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INFLUENCE OF HETEROGENEITY ON EFFECTIVENESS OF ISCO TREATMENT: STEP 1
22nd Annual International Conference on Soil, Sediments, and Water
University of Massachusetts at Amherst
October 16-19, 2006
James Ewart*, N.A. Water Systems, Moon Township, PA
Philip T. Harte, U.S. Geological Survey, Pembroke, NH
Richard Goehlert, U.S. Environmental Protection Agency, Boston, MA
Thomas Andrews, NH Department of Environmental Services, Concord, NH
*presenting author
Abstract
Insitu chemical oxidation (ISCO) treatment can effectively destroy chlorinated solvents, such as tetracholoroethylene (PCE). Treatment effectiveness depends on the distributions of nonaqueous and aqueous-phase masses, stratigraphy, groundwater velocity, geochemistry, and adequate reaction time.
ISCO treatment was initiated in September 2003 at the Operable Unit 1 (OU1) of the Savage Superfund site in Milford , NH . The site has a large (0.5 mi 2 ) volatile organic compound (VOC; primarily PCE) plume. Remediation of OU1 began in 1998 by installing a slurry wall through glaciofluvial deposits surrounding suspected source areas. Among these sources is a former drain and pit area, now targeted by a test well field (INEEL well field). The ISCO treatment injected 8,500 pounds of permanganate in an active flow scheme using two injection and two extraction wells in the INEEL well field. The ISCO test was tracked for reactants and reaction byproducts for over 1 year.
Estimated amounts of PCE destroyed ranged from 5 to 300 times preinjection aqueous-phase concentrations, indicating that the bulk of the oxidized VOCs were in nonaqueous phases prior to the injection. The higher rates were in areas of low preinjection concentrations, indicating that nonaqueous VOCs were probably more susceptible to oxidation than those in areas of greater concentration. Permanganate persisted more than 1 year in selected areas, which helped suppress aqueous phase concentrations of VOCs.
A primary factor affecting the persistence of permanganate was convective mass transport. Extraction well pumping induced transport along a northeasterly sloping basal stratigraphic contact between a permeable coarse sand layer and a less permeable basal till layer. This contact had the highest initial dissolved VOC concentrations suggesting a likely DNAPL source. Although, the DNAPL position is affected by the contrasts in vertical permeability between the coarse sand and basal till, the permanganate transport is affected by the lateral transport in the coarse sand layer.
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