Schaefer, C.E., G.M. Lavorgna, A.A. Haluska, and M.D. Annable.
Groundwater Monitoring & Remediation 38(3):65-74(2018)

High-resolution soil and groundwater monitoring was performed to assess the long-term impacts of bioremediation using bioaugmentation with a dechlorinating microbial consortium and sodium lactate as the electron donor in a well-characterized TCE DNAPL source area. Monitoring was performed up to 3.7 yrs following active bioremediation using a high-density monitoring network that included several discrete-interval multi-level sampling wells. Results showed that despite the absence of lactate, lactate fermentation transformation products, or hydrogen, biogeochemical conditions remained favorable for the reductive dechlorination of chlorinated ethenes. While ethene levels measured 3.7 yrs after active treatment suggested relatively low (2-30%) dechlorination of the parent TCE and daughter products, carbon stable isotope analysis showed that the extent of complete dechlorination was much greater than indicated by ethene generation and that the estimated first-order rate constant describing the complete dechlorination of TCE at 3.7 yrs following active bioremediation was ~3.6/yrs. Overall results suggest that biological processes may persist to treat TCE for long periods of time after cessation of active bioremediation. For more information, see the reports completed under ESTCP Project ER-201428 at https://www.serdp-estcp.org/Program-Areas/Environmental-Restoration/Contaminated-Groundwater/Persistent-Contamination/ER-201428.