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LONG-TERM EVALUATION OF MULCH BIOWALL PERFORMANCE TO TREAT CHLORINATED SOLVENTS
Walker Jr., K.L., T.M. McGuire, D.T. Adamson, R.H. Anderson.
Groundwater Monitoring & Remediation [Published online 9 January 2020 prior to print]
Ten years after the installation of seven mulch biowalls at Altus Air Force Base, soil and groundwater sampling showed long-term efficacy for CVOC degradation. TCE was not detected in five of seven groundwater samples collected from the biowall despite upgradient detections above federal drinking water standards. Microbial sampling indicated high reducing conditions within the biowalls and favorable conditions for CVOC destruction via microbial reductive dechlorination. High cellulose content (>79%) of the mulch, elevated total organic carbon (TOC) content in groundwater and elevated potentially bioavailable organic carbon (PBOC) measurements in soil samples further supports an ongoing, long-lived source of carbon. In addition, concentrations of bacteria, TOC, PBOC, and other geochemical parameters suggest a modest impact of the biowalls downgradient. The continued presence of CVOCs downgradient may be attributable to back-diffusion from low-permeability shale. However, the biowalls continue to provide benefits by removing CVOCs in groundwater, thus reducing further CVOC loading to the downgradient, low-permeability strata.
Groundwater Monitoring & Remediation [Published online 9 January 2020 prior to print]
Ten years after the installation of seven mulch biowalls at Altus Air Force Base, soil and groundwater sampling showed long-term efficacy for CVOC degradation. TCE was not detected in five of seven groundwater samples collected from the biowall despite upgradient detections above federal drinking water standards. Microbial sampling indicated high reducing conditions within the biowalls and favorable conditions for CVOC destruction via microbial reductive dechlorination. High cellulose content (>79%) of the mulch, elevated total organic carbon (TOC) content in groundwater and elevated potentially bioavailable organic carbon (PBOC) measurements in soil samples further supports an ongoing, long-lived source of carbon. In addition, concentrations of bacteria, TOC, PBOC, and other geochemical parameters suggest a modest impact of the biowalls downgradient. The continued presence of CVOCs downgradient may be attributable to back-diffusion from low-permeability shale. However, the biowalls continue to provide benefits by removing CVOCs in groundwater, thus reducing further CVOC loading to the downgradient, low-permeability strata.
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