Purpose:

Approximately 59 percent of U.S. Department of Defense (DoD) sites have groundwater impacted by heavy metals, of which hexavalent chromium is a major component. Plating and boiler operations and equipment repair and fabrication, among other activities, generate hexavalent chromium. Current remediation technologies to eliminate the problem primarily consist of plume containment methods rather than source control technologies. The purpose of this project is to demonstrate a cost-effective, rapid in-situ technology to eliminate dissolved hexavalent chromium by using both chemical reduction and ferrous iron precipitation to form an insoluble mineral precipitate this is stabilized in the subsurface.

Description:

Chemical reduction is a transfer of electrons between ions resulting in a lower valence state in the reduced element. Different valence states of an element have different reactive properties. Hexavalent chromium (Cr⁺⁶) forms very soluble, non-reactive compounds in groundwater and is highly toxic to organisms and plants, whereas trivalent chromium (Cr⁺³) forms insoluble mineral precipitates and is considerably less toxic. In this test, ferrous iron (Fe⁺²) will be used to chemically reduce Cr⁺⁶ in groundwater, resulting in the formation of Cr⁺³ and Fe⁺³. Dilute hydrogen peroxide and sulfuric acid will be used to destroy soluble organic chromium complexes, adjust groundwater pH to an optimal range, and displace Cr⁺⁶ from mineral surfaces. The Fe⁺³ rapidly precipitates as iron oxyhydroxide minerals and entrains the Cr⁺³ in the precipitate. Iron oxyhydroxide minerals are very insoluble in groundwater; thus the reduced chromium is permanently and irreversibly removed from groundwater and stabilized in the subsurface. Laboratory investigations indicate this process can result in substantially complete removal of chromium from solution. Results from a field pilot test of an earlier version of this technology at Anniston Army Depot, Alabama, indicated the removal of 67-100 percent (on average 89 percent) of chromium from groundwater, with 4 out of 5 sampling locations yielding chromium concentrations below primary drinking water standards.

Benefits:

In-situ chemical reduction has the potential to be a very rapid and effective process for the cleanup of groundwater impacted by chromium. Anticipated cost savings are approximately 30-80 percent over accepted cleanup methods such as pump-and-treat. The in-situ method eliminates long-term operation and maintenance and sludge disposal, is applicable to sites with other co-mingled inorganic and organic contaminants, and provides minimal mission disruption of DoD facilities. Additionally, the technology is a source reduction process rather than a plume containment process and thus eliminates the long-term source of groundwater contamination. Potential future applications of this technology include treatment of unsaturated soils and remediation of other heavy metal contaminants.

Contacts:

Technical Contact:
Dr. Dan Bryant
GeoCleanse International, Inc.
4 Mark Road, Suite C
Kenilworth, NJ 07033
Telephone: (908) 206-1250
Fax: (908) 206-1251
E-mail: dbryant@geocleanse.com

DoD Liaison Officer:
Ms. Kimberly Watts
U.S. Army Environmental Center
ATTN: SFIM-AEC-ETD
5179 Hoadley Road
Aberdeen Proving Ground, MD 210105401
Telephone: (410) 436-6843
Fax: (410) 436-6836
E-mail: kimberly.watts@aec.apgea.army.mil