State pollution control officials are monitoring the cleanup of a large manure spill in Stearns County, where 20,000 gallons of liquid waste leaked from a tank on a dairy farm and may have contaminated local waters.

A failed valve on the aboveground tank was to blame for the spill, according to the county’s environmental services department.

The leak, reported Tuesday by the farm’s owner, was stopped within a few hours. But some of the spilled waste reached an adjacent intermittent stream and swampy area, where it was contained with a trench and berm, according to the Stearns County Sheriff’s Office. The farm is near Holdingford, and the swampy area drains to Krain Creek, north of Two Rivers Lake.

No criminal charges will be filed. A Minnesota Pollution Control Agency (MPCA) spokesman said an emergency staffer checked the site Thursday to ensure the spill was being properly cleaned up. The agency hasn’t determined yet whether an enforcement action is necessary.

Manure from feedlots is a valuable fertilizer when applied to crop fields. But the handling and spreading of large quantities of manure has generated controversy because commercial fertilizers and manure are also key sources of nitrate pollution in groundwater, wells and lakes and streams.

The farmer, Mark Leukam, 63, of Albany, could not be reached for comment.

Leukam called 911 Tuesday to report the problem, according to Stearns County Sheriff’s Captain Jon Lentz. Deputies went to the scene, contacted the county’s Environmental Services team and snapped some aerial photos with a drone.

Becky Schlorf, a supervisor for Stearns County Environmental Services, characterized the spill as fairly large and unusual for Stearns County, saying: “I don’t think we even have one a year.”

She said that while many farmers store manure in aboveground tanks — Leukam’s holds 400,000 gallons — livestock waste is more commonly stored in pits in the ground.

Tuesday’s incident was the first time Leukam’s farm has had a spill, Schlorf said. The farm has no history of compliance problems, enforcement records show.

The farm is permitted for about 139 animal “units,” a standard livestock measure that takes into account the number of animals and their size. It’s required to keep manure application records on file, but isn’t required to have a manure management plan, as are some larger livestock operations, Schlorf said.

Leukam’s operation is one of nearly 3,000 farms in Stearns County, which ranks No. 1 in the state as measured by the number of animals. It’s big dairy country, but also home to large numbers of turkeys and chickens — Pilgrim’s Pride and Jennie-O have operations there, Schlorf said. Roughly half its 11 million animal “units” are chickens and turkeys.