Ensuring the continued success of a mulch biowall at a TCE-contaminated superfund site: lessons learned

Authors: KJELLERUP, BIRTHE - University Of Maryland; SAFFARI GHANDEHARI, SHAHRZAD - University Of Maryland; CHENG, SHIH-HUAI - University Of Maryland; Hapeman, Cathleen; JACKSON, DANA - US Department Of Agriculture (USDA); TORRENTS, ALBA - University Of Maryland

Submitted to: Remediation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/13/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary: Trichloroethylene (TCE), a solvent used as degreaser and dry-cleaning fluid, is a known toxin and carcinogen, and is one of the most frequently found groundwater contaminants in the United States and around the world. A landfill in Maryland contaminated with high levels of TCE decades ago was added to the U.S. Environmental Protection Agency National Priority List (NPL) for clean-up in 1994. A biowall was installed on the site in 2013 to promote the bioremediation of TCE and its subsequent degradation products. A few years after installation, monitoring data showed that although the wall was degrading TCE, the intermediate products were accumulating, particularly the more toxic compound vinyl chloride. The entire system was examined to determine the reason for the biowall inefficiency, and laboratory studies were conducted to consider changes to the remediation process. Results suggested that the natural flow of the contaminated plume through the biowall was too fast and that the acidity needed to be adjusted. Thus, a trench with biochar and limestone (which adjusted the acidity) enhanced biosolids was designed and installed in front of the biowall. This study demonstrates that the long-term success of the biowall requires a continuous collaboration of government, university, and engineering firms. Documentation of this process will be useful to management of other biowall projects throughout the U.S. and globally.

Technical Abstract: Trichloroethylene (TCE), a solvent used as degreaser and dry-cleaning fluid, is a known toxin and carcinogen, and is one of the most frequently found groundwater contaminants in the United States and around the world. A landfill in Maryland contaminated with high levels of TCE decades ago was added to the U.S. Environmental Protection Agency National Priority List (NPL) for clean-up in 1994. A biowall was installed on the site in 2013 to promote the bioremediation of TCE and its subsequent degradation products. A few years after installation, monitoring data showed that although the wall was degrading TCE, the intermediate products were accumulating, particularly the more toxic compound vinyl chloride. The entire system was examined to determine the reason for the biowall inefficiency, including the background of the site, remediation plan, installation, the geochemical and physical characteristics, and the monitoring data. This analysis coupled with laboratory studies suggested that retention of the plume in the biowall was overestimated and that plume flow retardation was required. Thus, a trench with biochar and limestone enhanced biosolids was installed before the biowall. Furthermore, the long-term success of the biowall requires a continuous collaboration of government, university, and engineering firms. Documentation of this process will be useful to management of other biowall projects