Laserfiche WebLink
Draft Ground Water ROD Memorandum -4- 21 May 1992 <br /> DDRW, Sharpe <br /> completed, it is premature to state that all heavy metals contamination is present <br /> at background levels. <br /> Use of Older Data. The Draft Ground Water ROD is based on second quarter 1990 data. <br /> Our concern regarding use of older data was discussed in our 16 September 1991 <br /> letter on the review of the Draft FS Report. In our review of the Draft Final FS <br /> Report (letter dated 2 January 1992) , we concurred with Sharpe's commitment to use <br /> the most recent quarterly ground water monitoring data for the design of the <br /> remedial action. However, we question the use of two year old data because as <br /> presented in text, the ROD misrepresents current knowledge regarding plume extent <br /> and capture. The ROD should present the most current data and the text should be <br /> revised accordingly. <br /> Waste Solvent Tanks. Section 5.0 of the ROD summarizes the site characteristics. <br /> However, two waste solvent tanks (Tanks No. 29 and 52) were not investigated in the <br /> first phase of the UST investigation and may be potential sources of solvent ground <br /> water contamination. Additional investigation of these source areas is needed and <br /> may be readily incorporated into the investigations to be conducted for the Soils <br /> FS. If it is determined that ground water has been impacted from these waste <br /> solvent tanks, then additional ground water remediation for VOCs may be necessary as <br /> part of the Soils FS and ROD. <br /> Plumes 1 and 3. The ROD indicates that there are six TCE plumes. Based on the maps <br /> from the two quarterly monitoring reports (Second and Third Quarter 1991) , there <br /> appear to be, at the most, only five TCE plumes at the site. Plumes 1 and 3 may be <br /> one plume. Due to data gaps between the leading edge of Plume 1 and the up gradient <br /> edge of Plume 3, this issue has not been resolved. This observation regarding the <br /> plumes was one of our comments on the Draft RI Report (letter dated 21 March 1991) . <br /> This issue should be clarified as the presence of one or two plumes and the <br /> associated source areas will affect the remedial design. The ROD should state that <br /> additional data will be collected prior to the final design to resolve this issue. <br /> Contaminants of Concerns and Cleanup Levels. The contaminants of concern in the ROD <br /> are listed on page 23 of the ROD. The aquifer cleanup levels are listed in Table 8 <br /> (page 43) . In comparison of the two lists, it appears that for some of the <br /> contaminants of concern, aquifer cleanup levels were not proposed. These <br /> constituents include: bromodichloromethane, cis-1,2 dichloroethene, <br /> dichlorobenzene, trans-1,2 dichloroethene and 1 , 1,2 trichloroethane. It is unclear <br /> why the ROD did not specify the cleanup level for each constituent of concern. <br /> In addition, ethylbenzene was not listed as a constituent of concern in the ROD. <br /> However, ethylbenzene has been detected in some of the monitor wells, most recently <br /> in First Quarter 1992 (MW-408A) . Ethylbenzene is commonly associated with benzene, <br /> toluene and xylene as a petroleum-based contaminant. The ROD should include <br /> ethylbenzene as a constituent of concern, but only if benzene, xylene and toluene <br /> are also included. <br /> Bromacil Concentrations. Figure 11 presents the concentrations of bromacil in <br /> ground water in the shallow zone (A Zone) . The map depicts the contours extending <br /> off-site along the eastern boundary. It is unclear what data were used to indicate <br /> that the elevated concentrations are present off-site in an up gradient direction. <br /> The elevated concentrations of bromacil in this area may be associated with the <br />