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ISCO'S LONG-TERM IMPACT ON AQUIFER CONDITIONS AND MICROBIAL ACTIVITY (ABSTRACT)
Citation:
LUHRS, R. C., R. W. LEWIS, AND S. G. HULING. ISCO'S LONG-TERM IMPACT ON AQUIFER CONDITIONS AND MICROBIAL ACTIVITY (ABSTRACT). Presented at Battelle's Fifth International Conference on Remediation of Chlorinated and Recalcitrant Compounds, Monterey, CA, May 22 - 25, 2006.
Impact/Purpose:
To inform the public.
Description:
Permanganate has been successfully used in in-situ chemical oxidation (ISCO) to transform a wide range of organic contaminants under diverse geologic and geochemical conditions. Here, a critical analysis is presented of several technical issues commonly raised during in-situ chemical oxidation (ISCO) with permanganate including permeability reduction by MnO2(s), post-oxidation impact on biological natural attenuation, and variability in ground water contaminant concentrations. Pore filling of aquifer media from precipitation and accumulation of MnO2(s) appears to be an unlikely explanation of permeability reduction. Non-uniform accumulation of MnO2(s), injection of solids (KMnO4(s), MnO2(s), silicates), precipitation of KMnO4(s), and CO2(g) production also cause reductions in permeability. MnO4- is an antiseptic and will inhibit and/or kill microbiota at lower concentrations than used in ISCO. Non-ideal contact conditions at field-scale permit soil microbiota to survive rigorous applications of oxidant. The impact of the oxidant on microbial activity is temporary, localized near the injection areas, and given sufficient time after ISCO, the microbial populations, microbial activity, and the rate of biodegradation appears to increase, possibly to levels above pre-oxidation conditions. No known cases have been documented where aquifer material was sterilized or where microbial activity has been permanently inhibited. Unexpected increases in contaminant concentrations are not uncommon in ISCO and cause significant concern to the parties involved in the site remediation program. These unexpected concentrations result from various mechanisms including injection or mobilization of heavy metals, mobilization of organics, and contaminant rebound. The causes and implications of these mechanisms are discussed. This is an abstract of a proposed presentation and does not necessarily reflect EPA policy.