City stays busy patching leaks
City officials said leaky waterlines are inevitable given the age of the water system’s distribution system, but they’re no less vigilant in ensuring the highest possible percentage of treated water reaches the system’s more than
36,000 meters.
The Arkansas Department of Health’s 2016 Sanitary Survey of the water system showed unaccounted-for water at 27.72 percent, down from the 28.53 percent found in the
2014 survey and the 42.7 percent in
2010. Unaccounted-for water, or nonrevenue water loss, represents the difference in the amount of water produced and the volume for which customers get billed.
“The goal is to get to 12 to 16 percent,” said Monty Ledbetter, director of the city’s utilities department. “I’d love to be able to get there, but with the size of our city and the pipes we have, it’s going to be tough. But we’re going to try.”
Deputy City Manager Bill Burrough said the city spends more than
$1 million a year fixing leaks. “Our No. 1 priority is fixing leaks,” he said. “You’re never going to stop repairing leaks in a system that’s 80 years old.”
The city hopes the 16-foot section it’s replacing in the 24-inch diameter, pre-stressed concrete transmission line that connects the Ouachita Plant on upper Lake Hamilton to the 3-million-gallon storage tank on Music Mountain will lower the amount of treated water that doesn’t reach customers.
Using echolocation technology, a company contracted by the city to detect leaks found several in the 24-inch line about 5,000 feet downstream of the Ouachita Plant. The entire length of the 7-mile line was taken out of service last week to replace the 16-foot section. It was put back in service Friday afternoon, Ledbetter said.
In the interim, the 30-inch, duc-
tile-iron transmission line from the Ouachita Plant had to take on twice the throughput to meet the system’s demand, which, according to the survey, averaged 15.2 million gallons a day last year.
Instead of one pump pushing water from the plant at a rate of 2 feet per second, two pumps increased flow to 5 fps to account for only one of the two transmission lines being in service. Ledbetter said the resulting change in flow dynamics led to the discolored water some customers saw coming out of their taps.
The water that comes out of the tap usually never comes in contact with the interior walls of the line, Ledbetter said. It bores through the middle of the flow, with the outer part never reaching the tap. Pushing a higher volume of water through the line forced the outer edges of the flow inward, Ledbetter said, and the deposits it accumulated from the interior of the 30-inch line showed up in the tap water.
“The water is chlorinated,” he said. “It looks bad, but it won’t hurt you. The dingy looking water is natural minerals.”
The city flushed the line to remove the discolored water, pulling plugs from fire hydrants to purge the water from the system.
Burrough said in the future the city will do a better job alerting customers when line repairs are scheduled that may cause discolorations. He said all the rain in the area made it a good time to work on the 24-inch line, as fewer customers use their sprinklers in wet weather. The drop in demand allowed one transmission line to service the system.
“We have a standard operating procedure in place now for events such as this,” he said. “When we know something like this can happen, we’ll be more proactive about letting customers know what’s going on.”
Ledbetter said the 24-inch line was flushed before being put back in service Friday, but he said some discoloration may still occur. Water flowing through it had to pass two consecutive bacteria samples before the Health Department would allow it back online, he said.
Ledbetter said the city has heeded the advice of Crist Engineers, the city’s water system consultant, and made more use of the line connecting the Music Mountain tank to the 1-million-gallon storage tank on Hollywood Avenue. The connection gravity feeds the Hollywood tank as opposed to the pump station that feeds it from the twin tanks on Cooper Lane, where water has to be pumped more than 150 feet uphill to reach the Hollywood location.
Less pumping is required when the Cooper tanks’ role as an intermediary between the Music Mountain and Hollywood Avenue locations is limited. Crist told the city last year that the pumping required to send water to the system’s seven different elevation levels stresses waterlines and contributes to unaccounted-for water.
The survey said the usable storage provided by the system’s 11 tanks is adequate for 10.84 hours of average demand and fewer than nine hours of maximum demand, which, according to the survey, was 20.11 mgd last year. The Arkansas Department of Health recommended that the city increase its storage capacity, giving it a larger reserve to serve customers in the event of operations at one of the two treatments plants being interrupted.
The Hollywood and the 250,000-gallon Industrial Park tanks have 100-percent usable storage. Because they are elevated, all the water they hold is above the highest parts of the service area. Most of the city’s other tanks are at ground level, making only their top halves usable.
Only 6.8-million gallons of the city’s 15.2-million-gallon storage capacity are considered usable storage. The rest of the water in the tanks acts as a support, holding up the water above it.