The closure of a major North Dakota oil pipeline last year has raised concerns about safety at a key hub in the nation’s crude-exporting region.
But experts are still waiting for answers.
Here are the latest developments.
The pipeline shut down in May The Lame Deer Pipeline spoke of the North Dakota Bakken shale in Bismarck, North Dakota, on its way to the state’s oilfields.
It was one of the most significant pipelines to be closed in the state since it was completed in 2009.
The pipeline’s owners had said it would serve as a “gateway” for pipeline exports, but the US Environmental Protection Agency (EPA) ruled in November that it was in danger of breaching the nation resilience” limit.
The shutdown of the pipeline prompted a wave of protests by residents, ranchers, landowners and environmentalists.
Lakota Nation lands at risk from pipeline shutdown In December, the US Army Corps of Engineers ruled that the pipeline was unsafe for transporting crude oil.
The Army estimated that the spill could cause more than $100m (£61m) in damages.
It cited the pipeline’s design, infrastructure and operations, as well as the possibility that it could contaminate groundwater.
But the EPA did not rule out the possibility of environmental damage in the event of a rupture.
The decision also found that the closure would cause environmental harm to Native American communities and threaten tribal rights.
Oil pipeline shut-down is just the start of a pipeline fight The pipeline was built by North Dakota-based Bakken Energy, which has been the subject of several pipeline spills.
The company has been fined for spills at sites in Pennsylvania and Pennsylvania State University, and for other incidents including a ruptured oil pipeline near the town of Waring, Pennsylvania, in September 2017.
It also faces numerous complaints from local communities.
In January, the company appealed the decision by the US Army to the District Court of the Creeks, an appellate court that has jurisdiction over matters that are federal or state, including environmental issues.
The appeal came in response to a complaint by a coalition of tribes, environmental groups and the Lakota people who had sought a temporary injunction to prevent the pipeline from being constructed.
Plans for the pipeline to be rebuilt are under review by US Army Following the US government’s ruling in December, the pipeline company, Lakeau Resources, announced plans to build a second line to carry more crude oil from the Bakken region to Illinois.
The second line is to be constructed with a 1.3 billion-gallon (3.1 billion-litre) oil pipeline.
But a group of local tribes, tribal representatives and other activists has challenged the construction of the second line, arguing that it violates the treaty between the two nations and the US constitution.
The tribe of Lake Superior, for example, said in December that it would oppose any project that would cause its people to lose their lands, water and livelihoods.
The Lake Superior Sioux tribe has reached an agreement with the US Energy Department (USDOE) on the pipeline and has signed a memorandum of understanding that allows the pipeline construction to begin.
Pipeline closure may affect climate change The Lakes of the Woods tribe in the Pine Ridge Reservation in South Dakota has spoken out against the proposed pipeline in the past.
The reservation was home to the first documented contact between humans and the Neanderthals in the region, but in December, a statement from the Lears said that a pipeline would cause climate change.
The statement said that the Laks people are not fit to live in a climate dominated by carbon emissions, and that a significant amount of natural resources would be lost in a carbon exchange with a coal company.
Climate change is linked to pipeline shutdowns and spill-related deaths in North Dakota An estimated 1.5 million people are currently living on the North Dakotas Indian Reservation, which is the home to one of America’s most densely populated countries and the nation´s most densely populated state.
The state has experienced several major pipeline spills and serious flare-ups in recent years, and there have been multiple deaths linked to the oil spill.
But despite the recent climate crisis, many people are concerned about the health and safety of people living on Indian reservations.
Native American tribes want the pipeline built again In November, the US Department of Intergovernmental Cooperation on Environmental Justice (ICEJ