Table 13. Dependence of total percent relative standard deviation (CT) on
compositing and analysis schemes using various assumed values for sam-
pling and analysis standard deviations.
Number of
Number of
Percent relative
samples
replicate
standard deviations
composited
analyses
Sampling
Analysis
Total
Cost of procedure ($)
(n)
(k)
(CS)
(CA)
(CT)
On-site
Lab
1
1
50
10
51.0
81
337
4
1
50
10
26.9
86
342
7
1
50
10
21.4
90
347
7
2
50
10
20.2
166
680
1
1
100
10
100.5
81
337
4
1
100
10
51.0
86
342
7
1
100
10
39.1
90
347
7
2
100
10
38.5
166
680
1
1
150
10
150
81
337
7
1
150
10
57.6
90
347
7
2
150
10
57.1
166
680
1
1
100
5
100
81
337
7
1
100
5
38.1
90
347
7
2
100
5
38.0
166
680
1
1
50
20
53.9
81
337
7
1
50
20
27.5
90
347
7
2
50
20
23.6
166
680
7
1
100
20
42.8
90
347
7
2
100
20
40.4
166
680
of k given the relationship of CS to CA. If desired,
the magnitude of both short- and long-range het-
plots of CT vs. n could be formed for various
erogeneity. From these results, a flexible sampling
values of CS, CA and k. We should also remember
plan would evolve with the understanding that it
that the values of CT are for a single composite.
was subject to modifications (if necessary) as re-
Uncertainty in a mean of several composites
sults accumulate. It is our intention to conduct
would be reduced by 1 N where N is the num-
one or more such studies (demonstration projects)
ber of composites averaged.
as the next phase of this research.
Table 13 very obviously shows that improved
reliability of concentration estimates can only be
LITERATURE CITED
to CA. On-site analysis is just as reliable as labora-
tory analysis for TNT in surface soils, and the
Barcelona, M.J. (1988) Overview of the sampling
analysis step doesn't contribute much error any-
process. In Principles of Environmental Sampling
way. When we look at the cost estimates (Table
(L.H. Keith, Ed.). Washington, D.C.: American
13) for on-site vs. laboratory analysis and com-
Chemical Society, p. 123.
bine that with the fast turnaround of on-site analy-
Barnard, T.E. (In press) Extending the concept of
data quality objectives to account for total sample
sis, the advantages of field analysis are clear. In
variance. In Principles of Environmental Sampling,
arriving at the cost of on-site analyses, all materi-
als and their disposal were included along with
2nd Edition (L.H. Keith, Ed.). Washington, D.C.:
capital equipment costs and labor. An allowance
American Chemical Society.
was also made for 10% of the samples to be sent
Cameron, D.R., M. Nyborg, J.A. Toogood and D.H.
for laboratory analysis. Clearly, the cost of
Laverty (1971) Accuracy of field sampling for soil
compositing is relatively small compared to the
tests. Canadian Journal of Soil Science, 51: 165175.
benefits. Unless CS is much lower than found for
EPA (1995a) Nitroaromatics and nitramines by
the sites studied so far, there is no justification for
HPLC. Second Update SW846 Method 8330.
performing replicate analyses of composites.
EPA (1995b) Soil screening for trinitrotoluene
The approach to a new site should involve a
(TNT), SW846 Method 8515. Third Update (Draft)
preliminary field survey to obtain information on
January 1995.
37
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