Using Ice to Clean Sediments in Underground Mains

Millions of miles of underground pipes deliver clean, potable water to faucets, taps and hydrants throughout the nation every day—but how clean is it? Complex water treatment systems use a combination of coagulation, sedimentation, filtration and chemical disinfection to rid drinking water of particulates and bacteria before it enters the network of storage tanks and pipes that make up a typical distribution system. But even with extensive treatment, tap water often still contains minute amounts of minerals and bacteria that, over time, can settle in water mains. KCI helped the town of Smyrna investigate ice pigging as an easier, more environmentally-friendly and somewhat chillier method to remove buildup inside water lines.

New to the United States, the cleaning system uses a slurry of ice, called a pig, that travels through underground pipes, scraping the sides and pushing sediments ahead and out of an exit point, usually a downstream fire hydrant. “A mixture of ice and salt lowers the freezing point so the pig doesn’t become rock hard and can conform to the shape and diameter of the pipe,” said KCI project manager J. Ryan Flickinger, PE. “It’s about the consistency of a slushy, and because it’s just ice and salt, it’s completely harmless.”

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Traditional pigs are usually made of metal, are inflexible and can get caught in complex pipe networks, while ice pigs simply melt in place if stuck. Other water main cleaning technologies include flushing, jetting, foam swabbing and air scour, but none are as effective, efficient, and environmentally friendly as ice pigging.

The Delaware town of Smyrna wanted to investigate the system as an alternative to their quarterly hydro-flushing program. Grant writer Nichole D. Davis helped the municipality secure $40,000 from the state Office of Drinking Water for an evaluation. Flickinger and his team completed the up-front analysis to identify which pipes would benefit most from a cleaning, verify hydrant and valve locations, and develop sequencing.

On a warm summer day, town officials joined KCI’s team and 39 representatives from area community, county and state agencies for a field demonstration—the first in northeastern United States—led by water quality management company Utility Service Co. Inc. In just under 15 minutes, valves were shut down, the slurry inserted, water samples taken, the pig collected, and water service restored to nearby residents, cleaning 400 feet of pipe.

We were able to demonstrate that ice pigging is an extremely effective tool to help water systems clean their pipes where flushing hasn’t been effective and the disruptions to the system using traditional pigging methods are too much for operators and customers.

Kirt Ervin, PE, Vice President, Utility Service Co. Inc.

“The pig travels at approximately two feet per second and can negotiate in excess of 1,000 feet before melting,” said Davis. “As it progresses, the visual change in the discharged water is dramatic.” Testing has revealed that in some cases, ice pigging can be 1,000 times more effective and can offer five times more cleaning energy than regular flushing.

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During pigging, water quality at the downstream hydrant is tested constantly, offering a very visual indication of the technique’s effectiveness in cleaning underground mains. A computer tracks quality levels in the water as well as temperature, and computes the speed at which the pig is moving.

KCI sees the benefits and is recommending the technology to other municipalities. Engineers also see an opportunity to use ice pigging to clean sewage force mains.

It’s amazing how much energy is spent trying to pump sewage through clogged force mains. This could become a pro-active approach in improving the efficiency of a system.

Thomas G. Sprehe, PE, BCEESenior Vice President, Director of Innovation and Technology

Thomas G. Sprehe, PE, BCEE

Cleaning force mains and restoring full use of pipe diameters could reduce pump cycles, electrical costs and unnecessary and expensive upgrades. “Ice pigging would be a practical alternate because pump station sites offer a built-in access point,” said Flickinger. “For long runs with insufficient access points, the pig would simply melt in the main instead of having to be removed via excavation or pipe cutting.”

Whether used in water or sewage mains, it’s clear that ice pigging offers utility operators another tool in their toolbox for improving efficiency and customer service.

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The buildup of raw minerals in raw drinking water along with deterioration of a pipe network can lead to sedimentation and can affect the appearance of water from the tap.