SITE INFORMATION AND CORRESPONDENCE_1988-1991

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i • Oxidation Pond Conversion -2- 18 December 1990 Sharpe Site concentrations to laterally and vertically characterize the unsaturated zoneprior to the proposed conversion. The lateral locations were selected based on the boring locations that had previously shown the highest concentrations of heavy me als and heavy oils. Two borings will be installed at the northern end of the pond iear the inlet (locations J and K) , one boring will be installed in the central portion (location N) and one boring at the southern end of the pond (location T) , Two soil samples will be collected from each boring to provide the vertical characterization of the residual waste concentrations. One soil sample is to be collected within the upper foot and the other is to be collected within two feet of the current ground water table. The waste constituents of concern for the soluble analyses are the heavy metals of arsenic, barium, cadmium, chromium, lead, vanadium and zinc and heavy oils, specifically lubricating oils (Method 8015 Modified), total petroleum hydrocarbons (TPH) and oil and grease (0&G) . The specific heavy metals were selected baseo on the 1988 and 1990 total concentrations which showed elevated concentrations Of these constituents above background concentrations. VOCs were not considered for Onalysis because they had previously not been detected within soil samples collected wi hin the pond soil samples. The soil samples need to be analyzed for soluble concentrations to determine whether the waste constituents pose a threat to water quality. T e Waste Extraction Test (WET) , using either dilute citric acid or dionized water as the extraction solution, was discussed. A citric acid extraction solution is used when there are acidic conditions. It was decided that the citric acid would be used for the WET. Potential remedial measures were discussed. The method of cleanup of the oxidation ponds will be determined based on the analytical results of the soluble analy es. If it is determined that there are soluble residual waste constituents in the uns turated zone, then excavation of the "hot-spot" areas within the oxidation pond, conf rmation sampling and backfilling may be needed as a remedial measure prior to the pond conversion. Bioremediation was also considered as a remedial measure for cleanup, but may not be a viable alternative because of the metals concentrations. If the analytical results of the soluble analyses indicate that the waste constituents are not soluble and the concentrations are at background levels, then the pond conversion may proceed without any remedial measures because it will have been determined hat the residual soil contamination does not present a threat to water quality. Because the storm water retention basin will not have a five foot separation between the base of the pond and the highest known ground water level and because the total concentrations of the residual waste constituents indicate that there m y be a potential threat to water quality, it was decided that a soil bentonite liner flay need to be installed in the storm water retention basin. Although a sample from the first major storm event of the wet season is preferred, Sharpe plans to collect a sample of the storm water runnoff from this season as a preliminary waste character izati on. The storm water runoff should be analyzed for VOCs, Title 22 metals, Modified 8015, TPH and 0&G. If the waste characterization indicates that the storm water runoff is a waste then the structure would need meet the classification and siting criteri under Sections 2510, 2530 and 2540 of Chapter 15. If it is determined that the sto m water runoff is not a waste, then the land disposal criteria under Chapter 15 would not be applicable because the runoff would not represent a threat to water quality. The design of the storm water retention basin is to be based on a 100 year flooc event. Sharpe indicated that they would prefer a 70 percent expansion of the current o idation