Innovative Uses of Compost
Composting of Soils
Contaminated by Explosives
Introduction
oil at more than 30 munitions sites across the United States is
contaminated with explosives. The U.S. military has discovered
that the composting process, and the use of finished (mature,
cured) compost can effectively remediate munitions-contaminat-
ed soils. To incorporate such soil into the composting process, the soil is
excavated and mixed with other feedstocks. The end-product is a contami-
nant-free soil, containing nutrient-rich humus that can enhance landscap-
ing and horticultural 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 con-
taining humus. By using composting instead of incineration, Umatilla
saved approximately $2.6 million. Clean-up goals for Umatilla were estab-
lished at 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 explo-
sives. Contaminant byproducts were either destroyed or permanently
bound to soil or humus.
The success at Umatilla indicates that composting of explosive-contam-
inated 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.
> Printed on paper that contains at least 20 percent postconsumer fiber.
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How Contamination Occurred
at Umatilla
ver 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 decom-
missioned 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 tech-
nique at the time, it caused an unforeseen prob-
lem. 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.
Photo courtesy of Bioremediation Service, Inc.
Workers, using highly specialized mixing equipment, turn steaming windrows of soil
amendments mixed with explosive-contaminated soil from the Umatilla Army Depot.
How Composting of Explosive-
Contaminated Soils Works
hrough the process in which compost is
made, naturally occurring micro-organ-
isms break down the explosive contami-
nants in the soil. Using the
contaminants as "food," the micro-organisms
convert them into harmless substances consisting
primarily of water, carbon dioxide, and salts. In
addition to this food source, micro-organisms
require nutrients, such as carbon, nitrogen, phos-
phorous, 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 con-
taminated soil at Umatilla.
Before beginning work at Umatilla, extensive
tests were performed to determine the best mix-
ture of contaminated soil and soil amendments to
be used in the composting process. Numerous
factors influence what mix of these ingredients
provides micro-organisms
with the optimum environ-
ment in which to live. The
most important factor is the
carbon to nitrogen ratio.
Other factors influencing the
choice of soil amendments
include moisture, pH,
degradability, percentage of
organic matter, and availabil-
ity of specific soil amend-
ments. The composting
feedstocks used at Umatilla
were 30 percent contaminat-
ed soil, 21 percent cattle
manure, 18 percent sawdust,
18 percent alfalfa, 10 percent
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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 con-
structed to control fumes and ensure optimum
conditions for the composting process. The mix-
ture 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
Explosive-Contaminated Soils
omposting 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 com-
posting process to remediate explosive-contaminat-
ed soil could be $2.75 million. By contrast, the
end-product of combustion has limited commercial
value, and represents minimal potential revenue.
Combustion Versus Composting at Umatilla Army Depot
COST
Total Clean-up Cost for 15,000 Tons
BENEFIT
Value Added from Sale of 15,000
••••• 1 nf Contaminated Soil* ••••••••I Tons of Treated Soil
$8,000,000
7,000,000
6,000,000
5,000,000
4,000,000
3,000,000
2,000,000
1 ,000,000
0
-
$7,905,000
$5,305,000
Saves |
$2.6
Million
Combustion Composting
$150,000
120,000
90,000
60,000
30,000
0
$150,000
Earns
$150
| Thousand
$0 |
Combustion Composting
Savings and Revenue From Composting $2,600,000 + $150,000 = $2,750,000
Based on information contained in "First Production-Level Bioremediation of Explosives-Contaminated
Soil in the U. S." by David D. Emery and Patrick C. Faessler, Bioremediation Service, Inc.
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Photo courtesy of Bioremediation Service, Inc.
Large, temporary buildings controlled fumes and ensured
optimum conditions for the composting of explosive-
contaminated soil at the Umatilla Army Depot.
The U.S. Army Corps of Engineers has estimat-
ed 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 compost-
ing windrows. Incinerating soil at hazardous materi-
al disposal facilities results in ash that must be
handled and disposed of as hazardous residue. By
contrast, composting produces a nutrient-rich prod-
uct 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 and
that the contaminants were no longer present.
According to Dr. Michael Cole, an expert in the
United States
Environmental Protection Agency
(5306W)
Washington, DC 20460
Official Business
Penalty for Private Use
$300
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 produc-
tion-level bioremediation of explosives-contaminat-
ed 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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