SITE INFORMATION AND CORRESPONDENCE

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FEB 2b '95 04:38PM CLEgRWRTER GROUP CLEARWATER c R 0 LT P, I ra C:. In order to ensure that the most appropriate means Of Site remediation had been recommended, Clearwater reviewed the information presented in all applicable pro}ect doour ents. 'I"v-results of this review were discussed with the PHSIEHD on September 14, 1994, and are listed as follows: + The moet significant area of hydrocarbon contamination was detected in samples collected from borings drilled in the vicinity of the farmer dispenser island. While field readings indicated the presence of contamination in the 12.5 - 41.5 foot interval in this portion of the site, no soil samples were forwarded 'to the project lab for analysis, •. VW-2 had been completed near, but not within, the area of contaminated soil (as evidenced by lab data). VLA-2 was screened from 20 - 50 feet bgs, almost 10 feet below'the area of highest documented concentrations of gasoline compounds. VW-2 was, not constructed in a manner that would facilitate the recovery of hydrocarbons from the fine-grained unit noted to be present at 40 feet bgs, as the screened interval extended into the coarse-grained materials above ,this depth (which would result in preferential extraction from the upper unit, with little or no extraction from the fine-grained sediments at depth). ,Additionally, VW-2- was completed in the tank backfill, and the possibility of a "short circuit" in the vapor extraction system as a result of vapors seeking the path of least resistance (thiough 'the backfill to the screen, as opposed to through native soil to the screen) waa very real. While the analysis,af vapor samples collected during the test on ;IVY-2 indicated the recovery of gasoline hydrocarbons, the location and construction of the well were seen to marginalize the utility of this well in terms of remedial effectiveness. • VW-1 was completed in an area that had been shown, by tank floor and soil boring samples, to be free of hydrocarbon contamination. The benefits associated with the incorporation of this well into the remedial plan were seen to be questionable. + VW-3 was completed in the vicinity of the portion of the former tankfield that had been shown., through the collection and analysis of excavation floor samples, : to contain moderate concentrations of gasoline constituents. ' The fact that the sample collected from 15.5 feet bgs in the boring for VW-3 contained gasoline constituents, albeit in very low concentrations, supports the assertion that soils in this area of the site may contain concentrations of gasoline constituents. it was considered unfortunate that the screened interval of this well was not extended into the soils that were shown to contain the highest concentrations of hydrocarbons (screened interval begins at 20-feet bgs). • Based on the-facts presented above, Clearwater recommended the installation of a pair of additional vapor extraction wells (VW-4 and VW-5). The wells were proposed for installation in the immediate vicinity of the most contaminated area. VW-4 was proposed to be completed at 40 feet bgs, and screened from 10-40 feet; VW-5 was proposed to be completed at 50 feet bgs, and screened from 3