SITE INFORMATION AND CORRESPONDENCE_2006-2007

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&ARR ASSOCIATES Mr. Mark Adams August 8, 2006 Page 2 of 3 In addition to adding air/ozone sparging points beneath Benjamin Holt Drive, LPL also requests that additional sparging points be installed and operated to the east of the eastern edge of the currently proposed sparging wells (ie., east of MIP-12 and MIP-13). The additional eastern sparging points should extend the currently proposed sparging-point layout to address the entire source area associated with historical liquid waste leaks from the former Norge Cleaners. The high PCE concentrations to be targeted for remediation in the shallow groundwater zone within the expanded Historical Source Area(including the areas beneath Benjamin Holt Drive and eastward past the former Norge Cleaners sewer lateral), appear to have been derived primarily from liquid wastes emanating from the former Norge Cleaners (historically located just east of MIP-12). Norge Cleaners' former sewer lateral extended northward from the Norge, Cleaners building to the sewer line which runs westward on the south side of Benjamin Holt Drive. Site data indicate that liquid waste from the former Norge Cleaners leaked into the subsurface beneath the building and along the sewer lateral, and along the sewer line running along the south side of Benjamin Holt Drive. Because the local subsurface sediments appear to be horizontally bedded, leaks of liquid waste from the sewer line on the south side of Benjamin Holt Drive would be expected to spread in a symmetrical fashion, with nearly equal volumes of waste spreading both north and south of the sewer line. We believe this is why high PCE concentrations are found to the north of Benjamin Holt Drive, as reflected in the MIP and CPT data. There are no separate known or suspected sources of PCE in the vicinity of the currently targeted treatment area just north of Benjamin Holt Drive, and there is inadequate support for LFR's dashed/inferred delineation of the northern extent of the "Historical Source Area," which is shown on Figure 9 of the Phase IV IRA Plan to be coincident with the southern edge of Benjamin Holt Drive. Figure 9 should be revised to reflect the Historical Source Area extending beneath Benjamin Holt Drive, and as discussed above, the significant PCE source area beneath Benjamin Holt Drive should be addressed with the installation and operation of additional sparging points beneath Benjamin Holt Drive. Over a period of many years, the SVE system may have been fairly effective in treating the vadose zone sediments beneath Benjamin Holt Drive through the action of gaseous diffusion, which has aided in the transport of PCE from beneath the roadway to the SVE wells north and south of the roadway. In the case of shallow groundwater remediation, however, the diffusion of PCE will not be an effective transport mechanism due to the fact that aqueous diffusion in the saturated zone proceeds at approximately 1/10,000"the rate of gaseous diffusion in the vadose zone. Again, this is the reason that direct treatment of the PCE-contamination beneath Benjamin Holt Drive is required. As discussed in our July 12" meeting, LPL recommends that LCERT also consider installing and operating vertically staggered sparging points or dual-completion sparging wells in locations where the vertical extent of significant PCE contamination exceeds approximately 10 feet. The use of vertically-staggered air/ozone injection points will increase the effectiveness and efficiency of remediation by effecting a more complete and more uniform distribution of injected air/ozone throughout the targeted groundwater zone. Air/ozone injected through sparging points