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The Bonneville Power Administration is planning a $428 million project to improve an electrical transmission line that runs through the Columbia River Gorge.

The transmission line, the 3,100 megawatt Pacific Direct Current Intertie, delivers hydropower and wind power to California. It also carries electricity north to the Celilo Substation in The Dalles, its northern terminus.

Proposed improvements would increase the line’s capacity and strengthen it against weather and other forces that have caused increasing outages since the line was built more than 40 years ago.

The BPA is beginning a mandated environmental review process and will decide later this year whether to proceed with the upgrades. If the BPA decides to go forward, it will put the project out to bid toward the end of 2012, BPA spokesman Doug Johnson said.

The contractor would develop a detailed project schedule, paying special attention to the procurement of the specialized equipment that is needed for the upgrades. Production lead times can be as long as two years, so accurately timing the orders and product deliveries is critical.

Construction is expected to start in early 2015 and finish in early 2016 if the project moves forward.