Mountain Fuel Supply Co. is moving forward with plans for an 11-mile line extension from northern Utah into Franklin County, Idaho.

The project cleared its final hurdle this week when the Federal Energy Regulatory Commission approved the project. Two weeks ago the Idaho Public Utilities Commission approved an interstate agreement giving the Utah Public Service Commission rate-setting authority over Mountain Fuel's Idaho customers. The agreement stipulates that Idaho customers cannot be charged more than Mountain Fuel's Utah customers receiving service from the same trunk line.Mountain Fuel plans to recover the cost of the line through a 22 percent surcharge on billing for the 1,200 Idaho and northern Utah customers who have signed on for service. The surcharge will be in place for about 10 years.

The FERC ruling gives Utah and Idaho agencies regulatory control over the line. Federal law gives FERC regulatory control over all gas pipelines crossing state borders. FERC can assign control to state agencies when practical.

Mountain Fuel hopes to complete construction in time to provide winter service to its new customers.

The main line will be constructed by M.H. Cook Pipeline Construction Co., Salt Lake City. Niederhauser Construction, Logan, will install distribution lines in Franklin County while Tempest Co., Salt Lake, will install the Preston, Idaho, distribution system.