'Pigs' clean North Liberty sewer line

NORTH LIBERTY - This little piggy went wee, wee, wee all the way through 1.5 miles of sewage.

The city of North Liberty tried a new tactic Thursday on an old, stinky problem. A city crew, working with an out-of-state company, sent a series of objects that resembled large bullets through a stretch of sewer main to try to clear away built-up sludge.

It's known as “pigging,” reportedly because when the method was first used to clean oil pipelines, the object would squeal as it went through the pipes.

The North Liberty sewer line is made out of plastic, so there was no pig-like sound. But with the first pig emerging from the pipe covered in a brown, foul-smelling slime, the name still seemed appropriate.

City officials hope the process removes buildup and resolves problems with bad odors that occasionally come up from manhole covers on the northwest side of town.

The sewer line that was serviced runs along Penn Street, from just west of Interstate 380 to Jones Boulevard. It also goes south on Jones Boulevard, where a newer housing development is and, for the past couple of years, residents have complained of smells of sewage, said Don Colony, North Liberty's streets superintendent.

Because the area is lightly developed – there also are some industrial users nearby – the resulting low flow in the sewer main is not enough to properly clear the waste, which settles inside the pipe.

“Kind of like a creek with no flow,” Colony said.

The city flushes the main using a fire hose a few times a year, he said, but that's not doing enough.

After some research, city staffers learned of pigging and hired Mayer Specialty Services out of Kansas for this project.

The cost is about $32,000 for parts, labor and setup and $11,000 for the pigging, Colony said. City staff will do the work themselves in the future, at a cost of about $3,000 annually.

“Over time, these lines will build up with grease, soap … so this is just a good way to keep the line free and at its peak efficiency,” said Todd Mayer, owner of Mayer Specialty Services.

The pigs ranged from 8 inches to 10 inches in diameter and about a foot long. The first three were foam, and the final one was harder and shaped like a bullet. All four were to go through the pipe in succession.

A North Liberty fire truck helped push the first pig through the 10-inch pipe by pumping about 750 gallons of water a minute. It took exactly one hour to traverse the 1.5 miles of pipe, with Mayer catching the object with a net as the water, which turned darker as the process played out, continued to rush on.

Mayer said that outside of the oil industry, pigging is primarily used to clean drinking water lines. But in the past decade, it's use on sewer mains has increased, he said.

Russell Royce, an environmental specialist for the Iowa Department of Natural Resources, said some large wastewater treatment plants use pigging on sewage sludge lines, but sanitary sewers usually use jetting equipment and video robots.

Iowa City has used pigs for 20 years in force mains, in which water is pumped instead of using gravity to flow, said wastewater superintendent Dave Elias. North Liberty was treating a force main Thursday.

Gravity sewers are far more common, Elias said, and for those Iowa City uses a jetting system to flush the line with a high-pressure hose.

The North Liberty work was ongoing as this article was written.