SITE INFORMATION AND CORRESPONDENCE_1993-1996

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LEOVINE • FRICKE ENGINEERS,HYDROGEOLOGISTS&APPLIED SCIENTISTS as DNAPL or high concentrations of detected Hazardous Substances that could act as ongoing sources to groundwater. Based on the volatile nature of the detected Hazardous Substances, the desire to minimize impacts to operations at Lincoln Center and the findings of the source investigation, we anticipate that soil IRAs could conceptually include soil-vapor extraction(SVE) and treatment. Vapors would be recovered by applying a vacuum to wells screened in the vadose zone to volatilize the detected Hazardous Substances from subsurface soils. Extracted vapors would be conveyed to a centralized process area where they would be treated by adsorption onto granulated activated carbon, or by combustion using catalytic oxidation. We anticipate that the SVE wells would be located in the vicinity of sanitary sewer lines and the former dry cleaning facilities. The exact locations of SVE wells would be contingent upon the findings of the source investigation, which includes extensive soil-gas sampling and analysis, cone penetration testing (CPT) to evaluate vadose zone lithology, and follow-up soil borings and soil sampling and analysis. As required by the Federal Court, the SVE wells would also be located, to the maximum extent practicable, so as to not interfere with operations at Lincoln Center. The accompanying soil-vapor treatment unit would optimally be located near the soil-vapor extraction wells, but could be placed a reasonable distance away to comply with applicable law and to accommodate operations at Lincoln Center. GROUNDWATER INTERIM REMEDIAL ACTIONS Based upon our evaluation of existing groundwater analytical data, Levine-Fricke is recommending the implementation of groundwater IRAs in the A zone at Lincoln Center. The existing groundwater monitoring data indicate the presence of relatively high concentrations of detected Hazardous Substances in A-zone groundwater monitoring wells (MW-4, 6, 7 and 11). Concentrations of PCE detected in groundwater samples collected from monitoring well MW-11 (located near the downgradient boundary of Lincoln Center) during the November 1995 and February 1996 sampling events were significantly higher than PCE concentrations detected in samples from MW-11 during previous sampling events. These data may indicate active movement of high concentrations of PCE in A-zone groundwater in this downgradient area at Lincoln Center. Levine-Fricke is currently contemplating two types of groundwater IRAs, one to minimize the off- site migration of A-zone groundwater containing relatively high concentrations of detected Hazardous Substances, and a second to provide mass removal of detected Hazardous Substances in A-zone groundwater at or near source areas at Lincoln Center. We anticipate that groundwater IRAs would likely consist of groundwater extraction and treatment, and possibly air sparging with soil-vapor treatment. Conceptually, groundwater extraction at the Site would use a series of wells screened in the A-zone to extract contaminated groundwater, and the water would be conveyed through pipelines to a centralized treatment unit. Treatment for groundwater containing detected Hazardous Substances could include, for example, adsorption onto granulated activated carbon, air stripping, or ultraviolet (UV) oxidation. Air sparging would use wells screened beneath the water 3966-IRA.LTR:wkh 2