Underground Construction - October 2019 - 24

Hydraulic Pigs Clear Quagga Mussels from Lake Ontario Intake Pipelines

into the launcher behind the pig it would be forced through
the launcher taper, through the elbow connection, through a
45-degree wye within the valve chamber, and then shoot off on
its passage along the length of intake until finally exiting at the
mouth offshore in Lake Ontario.
Pigs were propelled by water pumped into the launcher at a
rate of 18,000 to 20,000 gpm, but the layout of delivery piping
was complicated by the constraints on Toronto Island. Water had
to be drawn into deck-mounted pumps aboard a Galcon barge
positioned within a sheltered inlet adjacent to the treatment
plant. The valve chamber and pig launcher, however, were located
on the opposite side of Lakeshore Avenue which, by contract
specification, had to remain unobstructed to ensure full road
access, including emergency vehicles, across the island.
A pig was loaded, the end flange of the launcher barrel secured
in place, and the supply pumps could then be brought online. Each
pig was tracked and recorded as it left the launcher and again as
it passed across the shoreline into Lake Ontario, at a distance
approximately 100 yards downstream of the valve chamber.
Pressure gauges and data logging instrumentation mounted
aboard the launcher were configured to identify the pig location
if problems should arise or if it became stuck in the pipe. The
consequences of a "stuck" pig were a critical concern because the
Island WTP was the only source of cooling water for the city. Two
intakes had to be kept in continuous service, with only minimal
flow interruption intervals allowed in the third line while it was
being cleaned.

Run times
Typical pig run-times varied between 75 and 90 minutes,
depending upon the length of the intake and the specific design of
each pig. Capture and retrieval of discharged pigs was a significant
issue because they were not allowed to be "lost at sea" and a
spent pig might either float or sink. Galcon would anchor their
surface support vessel on station above the intake terminus and
then deploy a ROV to verify pig exit from the intake mouth and
to observe the volume of mussels, sediment, and debris being
discharged. This ROV was equipped with video cameras and
could hover in position at the intake mouth to view and record
conditions as the pig emerged from the pipeline.
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OCTOBER 2019 | UConOnline.com

A trickle of mussels would first be observed as the pig
approached the terminus, and this was followed by a murky
cloud of sediment created from water bypassing around the
pig in transit. As the pig neared the intake mouth, a surge of
black water, sediment and mussels would erupt and temporarily
obscure all submerged visibility.
Depending upon the specific design of the pig and its
fabrication procedure, it could either float or sink after exiting
the pipeline. "Floaters" could be readily captured on the surface,
hooked up, and towed to the Galcon Marine yard for removal
from the water. A pig that exited the intake but sank to the
bottom, represented a different and unique capture problem.
The ROV was equipped with sonar which clearly identified the
pig if the video cameras were ineffective, and the pig also was
equipped with an acoustic transponder so it could be tracked by
the ROV over long distances.
After a sequence of three pig runs had been executed through
an intake, operations would pause for a 12-hour interval while
the city engineers analyzed the cleaning results achieved.
All intakes were completed with only three pig runs each,
and C-Factor analyses performed by the city indicated that flow
conditions were even better than when the intakes had been
originally installed. Pigging operations were completed on time
and on budget, without significant disruption to Toronto's
critical supply of cooling water.

West intake
The 16,600-foot-long west intake was the first to be cleaned. A
dye test was performed to determine pump volume and estimate
the expected travel time of the pigs. The first shot was a 60-inch,
2.5 pcf swab that made its trip in 122 minutes, as continuous
pressure monitoring indicated a smooth transit without
significant surge or back pressure. Upon exit, this swab sank to
the bottom of the lake and had to be retrieved by the ROV.
"The discharge of mussels and sediment," Murphey explained,
"completely obscured video images provided by the ROV stationed
on bottom at the intake mouth, but sonar clearly depicted the
swab plopping to the lake-bed just beyond the intake."
A plain, uncoated RX-3 was launched next, followed by an RX4, a coated or crisscross pig, to remove any remaining mussels.
After exiting the mouth of the pipe, both pigs surfaced and were
towed to shore and removed from the water.

Center intake
After flushing, the 17,600-foot-long center intake was pigged in
sequence with RX-3, RX-4 and RX-SS, a bristle pig. All pigs were
recovered in a single day.
"Unexpectedly," said Murphey, "this entire series of pigs
floated to the lake surface."

East Intake
The first pig, an RX-3, passed through the 17,000-foot long
pipeline without incident. A pressure drop indicated that the
second pig, an RX-4, had exited the pipe. However, it did not
float to the surface.
"To avoid any potential of a pig jamming within the intake,

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Underground Construction - October 2019

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