Silt Fence Testing for Eagle River Flats Dredging
KAREN S. HENRY AND SUSAN T. HUNNEWELL
tinue to be used for other types of artillery impact
INTRODUCTION
during winter months when there is a solid ice
cover.
Eagle River Flats (ERF) is an estuarine salt
One of the remediation techniques being con-
marsh on the Cook Inlet that has been used by the
sidered for the ERF is the use of a remotely-con-
A r m y a s a n a r t i l l e r y i m p a c t a re a o n F o r t
trolled dredge to excavate WP-contaminated sedi-
Richardson in Anchorage, Alaska, since 1949. It is
ment. Dredged spoils, containing various-sized
also used by up to 5000 waterfowl per day during
particles of WP, will be placed into a 90- by 90-m
annual migrations (Racine et al. 1992). An esti-
settling pond (or retention basin) with 2-m-high
mated 1000 to 2000 waterfowl deaths have been
berms. There is a 7-m-wide 1.2-m-high weir at
noted annually in ERF since 1980. It was recently
one corner of the settling pond for the purpose of
determined that ingestion of unburned white
decanting water. The weir is fully adjustable in
phosphorus (WP) particles deposited by smoke-
height, in increments of 3.8 cm. Spoils will be
producing incendiary is the primary cause of mor-
pumped into the basin, then allowed to settle un-
tality (Racine et al. 1992). Waterfowl that circulate
til a clear layer of water forms on top of the sedi-
bottom sediment through their bills and retain
ments (a minimum of two hours). The water will
food-sized particles for ingestion (e.g., dabbling
then be released over the weir, across a 2-m-wide
ducks and swans) are the most susceptible (Racine
section of concrete pad, through a geotextile (re-
et al. 1992). All firing of WP rounds into the ERF
ferred to as a silt fence) and across the concrete
ceased in 1990 and remediation of the site is cur-
pad to a drain into the ERF (Fig. 1 and 2). The
rently being planned; however, this area will con-
90 m
0.6 m
Outflow Pipe to ERF
Inflow
Structure
Silt
Fence Concrete
Adjustable
Wall
To
Inflow Pipe
Weir
Chain Link
Dredge (25.5 cm )
Cage
Clear Water
1
Silt
3:
1.2 m Drop Inlet
w/0.6 m Culvert
127 m
A-A'
Figure 1. Plan view and cross-section of the retention basin, with the inflow and
outflow structures.
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