1,2-Dibromoethane (EDB) is a suspected human carcinogen and a chemical of concern (COC) in the United States. Because analytical methods for volatile organic compounds (VOCs) often used at fuel-related sites (e.g., U.S. Environmental Protection Agency 8260B) have detection limits greater than the Federal maximum contaminant level (MCL) for EDB of 0.05 µg/L, the extent of EDB contamination at military and civilian sites is unclear and may be under-appreciated. The objectives of this project were to: (1) evaluate EDB attenuation, particularly using novel compound specific isotope analysis (CSIA) tools; and (2) determine whether biostimulation or bioaugmentation could effectively enhance in situ treatment of EDB.

Carbon isotope fractionation of EDB can be used to help in the understanding of EDB attenuation. During this project, improved CSIA methods for measuring isotope composition with low concentrations were developed and applied. Differences in the isotopic composition of EDB among field samples provided valuable insights regarding EDB degradation processes.

After successful treatability testing, a lactate-based anaerobic in situ bioremediation (ISB) approach like that used for many chlorinated VOCs (e.g., trichloroethene) was also applied in a highly impacted source area. The goal of this ISB effort was to demonstrate that higher EDB concentration source areas can be treated for cases when attenuation processes themselves are insufficient to protect receptors.

Two conditions made CSIA measurements challenging: interest in very low concentrations of EDB, and high concentrations of co-located non-target VOCs (e.g., benzene, toluene, ethylbenzene, and xylene). During this project, the project team demonstrated that informative CSIA measurements were possible when each condition was examined exclusive of the other (i.e., in dilute plume or hydrocarbon-rich source areas), but when the two conditions were combined (e.g., very dilute EDB in hydrocarbon-rich source area), CSIA measurements were challenging or impossible at this time. CSIA data from the field clearly demonstrated that EDB degraded at the site prior to intensive remediation efforts.

Large decreases in EDB concentrations resulted from the ISB treatment approach demonstrated, with observed reductions exceeding 99%. In almost all cases, final EDB concentrations were less than the MCL for EDB after treatment. EDB degradation was evident through comparison to other COCs, increases in degradation products, and changes in isotopic composition.

Application of the improved methods for examining EDB attenuation and source zone treatment demonstrated during this project may result in significant cost savings when EDB is a significant driver of remediation costs.

No issues encountered during this project affected the conclusions drawn; although two issues encountered should be considered when applying the technologies: (1) difficult CSIA measurements in hydrocarbon rich source zones when EDB concentrations are low; and (2) fouling of groundwater treatment systems during long-term operations. (Project Completion - 2022)

Koster van Groos, P.G., P.B. Hatzinger, S.H. Streger, S. Vainberg, R.P. Philp, and T. Kuder. 2018. Carbon Isotope Fractionation of 1,2-Dibromoethane by Biological and Abiotic Processes. Environmental Science and Technology, 52(6):3440-3448. doi.org/10.1021/acs.est.7b05224.