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.

 
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     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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