white phosphorus contamination and potential treata-
be occurring at a highly contaminated site (Site
bility at Eagle River Flats, Alaska (C.M. Collins and
883) in the intermittent pond of Area C. When 41
samples were taken at this site in the fall of 1995 at
D. Cate, Ed.). CRREL Contract Report to U.S.
the same locations as 41 samples in the fall of
Army, Alaska, Directorate of Public Works, FY96
1992, the number of samples with WP concentra-
Final Report, p. 3550.
tions greater than 10 g/g declined from four to
White phosphorus is a difficult contaminant to
zero, and the number of samples below 0.001 g/
characterize in the environment. Spatial hetero-
g has increased from 15 to 28. In addition the
geneity of concentration estimates is extreme,
number of WP particles at this site has decreased;
varying over many orders of magnitude for close-
in 1992, when 270 mL of sediment from this site
ly spaced discrete samples. Therefore, any
was sieved, over 100 WP particles were isolated.
attempt to determine remediation success at ERF
In 1995, 1000 mL of sediment was sieved using the
based on concentrations found in sediment sam-
same procedure, and only one WP particle was
ples would be costly owing to the enormous num-
found. Sediments at this site were desaturated
ber of samples required to make an informed
during the summers of 1993 and 1994 when
decision. Because the goal of remediation at Eagle
weather conditions and the length of time be-
River Flats is to reduce waterfowl mortality, we de-
tween flooding tides were favorable for pond
veloped a composite sampling method designed
shrinkage. During 1995, flooding tides occurred
specifically to determine the presence of white
monthly, and sediments at this site were continu-
phosphorus particles (the form responsible for
acute poisoning of waterfowl at ERF), and we
ally under water.
demonstrated the feasibility of this approach in a
Samples were also obtained from the crater
produced from the detonation of a WP UXO in
contaminated pond in Area C.
1992. The crater is also in the intermittent pond of
To form each composite, many small samples
Area C. The rim of the crater, which had a WP con-
were pooled and passed through a 0.59-mm mesh
centration of nearly 1000 g/g when sampled in
to remove the fine-grained material. The material
1992, had concentrations of 0.0051 and 0.0006 g/g
left on the mesh was examined for white phos-
when sampled in June and September 1995. The
phorus particles. The samples were collected on
bottom of the crater, which is 32 cm below the rim,
square and triangular grids, and the distance
still has high concentrations of WP. The bottom of
between samples was based on the assumption
the crater was exposed in 1993 and 1994, but for
that most of the available white phosphorus is
located in hot spots with radii of approximately 1
much shorter lengths of time than the rim. WP
m. Unless the number of hot spots is large, the dis-
particles were isolated by sieving 1000 mL of sed-
tance between samples must be on the order of 2
iment from the crater bottom, and over 100 parti-
m to maintain a low risk of not hitting a single hot
cles were found, most of which were less than 1
spot. The area we sampled was highly contami-
mm in length. WP particles were also isolated
nated, and white phosphorus particles are still
from a permanently saturated site on Racine Is-
abundant within the top 9 cm of sediment.
land. While most of the WP particles isolated were
For this study we also collected and analyzed
also less than 1 mm in length, several large parti-
individual discrete samples. The concentrations
cles (greater than 2 mm) were also found, with the
found in these samples showed that sites with
largest particle measuring 6.6 mm in length. Such
high white phosphorus concentration and con-
large particles were absent from sites in the inter-
taining solid pieces of white phosphorus are
mittent ponded areas. We hypothesize that when
indeed located within small areas (hot spots)
sediments are exposed and desaturate, the small-
punctuating a much larger area containing low
concentrations of white phosphorus. This spatial
pear relatively quickly since small particles have
heterogeneity necessitates closely spaced sam-
large surface-to-volume ratios and sublimation
pling, which in turn requires compositing to
occurs from the particle surface. Larger particles
are much more persistent but shrink during peri-
reduce analytical costs.
ods of desaturation.
We believe composite sampling will provide
cost-effective data upon which decisions may be
made as to whether an area remains contaminated
Walsh, M.E., C.M. Collins, and R.N. Bailey
(1997) Demonstration of sample compositing
with white phosphorus particles.
methods to detect white phosphorus particles. In
Interagency expanded site investigation: Evaluation of
Walsh, M.E., C.M. Collins, and R.N. Bailey
70
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