USGS

Biodegradation of Chlorinated Ethenes at a Karst Site in Middle Tennessee

Table 13. Summary and interpretation of multiple lines of evidence using data collected from deep wells

Well	Geochemical indicators (quarterly data)	Geochemical indicators (continuous monitoring data)	Chlorinated-ethene data
1D	Anaerobic, nitrate-reducing conditions.	Anaerobic, sulfate-reducing or methanogenic conditions.	cis-1,2-Dichloroethylene, vinyl chloride, ethene, and ethane detected.
3D	Anaerobic, nitrate-reducing conditions. Possible sulfate-reducing conditions at times (high sulfide concentrations detected).	Anaerobic, sulfate-reducing or methanogenic conditions. Aerobic conditions when the 9D pump-and-treat well is not operating.	cis-1,2-Dichloroethylene, vinyl chloride, and ethane detected.
2D	Fluctuates between aerobic and anaerobic conditions. Possible ammonia oxidization and nitrate reduction during aerobic and anaerobic conditions, respectively.	Rapid fluctuations between aerobic and anaerobic conditions. Oxidation-reduction potentials indicate manganese or iron-reducing levels.	cis-1,2-Dichloroethylene, vinyl chloride, ethene, and ethane detected.
12D	Fluctuates between aerobic and anaerobic conditions. Possible ammonia oxidization and nitrate reduction during aerobic and anaerobic conditions, respectively.	Anaerobic conditions only present for a few days after rainfall events. During dry periods, reducing conditions may be present for a few weeks.	cis-1,2-Dichloroethylene, vinyl chloride, ethene, and ethane detected. Higher molar concentrations of trichloroethylene than degradation products detected.
Other wells	Aerobic and anaerobic conditions	Data not available	Reductive-dechlorination degradation products detected.

Table 13. Summary and interpretation of multiple lines of evidence using data collected from deep wells--Continued

Well	Bacteria-identification data	Microcosms	Conclusions
1D	Ammonia oxidizers not detected. Methanotrophs detected. Data for other types of bacteria not available.	No significant aerobic degradation. Reductive-dechlorination degradation products present after a 10-month incubation.	Reductive dechlorination possible. No aerobic degradation because of the continuously anaerobic conditions.
3D	Ammonia oxidizers, methanotrophs, manganese and iron oxidizers, and sulfate reducers detected.	Significant aerobic degradation during a 3-week incubation. Reductive-dechlorination degradation products present after a 10-month incubation.	Reductive dechlorination possible. Aerobic degradation may occur when the 9D pump-and-treat well is not operating.
2D	Methanotrophs, manganese and iron oxidizers, and sulfate reducers detected.	Significant aerobic degradation during a 3-week incubation. Reductive-dechlorination degradation products present after a 10-month incubation.	Rapid fluctuations between aerobic and anaerobic conditions may prevent reductive dechlorination from occurring. Some aerobic degradation is possible.
12D	Ammonia oxidizers, methanotrophs, manganese and iron oxidizers, and sulfate reducers detected.	No significant aerobic degradation. Reductive-dechlorination degradation products present after a 10-month incubation.	Geochemical conditions would limit reductive dechlorination. Aerobic bacteria were present, but no aerobic degradation in microcosms.
Other wells	Aerobic and anaerobic bacteria detected in samples from 10D-B and 16D-B.	Microcosm data not available	Potential aerobic and anaerobic degradation. Additional data needed.

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