SITE INFORMATION AND CORRESPONDENCE

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Mr. Maurice Benson* March 4, 2010 Page 2 SWMU 33. The TCE tank, steam cleaner, and cleaning tank were removed prior to April 1992. Previous soil removal actions at SWMU 20 and SWMU 33 between 1997 and 1999 included removal of sumps, disposal of 332 cubic yards of contaminated soil, and in-place abandonment (grouting) of sections of the IWPL, along with implementing institutional controls to prevent impacts to the remedy. The planned demolition of Warehouse 10 in 2007 prompted the U.S. Army Corps of Engineers to conduct further site remedial investigations to assess the impacts to construction workers and evaluate soil disposal options. Analytical soil data from the 2007 investigation showed TCE concentrations up to 260 micrograms per kilogram, indicating that a persistent source still remained beneath the foundation. Further investigation of SWMU 20 was conducted in 2008 by additional CPT work and with installation of a groundwater monitoring well. CPT fieldwork efforts helped delineate the lateral and vertical extents of contamination in soil gas and groundwater, with results showing the highest concentration of 32.8 micrograms per liter (pg/L) at CP0851. Monitoring well LM193AU-NS was installed in the core of the groundwater plume beneath the SWMU 20 foundation in March 2009 and was sampled twice, 1Q09 and 2Q09. TCE concentrations in LM193AU-NS measured 73.1J+ pg/L and 104 pg/L, respectively, for the two quarters before the well was destroyed during demolition activities at the Warehouse. SVE Design The design specifies nine vapor extraction wells and five vapor monitoring well locations. The VEs are to be installed using pneumatic fracturing techniques to enhance preferential pathways in unsaturated soil, thus aiding mass removal. Extraction wells are to be constructed with a 4-inch diameter schedule 40 polyvinyl chloride (PVC) casing with a planned radius of influence of 40-feet (ft). Vapor extraction wells will be screened from 6 ft below ground surface (bgs) to 16 ft bgs. Two vapor monitoring points will be installed at each monitoring well with 6-inch screens planned at seven (7) and fifteen (15) ft bgs. Vapor monitoring wells will be located approximately 30-80 ft from the associated extraction wells. Based on pilot study results from 1999, SVE system's capacity is inferred to have a maximum flowrate of approximately 350 standard cubic feet per minute operating at or above 5.5 inches of mercury vacuum. System operation is anticipated for two years, followed by optimization efforts to meet the cleanup goal for TCE of 350 parts per billion volume.