Out of Sight

Leak correlation technology helps a rural Arkansas water district recover non-revenue water that never surfaced.
Out of Sight
Benton County uses an AccuCorr 3000 correlator with three outstations to pinpoint leaks.

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A 1,842-foot-deep well provided water to Benton County Water District #1 in Avoca, Ark., until 2000, when the Benton/Washington Regional Public Water Authority built a water treatment plant.

"When our transmission mains were installed in 1974, the well had no meter," says manager Eddie Cooper. "Once we began purchasing water from the plant, we realized some loss, but it wasn't too bad." That ultimately changed. By 2006, non-revenue water averaged 26 percent or 42.5 million gallons.

Since then, a leak detection and repair program has helped cut nonrevenue water by a total of about 101.1 million gallons at a cost of $207,257. The district repaired or replaced enough pipe to reduce leakage to an estimated one-quarter gallon per minute per mile — almost equal to the rate of evaporation.

Challenging terrain

Part of the district's problem was its location in the Ozark Mountains.

"We have very little soil, and our specifications at the time did not require bedding the mains," says Cooper. "Contractors backfilling the trenches with native rock punched holes in the PVC pipes or cracked them. We also had age-related leaks."

Because of the hilly, rocky terrain, many leaks never surfaced. To find them, the former district manager sent Cooper and technician Jordan Sullivan to a sister city
to evaluate its leak detection system. They shadowed the electronic technician all day and returned with a positive report.

In 2007, the district purchased equipment similar to what they observed: 10 Permalog leak noise data loggers, a Patroller II remote data collector, an AccuCorr 3000 correlator with three outstations, and a Xmic ground microphone, all from Fluid Conservation Systems.

Elusive quarry

The district has 120 miles of 2- to 12-inch PVC lines providing 380,000 gpd to a population of 4,950 within 50 square miles. A work crew repairs damaged sections of water mains, replacing them with PVC pipe. Since 2000, they bed pipes with Chat/Class 67 material (washed limestone 5/8-inch or smaller) and cover them with a 12-inch-deep layer of gravel beginning at the crown. Rocks larger than a fist are not used as backfill.

Before the district bought the leak detection equipment, Cooper and technicians used a test meter on valves to locate leaks. "We kept making the area smaller and smaller until we had a good idea of where to excavate," he says. "Sometimes we'd dig up 500 to 600 feet of line before we found the leak, but the effort was worth it."

Although most mains are only 3 feet deep, excavating through the chert and clay was slow and difficult. "Even my two very competent backhoe operators occasionally rolled a rock as they began digging, and it poked a hole in the brittle pipe," says Cooper. The district considered buying a hydroexcavator, but most rocks are three times the diameter of the 4-inch vacuum tube.

Gaining ground

When the leak detection equipment arrived, and after training from the manufacturer, Cooper sent Sullivan into the field. He attached the magnetic data loggers to water valves, fire hydrant valves, flowmeters, and anywhere he could connect with the transmission main to identify the general area of a leak. The next day, Sullivan collected the units and downloaded the information to the correlator for analysis. He then interpreted the numbers and used the ground microphone to target the leaks.

In the first month, Sullivan found two main leaks and numerous small service leaks estimated to account for 11.4 million gallons annually. However, the district needed Sullivan for other duties, and leak detection was relegated to occasional afternoons when nothing else was happening.

Water losses for 2008 and 2009 were 22 and 23 percent or about 25 million gallons. "The increase was a little surprising because we had upsized the backbone of our 6-inch system with 10 miles of 12-inch PVC pipe in 2009," says Cooper.

Cooper was promoted to district manager that year, and he planned an aggressive leak detection program. In 2010, he hired two employees and made Sullivan the full-time electronic technician. From June through December, Sullivan found 34 leaks equaling 17.3 million gallons. The construction crew repaired them immediately.

Next generation

"Practice with the equipment and trial and error improved Jordan's accuracy," says Cooper. "We initially dug a lot of dry holes, and then it became the occasional 10- to 15-foot-long dry trench. When that happened, Jordan put the equipment into the excavated pipe and further narrowed down the location of the leak."

In September 2011, Cooper met Simon Wick, vice president of Matchpoint, a water asset management firm in Wilmington, N.C. "He enlightened us on how to interpret the numbers so we'd know if we were looking at a leak, a potential leak, or an outside noise such as a power transformer," says Cooper.

Wick also had the next generation of Fluid Conservation Systems equipment. Cooper purchased the hydrophone kit for the correlator, 11 more Permalog units, a new Patroller unit, and training from Matchpoint. "Simon, Jordan and I spent a day simulating leaks," says Cooper. "The new equipment was phenomenal."

Sullivan finds the new data loggers simpler to understand because they only indicate whether they heard something or not. If the analysis is positive, he uses the hydrophones and correlator to come within two feet of the leak 80 percent of the time.

"It probably takes Jordan six months to check our whole system, and he does it annually," says Cooper. "Last year, he found 58 leaks totaling 4.6 million gallons, and 50 percent of them were undetectable without this equipment."

For 2011, the district's average water loss was 9.67 percent. Cooper's goal is to keep it below 10 percent. "When we compare that percentage with the minute water loss allowed by our engineers and the amount the American Water Works Association allows for testing pipeline, our water loss is zero," he says. The district saved enough money in recovered water to pay for all the equipment and Sullivan's salary.


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