WaterOne, the public utility serving approximately 400,000 people across a 272-square-mile area of Johnson County, KS, in the southwest quadrant of suburban Kansas City, has adopted a new method for locating and marking plastic or non-locatable water mains.
This technology is being implemented in conjunction with service expansion and the replacement of aging ductile iron pipes with new plastic piping, which began about five years ago. The region’s corrosive soil was causing original iron water mains to deteriorate, resulting in compromised customer service, and substantial maintenance and construction costs.
WaterOne often shares underground space in congested real estate that includes buried fiber optic cables along with gas, wastewater and electrical facilities. The new plastic mains were initially marked during placement with conventional tracer wire and located with equipment that requires energizing the wires with an electromagnetic detectable signal. With new road projects and expanding neighborhoods, conventional tracer wires and their access points are frequently damaged by excavators, and the utility finds that at least one-third of damage incidents are on difficult-to-locate pipes.
Even when locator wire is intact, this process presents multiple challenges, including false leads, signal bleed-of, route inaccuracy and difficulty in distinguishing between adjacent utilities. As a result, WaterOne is often unable to acquire the single point of access that is needed for accurate facility locating.
Damage to facilities represents significant cost to utilities across the country. The Common Ground Alliance reported in 2014 that excavator error accounts for 50 percent of all damage expense, with poor buried facilities recording and notification as the second-biggest cause (25 percent), and deficient locating performance leading to 17 percent of such incidents.
“We were looking for a route-marking alternative that would help alleviate these problems,” said Dusty Sease, WaterOne’s assistant manager of construction and maintenance. “Eventually we learned about 3M’s new radio frequency locate technology, which is based on non-conductive buried rope with integral electronic markers, that is impervious to corrosion, suited to rugged terrain and expected to deliver a service life equal to − or better than − the pipe itself.”
3M Electronic Marking System (EMS) Rope is made with regularly spaced electronic markers woven into the center of the strand for continuous path marking. Unlike conventional tracer wire, this marking method does not require continuous continuity, and the marked path can be accurately distinguished from adjacent buried utilities.
“Traced using our Dynatel locators, the EMS rope can be dependably located even in the presence of metallic conductors, fences, AC power lines and the electronic markers of other utilities,” said Denise Elliott, 3M account manager.
The Dynatel locator emits a radio frequency signal, which is reflected back by markers placed at eight-foot intervals inside the rope. These markers are passive, require no power source, and will last for years. Individual marker resonant frequencies are set for water/sewer, gas and telecommunications utilities, and a single locator accurately identifies which utility has been detected and its depth below grade.
In 2015, the Kansas water utility began testing the 3M system with 100 feet of new marker rope buried in a trench.
“We found the marker rope easy to place and equally simple to precisely locate, with minimal operator training and modest effort,” said Sease. “Radio-frequency locating is free of the problems of signal interference and false leads that can result when conventional tracer wire is buried near electrically conductive facilities. We found that even a relatively inexperienced technician can get accurate results after minimal training.”
Working with 3M, the Kansas water utility has found it possible to go below the specified four-foot depth, when necessary − to as much as five feet below the surface in some cases − with consistent and continuous path locating results.
Standard EMS Rope for open trench placement has a diameter of 0.66 inches, and a tensile strength of 200 pounds. A heavier, 0.91-inch rope with a tensile strength of 500 pounds is provided for horizontal drilling applications.
Nearly 50 percent of WaterOne’s iron water main line replacement and 10 percent of new installation involve horizontal drilling using company equipment. The larger-diameter EMS Rope is used for this work because it can withstand the pullback forces created as long sections of plastic main are pulled through horizontal bore holes. The rope is fed from 300-meter (984-foot) reels and attached directly to the pulling head. Horizontal bore runs are typically in the range of 500 to 700 feet.
Local laws commonly require that utilities restore the right of way to its original condition after trenching. This has led to the use of directional drilling wherever feasible to avoid surface disruption and restoration costs. The EMS Rope helps enable a utility to maintain path marking for non-conductive elements placed by means of directional drilling.
WaterOne does all of its own locates, Sease noted, with a typical annual volume of about 20,000 occurrences. The company uses an outside trainer to instruct the field staff on effective locate procedures, and also has in-house training capabilities.
According to Elliott, one utility has chosen to install marker rope serving individual residences rather than using a continuous, uninterrupted line and cutting the rope at each access point. This approach reduces the possibility of unintended excavator damage from disrupting full-line path detection. It has no impact on path detection accuracy or marker rope performance, since the detection process is tied to the regularly spaced markers and not to the rope itself.
More recently, Sease and his team tested 3M’s new EMS Caution Tape. The plastic marking tape uses the same passive electronic markers at eight-foot intervals, and functions in the same manner as marker rope. This product is used for path marking down to a buried depth of approximately 49 inches below grade, and can be placed well above plastic pipe mains to accurately mark the path when deeper main placement is necessary.
Marker tape requires less investment than rope for open trench marking. In the event of excavator error, the material is severed, leaving the buried markers on either side of the cut in place and continuing to define the path without disruption. With current technology, the material is pulled out if excavator error occurs. WaterOne expects to adopt 3M Caution Tape for most of the utility’s open trench pipe placement applications as an even more economical path marking solution.
WaterOne maintains timely graphic information system (GIS) records of its buried facilities, including GPS coordinates for every point of interest. Using buried electronic radio frequency marker balls (see sidebar) and the same hand-held locator used with marker rope and tape, the company pinpoints individual utility access points, valves, fittings and other important plant elements.
In the first year, 14 WaterOne crews worked daily on replacement and new installation projects across the service area totaling approximately 50,000 linear feet of EMS Rope, at an estimated cost of labor ranging from .15 to .80 per foot, depending on circumstances, plus material.
While this expense exceeds that of conventional tracer wire, results in improved asset management and quality service make EMS Rope an economical alternative.
With electronic rope marking, the savings on a single damage incident more than covers the cost difference between it and conventional tracer wire. Lower-cost marking tape will deliver even more savings in areas where its use is feasible. Increased location accuracy supports regulatory compliance and delivers productivity gains in installation, while avoiding problems such as un-locatable features, bad digs and mis-locates.
“It is a positive benefit to be able to define a water main path quickly and accurately without the limitations and uncertainty of tracer wire work,” Sease said. “Changing to this method has required buy-in from our workforce in order to realize its full value, and since the benefits are obvious and practical, transition is well underway.”
EMS technology is also gaining interest among wastewater and gas utilities in the WaterOne operating area. As it is more widely adopted, Sease believes the improved specificity and accuracy of this locating technology will further reduce costs and improve customer service. He hopes to eventually see this new marking process mandated across utilities as a means to reduce service interruptions and repair costs of all kinds.
About the author:
Tom Dewey, of Dewey Communications, is an industrial communications specialist with 30-plus years of experience writing about various technologies, including telecommunications, medical devices, electronics, aerospace, precision coatings and adhesives.