A crowd packs a State Water Control Board meeting Monday in Richmond. On Tuesday, the board approved permits for the Atlantic Coast Pipeline but delayed implementation until several environmental reports are completed. Protesters celebrated the delay as a victory. (Timothy C. Wright/For the Washington Post)

Opponents of a natural gas pipeline planned across some of Virginia's wildest terrain declared a partial victory Tuesday when a state panel delayed enacting water permits for the controversial project.

The State Water Control Board approved permits for the $5 billion Atlantic Coast Pipeline, which is backed by Dominion Energy, but took the unusual step of delaying the effective date until several environmental impact reports are completed.

The action came unexpectedly after a day and a half of tension-filled hearings, leaving supporters and opponents alike scrambling to determine exactly what had happened. The bottom line seemed to be that the project is at least temporarily on hold.

"They cannot start construction until the final erosion and sediment control plans are approved," state Department of Environmental Quality spokesman Bill Hayden said.

Dominion has said it that hopes to begin work on the 600-mile pipeline by the end of the year. But Hayden said that some of the required reports are not expected to be completed until March or April.

Dominion praised the board's action and said the permit approval was "a very significant milestone for the project and another major step toward final approval."

Asserting that the pipeline had received "the most thorough environmental review of any infrastructure project in Virginia history," Dominion spokesman Aaron Ruby said the company recognizes the new conditions and will work with the state "to complete all remaining approvals in a timely manner and ensure we meet all conditions of the certification."

The Water Control Board had approved a similar project just last week — the Mountain Valley Pipeline, which is planned for the far southwest corner of Virginia. Environmentalists and land rights activists had protested that pipeline during two days of hearings, and they came to the Atlantic Coast Pipeline hearings in greater numbers and with greater fury.

Warned at the outset against loud displays, scores of opponents snapped their fingers to show support for speakers or stood and turned their backs on those they disliked. Some speakers made angry personal attacks on board members — "I see through your well-groomed hair and know who you are," one young man rumbled angrily — and on Monday night, an opposition group claimed credit for draping an anti-pipeline banner from one board member's house.

The raw emotion of the crowd drew a heavy police presence. More than two dozen state police cruisers lined the parking lot of the suburban community center where the hearings were held, joined by Henrico County police, emergency vehicles and a mobile command center, not to mention plainclothes private security personnel deployed by Dominion.

But it was the sometimes-technical testimony of environmental experts and landowners that seemed to give the board members second thoughts.

The DEQ had recommended approving the permits and then reviewing plans along the way for several specific factors that impact water quality, including storm-water management, erosion control and efforts to monitor a complex limestone geography called karst. That geography features caverns and sinkholes, and is extremely sensitive to groundwater disruption.

Speaker after speaker warned the board against approving the permits without a better understanding of those factors. Tuesday afternoon, just as the board was preparing to take a vote that all the opponents thought was a mere formality, board member Timothy G. Hayes moved that the certification be amended so that it would not go into effect until all those reports are completed.

He said the move was intended so the board could "at least have the opportunity to have one more swing at it if we have to."

Department officials scrambled to figure out the impact of such a move. The project's fundamental approval came in October from the Federal Energy Regulatory Commission. If the state does not follow up on water permits within a certain period of time, federal officials can step in and greenlight the project themselves, Hayden said.

But he added that it is not clear what that time frame is, nor what control the state will really have if it does not like the environmental reports.

Even so, pipeline opponents took the outcome as a measure of vindication.

"The board today acknowledged what we've been saying all along, that this process is flawed," said David Sligh, who is retired from the DEQ and works as conservation director of Wild Virginia, a nonprofit organization. "This is an advance over what we thought we might get today."

A coalition of environmental groups filed a federal lawsuit Friday against the board's decision on the Mountain Valley Pipeline, but members said Tuesday that they needed time to digest the action on the Atlantic Coast Pipeline before deciding what to do next.

As the board shut down the meeting and lines of state troopers began herding the audience out, Sharon Ponton of Nelson County sang out: "People gonna rise like the water," she began, and others joined in: "Shut this pipeline down."

The opponents — from large groups such as the Sierra Club and the Southern Environmental Law Center, as well as activists from rural counties, artists and college students — said that they were ready to take the fight against both pipelines into the field. In the fall, some groups staged a training camp to practice resistance efforts carried out nationally against projects such as the Keystone XL pipeline near the Standing Rock Sioux Tribe's reservation in the Dakotas.

"Many people in Virginia are ready to take the next step. We will not allow this pipeline to be built," said Mara Robbins, a member of the Preserve Floyd group from Floyd County. "The next step is direct action. At this point, if they exhaust us of legitimate means, then we take it into our own hands."