A project to treat groundwater and soil contamination at NASA’s Marshall Space Flight Center in Huntsville, Ala., has attracted international attention and been added to a pilot program sponsored by the North Atlantic Treaty Organization (NATO).
The NATO Committee on the Challenges of Modern Society has picked one of the Marshall Center’s in-situ remediation projects as one of just four worldwide for further study and evaluation.
The Marshall Center studies are evaluating various technologies that can be used at locations where hazardous materials or their residues are present in the soil, subsoil and ground water. In this case, the focus is on removing chlorinated volatile organic compounds from soils and ground water. This contamination occurred from former waste management activities at the facility before the potentially harmful results of such activities were known.
In 1994, the U.S. Environmental Protection Agency (EPA) placed the Marshall Center on the National Priorities List of sites eligible for cleanup under the Superfund, an environmental program managed by the EPA to clean up hazardous waste sites throughout the United States. The Marshall Center studies are part of a process to identify, investigate, sample and restore 67 sites at Marshall where hazardous material was used. Since 1994, the Marshall Center has spent an estimated $24 million on identifying, investigating, sampling and restoring the sites.
The project selected by the NATO committee involves injection into the ground of zero-valent iron powder – small solid iron particles -- in slurry form using the Ferox sm process patented by ARS Technologies Inc., of Highland Park, N.J., an environmental engineering firm.
These chemical reduction pilot tests are to be conducted beneath two contaminated areas and are directed primarily at the treatment of trichloroethene, a solvent that was used to clean rocket engines, in the sub-surface soil and water. Investigations indicate that there are man-made chemicals, like these solvents, still present in the water. These types of contaminants are heavier than water and will keep moving through the subsurface until they find a resting spot. Along the way they can also leave small deposits at various depths, a result referred to as residual contamination.
The Marshall Center’s Environmental Engineering Department developed and implemented the remediation project in collaboration with CH2M HILL, an international consulting engineering and project delivery firm headquartered in Greenwood Village, Colo.
The study’s focus is on treatment of naturally oxygenated, contaminated groundwater within an interval area called the rubble zone – a transitional area between the clay soil and the limestone bedrock -- as well as on treatment of the clay soil above the rubble zone where there is a significant amount of contamination.
In one area, designated SA-2, trichloroethene groundwater contamination was as high as 70 milligrams per liter. The federal standard for allowable groundwater contamination of this substance is .005 milligrams per liter.
The SA-2 site is in a test area where in the 60’s and 70’s rocket engine parts were routinely cleaned following tests. Unexploded ordnance remaining from the World War II era was also present in the area, eliminating the simpler option of doing a general treatment of the entire contaminated area. Therefore, the approach taken was to inject zero-valent iron powder where possible in the most contaminated areas. Then overlapping injections were inserted into areas where water would naturally flow, creating a treatment zone for untreated water to flow through. Monitoring of the area after the injections showed contaminant concentrations in the affected area were reduced by more than 90 percent.
Monitoring results at another site, called SA-12, near a building where routine cleaning and degreasing of parts occurred (during development of the U.S. space program) were not as encouraging. Much higher levels of contamination than anticipated were found in this area that contains trichloroethene with some perchloroethene and Freon in both saturated and unsaturated zones. During the first tests unexpectedly high SA-12 trichloroethene concentrations -- approximately 350 milligrams per liter in the groundwater and 46 milligrams per kilogram in the unsaturated zone -- were encountered. The zero-valent iron powder injection was used for this area because of the groundwater depth and the presence of underground utilities in the area.
It was determined that not enough of the slurry was injected for the conditions being encountered. Therefore, follow-up laboratory tests were conducted to re-assess the use of the zero-valent iron powder slurry injections. Results indicate that the conditions at SA-12 are potentially treatable with this approach. However, other types of treatment are also under consideration.
Additional information about the project can be obtained from Amy Keith, a Marshall Space Flight Center environmental engineer, 256-544-7434, by e-mail: Amy.Keith@msfc.nasa.gov or from Bill McElroy, project manager, at CH2M HILL, 352-335-7991, or by e-mail: bmcelroy@ch2m.com.
To learn more about the technology, visit the ARS Technologies Web site at: http://www.arstechnologies.com