"When this first happened, it pretty much consumed my life," Monson said. "Now I don't even want to think about it."
The company has paid a $70,000 fine and committed to cleaning the site, but the case shows how difficult the cleanup can be. When brine leaks into the ground, the sodium binds to the soil, displacing other minerals and inhibiting plants' ability to absorb nutrients and water. Short of replacing the soil, the best option is to try to speed the natural flushing of the system, which can take decades.
Zenergy has tried both. According to a Department of Mineral Resources report, the company has spent more than $3 million hauling away dirt and pumping out contaminated groundwater 2014 nearly 31 million gallons as of December 2010, the most recent data available.
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.