Ensuring that a city’s water pipelines operate at top system performance levels is critical. Without the proper cleaning method, a pipeline’s performance can decrease.

A unique factor that some cities and towns face is the presence of invasive species, such as the quagga and zebra mussels. While native parts of Eastern Europe such as Ukraine, these aquatic hitchhikers made their way into Toronto’s Great Lakes. 

The damage that these invasive species cause is without question. Tom Nalepa, an emeritus research biologist and recognized expert on the species, stated that “the quagga mussel represents the greatest threat to the Great Lakes of any invasive species.”

Past quagga and zebra mussel removal methods have used various chemicals, such as chlorine. However, these methods have failed to present effective solutions to control increasing biofouling growth. 

An interesting alternative to dealing with the presence of these two mollusk species is hydraulic pigging. 

This article illustrates how pigging works to remove quagga and zebra mussels. Below, examine a project completed by American Pipeline Solutions in Toronto to address quagga mussel build-up. 

Quagga & Zebra Mussel Removal: City of Toronto, 2018

The Issue Caused by Quagga & Zebra Mussels in Toronto’s Water Intakes 

In the fall of 2018, Toronto found that the hydraulic capacity of its three water intakes at the Island Water Treatment Plant had reduced after 14 years of use. 

Quagga mussel build-up inside the deep-water pipelines caused the reduced hydraulic capacity. Quagga mussels adhere to submerged surfaces, such as pipes, and subsist on plankton in the nearby water. 

The accumulation of quagga mussels within Toronto’s intakes is known as biofouling or aquatic fouling. When an organism like the quagga mussel accumulates within water intakes, it can lead to structural or functional defects. 

This organism also has a major impact on the surrounding ecosystem. 

In addition, quagga mussels and their cousin, the zebra mussel, propagate quickly. Quagga mussels displace existing native species and alter the food chain, resulting in less game and commercial fish. 

American Pipeline Solutions’ Scope of Work

American Pipeline Solutions was contacted because the team had successfully pigged Cornell University’s 60-inch HDPE deep water intake in Lake Cayuga. 

After examining the Cornell project results, the City of Toronto engineers assessed the criteria, specifications, and required budget for hydraulic pigging to restore flow capacity at the Toronto Island WTP.

In preparation for the project, American Pipeline Solutions partnered with Galcon Marine Ltd., a local contractor with local offshore expertise. Galcon provided support with island transport, barge delivery, ROV (remote operated vehicle) operation, and other marine operations. 

Project preparation also included the specification of the scope-of-work, which was defined as the following:

• Design and manufacturing of a pig launcher and structural supports that would fit the intake valve chamber and piping system at the WTP. 

• Provide documentation of the process and design for hydraulic pigging procedures. These procedures were created for quagga and zebra mussel removal in all three WTP intakes. 

• Obtain any necessary regulatory permits and approvals for work. 

• Perform an inspection via ROV (remote operated vehicle) for all three water intakes before pigging. 

• Pigging for quagga and zebra mussel removal in water intake pipes. 

• Retrieval/salvage of all used pigs. 

During the project, American Pipeline Solutions was responsible for the overall hydraulic layout, the launcher's design, and the hardware designation. Additionally, American Pipeline Solutions handled pig design, the sequence of pigs used, tracking the pigs, and pig recovery procedures. 

Hydraulic Pigging Procedures Used in Quagga & Zebra Mussel Removal Method

1. Determine Proper Pig Sequence

Before the pigging process, American Pipeline Solutions assessed the pipe to determine the pig sequence.  

This sequence matters for most pigging procedures because the process must be completed as quickly as possible. Additionally, these procedures must be performed conservatively to avoid any pressure surges or a delay caused by a “stuck pig.” 

2. Load and Launch the First Pig

While most pigs used for cleaning are larger than the internal diameter of a pipe, the first pig used in Toronto was not. The Toronto WTP pipelines had internal diameters measuring around 61 inches. The first pig that was used was only 58 inches in diameter. 

A smaller-sized pig was used first to create enough bypass flow to start the initial cleaning process. However, the pig needed to be small enough, so it wouldn’t adhere to the pipe wall or have its movement restricted. 

3. Monitor Pig Movement & Mussel Debris Build-up  

After a quagga and zebra removal project begins, it is important to monitor the building debris. As the pig moves through the pipeline, the mussel debris can accumulate ahead of the pig, slowing or stopping the pig.  

The volume of the displaced quagga mussels was monitored as the pig moved through the pipe. This was done in real-time, using submerged cameras aboard an ROV at the intake’s mouth. 

When using foam pigs, such as those used in Toronto, this debris can be controlled, depending on the pig design. Foam pigs can be designed to channel some of the water, propelling the pig towards the pig's front. When this happens, displaced mussels are suspended in the moving water flow ahead of the pig. This prevents the pig from slowing or stopping because of mussel debris.

4. Launch Second and Third Pigs

Thanks to the real-time documentation of the mussel debris and the pipe’s pressure profile, American Pipeline Solutions was able to determine the next pig’s characteristics.

Typically, the foam density and diameter of a pig will increase with each subsequent run. The last pig that is run tends to be larger than the internal diameter of the pipe itself. 

For the City of Toronto project, the last pig was a full-size pig with embedded plastic bristles. These bristles thoroughly cleaned the pipe walls of quagga mussels. 

5. Assess the Cleaning Project’s Results 

Once all three pigs were run through the water intakes, the Hazen-Williams C-Factor for all three pipes was measured. This factor determined the smoothness of the interior walls of the pipes after cleaning. In addition, the results would determine if a fourth pig run was necessary. 

The C-Factor results improved, and after the initial three pig runs, the water intake’s hydraulic condition was better than when the pipes were installed. 

A perfect C-Factor is 150+. When built in 2004, the C-Factor for these pipes was estimated to be 137 to 140. Prior to cleaning, the pipes measured a C-Factor of approximately 110. After pigging was completed, all three intakes had C-Factors ranging from 149 to 152. 

In the end, these results proved that the project’s pigging process was a complete success. 

The process was able to clear the quagga mussels from the pipes and any additional debris. The project’s success shows that hydraulic pigging as a quagga and zebra mussel removal method is reliable.  

Are you looking for a way to solve your quagga and zebra mussel removal problem?

Contact American Pipeline Solutions at (201) 525-0088 to receive a comprehensive pigging solution that is crafted around your project’s unique needs.