1. Physical system processes can produce a
ponds can resuspend WP contaminated sediments,
natural attenuation or in-situ degradation and re-
as evidenced by analyses of resuspended materi-
moval of WP from a significant portion of the
als in sediment traps. Gully transport during ebb
ERF ecosystem (Fig. 55).
moves these sediments into the Eagle River.
2. Gully erosion and headwall recession will
Samples of material trapped by plankton nets
begin to drain large areas of contaminated ponds
record WP-contaminated sediment transport dur-
in about 1 to 10 years, potentially resulting in in-
ing ebb tide. Analyses of samples from sediments
situ WP degradation and attenuation from dry-
adhering to ice floes are evidence that ice can erode
ing; it is a cost-effective alternative to artificial
and transport WP-contaminated sediments. Field
remediation (Fig. 35a). Historical photographic
sampling of sediment in transport in a natural
analyses, field data and process analyses indicate
setting, rather than in a controlled laboratory, is
that Bread Truck Pond will probably begin drain-
difficult in the intertidal environment and was not
ing in 1 year; C/D-Pond, Lawson's Pond and a
possible in Eagle River or Knik Arm during tidal
large area of C-Pond will begin draining in 10 to
ebb. Given the fine particle size of both the sus-
15 years or less.
pended and bed loads, it is likely that these sedi-
3. Sedimentation rates appear sufficient to bury
ments are transported into Knik Arm where their
WP in certain ponds and can reduce the risk of
fate is unknown. Whether WP erosion, transport
feeding waterfowl being exposed to WP contami-
and redeposition make up a quantitatively impor-
nation.
tant biologic hazard cannot be assessed because of
4. Natural sedimentation, perhaps artificially
the limited number of samples acquired during
enhanced in some ponds by flocculation or other
this study and the generally random nature of WP
means, is a cost-effective alternative that removes
occurrence in ERF.
WP from feeding waterfowl through burial. Ar-
7. Racine Island Pond has neither high gully
eas of C/D-Pond, Lawson's Pond and A-Pond
erosion and recession rates, nor high sedimenta-
are sites where sedimentation and burial are im-
tion rates. It also floods at a relatively low tidal
portant in reducing exposure (Fig. 55). Sedimen-
elevation (4.35 m). Because the pond bottom sedi-
tation and burial may be the best solution in iso-
ments are rich in organics, a longer period is re-
lated and remote ponds where other techniques
quired for drying. Therefore, it appears that Racine
would be too costly. Erosion and recession of gul-
Island can be effectively remediated and readily
lies draining C/D-Pond and Lawson's Pond may
restored through artificial drainage or pumping
subsequently drain these areas and produce per-
of the pond, following construction of a tempo-
manent remediation.
rary berm to contain the former pond area and
5. Ice growth in ponds can be sufficiently thick
permit long-term drying to degrade the WP. By
that freezing extends into the sediments of the
removing the berm after in-situ degradation is
pond bottom. In so doing , it is possible that large
complete, the pond environment can be restored.
areas of sediment, including those contaminated
with WP, will be pulled from the bottom when the
Recommendations
ice cover is lifted by incoming tides or wind. Ice
Based upon our investigations in 1995 and pre-
floes have been observed with dimensions of over
vious years, we recommend the following (Fig.
7 to 8 m square, onto which sediments of up to 30
55):
cm thick were frozen. Wind and water currents
1. Cost-effective remediation can be accom-
move these floes throughout ERF during the flood-
plished across a large area of ERF by allowing the
ing tide and move them out into the Eagle River
physical system to remove or isolate WP contami-
and Knik Arm during ebb tide. Both ice floes with
nation.
pond sediments adhering to them and deposits of
2. WP contamination of Bread Truck Pond and
sediments from such ice were sampled; WP was
50% or more of C-Pond, including Lawson's Pond,
detected in several of these samples. It is, there-
should be treated by natural (or enhanced) drain-
fore, possible that large areas of contaminated sedi-
age and in-situ WP degradation by drying of the
ments (hot spots) could be entrained and trans-
former pond bottoms.
ported by ice floes to other areas of ERF, as well as
3. Sedimentation and burial of WP will, in cer-
into Knik Arm.
tain ponds, effectively remove it from feeding
6. Ice and water entrain and transport WP-con-
waterfowl over the short term. Over the long term,
taminated sediments within the ponds, mudflats
burial will reduce waterfowl mortality during
and gullies of ERF. Wind and water currents in
natural pond drainage, especially in parts of C-
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