Taking a Deeper Look at Pipe Conditions

Pennsylvania township gets proactive on inflow and infiltration to prevent bigger problems.

Taking a Deeper Look at Pipe Conditions

Justin Hollenshead sets up the location data and starts an Electro Scan inspection from inside the camera truck.

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The Hamilton Township (Pennsylvania) Municipal Authority is dealing with infiltration and inflow for all the right reasons. And a consent decree is not among them.

“We’re trying to be responsible and proactive, to work on it now and budget for it rather than waiting for a consent decree and then having to borrow,” says Sharon Purnell, manager of the municipal authority. “We want to have a way to pass critical information along to crews who come to work for the authority, and leave things as best we can for the next generation.”

The current team is hard at work with its GIS mapping system to identify, track and log crucial information about its 70-mile sewer system. And they’re using state-of-the-art Electro Scan technology, which utilizes electrical current to detect, measure and quantify defects. 

The pipe section to be inspected is fully flooded using the authority’s Vactor truck, and the Electro Scan probe is pulled back through. There is a cone attached to the end of the probe that helps to keep the probe fully submerged with water.

The scan results help with prioritization, and the information is valuable in making educated decisions in regard to remediation.

“If electricity can get out, water can get in,” Purnell explains.

It has its advantages over CCTV, she says, in that it enables the township’s crews to simulate full-pipe storm flow conditions without having to wait for wet-weather events with a limited window for sewer condition assessment. “We will scan a specific basin or area, prioritize the top 10 to 20 lines and follow up with CCTV to further investigate to visually see what the conditions are. They are both important and complementary tools in sewer condition assessment.”

Hamilton Township

Hamilton Township is situated near the borough of Chambersburg, about an hour southwest of Harrisburg. The township’s sewer system conveys wastewater to the Chambersburg wastewater treatment plant. The system consists of 14 pumping stations, three meter stations, 1,215 manholes and 70 miles of sewer line — 85% consisting of PVC and the rest asbestos concrete cement that’s now 30 to 40 years old. The system provides service to just over 4,000 customers.

The Chambersburg treatment plant was recently expanded due to the Chesapeake Bay strategy; as a result, the township’s capacity increased from 760,000 gpd to 2.0 mgd. 

But even then, I&I could be a problem. Heavy rains — such as last year when the area recorded a record 61 inches of rainfall — can result in more than 3 mgd of flow through the sewer system to the Chambersburg plant. The average daily flow in 2018 for Hamilton Township Municipal Authority was about 965 gpd.

New technology

To address the I&I issues, the township adopted a sewer system management plan in 2009 and developed a comprehensive metering plan using Teledyne ISCO 2150 area velocity meters to analyze the reaction of the system to wet-weather events. At the same time, Hamilton’s sewer crews used its RauschUSA CCTV camera as well as smoke testing and manhole inspections to try to spot cracks and breaks. Spot repairs were made using acrylamide grout, trenchless point repairs and dig-and-replace techniques. During heavy rains, crews often went out at night to isolate pipe sections in an attempt to identify I&I issues.

“There is no question the spot repairs made a difference, but there was still more going on in the pipe that we could not see with CCTV,” Purnell says. “We could only see the pipe conditions above the waterline. Had we had Electro Scan then, we would have realized more than spot repairs were warranted.”

The results were reported in a paper presented by Purnell and Mark Grabowski of Electro Scan at the No-Dig Show in Denver in March 2015.

Beneath Commerce Street — a busy thoroughfare — the Electro Scan device identified 51 locations of potential defects along 1,080 feet of asbestos concrete cement pipe, with an estimated leakage of 23 gpm, or over 33,000 gpd, assuming a 1-foot head. That’s more than 10% of the average daily flow through this pipe of 248,000 gpd, coming from four pumping stations and by gravity flow from four different developments, according to the township’s metering system. Extreme wet-weather events have yielded as much as 1.2 mgd with a peak hourly flow of 83,650 gpd.

Hamilton Township had never televised this section because of flooding and closure of the road to traffic during wet-weather events.

At a second site — known as Fern Lane — a 980-foot section of 10-inch PVC pipe runs along a creek bed and was suspected of serious I&I because flows increased when creek levels rose. Because of flooding, the pipe had never been inspected by CCTV since installation in 1977. The Electro Scan probe indicated, however, that the pipe was in good shape with low levels of potential infiltration. Only 10 defects were identified, having a total flow of about 4 gpm. Instead, the increases in flow were attributed to inflow, which will allow the township to concentrate on flow rather than pipe defects in the future.

Scanning for leaks

Based on the results of the pilot study, Hamilton Township decided to purchase its own Electro Scan technology, including a model ES-620 for sewer inspection and a model ES-38 for probing small-diameter pipes, including laterals. “Ballpark, our cost was around $200,000 for both,” Purnell says. “There was a discounted cost for the lateral unit, and we decided to take advantage of that.”

Currently, Hamilton is using the technology to inspect additional sections of sewers that have been troublesome in the past. In a recent project, the township inspected an entire gravity flow basin — known as Washington Street — which was one of the first sewer lines installed back in the 1970s. “We scanned everything we had access to,” Purnell says. “It’s an asbestos cement pipe trunk line that underlies a busy highway and travels over a creek and into the Chambersburg trunk line interceptor.

“We looked at the worst areas and followed up with our CCTV system. Based on condition assessment and meter data from the area velocity flowmeters, we could see there was potential for surcharging in one section of line during a major storm event. Additionally, we decided to abandon another section of mainline and tie into a newer interceptor.”

The township then used pipe bursting (Doli Construction) to completely replace the defective line. “It went rather well,” she says. In one area, the existing pipe was concrete-encased and had to be dug up and replaced.

Purnell says the Electro Scan technology is user friendly and easy to work with. “We set up our ground and have the electric current we need for the scanning. Electro Scan displays visual graphs to monitor the electrical current, water height and speed. We can look at the results on the run and make intelligent decisions right there on the spot. It’s easy to follow up with our CCTV unit.” 

Before, she explains, with CCTV it was difficult for township crews to see defects underwater, but now with the Electro Scan technology, defects are detected in a fully submerged pipe. “We are able to prioritize condition assessments and follow up with CCTV in the worst areas identified. It’s been very useful.” 

Looking forward

The monitoring, inspection and rehabilitation strategy is enabling Hamilton Township to approach future challenges responsibly and cost effectively.

By getting a better handle on I&I, the township is hopeful it can sustain available capacity for long-term growth, lower sewage treatment costs, avoid penalties for exceeding its capacity allocation at the new Chambersburg treatment facility and police itself against any environmental regulatory orders in the future.

Already, Hamilton has saved money by recognizing pipe conditions that called for replacement or CIPP lining rather than spot repairs and identifying areas that were in better shape than they were thought to be.

Purnell, who has been with the township for 35 years, feels a sense of responsibility to Hamilton and for those who will come after. “We strive to be proactive and prepare for the future, to leave things in the best shape possible, and are doing the best we can.”

Combating I&I is challenging and never-ending. “Reflecting back, a lot has changed over the years, and our I&I efforts and program have come a long way. Using a variety of tools including technology in conjunction with hydraulic modeling, we have developed a better understanding of the reaction within our sewer system in wet-weather events. We have a way to collect and pass information along to the next generation of field personnel in the future.

“Overall, that’s a big benefit to the township and our ratepayers.”

Electro Scan inspection technology

Electro Scan inspection unambiguously locates and measures in gallons per minute all potential leaks that are typically missed by CCTV, such as bad joints, cracks, holes, fractures, bad service reconnections and poorly cured liners. The technology was named to Fast Company’s prestigious list of 2019 World’s Most Innovative Technologies at SXSW in Austin, Texas, and is being used for locating infiltration and for certification of trenchless rehabilitation throughout the U.S. and U.K.

The technology is based on the concept that nonconductive materials naturally prevent electricity from passing through, or along, the wall of a pipe. “Electrical current should never be able to ‘leak’ from inside a pipe unless there is an opening in the pipe wall,” says Mike App, vice president of Electro Scan. “A defect in the pipe that leaks water will also leak electrical current. The larger the defect, the greater the electric current flow as described in ASTM F2550.”

Electro Scan ES-620 probes (such as the ones used at Hamilton Township, Pennsylvania) measure 32 inches long by 2.875 inches in circumference. They can be pulled downstream by a jet truck, are compatible with existing CCTV equipment and can detect leaks in dry or completely submerged pipes.

A smaller ES-38 unit, which Hamilton Township also owns, can be used to detect leaks in sewer laterals.


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