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5. In Section 3 .4 . 3 . 1 (page 3-156) of the current Work Plan a <br /> reference to a domestic well located less than 200 feet east <br /> of LM-76 is made. This well is assumed to be the Rose well <br /> and was reportedly sampled by the Regional Water Quality <br /> Control Board (RWQCB) in November 1991. The results of the <br /> analyses reportedly indicated TCE concentrations above the <br /> Maximum Contaminant Level (MCL) . State the actual <br /> concentration for TCE and other contaminants of concern. <br /> State the analyses performed. State whether well <br /> construction and lithologic logs are available on this well. <br /> 6. In order to define groundwater migration in the vicinity of <br /> each Solid Waste Management Unit (SWMU) and Underground <br /> Storage Tank (UST) , a smaller scale and more detailed <br /> potentiometric surface definition is needed. Due to the <br /> great variability of the subsurface geology within the local <br /> site boundaries, the direction of groundwater flow is likely <br /> to be more variable than indicated in figures showing a <br /> single flow direction across the site to the north-northeast <br /> location. <br /> 7 . The draft work plan for abandonment of the onsite water <br /> supply wells has not, to the reviewer' s knowledge, been <br /> accepted in final form. The sequence of events in the <br /> abandonment of the water supply wells is still <br /> contradictory. Televideo logs will be run (prior to or <br /> after purging and sampling) . Also, the Field Sampling Plan <br /> (FSP) needs to address well purging prior to sampling. <br /> BACKGROUND CONCENTRATIONS <br /> 8 . Background concentrations of contaminants in both soil and <br /> groundwater, particularly metals and all classes of <br /> pesticides, are essential in the evaluation of the onsite <br /> data for risk assessment purposes. Background levels in <br /> soils have not been adequately profiled. A high degree of <br /> confidence in these background levels is necessary for <br /> interpretation of the onsite data, and is crucial in the <br /> development of an appropriate baseline risk assessment for <br /> the site. These background estimates might also be useful <br /> for volatile organic compounds (VOCs) and for semi-volatile <br /> organic compounds (SVOCs) . The alternative for risk <br /> assessment purposes would be to assume that background is <br /> below detectable limits or non-detect (ND) for each class of <br /> contaminants, when no background data is available. <br /> 9 . The description of the proposed approach to gathering <br /> background metals data in Section 3 . 8 of the Work Plan does <br /> not give sufficient information on the locations or method <br /> of analysis (i.e. filtered or total metals) for a <br /> determination to be made as to the adequacy of the approach. <br /> I-2 <br />