Grouting and CIPP Put an End to I&I

Naperville, Illinois, turns to grouting as a complementary weapon to CIPP lining in the fight to tighten up its system.
Grouting and CIPP Put an End to I&I
Naperville Department of Public Utilities technician Dino Tinajero cleans up after flushing a sewer main with a Vactor combination truck. (Photography by Alyssa Schukar)

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Naperville, Illinois, has been battling stormwater inflow and infiltration in the city’s sanitary sewer collections system for years. But after a natural calamity a couple years ago, the staff of the city’s Department of Public Utilities realized they needed to step up their game.

Bringing a new approach to the problem has made a huge difference in just two years, and officials expect to continue reaping the benefits.

That new approach includes some new techniques along with some tweaks to other methods they have long relied on. But if there’s a breakthrough — a magic bullet — it’s the realization that there is no magic bullet, and it’s a willingness to go beyond relying on just one technology for I&I reduction.

The payoff for Naperville’s efforts has been reduced flows to the city’s sewer treatment plant so the city doesn’t have to treat more volume than necessary. And utility ratepayers have felt the payoff in their pocketbooks: For two years running, the utility has actually canceled previously scheduled rate increases.

They simply weren’t necessary, says Tony Conn, wastewater collections and pumping supervisor for the Naperville Department of Public Utilities. “One of the reasons why the flows are down at the treatment plant is due to our I&I program,” he says. “It’s knocked down maintenance costs.”

Windy City suburb

With just under 150,000 residents, Naperville is Illinois’ fifth-largest city, a mostly residential suburb 28 miles west of Chicago. The wastewater stream is typical for an American suburban community, with private homes and small commercial accounts generating most of the flow.

The two largest commercial wastewater sources are a chemical research and testing facility and a snack cracker factory. Both have pretreatment equipment, so their output isn’t significantly challenging, Conn says.

Most of the city’s sewer lines are clay pipe. The oldest go back more than a century to the early 1900s. The I&I sources are typical: roots that penetrate and crack pipes along with routine deterioration of the pipe materials. Many of the lines making up the system are past their life expectancy and long-term repair and replacement programs are underway.

I&I experience

Awareness of I&I problems is nothing new for Naperville. “We’ve been tackling I&I as long as I can remember,” says Conn, who’s worked for the city for 23 years.

But in the last decade Conn and his colleagues have amped up their attack. The first wake-up call came in February 2001, when heavy rains ran off frozen ground in the city causing floods that sent water pouring into the sewer system. After that, “we started getting heavily into all kinds of sewer rehabilitation.”

Naperville’s treatment of choice for sewer lines has been cured-in-place pipe for mainlines, circumference lining technology for laterals, and CIP or spray lining on manholes.

The city has taken an aggressive approach to lateral lining, especially since 2003. That’s when it became city policy to line the lateral as far up on private property as the property owner allows.

On lateral jobs, the city’s contractors are instructed to install a clean-out 18 feet inside the private property line and install the new CIP liner up to that point, paid for by the city.

“We know that by knocking off that additional I&I we’re going to save money in the long run in maintenance and treatment costs,” Conn says. The property owner also typically gets a chance to hire the contractor to line the rest of the lateral up to the foundation. “Because the lining company is already there, they’ll get a very good deal,” he adds.

New challenges

The lining programs that began in the early 2000s made some inroads, but over time they also showed limitations.

Another round of flooding in April 2013 swamped portions of the city, and once again I&I problems surged.

One of Naperville’s first responses was to go bigger on its rehab programs. While the city was already paying a lot of attention to fixing laterals and manholes, it began taking a more comprehensive approach. When a source of I&I is pinpointed now, says Conn, the city no longer takes a piecemeal approach to the site.

“We’ll do an entire basin rehab instead of the mains,” he says. “We rehab the mains, we rehab the laterals and we rehab the manholes.”

That helped, but it wasn’t enough.

Enter grouting

As the 2013 floodwaters were receding, crews took advantage of the chance to inspect where the I&I was worst. What they found was that a significant source of the leaks wasn’t just cracks or deterioration in the pipes themselves; leaking joints between two lengths of pipe were a major culprit, too. So were leaks at manhole terminations.

In the process, Conn says, he also came face to face with the limits of lining. “After we would line a sewer main, I&I wouldn’t go away,” he points out. “It would just move.”

The city had used grouting in the past as an I&I tool. But in recent years city officials had been hearing more and more about the potential role of grouting in I&I reduction.

There is more than one way in which leaks at pipe joints can cause problems even after lining. The most obvious is that water can get in the joints and into newly lined pipe, once again unnecessarily increasing the volume of water being treated.

But sometimes water doesn’t just enter the pipe itself — it actually penetrates the space between the liner and the host pipe. So sealing off the leaky joint not only reduces the groundwater flow into the sewer — it keeps the interface between pipe and liner free of water, too.

That’s where grout comes in.

Depending on the specific soil and other conditions, any of several different products can be used to seal pipe intersection seams and prevent groundwater from entering the line.

A June 2014 project showed just how big a difference grouting can make. A 2,500-foot length of 12-inch pipe was lined, but after a heavy rain, Conn says, “every joint was leaking heavily.” Once the joints were grouted, the leaking stopped. “There was no water migration between the host pipe and the liner.”

Naperville wasn’t a stranger to grout; the city had been using grouts for years to shore up cracked and leaky manhole structures. City crews originally used 3M products; more recently, they’ve begun using Aqua Seal grouting materials (Sealing Systems, Inc.).

Bolstering lining

The city now grouts leaking mains and laterals before any lining. At the termination point at every manhole, the city also installs Insignia end seals (LMK Technologies) and Sikadur 31 (Sika Corporation) to stop leaking between the host pipe and liner.

“Before, when you just put a liner in, you wouldn’t worry about the termination at the manhole,” says Conn. “That’s one of the biggest sources of leaks between the host pipe and the liner.”

The city uses outside contractors for the mainline and lateral lining work as well as for the grouting that is now included as part of those projects. “We take care of practically everything that has to do with the collections system,” says Conn. “I don’t have the manpower to do in-house grouting for lateral or mainline rehab, so we contract that all out.”

The city’s bid requests generally specify the use of AV100 grout from Avanti International. “We’ve had the best luck with it,” he says. “We just stay with it.”

Coming test

Naperville’s newest grouting initiative may be something of a test of grout used alone.

A section of the collections system with some 450 laterals has been targeted for the new project. The area has had major and persistent groundwater infiltration. The affected laterals are already under the groundwater table, making them especially susceptible to I&I even without rainfall.

Grouting where those laterals connect with the mainline had little effect, Conn says. “All it did was move the water to the joints upstream of the lateral.”

Yet inspections of those laterals showed little evidence of pipe deterioration in the clay laterals themselves. That pointed the finger of responsibility at joints in the laterals.

Naperville is starting with a group of 60 of those targeted laterals as a pilot project. “We are going to grout the laterals from the mainline connection all the way to the house foundation,” Conn explains.

Those laterals aren’t due for lining now, however, so the city is bypassing that step, sticking with its current priority list for parts of the system to be lined. And if the pilot project is successful, the city will proceed with grouting joints on the rest of that section’s laterals over a four-year period. These laterals will be lined in the future as a separate procedure, Conn says.

Not resting on laurels

The experience with grouting has led Conn to a balanced perspective on the many different ways to combat I&I. “I consider lining a sewer main as just one of the tools in your toolbox for I&I reduction,” he says.

With a focus on I&I as well as on regular maintenance, Naperville has much to show for its efforts.

“We don’t have dry-weather-related wastewater backups,” Conn points out. And then there were those two rate increases — 3 percent each — the utility canceled that Naperville’s ratepayers won’t have to pay.

In time, Conn hopes the city’s I&I program will minimize the effects of heavy rain or flooding events. In the meantime, Naperville will keep doing whatever it can to tighten up its system.

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