U.S. District Judge James Boasberg's decision will come as a blow to the Standing Rock Sioux, who have argued that an oil spill from the pipeline under Lake Oahe - from which the tribe draws its water - could harm the tribal community.
Boasberg found that it was likely the Army Corps of Engineers would be able to justify previous decisions made while permitting the pipeline.
'The corps must simply connect the dots,' he said. 'This, then, is not a case in which the agency must redo its analysis from the ground up.'
Boasberg also acknowledged that shutting down the pipeline would disrupt the energy industry, but said it wasn't a major factor in his decision.
Operating since June
The $3.8 billion pipeline built by Texas-based Energy Transfer Partners has been operating since June 1, moving oil from North Dakota through South Dakota and Iowa to a distribution point in Illinois. From there it can be shipped to the Gulf Coast and potentially lucrative markets abroad. It has the capacity to move half of the oil produced daily in North Dakota, the nation's second-leading producer behind Texas.
Energy industry officials applauded Boasberg's ruling, with North Dakota Petroleum Council President Ron Ness calling the pipeline 'a critical part of American energy infrastructure.'
President Donald Trump had pushed for the pipeline's completion, and the corps dropped a plan to conduct more environmental study after he took office.
Boasberg ruled June 14 that the corps had largely complied with environmental law, but he ordered the agency to reconsider certain areas of its analysis, and he took arguments on whether to shut down the 1,200-mile (1,930-kilometer) pipeline while the work was being done.
Boasberg in June said the corps hadn't adequately considered how an oil spill under the Lake Oahe reservoir on the Missouri River in the Dakotas might affect the Standing Rock Sioux. The tribe is among four that have challenged the pipeline in court over environmental fears that ETP says are unfounded.
The judge said the corps also hadn't adequately studied how the pipeline might disproportionately affect the tribal community - a concept known as environmental justice. That aims to ensure development projects aren't built in areas where minority populations might not have the resources to defend their rights.
In its analysis of the Missouri River crossing, the corps studied the mostly white demographics in a half-mile (0.8-kilometer) radius, which the agency maintains is standard. But if the agency had gone an additional 88 yards (80 meters), the study would have included the Standing Rock Reservation.
Boasberg in his ruling Wednesday said that issue was 'a closer call' than the others, but that it still did not justify shutting down the pipeline. He noted that the tribe's water intake had been moved about 50 miles (80 kilometers) downstream since pipeline construction began, and said an alternative river crossing near Bismarck that had been studied and rejected would pass much closer to a drinking water intake that serves tens of thousands more people.
'Risks presented to this tenfold increase in population must, of course, be considered,' the judge said.
Corps attorneys said the agency expected to be able by next spring to substantiate its earlier determination that the pipeline posed no significant environmental threats. ETP maintained that a shutdown would cost it $90 million monthly and significantly disrupt the broader energy industry as well as state and local tax revenue.
The North Dakota Pipeline Authority this week said that the Dakota Access pipeline had boosted the state's tax revenues by about $19 million in its first three months of operation.
Tribal attorneys argued that ETP had overstated the potential effects of a shutdown, and Boasberg acknowledged 'some cause for skepticism' regarding ETP's predictions. Tribal attorneys also said a shutdown would create incentive for the corps to take the review seriously.
The tribes had proposed a fallback plan if Boasberg decided against a shutdown. It includes increased public reporting of pipeline issues such as repairs, and implementation of a spill response plan - including equipment staging - at Lake Oahe.
Boasberg said he would hear arguments on the matter. He scheduled a status conference for October 18.