TCE plume management through edible oil injection and natural attenuation

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Two pilot-scale edible oil barriers were constructed in the upper portion of a 1,500 m long chlorinated solvent plume at Dover Air Force Base (AFB), DE. Edible soybean oil was injected into two 6.1 m-long barriers with monitoring wells spaced up to 4.6 m downgradient. Barrier 1 was treated by low pressure, direct injection of soybean oil into ten wells spaced 0.6 m apart. After eight months, a coarse emulsion was injected to increase the vertical and horizontal distribution of soybean oil. In Barrier 2, an emulsion of soybean oil and lecithin was injected under low pressure into four wells spaced 1.5 m apart. In both barriers, the injected edible oils have continued to release dissolved organic carbon (DOC) thirty-nine months after the initial injection with between 280 and 1,600 mg/L DOC found in injection wells of the two barriers. Before injection of the soybean oil, daughter products made up on average 34% of the total chlorinated ethenes and ethanes on a micromolar basis in Barrier 1. The daughter compounds increased to as much as 86.3% of total chlorinated ethenes and ethanes after 22 months. After 39 months, the daughter products represented an average of 78%. In Barrier 2, parent compounds initially represented an average of 55% of the chlorinated ethenes and ethanes. A maximum average of 77% percent daughter compounds was achieved after 9 months. Although little of the chlorinated ethenes and ethanes have been completely degraded, the edible oil in both barriers has been effective in supporting partial dechlorination of the parent compounds to daughter products which are then being degraded in the downgradient aerobic zone. Thus Dover AFB will be able to overall effectively remediate the site to target levels, without the need of reaching complete end products in the active treatment area. The emulsion barrier has recently been expanded.

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