U.S. military veterans plan to build a barracks on Dec. 2 at the Oceti Sakowin protest camp near the small town of Cannon Ball, N.D., to support thousands of activists who have squared off against authorities in frigid conditions to oppose the multibillion-dollar Dakota Access Pipeline (DAPL) project near the reservation of the Standing Rock Sioux Tribe.

Veterans volunteering to be human shields have been arriving at the Oceti Sakowin camp, where organizers say they will work with protesters who have spent months demonstrating against plans to route the DAPL beneath Lake Oahe near the Standing Rock Sioux reservation.

The Native Americans and other protesters say the $3.8 billion pipeline threatens water resources and sacred tribal sites.

Some of the more than 2,100 veterans who signed up on the Veterans Stand for Standing Rock group's Facebook page are at the camp, with hundreds more expected during the weekend. Tribal leaders asked the veterans, who aim to form a wall in front of police to protect the protesters, to avoid confrontation with authorities and not get themselves arrested.

Protesters began setting up tents, tipis and other structures in April and the numbers swelled in August at the main camp. There have been violent confrontations near the route of the pipeline with state and local law enforcement, who used tear gas, rubber bullets and water hoses on the protesters, even in freezing weather.

The number of protesters in recent weeks has topped 1,000. On Nov. 28, North Dakota state officials ordered them to leave the snowy camp, which is on U.S. Army Corps of Engineers land, citing harsh weather, but on Nov. 30, the officials said they would not enforce the order to vacate.

"There is an element there of people protesting who are frightening," North Dakota Attorney General Wayne Stenehjem said on Dec. 1. "It's time for them to go home."

U.S. President-elect Donald Trump said on Dec. 1 that he supported the completion of the pipeline, and his transition team also said he supported peaceful protests.

Members of the North Dakota Veterans Coordinating Council denounced the involvement of veterans in a protest that has damaged property, and asked them not to take part.

North Dakota Gov. Jack Dalrymple said on Nov. 30 that it was "probably not feasible" to reroute the pipeline, but he would try to rebuild a relationship with Standing Rock Sioux tribal leaders.

Freezing Cold

Morton County Sheriff Department spokeswoman Maxine Herr said 564 people have been arrested since the start of demonstrations.

State officials never contemplated forcibly removing protesters, and Dalrymple said his evacuation order stemmed mainly from concerns about dangerously cold temperatures. Engineers interviewed by Reuters also said such weather made some aspects of pipeline construction more difficult.

The temperature in Cannon Ball is expected to fall to 4 degrees Fahrenheit (F) by the middle of the week of December 5, according to Weather.com forecasts.

The 1,172-mile DAPL project, owned by Texas-based Energy Transfer Partners LP, is mostly complete, except for a segment planned to run under Lake Oahe, a reservoir formed by a dam on the Missouri River.

Protesters, who refer to themselves as "water protectors," have been gearing up for the winter while they await the Army Corps decision on whether to allow Energy Transfer to tunnel under the river. The Army Corps has twice delayed that decision.

The pipeline operator said in a legal filing in late November that delays following the projected Jan. 1 startup would cost about $84 million a month.

Trump is due to meet on Dec. 2 with Sen. Heidi Heitkamp, D-N.D. According to a source familiar with the matter, Trump is considering Heitkamp for either the Secretary of the Interior or Energy Secretary positions in his Cabinet.

Morton County Commission Chairman Cody Schulz said in a statement he hoped Heitkamp would be able to tell Trump about the serious impact that "professional protesters" from out of state were having on residents and the local economy, as well as the national energy economy.

"We have seen nothing but foot-dragging and unhelpful directives from the Obama administration," Schulz said. "I trust [Sen.] Heitkamp will use her meeting and her influence to ensure that help is on the way for the people of North Dakota when the president-elect is sworn in on Jan. 20."

The approaching frigid winter is also affecting the pipeline project itself: DAPL faces costly delays that have added millions of dollars to Energy Transfer Partners' construction tab. But, even if the line is approved, the freezing temperatures will bring their own challenges to finishing the drilling process.

Bitter Cold Affects Pipeline's Time Line

Frigid weather makes some aspects of pipeline construction more difficult, though not impossible, engineers and experts interviewed by Reuters said.

Construction on the Lake Oahe stretch of DAPL would be expected to take 90 to 120 days to finish, ETP has said.

Construction equipment used to bore under rivers can break through any layer of frost, said Eric Hansen, the director of environmental services at Westwood Professional Services, a surveying and engineering firm in the Upper Midwest.

At issue, however, is the fluid construction companies use to lubricate the drillhead. That drilling fluid, which circulates to clear out debris and keep parts lubricated, freezes at air temperatures between 10 and 20 degrees F.

To avoid this, pipeline crews will keep equipment running nonstop, which allows them to avoid warming up equipment that's been turned off in cold weather, said an engineer who has done work in North Dakota but declined to be named.

The median temperature in Morton County, near the pipeline route, is 13 degrees Farhenheit between December and February, according to the National Weather Service (NWS). The NWS is forecasting a 60% chance that temperatures will be lower than that median for the next three months.

Hansen added that the high winds in North Dakota and heavy snow accumulation can also slow operations. The temperature in Cannon Ball was 30 degrees F on Dec. 1.

As the U.S. government weighs whether to grant Energy Transfer the easement, the pipeline operator said in a legal filing in late November that delays following the projected Jan. 1 startup would cost about $84 million per month.

Energy Transfer Partners said the week of Nov. 28 that it still expects to complete the pipeline in the first quarter of 2017.

Even if boring started at the beginning of 2017, the 90- to 120-day time frame for completion could mean additional costs of between $252 million and $336 million.

The company has moved equipment to begin drilling under Lake Oahe as soon as it receives the easement. The pipeline was originally slated to begin transporting oil out of the Bakken shale to the U.S. Midwest by the end of 2016.

The segment of the Dakota Access that needs completion will burrow under the ground before Lake Oahe, and then cut about 100 feet below the bottom of the river, according to environmental assessment documents from the Army Corps of Engineers and Dakota Access company.

Pipeline companies accustomed to working in freezing temperatures have ways to combat the elements, such as using heated shacks at the site to protect welders, said John Stoody, vice president of government and public relations at the Association of Oil Pipelines, an industry group.

Capital-intensive pipeline projects are underpinned by firm commitments from shippers, meaning an exodus of shippers due to delays could erode the economic viability of the line.

"Loss of shippers to the project could effectively result in project cancellation," the company said in a court filing.

Energy Transfer cannot access the remaining $1.4 billion of its credit facility without all necessary approvals for the line, the company said on its quarterly earnings call.