SITE INFORMATION AND CORRESPONDENCE

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Mr. Mike So *odward•C:yde Consuitants LOF Glass April 17, 1986 Page 2 hydraulic conductivity of 100 gal/day/ft2 and an area of contamination of 200 ft by 200 ft we estimate that a minimum of 10,000 gal/day of water would be required to raise the water table two feet in the immediate vicinity of the wells. The actual rise near the center of the spill area would be considerably less if at all. Raising the water table to ground level would likely require a quantity of water at least an order of magnitude greater than 10,000 gal/day. To raise the water table two feet over the entire area assuming no outflow (e.g. , an impermeable barrier around the contaminated area) it would require approximately 90,000 gal of water. Other problems involved with raising the water table include contamination of previously clean sediments, reduction of recoverable oil and foundation instability. Raising the water table above maximum natural levels, especially up to ground level, would transport the floating oil through clean sediments. A small amount of oil would adhere to soil particles which would not be removed by the following water table. This would act to continually reduce the quantity of free oil as would other processes such as oil becoming trapped in dead end pores and below lower permeability areas. Similar processes occur under declining water table conditions. The drop in water levels of one to two feet following last years spill apparently immobilized the majority of free oil until this year's heavy rains. Artificially, raising the water table two feet above the level present at the time of the spill would also be expected to immobilize the majority of the free oil. In the event the oil could be floated up to ground level, the sediments from a depth of 10 to 12 ft up to the surface would be contaminated. Surface contamination would have to be excavated and replaced with clean materials to avoid a health and safety hazard. The increased contaminated substrate would also pose a greater potential for percolating rain water to become contaminated and, in turn, contaminate the groundwater. A significant water table rise could also affect foundation stability by increasing the settling potential. Regarding Mr. Eckman's concern of a significant amount of oil being left in soil pores during water table depression, we concur that some oil will be left behind but we think that the amount at this time is minimal. During the initial water table decline after the spill some of the oil entering previously uncontaminated pores will adhere to the surrounding grains and some will become trapped. The following water table rise will refloat or remobilize the trapped oil but the adhered oil remains in the pores as residual contamination. The next time the water table drops either naturally or artificially, very little additional oil will adhere to the sediments and only the small portion that becomes trapped remains in the pores. Since the water table has already completed one cycle much less oil will be held in the pores during subsequent declines. What oil that does remain in the pores can be recovered next winter when the water table reaches the top of its natural range.