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-Ai 0_ 0mom, PROBLEM ASSESSMENT REPORT Moore Petro[eun, Inc. 14800 N. Frontage Road, Manteca, CA RGA Project No. 10.90-479 Page 17 Examination of the tables of drawdowns generated by DREAM for both scenarios :indicate that tha modeled pumping rates could be maintained by the aquifer. Figure 8 shows ground water flowlines generated by DREAM for Scenario 1. Examination of Figure 8 indicates that this scenario would easily capture the interpreted extent of dissolved hydrocarbons and prevent further migration of the dissolved plume. Figure 9 is a contour map of ground-water travel times produced by pumping under Scenario 1. Figure 9 shows that while a significant portion of the dissolved plume would reach pumping wells MW-3 or MW-4 in less than 200 days, ground water located between MW-3 and MW-4 could require in excess of 400 days to reach either pumping well. Because of adsorption and desorption of hydrocarbon constituents ° by aquifer materials (particularly fine-grained sediments and organic material) , it is likely that petroleum constituents will migrate somewhat slower than ground water. A conservative estimate of the relative rate of movement of dissolved petroleum ; y constituents compared to the rate of.ground-water movement would probably be a ratio of about 1.5 to 1.0 (i.e. , petroleum constituents will migrate 1.5 times slower than ground water) . E A reasonable estimate of the total volume of water necessary to remove all dissolved hydrocarbons (assuming that hydrocarbons are not added to the ground-water system) would be on the order. of 3- r , 5 pore volumes of water (1 pore volume equaling the total volume of water contained within the dissolved hydrocarbon plume). From examination of Figure 9, it is likely that removal of 1 pore volume of water would require in excess of 400 days under scenario 1. In order to attempt to decrease the length of time needed for ground-water cleanup, Scenario 2 was modeled. Figure 10 shows that all ground water within the dissolved plume would still be captured under this scenario. Figure 11 shows a significant decrease in ground-water travel time necessary to remove 1 pore volume of water. Under this scenario, about 1 pore volume of ground water within the dissolved hydrocarbon p lu7Re would be removed in less than 300 days, a significant decrease as compared to Scenario 1. The small area located between NW-9 and MW-3 on Figure 11 that would require in excess of 300 days to reach MW-3 could likely be recovered faster by alternating pumping between MW-9 and MW-3. Under Scenario 2 a conservative estimate of the time required for removal of dissolved hydrocarbons would be on the order of 900-1500 days (3-5 pore volumes) . Treatment of ground water extracted under Scenario 2 would be by air stripping. Air stripping would be accomplished by bubbling air