TRACKING THE PROGRESS OF BIOAUGMENTATION IN THE REMEDIATION OF CHLORINATED ETHENES IN GROUNDWATER FROM FRACTURED ROCK USING STABLE ISOTOPES OF CARBON AND HYDROGEN, DISSOLVED GAS CONSTITUENTS, AND MICROBIAL COMMUNITIES

Bioaugmentation (BA) was used to accelerate the dechlorination of Trichloroethene (TCE) in groundwater at the Naval Air Warfare Center (NAWC), Trenton, NJ. In the BA experiment, an electron donor source with a microbial consortium known to degrade TCE and its degradation products under anaerobic conditions was injected into a well in fractured Triassic mudstone. Water enriched in deuterium was also injected as a tracer; allowing tracking of the movement of the BA solution and its dilution into background water to distances up to 41 meters from the injection well. The spatial distribution of δ²H in groundwater from monitoring wells was used to track groundwater movement along flow directions; and the elevated concentrations of H₂ gas, the enhanced electron donor, in comparison to pre-test conditions was used to indicate the presence of BA in the monitoring wells. The δ²H of water and the concentration of dissolved H₂ gas were more sensitive indicators of BA than the δ¹³C of TCE, cis-dichloroethene (cDCE), vinyl chloride (VC), and the abundance of the microbial communities. The combined evidence suggested that the effects of BA were detectable up to 15 m from the injection well, and to a lesser extent up to 26 m along the pathway which was monitored for more than a year after injection. The data showed that the sum of the molar chlorinated hydrocarbon ethene concentrations in post-BA water was higher than the sum of the pre-BA background molar chlorinated ethene concentrations in water from those wells where the biodegradation was stimulated intensively by BA. The concentration ratios of TCE/(cDCE+VC), the carbon isotope mass balance calculation of these compounds and the carbon isotope composition of the TCE indicated that the increase in molar chlorinated hydrocarbon ethene concentration might be the result of degradation of a less degraded TCE, that was possibly eluted from the rock matrix by the soy bean oil injected with the microbial consortium.