WILLISTON, N.D.-A reported spill of more than 2,700 barrels of saltwater northeast of Williston over the weekend reinforces the need for oil well pads to have adequate containment berms, one state agency said Monday.

Zavanna staff discovered the spill of 2,733 barrels, or 114,786 gallons, of produced water about 10 a.m. Sunday at an oil well pad about 4 miles northeast of Williston.

About 215 barrels that spilled remained on the oil well pad location and the remaining 2,518 barrels got off location, said Travis Pfaff, production manager for Zavanna.

The saltwater-a byproduct of oil production-contaminated an estimated three-tenths of a mile of privately owned pasture land, Pfaff said.

The cause of the spill was attributed to an above-ground valve that failed, Pfaff said, adding that the valve had been pressure-tested two weeks earlier.

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The North Dakota Department of Health has had an inspector on site and work is still ongoing to determine the extent of the damage, said Bill Suess, spill investigation program manager.

No surface water was affected, but it's unknown if the spill affected groundwater, Suess said Monday. An undetermined amount of the spill flowed into a dry drainage area, Suess said.

Zavanna is coordinating with the landowner, health officials and the North Dakota Industrial Commission to clean up the spill, Pfaff said.

The well pad location was surrounded by a containment berm of at least 26 inches tall, which is not required by North Dakota rules, said Alison Ritter, spokeswoman for the Department of Mineral Resources.

But the berm was not properly maintained near a cattle guard, which allowed the spill to get off the location, Ritter said.

The North Dakota Industrial Commission is considering proposed changes to state oil and gas rules, including a proposal to require oil sites to be surrounded by 1-foot containment berms to keep more spills on location.

Because such berms are not required by the state, they're not subject to maintenance requirements, Ritter said.

"Had this rule been in place, inspectors could have caught where the berm had eroded by the cattle guard and required the operator to make the necessary corrections," Ritter said.

Recently, about 75 percent of oil-related spills in North Dakota were contained to the well pad or location, but that statistic has slipped to below 70 percent, according to the Department of Mineral Resources.

Public hearings on the proposed rule changes are scheduled for the week of April 11.