No site characteristics were provided in the references abstract.
Targeted Environmental Media:
 Dense Non-aqueous Phase Liquids (DNAPLs) - Fractured Bedrock
1,2-Dichloroethene, Tetrachloroethene, Carbon Tetrachloride, and other contaminants were stored at a disposal site and improper drum storage resulted in the accumulation of DNAPLs within the fractured rock aquifer. A sulfur stockpile and sulfuric acid spill and seepage from adjacent slime dams resulted in a soluble chlorinated hydrocarbon contaminant plume with a pH less than 4 and sulfate higher than 2,000,000 ug/L.
Major Contaminants and Maximum Concentrations:
- 1,2-Dichloroethene (0 µg/L)
- Tetrachloroethene (0 µg/L)
- Carbon tetrachloride (0 µg/L)
- Sulfate (0 µg/L)
No technologies selected.
- Bioremediation (In Situ)
- Reductive Dechlorination (In Situ Bioremediation)
Comments:
A series of push-pull tests were performed in boreholes that were located on the fringe of the DNAPL and in the source zone. Three organic substrates were tested and a fourth well was used as a control and biodegradation rates were compared. Each substrate was injected into a separate borehole with a conservative tracer. Samples were taken from each well and the decay rate was calculated using stable carbon isotopes and mass balance calculations using Natural Attenuation Software. Gene tracking and pyrosequencing identified the bacterial DNA population located in the sub-surface to indicate if bioaugmentation was required to speed up degradation. Emulsified oil substrate (EOS®) was found to promote conditions conducive to anaerobic reductive dechlorination but bioaugmentation was advised in order to optimize degradation processes.
A large-scale field program was implemented; approximately 100,000 kg of EOS® were injected via three 1000 mm diameter injection wells that were 50 m deep. The EOS® was chased with 800 m3 of water in order to distribute the substrate through the 30 m thick treatment zone. BAC-9" bioaugmentation culture was injected once anaerobic conditions were identified.
No remediation goals were identified within the references abstract.
Monthly monitoring will be undertaken to determine the effectiveness of the approach.
Low pH and high sulfate conditions are not normally considered favorable for dechlorinating mechanisms, however the presence of daughter products and microbial DNA within the plume suggest that a bacterial population can be supported.
References:
Cameron-Clarke, I.S., D.M. Duthe, M. Pienaar, D. Hunkeler, and M.T. Lieberman. Enhanced In Situ Bioremediation Trials for a Mixed Contaminant Plume in a Fractured Rock Aquifer, South Africa. Presented at the Tenth International In Situ and On-Site Bioremediation Symposium. Baltimore, MD. May 5-8, 2009.
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