With Dakota Access pipeline halted, what happens now?

The U.S. Army Corps of Engineers announced Sunday that more analysis is needed before it will allow the Dakota Access pipeline to cross the Missouri River just north of North Dakota's Standing Rock Indian Reservation.

The pipeline is part of a four-state, $3.8 billion project announced in 2014 to transport approximately 470,000 barrels per day of sweet crude oil from its production point in North Dakota to an existing pipeline in Illinois. The Corps' announcement that it would not grant a key easement for the pipeline to cross the Missouri River at the proposed point put pipeline construction on hold.

Several thousand protesters have been camped near the construction site for months, saying the pipeline's current route would threaten a water source and Native American cultural sites.

The pipeline is largely complete except for the now-blocked segment underneath Lake Oahe, a reservoir of the river that stretches from Pierre, S.D., to Bismarck, N.D., and is created by the Oahe Dam. Assistant Secretary for Civil Works Jo-Ellen Darcy said in a news release that her decision to halt construction was based on the need to "explore alternate routes" for the pipeline's crossing.

The company has said it already considered other routes but settled on the Lake Oahe route because it was the least environmentally risky.

How do companies decide where to build a pipeline in the first place?

Companies like Energy Transfer Partners, which is building the Dakota Access pipeline, do a lot of research to determine the cheapest way to move oil from where it exists underground to where they can sell it.

It's a calculation of many things: How much steel and other materials will it need to build the pipeline itself? But also: How much risk comes along with building a pipeline in one place or another?

For instance, if a company plans to route a pipeline near a population center, a body of water or wetlands or farmland, officials draw up different scenarios to figure out the cost of responding to possible spills along the route.

A company must also anticipate what disputes might arise over the placement of the route — and figure out how to navigate those disputes.

How did Energy Transfer Partners settle on the current route for this pipeline?

The company decided on the route, which runs about a half-mile north of the Standing Rock Sioux Reservation's border underneath the Missouri River at Lake Oahe, after considering a combination of those factors above.

During that process, the company considered an alternate route in North Dakota, which would run about 10 miles north of the state capital, Bismarck, and cross the Missouri River farther away from Standing Rock than the current route.

That alternate route would have bypassed the 1851 Fort Laramie Treaty area — a large tract of land where the U.S. government ensured hunting and fishing rights for Sioux Indian tribes in exchange for moving them to reservations in the late 19th century, when white settlers were moving into the Dakotas.

But Energy Transfer Partners cited problems with that route alternative. It did a side-by-side comparison of all the water crossings and sensitive areas the route would include, and decided that it would be much riskier, from an environmental standpoint, to use the alternate. So it decided on the current route, just north of the Standing Rock Indian Reservation.

Did the Army Corps of Engineers agree with the company's assessment about that alternative route being more risky?

It did.

In July, the Army Corps of Engineers published a 1,200-page document concluding that the current route, just north of Standing Rock's borders, would not bring with it significant environmental impacts.

The agency also said in its report that the Dakota Access pipeline would get the federal permits it would need to cross bodies of water.

Most of those permits were issued, and Energy Transfer Partners began putting pipe in the ground — but the company was still waiting on the final paperwork for an easement to cross Lake Oahe.

While it was waiting, the Obama Administration stepped in and put construction on hold, saying the pipeline needed more vetting before the company could dig under the lake.

Energy Transfer Partners has said the pipeline is now more than 90 percent complete. How feasible is it to move the route at this point?

It would cost hundreds of millions of dollars to move the route at this point.

But the Army Corps of Engineers isn't concerned with feasibility. Corps officials want to make sure the pipeline route is thoroughly analyzed. They say more study is needed, and add that the process needs to have more tribal and public participation.

Corps officials say that additional analysis should include the route north of Bismarck but also other possible routes that no one is really talking about right now.

How is the company reacting to the announcement? What about the oil industry?

Sunday's developments have shocked the oil industry.

For a long time, companies were able to build pipelines with opposition here and there, but nothing like the opposition that has coalesced at Standing Rock.

Energy Transfer Partners maintains that its current route, crossing the Missouri at Lake Oahe, is the best option — it's next to existing pipelines and is less risky, overall.

Ron Ness, president of the North Dakota Petroleum Council, said industry officials hope that when President-elect Donald Trump takes office, the Corps of Engineers will reverse course. "The Army Corps has been supportive of this project," he said, adding that it appears their current actions came through a White House directive.

Does that mean a Trump administration could reverse the Army Corps' decision?

It certainly could.

But, for context: Any of these decisions made by federal government officials can — and likely will — be challenged in court.

That means the fight over the Dakota Access pipeline's route is far from over.

A Facebook Live Q&A with MPR reporter Elizabeth Dunbar: