Contamination may be occurring in areas
ment of the anchoring system, use of a wire-
that were not dredged to a full depth of 90 cm
less remote control system, additional ex-
(36 in.), leaving contaminated sediments be-
tended cutter tines, and relocation of the
hind. Some post-dredging sedimentation
auger drive should all be considered.
and recontamination may have occurred.
2.
Retention basin hydraulic conductivity has
This is highly unlikely.
increased to the point where it will be neces-
Results cannot be compared with discrete sam-
sary to recompact the liner before reuse. Use
pling method results because of the compositing
of a geotextile fabric as a liner may be neces-
of subsamples.
sary for long-term stability due to the sus-
The area dredged in 1996 was about 0.3 ha (0.7
ceptibility of the liner to freezethaw decon-
acre). The average depth is 63 cm (25 in.), a depth
solidation.
sufficient to break the contamination pathway for
3.
The capacity of the basin is sufficient for at
mallards, the largest of the dabbling ducks. The
least two more seasons. It is not necessary
area dredged in 1995 was about 0.15 ha, bringing
from a capacity viewpoint to remove the sed-
the total area dredged since the inception of the
iments at this time, although they may have
dredging study to about 0.45 ha, or 1 acre.
to be removed for effective recompaction of
No dead ducks or swans were observed in or
the liner.
near dredged areas. The length of the channel
4.
The use of a coagulant such as aluminum sul-
dredged out to C Pond in 1996 will not be suffi-
fate (alum) or a polymer will facilitate the
cient for the blast and drain approach. It also does
flocculation and settlement of suspended sol-
not increase the connectivity between the Clunie
ids in the basin and should reduce the rein-
Pond area and Pond 183 in Area C, a highly con-
troduction of trace amounts of colloidal
taminated area that is a candidate for further
white phosphorus into ERF. Alum is effective
dredging or pumping.
for pH values of 5.5 to 8.0 (Corbit 1990),
Results of the abbreviated attenuation study for
which covers the range of conditions found
dredging are limited. Overwinter conditions are
in ERF (Racine et al. 1993). Polymers have
not conducive to drying of sediments. Sediment
been used effectively to treat runoff at mine
sample soil moisture contents averaged around
sites in Alaska such as the Usibeli Coal Mine
77% in June in areas where thickness exceeded 18
at Healy.
cm. Some attenuation of contaminant will occur
5.
Basin investigations should be continued to
even under these less-than-ideal conditions.
ensure the viability of the system. The basin
About 20% of the WP particles in planted plugs
hydraulic conductivity should be checked
disappeared overwinter in moist areas, and all the
yearly to ensure integrity.
WP was gone at the one dry area.
The organic content of dredged sediments
6.
Closer monitoring of the dredging operation
reflects those typical of the Flats in area adjacent to
by the Contract On-site Representative
the spoils line (≈ 4.5%). Sediments farther from the
(COR) may be necessary to ensure that the
deposition delta appear to be inorganic. The
parameters of the contract are being met and
organic content of the basin sediments highly
progress is being reported correctly. We
influences attenuation of contaminant. Results of
found the dredged area to be half what the
limited basin sampling prior to the 1996 dredging
contractor claimed anAd the dredged depth
indicate that most of the contaminant is gone from
was not to specifications.
the sediments.
7.
The attenuation study should be continued
to monitor the efficiency of the natural atten-
uation process in the basin. Without this in-
RECOMMENDATIONS
formation, too many assumptions will have
to be made in determining the treatment and
The following recommendations are made
remediation of the contaminated sediment.
based on work done from 1993 through 1996.
The basin is a safe, representative area in
They are listed to correspond to the order of the
which some controlled attenuation studies
subject matter in this report and are not in order of
may be conducted.
importance or urgency.
8.
The absence of waterfowl mortality in and
1. Further optimization of the dredge system
adjacent to the dredged areas, which were
will facilitate the dredging process. Refine-
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