360
LIST ET AL.
SAMPLE COLLECTION AND ANALYSIS
The samples were taken with two instruments: a “cookie cutter”
that removés a 3.5-in.-diameter core to a depth of 2 in. and an orchard
auger which cuts a hole the same diameter as the cookie cutter and
removes the soil to the desired depth from a beginning depth of 2 in.
The cookie
cutter is used for the first 2 in. because the auger has a
tendency to make a hole larger than its diameter as it cuts through a
mat of grass and roots. In all cases, the error in the measurement of
the sampled area was ndt greater than 1 or 2%.
The sample includes all the vegetation, both living and dead. The
final aliquot for analysis includes the proper fraction of vegetation that
segregates during sample preparation. Also, all rocks are crushed and
included in the analyzed sample. The sample is usually a composite of
20 individual cores. The weight of the sample ranges from 20 or 30 lb
for highly organic or peaty soils to as much as 100 lb for samples
taken to a depth of 10 in. from dense soils.
After the soil was dried, crushed, and homogenized, aliquots of
about 1 Ib, identified only by number, were sent to the Health and Safety
Laboratory (HASL) for analysis. Two aliquots were sent from each
sample, but each member of the pair was sent in a different group to
include a time-of-analysis variable. In addition, single blind aliquots
of 41 of the soils were also analyzed at the Soil Survey Laboratory of
the Soil Conservation Service at Beltsville, Md. The results of the comparison of the two analyses performed on each sample by HASL are
shown in Fig. 1, An intercomparison of the HASL and the Soil Survey
Laboratory results is shown in Fig. 2.
The extraction of the Sr was accomplished by an HCIleach.
However, there are unresolved differences between the results obtained
by an HCl] leach and by a more complete dissolution of the sample by
fusion. The HCl leach values are about 5 to 10% lower than the fusion
values. These differences are currently under intensive study, and it
is hoped that they will be resolved in the near future. Until that time
the reported soil data must be viewed as tentative.
Samples
collected in the 1963 to 1964 survey were taken toa
depth of 8 in. Previous studies‘ have shown (Fig. 3) that virtually all
the *Sr is contained in the upper 8 in. of soil.
It is also possible to compare the fallout of Sr in the period
from 1960 to 1963, as indicated by the soil samples, with that collected
by means of pots and ion-exchange columns inthe monthly precipitation
sampling network of HASL. At 15 sites the soil samples were taken
within a few miles of the precipitation samples and at approximately
the same elevation. A comparison of the soil increment with the total
observed precipitation deposition over the same interval is shown in
Fig. 4. The unlabeled points in the lower portion of the diagram repre-