Physical Processes and Natural Attenuation Alternatives
for Remediation of White Phosphorus Contamination,
Eagle River Flats, Fort Richardson, Alaska
DANIEL E. LAWSON, LEWIS E. HUNTER AND SUSAN R. BIGL
would alter the pond environments, removing or
INTRODUCTION
blocking the WP pathway to migrating water-
Eagle River Flats (ERF) is a 865-ha salt marsh
fowl. We also examined WP erosion and trans-
at the mouth of the Eagle River on the Knik Arm,
port to evaluate the potential for its off-site mi-
northeast of Anchorage, Alaska (Fig. 1). The salt
gration. These studies included analyses of the
marsh has been used as an artillery range since
tidal and river hydrology and associated factors
the early 1940s. Previous work by CRREL has
critical to evaluating proposed remedial technolo-
shown that an unusually high mortality of migra-
gies for WP contamination. This report describes
tory waterfowl, particularly ducks, is attributable
the results of 1995 investigations of the physical
to the ingestion of elemental white phosphorus
ecosystem of Eagle River Flats and its role in the
(WP) particles (Racine et al. 1992a,b). WP par-
natural attenuation or intrinsic remediation of WP
ticles were introduced by smoke-producing com-
contamination.
pounds in devices detonated during military train-
ing (Racine et al. 1992a, 1993). WP is now present
as particles and is also adsorbed to near-surface
ENVIRONMENTAL CONDITIONS
sediments at numerous locations in ERF, most
notably in pond and marsh bottom sediments
Eagle River Flats is one of several estuarine salt
where dabbling ducks ingest it during feeding. In
marshes in upper Cook Inlet, south-central Alaska
addition, WP-bearing sediment can be remobi-
(Fig. 1). Located at the mouth of the Eagle River,
lized and transported to other locations within or
ERF is about 2.8 km wide at the coast and nar-
external to ERF where it is redeposited (Lawson
rows inland. This subarctic region has a transi-
et al. 1996) and may pose a threat to unidentified
tional maritime to continental climate, with mod-
erate annual temperatures (daily mean 1.9C;
receptors.
minimum mean 2.2C) and precipitation (330
Our studies in 1993 and 1994 (Lawson et al.
1995, 1996) show that the physical system, and
508 mm; Evans et al. 1972). Inundation results
specifically the processes of erosion and recession
from both the semi-diurnal macrotidal fluctua-
of gullies draining the contaminated ponds and
tions of 9 to 11 m in Knik Arm and the resultant
mudflats, can naturally attenuate WP contamina-
overflow from the Eagle River as it meets the
tion by increasing exposure and drying time of
rising tide.
The Eagle River drains a 497-km2 basin in the
pond-bottom sediments. Until this takes place,
natural sedimentation may reduce waterfowl ex-
Chugach Mountains, 13% of which is covered by
posure risks to WP ingestion by producing a thick
glaciers that significantly affect the runoff and
sediment yield of the drainage basin (e.g., Lawson
sediment barrier between the surface and con-
1993). Glaciers modify peak discharges, the tim-
taminated sediments.
ing and volume of hourly, daily and seasonal
Therefore, in 1995, we focused our efforts on
discharges, the lag between precipitation and the
understanding the rates at which these processes
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