In-Situ Measurement of TCE Degradation Using a Single-Well "Push-Pull" Test
Goal
The overall goal of this project is to further develop the single-well, push-pull test method for use in quantifying rates of anaerobic
microbial transformations of chlorinated aliphatic hydrocarbons (CAHs) such as trichloroethene (TCE) in groundwater aquifers.
Rationale
It is becoming increasingly apparent that in-situ testing methods will be required to fully understand microbial processes occurring
in the deep subsurface, especially in contaminated environments, which typically display steep geochemical gradients. The recently developed,
single-well, "push-pull" test method is a potentially powerful method for obtaining quantitative information about microbial metabolic activities
in groundwater aquifers. A push-pull test consists of the controlled injection of a prepared test solution into an aquifer followed by the
recovery of the test solution/groundwater mixture from the same location.
Approach
Microcosm experiments constructed with groundwater and sediment from a TCE-contaminated field site are used to select
combinations and concentrations of cometabolic substrates to use in field push-pull tests. Field push-pull tests are then conducted in wells
located in both pristine and TCE-contaminated portions of the field site to obtain in situ rates of introduced substrate transformation and TCE
degradation. In situ rates are compared with rates observed in microcosm experiments and with various geochemical indicators including
contaminant concentrations and concentrations of potential electron donors, electron acceptors, and metabolic products.
Status
Laboratory and microcosm experiments have been completed to identify appropriate cometabolic substrates for use in field push-pull
test measurements of reductive transformations of TCE. Laboratory microcosm experiments and field push-pull tests have been conducted to
study the transport and transformation behavior of a fluorinated analog for TCE, trichloroflouroethene (TCFE). In situ transformation rates of
TCE and TCFE have been quantified with and without the addition of exogenous electron donors. Laboratory microcosm and field push-pull
tests have been used to quantify spatial variability in gluocosidase activity and lipid-bound phosphate as indicators of microbial biomass and to
develop correlations between these parameters and measured rates of TCE and TCFE transformations.
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Last modified on: March 16, 2000.
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