SITE INFORMATION AND CORRESPONDENCE

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Mr. Welch 2 6 November 1996 addition,concentrations of tph-d in MW-5 have increased from non-detect in December 1995 (and all sampling rounds prior to that) to 100µ/L in the September 1996 round. Concerns raised by these results: 1. Possibility of a new release: Staff acknowledges that except for the concentrations in MW-3, the figures are low. Staff has previously expressed concern that the presence of tph-d in MW-5 suggests that the full extent of the dissolved plume and/or soil residual is not yet known.MW-5 is the most distant well from MW-3 and is not downgradient of it or of any other impacted well. Combining this observation with the increases in dissolved and free product in MW-3 and the fluctuating results in other wells raises concern that an additional release may have occurred. To address this concern, staff presently requests only continued monitoring in all wells. But if concentrations do not drop or stabilize within a round or two, some additional site investigation or, at minimum, submittal of product inventory records, will be requested. 2. Gasoline and BTEX components in MW-3: Staff acknowledges that Superior laboratories stated that the chromatograms for the tph-g in MW-3 did not resemble a gasoline pattern. The monitoring reports attributed this result to the presence of diesel in MW-3. But,though benzene has not been reported from MW-3 for several sampling rounds, other gasoline components, including ethylbenzene and xylene, have been detected. Presence of these components, and absence of benzene and toluene is consistent with weathered gasoline. The reported proportions are such that might be expected from a weathered gasoline plume rather than diesel. The BTEX components, all within the C6 range, occur only as minor components of diesel, which dominantly comprises components in the C12-C18 range. Based on this concern, staff requests submittal of the chromatograms in question. Staff further requests that a sample be taken of the free product and an analysis be done. Staff understands that analysis can be accomplished even with only a very small sample of the product, taken in a capillary tube, even if there is only a small fraction of an inch of product. Please submit this analysis, and the chromatograms, with the next monitoring report. OTHER ISSUES: Skimmer in MW-3: Staff concurs with SECOR's recommendation that the free product skimmer be reinstalled in MW-3. Monitoring for MTBE: SECOR's 14 August 1996 letter stated that analyses for Methyl-tert-Butyl Ether(MTBE)will be performed as requested by Board staff during the third quarter sampling round. This was not done. Staff again requests that samples from all the wells be analyzed for MTBE. If USEPA method 8020 is used and negative results are obtained,further analysis will not be required except in the case of an apparent change in site conditions. If positive results in the 20 to 50 ppb range are obtained, SECOR and Westrec may wish to confirm at least one sample,using USEPA Method 8260. Positive results will be considered indicative of a gasoline release at the site.