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Environmental Mr.Harlin Knoll %%00Resources 12 July 2000 Management Page 3 collected adjacent to the existing downgradient-most monitoring well at each tank location (HB-22 and HB-24). These samples will be used to demonstrate that impacts are not migrating to greater depths downgradient from the former tank sites. Each HydroPunch sample will be collected at a depth of approximately 40 feet bgs. Based on previous HydroPunch results, this depth is anticipated to be at or below the depth of dispersion of TPH-g and BTEX. The ground water samples will be analyzed for TPH-g by EPA Method 8015 and BTEX by EPA Method 8020. We believe that the collection of repeated samples at depth (i.e., using additional monitoring wells) to monitor changes in the vertical extent of the plume is unnecessary. As described above, the ground water impacts are greatest at shallow depths. Therefore, collection of samples from shallow monitoring wells will provide information on changes in the extent of the ground water plumes. As discussed in the underground Storage Tank Closure Report, the results of samples collected in these wells indicate that the concentration of TPH-g and BTEX are decreasing. Furthermore, analysis of biodegradation indicator compounds demonstrates that biodegradation of the plume is and will continue to occur. As part of the additional ground water sampling effort, a round of ground water samples will be collected in the existing monitoring wells at the site. The wells will be sampled for TPH-g and BTEX using the methods described previously. The results of these samples will be compared to the results of the numerous previous sampling events conducted at the site to evaluate changes in the concentrations of TPH-g and BTEX at each former tank site. We believe that the results of the deeper HydroPunch samples will sufficiently characterize the depth of impacts at each former tank site and that the HydroPunch samples will demonstrate that the concentrations of TPH-g and BTEX are much lower than the concentrations in shallow ground water. Finally, we believe that the results of ground water samples collected in the shallow monitoring wells will be consistent with the results of previous sampling events, indicating the plumes are stable or decreasing. If these are the results of the sampling activities proposed in this letter, an additional request for site closure will be submitted.