The New Zealand Department of Health (1974) has reported on the deposition of
238py from the SNAP-9A atmospheric burnup.
The method of sampling the seil
surface was that used by Health and Safety Laboratory (HASL) as previously
discussed by Alexander et ai. (1960).
The high probability of smearing as a result of using the coring tool was
tecognized and caused the authors to conclude that coring, as a sampling
method, should not be used if reliable data are to be obtained for profile
analyses,
Michels (1974) reported on sampling in the Red Desert Basin of Wyoming using a
10-em square “jig" to cut the perimeter of the sample.
Profile samples at the
O- 5-cm and the 5- 10-cm depth intervals were then obtained with a flat-bottomed
scoop.
Although sampling in this case was for 137cg content, the procedure
has been used by others in sampling the soil surface for transuranics.
It is
comparable, except for configuration, to the ring method used by the Nevada
Applied Ecology Group (NAEG) as discussed in the next section.
It is of historical interest to note that a group of scientists interested in
environmental radioactivity met in Washington, D.C., in October, 1970, at the
request of U.S. Atomic Energy Commission to address problems associated with
sampling for plutonium.
The objective of the working group was to provide
guidance relative to sampling techniques.
Essentially the group recommended
the HASL method of sampling (Harley, 1972), but recognized sampling problems
associated with accidentai or operational releases that could not be covered
by the HASL method.
The meeting occurred after the experience of cleanup of
plutonium from two nuclear devices accidentally destroyed at Palomares, Spain,
but prior to the initiation of studfes at the Nevada Test Site (NTS) by NAEG.
The full impact of the problems associated with accidental or operational
releases was probably not recognized.
Aarkrog and Lippert (1974) sampled a variety of soils in Denmark for ?°%Ssr,
137cg, and "gamma radioactivity." Samples were obtained with a Van Veen
sampler; however, that sampler did not well define the depth sampled.
For
profile samples, a "HAPS" bottom core tool was used.
The HAPS sampler was
designed for sampling bottom sediments but was tested on terrestrial soils.
It is of interest that the authors did compare results obtained by the two
methods and concluded that the same degree of accuracy was obtained with
samples collected by both methods to a 4-cm depth.
Aarkrog and Lippert (1975)
later reported on sampling to a depth of 50 cm with a HAPS bottom corer.
The
nature or description of both the Van Veen and HAPS samplers could not be
found except that they both appear to be modifications of coring tools.
Hardy (1974) has used a sampling procedure similar to the NAEG trench procedure
to obtain profile samples to determine depth of penetration and the distribution
of global fallout 239°240py in soils.
He cautioned against using the procedure
where rocks and stones are prevalent and where cross-contamination of lower
profile cuts with higher radioactive material from above could occur.
The
cross-contamination effect of worms and burrowing insects, cracks from swelling,
and other biological and physical disturbances were alluded to but not discussed.
Accidental or Operational Releases
Sampling techniques used in evaluating the accidental or operational releases
of radionuclides depend on the Specific mission aad may or may not be similar
to those used for global fallout.
Differences in the methods are dictated by
the nature of the radionuclide distribution in the soil, the range of particle
sizes, and the generally higher levels of radioactivity associated with accidental or operational releases compared to global fallout.
Fowler et al. (1968) initiated an extensive soil sampling program at Palomares,
Spain, after the accidental destruction of two nuclear devices.
The mission
designated sampling for plutonium to a depth of 45 cm to determine inventory
and to estimate vertical distributions.
A core tube (King tube) was used and
efforts were made to divide the profile into discrete segments.
Results among
replicates at common depths obtained from areas of high contamination were
considerably variable (up to two to three orders of magnitude); hence, data
were treated en masse rather than as discrete sections of profiles.
28
Poet and Martell (1972) discussed the measurement of plutonium and americium
contamination levels in the environs of the Rocky Flats plutonium plant and
elsewhere in the greater Denver area cf Colorado.
Their sampling procedure
was not discussed in detail but consisted of collection of both surface samples
to a depth of 1 cm and soil profiles to a depth of 14 cm.
Surface samples
were collected from even, undisturbed sites that had not been subjected to
irrigation or plowing. Where the history of the site was not known, samples
were taken along old fence lines midway between posts. Each soil sample was
collected over an area of 1000 cm* by spatula to the desired depth as uniformly
as practical.
Profile sampling was not discussed except that precautions were
taken to avoid contamination from the shallow soil horizons.
In 1970, the Soils Sampling and Analysis Committee of the NAEG outlined a
sampling technique to be used in areas at NTS where plutonium, americium, and
uranium were dispersed in localized areas.
A detailed discussion of that
sampling technique was presented by Fowler et ai. (1974).
In brief, sampling
polnta are selected randomly and may be grouped into strata {regions of similar
radioactivity levels, or of a similar physical nature) in order to reduce the
variability.
The surface sampling tool is a steel ring 12.7 em in diam and
either 2.5 or 5 cm deep.
A lip is welded to the upper edge to provide rigidity,
a surface for application of pressure, and to assure constant depth of penetration. The 12,.7-cm diam of the ring is dictated by the diameter of a radiation
detector used to obtain tn situ measurements of associated radioactivity (in
this case, the 60 keV gamma emissions of 74!am).
Surface area and depth
define the volume; the weight of that volume of dry soil defines the field
bulk density. Those data are necessary to convert radioactivity per unit
weight measured by analytical techniques to radioactivity per unit surface
area, Soil adjacent to the exterior of the ring is removed to the depth of
the ring; the confined volume is then transferred to a plastic bag using an
appropriate tool.
Depth profile samples may be drawn using this method by
repeating the steps for each subsequent depth to be sampled.
Removal of soil
exterior to the ring is necessary to minimize the possibility of cross-contamination of deeper, less radioactive fractions; rings and tools must be decontaminated or replaced after each use.
29