City finding savings in fixing pipe leakage

Sean C. Morgan

Technology, innovation and simplicity are bringing down the cost of repairing manholes in Sweet Home.

Public Works Director Greg Springman is reluctant to estimate the potential savings of a new technique for manhole repair because the city hasn’t started implementing it yet and therefore lacks data. But Dominic Valloni, acting maintenance superintendent, isn’t shy about letting people know he predicts it will cut repair costs by as much as half.

Public Works will know how effective it is in a matter of months as the wastewater collections crew begins using an old paint sprayer to inject a water-activated grout behind the cracks in manholes. When groundwater interacts with the grout, it expands about 20-fold to fill the cracks with a sheet of material with a plastic texture, which prevents water from entering the sewer system.

Sweet Home has been wrestling with inflow and infiltration I&I for years, and about 14 years ago, it began replacing large sections of the sewer system to reduce I&I. As a result, maximum wastewater flows during heavy rains have decreased by nearly half, from about 22 million gallons per day to around 12 million gallons per day. The city is currently planning to upgrade the Wastewater Treatment Plant to handle the remaining excess flows. At this time, the plant can handle up to about 7 million gallons per day.

I&I is water that reaches the sewer system through cracked pipes and manholes or through cross connections to storm drains. During heavy rains, it can cause the system to overflow, causing a bypass of highly diluted but untreated wastewater.

Last year, Springman said, the city and Jacobs Engineering, which has purchased CH2M Hill and now operates Sweet Home’s water and wastewater treatment plants, upgraded the Wastewater Treatment Plant’s belt press system, which is used to dry solids into a cake-like consistency and prepare them for removal and transportation to a landfill.

“There was an inability to treat solids in the Wastewater Plant efficiently,” Springman said. The belt press was breaking down frequently. Jacobs changed the bearings and the pump used to deliver the solids. It is operating quicker than it did in the past.

“They can push more solids through it,” he said. What used to take 14 to 15 hours takes about six, which means it’s not backing up into the clarifiers.

As a result of the project, the city had no bypasses related to I&I last winter, Springman said. He believed there were two the previous winter.

Sweet Home did have one bypass last winter as a result of mechanical failure, right before the dechlorinization step, Springman said.

He credited Jacobs Project Manager Steven Haney for his part in the project.

“He’s optimized the plant to the best of his ability,” Springman said, and it seems to be appreciably better.

Out in the collections system, the city’s four rehabilitation projects, which cost roughly $15 million, have done a great job, Springman said, but the city continues to work on the collections system as even those projects are beginning to age.

Zooming closer to the system, Wastewater Crew Leader Dean LeBret is trying to improve manhole repairs, one of the common places where ground water enters the sewer system.

Manholes provide access to the wastewater pipes for maintenance and repair. LeBret said the city has more than 1,000 of them.

“Working in the system, the focus was on replacing defective pipeline,” LeBret said,

The pipes are in much better shape now, although some are aging and they have issues in spots, Valloni said.

The city will never get away from repairing I&I problems, Springman said.

But the system has issues in its manholes, which form cracks in the walls. Water also gets into the sewer system through seams and those pipe connections.

The city budgets annually for manhole repair, Springman said.

To repair manholes, the city has used contractors for about 13 years. Prior to that, Valloni and other crew members would use a more dangerous form of grout, which required substantial personal protection.

Right now, 140 to 160 manholes have a “decently sized” leak, Valloni said.

Contractors tend to want to perform a full “rehab” on manholes, which is expensive, LeBret said, but city crews can repair the cracks.

Valloni came up with the idea of using an old paint sprayer to inject a relatively new hydrophilic into cracks that is safer than what the city has used in the past.

After seeing a demonstration of the concept, Valloni asked Le-Bret if Sweet Home could do it, and LeBret took on the project and conducted some experiments. At this point, he is awaiting fittings for the old paint sprayer.

“This stuff is so much safer,” LeBret said. No respirator is necessary – just some rubber gloves and an apron to stay clean. “It was always a challenge of getting behind the leak.”

To complete a repair, a worker drills a hole into the walls of the manhole, around the cracks and seams, and inserts a “zerk” fitting, he said. The injector attachment on the paint sprayer attaches to the fitting and injects grout behind the manhole, filling the space behind it until it can be seen coming back through the cracks.

It may take several fittings to fill the space in and behind a crack, LeBret said, and that causes the cost of each manhole to vary substantially, depending on how many treatments are needed.

Using cartridges in a caulking gun, LeBret and his crew were able to stop 80 percent of a leak, 40 gallons per minute, in one manhole test. He said a 5-gallon bucket of grout could handle some eight to 12 manholes.

The price on the grout has fallen from upward of $140 per 12-ounce tube to less than $80 over the past decade, LeBret said. Purchasing it in bulk 5-gallon buckets is even less expensive.

Full rehab by contractors may cost upward of $1,000 to $1,200 per manhole.

“I think we’ll see 50 percent (savings) right off the bat,” Valloni said.

The 40 gpm reduction took six tubes of grout at about $75 each, a total of $450 in material.

Springman said that Public Works can control costs better using its own personnel, noting that replacement of manholes generally costs $5,000 to $6,000 – and much more in busier locations.

He said that Public Works will track its gains and costs for each repaired manhole and create a report on the results.

The Public Works crews have been looking for other ways to save cash, and they’ve also made some gains in “hydro-excavation.”

“We have the Vactor for doing hydro-excavation, but it is an older truck that was designed for cleaning sewers, much more than hydro-excavating,” LeBret said. “It lacked the high-pressure earth mover that the newer trucks have.”

The newer trucks cost up to half a million, LeBret said. A smaller hydro-excavation machine is available for less than $200,000, but it’s still way beyond Sweet Home’s budget.

With some help and guidance from Owen Equipment, city mechanic Tim Riley and LeBret figured out how to engineer a high-pressure system for hydro-excavation that is on par with the newer, more expensive machines.

“We built the system for just over $2,000, and it has cut the time it takes to excavate dramatically,” LeBret said. With the new system, Public Works was able to open a hole and expose a water main for repair and create a safe ingress and egress in less than a half hour with the new system. With the previous system, the hole would have taken three to four hours.

The system saves money on labor and uses one-third less water per project, while requiring Public Works to commit equipment to a single project for a shorter period, LeBret said.