SITE INFORMATION AND CORRESPONDENCE

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Mr. Welch 2 '11 July 1996 procedures. The field logs for well purging show that the depth to water as measured with the socks in place was used to calculate total water column height and purge volume. Given that the socks must displace a significant volume of water in a shallow,small-diameter well with a 104ell screen, we believe that it might be more logical to re-measure depth to water for purging purposes following sock removal and allowing the water level to stabilize (in effect,a slug test). Using the original depth to water measurements leads to purging a greater volume of water from the well not necessarily an undesirable situation,especially when purging with a bailer—but it also may lead to erroneous conclusions regarding amount of actual water level rise and may make comparisons difficult between wells and with conditions before placement of the socks. Addition of MTBE to site monitoring_ Based on the widespread use of methyl tert-butyl ether (MTBE) as a fuel additive and on the reported storage of additives at the Banta terminal, we request that future sampling events include routine monitoring and confirmation for MTBE. MTBE may be analyzed for by USEPA Method 8020, appearing in the C5 range, but requires- confirmation by USEPA Method 8260. This request is being made for all of the Board's active hydrocarbon investigation sites. Please review your past analyses to determine if MTBE has been present,but not reported. Monitoring for dissolved lead: MRP Order 95-802 requires quarterly monitoring for dissolved lead in those wells which have not previously been sampled for lead. If lead is detected, verification sampling shall be performed within 30 days of submittal of the report. Continued quarterly monitoring for lead will be necessary only if lead is confirmed.The MRP requires that MW-3 shall be sampled for dissolved lead once free product has been removed. We suggest that, instead of filtering the samples in the field--a method that may allow colloidal particles carrying lead to pass through--the samplers instruct the lab to centrifuge the samples before analysis, and analyze only the supernatant. This procedure provides greater assurance that only dissolved materials are being analyzed and probably is less expensive than the additional field handling. Proposed additional monitoring parameters for biological activity SECOR states in the 6 May 1996 letter report that hydrocarbon-oxidizing microbial activity will be monitored during future quarterly monitoring events. They do not state how this will be done. This monitoring, accompanied by monitoring of carbon dioxide levels, is proposed for well MW-3, which contains ORC socks and is the well with the highest hydrocarbon concentrations, and for MW-5,which has no socks and is the well with historically the lowest concentrations. Staff requests that at a minimum, all the wells with socks be monitored. Need for consideration of alternative or additional remedial measures: The effectiveness of the ORC socks is undemonstrated. Continued use of the socks and more definitive monitoring for effectiveness, with inclusion of additional parameters to indicate microbial presence and activity, may provide more favorable results,especially if the conditions of rising ground water levels change. Staff considers,however,that SECOR and Tower Park should begin to examine alternative passive or active measures. SECOR has suggested the possibility of pursuing a risk- based corrective action (RBCA) approach to this site. Staff is willing to consider such a proposal, but based on present site conditions and existing policy, a risk-based approach must consider impacts to environment and beneficial uses of the water as well as human health.