ther the processes of gully erosion, headward
potential remedial measures and their probable ef-
recession, and drainage of contaminated ponds,
fectiveness and success over the short (15 years)
and long (1050 years) term. It is equally impor-
and of burial of contaminated pond sediments,
tant that the impact of these treatment methods on
the physical system be evaluated before a reme-
tamination. The erosion and potential for off-site
dial technology is selected. For example, in some
transport of WP was examined.
areas dredging may create conditions that will
Several important conclusions result from this
enhance sedimentation and significantly reduce
and previous year's work:
Physical system processes result in the burial
dredging may modify the hydrology such that
and transport of WP.
gully erosion increases, thereby altering the drain-
Gully erosion and headwall recession will
age system and perhaps extending it into the
drain areas of contaminated ponds in about
dredged area. Dredge operations may disturb
110 years, potentially resulting in in-situ WP
underlying sediments, thereby increasing their
degradation and attenuation via drying. This
susceptibility to erosion.
is a cost-effective alternative to artificial
Site-specific effects of erosional processes must
pond draining. Historical analyses, field
be considered before remediation is initiated. Ero-
data, and process analyses indicate that
sion, for example, can affect the integrity of meas-
Bread Truck Pond will probably begin drain-
ures such as capping by AquaBlokTM or geotex-
ing in 1 year, while C/D, Lawson's Pond, and
tiles. Both ice and currents are critical mechanisms
a large area of C Pond will begin to drain in
1015 years or less.
is remediated by temporary drainage and drying
Pond sedimentation rates are high and could,
may subsequently have clean sediments uplifted
over time, bury WP-contaminated pond sedi-
and removed by ice, thereby exposing WP-bearing
ments to a depth sufficient to prevent feeding
sediments below. Similarly, areas remediated by
waterfowl exposure.
removal of WP-bearing sediments may be infilled
Natural sedimentation and burial, perhaps
with WP-bearing sediments that were eroded else-
artificially enhanced in some locations by
where in ERF and then transported and redeposited
introducing additives to increase floccula-
at the site.
tion, is a cost-effective alternative to the
installation of a barrier, particularly in cer-
Information needs
tain pond areas. Gully erosion and extension
A conceptual model of the physical ecosystem
may subsequently drain and dry these same
and WP fate and transport remains to be devel-
areas, furthering the permanency of reme-
diation.
oped. Some specific gaps in knowledge of the
Ice rafting can move WP by plucking it from
physical system include very limited data on WP
transport and persistence, groundwater hydrol-
the bottoms of contaminated ponds and
ogy of ponds and marshes, environmental con-
moving it to other areas.
trols on WP deposition in the Eagle River and Knik
WP in sediments is eroded from ponds and
Arm, and the factors, controls, and interactions of
drainages by ice and water and subsequently
processes causing long-term morphologic changes
transported by currents into the Eagle River
that will affect WP remediation.
and possibly off-site (Knik Arm), where its
fate is unknown. Contaminated sediment is
Lawson, D.E., L.E. Hunter, and S.R. Bigl (1996)
also transported to other locations within
Physical system dynamics, WP fate and transport,
ERF.
and remediation. In Interagency expanded site inves-
Racine Island Pond has neither high gully
tigation: Evaluation of white phosphorus contamina-
erosion and headward recession rates, nor
tion and potential treatability at Eagle River Flats,
high sedimentation rates. This pond also
Alaska (C.H. Racine and D. Cate, Ed.). CRREL Con-
floods at relatively low tidal heights and con-
tract Report to U.S. Army, Alaska, Directorate of
tains organic-rich sediments. It appears,
Public Works, FY95 Final Report, p. 21112.
therefore, that it can only be effectively reme-
The focus of these investigations was on the
diated and readily restored through artificial
role of the physical system in the burial or trans-
drainage and temporary berm containment
port of white phosphorus in this tidal flat area.
to permit long-term drying and in-situ WP
Specifically, these investigations evaluated whe-
degradation.
49
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