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12 August 1991 GeoAudit CV 30-34E2-1.6 Page 3 of 5 2. The presence of contaminated soil in all borings drilled to date indicates that the vadose zone contamination plume has a radius in excess of 40 feet (Figure 3) . The maximum lateral extent has not been determined. 3. The water.-bearing sand body at 40 feet appears to have sufficiently good hydraulic conductivity to permit the successful recovery of free product and/or dissolved contamination. 4. The water table has apparently dropped approximately 5 feet since 1938. When measured on 4 June 1991, the water table appeared to be essentially flat, although there may be a very slight gradient to the south. However, the presence of free product in MW-1 and MW-2 suggests that gasoline has migrated northeastward along the water table at least 25 feet from the 10,000-gallon tank. Gasoline may also have migrated southward, but not in sufficient quantities to form free product in MW-3. Northward migration of gasoline may be due to somewhat greater permeability to hydrocarbons in that direction. Alternatively, the contamination.in the..apparently up- gradient well. (MW-2) could be due„ to some . other source of contamination. 'north .of the tank cluster, such as the .dispenser area. 5. The total volume of free product cannot be accurately determined ~ until the average thickness and lateral extent of free product have been defined and the porosity of the soil has been measured. However, assuming that 1) the plume is cylindrical in shape and has a diameter of 80 feet and an average thickness of 4 inches (i.e. roughly bog of the measured thickness) , and 2) the effective porosity of the soil is approximately 30 %, between 3000 and 4000 gallons of product are estimated to be present. 6. The lateral extent of the dissolved contamination plume is probably m considerably larger than the lateral extent of free product. RECOMHENDATIONS Free product floating on the water table continuously introduces contaminants to the groundwater. We therefore recommend that the free product be recovered as soon as possible. The existing wells can be utilized as recovery wells. We have already discussed the required equipment and procedures with dim Hoblitzell of Falcon Energy, who will perform the extraction. The depth to ground water and/or.the interface between water and product should be measured to recheck the ground-water flow direcction. If flow to the south is confirmed, the possibility of an additional source of contamination should be addressed.