Dr. Don Hendricks
specified spots.
-8-
August 28, 1972
It should also be understood that there is no purpose in
replacing or substituting sample locations.
If there is some obstacle to
sampling at a specified location (e.g., a concrete pad) then that fact
should be recorded in the field and no sample taken.
for this point.
There are two grounds
One, the heterogeniety of concentrations is such that shifting
over a few feet prohibits calling the new location typical of the old, and,
two, that obstacles to sampling are important in clean-up considerations -a chunk of concrete or a tree will offer problems, and the frequency of such
problems ought to be estimated from the survey.
While it is sometimes
hard forfield workers to accept the policy of "no substitution", I think it
is an important consideration and ought to be a hard and fast rule.
If it
seems desirable, some extra allowance in sample size can be made to get
"enough" actual samp'tes, but the statistical evidence is simply "no sample
point = no information" (or information of another kind, i.e., x% of the area
has obstacles of a Specified kind).
If there is reason to treat certain
kinds of areas differently, then where possible, those areas ought to be set
up in advance as specified sampling units.
In particular, disturbed areas
might fall into such a class.
The above procedure may need to be cleared up in telephone conversations
of other discussions.
The essentials are to decide in advance what areas
are to be treated as units, to set up maps of these units and to locate
sample points at random on those maps.
Where several islands are to be
combined, the sampling should be at random over the group of islands, and
not limited to a fixed number per island.
If, however, a decision is made
to fix the number of plots per island, we can handle this in the subsequent
analysis.
You will pay a price for this in«cthe sense of taking a somewhat
larger sample than needed for statements about islands as a group {or
by getting a wider confidence interval).
Double-sampling
The above proceeds as though wet-chemistry analyses for plutonium are to
be made for all samples.
Very likely this is not practical, and we are
assuming that it may be possible to use a combination of wet chemistries and
readings by a Ge/Li ("Gelly") detector.
To do this within the limitations
of statistically acceptable practice calls for some finesse, and constitutes
the biggest source of worry for us in the entire survey.
For one thing,
there are some technical points we're not quite sure of, and these may take
a fair bit of time and effort to sort out.
Obviously there may be places
where the Am/Pu ratio may be so variable as to make the technique unusable.