COEUR d’ALENE — The Post Falls City Council approved plans Tuesday night for Avista Utilities to bore under the Spokane River to replace an aging natural gas line. The work starts at the end of October.

Avista currently has a 4-inch natural gas main positioned under the Spokane Street Bridge that serves customers on the south side of the Spokane River, but it is aging and cannot be properly inspected because of the way the bridge was built, said Josh Fort, an engineer in Avista's natural gas distribution division.

Fort told the council Avista looked at two options to replace the line after the Idaho Public Utilities Commission recently told Avista the inspection issues needed to be resolved.

“We looked at putting a new pipe under the bridge,” Fort told the council, adding that option would be expensive because it would require the company to make structural changes to the bridge and that would involve closing traffic on the bridge for a considerable length of time.

The Horizontal Directional Drilling technique was selected because Avista has had considerable success with that technology on other projects. In fact, Fort said, Avista successfully used that method to drill under the Spokane River near the Highway 95 bridge in the past.

The process would require Avista to use a portion of Q’emiln Park starting toward the end of the month through mid-December. However, Fort told the council Avista plans to use a wooden mat material to minimize any damage to park land, and the company will repair all damage done by the drilling project and install new stormwater runoff infrastructure for the city.

The new 6-inch gas line will run 30 feet under the river adjacent to the Spokane Street Bridge and span from Q’emiln Park and the city’s water tower on the northwest corner of the bridge.

“This will have very little impact to the public,” Fort said. “Except it will have a small impact on residents with the noise from the drill.”

Fort said all of the drilling will be done during the daylight hours and the company will take measures to minimize the noise.

There will be one day toward the end of the project where Avista may have work one 24-hour shift to pull a 1,700-foot pipe through the bore hole. Fort said the process would ordinarily take about 12 hours, but he asked the council to permit the company an additional 12 hours in case something goes wrong.

“Once we get started pulling the pipe, we can’t stop,” he said. “We have to keep going until it’s done.”

During the pipe pulling, Fort said, traffic will have to be detoured.

Within the next couple of weeks, Avista will begin staging equipment in the area with hope of getting a drill ready around Oct. 26.

“As soon as we are done, everything will be as good as ever — if not better,” he said, adding the whole process will be interesting to see.