Fighting Inflow and Infiltration One Basin at a Time

City shifts focus away from individual problem lines and sees big results in inflow and infiltration reduction.

Fighting Inflow and Infiltration One Basin at a Time

A Naperville Water Department crew member sets up at the bottom of a manhole for rehabilitation work.

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Tony Conn is pleased with how far the city of Naperville, Illinois, has come in fighting inflow and infiltration over the last two decades.

As the city’s water distribution and collections manager, Conn is responsible for wastewater collection, stormwater pumping, water distribution and water supply and he’s seen the changes firsthand.

“We’re working through a 10-year I&I program right now, but we’re working on updating it currently,” Conn says. “I can definitely see us going another 20 to 30 years with I&I reduction work with a city our size.”

The city has seen big changes with its flows since starting a program in the late 1990s to target I&I. Since 1998, the population of Naperville has increased by roughly 30,000 people — or about 20%. Yet, when looking at the average amount of water treated at the Springbrook Water Reclamation Center, flows have decreased by roughly 18% over the same period.

The old ways

In 2004, Naperville had a population of 142,000, with 2,49 million feet of sanitary sewer main, 2,85 feet of service lines, 19 lift stations, 11,500 sanitary manholes and one treatment plant.

The city began experiencing heavy rainfall events in the early 2000s that put officials on alert. In October 2001, the city experienced a 4.5-inch rainfall over a 12-hour period. There were approximately 200 reported sanitary sewer backups, predominately in nine subdivisions of the city. The city had already identified the area affected as a major contributor of infiltration and was actively renewing laterals using pipe bursting technology. The city was also lining mainlines and rehabilitating manholes, yet it still encountered the serious flood.

“Back in the day, everybody was like, ‘You attack the worst stuff,’” Conn says of the plan in the early 2000s. “Before 2003 we were lining sewer mains all over the city.”

Making a change

The utility department spent almost a year televising sanitary mains and service lines, visually inventorying manholes, surveying buildings and acquiring information from homeowners. They also investigated sanitary sewer and manhole rehabilitation techniques and followed up with a six-year rehabilitation plan.

“That’s when we found out you can line a piece of pipe but water is going to migrate to the next place, so it’s either going to migrate to a manhole or a lateral,” Conn says.

In 2003 the city began focusing on spending the dollars on an entire subdivision before moving on to the next.

“We would line the sewer mains, the water would migrate to the laterals and we’d line the laterals,” Conn says. “Then the water would migrate to the manholes, and we would take care of the manholes. We started taking care of all the assets in that basin to stop water migration to actually achieve I&I reduction.”

Significant results

It didn’t take long for the new approach to yield results.

“We’ve had such great success with doing rehab this way that it’s the only way we operate now,” Conn says. The city has since added grouting of manholes and laterals to its work in the years since.

Customer service calls have gone down from 600 in 2007 to 280 in 2018. Sewer maintenance costs have also dropped, with a shift from annual root cutting to jet flushing every four years, equating to $39,000 in savings per year.

Treatment plant flow is now at 19.75 million gallons per day, compared to 26.75 before the I&I reduction plan.

Naperville also experienced its wettest June in history in 2015, receiving 2.2 more inches of rain in 2015 than in 2013, resulting in groundwater being 4.3 feet higher than the 2013 levels. Groundwater was 5.8 feet higher than the sewer crown that year as well, but thanks to the I&I work already completed, there were zero wastewater backups that year.

More to come

Conn says current work is still focused on areas where they know there are I&I problems, but with a city so big, officials knew planning ahead was a necessity.

“In 2016 we started a program where we do microbasin flow monitoring to help us with future projects, so when we’re done with this area, we know where to go next,” Conn says.

Flow monitors are installed for a six-month period in basins depending on annual rainfall-dependent I&I, breaking the basins down to as little as 1,000 feet all the way up to 18,000 feet.

“It really helps us pinpoint where the worst I&I is in that basin and we’ll start in that area and fan out to cover the rest of the basin,” Conn says. “So we’re hitting the big-ticket items first and then fanning out and hitting all the water migration.”


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