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•-� 4` IT CORPORATION Mr. J.JKell Williamson Kelly Kayo Oil Company April 18, 1985 Page 3 volume to the assumed concentration of hydrocarbons (sum of xylene, benzene and toluene) in the soil . The concentration of hydrocarbons is the parameter with the greatest uncertainty, since only a few concentra- tions are known for each site. Therefore, the amount of product in the soil at any particular site will tend to be overstated, especially if the volume of soil involved is large. rhe graph shows hypothetical volumes of 20,000 and 40,000 cubic feet of contaminated soil. Dote that a small difference in the assumed concentration of hydrocarbons will dramatically effect the predicted volume cf hydrocarbons present. The ' larger the volume of soil involved, the more dramatic this relationship will be. REMEDIAL ALTERNATIVES i The majority of contamination is too dee for excavation to be cost- effective, especially since some contamin tion appears to exist below both highways adjacent to the station. S nce the water table has been found with free hydrocarbon present, a pum ed recovery system is appro- priate for preventing the further spread of the plume and recovering contaminated- water from under the site. There does not appear to be sufficient gasoline in the sails to require a second pump for skimming gasoline from the recovery well . If gasoline accumulates in the recov- ery well , it can be removed via manual pumping. We have preliminary ; data that indicates that there are bacter 4 la in the soil that will con- sume petroleum hydrocarbons. These bacteria could be stimulated by recirculating the water into the tank backfill and adding appropriate amounts of oxygen, phosphorous, and nitrogen to the water. RECOMEN0ATION i The tank inlets should be equipped with spill prevention devices to prevent the further introduction of hydrocarbons into the subsurface. IT Corporation recommends that a recovery well be installed between monitor wells MW-6 and MW-7 and a cone of depression established under the site that will prevent the further spread of contamination. Three additional monitor wells should be installed in the locations shown in Figure 5. The well adjacent to the tanks will verify that the contami- nation is moving straight down. The two wells in the adjacent highways will verify that the plume has not migrated a significant distance beyond the edge of the station property. The estimated cost for construction of the recovery well and the associ- ated .water handling system is $63,000, assuming that the water can be _discharged to a sanitary sewer. If a surface discharge permit is required, the cost of the water treatment (carbon adsorption) system is estimated to be $57.,000. If biostimulati n is added to the system, the ,additional start-up costs are estimated to be $60,000. W 1 +