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Sustainability of TCE Removal in the Mulch Biowalls at Altus AFB
Citation:
WILSON, J. T. Sustainability of TCE Removal in the Mulch Biowalls at Altus AFB. Presented at The 2010 Restoration and Technology Transfer Workshop, San Antonio, TX, April 06 - 09, 2010.
Impact/Purpose:
Observing TCE removal in mulch biowalls.
Description:
A permeable mulch biowall was installed in June 2002 at Landfill 3 (LF-03), Operable Unit 1 (OU-1), Altus AFB, Oklahoma. The demonstration was conducted by Parsons for the AFCEE Technology Transfer Outreach Office. The biowall is approximately 455 feet long, by 24 feet deep, by 1.5 feet wide, and is composed of shredded bark mulch, cotton gin compost, and sand. The mean residence time of ground water in the biowall was 10 days. In the initial years of operation, the biowall effectively converted TCE to cis-DCE and low concentrations of vinyl chloride. Approximately 99% of the TCE was removed by passage through the biowall. At each sampling time, the concentrations of cis-DCE in the biowall were higher than concentrations of TCE coming into the biowall from up gradient (data not shown). In the later years of operation, most of the cis-DCE was removed in the flow path from the biowall to the down gradient monitoring wells. After six years of operation (2008), along one flow path, the treatment of TCE was less effective. Although the overall concentrations of TCE were, the concentration of TCE was higher than the concentration of cis-DCE in one of the monitoring wells down gradient of the biowall. Sampling in 2009 confirmed this observation. The effective lifecycle of the mulch in the biowall was on the order of six years.