5.
The chairman asked participants to consider the question of what
can be concluded from the available data and whether that data can
lead to a better definition of the scope of work under conditions
prevailing on Runit Island.
There were discussions of the methods
used to obtain available data; the relative degree of preciseness of
aerial in-situ survey and van in-situ survey.
The aerial survey
technique integrates readings over approximately one hectare each
second to approximately three centimeters depth.
Aerial survey isopleth lines are probably limited to an accuracy of + 100 feet.
The
in-situ survey integrates over a field of view of 68.8 feet diameter
and approximately three centimeters depth.
It was concluded that the
data presently available would not support refinement of the scope of
work involved.
6.
Further data is highly desirable.
The chairman then addressed the obtaining of such data.
discussion of methods of measuring both surface level and
contamination levels and the specified removal criteria.
read extracts from the four removal criteria contained in
plan (OPLAN 600-77) (encl 6).
Miss Barnes stated that it
There was
subsurface
Mr. McCraw
the operations
would be
impossible to reach even the 50 percent confidence level of not having
missed significant subsurface contamination without doing much more
profile sampling.
A lower density of measurements would result in lower
confidence in the estimate and a greater error term.
For example, to
find a particular region of contamination two feet wide, under worst
case with the seam parallel to the grid lines, would require sampling
every four feet.
To provide such characterization would require commit-
ment of substantial resources.
a.
If the characterization is done on a simple yes-no criteria
i.e. contamination exceeds a specified level, the sampling need not be
so precise.
Using the highest contamination level recorded on the
island, 3200 pCi/g, Dr. Crites demonstrated a calculation showing that
a pocket of contamination which would average greater than 400 pCi/g
over a 21 meter (68.8 ft) field of view would be approximately seven
meters in diameter.
Thus sampling on a grid of less than seven meters
should locate such a minimum pocket size subsurface contamination of
interest (see also encl 8).
b.
There was discussion on the one half distance technique for
determining the presence or absence (yes-no) of subsurface contamination.
Available data indicates only a few sample locations showing subsurface
contamination at greater than 400 pCi/g levels.
Sample locations are
spaced on approximately a 200 foot grid. Moving one half the distance
between greater than and less than sample points iteratively should
provide boundary definition of contamination areas of interest (see
encl 8).
This investigation would be limited to those areas where
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