Staunching the flow
A Georgia county's $800,000 leak detection survey identifies the usual suspects—as well as some unlikely ones.
When the Metropolitan North Georgia Water Planning District mandated a water supply and management conservation plan, one of Georgia's largest municipal water utilities was among the first to comply.
“We sell water, so it's good business sense to try and minimize our losses,” says George Kaffezakis, chief engineer with the Gwinnett County Department of Water Resources engineering and construction division.
The utility began a comprehensive leak detection study, which consists of analyzing more than 3000 miles of water main over 18 months, in March 2006. More than 500 leaks have been detected since then, equaling water losses of 2.7 mgd. Though the survey isn't complete, the utility has repaired the leaks responsible for about half of that loss.
“What was most exciting was that we've found a fair number of hidden subsurface leaks that we would've never found without the survey,” says Kaffezakis.
“Some of those leaks were probably hidden for years,” adds Eric Olson, a member of the utility's program management team. “They could have continued leaking for 15 more years—and no matter how small the leak, that adds up.”
The utility was surprised to find small leaks coming from fire hydrants that weren't closed all the way, and plans to work with fire departments to address the issue. The survey also enabled the utility to update its geographic information system and create a leak-location database to be analyzed for future action plans.How they do it
The $800,000 survey is funded through the utility's capital improvement program. Omaha, Neb.-based architectural, engineering, and consulting firm HDR Inc. and Valparaiso, Ind.-based water service technology provider M.E. Simpson Co. Inc. are providing two technologies to detect leaks:
Electronically enhanced acoustic leak detection. Operators listen for leaks in the distribution system. Smaller, high-pressure leaks amplify a mid- to high-frequency noise, while larger, low-pressure leaks emit a low-to mid-frequency noise. A listening device transmits the sound to a computerized leak correlator, which uses sensors to pinpoint leak location.
Flow measurements through pitot flow testing. Pipe calipers and pitot rods are used along water mains, and a differential pressure recorder analyzes each main to determine potential leaks.
The survey is just one way the Gwinnett County Department of Water Resources is minimizing water loss. Other projects include water audits, pressure management manipulation (see sidebar on page 56) and water meter and service line replacements. The utility is also planning a large-meter calibration program.Recovery effort
Guidelines for controlling water loss.
The American Water Works Association recommends the following three steps to maximize system performance.
Perform a water audit. Like a bank statement that logs deposits, withdraws, and transfers, an audit shows how water is flowing into and out of the distribution system to the customer, enabling utilities to determine where water and subsequent revenue losses are coming from.
Routine audits also pinpoint data transfer and analysis errors.
In an exclusive PUBLIC WORKS survey, 69% of respondents conduct audits or water loss surveys. Of that percentage, two-thirds do so annually.
Forget about “unaccounted-for” losses and percentages. The true measures of how well a water system is performing are the volume and cost of lost water.
Implement a maintenance and management program. For example:Leak detection surveys. Locate weak pipes and leaks before they turn into large problems. Perform a leak-detection survey at least once every three years, but preferably annually. Locating and sealing leaks is the best source of new water for utilities facing shortages.Pressure management. Over-pressured systems lead to breaks and water volume loss. Reducing pressure aids conservation, reduces transients and overflows, and increases safety of emergency flows.System management. Water systems in older communities are reaching the end of their lifecycles. Pipe cleaning and relining, network replacement, service replacement, and valve and hydrant maintenance keep a system in working order and leak-free.Meter maintenance. Good installation, selection, and sizing; routine testing and inspections; and regularly scheduled replacements can prevent many meter failures, as well as theft and illegal consumption. The master/source meter should be the first thing a utility checks when determining where losses are coming from.Education and guidelines. Operator education and clear operator guidelines reduce data analysis errors.