Fighting water system leaks is an obsession for the efficiency-focused staff of Wilson County.
In Wilson County, Tennessee, achieving the least is top priority.
The Wilson County Water and Wastewater Authority supplies water service to 25,000 residents, purchasing all potable water from outside sources. Since purchased water represents its single biggest expense, the authority has ramped up efforts to reduce system losses to their statistical minimum, using only free software, district metering and step testing.
Wilson County is located just east of Nashville. The authority provides water service to the eastern half of the county, excluding the cities of Lebanon and Watertown. The authority purchases treated water from different sources, including Lebanon.
Chris Leauber is executive director of the authority and chair of the American Water Works Association’s Water Loss Control Committee.
“We’re always looking to control costs,” he says. “When the authority was formed, it wasn’t economically feasible to build our own water treatment plant. As the system continues to grow, we’d consider the possibility of building a water treatment plant and associated infrastructure, but it continues to make more economic sense to purchase water and concentrate on leak detection to lower costs.”
He describes Wilson County’s underpinnings as “one solid limestone rock.”
“People joke that, if you hit it with a hammer in one county, you can hear it in the next,” he says. “All water main installation is done by blasting and using rock trenchers. The major failures that occur on the mainline infrastructure are typically caused by poor installation years ago, where rock in the backfill has split the PVC pipe from underneath.”
A new water system
Water is distributed through 340 miles of main, ranging in diameter from 2 to 10 inches, with the majority running at 6. It’s a fairly new system, with the oldest section dating back to 1975. Other than one short section of ductile iron, pipes are made of PVC.
The distribution system consists of nine pumping stations and five ground-level storage facilities ranging from 50,000 to 500,000 gallons in capacity.
The authority handles all operations and maintenance on the water distribution side. The in-house staff installs 2-inch water service lines using a Grundomat horizontal boring tool by TT Technologies. Larger construction projects are typically outsourced.
The earliest leak surveys on the system were conducted in the early 1990s under the Tennessee Energy and Water Conservation Program. “I was the project manager as a member of the consulting firm that was awarded the contract to conduct water audits across the state, and Wilson County was the first system we inspected,” Leauber says.
Sonic leak detection drove the program, and the utility quickly adopted the technology for ongoing inspections. Leauber joined the authority in 2006.
“When they originally brought me on as assistant executive director, it was primarily because of my expertise in water loss control,” he says. “Then as now, the overall condition of the infrastructure was in good shape. It’s the cost of water supply that’s driving further efficiency in leak detection and repair.”
The best things in life are free
The authority uses the free Water Audit Software provided by the AWWA, a regulatory requirement in the state of Tennessee. This software calculates the utility’s infrastructure leakage index (ILI) — total system losses divided by unavoidable system losses. It also uses the AWWA Water Audit Software Compiler, which provides year-to-year analysis and comparisons of water loss records.
“District metering was one of the first concepts we implemented to drive efficiency,” Leauber says.
District metering requires the water system to be divided into discreet district metered areas (DMAs) that are relatively easy to isolate from the system using the fewest shut-offs.
“Establishing DMAs can reduce the time required to isolate a leak to just a day instead of having to check the entire system over possibly months,” says Leauber.
The authority has already recorded benchmark minimum night flow data for each of the system’s 21 DMAs, which typically occurs between 1:30 and 3:30 a.m. Legitimate nighttime consumption averages 1.5 gph, per connection. The SCADA system generates a call to on-duty personnel if it detects major system demand exceeding the minimum night flows in any DMA.
“You don’t always assume it’s a leak,” says Leauber. “It could just be unusual consumer demand, such as filling a swimming pool. If the flows exceed the benchmark, and we feel it involves leakage, we’ll go through a process called step testing. Our standard operating procedure includes the GIS data required to locate the mainline valves we need to shut in sequence to reduce flows by the exact amount required to match the volume of the leakage. We try to do this for no more than five minutes, because you don’t want to depressurize the system.”
For large leaks, step testing will be conducted during the day. For minor leaks, crews will hold off until the next night’s minimum flow period. That’s because it’s easier to measure the smaller leakage during the minimum night flow period when the ratio of leakage to total flow is greater than during the day.
Knowledge is power
While the valves are identified through GIS, crews still need to apply their training to manipulate the valves to counterbalance the leakage. Leauber and the authority’s project manager are state-certified distribution operators, as are four of the six members of the field crew — the other two are studying for their exams. “We have a goal that everybody who touches our water infrastructure is a certified operator,” he says. “It elevates their capabilities and knowledge level.”
Typically, the leak is isolated first to a DMA and then to a shorter length of pipe in a few hours. From there, crews look for an actual leak, starting with visual inspection. If no leaks are visible, the next step is to use direct contact sounding on system valves, hydrants and customer service lines. PVC is less conductive to leak sounds, so ground microphones can also be used to locate leaks within a radius of a few feet. Crews most commonly use the Heath Aqua-Scope, which can provide both ground and direct contact miking.
Crews also look at other evidence of leaks, including unusual flows to and from storage tanks or increased flows in pump stations via flowmeters.
“Even though we use telemetry, we keep flowmeters installed outside in the open,” Leauber says. “We like the ability to drive up and read the meter manually. If someone is manually operating a valve, the SCADA system does not always reflect the changes instantaneously, but a crew member can monitor the meter in real time.”
One-man step test
The procedure has been refined to “one-man step testing.” The process requires an extremely accurate flowmeter — the authority has used the electromagnetic evoQ4 by Elster, which provides flow data to a local read-out and to the SCADA system via telemetry. Pressure data is also collected and transmitted.
“Most meters put out a pulse for every 100 gallons of flow,” says Leauber. “That’s not fast enough to perform a step test in under five minutes. The evoQ4 puts out a pulse for every one gallon of flow. We worked with Verizon to find a black box that would allow crew members to communicate directly with the meter via smartphone text service to get instantaneous readings.”
By simultaneously adjusting valves and reading the meter via smartphone, step testing is reduced to a one-person operation.
Leauber notes that the authority squares the approximate $5,000 cost of retrofitting real-time telemetry on an existing DMA meter against the cost of lost water from an unlocated leak. The payback period amounts to just a few months.
“Once we locate a leak, it’s generally easy to excavate into the existing limestone trenches to make a repair,” Leauber says. “Only if the pipe is lying on the bottom of the trench do we have to hoe ram a little rock underneath the pipe to complete a clamp repair. In many cases, we get the leak repaired without any noticeable service interruption to the customer.”
Down to the minimum
Using these simple tools and procedures, Wilson County often achieves an ILI of just 1.0 — the technically achievable minimum in any system.
However, Leauber cautions utilities that each situation is different. Utilities must set an ILI goal that includes an economic analysis to determine the cost of achieving that goal against the actual cost of lost water. Another free tool, the Water Research Foundation’s Leakage Component
Analysis software, will help identify a cost-effective ILI target against the cost of water loss control and pressure management programs.
“A leakage control program is an investment,” he says. “That makes pursuing water loss a delicate fiscal balancing act. While nobody wants to waste water, the economic goal of a good leak detection program is to achieve an ILI that maximizes the amount of water we can provide while delivering water to customers for a reasonable price.”
Five simple steps toward developing a water loss control program
Here are five steps designed to help any water utility to reduce avoidable water loss, courtesy of Chris Leauber, executive director of the Water and Wastewater Authority of Wilson County, Tennessee:
- Use the free American Water Works Association water audit software to determine the utility’s Infrastructure Leakage Index and other performance indicators.
- Consider having a completed water audit validated by a knowledgeable third party who can check to see if the methodologies used to collect data are sound. For example, if you’re not checking your input meters for accuracy on a regular basis, all the data that follows may also be inaccurate. Don’t make investments to correct water loss unless you’re confident that the data is free of major errors.
- Analyze the two categories of water loss identified by the Water Audit Software. “Apparent loss” is typically the result of inaccurate customer meters. That may require some field testing of sales meters. “Real loss” is a reflection of system leakage. Look at leak detection programs that can reduce water loss.
- Make sure that the increase in water revenue gained by reducing apparent loss and the decrease in water costs from a leakage control program are cost-effective. The Water Research Foundation’s free Leakage Component Analysis software will help identify a target ILI that’s cost-effective.
- Monitor system losses on an ongoing basis. The AWWA’s free Water Audit Software Compiler provides year-to-year analysis and comparisons of water loss records.