August 20, 2014
The Las Vegas Valley Water District (LVVWD) began providing water to the Las Vegas Valley in 1954. Over the years, the City’s water delivery system has grown to more than 4,500 miles of pipeline, 350,000 service connections and a reservoir system capable of storing more than 900 million gals of water. Today, the district provides water to more than 1 million people in Las Vegas and Clark County Southern Nevada. According to the U.S. Environmental Protection Agency (EPA), 700 water main breaks occur every day in the United States, amounting to approximately 250,000 breaks each year. Also, on average, 14 percent of treated water is lost to leaks. The LVVWD has a relatively young water infrastructure that experiences very few main breaks per mile as compared to other major utilities and has less than 6 percent losses. However, some of its pipes have started to fail more often due to corrosion and other factors. A particularly troublesome section of the LVVWD was part of a 6.5-mile span of 16- to 24-in. mortar-lined, steel cylinder pipeline that ran underneath some of the City’s most popular thoroughfares. The pipe was installed in the 1950s without any cathodic protection or corrosion control and had experienced three main breaks over the past five years. While examining a break that occurred underneath a section of the famous Las Vegas Boulevard, crews noticed that the pipe walls had been worn thin due to corrosion. Seeing the pipe’s deteriorated condition, LVVWD expected that it may have to replace the entire 6.5-mile span of pipe — a major expense that could cost the LVVWD as much as $300 per ft of pipe — a total cost of nearly $10.3 million — and would disrupt busy roadways. Action To prioritize sections of pipe that were in most need of repair, LVVWD turned to Toronto-based Echologics Engineering., a leader in the development of water infrastructure diagnostic technologies for water loss management, leak detection and pipe condition assessment. Echologics ePULSE technology is a non-invasive pipe condition assessment solution that provides water utilities with an accurate measurement of the remaining average wall thickness of selected pipe segments. To measure the remaining wall thickness of the pipe using ePULSE technology, two acoustic sensors are placed on any existing appurtenances. Following a leak detection survey of the pipe section, a third access point is used to create an “out-of-bracket” noise source either by flowing a hydrant, tapping on a valve or modal excitation units. The propagation velocity of the sound wave is then measured based on the sensor spacing and the measured time delay between the two sensor locations. The average wall thickness of the pipe section between the acoustic sensors is then back calculated from a theoretical model. As the pipe wall thickness decreases over time, the acoustical wave velocity decreases. The acoustic velocity measured is 100 to 300 m; however, this distance can be decreased to anywhere between 30 to 100 m if an anomalous measurement is found that could represent a degraded pipe. This acoustic velocity measurement is performed using LeakFinderRT correlator, Echologics’ flagship product. LVVWD was already familiar with Echologics, as its distribution maintenance crew regularly uses the company’s acoustic listeners and correlators to detect leaks on smaller size pipes throughout its system. However, before leveraging Echologics for such a large scale assessment project, LVVWD maintenance engineer Ryan Benner and district engineering project manager Charles Scott wanted to gauge the accuracy of Echologics’ condition assessment capabilities. LVVWD had Echologics assess the condition of a section of 6-in. asbestos cement pipe that had been scheduled to be abandoned. After the test, the unearthed sections of pipe were sent to a lab specializing in asbestos cement pipe testing. The lab results were compared to the condition assessment report provided by Echologics and found to be nearly identical. As a result, LVVWD selected Echologics to conduct the assessment project. Results Echologics and LVVWD assessed the entire 6.5-mile span of pipe in only two weeks. The assessment found that the majority of the pipeline, which LVVWD initially expected to replace at the cost of nearly $10.3 million, was still in good structural condition, as it contained more than 95 percent of its original wall thickness. In addition, a number of previously unidentified leaks were identified by Echologics, and LVVWD was able to quickly repair them helping to reduce non-revenue water and prevent future water system and roadway damage. Ultimately, only 15 to 20 percent of the pipes in the system were found to have lost a significant amount (more than 15 percent) of their original wall thickness to corrosion and other factors and were prioritized for renewal. By working with Echologics, LVVWD was able to efficiently address non-revenue water and prioritize system replacement by getting a thorough, non-invasive assessment of the pipeline’s structural integrity — without breaking ground or disrupting the city’s busy streets that are vital to its tourism industry. And, by identifying that only a fraction of the system was in poor condition and needed to be prioritized for renewal, the district was able to avoid needlessly spending millions of dollars on the premature replacement of the entire pipeline. LVVWD has since initiated a similar program that leverages the same acoustic-based leak detection system to assess the condition of a section of asbestos cement pipe. To date, most of the pipeline has been confirmed to be in good condition and LVVWD has been able to locate and prioritize several sections of degraded pipe for rehabilitation. Marc Bracken is vice president and general manager of Echologics Engineering Inc., based in Toronto, Canada.