U.S. EPA Contaminated Site Cleanup Information (CLU-IN)

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U.S. EPA Technology Innovation and Field Services Division

Search Result from the February 2009 Issue

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Lewis-Russ, A., R. Henning, D. Fenske, E. Hicks, J. Haramut, M. Goan, J. Perkins, and C. Bury. Proceedings of the Sixth International Conference on Remediation of Chlorinated and Recalcitrant Compounds (Monterey, CA; May 2008). Battelle Press, Columbus, OH. ISBN 1-57477-163-9, Abstract B-080, 2008

A pilot test in the upper Midwest was implemented to evaluate the applicability of hybrid poplars to ground-water withdrawal and to assess the degree of metals transport. The test site is located adjacent to a river that experiences diurnal fluctuations of up to one foot in elevation. The ground-water table is shallow (4 to 6 feet below ground surface) and contains elevated arsenic concentrations. The remedial method being considered for the site is ground-water containment using a cut-off wall that would surround the site. To avoid potential mounding of ground water within the containment wall, water must be removed, but previous experience indicates ex situ treatment would be difficult due to the site's chemistry. The design calls for ground-water removal via extraction by tree roots, with an engineered pumping system in reserve, if needed. For the pilot test, nearly one acre of poplars containing over 1,000 trees was planted in June 2006 using the trenching method. Ten piezometers were then installed and instrumented with transducers and dataloggers. Water level fluctuations in the river and precipitation data also were recorded. Initial data indicate a ground-water depression formed in the center of the tree plot. Also, diurnal fluctuations decreased abruptly in magnitude following the first hard freeze. These results provide evidence that the trees are affecting ground-water levels. The plot has been extended and monitoring continues. To evaluate translocation of arsenic, samples of leaves and other tree tissue were obtained from newly planted trees, existing trees on site, and associated soil and ground water. Information from the literature indicates that arsenic content of tissue is affected by soil concentrations, plant species, and time of year, as well as other factors. Tree tissue samples were obtained in the fall before leaf drop, as well as in July and August 2006. Analytical results indicate that arsenic concentrations are less than the site-specific soil background concentration of 6.3 m/kg; hence, movement of arsenic from ground water to the soil surface should not prevent use of trees for hydraulic control at this site.

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