crete samples to represent a grid, and either ana-
samples using data from Method 8330. In addi-
lyze each separately, or produce a composite
tion, the HMX results for the four composites from
sample. The composite sample is a physical aver-
the 0- to 15-cm depth are also in good agreement
age of the discrete samples and it can be analyzed
with the mean of the discrete samples analyzed
instead, with replication when needed. Analysis
using the on-site colorimetric method. Develop-
of a large number of discrete samples is quite
ment of improved procedures for dealing with
attractive scientifically, but it is impractically
dust losses will likely further improve the agree-
expensive using currently available methods. The
ment.
use of composites is attractive from a financial
Overall, the results from this experiment verify
point of view, but it must be shown that compos-
our earlier conclusions (Jenkins et al. 1996, 1997a)
ites can be prepared using simple, fieldable pro-
that it is feasible and inexpensive to produce com-
cedures, and that the resulting composites are rep-
posite samples on-site using simple procedures,
resentative of the discrete samples from which
and that the resulting composites are a good way
they were prepared.
to estimate mean explosives concentrations within
Research conducted at a number of explosives-
grid-sized areas. When the objective is to obtain
contaminated sites has demonstrated that a simple
an unbiased estimate of the mean concentration
method quite successfully produces composites
within a grid, it may be appropriate to collect
that are in good agreement with the mean
samples randomly, in so far as that is possible in
values of the discrete samples making them up
the presence of UXO.
(Jenkins et al. 1996, 1997a). To ensure that this is
also true for the soils at the inland ranges at Fort
Ord, an experiment was conducted using the dis-
SUMMARY AND CONCLUSIONS
crete samples from area 1-44. Composites were
prepared for three depth intervals from the four
A set of 280 soils samples was collected from
grids in this sampling area. The results from
depths ranging from 015 cm to 105120 cm at in-
extraction and colorimetric analysis of these com-
land firing ranges 44 and 48 at Fort Ord in August
posites are presented in Table 9. In all cases, the
1997. Analysis of these samples showed that HMX
results for HMX in these composite samples are
was the explosives residue that was present in
within the range produced by the mean plus or
highest concentration at these ranges. Concentra-
minus a standard deviation for the discrete
tions as high as 587 mg/kg were measured in sur-
Table 9. Results for assessment of composite preparation method.
HMX concentration (mg/kg)
Discrete sample
Discrete sample
Composite
mean from
mean using
sample using
Sample
Method 8330
on-site method
on-site method
295 142
1-44-(1-4) (015 cm)
231
262
0.6 0.3
1-44-(1-4) (3045 cm)
0.4
2.5 3.1
1-44-(1-4) (105120 cm)
2.6
320 246
1-44-(5-8) (015 cm)
198
186
0.6 0.2
1-44-(5-8) (3045 cm)
0.5
3.1 3.3
1-44-(5-8) (105120 cm)
0.7
109 133
1-44-(9-12) (015 cm)
66.2
95.8
0.7 1.2
1-44-(9-12) (3045 cm)
0.5
0.5 0.6
1-44-(9-12) (105120 cm)
0.4
1.4 1.9
1-44-(13-16) (015 cm)
0.7
ND
1-44-(13-16) (3045 cm)
ND*
ND
1-44-(13-16) (100120 cm)
ND
NA†
*Not detectable.
†Not available.
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