The environmental restoration team for the Cornhusker Army Ammunition Plant, using custom-designed injection materials and careful analysis of groundwater contamination patterns, successfully implemented a remediation plan that cut years off the restoration timeline and saved millions of dollars.
The team, led by the U.S. Army Corps of Engineers’ Omaha District and the U.S. Army Environmental Command, was responsible for remediating a groundwater plume of explosive compounds that had migrated several miles off-site. The site, which is 12,042 acres, was constructed in 1942 and intermittently operated, producing artillery shells, mines, bombs and rockets during World War II, the Korean War and Vietnam War, and had ceased production operations in 1973.
By creating a remedy optimization plan, coupled with a long-term monitoring project, and by decommissioning extraction wells and the existing groundwater treatment facility through process improvements, the team estimates it was able to shave seven years off the estimated restoration timeline and saved approximately $6 million.
The remediation effort at the site had previously operated and maintained a groundwater extraction and treatment system since 1988. As part of this, groundwater was transported upstream of a two-stage granular activated carbon treatment process, and then effluent was discharged into a nearby canal. Historically, the team had operated up to seven extraction wells, but after the bioremediation began, only one extraction well was operated, at 300 gallons per minute, to prevent migration of contaminated water.
In 2013, the team also began subsurface injections, designed for bioremediation of the plumes on site. These injections, to which the team added different amendments to last longer, stay in place and increase effectiveness, were customized to the site. The injections, which contained molasses, are inexpensive, readily available and locally sourced by working with a community livestock feed provider.
Together, the improved process appears to be working well – the plume is not migrating offsite, and the injections have significantly reduced TNT and RDX concentrations in the groundwater to below regulatory limits except in one area.
“The combination of increased monitoring, with customized injections built for this site have together really helped to improve the efficiency and effectiveness of the remediation effort,” said Linda Albrecht USAEC environmental support manager for CHAAP. “We believe this approach applied to and customized to other sites, could be a viable option for future cleanups of explosives-contaminated sites.”
At the Cornhusker site, scientists and engineers had to develop a thorough understanding of the site-specific hydrogeology, including the depth of the groundwater, the lithology (or understanding of the rock formations in the environment), movement of water and chemistry of the aquifer.
As part of the Army’s plans to convert the site for beneficial re-use by private landowners, more than 12,000 acres of the site have already been transferred. The ongoing cleanup, once completed, will allow the remaining 16.15 acres to be transferred to private owners.
“For this project, our team successfully operated a five-year project with 13 options and completed all of our performance objectives on time and on budget,” said Brian Fettin USACE project manager for CHAAP. “This will allow us to serve the community, convert the property to private ownership sooner than planned and at a much lower cost.”