Sufficient soil (62.5 g) and distilled, deionized, deoxygenated water (250 ml)
were added to 500-ml polycarbonate centrifuge tubes to make a soil-to-water
ratio of 1:4. Tests containing the aquifer soils were spiked with a stock solution
of 2,6DNT to a final concentration of 10 ppm. Tests with the surface soil were
loaded and sampled like the aquifer soils, but were spiked with a 10-ppm mixture
of TNT, 2,4DNT, 1,3,5TNB, 1,3DNB, and 2,6DNT. Samples were placed on a
reciprocating shaker at 280 excursions per minute. At predetermined sampling
times (0.5, 1, 6, 24, 48, 72, 96, and 168 hr), a 10-ml aliquot was removed and
centrifuged at 8,288 relative centrifugal force (RCF) for 30 min. The aqueous
sample was removed and frozen until analyzed for all EPA SW-846 Method
8330 (USEPA 1994) analytes plus 2,6DANT, 2,4DANT,and 4,4'AZOXY. The
aqueous samples from the surface soil were preserved with
ethylenediaminetetraacetate (EDTA) to a final concentration of 5M (Brannon,
Price, and Hayes 1998). At the completion of the 168 hr the soil was also
analyzed. The testing was carried out in duplicate.
Adsorption partitioning
Adsorption partitioning was conducted with the same soils and in a 1:4 ratio
of soil to water. Concentrations of explosives were 10, 7.5, 5, 2.5, and 1 g per
ml of solution phase. The LAAP-C test was spiked with 2,6DNT; the LAAP-D
test was spiked with 2,6DNT and 2,4DNT separately; and the Yokena clay was
spiked with the mixture described in the previous paragraph. Duplicate samples
were shaken for 24 hr, centrifuged at 8,288 RCF for 30 min, and the aqueous
phase removed and analyzed for the same analytes as in the kinetics test. The
aqueous samples from the Yokena clay were preserved with EDTA to a final
concentration of 5 M.
Dissolution kinetics
Dissolution kinetics were determined on three high explosives (TNT, RDX,
and HMX) and three explosives formulations (octol, Composition B, and LX14
(Table 15)). Military explosives were available on site at EL. Formulations were
obtained from U.S. Army Artillery Research Development and Engineering
Command (ARDEC), Picatinny Arsenal, NJ. These studies were designed to
estimate the rates of dissolution of the high explosives during rainfall events of
various intensities.
Environmental variables. Initial range finding studies identified
temperature, surface area, and energy input as significant to the dissolution
process, and present under possible exposure scenarios. To determine the impact
of each variable on dissolution rate, one variable was allowed to change (for
example temperature at 10, 20, and 30 oC), while the other two variables were
held constant (i.e., surface area and stirring rate). Each set of conditions was
performed at least twice. Beakers covered with aluminum foil containing 500 ml
of reverse osmosis water were allowed to equilibrate to temperature overnight.
Stirring propellers from overhead mixers were lowered into the beakers, adjusted
to the proper rpm setting, and dry explosives added to the beaker sequentially. At
53
Chapter 3 Transport Parameters for Firing Range Residues
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