Sampling for cleanup would most likely be
done in a sequencial manner in order
to keep costs to a minimum.
The basic idea would be to take a limited
number
of samples and make a decision whether
to clean up or to withhold judgment :
until more samples are collected. The general
approach as it igs ap lied Li
industry is discussed by Burr (1976, Chapter
12).
The use of acceptance .
sampling using either attributes or average
concentrations requires that
samples be collected at random within relativ
ely homogeneous areas
The
Procedure outlined above should thus be
applied separately within each such
area. The assumption of random sampling
within areas is important in order to
preserve the chosen a and 6 risks.
Consequently, the use of alternative
sampling plans such as sampling on a systema
tic grid would need to be carefull
evaluated before being used in a field study.
_
Once the initial cleanup operation has been
completed, additional samples will
be required to assure that cleanup to the level
desired has been accomp lished
The design of this phase of the sampling
program can also be based on acceptance
sampling, although the details may change
from those described above.
Tf a
final demonstration (certification) is require
d and the attribute approach is
adopted, then Table 12 in Burstein (1971)
can be used to determine the number
of samples required to be 100(1-8)% sure
that the true Proportion of samples
with concentrations greater than the cleanup
level, L, is less than P
"This
approach fs based on the assumption that
the cleanup operation has ben success~
a 50 that an samples will have concent
rations less than L.
Sampling to
ans
tha eous areas ene have been met
nsure
homogen
should also be done independently
The design of a cleanup sampling plan
may involve a combination of in situ
measurements and Pu concentrations in soit
samples.
If so, these two measurement systems must be well calibrated so that
their results can be related
The double sampling approach investigated
by Gilbere and Eberhardt (1976) at
NTS safety-shot sites offers an approach to
estimate the optimum allocation of
effort between the in situ measurements and
soil samples.
°
SAMPLING DESIGN GUIDELINES
Based on our experfence in helping design some
of the NAEG soil and vegetation
studies at safety-shot sites, we would like
to suggest several guidelines
relative to the design and statistical analysis
of environmental radionuclide
studies, These guidelines are directed towards
estimating the total amount
and spatial distribution of transuranics, but
the design principles are als
applicable to ecosystem-type studies,
°
Guideline 1:
Break Study Area Into Homogeneous Subareas
On the basis of field surveys, information from
similar studies, topography of
the land, vegetation patterns, or any other
relevant information attempt to
divide the total study area into subregio
ns (commonly termed "blocks" or
strata") such that the variability in radionuc
lide concent rations within
subregions is less than that expected for the entire study site.
If this
stratification is successful, the end result should be a more precise estimate
of inventory for the whole site.
In addition, of course, estimates of inventory
will be obtained for each stratum separately, which are useful for relating
trends in soil concentrations with concentrations in other ecosystem components,
The success achieved in increasing the precision of the inventory estimate for
the entire study site depends on how effective the stratification has been in
dividing the area into relatively homogeneous blocks or strata (Gilbert et
al., 1975). An inappropriate choice of strata will yield little if any benefit
in increased precision.
It has been our experience that it may not be possible
to construct a satisfactory statification plan without conducting field surveys
and/or collecting samples prior to the main study. This leads us to the next
guideline.
Guideline 2:
Consider Pilot Studies
If relevant information on the variability and spatial pattern of the radionuclide is not available, a pilot study may yield information that will aid in
the design of the main study.
It will, hopefully, give indications of trends
and levels of variability necessary for defining strata. The kind of information obtained in the pilot study should be appropriate for estimating the
number of samples needed in each of the strata to achieve the maximum possible
increase in precision of the estimate of inventory or to achieve a specified
precision needed to meet the objectives of the study. For example, FIDLER
survey readings for 7"!Am would not in themselves be adequate for estimating
the variability of 24!am concentrations in 10-gram aliquots of surface soil.
A FIDLER survey in conjunction with soil samples collected at a number of
FIDLER locations would, in general, be a better approach, Then it might be
possible to relate the variability and level of FIDLER readings to those for
soil sample concentrations in order to approximate the optimum number of
samples for each strata. Of course, the total funds available for the study
put an upper limit on the total number of samples that can be collected and
analyzed, The number of samples allocated to the various strata could also
involve costs of collecting samples if this cost varies substantially between
Strata. Gilbert et al. (1976a) discuss how the allocation was accomplished
for the Area 13
(Project
57)
safety-test site on NTS.
Guideline 3: Use Random Sampling Within Strata or Random Sampling in
Conjunction With Systematic Sampling
Careful consideration needs to be given to the method used to determine the
actual sampling locations. Statisticians tend on theoretical grounds to favor
random over systematic sampLing. The theory of statistics that permits the
formulation of probability statements and inferences about the universe from
which sample data are taken 1s based on the notion of drawing samples at
tandom. However, the greater ease with which systematic samples on a grid,
say, can be collected under field conditions, and the need in many cases to
insure that all portions of the study site are sampled are reasons for considering systematic sampling.
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