described for samples from other sam-
Table 5 (cont'd). Results from sampling location 5, Hawthorne
AAP site.
pling locations (Table 5b). The best fit
linear regression is shown in Figure 6.
b. Statistical analysis of TNT concentrations (g/g) for discrete
The slope for the best fit line with
and composite.
intercept was 0.688, which was con-
Discrete samples
siderably lower than the slope for the
On-site analysis
Laboratory total
best fit line with zero intercept (slope
Sample
Mean
Mean of logs
Mean
Mean of logs
= 0.847). Nevertheless, a paired t-test
of field vs. lab results indicated that
126d†
1
2.101d
117d
2.065d
results for the two methods were not
2
110e
2.039e
271b
2.433b
significantly different at the 95% con-
3
373a
2.571a
375a
2.573a
fidence level. As can be seen in Figure
6, the two highly divergent samples
4
57.6f
1.760f
52.7e
1.722e
from the fitted model are on opposite
5
12.9g
1.109g
12.7f
1.102f
sides, which is to say that the large
6
172c
2.234c
244c
2.387c
random error tends to mask the sys-
tematic difference. However, ANOVA
7
243b
2.385b
105d
2.019d
comparing field and lab data for the
† Numbers
designated with the same letter are not significantly different at the
composite samples yielded an F ratio
95% confidence level.
of 60.8, which was significant at the
ANOVA for on-site and lab analyses
99.9% confidence level. The ratio of
field (139 g/g) to laboratory (193
Untransformed
On-site
Lab
g/g) results is 0.72, which is in excel-
F ratios
1061***
282***
lent agreement with the slope (0.688)
Error MS
27.601
122.00
of the linear least squares model (Fig.
Least sign. diff.
12.4
26.1
6) and confirms the presence of bias.
Analysis s
5.3
11.0
Sampling s
121
131
Overall, the relationship between the
(s = standard deviation)
field and lab methods for location 5 is
poorer than those found for other sam-
Linear correlation analysis for on-site analysis vs. lab analysis
(r = correlation coefficient)
pling locations. Thus, while the accu-
Slope
Intercept
r
racy of the field method for soils at
location 5 is not optimal compared
untransformed, non-zero intercept
0.688
40.63
0.745
untransformed, zero intercept
0.847
0
0.714
with what we have described previ-
log-transformed data
0.848
0.296
0.894
ously, it is still acceptable in light of
the large degree of concentration het-
Results of paired t-tests for on-site vs. lab results
erogeneity.
Means of seven discrete samples, t = 0.35 (NS)
Composite samples
Sampling location 6
On-site analysis
Laboratory total
Acetone extracts for soils at sam-
n
7
7
pling location 6 were bright fluores-
mean value
139
193
standard deviation
16.6
7.72
cent-yellow, an indication that the
RSD
12.0%
4.0%
major contaminant was probably am-
monium picrate. Laboratory results
ANOVA comparing on-site and lab analyses
F ratio = 60.8***
confirmed that ammonium picrate
was the contaminant present at high-
* Significant at the 95% level
*** Significant at the 99.9% level
est concentration, with TNT and other
** Significant at the 99% level
NS Not significant at the 95% level
nitroaromatics present at lower con-
centrations (Table 6a). Reaction of
these acetone extracts with the EnSys TNT re-
for sampling standard deviations were 121 and
131 g/g. Thus, here again, sampling error over-
agent produced very erratic results; the test was
probably not functioning properly in the pres-
whelms analytical error by over an order of mag-
nitude.
ence of ammonium picrate. Subsequent labora-
Linear correlation analyses for the field and
tory experiments confirmed that ammonium pi-
lab results were conducted in the same manner as
crate interferes with the on-site TNT analysis test.
20
Previous Page
