SITE INFORMATION AND CORRESPONDENCE_FILE 2

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Harold and Dena Knowles - NW 102 S. Wilson Way Page 2 of 3 GZA has interpreted the dissolved contaminant data to show that three distinct plumes are impacting your site, two of which appear to be coming onto your site from adjacent sites. GZA has requested that other parties be given the responsibility and ownership of those wells monitoring the dissolved MTBE plume. EHD cannot assign ownership and responsibility for wells to other parties, but can direct responsible parties to properly investigate, characterize and monitor their plumes. Exchange of well ownership, etc, must be worked out between the parties involved. At this time, EHD believes that the circumstances and data from your site make it unlikely that the MTBE plume is related to your release, however EHD has not been able to confidently identify the likely responsible party or parties, or the proportions contributed by each party to directly seek their assistance on this matter. To help EHD assist you in this matter, please have your consultant review the data from the three known sites in the area and, in the context of an overall site conceptual model (SCM), offer a professional opinion as to the source or sources of the MTBE and the proportions contributed by each. The model should show contaminant migration pathways consistent with the hydrogeological framework in the SCM and account for the observed contaminant mass distribution and migration history. The model should adequately demonstrate all your consultant's interpretations and opinions. Please submit this opinion and SCM to EHD by 03 January 2006. At this time it appears that monitoring well MW-15C demonstrates the vertical extent of COCs to be less than 110 to 120 feet below surface grade (bsg) in the down-gradient direction except for 1,2-DCA. EHD believes the data indicates that the primary source of the 1,2-DCA plume was on your site. Laboratory analysis of the grab groundwater samples from CB5 has shown that intensely impacted groundwater occurs at 74 feet bsg and at 88 feet bsg, moderately impacted groundwater at 114 feet bsg and less intensely impacted at 140 feet bsg. Groundwater in MW-13B and MW-16B, both screened 70 to 80 feet bsg is intensely impacted and no deeper wells are located in the source area. The data justifies installation of a deeper well in the source area, and the CPT1 data and MW-15C data indicated a depth of 110 to 120 feet bsg would be appropriate. Submit a work plan to install such a well in the source area to EHD by 01 November 2005. While the vertical extent of impacted groundwater in the source area is not clearly delineated, the high concentrations of contaminants indicates that interim remediation of the groundwater would be appropriate. Groundwater is intensely impacted to depths as great as 88 feet bsg (C135), indicating a column of intensely impacted groundwater at least 45 feet thick (recent depth to water approximately 43 feet). Dissolved contaminant concentrations are as high as 140,000 micrograms per liter (µg/1) TPH-g, 23,000 µg/I benzene and 1,200 pg/I