Frozen Soil Barriers for Explosives Containment
GILES M. MARION AND DEBORAH K. PELTON
INTRODUCTION
TNT, and picric acid in soils; 2) test the concept of leach-
Explosives are a major contaminant of Department
ing contaminated soils above a frozen barrier as a meth-
of Defense (DoD) sites. Explosives enter soil and water
od for soil cleanup; and 3) compare the mobility and
at production facilities, solid waste destruction sites,
stability of explosives in an aged, field-contaminated
packing and warehouse facilities, and from dispersed
soil versus a freshly contaminated soil.
exploded and unexploded ordnance (McGrath 1995,
Brannon et al. 1997, Hundal et al. 1997). Many explo-
METHODS AND MATERIALS
sives are mutagenic, carcinogenic, or otherwise toxic
for plants and animals (Pennington and Patrick 1990,
Soil preparation
Bradley et al. 1994, Comfort et al. 1995). Cleanup of
Clean soil (a sandy silt made from a mixture of Wind-
explosives-contaminated sites is a major DoD priority.
sor silt loam and a sand) was prepared by air drying,
The mobility of explosives in soils is governed by
sieving through a standard #40 sieve, and adding suffi-
1) advective-dispersive transport, 2) solubility, 3) sorp-
cient water to reach approximately 20% moisture con-
tion, 4) volatilization, 5) biotransformation, and 6) abi-
tent. The clean soil was thoroughly mixed and stored
otic processes (Selim and Iskandar 1994, McGrath
in the refrigerator for several days to equilibrate with
1995, Brannon et al. 1997). The solubilities of RDX,
respect to moisture.
TNT, and picric acid are 45, 150, and 12,400 mg L1 at
Explosives soils contaminated with RDX, TNT, or
25C (McGrath 1995). Grant et al. (1995) demonstrated
picric acid were collected from the field during previous
that freshly added nitramines (e.g., RDX) were stable
studies conducted at CRREL. Picric acid soils were
over an eight-week period at all storage temperatures;
from Hawthorne Army Ammunition Plant, Nevada; TNT
freshly added nitroaromatics (e.g., TNT) degraded rap-
soils were from Volunteer Army Ammunition Plant,
idly at room temperature and more slowly under refrig-
Tennessee; and RDX soils were from Newport Army
eration. In contrast, both nitramines and nitroaromatics
Ammunition Plant, Indiana. Each soil was air-dried and
were quite stable in aged, field-contaminated soils.
sieved through a standard #40 sieve prior to weighing
Soil freezing has been examined as a means for con-
and mixing. The RDX portion of the contaminated soil
centrating explosives and heavy metals as well as a
mixture was made from three separate samples to obtain
barrier to prevent migration of hazardous wastes (Ayor-
sufficient quantities for our target concentrations (Table
inde et al. 1989, Boitnott et al. 1997, Iskandar and Sayles
1). The TNT- and picric-acid-contaminated soils were
1997). Because of the high solubility and ionic nature
mixed with the RDX soil, and the resulting explosives-
of explosives such as picric acid, there is concern that
contaminated mixture was diluted with clean soil. Suf-
such explosives might leach into frozen barriers.
ficient water was added to the contaminated soil mix-
There are many uncertainties with respect to the
ture to reach a moisture content of approximately 20%.
mobility and stability of explosives in soils. The spe-
The moist soil was thoroughly mixed and stored in the
cific objectives of this work are to 1) test the efficacy
refrigerator for several days to equilibrate with respect
of frozen barriers in restraining the movement of RDX,
to moisture.
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