> to design a groundwater extraction/air sparging system that will minimize the potential to mobilize <br /> DNAPL in source areas, and provide the most effective mass removal in the source areas. <br /> Like the soil vapor treatment system, a groundwater treatment system would optimally be located <br /> near the groundwater extraction system, but could be placed a reasonable distance away to comply <br /> with applicable law and accommodate operations at Lincoln Center. <br /> SCHEDULE <br /> Given the need to collect additional Site-specific data, and in light of the requirements set forth in <br /> the First Final Consent Decree (FFCD) concerning IRAs, we anticipate that a groundwater IRA <br /> could be implemented at Lincoln Center by the summer of 1997. Section XI.A.4 of the FFCD sets <br /> forth specific procedures for proposing and implementing IRAs at the Site. These procedures <br /> include, for example, submittal of a "detailed plan" setting forth the proposed IRAs, a 45-day <br /> 3966-IRA.LTR:wkh 3 <br />