a contract for equipment lease, support and main-
canting structure at one end, contingent upon re-
tenance for a dredging system for the Flats. A for-
sults of field and laboratory tests of the basin and
mal set of technical specifications was written up
pad characteristics. The Alaska District of the U.S.
by CRREL and used by USARAK's Contracting
Army Corps of Engineers was tasked with design
Office in its request for bids.
of the structure based on testing performed by
Using the specifications as guidelines, CRREL
CRREL. They were also responsible for oversee-
engineers reviewed the technical portion of the
ing the construction of the structure. Actual con-
bids received by the Contracting Office. These re-
struction was carried out by the Roads and
views were used in the overall evaluation of the
Grounds Office of the Directorate of Public Works
bids and the contract was awarded to the entity
(DPW) at Fort Richardson. CRREL engineers con-
deemed most appropriate by the Contracting Of-
ducted the investigations into the basin and pad
fice: ChemTrack Services Group of Anchorage,
surface hydrology and acted as technical consult-
Alaska. The dredges to be used are from Liquid
ants throughout the effort.
Waste Technology, Inc., of Somerset, Wisconsin.
Settlement times
Initial design studies focused on settlement
times for the spoils. The treatment strategy was to
BASIN INVESTIGATIONS
pump the material into a retention basin, allow
Two of the most difficult issues to resolve dur-
the solids to settle, and decant the supernatant over
ing the pilot project were where and how the spoils
a weir, a strategy similar to that advocated by
are to be contained during treatment. The most
Poindexter (1984) and Palermo (1984). The drained
obvious choice for a basin site is the EOD pad, a
sediments would then be allowed to dry naturally,
6.3-ha gravel pad used until 1990 for the burning
and, climatological conditions permitting, the WP
and detonation of dated, faulty or excess ordnance.
would sublimate. Settlement times are important
The original plan was to clear vegetation from the
in determining the dredge cycle as well as how
pad and use as much of the pad as practical. A
much water will percolate through the bottom of
low berm would be constructed and the spoils
the basin.
from the dredging operation allowed to drain
The objective of the settlement studies was to
through the pad. However, the presence of con-
determine settlement rates and times for a one-
taminants in the EOD pad has resulted in the area
day dredge cycle: 810 hours of dredging at 380
m3/hour. The sediment cutoff size was 0.1 mm,
being declared a Resource Conservation and Re-
covery Act (RCRA) site, thus requiring more thor-
the minimum WP particle size thought to be prob-
lematic in the waterfowl die-offs (Walsh 1994).
ough investigations into the use of the pad as a
Initial models using sediment particle sizes from
treatment site. Although this is an uncapped site,
previous analyses (Lawson and Brockett 1993) in
the Remedial Project Managers (RPMs) involved
freshwater indicated that settlement times for a
with the project felt that water filtering through
3/4-ha site would be on the order of days (Table
the pad from spoils drainage was not acceptable
1). This model was based on Stoke's Law:
and should be minimized.
Permission was granted for construction of a
v = g(ρ1 ρ)d2/18
(1)
small, 0.8-ha retention basin with a controlled de-
Table 1. Settling times for spoils in fresh water.
Retention
Settling
Settling
Silt
WP
Dredge
pond
Particle
velocity:silt
velocity:WP
Pond depth
settling
settling
cycle
size (ha)
size (cm)
(cm/s)
(cm/s)
(cm)
time (hr)
time (hr)
(days)*
0.75
0.01
7.0E-1
3.6E-1
40.53
0.02
0.03
0.3
0.75
0.001
7.0E-3
3.6E-3
40.53
1.61
3.14
0.5
0.75
0.0003†
6.3E-4
3.2E-4
40.53
17.89
34.88
1.8
*8-hour dredging plus retention time. No decanting time included.
†Median particle size (Lawson and Brockett).
4
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