A Tale of Two Manholes

By: Suzan Marie Chin

It was the best of times; it was the worst of times… For two experienced municipal contractors, one in the cold northern Great Lakes region, the other on the tropical coast of Florida, the added complication of extreme weather conditions to already challenging projects required creative thinking and job planning skills. Spray-applied polyurethane technology, along with site-specific preparation methods, proved to be the right combination for a successful rehabilitation in both cases.

Manholes in the Canadian Cold

Over the spring and summer, the region of Peel in Hamilton, Ontario had completed the construction of four new manholes that were to be part of a newly rehabilitated 72-inch diameter interceptor line. The refurbished interceptor was ready to go online until inspectors discovered that the manhole structures were improperly constructed and cracking due to a design oversight and the extremely high water table in the surrounding area. High levels of infiltration were occurring, and, although it was already late autumn, corrective measures were immediately necessary.

It was decided that Spraywall, a spray-applied polyurethane rehabilitation material from Sprayroq, was the best solution. The polyurethane would not only correct the cracks and eliminate the infiltration, but also protect against the corrosive effects of hydrogen sulfide (H2S).

Elmer’s Crane and Dozer, Inc. of Michigan (Team Elmer’s), a Sprayroq Certified Partner, was contracted to perform the emergency rehabilitation. Knowing that late autumn in eastern Canada brings average daily high temperatures of 40 degrees, paired with high humidity and frequent rainfall, the Elmer’s crew had to carefully plan.

In addition to the equipment and crew preparation, the structures themselves required extensive prep work before the spray process could begin. John Prescott, Estimator/Project Leader for Team Elmer’s relates, “There was cracking that we knew we would have to deal with but the biggest problem was the ground water infiltration around the seams of the structures.”

To correct this, a second contractor was hired to seal and grout the structures with the assistance of the Team Elmer’s crew. Once this was completed, Team Elmer’s crew pressure washed the structures. Next, they applied a cementitious mortar by Preco to create a smooth, uniform surface on the walls of the structures.

Before spraying began, using a 7,000,000 BTU jet heater, the crew heated each structure, eliminating any residual moisture from the concrete surface. They also used a specially designed Graco spray gun wrapped with pipe foam insulation to help keep the Spraywall material at the proper constant temperature.  

Prescott explains the application process, “Because of the depth and ground water infiltration, we started at the top and worked our way to the bottom. That way, if we did encounter a leak, we weren’t chasing it as the top was already sealed so it wouldn’t have anywhere to go.”  An application of 250 to 300 mils thick was applied to all surfaces of the structures. Each manhole required approximately four to five hours of spray time with preparation taking approximately one to two days apiece.

Moving to Points South…

Manhole rehabilitation in warmer, coastal climates brings its own set of challenges. National Pipe Services (NPS), the Sprayroq Certified Partner for Florida, was tasked with performing sewer system rehabilitation for the affluent vacation resort island of Long Boat Key.
As with the Ontario project, weather conditions play a big role -- extremely high water tables, tidal patterns, daily rains, and extremely high temperatures were all important considerations in insuring a successful outcome.

In June, NPS was contracted to begin the work of rehabilitating 28 manholes and a 17-foot deep lift station situated at the island’s marina. During the summer months, it rains daily at a level of one to two inches over a short one to two hour period in late afternoon. This rain pattern, coupled with high temperatures, hydrogen sulfide levels, humidity, and tidal patterns impacts both underground structures and repair crews significantly.

To overcome these challenges, crews were outfitted with PPE and special cooler vests to combat the risks of heat stroke and dehydration. NPS performed any required pressure washing, injection grouting, and sealing work for each structure during low tide. Rodney Jones, Business Development Manager for NPS explains, “By timing the work in this way, the grout and mortar has sufficient time to set before high tide occurred approximately six to eight hours later. This scheduling also put the crews in a timeframe to complete their work and avoid the daily summer rain patterns.”

High water tables also needed to be considered. The manholes to be rehabilitated ranged in depth from three to 17 feet. In some, groundwater levels are just 12 to 18 inches below the ground surface. This factor contributes to high levels of inflow and infiltration (InI) cracking and shifting of the structures in the ground.

However, the lift station posed the biggest challenge. It was unusually deep for its location and numerous cracks had to be addressed before rehabilitation could begin. A large volume of De Neef grout was required along with special detailing. In addition, the lift station serviced an active line so bypass pumping was required for the duration of the project. 

NPS first pressure washed the walls and applied a sealing mortar cream. Once all of the prep work was completed, the spray process began with the crews taking approximately a day and a half to finish applying a one-inch thick application of the Spraywall product per the Manatee County (Florida) specifications.

Regardless of location or climate, spray-applied polyurethane technology is worthy of consideration for sustainable and effective structural rehabilitation. With proper training, planning, and execution, even the toughest environments can be conquered and old infrastructure can be returned to optimum performance.  

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