Nothing beats a nice tall glass of red water. Well, maybe a glass of orange lemonade.
It’s easy to make light of red water when it’s not coming out of your taps, but for the residents of McKinney, Texas, the water situation was no laughing matter.
McKinney, with a population of roughly 105,000, sits at the northeastern edge of suburban Dallas. The U.S. Census bureau listed McKinney as the nation’s fastest-growing city from 2000 to 2003 and again in 2006 (among cities with more than 50,000 people). Clearly, this growth has not been due to the red water.
Various water quality problems attributable to corrosion plagued the city’s water pipes. Most of the pipes in the system were 60 and 75 years old and, while structurally sound, suffered from poor flow and water quality issues. Periodic complaints of discolored water over the past nine years increased beginning in 2005. Some pipe was structurally deficient and/or undersized and needed to be replaced.
Initially, the City Council approved a $7.5 million project to dig-and-replace all 50,000 lf of 4-, 6-, 8-, 10- and 12-in. cast iron water distribution pipe. City water superintendent Harlyn Farrell researched trenchless technology and opted for pipe bursting and epoxy spincast lining as alternatives for approximately 30,000 lf of the project.
“Time was of the essence to reduce our discolored water calls so we looked first at those trenchless contractors that were currently on government purchasing contracts and/or lining processes that had short cure times where water service could be restored as quickly as possible,” said Farrell.
The initial scope of the project had city crews performing all of the pipe work with no outside help, but using a new system meant reassigning aspects of the project for greater efficiency. Specifically, contractors would be brought in for the relining portions of the project. City crews retained responsibility for pit digging, bypass operations, fittings replacements, inspections and reconnections. CuraFlo Spincast Services was contracted to perform pipe cleaning and epoxy lining. The project breaks down to 4,800 lf trenched pipe replacement, 10,000 lf of pipe bursting and 10,000 lf epoxy lining.
Gary Sorohan, general manager of CuraFlo Spincast Services, outlines the benefits of the selected trenchless rehabilitation methods as follows: Pipe bursting allows for longer runs, replaces failing pipe with new structural HDPE pipe and, in some cases, increases size. Epoxy spincast rehabilitation requires no digging for service connections, completely restores flow of the host pipe, reduces pumping costs, offers optimal water quality, is perfectly suited to short- or mid-length runs with bends and transitions and offers long-term protection, thus preventing a reoccurrence of the problems the pipe was suffering from. Both methods are typically more cost-efficient while causing little disturbance aboveground or with other utilities.
The revised budget for the proposed three-year project allots roughly $1 million yearly, just 40 percent of the initial budget. Further, according to Farrell, the project has cost even less than the revised budget had outlined.
“Based on historical in-house line replacement data and estimated per-foot costs from trenchless contractors, we budgeted an average cost of $45 per ft. Current costs for the 24,800 ft completed to date are running about $44 per ft,” Farrell said.
How It Works
The Curaflo Spincast System of epoxy lining is an eight-step process designed to repair and protect metal and cement-based pipe by centrifugally casting 1 to 5 mm of a solvent-free, protective coating on the interior of the pipe.
Work begins by creating access points at the fittings, such as valves, tees, fire hydrants and so on. As in the case of the McKinney project, this work is completed by city crews. Pipes can be located via original schematics, aboveground fittings or by using underground locating equipment. Also important at this point is the proper identification of other utility lines so as not to adversely affect neighboring lines while excavating for access points.
Once these access points are available, sections of the pipe are isolated by closing valves within the system to cut off flow in the designated area. If needed, an aboveground bypass system can be employed to maintain drinking water to consumers affected by the work.
The third step involves cleaning the section of pipe, first by removing the pipes and fittings from each access point. The two primary pipe cleaning methods are power boring and drag scraping. Power boring sends high-tensile steel rods approximately 20 ft in length into the pipe. The rods are coupled together and rotated with the power boring rig while a flail head (a steel squid-like attachment) reaches the full interior diameter of the pipe, scraping away debris. Drag scraping employs a scraper tool pulled through the pipe in each direction with steel cables. In either case, the interior of the pipe is typically dried using cylindrical foam swabs blown through with filtered, compressed air.
Other pipe cleaning methods include sand blasting, high-pressure jetting, pressure scraping, wire brushing and chemical cleaning. More than one method may be used to ensure a thoroughly cleaned pipe.
Next, closed-circuit television (CCTV) is used to inspect the pipe. The CCTV inspection will identify any problems with the pipe that would prevent lining, as well as verify that the relining process can continue.
Following inspection, a specialized rig is positioned at one access opening and a plural-component hose is pulled through the pipe. When the hose reaches the end of the pipe, a spray head is attached. Quality assurance and pre-lining checks are performed, the pumps are activated and as the hose is winched back through the pipe, epoxy is centrifugally cast along the interior of the pipe. The rig operator monitors the thickness of the coating via computerized metering and mixing equipment. Once the lining is complete, the pipe is then closed at each end to allow the lining to cure.
Following the cure period, another CCTV inspection ensures the overall quality and uniformity of the
rehabilitation. The final two steps involve disinfecting and flushing the newly lined pipe and reconnecting to the system.
One potential hitch with the plan could have occurred as city crews and contractors worked together. Careful planning and pre-construction meetings laid out the general requirements on each side of the project to ensure that crews weren’t stepping on one another’s toes. Once work began, city crews quickly familiarized themselves with the lining process to better anticipate how to maximize productivity alongside CuraFlo’s crews.
Pipe bursting and pipe replacement work began in early 2007, with epoxy lining beginning in September. According to Farrell, early reviews are positive. In the four months prior to the project, the city received 140 discolored water complaints and in the most recent four-month period, just four complaints. The overall project is anticipated for an October 2009 completion.
Greg Thompson is an assistant editor of Trenchless Technology.