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Mr. John Kiel -2- 27 August 1992 <br /> resurveyed using an established permanent benchmark referenced from mean <br /> sea level . If this was not done for the new wells they should also be <br /> resurveyed. <br /> 5. Page 5 states periodic measurement of ground water levels will be <br /> conducted. However, no frequency was specified. If ground water <br /> elevations are unavailable or if local ground water flow direction has <br /> not been established from the existing MWs, then monthly ground water <br /> elevations should be taken to determine the effects of other wells <br /> pumping in the area. <br /> 6. Page 5 also states that ground water samples provide a method to <br /> evaluate water quality and investigate potential migration from sources <br /> other than the known oil spill . We request that in addition to imple- <br /> menting a ground water monitoring program, LOF submit a report on site <br /> operations and history which could identify if there are other potential <br /> source areas. <br /> 7. Page 6 states that among the soil samples to be taken at each borehole, <br /> one sample will be used for field screening using a portable organic <br /> vapor analyzer (OVA) . We recommend that OVA screening be conducted in <br /> accordance with the headspace analysis method to minimize the loss of <br /> volatile compounds. <br /> 8. Page 6 also specifies the monitoring well design. The latter may be <br /> appropriate for the onsite subsurface conditions. However, the actual <br /> design of each well should be based on site specific conditions at each <br /> well location and not pre-engineered offsite. <br /> Your 12 August 1992 letter provided an update and some sample results, but did <br /> not specify a completion and submittal date for the full site assessment <br /> report including boring logs and well installation details. That letter also <br /> requested our approval to backfill the excavation. Following are our comments <br /> on the 12 August 1992 update: <br /> 1. The letter does not specify which of the existing wells were redevel- <br /> oped, how many soil borings were drilled and soils samples taken, and <br /> why only two MWs were installed when the work plan proposed three. <br /> 2. The letter states a small localized area of discolored soil at the <br /> excavation bottom has developed. However, page 2 of the work plan <br /> states that the excavation was deepened to approximately 12 feet where <br /> ground water was encountered. Please clarify this discrepancy. <br /> 3. The letter proposes removal of the discolored soil until the area is a <br /> determined to be clean via visual observation and via an OVA. We recom- <br /> mend that excavation be continued beyond the water table if saturated <br /> soils also are contaminated. Excavating below the water table would <br /> indicate if there is free product on the ground water. If there is, <br /> free product should be recovered prior to backfilling. Removal of free <br /> product would facilitate future remediation efforts. <br /> 5. The letter states backfilling of the excavation is justified because a <br /> majority of the impacted soil has been removed, the existing excavation <br />