But more than a dozen acres of Monson's pasture remain fenced off and out of use. The cattle no longer drink from the creek, which was their main water source. Zenergy dug a well to replace it.
Shallow groundwater in the area remains thousands of times saltier than it should be and continues to leak into the stream and through the ground, contaminating new areas.
There's little understanding of what long-term impacts hundreds of such releases could be having on western North Dakota's land and water, said Micah Reuber.
Until last year, Reuber was the environmental contaminant specialist in North Dakota for the federal Fish and Wildlife Service, which oversees wetlands and waterways.
Reuber quit after growing increasingly frustrated with the inadequate resources devoted to the position. Responding to oil field spills was supposed to be a small part of his job, but it came to consume all of his time.
"It didn't seem like we were keeping pace with it at all," he said. "It got to be demoralizing."
Reuber said no agency, federal or state, has the money or staff to study the effects of drilling waste releases in North Dakota. The closest thing is a small ongoing federal study across the border in Montana, where scientists are investigating how decades of oil production have affected the underground water supply for the city of Poplar.
Joanna Thamke, a groundwater specialist with the U.S. Geological Survey in Montana, started mapping contamination from drilling 20 years ago. She estimated it had spread through about 12 square miles of the aquifer, which is the only source of drinking water in the area. Over the years, brine had leaked through old well bores, buried waste pits and aging tanks and pipes.
In the Poplar study and others, Thamke has found that plumes of contaminated groundwater can take decades to dissipate and sometimes move to new areas.
"What we found is the plumes, after two decades, have not gone away," she said. "They've spread out."
Poplar's water supply is currently safe to drink, but the EPA has said it will become too salty as the contamination spreads. In March, the agency ordered three oil companies to treat the water or to find another source.
North Dakota officials are quick to point out that oversight and regulations are stronger today than they were when drilling began in the area in the 1950s. One significant difference is that waste pits, where oil companies store and dispose of the rock and debris produced during drilling, are now lined with plastic to prevent leaching into the ground.
New rules, effective April 1, require drillers in North Dakota to divert liquid waste to tanks instead of pits. Until now, drillers could store the liquid in pits for up to a year before pumping it out in order to bury the solids on site. The rule would prevent a repeat of the spring of 2011, when record snowmelt and flooding caused dozens of pits to overflow their banks.
But Reuber worries that the industry and regulators are repeating past mistakes. Not long before he left the Fish and Wildlife Service, he found a set of old slides showing waste pits and spills from decades ago.
"They looked almost exactly like photos I had taken," he said. "There's a spill into a creek bottom in the Badlands and it was sitting there with no one cleaning it up and containing it. And yeah, I got a photo like that, too."
Keller has grown so dispirited by the changes brought by the boom that he is considering retiring after 30 years with the Army Corps and moving away from Williston. He runs a side business in scrap metal that would supplement his pension.
Still, determined to protect the area, he keeps alerting regulators whenever he spots evidence that oil companies have dumped or spilled waste.
Last July, when he saw signs of a spill near his home, Keller notified the Health Department and sent pictures showing a trail of dead grass to an acquaintance at the EPA regional office in Denver. The brown swath led from a well site into a creek.
If the spills continued, he warned the EPA in an email, they could "kill off the entire watershed."
EPA officials said they spoke with Keller, but did not follow up on the incident beyond that. The state never responded, Keller said. The site remained untested and was never cleaned up.
"There was no restoration work whatsoever," Keller said.
Republished with permission.