The City of Bonney Lake is moving forward with a call to bid on the replacement and upgrade of a problematic North Tapps water main.

The Evergreen Point water main, located primarily on 184th Avenue Court East in its namesake neighborhood, had become a sticky wicket for Bonney Lake’s Public Works department over the past four years. Since 2009, the aging steel pipes have sprung nine leaks spilling water at rates ranging from five to 25 gallons-per-minute. A homeowner adjacent to a 25 gallon-per-minute leak that broke open in 2011 found their basement flooded. Public Works replaced a 25-foot section of pipe last year when another homeowner discovered leakage into the concrete driveway.

The leaks are caused by the steel material’s natural corrosion, Public Works Director Dan Grigsby said. Corrosion leads to weakened steel, weakened steel leads to pinhole leaks, and the pinhole leaks can eventually lead to larger leaks that lose higher volumes of water.

Public Works estimated the water lost over the past three years at 69 million gallons.

As the summary to the agenda bill submitted to council put it, only partially tongue-in-cheek: “We are now patching patches.”

A replacement — estimated at a cost of more than $460,000 — had already been scheduled for 2013 last year, but unforeseen costs on the Ponderosa Estates main replacement and other projects drained the city’s Public Works Trust Fund loan to $60,000.

“It’s … a design issue,” Grigsby said. “When projects are approved by the council, you don’t always have a design with the best engineer’s (cost) estimate.”

Differences in the final cost of projects are common and amended later through change orders brought before council.

Under the resolution passed, the difference will be made up with the city’s water capital fund, funded by water system connection fees on new development and monthly water charges.

Under the replacement project’s design, the 4- and 6-inch diameter steel piping will be replaced with 8-inch diameter ductile iron less prone to corrosion. The higher diameter piping will improve the stability of water pressure in the neighborhood, Grigsby said.