SITE INFORMATION AND CORRESPONDENCE FILE 1

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620 Charter Way Page 2 of 3 • Groundwater samples collected at 80.5, 84, and 97 feet bsg were non-detect for the constituents-of-concern in borehole CPT-5; however, high concentrations of gasoline constituents were detected in a groundwater sample collected at 91 feet bsg. Therefore, groundwater data collected in boreholes CPT-10 and CPT-11 at 71, 73, 77, and 81 feet bsg do not necessarily demonstrate the vertical extent of contamination at this site. • Groundwater levels have been above the screen intervals in MW-10 since August 1996, and above the screen intervals of MW-1 and MW-5 since February 1998. The remaining monitoring wells have historically had the groundwater levels above the screen intervals during May 1998 through August 2002. Groundwater data collected during these times of high groundwater elevation may not be entirely representative of contamination concentrations present in the screened portion of the aquifer if groundwater in the well casings has not been properly purged prior to sampling, and/or the groundwater samples have not been collected within the screen intervals. Further investigation will be necessary to assess the lateral extent of impacted soil and groundwater at this site. Please submit the report of findings from the recent advancement of the two CPT borings in the context of a site conceptual model (SCM) that incorporates findings from all eleven CPT borings. The SCM can then be used as a tool for future site investigation. The-general purposes for an SCM are to demonstrate where the contaminants came from, where they are at the present time, how they move through the subsurface, how they will respond to changes in the groundwater flow characteristics or to potential remediation efforts, what the contaminants' ultimate environmental fate will be, and to help evaluate the risk posed by the contaminants to groundwater supplies and sensitive receptors. In addition, the SCM may demonstrate data gaps, thereby illustrating where additional investigation is needed. To be sure that the SCM will adequately address the assessment, remediation and, ultimately, final closure requirements for this site,please include the following, as appropriate, in the SCM: • Local and regional plan view maps with sources, boring and monitoring well locations, lines of cross section, extent of contaminants in each media, direction and rate of groundwater flow, and receptor locations,including water supply wells within 2,000 feet of the site • Cross sections showing subsurface geological features, depth to groundwater, man-made conduits, monitoring well construction and the interpreted vertical extent of soil and groundwater contamination • Cross-plots of key chemical concentrations verses time for representative wells that demonstrate significant contaminant concentration trends • Summary tables of contaminant concentrations in the different media • Well and boring logs • Narrative description of the SCM that describes controls on contaminant distribution; contaminant migration mechanisms, pathways and rates; plume disposition over time; and sorbed and dissolved contaminant masses.