VICKSBURG, Miss. - Cleanup efforts on the former motor pool site at the U.S. Army Engineer Research and Development Center (ERDC) in Vicksburg, Mississippi, were recently completed and incorporated some new, cutting-edge technology, making the process more environmentally friendly and economical.
The motor pool operation utilized mechanics to perform maintenance and repairs on vehicles and heavy equipment from the early days of the Waterways Experiment Station until 1996, when the station transitioned to leased and rented vehicles and equipment. The motor pool building served a variety of other purposes, including logistics offices, until 2009, after which time it remained empty until its demolition in 2012.
The ERDC enlisted the assistance of the U.S. Army Corps of Engineers (USACE) Omaha District and its Environmental Remediation Branch to conduct a three-phase cleanup project on the motor pool site.
The key component of the cleanup was the Vapor Energy Generator (VEG) soil remediation system at the site. The patented VEG technology houses a completely enclosed treatment chamber within which the soil and associated contaminants are heated by introducing steam at temperatures as high as 1,100 degrees Fahrenheit into the chamber. As an internal auger rotates the soil, the steam causes contaminants to be released and captured by a vacuum system inside the enclosed treatment chamber. The captured gases are then run through a series of patented acid gas and emission-reducing filters before being routed back to the generator to be burned as fuel to run the treatment system.
Using this process, the plant actually uses less and less fuel as project time goes on. The system operates completely on recycled water, making it environmentally friendly. Most significantly, once the contaminated soil is treated - in this case to achieve non-detectable levels for all chemicals of potential concern at the site - the clean-treated soil is then placed back into its original location and compacted for reuse, eliminating the need and expense of offsite transportation and disposal of soils at a landfill.
At ERDC, the need to purchase fill soils was eliminated through full reuse of treated soils, and the organization’s liability for contamination was eliminated through complete treatment rather than by transporting contamination to a landfill, where ERDC would remain responsible for its ultimate fate.
All of these accomplishments occurred while achieving remediation carbon footprint reductions on the order of 80 percent over the transport and disposal of soils at an offsite landfill.
“This project is great example of both USACE’s and ERDC’s commitment to implementing effective and innovative remedial actions in a timely and sustainable manner,” said Dezso Linbrunner, contracting officer’s representative for the Omaha District.
“Using this soil remediation system resulted in the removal and onsite treatment of a significant amount of contaminant mass that otherwise was slated for disposal at a landfill,” said Douglas Simpleman, project manager with the Omaha District. “As a result, fully treated soils were reused onsite without restrictions, generating significant reductions in cost, liability, vehicle traffic through residential areas, and significant reductions in carbon dioxide and other atmospheric emissions that would otherwise have occurred throughout the soil remediation process.”
The full treatment and reuse of soils also helps minimize the potential for future groundwater impacts from chemicals leaching through soils, thereby aiding groundwater treatment activities in achieving site closure.
“To the extent that the technology is applicable to all organic compounds, we have expanded our interest in testing and applying this technology for treatment of other chemicals, including munitions constituents in soil,” Simpleman said.
Phase one of the project involved groundwater testing on the site, followed by in-situ treatment of chlorinated solvents present in groundwater from approximately 20 to 35 feet below grade. The groundwater treatment implemented was purposely aggressive to help meet an expedited project timeline, involving the injection of microorganisms that feed on contaminants, a micro-emulsion food source for the microorganisms, and a chemical reducing substrate which degrades contaminants rapidly by introducing ferrous iron into the groundwater system. This treatment was accomplished over a one-week period.
Phase two of the cleanup targeted soils from the ground surface to approximately 20 feet below grade and was completed in mid-August. Twenty-five hundred cubic yards of soil were excavated from the site. From this soil, approximately 800 cubic yards were found to contain chlorinated solvents consistent with those in the groundwater, including trichloroethylene (TCE), perchloroethylene (PCE), and several of their byproducts, such as vinyl chloride. TCE and PCE have both been used extensively as solvents in the automotive and dry cleaning industries for many years, among other uses. TCE was also used as an anesthetic until the 1980s, routinely mixed with nitrous oxide.
“The soil contamination at ERDC presented an interesting scenario,” Simpleman said. “The chlorinated-contaminated soils were below Resource Conservation and Recovery Act characteristic waste levels, but the levels were above migration to groundwater risk-based screening levels. They were contributing to a small groundwater plume at the site. As such, we understood soils would have to be cleaned up to below migration to groundwater risk-based screening levels,” Simpleman said.
“It is relatively easy to achieve a large mass reduction of contaminants with a technology when contaminant levels are high; however, it is often difficult to treat contaminated media down to very low levels. We were optimistic that the VEG technology would allow us to treat soils to the very low required levels. The team was especially pleased when we were able to treat the soils down to no detectable contamination, which were even better results than we had originally hoped to achieve,” Simpleman said.
The final phase of the cleanup involves routine monitoring of groundwater quality to ensure that the treatment efforts, especially those associated with the expedited groundwater injection activities, were adequate to sufficiently treat the groundwater and achieve closure of the environmental case at the site.
“We have been working with the U.S. Environmental Protection Agency (EPA) for years on a variety of cleanup issues around the facility, actually since 1988,” said Jerry Haskins, chief of the ERDC Safety and Environmental Management Office. “Ultimately, our goal is to have EPA approve our recommendation of ‘no further action’ for the old motor pool area. That approval will come after several rounds of groundwater sampling demonstrate that any contamination has been reduced to a very low level.”
Specifically, four rounds of quarterly monitoring of groundwater quality are planned, begun in the 4th quarter of fiscal year 2014 and going through the 3rd quarter of fiscal year 2015. This information will be used to finalize recommendations for further action, if any, relative to groundwater quality treatment at the site.