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SOURCE CONTROL BY HYDROLOGICAL ISOLATION: APPLICATION OF THE ANKENY MOAT
Citation:
Kaiser*, P. M., J T. Wilson*, AND J. Thacker. SOURCE CONTROL BY HYDROLOGICAL ISOLATION: APPLICATION OF THE ANKENY MOAT. Presented at 2004 LUST National Conference, New Orleans, LA, March 01 - 03, 2003.
Impact/Purpose:
To inform the public.
Description:
Treatment of NAPLs as source areas for plumes of contamination in ground water has proven problematic under certain regulatory programs. Under the EPA risk management paradigm, hydrological isolation of a fuel spill is a valid and acceptable alternative to treatment. A system of connected lateral drains placed in a highly conductive soil zone has been installed around a diesel spill to create a moat. The moat isolates the source zone from the flowing ground water by providing a preferred pathway for ground water flow. Water levels in the moat risers and wells in the source zone, up-gradient, and down-gradient are being monitored regularly to measure system performance on moving water through the moat and back into the surrounding aquifer. BTEX (benzene, toluene, ethylbenzene, and xylenes) and terminal electron acceptors are also being measured. The moat lowered the gradient through the source zone by approximately 40-5-%. Reducing the flow of ground water through the source zone reduced the biological electron acceptor demand in the ground water to degrade the contaminants. The moat is being tested at a diesel spill site. There are insufficient electron acceptors in the region of the plume near the source zone to degrade the BTEX. The moat also delivers fresh ground water to the plume down-gradient of the source. The concentration of the electron acceptors in the down-gradient region of the moat, measured in the southeast riser, are twice as high as the electron donors, 6.64 meq/L and 3.23 meq/L respectively.