Hydraulic pipe pigging was utilized during a recent project in Canada to clean invasive quagga mussels from three large-diameter freshwater intake pipelines. The deep-water intakes, each more than 3 miles long, bring water from Lake Ontario into the Island Water Treatment Plant owned by the city of Toronto.
One of four serving Toronto, the Island treatment plant provides the sole supply of the city’s deep lake water cooling (DLWC) partnership with Enwave Energy Corporation. The DLWC system operates 24 hours a day, 365 days a year.
Mouths of the pipes are approximately 270 feet below the lake’s surface and run along the natural slope of the lake bottom, following the near-shore embankment and contained on the lake floor by concrete anchor blocks, comprised of 9,550 cubic yards of concrete.
The project was initiated after an underwater inspection in 2014 conducted by a remotely operated vehicle (ROV) verified the presence of quagga mussels throughout the entire length of each intake line. The inspection confirmed that the accumulation of mussels had significantly reduced water flow from the lake into the treatment plant.
Small quagga mussels breed rapidly, and quickly clog pipe inlets or outlets, ultimately requiring physical removal. They also can disrupt natural ecosystems by facilitating the growth of nuisance weeds along the bottom of lakes and rivers. Quagga mussels have spread from Eastern Europe to the United Kingdom and now have invaded North American waters.
Flow test results prompted the city to initiate planning to clean all three intakes via hydraulic pigging. This involved inserting and propelling a device, or “pig,” to scrape and clear the pipe interior.
The owner, City of Toronto, tendered the project as a design-build contract due to limited regional pipe-cleaning expertise, said Niall Robertson, Island Water Treatment Plant manager. This approach placed the project risk and the methodologies into the hands of those best-informed and best-equipped to plan and execute it, reducing the city’s exposure and making project delivery efficient.
Galcon Marine, the general contractor, developed and executed a plan for cleaning the intake lines and provided complicated marine logistics and construction support. Montauk Services was designated as the pigging contractor, Associated Engineering was the engineering consultant and Bennet Mechanical constructed the pig launcher.
Timeline
The project scope of work specified that pipe cleaning had to be accomplished between Oct. 15 and Dec. 15, 2018, even though weather conditions during that time of year could complicate marine operations. However, weather was expected to be even worse later in the winter, and could affect all work operations, particularly the pumped water delivery necessary to propel pigs through the intake lines.
“The two largest challenges,” said Ryan Vogt, project manager with Galcon Marine, “were completing the project within the allocated time frame, due to poor weather conditions, and constructability of the project, which required maintaining full access on the island for resident and emergency vehicles.”
Vogt said the time frame chosen was good for the city because it was the lowest usage interval for its clients. But from a marine standpoint, the prevailing winds at that time of year are predominantly from a bad direction, making the retrieval of pigs, ROV operations and drawing water for the operation very difficult.
“Using smaller gear for retrieval, proper planning, outside-the-box thinking and lots of luck from the weatherman,” Vogt continued, “we were able to launch and retrieve pigs in a higher sea state. The water used to push the pigs through the line had to come from the inner lagoon. This forced us to run three 18-inch HDPE lines across the main road for the island, resulting in having to construct a highway-rated, temporary bridge to allow continued roadway access.” (The lines couldn’t be buried due to underground utilities.)
“This was a large undertaking and very unconventional,” he said. “In addition, we had to construct the launcher and support system, pour a concrete reinforcing pad for the launcher, manage the pumping operations, facilitate the pig launching and retrieval, coordinate site revetment, construct a display for the launcher, ensure the system could handle the pressure requirements of the operation, and produce a pigging manual for future reference.”
Pigging operations
Rex Murphey, Montauk Services CEO, explained the actual pigging operations. “In order to be prepared for any cleaning contingency, we provided 18 pigs for the project,” said Murphey. “Pigs were constructed of open cell polyurethane foam with various densities. We used standard pigs but selected their sequence and diameters to gradually clean the pipelines. The 2.5 pcf density swab utilized a blue elastomer foam, which was new to the market and gave us the flexibility of a standard swab, but with a much better cleaning ability. Standard swabs are usually one-pound density and shot only to ‘prove’ the pipeline prior to the utilization of harder pigs.”
The three intake pipes converged downstream from the common inlet. The chamber had three 60-inch connection flanges where the pig launcher was attached. The launcher design was a joint effort between Montauk Services, Galcon Marine and Associated Engineering, with the local fabrication managed by Galcon.
All pigs were easily inserted into the oversized bore of the horizontal launcher and then pushed forward against a tapered barrel section, which reduced the diameter to 60 inches, corresponding to the nominal pipe size. When water was pumped 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.
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 RX-4, 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, work was stopped until this RX-4 could be located and recovered,” Murphey said. “Foul weather delayed the search one week until the weather improved. The pig had, in fact, exited the mouth of the pipe but became lodged within the truncated intake structure. The ROV attached a haul line to the wire ‘bow loop’ of the pig, and it was towed clear of the intake without significant effort or any damage to the structure. An RXSS ‘bristle pig’ was then immediately shot through the line.”
According to Toronto Island Water Plant Manager Robertson, the pigging methodology was successful in restoring the original C-factor flow.
“Excessive intake head-losses had been alleviated, thus increasing production capacity,” he said. “The city anticipates energy savings from pumping costs.
“With a validated procedure now defined, the city will utilize the pigging methodology for periodic cleaning of the raw water intakes. Annual flow tests will be performed at the Island WTP to assess and track pipeline frictional losses due to future quagga mussel colonization. The future pigging rehabilitation period is yet to be defined.”
Toronto Water is responsible for all aspects of drinking water treatment and supply, wastewater collection and treatment, and storm water management. The city ensures that residents, businesses and visitors have access to clean, safe drinking water through a complex water treatment process and continuous testing, so water always meets or exceeds the Safe Drinking Water Act set by the Ministry of the Environment. Each day, Toronto treats more than 1 billion liters of safe drinking water.
Associated Engineering Water Division Manager Elia Edwards, M.A. Sc., P.Eng., described the intake cleaning project as a truly unique and complex undertaking with no room for error, as the impact to Toronto’s drinking water supply would be devastating to the city.
“Galcon and Montauk were impressively diligent in the risk review and then in the subsequent development and implementation of a comprehensive risk-managed cleaning program that was delivered without flaw,” said Edwards.
Established more than 70 years ago, Associated Engineering has 23 offices across Canada and provides a broad range of services. Participated in world-class projects in Canada and around the world, Associated Engineering has been recognized as one of Canada’s best-managed companies for 10 consecutive years.
Galcon Marine Ltd., Toronto, is a full-service marine construction company providing a range of specialist services including diving, support barge cranes, and workboats to accommodate all phases of marine construction.
Montauk Services, based in Hackensack, N.J., is one of North America’s most experienced pigging and pipe testing companies. It has pigged more than 2 million feet of pipelines, restoring them to original or near-original condition. Many previous projects have included removing mussels from pipelines. •
Reprinted with permission Underground Construction October 2019. Author: Jeff Griffin, Senior Editor.
FOR MORE INFORMATION:
Montauk Services, (800) 632-8893, montaukservices.net
Associated Engineering, (416) 622-9502, ae.ca
Galcon Marine Ltd., (416) 255-9607, galconmarine.com