Two utilities follow different but highly effective approaches to protect the integrity of their pipe infrastructure and minimize water losses.
As rising demand stresses water supplies, and as treatment and distribution costs increase, reducing leakage becomes more important to water utilities.
Besides the economic imperative to reduce leaks, there are increasing regulatory requirements related to leak reporting and loss reduction. Two water utilities in different regions illustrate productive approaches to identifying and dealing with leaks.
The Water & Wastewater Authority of Wilson County (WWAWC), a retail water supplier in Lebanon, Tenn., aggressively and constantly checks its system for leaks and responds quickly with repairs.
The Tarrant Regional Water District (TRWD) in Fort Worth, Tex., a wholesale water supplier, uses technology to check the integrity of its large-diameter transmission mains and uses the data to set repair and replacement priorities.
In the late 1980s, Chris Leauber was project manager for the Tennessee Energy and Water Conservation Program (he is now executive director of the WWAWC). “Through the program, we conducted water audits, meter testing and leak detection for nearly 400 water systems in the state,” he recalls.
Before then, water departments had done a good job of repairing visible leaks. “However, the majority of leaks we found through this program showed no evidence at the surface,” says Leauber. The program was effective. The biggest payoff was in energy savings from reduction in pumping.
However, when the program ended in the 1990s, so did the vigilance. “For most water districts, leaks are out of sight, out of mind,” says Leauber. “If they don’t see anything, then they assume things are OK.”
Leauber went to work for WWAWC in 2006 and became executive director in 2008. “When I was working with the state, I always wondered why district directors didn’t pay more attention to leaks,” he says. “Once I arrived here, though, I quickly realized the reason. They have their hands full with a lot of other work, especially regulatory activities and paperwork.”
No longer voluntary
However, while managing water leaks was once voluntary in Tennessee, it became a requirement in 2007, when a law was passed requiring utilities to report water losses in their audited annual financial statements. The law was triggered after one utility raised its rates, and investigation later found that it was billing for only half the water delivered into its system. Since 2013, Tennessee’s water utilities have been required to use AWWA Water Audit software to report water loss information to state regulatory bodies: the Utility Management Review Board and the Water and Wastewater Financing Board.
In addition, there are performance indicator triggers based on scores that measure the validity of data submitted in audits. Validity scores look at factors such as the existence and frequency of meter testing, the presence of a SCADA system, and the use of automated meter reading, advanced metering infrastructure and GIS mapping.
A validity score below a certain threshold, as determined by the software, triggers referral to one of the regulatory boards for noncompliance. The utility then must create an action plan to reduce losses. The validity score triggers are made more stringent every two years.
“As a result, Tennessee probably has the strictest regulations in North America in terms of water loss,” said Leauber. “Similar regulations are being considered in other states.”
How has WWAWC responded to the state requirements? Quite well. In fact, the utility has always been “way ahead of the curve,” routinely achieving virtually perfect scores, according to Leauber. WWAWC has about 326 miles of main and 7,000 service connections.
“Regulatory-wise, we are in great shape,” says Leauber. “We are easily meeting minimum requirements. However, we don’t want to stop there, because we purchase 100 percent of our water from four different suppliers, and we don’t want to be wasting money.”
One reason the utility is so successful in managing water leaks is that it checks for them on a daily basis. “Since we are almost 100 percent PVC rather than metallic, it is very difficult to hear leaks,” says Leauber. “Instead, we do minimum night flow measurements.”
The utility is divided into 16 district metered areas (DMAs). “We look at flows on the system between one and three in the morning, when most customers are sleeping,” Leauber says. “In areas that are gravity-fed, we look at 24-hour flows.”
Each day, utility staff members look at the leakage rate in each DMA. If a DMA gets above a certain ratio that calculates the “technical minimum” via the AWWA software, the utility springs into action. “The next night, we go out and do a minimum night flow test using strap-on ultrasonic units that report flows every 30 seconds,” Leauber says. “We measure the drops and identify where the leaks are occurring.”
The Tarrant Regional Water District (TRWD) is one of the largest raw water suppliers in Texas, supplying more than 30 wholesale customers in the north-central part of the state that in turn serve 1.7 million end-users.
In the 1970s and 1980s, TRWD installed more than 160 miles of prestressed concrete cylinder pipe (PCCP) in its system, which consists of two major pipelines. One pipeline, built in 1972, consists of 72- and 84-inch pipe. The other, built in 1988, includes 90- and 108-inch pipe.
Failures in the pipelines began occurring within a few years of construction, mainly from corrosion of prestressing wires, hydrogen embrittlement and thrust restraint. “In the late 1980s, we were starting to have failures of this PCCP,” says David Marshall, engineering director. “Since our system fed about 70 percent of the water used in Fort Worth, the integrity had to be brought up to a higher standard.”
At the time, according to Marshall, there were no good nondestructive inspection techniques other than dewatering and inspecting internally. “We could visually inspect the pipe and sound it with a hammer,” he recalls. “Acoustic reflection technology was also available.”
Through the Water Research Foundation, the utility became part of a study that involved the use of four new nondestructive technologies: “We were able to test all four of these.” In 1998, TRWD chose electromagnetic technology offered by Pressure Pipe Inspection Company (PPIC), which was acquired by Pure Technologies in 2010.
TRWD launched a comprehensive inspection program for its pipes, designed to map its entire system. PPIC inspected all of the 72- to 108-inch pipes in the two pipelines. “We were PPIC’s second customer to use their eddy-current electromagnetic technology,” says Marshall.
Through the initiative, TRWD found that its existing maps were inaccurate. In addition, the electromagnetic technology helped identify areas where pipe wires were broken or prestressing. From there, the utility developed a system of setting pipe repair and replacement priorities.
Subsequently, TRWD and seven other agencies funded a study by the Simpson Gumpertz & Heger engineering firm to develop a strength model and risk information system that could better define pipe replacement needs based on wire breaks from corrosion and hydrogen embrittlement.
“From there, we were fully able to identify what pipes needed to be replaced and what damage we could live with, and then set up a system of continuing inspection,” Marshall says. “In other words, we manage based on condition. Since we operate 24/7 year-round, we need to be very prudent in how and when we schedule outages, so we can get the biggest bang for our buck.”
The utility’s first electromagnetic inspection was in 1998. “By 2005, the technology had matured to where it was truly accurate,” Marshall says. In 2006, TRWD asked PPIC and Simpson Gumpertz & Heger to integrate the inspection and pipeline operation information that existed in the district’s database with the failure risk analysis curves the engineers had developed, in order to evaluate pipe failure.
Inspection of all 160-plus miles of PCCP, completed in 2009, gave TRWD an accurate map of its pipeline segments, hydrants and valves, and inspection results. The map is now part of a GIS database that allows the district to prioritize pipe replacements each year, based on failure risk analysis information.
More recently, TRWD has expanded its inspection program to include a full asset management program, which consists of periodic inspections that rely on electromagnetic technology, calculation of failure risk (based on the most recent inspection results) and the GIS database. To help prevent pipe failures, TRWD now uses three strategies:
- Transient pressure control by modifying pump control valves so that a programmable logic system can control valve closing times to reduce transient waves.
- Cathodic protection using zinc anodes attached to the pipelines.
- Pipe segment replacement based on priority needs.
“We conducted root-cause analysis on corrosion and ended up retrofitting the 160 miles of pipe with cathodic protection,” says Marshall. “We also need to accurately monitor the cathodic protection system and make sure we don’t overcharge it, because that can lead to its own problems with embrittlement.”
As Marshall sees it, had the utility done nothing, it probably would be repairing or replacing a segment of pipe every month or more — an estimated 41 failures per year in its two pipelines. Instead, in the past five years, TRWD has had three failures. The district estimates that replacing its 300 highest-priority segments would cost about $12 million over several years, significantly less than for pipe replacement after failures.