North America’s northernmost metropolitan water utility conquers the challenges of delivering high-quality water and great service.
When the residents of Anchorage, Alaska, turn on their faucets, it’s a good bet that they have little understanding of the challenges the Anchorage Water and Wastewater Utility must overcome to supply them with clean, clear water.
“It’s the most complicated water system in the world,” says Joe Polowy, AWWU distribution operations supervisor.
That’s not an overstatement: the majority of the source water is drawn from Eklutna Lake, some 20 miles from the city proper; the piping must be buried at least 10 feet deep to avoid freezing; and the water passes through heat exchangers at the local power plant to warm it up to 59 degrees F (see sidebar).
The pressure zones in the system are the most critical factor, however. “We have some customers at sea level and then other customers just a few miles away at 1,200 feet above sea level,” says Polowy. The system is comprised of 70 pressure zones and 500 pressure-regulating valves. “Managing, boosting and regulating pressure is a big job for us.”
In fact, Anchorage conducts a comprehensive PRV training program and maintains one of the few live PRV training facilities in the world.
The AWWU serves a greater Anchorage population of 263,000 through 52,000 customer accounts. Average daily demand is 23 mgd, and average peak daily demand is 55 mgd. Storage capacity is 65 million gallons.
Raw water — glacial runoff, rain and snow from the Chugach Mountains high above the city — is drawn from the 8-mile-long Eklutna Lake and piped via a tunnel through canyons to one of two water treatment plants. It’s the last glacier-fed source in the country, and the utility’s website calls it a “pollution-free source that will last well into the 21st century.”
The majority of the flow is treated at the 35 mgd capacity Eklutna Lake plant (Brian Yonkoske, superintendent), which has been operational since 1988. The 24 mgd Ship Creek plant (Polowy, superintendent) is used as a backup, though it is kept in a constant state of readiness. In 2014, when the Eklutna Lake plant was shut down, all of the flow was processed through the Ship Creek plant, which dates back to 1962. In addition, the utility’s distribution staff is headquartered there. A smaller, 500,000 gpd plant serves the community of Girdwood at the far southern end of the system. Gene Biever is superintendent there.
Treatment at both the Eklutna Lake and Ship Creek plants consists of coagulation with polyaluminum chloride, mixing, sedimentation and multimedia filtration. Sodium hypochlorite — generated on-site — is used for disinfection, and the finished water is fluoridated.
The utility also maintains several groundwater wells that can supplement the drinking water supply.
The distribution system is mostly gravity-flow and consists of 800 miles of pipe, primarily cast iron, ductile iron and PVC. The utility maintains 7,000 hydrants.
Polowy explains that the distribution team is responsible for more than 200 water distribution facilities, including well sites, PRVs, boosters, vaults and reservoirs. “If we have to lay pipe in lengths greater than 1,200 feet, we contract that work out,” he says.
Despite this multitude of tasks, Polowy’s staff remains focused on the PRVs. “Maintaining them is an art form,” he says.
The utility offers a rigorous program of training on the valves, with a two-day course on their operation and maintenance that’s offered to operators and engineers. Operators from the distribution operations group are identified for a more advanced course that lasts six weeks.
All told, Polowy says it takes five to seven years of training and experience for an operator to become fully qualified and certified. “Of our existing staff, about one-third are at the advanced level, one-third at intermediate, and one-third at the beginning level,” he says. “It takes a long time and lots of hands-on experience.”
While AWWU operators get plenty of that in the field, they can also train in one of the few live classrooms in the industry. “We have PRVs in the training facility, so operators can learn in a no-fear atmosphere,” he says.
It’s not a simple matter of on and off. Polowy explains that Anchorage is not just trying to reduce high pressure as the water travels down to the main population areas; but rather, the system is configured to sustain certain pressure levels in certain pressure zones. The system even has PRVs in all three of its water treatment facilities. “We need to sense high-pressure events in order to prevent breaks or ruptures in our customers’ lines,” he says.
Rob Rose is AWWU’s system maintenance foreman in charge of the utility’s leak detection program.
“Each year, we have a contractor assess segments of water main to determine condition of pipe and the likelihood of failure,” he says. This year, the utility plans to analyze some 20,000 feet of pipe and another 10,000 feet if funds are available.
Rose says that the evaluation process often turns up existing leaks that call for repair. “We go out and verify we have an active leak by listening on valves in the area, using an LC-2500 Leak Correlator (SubSurface Locators),” he says. “The operator puts in certain information like pipe length, pipe type, and size, and then turns the repair over to our excavation crew. We also get reports of leaks from crews who are out working on hydrants or valves.”
He adds that water surfacing frequently indicates leaks, but because of factors like the depth of the pipe or frost in the winter, the leak is not always near the location of the surfacing water.
“Again, we will use our SubSurface leak correlation equipment to locate the leak to minimize the area of an excavation.”
Polowy points out that new and better materials like epoxy coatings and stainless steel lines have helped the utility reduce leaks and breaks. He also credits the utility’s engineering staff, corrosion expertise and planning, and robust pipe replacement program.
To continue to provide high-quality water in the future, the AWWU developed a master plan in 2012, identifying and justifying more than $52 million in water projects, including rehabilitation, repair and replacement of waterlines.
The Railroad Yard pipeline replacement project, which just wrapped up, presented a unique set of challenges.
“It was one of the most complex pipeline projects I’ve encountered,” says AWWU project manager James Armstrong about the replacement of roughly half the waterlines serving the Alaska Railroad Corp.’s rail yard, located in the Cook Inlet drainage area.
The old lines dated to the 1940s and consisted of unlined cast iron with considerable interior corrosion. Leaks had become a serious problem, especially a 2009 incident that resulted in abandonment of some of the lines and interruptions in hydraulic connectivity that reduced fire flow. Plus, stagnant water in dead ends was creating water-quality issues. In some cases, the damaged lines were too close to railroad tracks to allow repair without disrupting railway operations.
The replacement project involved approximately 6,000 linear feet of old lines and was divided into two phases: north and south.
Armstrong explains that in the north section, open cut trenching and replacement of the old 4- through 10-inch-diameter lines with PVC was the choice. CIPP was specified for the south section’s 10-, 12- and 16-inch pipe. Frawner Corporation of Anchorage was the contractor on both phases.
“The north phase was bid and awarded in spring 2016. The contractor immediately proposed a value engineering change to use horizontal directional drilling to install the majority of the pipe,” reports Armstrong. He estimates the HDD approach saved about 5 percent of the overall project cost. HDD generated less unusable contaminated soil, produced fewer dewatering discharges, simplified working around other utilities, and avoided remnant building structures.
While the north phase was completed in late 2016, the south phase was just recently finished. “We chose CIPP due to the potential cost of relocating pipes away from tracks and structures,” says Armstrong. “The work occurred within a few feet of the tracks and inside buildings. We could not have done the work as effectively without using CIPP lining.”
Anchorage prepared thoroughly for the line replacements, using a camera system to determine the condition of existing pipes. The utility was just as careful throughout the course of the project because American Railroad Engineering and Maintenance-of-Way Association standards had to be met and there were numerous geotechnical and environmental issues that had to be addressed.
The weather and the Alaskan tourist season also came into play. Armstrong explains that the rail yard supports tourist trains and cruises from May through September, meaning the pipeline rehabilitation had to be conducted during the colder months. “Temperatures for October through April average near or well-below freezing here,” he says. “Temporary waterlines and replacement soil on the surface had to be heated and covered during the project.”
Temperature, terrain, tourism, and training were all part of the unique challenges facing the largest water utility in Alaska and the northernmost metropolitan water utility in all of North America. But the AWWU has overcome these obstacles and more. In fact, over the years, they’ve racked up awards for best-tasting water and for fluoridation. Their self-imposed turbidity limits of .01 NTU easily beat the requirements.
But that wouldn’t mean a thing without customer satisfaction. Polowy sums it up: “We want to make sure everyone is getting good pressure to their homes and for fire protection, and that the best quality water is reaching our customers.”
People are the key, he says. “They put all of themselves into their work and take full responsibility for water quality and fire protection throughout the district. They are our strongest asset.”
You could call it temperature trading. Through a longstanding cooperative agreement between the Anchorage Water and Wastewater Utility and Municipal Light & Power, the two organizations are realizing numerous mutual benefits.
About 19 mgd of treated water from the AWWU’s Eklutna Lake plant passes through heat exchangers adjacent to ML&P’s Plant 2A, located at the utility’s Ship Creek campus.
The exchange heats the drinking water from approximately 44 degrees F to 60 degrees F to prevent freezing in system piping during the winter months.
At the same time, the process cools water for the cooling towers at the ML&P Plant 2A, and much of the thermal energy contained
in the waste heat from the power operation is captured — as opposed to being exhausted to the atmosphere. The thermal efficiency of the power plant is improved dramatically, and air pollution is reduced.
“Heating water for residential and commercial use is very energy intensive,” explains Todd Carroll, AWWU engineer. “And exhausting waste heat from power generation facilities into the atmosphere contributes to air pollution and power plant efficiency loss.
“By capturing waste heat from the power generation process, AWWU helps prevent water distribution and service pipe freezing and helps optimize power plant efficiency while also lowering the energy used by AWWU customers to heat their potable water.” Reduced water consumption and wastewater production at the power plant is yet another benefit.
Carroll also reports that this cooperative effort — which has been in existence for years — is improved through the development of ML&P Plant 2A. In the past, ML&P Plant 2 was only able to heat a portion of the potable water headed into Anchorage from AWWU. The new facility contains new double-wall plate heat exchangers from Sondex (Danfoss Water and Wastewater), which improves the process such that more of AWWU’s distribution system can receive the heated water. “In the old system the bulk of the heated water could only be distributed to a portion of AWWU’s water distribution system due to pipe configuration. The construction of the new heat exchanger will include piping upgrades to allow heated water to be distributed to a wider area of AWWU’s distribution system.”
Carroll notes that the project is unique in its scale for potable water waste heat recovery and would not be possible without a large municipal water pipeline with low water temperature adjacent to a power plant.