A Tale of Two Sites - Enhanced Bioremediation of Explosives Impacted Soils
The problem with OE compounds in soil
A variety of organic explosive (OE) compounds have been used for military, geological and industrial applications throughout North America, and in most industrialized nations. During their manufacture, formulation and storage, these compounds have migrated to the soil. Compounds such as 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazine (HMX) often persist for extended periods in soil or groundwater. As suspected carcinogens, many OE compounds are regulated as priority pollutants.
The Iowa Army Ammunition Plant and the Yorktown Naval Weapons Station were two sites that had discovered OE compounds in their soil. To address the problem, the U.S. Army Corps of Engineers and the Atlantic Division of Naval Facilities Engineering Command selected a patented bioremediation technology developed by Adventus Americas to remediate impacted soils. The technology was selected because of its effectiveness in the presence of heavy metals (barium at the ammunition plant) and the potential cost savings over alternative bioremediation technologies that were studied.
The bioremediation method enhances and promotes natural biodegradation rates by adjusting conditions in a soil or waste matrix to stimulate in situ chemical reduction (ISCR) of target compounds by indigenous microorganisms. The key to the technology is the application of sequential anaerobic and aerobic conditions, or treatment cycles, generated through the application of proprietary organic and inorganic amendments. Moisture content, pH and oxidation reduction potential are controlled during the process.
The technology can be applied ex-situ using a land treatment process in turned windrows, and has been successfully applied in-situ to depths of 12 feet. The remediation is typically performed using simple machinery – such as a tractor-driven rotary tiller and agricultural irrigation equipment.Soil treatment using the technology offers several advantages over alternative soil treatment approaches, such as an absence of bulking or dilution due to low amendment volumes, complete degradation of target compounds, cost effectiveness, and reduced soil toxicity.
Case study: Iowa ammunition plant
The Iowa Army Ammunition Plant is a government-owned, contractor-operated facility that encompasses approximately 19,000 acres. Production of ammunition at the plant began in 1941; current activities at the plant include what the Army terms “load, assemble and pack” production operations for various conventional ammunition items. Past operations at the plant have resulted in the contamination of soil and groundwater through the discharge of wastewater containing explosives and explosive byproducts, and through open burning and land disposal of production wastes.
Soil at the site was impacted by RDX, TNT, HMX and barium. Initial RDX concentrations ranged from 819 mg/kg to 2,270 mg/kg with a mean concentration of 1,530 mg/kg. The initial HMX mean concentration was 1,112 mg/kg; the initial TNT mean concentration was 95.8 mg/kg. Removal efficiencies greater than 97 percent were required to meet the remedial goals of 53 mg/kg for TNT, RDX and HMX. Sequential treatment (five to six cycles) of treatment reduced the mean RDX concentration by almost 99 percent to 16.2 mg/kg; the mean concentration of HMX was reduced by 92.4 percent (from 1,112 mg/kg to 84.5 mg/kg); and the mean TNT concentration was reduced by 93.7 percent, from 95.8 mg/kg to 6.1 mg/kg.
Case study: Yorktown naval weapons station
Originally named the U.S. Mine Depot, the Yorktown station was established in 1918 to support the laying of mines in the North Sea during World War I. Currently the station is charged with providing ordnance, technical support and related services to sustain the war-fighting capability of the armed forces in support of national military strategy. The Site 6 Study Area covered approximately 94 acres and included an explosives-contaminated wastewater impoundment area with associated drainage way, as well as an excavated area and a tributary to Felgates Creek. The explosives reclamation facility released solvents such as trichloroethene and nitramine compounds such as TNT and RDX to the impoundment area.
To implement the remediation, one high-density polyethylene double-lined treatment cell was constructed and enclosed by a polyethylene covered greenhouse, which was assembled in place to cover the treatment cell. The cell had a capacity of approximately 1,200 tons of soil per batch of soil treated.
The concentrations of the target contaminants were rapidly and substantially reduced through the application of seven to 12 treatment cycles, depending on the initial contaminant concentrations of the given batch of soil. Mean TNT concentrations were reduced from an initial 10,884 mg/kg to 4.9 mg/kg, corresponding to an overall mean reduction in TNT concentrations of greater than 99.9 percent. Similarly, mean RDX concentrations were reduced from 400 mg/kg to 1.6 mg/kg, for a reduction of 99.6 percent. In addition to the effective removal of the principle contaminants, results indicated that there was no accumulation of amino compounds or any other known biodegradation intermediates.
ISCR describes the combined effect of stimulated biological oxygen consumption (via fermentation of added organic carbon sources by indigenous microbes), direct chemical reduction with reduced metals (such as zero-valent iron; ZVI) and the corresponding enhanced thermodynamic decomposition reactions that are realized at the lowered redox (Eh) conditions.
Following placement of ISCR reagents into the soil or subsurface environment, a number of physical, chemical and microbiological processes combined to create very strong (i.e., Eh less than -550 mV) reducing conditions in situ that stimulated rapid and complete dechlorination of organic solvents and other recalcitrant compounds. In addition, the valence state of various inorganic compounds (e.g., heavy metals such as arsenic, barium, chromium, lead and mercury) were reduced, allowing these materials to participate in various sorption and generally irreversible precipitation reactions.
Depending on a number of recognized site-specific conditions, bioremediation is a potentially viable remedial solution for the treatment of soils, sediment and groundwater environments impacted by organic explosives and many other compounds[3,5]. Since its inception in the mid-1990s, ISCR technology has been used to treat over 1 million tons of soil/sediment impacted by organic explosives and other problematic contaminants.
The above projects incorporated the Daramend® technology from Adventus Americas. For more information, contact Dr. Jim Mueller, Director Remedial Solutions.
1. Keith and Telliard, 1979
2. Jerger, D.E., and P. Woodhull, 2000. “Applications and Costs for Biological Treatment of Explosives-Contaminated Soils in the U.S.” In: J.C. Spain, J.B. Hughes, and H. Knackmuss, (Eds.) Biodegradation of Nitroaromatic Compounds and Explosives, pp 395-423. CRC Press LLC, Boca Raton.
3. Seech, A. G., J. E. Cairns, and I. J. Marvin, 2000. Composition and Method for Dehalogenation and Degradation of Halogenated Organic Contaminants. United States Patent Number 6,083,394.
4. Spain, J.C. 2000. Introduction. In: J.C. Spain, J.B. Hughes, and H. Knackmuss, (Eds.) Biodegradation of Nitroaromatic Compounds and Explosives, pp 1-5. CRC Press LLC, Boca Raton
5. Mueller, J.G., C.E. Cerniglia and P.H. Pritchard. 1996. Bioremediation of Environments Contaminated by Polycyclic Aromatic Hydrocarbons. In R. Crawford and D. Crawford (eds), Bioremediation: Principles and Applications. Chapter 5, Pages 125-194. Cambridge University Press.