SITE INFORMATION AND CORRESPONDENCE_1993-2003

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.992 Annual Report Memorandum -2- 17 May 1993 )DRW, Sharpe 601/602 and total petroleum hydrocarbons (TPH) . Wells with historical detection of benzene, toluene and xylene (BTX) would also be tested semi- annually for EPA 602 compounds. Because the ground water is known to be contaminated with benzene, toluene, xylene and ethylbenzene (BTXEs) and because the fuel UST investigation is incomplete, semi-annual monitoring described above is unacceptable. Quarterly monitoring of wells in the area of the USTs that have had historical detections of BTXE should be conducted until the UST investigation is complete. Annual sampling of monitor wells for those wells that have historically shown non-detect for aromatic VOCs is acceptable. b. The Annual Report does not discuss the sampling or rational for testing for polychlorinated biphenyls (PCBs) , heavy metals or bromocil , even though testing for these contaminants are included in the monitoring program. A full explanation and description of the solid waste management unit (SWMU) or UST sites potentially responsible for the contamination should be provided. Proposed monitoring of contaminants not related to Operable Unit No. 1 (OU-1) monitoring should be integrated into the site-wide (OU-2) monitoring program which will be developed as part of the Draft Final Feasibility Study. The annual and semi-annual sampling frequencies proposed for PCBs and heavy metals are unacceptable because the investigations for the SWMUs and USTs are incomplete. Quarterly monitoring for those wells in the immediate area of SWMUs and USTs should be conducted. In general , and until the site-wide investigation is completed for all SWMUs and USTs, we recommend the following sampling criteria for frequency: • Quarterly monitoring for those wells that have had historical and confirmed detections of specific contaminants. • Semi-annual monitoring for wells that have had sporadic detections of contaminants and are down gradient of a potential source area. • Annual monitoring in all other monitor wells for potential contaminants. Well designated for monitoring the VOC plumes should continue to be monitored on a quarterly basis. DDRW, Sharpe should prepare a base map identifying all SWMUs, USTs, chemicals of concern and monitoring wells located in the vicinity of these areas. DDRW, Sharpe may continue testing the proposed wells for PCBs, heavy metals, and bromocil until the monitoring program for OU-2 is established. Page 6-1 states that wells with potential or previous high metals or PCB contamination will be placed on a quarterly schedule for these constituents. However, Appendix B, Proposed Monitoring Program, indicates that these wells will be sampled annually or semi-annually for these constituents. This discrepancy must be clarified.