RICHMOND, Va. (AP) - A panel of Virginia environmental regulators granted a conditional permit Tuesday for the proposed Atlantic Coast Pipeline, making its approval contingent on getting more information about the project’s impact on water quality.

The Virginia State Water Control Board voted 4-3 to approve a key Clean Water Act permit referred to as a 401 water-quality certification. The citizen board of gubernatorial appointees was charged with determining whether there is “reasonable assurance” water along the route won’t be contaminated during construction of the approximately $5 billion, 600-mile (965-kilometer) natural gas pipeline.

The permit won’t take effect until several additional studies - including an erosion and sediment control plan, stormwater management plan and testing on sensitive karst topography - are reviewed and approved by the Department of Environmental Quality, spokesman Bill Hayden said. A full text of the amendments the board voted to include wasn’t immediately available late Tuesday.

The department will not allow pipeline construction to begin until the erosion and sediment control plan is completed and approved, which might not be until March or April, Hayden said.

Pipeline spokesman Aaron Ruby called the decision “a very significant milestone for the project and another major step toward final approval.” The company will work closely with state authorities “to complete all remaining approvals in a timely manner and ensure we meet all conditions of the certification,” he said in a statement.

Richmond-based Dominion Energy is the lead developer of the project, which would start in West Virginia and cross into Virginia and North Carolina. A company executive has also suggested it might extend into South Carolina, but officially the company has said no decision has been made about a possible expansion.

Many of the opponents who question the need for the project and say it will damage the environment, infringe on property rights and commit the region to fossil fuels, characterized Tuesday’s decision as a partial victory.

“While this outcome buys us time, it’s still far from the end result for clean water we wanted - a flawed application that didn’t include required details outlining how Dominion planned to mitigate water pollution from its unnecessary pipeline shouldn’t have even gotten a hearing in the first place,” Lee Francis, communications manager for the Virginia League of Conservation Voters, said in a statement. “It’s at least a promising sign that regulators sent Dominion back to the drawing board.”

The Southern Environmental Law Center is exploring the legal implications of the decision and what it means for construction, senior attorney Greg Buppert said in a statement.

Pipeline supporters, including Virginia Gov. Terry McAuliffe, say the project will lower energy costs, help the region move away from coal, and boost economic development by contributing tax revenue, creating jobs and opening the doors to large-scale industry that needs a steady supply of natural gas.

The water board’s decision comes after it granted a 401 certification last week for the Mountain Valley natural gas pipeline, which would also start in West Virginia and cross western Virginia.

The board did not explain why it took a different approach this time, Hayden said.

A coalition of environmental groups quickly filed a lawsuit challenging the board’s Mountain Valley decision.

A certification for the Atlantic Coast Pipeline is still pending in North Carolina, which has sent four letters requesting additional information about the project. West Virginia recently waived its right to issue a certification.

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