Avista Corp. plans to upgrade a 3.5-mile section of its natural-gas distribution line just northwest of Spokane.

The Spokane-based energy company doesn't have a cost estimate for the project yet, but will put it out to bid this month, spokeswoman Laurine Jue says.

The project will include replacing about 2.25 miles of pipe along state Route 291 south of Seven Mile Road. The replacement line will continue north beyond Sun Dance Golf Course, where it will cross the highway. The remaining 1.25 miles of the project will extend north outside of the highway right of way.

Avista will replace the current 8-inch-diameter steel pipe with 12-inch pipe.

The pipeline is Avista's main natural-gas supply line that serves about 7,500 customers between Spokane and Kettle Falls Wash., Jue says.