Lifting the Lid on Sneaky Sources of Infiltration

Rocky Mountain coatings specialist sees often overlooked sources of I&I.

Lifting the Lid on Sneaky Sources of Infiltration

Austin Huggins of Advanced Lining sprays OBIC polyurea lining inside a new manhole at a work site in the Rocky Mountain region of Park City, Utah, an area with high water tables.

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With any collections system and municipal utility looking to reduce the burden on its wastewater treatment facility, pinpointing the source of inflow and infiltration is critical. As a trenchless technology rehabilitation contractor, Advanced Lining of Clearfield, Utah, sees some common and overlooked issues when it comes to addressing inflow and infiltration.

“Municipalities will address their collections system mainlines with either cured-in-place pipe (CIPP) or other trenchless methods such as bursting, or traditional dig and replace, with many starting to incorporate laterals as part of their cured-in-place (CIP) programs, but we’re finding that manholes and lift stations are often overlooked,” says Seth Huggins, co-owner of Advanced Lining. Huggins and his team have quickly recognized that these vertical structures are often some of the largest contributors of extensive I&I in their service area of the Rocky Mountain states of Utah, Idaho, Wyoming, Montana and Nevada.

Environment plays a role

Advanced Lining is the sister company of Advanced Pump and Equipment, which has been servicing lift stations, wet wells and wastewater treatment plants in the Rocky Mountain region for several decades. In the areas it operates water tables are high. There have been some recent anecdotal studies indicating that upward of 50% of the water that’s being treated in local wastewater treatment facilities is due to infiltration and not actual sewage. This is becoming a huge financial and operational drain on wastewater treatment plants, and they’re finding themselves having to expand to meet increasing demand.

“It is exceedingly rare, if ever, that we come onto a job site involving manholes that do not either have the presence of I&I or show that I&I exists,” Huggins says. “Although water tables do tend to drop throughout the wintertime, and may be dry of active infiltration, we can see evidence that during wet seasons it is highly active.”

Most of the infrastructure that Advanced Lining deals with is on average 30 years old; however, it is not uncommon that some brick structures are upward of 80 years in age. The company is working to create an awareness in the market about the importance of addressing structures like manholes and lift stations — the verticals in a collections system — because of their contribution to the overall I&I issue. Ignoring those issues will only make it harder for municipalities to reach their mitigation goals.

Because of this, some client cities are realizing that infiltration will exist regardless of what they do, even in brand-new construction. They’re deciding to deal with it proactively so they will not have to worry about the structure later in its life cycle. As a case in point, the company recently took on a project in Nevada encompassing the installation of five new manholes, a lift station and a wet well that included a requirement to be lined with a protective polyurea coating. It’s a good thing the job called for the coating, too, because by the time the wet well had been placed — within a week of installation and just before it was due to be lined — it had already begun to experience active infiltration inside the structure. Advanced Lining crews were able to dry the structure and perform the lining before it went into active service, and the city’s decision to be proactive was reinforced as a wise move.

“There can be tremendous sources of I&I, even in a brand-new system structure, so taking the opportunity at this stage is an efficient and relatively inexpensive thing for cities to consider as a way to seal current and future I&I from the system,” Huggins says.

A major leak

In another job, officials from the City of Shelley, Utah, approached Advanced Lining to discuss an issue they were having with their wastewater treatment plant being overwhelmed in the summer. They believed that the source of the problem was probably infiltration, and that the plant couldn’t handle the number of gallons coming in at its current capacity. Shelley was looking at a multimillion-dollar upgrade to its plant to address the capacity issues, but the officials decided to explore other options. In looking at some of the collections system’s manholes, the city discovered there were several structures along a main trunk line, adjacent to an irrigation ditch, that were leaking more than 250,000 gpd of infiltration during peak summer months.

One particular manhole was 8 feet in diameter, 25 feet deep and situated in the middle of an alfalfa field. The structure was experiencing infiltration through all its joint seals, two inlets, the outlet and was constantly full of water. It was consistently leaking when the Advanced Lining crews inspected it during the summer months, so they waited until winter when irrigation season was over to assess the true levels of I&I and plan to effectively seal it.

Historically, this structure was the leading source of the infiltration, averaging 250,000 gpd of infiltration through it, as it was in a field that was receiving daily irrigation water. The manhole was also an intersection for a trunk main that services two adjoining cities and traverses to the local wastewater treatment plant. The incoming lines were 38 and 42 inches in diameter.

Shelley had been aware of the issue for some time and had tried lining the structure previously, but the attempt failed. Advanced Lining removed the existing liner and re-grouted the structure to fill some of the voids and gaps that were in the concrete. It then applied OBIC 1000, a spray-applied polyurea lining from OBIC LLC, and sealed the structure substrate all the way up to the chimney.

The following summer, the crews went back to visit the site to study how it was performing during the irrigation season. Upon inspection, the manhole was found to be watertight with no infiltration, and it remained that way for the entire summer season. A follow-up inspection was done the next winter, and there was still no sign of infiltration.

“The beauty of using these linings in these types of structures is that we can take active infiltration and stop it even when it only exists at certain points of the year,” Huggins says. By lining this structure, the city is now saving over 1 million gallons per week of irrigation water from being treated. And that water is now available in the ground for the local farmers who are saving operational costs since their irrigation water is no longer being washed down the pipe.

A quiet villain

In a collections system, manholes are often recognized as a source of I&I; however, Huggins has seen significant I&I in places that have often been overlooked as possible sources: lift stations and wet wells. As a rule, wet wells are at a low point, so they will always be deeper than manholes. And when water tables are high, there is always infiltration.

“One of the reasons I believe these particular structures do not necessarily get the attention is because there’s always water present there, so I&I is not as obvious,” Huggins says. “With a wet well or lift station, because there’s typically water present, you won’t necessarily recognize the issue. But when you pump it dry and clean it, it’s easy to see infiltration all over.”

Huggins says it’s rare that he’s performed an inspection or maintenance on a wet well and not encountered infiltration. He recommends that during regular maintenance and cleaning cycles for wells and lift stations, maintenance crews look at all seams that are stacking up to the chimney, as these seams are pain points for I&I and corrosion issues. The freeze-thaw cycle will create cracking, and when water tables are high, water will always find a way in. Using a lining to coat the walls of these structures could do a lot for eliminating I&I from these hidden culprits.

“I&I can be hiding in unexpected places,” says Huggins. He advises his clients to consider the entire system and all its integrated structures as having potential weak points and to seek them out. “It’s often a tedious process, chasing leaks, but just taking a few preventive steps and lining proactively, we are able to mitigate more I&I than imagined and save treatment dollars in the long run.” 


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