controlled dredge designed to remove sediments
In December 1995, a list of possible improve-
from contaminated ponded areas and to continue
ments to the equipment was given to the contrac-
an efficacy study of the treatment of the spoils in
tor. A few of these changes were implemented pri-
an open retention basin. The treatment method
or to dredging and more during dredging as the
will be the natural attenuation of the white phos-
contractor saw the need for them after familiariza-
phorus, once conditions of the sediments in the
tion with the equipment and operation. The pri-
basin are conducive to sublimation.
mary change to the equipment was the placement
Dredging was chosen as a method of remedia-
of the auger drive behind the augerhead, rather
tion because of the positive removal of the con-
than on its side. This change was not implemented
taminated material and the ability to treat the
as recommended, however, and the 3-in. protru-
material in a controlled environment. By using a
sion on the side of the augerhead enclosing the
small, remote-controlled dredge, limited areas
drive continues to be problematic. Stress on the
could be dredged, and the contaminated material
augerhead cutter resulted in the breakage of one
(spoils) can be quickly and efficiently transported
auger assembly, which was quickly replaced by
to a retention basin for treatment. Environmental
the contractor using one of the spare units on
impact to the salt marsh system, although not neg-
hand. The contractor made some improvements to
ligible, can be minimized through a careful dredg-
the system, and the system continues to work fair-
ing strategy. Because of the presence of unex-
ly well. A patent application has been submitted
ploded ordnance, an unmanned system was
for this device.
required.
Anchoring points continue to be problematic.
This is the third year of the dredging project at
The contractor was convinced shortly after startup
Eagle River Flats. The first year primarily involved
that the lateral winch system was not feasible in
processing a contract for the dredge equipment;
the Flats environment, and a manually adjustable
designing, constructing, and testing a spoils reten-
system was devised using telephone pole anchors,
tion basin; integrating specialized equipment to
similar to the anchoring system used last season.
the dredge; getting the leased equipment opera-
This eliminated the need for helicopter support,
tional; and test dredging a small area at the Flats.
thereby saving a substantial sum of money and lo-
During 1995 three tasks were undertaken: contin-
gistical effort. Further work on this system is
ued investigation of the hydrological properties of
required. Improvements to the spoils transfer line
the retention basin; dredge operations; and initia-
eliminated any blowouts like those experienced
tion of the attenuation study in the Basin. This
last year. The contractor is currently looking into a
year, 1996, the operation of the equipment was
radio-control package to improve reliability of the
turned over to a local contractor. An area was des-
dredge control system.
ignated for dredging, and technical assistance was
In September, funding was received to enable a
provided for the initial setup and operation of the
trip to collect and analyze bottom samples and to
equipment.
survey the area dredged. Survey data indicate that
Although all sampling and testing was origi-
the dredged depth is around 51 cm, significantly
nally cut from the project proposal, limited sam-
less than the 90 cm specified. The area dredged is
pling and testing were conducted in the basin and
approximately 0.29 ha. Results of the spoils line
on the spoils entering the basin. Datalogger sta-
sample analyses indicate that contaminated mate-
tions were reinstalled in the basin to monitor such
rial continues to be transferred from the Flats to
parameters as air and soil temperature, soil mois-
the retention basin. Of 12 spoils samples analyzed,
ture, and water level. Prior to the start of dredging,
three were contaminated with white phospho-
two percolation tests were performed in the basin.
rous. One of five water samples taken from the
outflow line was slightly contaminated (<1 g/L).
Both tests indicated a percolation rate above the
acceptable level of 106 cm/s. The higher percola-
The small number of samples taken limits the con-
tion rates are probably attributable to the reduction
clusions that can be drawn from the data, al-
in liner density caused by the severe freezethaw
though results are similar to the larger sampling
cycling that occurred over the previous winter,
program conducted in 1995.
when lack of snow exposed the liner to solar and
temperature variations. The lack of funds for
Walsh, M.R., C.M. Collins, and D.J. Lambert
improving the liner, as well as the proximity of the
(1998) Implementation of a remote pumping sys-
test results to acceptable levels, resulted in the use
tem for white phosphorus remediation in Pond
of the basin in the condition found.
183. In Interagency expanded site investigation: Evalu-
74
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