CONCORD, N.H. — New Hampshire Gov. Maggie Hassan has asked U.S. Secretary of State John Kerry for a thorough environmental and permitting process before allowing any existing pipelines in the state to transport tar sands oil.

Two conventional crude oil pipelines owned by the Portland Pipe Line Corp. go through five New Hampshire towns and end in Montreal. Portland Pipeline has considered changing the contents of those pipelines to tar sands oil.

Critics say tar sands oil poses greater environmental and safety risks than conventional crude, but oil industry representatives disagree.

Under federal law, the secretary of state has the authority to issue permits for the construction, connection, operation or maintenance of pipelines at the borders of the United States with Canada.

“I am writing to ask you to act to protect New Hampshire’s economy and environment,” Hassan wrote to Kerry on Monday.

“The state of New Hampshire has limited authority over pipelines that cross state borders and therefore relies heavily on federal review and regulation. It also receives little or no benefit from their presence in the state. However, should anything go wrong with such a pipeline — a leak or worse — New Hampshire’s taxpayers bear the responsibility and cost of cleanup.”

The New Hampshire towns through which the pipeline runs are Lancaster, Jefferson, Randolph, Gorham and Shelburne.

Environmentalists have expressed concern that the pipeline that now carries oil from South Portland to Montreal could have its flow reversed and carry Canadian tar sands oil through Vermont, New Hampshire and western Maine.

Last week, environmental regulators in Vermont ruled that the state’s Act 250 land use law would apply to any proposal to reverse the flow in an oil pipeline system that crosses northern Vermont.

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