Page 9 of the PAERAB's Spring 2011 Community Update Newsletter

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Close to ROD for Site 78? ( continued from p. 8)

Text Box: in vinyl chloride was occurring and, as a result, the risk assessment was revised to account for the higher levels of vinyl chloride. The revised risk assessment resulted in an increased calculated risk level for hypothetical future resident users. As indicated in comment response 1, in 2010 regular quarterly sampling was initiated by the Army despite delays in ROD approval, and these data indicate that the expected decrease in vinyl chloride concentrations is now occurring and data show a decreasing trend consistent with expected time-frames. The only data set that indicates a slightly increasing trend is 78-MW-001. However, concentrations in this well are all below the associated standard and recent 2010 data indicates concentrations are starting to decline. The only exceedances detected in recent sampling were for vinyl chloride at 78-MW-003 and 78-MW-006. As stated, these detections are now decreasing. Continued quarterly monitoring will be conducted and reported on a regular basis”. Mr. Putnam also questioned why a revised risk assessment was conducted in 2007? The Army responded to this inquiry with the following: “As noted in Section 2.8.1 of the ROD, a supplemental risk assessment was performed after the sodium lactate injection pilot study to reevaluate the risks associated with vinyl chloride in groundwater as temporal concentration increases of this compound were observed post injection. As noted

Text Box: in comment response 3 the revised risk assessment showed an increase in calculated risk levels”. Mr. Putnam submitted the following comment regarding the selection of an MNA remedy rather than an active remedy whose overall costs are only nominally higher: “5. Why was the MNA remedy (GW-2) (estimated time frame- 13 years) chosen over the (GW-4) potassium permanganate injection alternative (estimated time frame- 6 years) for a mere $45,000 cost difference”. The Army responded: “Injections of sodium lactate in 2006 removed essentially all of the parent compounds present at the site. As a result the primary compound to be addressed is vinyl chloride, a compound that degrades most effectively under aerobic rather than anaerobic conditions. Further, conducting chemical oxidation so close to Green Pond Brook and within a wetland area may have negative impacts on both the surface water body and wetlands for little additional benefit. MNA was recommended as the preferred remedy as injections to enhance the conditions of the aquifer would have little added effect to the now documented decreasing vinyl chloride trends. As such the selection of the MNA remedy was based upon its ability to adequately achieve each of the threshold and balancing criteria. Through this process it was determined that MNA could achieve the desired result within a reasonable timeframe and would be the most appropriate remedy. Regular monitoring of the groundwater

Text Box: to establish declining trends will be conducted and reported to DEP. Should declines not be demonstrated as expected then additional measures would be taken”. Finally, Mr. Putnam asked whether or not dioxane had been analyzed for: “6. Figure 3 shows that 1,1,1-TCA was detected in 2000 samples from P-78-GP-002 and 003. 1,4 Dioxane is often associated with releases of TCA. Were any groundwater and or surface water samples analyzed for Dioxane?” Mr. Putnam elaborated in an e-mail sent on June 9, 20011 that his concern was primarily for the possible presence of 1,4, Dioxane rather than Dioxin since they are two very different compounds. The Army responded as follows: “The 1,1,1 – TCA detections shown on Figure 3 were the only historic detections of this analyte. Both geoprobes had detections of 1,1,1-TCA well below the associated MCL of 200 ppb, but one (GP-78-003) was reported above the NJ Standard of 30 ppb. Permanent monitoring well 78-MW-001 is located in the direct vicinity of this data point and has been sampled on numerous occasions without any detection of 1,1,1-TCA, nor has the compound been reported in any other well. As there has been no detection of 1,1,1-TCA since 2000, and 1,4-Dioxane if present was typically a minor component, it is unlikely that the compound is present at the site and it was

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