SITE INFORMATION AND CORRESPONDENCE_1988-1991

Home Browse Search

Ground Water FS Report -2- 16 September 1991 DDRW, Sharpe Site installation of the extraction wells near MW-505A, MW-407C and MW-524C. The existing and proposed extraction systems need to be reevaluated and a revised design for the extraction systems needs to be presented, showing complete plume capture, for the final remedial action for ground water. The Board continues to advocate reclamation/recharge over surface water discharge for the disposal of the treated ground water. We commend Sharpe on the existing reuse of the treated ground water. However, as presented in the Draft FS Report and as was discussed in the August 1991 Project Manager's Meeting, disposal of the treated ground water appears to be a critical factor in the selection of the final remedial action. It is the Board's position that the impacts of disposal to land of treated ground water, with elevated concentrations of any inorganics, must be mitigated to protect the beneficial uses of the ground water. The presence of inorganics in the treated ground water impacts the selection of the disposal alternatives. The ground water may have to be treated for inorganics prior to disposal . Another major concern is that the Draft Ground Water FS Report documents that the plumes at the Sharpe Site have not yet been completely defined. In particular, the vertical extent of Plumes 1, 4&5 and 7&8 have concentrations of VOCs from the deepest monitor wells in well cluster that exceed 50 micrograms per liter (µg/1 ) . Additional monitor wells need to be installed not only to completely define the extent of the plumes, but to verify the effectiveness of the final remedial design for ground water. These additional wells must be installed prior to selection of the final remedial design. This was an outstanding issue in the Final RI Report. Listed below is a summary of my technical concerns. These concerns must be addressed in the Final Ground Water FS Report. If the final remedial design for ground water contains the same proposals for the extraction system and does not include proposals for additional monitor well installations, I recommend that we do not approve of the final remedial design. SUMMARY OF TECHNICAL CONCERNS DATA EVALUATION 1. Section 1 of the Draft FS Report presents evaluations for each plume based on the second quarter 1990. These data are now over a year old. Prior to the final remedial design for ground water, Sharpe needs to update the plume maps and concentration contour cross-sections with the most recent data. The final remedial design needs to be based on current data, accounting for historical trends, rather than on older data. 2. The elevated concentrations of arsenic above 50 µg/l , the Primary Drinking Water Standard (DWS) primarily occurs in the upper portion of the aquifer. The average concentration of arsenic in the Central Area is 58 mg/l . The Draft FS Report did not indicate whether or not the tendency for higher concentrations of arsenic in the Central Area may be due to waste disposal in soil waste management units (WMUs) . The Report should clarify any previous findings on the relationship between the elevated arsenic concentrations in ground water and WMUs. In addition, the potential impacts to ground water from WMUs, (by both inorganic and organic constituents) will need to be presented in the Soils FS Report. The final remedial action for soils for each WMU needs to be determined through an