within the pond, exposing much of the pond bot-
tom sediments for an extended period during the
tamination. Maximum soil temperatures at the
5-cm depths were 25C for both sites, with an
summer. These sediments would then be moni-
average temperature of 16C. The siphon lowered
tored to determine soil moisture conditions and
any decreases in WP concentrations.
the pond water level faster than natural draining
and evaporation alone, but it was slow. However,
Collins, C.M. (1995) Pond draining treatability
it probably did not lower the pond level below
study. In Interagency expanded site investigation:
that which it would have attained without the
Evaluation of white phosphorus contamination and
siphon. The soil moisture sensors at all depths at
potential treatability at Eagle River Flats, Alaska
both sites did not change during the summer,
(C.H. Racine and D. Cate, Ed.). CRREL Contract
indicating that the sediment remained saturated
Report to U.S. Army, Alaska, Directorate of Public
throughout the period.
Works, FY94 Final Report, p. 529562.
Work by M.E. Walsh has shown that WP con-
Collins, C.M., E.F. Chacho, M.R. Walsh, and M.E.
tamination in intermittently flooded pond bot-
Walsh (1996) Pond draining treatability: 1995
tom sediments will also begin to sublime in situ if
studies. In Interagency expanded site investigation:
Evaluation of white phosphorus contamination and po-
the sediments are subaerially exposed long
tential treatability at Eagle River Flats, Alaska (C.H.
enough for the sediment to dry below saturation.
Whether the WP particles will disappear and how
Racine and D. Cate, Ed.). CRREL Contract Report
fast will depend on how long the sediments
to U.S. Army, Alaska, Directorate of Public Works,
remain unsaturated and what the average soil
FY95 Final Report, p. 250310.
temperature is. Isolated ponds that are contami-
The overall objective of this treatability study
nated with WP may not normally become dry
was to assess if pond draining is a viable option
enough to expose the contaminated pond bottom
for remediating the WP-contaminated Bread
sediments or expose them long enough to
Truck Pond in Eagle River Flats. To achieve that
become unsaturated. Therefore, artificially drain-
objective, several tasks were undertaken to deter-
ing the pond, either temporarily or permanently,
mine if pond draining was technically feasible
would expose much of the WP-contaminated bot-
and what environmental conditions occur in the
tom sediment, thus possibly allowing for the in
pond-bottom sediments following draining. Task
situ sublimation of WP particles.
1 was to determine the environmental conditions
In this study the potential for draining a con-
in BT Pond before and after temporarily lowering
taminated pond to a level where natural attenua-
the pond level by using a pump system. We
tion of WP could occur was investigated. The
installed instrumentation at eight sites along a
study was carried out in the Bread Truck (BT)
transect through the intermittently and perma-
nently flooded areas of the Bread Truck Pond to
Pond. Four sites were instrumented to monitor
measure the sediment moisture and temperature
pond levels, sediment moisture, and temperature
monitored at 5- and 10-cm depths in the pond bot-
along a transect from a deeper, permanently
tom sediment. We also continuously measured
flooded pond area, through the shallower, inter-
the water surface elevation of the pond. WP parti-
mittently flooded area. A survey of the marsh
cles were planted in May at a depth of 5 cm at each
area to the east of BT Pond showed that there was
site to monitor any reduction in size. Because of
no direct connection between BT Pond and the
procurement delays for the pumping system, the
C/D marshpond complex in the form of a chan-
pond was not drained and sediments remained
nel or drainageway that would allow direct flow
between the two areas. Site elevations ranged
saturated throughout the summer.
from 4.80 to 4.90 m.
Task 2 was to design, procure, deliver, and
A siphon system consisting of 165 m of 6.1-cm
install in the BT Pond a large dewatering pump
(4-in.) ID rigid PVC plastic pipe was installed
system to be used to temporarily drain it. Design
from BT Pond to a tidal gully north of the pond.
specifications of the integrated pump and genera-
The siphon was filled and started on 25 June fol-
tor system were determined in January 1995. We
lowing the last flooding high tide. The pond level
specified an integrated system consisting of a
started dropping as water flowed out through the
2000-gal./min electric-powered pump mounted
gully as well as through the siphon.
on a float platform. A diesel-powered electrical
Even though large areas of pond bottom sedi-
generator to power the pump was mounted on a
ment were subaerially exposed, they did not dry
separate float platform. Integrated controls
38
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