30
Boundaries Corresponding to
Ratios of 0.10 to 10.0
20
10
0
QC
Logs of
Concentration Ratios
QA
Figure 4. Frequency histogram for soil VOC QC/QA concentration ratios.
would be inappropriate to establish acceptabil-
99
98
ity limits based on this data. In a recent article
dealing with methods for regulatory analytical
95
environmental chemistry, Kimbrough and Spin-
90
ner (1994) wrote, "If year after year certain meth-
ods produce wildly inaccurate results, then this
should be a signal that the method ought to be
70
evaluated and hopefully improved. The accep-
50
tance of very wide control limits basically sends the
message that if everybody is wrong, then everyone
30
is right." (Italics are ours.) We heartily concur
with these statements and we believe that it is
time to make concerted efforts to improve the
10
situation. If the Corps wishes to use temporary
5
limits while procedures are being brought un-
2
der better control, we suggest 0.254.00. Clearly
0.8
0.4
0
0.4
0.8
QC
this will result in many values being questioned,
Log of VOA in Soil
Concentration Ratios
QA
but wider limits will not encourage the needed
Figure 5. Lognormal probability plot for QC/QA concen-
improvement.
tration ratios of all VOCs in soils with ratios between
Obviously, it is not a trivial task to signifi-
0.1010.0.
cantly improve the procedures used to estimate
VOC concentrations in soils. Before consider-
ing our suggestions for improvement, let's first
arise as a consequence of random rather than sys-
ask if there is more to learn from the archived
tematic errors. The standard deviation is larger
data. We failed to associate any specific laborato-
than expected for a normal distribution and the
ries with either good or bad results. In the ab-
tolerance intervals are excessively wide.
sence of standards and with numerous laborato-
What can we conclude from these computa-
ries participating (including some that serve either
tions? Even after excluding 24% of the ratios rep-
the QC or the QA function on different projects),
resenting the most divergent values, the agree-
ment between laboratories for the determination
it was impossible to establish a pattern. Clearly,
of VOCs on split soil samples is so poor that it
the more laboratories that submit results, the more
9
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