vent damage to the genset and the possible spill
was mounted above it; this would switch on the
of fuel and lubricant in case of ingestion and det-
genset and then the pump when the water level
onation of unexploded ordnance by the pump.
rose in the sump, floating the pump. In operation,
Originally, the pump was to be placed in the
the reed-type switches were subject to being
deepest section of the pond to be treated. The
clogged by the fine-grained silt in the muddy
pump would then scour a small sump while
water. Problems with these switches precluded
drawing down the pond. Prior to deployment,
operating the pump overnight during the first
however, we decided to blast a sump and place
phase of testing. Replacement of the reed switches
the pump within the preformed sump. The sump
and modification of the control circuitry im-
serves as a deep reservoir for the pump, reducing
proved the system reliability to the point that it
cycling of the system and thus conserving fuel.
was operational by 21 May. The area continued to
To form a 2-m-deep 6-m-diam. sump, two 18-
slowly dewater, and by 22 May, Pond 183 was
kg shape charges and two 18-kg cratering charges
essentially drained. Only isolated pockets of
are placed and detonated by military engineers.
water remained in depressed areas not draining
After the area has been cleared of ordnance, Ban-
into the sump. These areas eventually dried
galore torpedoes (prepackaged line charges) are
through evaporation.
used in four locations to breach the rim of the
The reed switches were replaced with fully en-
sump, allowing free flow of the pond water into
closed float switches, a more robust arrangement.
the sump. Detonation cord is then used to form
Consideration of flooding tides led to the
small drainage ditches from the sump to low
incorporation of a third float switch to shut the
points in the pond. Finally, a minimal amount of
system down during flooding events. Circuitry
hand-ditching with a shovel is done along
needed to be added and the existing control cir-
cleared lanes to address problem spots.
cuitry needed modification. In July, the third
The system was initially installed in Pond 183
switch was added for the detection of flood tides.
in May of 1997. Both the pump and genset were
The flood tide switch was mounted away from
flown to their locations using a UH-60L Black-
the pump near the rim of the sump to better de-
hawk helicopter (capacity 4080 kg). Placement of
tect the rising tidewaters. The modifications were
the genset in a channel previously dredged
tested and operational prior to the flooding tide.
between Pond 146 and the edge of Pond 183
On 21 July, a 9.7-m tide inundated Pond 183, trig-
allowed refueling of the genset via a skiff, which
gering the flood tide switch and shutting down
could be loaded from the pad near Clunie Creek.
the system. The flood tide switch was set to trig-
A 20-cm-diam. discharge line, consisting of 6-m
ger off when the natural drainage after the tide
sections of polyethylene pipe and various length
was nearly complete. This maximizes fuel con-
sections of rubber hose, was installed between
servation by taking advantage of the natural
the pump and B-gully (a drainage gully adjacent
drainage of the area. Pumping resumed on 25
to the discharge line in Pond 183, west of the
July. Drawdown of Pond 183 occurred over the
pump), a total of 335 m. The 6-m sections of poly-
next three days. The configuration worked so
ethylene pipe were transported by UH-1H heli-
well during testing that the highwater switch was
copter. Eight to ten sections at a time were loaded
also mounted off-pump near the sump rim. This
sideways through the open doors and flown out
further reduces cycling by delaying the resumption
to locations along the planned right of way. The
of pumping until the sump completely fills. A dia-
pipe was then carried into position and assem-
gram of the final switch logic is shown in Figure 8.
bled by hand. Pump-down of the pond was initi-
During the marginal (9.47-m) flooding tide of
ated at 1125 on 16 May. By 0900 the following
20 July, infiltration routes from the river to Pond
morning, Pond 183 had been drawn down such
183 were scouted. The major infiltration passage
that water entering the sump was confined to a
was found to be B-gully. To prevent pond flood-
ing during marginal flooding events (≤ 9.57 m), a
few channels through the sump rim. Initial draw-
down for this 2.9-ha pond occurred in less than 12
tide gate was designed for installation at the
hours.
highest, narrowest point of the gully. This gate
Initially, only two pump-mounted reed-type
serves as a one-way valve, preventing influx of
water level switches were used to control the sys-
water during lower flooding tides, but allowing
tem. One was mounted on the pump such that it
passage of water out of the pond after higher
turned the pump off when the sump was
flooding tides. A gate was fabricated and
pumped out. The second, a high-water switch,
installed in September in time to test it during a
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