in the field, and initial flow rates through it
Eagle River Flats (ERF) is a subarctic estuary
matched those predicted in the laboratory. Unfor-
and salt marsh that has become the site of exten-
tunately, the silt fence was removed because it
sive environmental study due to the high mortal-
clogged, primarily because of unexpected high
ity of migratory waterfowl during the 1980s and
amounts of suspended sediment in the super-
1990s. Investigations by CRREL identified that
natant.
small particles (~1 mm) of white phosphorus
ingested by waterfowl feeding from pond bot-
Hull, J. H., J. M. Jersak, P. A. Pochop, and J.L.
toms, was the cause of observed high mortality
ping technology for mitigating contaminated
rates. Although the use of WP-bearing munitions
sediments. In Proceedings of the 15th World Dredg-
was halted February 1990, ERF remains an active
ing Congress, 28 June2 July, Las Vegas, Nevada. Vol.
impact area and limited sections of the marshes
1, p. 555576.
and ponds retain high levels of WP contamina-
Dredging and removal may be the most practi-
tion.
cal method for mitigating contaminated sedi-
Investigations of physical system dynamics as
ments in many situations. However, in some cir-
part of the site assessment are to develop physical
cumstances, dredging as a mitigative technique
models of the depositional system and WP fate in
may be neither cost effective nor environmentally
the system, and to evaluate system response to
protective in light of the volume of sediments
remediation. Studies include sediment trapping,
impacted, the potential for sediment resuspen-
measuring water quality parameters and sus-
sion during dredging, and potential impact to
pended sediment concentrations, monitoring
aquatic life and habitat during dredging and
tidal and river dynamics, measuring river and
removal activities. The technique of in-situ sedi-
gully bank erosion, bathymetric mapping of Knik
ment capping is being more often considered as a
Arm near the mouth of Eagle River, and sampling
for WP in ERF sediments and transport (water
relatively non-intrusive and cost-effective alterna-
and ice). These studies have monitored WP in
tive to dredging. Most in-situ capping projects in-
volve the use of sand-sized sediments. Such
transport within the ERF system and indicate that
coarser-grained materials may adequately isolate
it may be exiting through ice and river transport
contaminated sediments physically, but do little
into the Knik Arm. Processes relevant to this
to chemically attenuate sediment-borne contami-
paper are particulate resuspension of soft muddy
nants. Such materials may also be more prone to
pond substrates, gully erosion and transport, and
erosional losses and redistribution. Summarized
ice freeze-on, plucking, and rafting of contami-
here are field-scale studies developed to test a
nated sediments.
new, clay mineral-based (composite aggregate)
Field studies indicate that physical system pro-
barrier technology for use in in-situ capping in
cesses must be considered before remedial meas-
wetland and riverine/estuarine environments--
ures are taken. Rapid sedimentation rates in
dynamic and contrasting ecosystems that offer a
ponds (1030 mm/yr) may provide natural reme-
broad range of stressing factors for evaluating
diation; however, gullies are eroding towards the
most heavily contaminated ponds and may begin
barrier effectiveness. Specifically, data are pre-
draining them in the next 15 to 50 years. Natural
sented from one study indicating that this barrier
pond drainage may accelerate the natural decom-
is effective in isolating phosphorous-contaminat-
position of WP, if sediments can dry sufficiently.
ed wetland sediments from Alaskan waterfowl
Rapid erosion may also release WP into gullies,
populations. Also presented are methodologies
making it available for natural transport and
and available laboratory results from another
redistribution. Gully erosion may be accelerated
study in which this technology is being tested for
by proposed dredging operations that alter sur-
isolating soft, fine-grained PCB-contaminated
face morphology, drainage, and sediment charac-
river sediments.
teristics. Capping of contaminated regions is also
threatened by gully processes that can under-
Hunter, L.E., D.E. Lawson, S.E. Bigl, B.M.
mine remediated regions while ice processes can
Nadeau, P.B. Weyrick, and J.H. Bodette (1995)
produce plucking or shoving capping materials
White phosphorus mobilization at the Eagle River
and ripping of geotextiles.
Flats, Ft. Richardson, Alaska. In Proceedings, Geo-
logical Society of America, Fairbanks, Alaska, p. 27.
26
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