United States Environmental Protection Agency Solid Waste and Emergency Response (5306W) EPA530-F-97-045 October 1997 http://www.epa.gov INNOVATIVE USES OF COMPOST COMPOSTING OF SOILS CONTAMINATED BY EXPLOSIVES INTRODUCTION Soil at more than 30 munitions sites across the United States is contaminated with explosives. The U.S. military has discovered that composting can effectively be used to remediate this soil. Using this process, contaminated soil is excavated, mixed with other feedstocks, and composted. The end product is a contaminant-free humus that can enhance landscaping and horticulture applications. Composting costs considerably less than soil excavation and incineration, the traditional method used for these cleanups. The Umatilla Army Depot in Hermiston, Oregon, has successfully used composting to convert 15,000 tons of contaminated soil into safe soil containing humus. By using composting instead of incineration, Umatilla saved approximately $2.6 million. Cleanup goals for Umatilla were established at explosives concentrations of less than 30 milligrams per kilogram for 2,4,6 Trinitrotoluene (TNT) and Royal Demolition Explosives (RDX). The project exceeded these expectations by achieving nondetectable levels of explosives. Contaminant byproducts were either destroyed or permanently bound to soil or humus. The success at Umatilla indicates that composting of explosive-contaminated soil is a cost-effective and environmentally sound clean-up method. Millions of dollars could be saved if the composting process were used rather than conventional incineration to clean up contaminated soils at these and other military operations in the United States. Other sites using composting for explosives include the U.S. Naval Submarine Base in Bangor, Washington; the Navy Surface Warfare Center in Crane, Indiana; and the Sierra Army Depot in Herlong, California. HOW CONTAMINATION OCCURRED AT UMATILLA Over a 15-year period during the 1950s and 1960s, workers at Umatilla used water and steam to clean TNT, RDX, and other explosives out of decommissioned 500- and 750-pound bombs. In the process of cleaning these bombs, more than 80 million gallons of explosive-contaminated "pink water" (named for its characteristic color) were washed into two 10,000 square-foot lagoons. When the water evaporated, workers excavated and transported the residual solids to another area and burned them. While the use of evaporative ponds was the accepted wastewater disposal technique at the time, it caused an unforeseen problem. Contaminants seeped into the soil and the ground water underlying the evaporation lagoons. In 1987, Umatilla was put on the Superfund list for hazardous waste cleanup because of TNT and RDX levels of 4,800 parts per million. HOW COMPOSTING OF EXPLOSIVES-CONTAMINATED SOILS WORKS Through the composting process, naturally occurring microorganisms break down the explosives contaminants in the soil. Using the contaminants as "food," the microorganisms convert them into harmless substances consisting primarily of water, carbon dioxide, and salts. In addition to this food source, microorganisms require nutrients such as carbon, nitrogen, phosphorous, and potassium in order to thrive, digest, and reproduce. To provide these nutrients in sufficient quantities, soil amendments such as manure and potato waste were added to the contaminated soil at Umatilla. Before beginning work at Umatilla, extensive tests were performed to determine the best mixture of contaminated soil and soil amendments to be used in the composting process. Numerous factors influence what mix of these ingredients provides microorganisms with the optimum environment in which to live. The most important of these factors is the carbon to nitrogen ratio. Other factors influencing the choice of soil amendments include moisture, pH, degradability, percentage of organic matter, and availability of specific soil amendments. The composting feedstocks used at Umatilla were 30 percent contaminated soil, 21 percent cattle manure, 18 percent sawdust, 18 percent alfalfa, 10 percent potato waste, and 3 percent chicken manure. In other geographical areas, substitutions may be made depending on the cost and availability of ingredients. Large, temporary mobile buildings were constructed to control fumes and ensure optimum conditions for the composting process. The mixture of contaminated soil and soil amendments was placed into windrows. Workers, using highly specialized mixing equipment, turned these steaming piles three times daily to: (1) ensure that the compost received sufficient oxygen; (2) release trapped heat, water vapor, and gases; and (3) to break up clumps. Treatment time for a 2,700- cubic-yard batch of soil was 10 to 12 days. BENEFITS OF COMPOSTING EXPLOSIVES-CONTAMINATED SOILS Composting of explosive-contaminated soils has significant economic and environmental benefits. At Umatilla, composting saved an estimated $2.6 million over incineration for cleanup of the entire site. Clean-up costs at Umatilla were estimated to be $527 per ton for combustion and $351 per ton for composting, resulting in a savings of $176 per ton. In addition, the end-product of the composting process, humus-rich soil, generally sells for at least $10 per ton, resulting in potential revenues of $150,000. Together, the savings ($2.6 million) and potential revenue ($150,000) from using the composting process to remediate explosive-contaminated soil could be $2.75 million. By contrast, the end-product of combustion has limited commercial value, and represents minimal potential revenue. ************************************************************ Graphic ************************************************************ The U.S. Army Corps of Engineers has estimated that if composting were used to clean up the remaining U.S. munitions sites, $200 million could be saved. While incinerators use large quantities of fossil fuel, a nonrenewable resource, only a small amount of fuel is needed for the machines that stir composting windrows. Incinerating soil at hazardous material disposal facilities results in ash that must be handled and disposed of as hazardous residue. By contrast, composting produces a nutrient-rich product comparable to an enriched top soil that can be used in landscaping and agricultural applications. In fact, tests on plants grown in remediated soil showed no toxic effects from the contaminants. This demonstrates that the contaminants are no longer present. According to Dr. Michael Cole, an expert in the degradation of organic contaminants in soil, composting, more than any other soil cleanup technique, results in an enriched soil end-product and restores the earth to a better condition than before it was contaminated. References Emery, D.D., and P.C. Faessler. 1996. First production- level bioremediation of explosives-contaminated soil in the U.S. Weston, R.F., Inc. 1993. Windrow composting demonstration for explosives-contaminated soils at the Umatilla Depot Activity. Hermiston. Document No: CETHA-TS-CR-93043. Williams, R.T., and P.J. Marks. Optimization of composting of explosives-contaminated soil. Washington: U.S. Army Corps of Engineers. CETHA-TS-CR-91053. Williams, R.T., P.S. Zieganfuss, and W.E. Sisk. 1992. Composting of explosives and propellant contaminated soils under thermophilic and mesophilic conditions. Journal of Industrial Microbiology. 9:137-144. 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