Why Water Mains Break

One of the biggest concerns for water utilities during extremely hot or cold weather is water main breaks. Water mains are expected to last a long time – as long as 100 years in many cases. But with many miles of pipe buried underground, it’s reasonable to expect a particular section of pipe will fail or break at some point. The challenge for water utilities is to work proactively to minimize the number of breaks and to respond effectively when a main does break.

While the oldest water mains were made of wood, by the late 1800s, a variety of iron pipe was being used to construct water distribution systems. Common iron varieties included cast and galvanized in the early part of the 20th Century, with galvanized used primarily for smaller diameter pipe. Cast iron pipe was used until the late 1950s when stronger, more flexible ductile iron pipe became common. Plastic pipe, including Polyvinyl Chloride (PVC) and High Density Polyethylene (HDPE) became common in the 1970s. The primary difference between these two plastic pipes is that PVC is stiffer than HDPE, which is more flexible. Even though pipe is expected to last for decades, that doesn’t mean it won’t break at some point. While it is impossible to predict specific pipe breaks, we know that environmental conditions are a major factor in water main breaks.

In the northern and northeast areas of the country where winters are more extreme, cold soils and cold water combine to add stress to pipes, which can—and often do—result in breaks. Iron, like all metals, contracts as temperatures drop. This problem is more common when the source water is surface water (rivers and lakes). These waters are significantly affected by air temperature and can drop to near freezing in the winter. A temperature difference of just 10 degrees in water or air temperatures can cause pipes to contract or expand. Additional stress inside and outside the pipe occurs as temperatures near the freezing point, making the pipe vulnerable to breakage. Water temperature changes more slowly than air temperature changes so the impact of cold water on pipes can cause breakage to take place as many as a couple days after temperatures freeze. Water systems with groundwater sources (wells) have more stable water temperatures because the water is not affected by air temperatures, and therefore, not as significantly impacted. 

Just as pipes are adversely affected by cold weather conditions, they are also affected by severe heat. In some groundwater systems in the southern and southwestern states, the soils are like sponges and hold lots of water. However, during extended periods of hot temperature when high demands for water increases water withdrawal from the aquifers, the soil becomes very dry. In these conditions, the soil contracts and subsides, pulling away from the pipe and diminishing support for the water main. The absence of support for the main can cause it to break. This particular problem led the City of Houston, Texas to begin to convert its groundwater supply to surface water.

Although older mains are generally more susceptible to breaks, breaks can occur on newer mains. This is most likely the result of improper installation or a manufacturing issue with that particular section of pipe. By examining trends in water main breaks over time, a utility is better able to identify categories of pipe that are more prone to breaks, and thus proactively target that pipe for replacement. Aqua employs such tactics in determining which mains to replace. By the end of 2013, Aqua expects to have spent $170 million of its $325 million capital improvement program on water main replacement and associated work.

Share This Post:

Sunny Outlook

It’s another sunny workday in southeastern Pennsylvania. Dave Marozzi logs on to the web-based monitoring system that tracks the performance of the new 1-megawatt photovoltaic power system at Aqua’s Ingram’s Mill Water Treatment Plant. Not a cloud is in the sky as Marozzi, superintendent of the Pickering and Ingram’s Mill plants, observes the graph that tracks the output of the solar field. As expected, the solar field started producing energy soon after sunrise. 

When performance peaks sometime between 1:30 and 2 p.m., the 3.8-acre solar field will be really humming, generating enough electricity to power the plant essentially for free.

“At peak performance, Ingram’s Mill consumes, on average, about 700 kilowatts of electricity,” Marozzi explains. “So for four to five hours a day, we are basically getting free power and selling the excess back to PECO Energy.”

The Ingram’s Mill solar field went into service in December 2009. “Since it came up to full power, it has been exceeding our expectations,” says Karl Kyriss, executive vice  president of Aqua America.

“The solar energy supplements our power demand at Ingram’s Mill, providing approximately 30 percent of the power required to operate the plant. That offsets $115,000 of expense at the anticipated yearly cost of electricity.”

Overall, the project made good economic sense. “The price of solar panels has come down, and the availability of grants and tax incentives made it a viable economic alternative to help us supplement our energy demand and to help us manage rising energy costs as we go forward,” Kyriss says.

In addition, the investment in solar energy pays annual “dividends” in the form of solar renewable energy credits (SRECs).

In 2011, utilities’ energy portfolios must contain at least 3.5 percent renewable energy. Those that do not meet their individual solar goals must make payments into a renewable energy fund at a rate of 200 percent of the market value of the SRECs.

On the plus side, owners of a facility such as the solar field at Ingram’s Mill receive one SREC for each 1,000 kilowatt-hours of electricity produced. These credits can be sold or traded to other companies that have not met their required goals through online trading sites such as the Flett Exchange.

For example, the solar field at Ingram’s Mill is anticipated to produce 1,280 SRECs in its first year of operation. At the current ‘spot’ market value of $325 per SREC, its total SREC value for the year is projected to be $416,000. 

 

For More Information:

Aqua Sustainability Report

 

Share This Post: