Vermont Gas Systems has asked state regulators for permission to begin preparing for the construction of its Addison County pipeline extension before it secures a federal wetlands permit from the U.S. Army Corps of Engineers.

This is the final permit needed by Vermont Gas Systems, which is a subsidiary of Gaz Metro with a Vermont headquarters in South Burlington, before it begins construction of the 41-mile pipeline extension from Chittenden County to Middlebury. The pipeline will temporarily impact about 23 acres of wetlands, the largest area of Vermont wetlands ever reviewed by the Corps.

The company is required to obtain all necessary permits before beginning construction or site preparation as a condition of its certificate of public good granted last December.

Vermont Gas had planned to begin construction this month, and in its filing to the Vermont Public Service Board last week seeking a waiver, it said the permit delay could affect the cost and schedule of the project.

When construction is complete, the wetland should return to normal in about a year, state and federal officials said.

"It should operate the same," said Michael Adams, permit project manager for the Corps, about the wetlands when the construction is complete. "The function and values should return."

A Vermont Gas spokesperson was not available for comment before this story was published on Tuesday.

In a filing to the Public Service Board, Kimberly Hayden, an attorney with Downs Rachlin Martin who is representing Vermont Gas, said the Agency of Natural Resources, the Agency of Transportation, the Army Corps of Engineers and the Department of Public Service support the waiver request.

Adams of the Army Corps of Engineers said the company would be beginning construction at its own risk.

"Our decision hasn't been made on their application," he said. "And they could be doing work that is contrary to our final decision."

He did not say when the application review is expected to be complete. The permit is required under the federal Clean Water Act.