In 1905, when the 5,000 citizens of Greeley, Colo., voted to build a new water plant, they were making a decision with greater consequences than they could have predicted. Completed in 1907, the Bellvue Water Treatment Plant is still in operation, and still provides more than half of Greeley’s water.

And it’s still about 33 miles from town, high up in the mountains, near high-altitude reservoirs and the headwaters of the Cache La Poudre River.

“Thirty-three miles was a tremen-dous distance for a pipeline, even in those days, when there wasn’t much development,” says Dan Moore, P.E., a water systems engineer and project manager for the city. “Wells near town had become contaminated, and our forefathers decided it was a good idea to be upstream of any possible pollution sources.”

Moore says the high-quality water and reliable gravity flow make the Bellvue plant worth keeping. But there is a downside. One hundred years later, Colorado’s fifth-largest city, Fort Collins, has sprung up between Greeley and its primary treatment plant. That complicates pipeline repairs, leak detection and maintenance, and greatly increases the cost of line replacement and augmentation.

And high mountain water sources are variable, as snow pack varies from year to year and reservoirs wax and wane. Moore estimates that 25 percent of water department resources are devoted to the legal costs of water and easement acquisition.

Keeping the water flowing in the face of these challenges requires thinking flexibly, thinking creatively, and, most of all, thinking ahead. The city has safeguarded its water supply by upgrading the delivery system from the Bellvue plant and by aggressively rehabilitating aging water mains throughout the distribution system.

Swagelining also useful

The Bellvue plant transmits water through two 27-inch steel lines, both about 50 years old. Partially due to a neglected sacrificial anode system, 8,000-foot sections in both pipes developed severe corrosion and sprang frequent leaks. In 1995, a severe leak near a railroad track caused serious problems and gave notice that something had to be done. Another issue was a planned pressure increase that would aggravate the situation.

But replacement would be difficult because of heavy development over the lines — residential, commercial, and a cemetery. Supply disruption had to be avoided, as the two lines deliver about 20 mgd in summer, all of it needed.

Spray-on lining of the damaged sections was not a solution because such processes typically do not restore structural integrity. Sliplining would reduce the size of pipes that were already too small (the reason for the planned increases in pressure was to increase capacity).

After a lengthy proposal and evaluation process, Greeley decided on the Swagelining process, developed by BG plc (formerly British Gas plc) for rehabilitating its gas lines. The city did the work in winter, when supply is relatively low. To minimize service disruption, just one section per season was lined.

Swagelining uses HDPE pipe with outside diameters slightly larger than the inside diameter of the original pipe. To accomplish this seeming impossibility, the pipe is warmed and pulled through a reducing die, and then pulled through the host pipe.

As the HDPE pipe relaxes, it expands and cleaves tightly to the inside of the host pipe, leaving no annular space. The pipe’s carrying capacity remains about the same, because the pipe diameter is reduced only by the new pipe’s wall thickness, and because the HDPE pipe is usually smoother than existing pipe and reduces resistance to flow.

Swagelining can be performed in straight pulls of up to 1,500 feet, but bends of more than 15 degrees in the Greeley lines limited pulls to about 1,000 feet. Because wind chills during work days were well below zero, the crews used plywood “tents” and special heaters to warm the pipe sufficiently for the process. Even with this extra requirement, workers usually completed pulls of 1,000 feet in less than four hours.

The new HDPE easily spans large gaps in the existing pipe, and standard design life is at least 50 years. Work was done in 1996 and 1997, and the rehabilitated sections have been leak free ever since.

Long-term planning

In the longer term, Greeley officials knew that rehabilitation of the two 27-inch lines was not enough. When the city completed a water system plan in 2003, a key component was installation of a new 60-inch line from the Bellvue plant to complement existing lines.

The costs of the project were judged to be less than the additional maintenance costs of pressurizing the existing lines and would guarantee continued gravity-fed access to Bellvue’s high-quality water. (The city built a pump station as a stopgap.) Financial constraints dictated a 10-year timeline, and work was divided into five segments. City staff used three factors to determine the order of segment completion:

• Ease of construction (quickly installing long sections would give momentum to the project).

• Effect on hydraulic capacity.

• Level of existing and proposed development along the segment corridor.

Sophisticated GIS technologies aided route planning. Existing development meant that sometimes a straight line wasn’t the shortest route. To compare and contrast proposed routes quickly, the staff divided the entire study area into 5-foot grid cells, with the help of ESRI ArcView Spatial Analyst.

Each cell was intersected with existing data layers, like zoning, level of development, and environmental factors, to assign a per-foot pipeline installation cost, broken down into pipeline costs, easement costs, and costs of road crossings. Staff also assessed proposed developments in conceptual or approval phases. With this work complete, engineers had a powerful tool to evaluate alternatives that might not have been obvious otherwise, and to confirm intuitive judgments.

A number of other challenges appeared along the way. For example, most routes had several railroad crossings and long stretches along railroad corridors. Fees proposed by the railroads were exorbitant, and Greeley challenged them using Colorado legislation that empowers municipalities when dealing with utility companies.

The city was prepared to go to court, but the railroad companies settled at more favorable rates, and an important precedent was set. Similarly, tough negotiations with irrigation companies saved tens of thousands of dollars and reduced onerous liabilities and restrictions over the life of the project.

Early in the planning phases, Greeley paid for a non-mandated engineering study to alleviate environmental and historical concerns of owners along the final proposed route. Fluctuating steel costs have been another headache, and budgets have been adjusted to accommodate rising prices.

As of spring 2008, the pipeline project is half done. Segments of five to seven miles are being completed annually, and completion is scheduled for 2012. Some finished segments have been tied into existing lines to increase cross-sectional area for flow, thus realizing some increased capacity before completion.

Cement lining

While making major investments in the transmission pipelines, the city took strong action to improve its distribution system, much of it consisting of unlined cast iron pipes installed in the 1940s or before. Seventy years later, the pipes, from 4 to 27 inches, have heavy tuberculation that severely reduces flow and pressure and turns the water brown.

Because the area has developed, most of the cast iron pipe is prohibitively expensive to trench and replace, and traffic disruptions are also a factor. Fortunately, the city has options other than replacement, and they include cement mortar lining.

Each year from 1991 to 2007, the city has lined 20,000 to 50,000 feet per year, for a total of more than 200,000 feet. Moore expects eventually to mortar nearly all unlined pipe. “You have to be willing to say the pipe is good,” he says. “We have some that’s almost a hundred years old. But if there’s enough metal to support cement, you can have a very successful project, with a life expectancy of 50 years. Replacement can cost two to three times as much.”

The city considered epoxy lining but found cement lining better for Greeley’s purposes. “Epoxy is expensive,” says Moore. “The pipe has to be cleaned spotlessly, and the coating is applied in such a thin layer that it won’t even cover pits left by rust. To me, there’s more room for error with cement.” One downside is the relatively low number of cement mortar lining contractors: Greeley has worked with six, and Moore estimates that there are only about 10 nationwide.

Cement mortar lining is simple. About every 400 feet, usually at intersections, a crew excavates a 10- by 10-foot hole for access. A rotating scraper, bottle brush with metal tines, is winched through several times, cleaning the pipe nearly to bare metal.

Then a spinning spray nozzle, supported by springy steel and powered by a 2-inch reinforced air hose, is pulled back through the pipe. The rate of withdrawal determines the mortar thickness. The mortar is smoothed by a spring-loaded conical trowel, which follows the spray nozzle.

The mortar isn’t intended to seal leaks but to prevent corrosion. “Because there’s a lot of calcium in concrete, which is high pH, the mortar creates a barrier that neutralizes our low-pH water, so it doesn’t corrode pipes aggressively,” Moore says.

Back to the well

Half or more of Greeley’s water supply is tied up in one problematic asset — the pipeline from the Bellvue plant. Keeping that plant productive has taken high-quality planning and innovative thinking. On the other hand, the effort has given Greeley continuous access to superb water with all the benefits of a gravity-fed system.

Keeping the whole system functioning has also required conservation. “Basically, despite all the trees, we’re in a desert here,” Moore says. The city works hard at leak detection and has been a national leader in the use of non-potable water for irrigation at industrial and municipal sites.

It would be easy to complain about the difficulties of long transmission lines that pass through a heavily developed neighboring city, but instead Greeley has focused on the virtues of the Bellvue plant. As a result, the city is still reaping the benefits of a decision made more than a century ago.