Two Minnesota companies have been fined for neglecting a massive sand mine spill that flowed into the St. Croix River for five days before being discovered by a hiker.

Interstate Energy Partners, LLC, of Plymouth and Tiller Corporation of Maple Grove were ordered to pay a total of $80,000 for not maintaining necessary dikes and berms in violation of Wisconsin law. The fine-grained sediment spilled from a frac sand mine in Grantsburg, Wis., in April 2012.

"Wisconsin will continue to ensure our high-quality rivers and streams are protected, and operators will be required to adhere to the laws and regulations designed to prevent pollution of our natural resources," Wisconsin Attorney General J.B. Van Hollen said.

The spill drew intense scrutiny from state and federal agencies charged with protecting the river from such mishaps. Ultrafine sand being prepared for oil drilling was washed through a flimsy berm into a nearby creek that funneled it to the St. Croix River. The sand, described as the color of milk in coffee and not native to the river, possibly smothered sensitive fish spawning areas and mussel beds, conservationists have said.

The mine is owned by Interstate and operated by Tiller.

The Wisconsin Department of Justice lawsuit said neither company reported the spill. It also said that in February 2012, Burnett County determined that the mining pit was 51 acres in size rather than the 38 acres allowed under the operating permit.

A complaint filed in Burnett County Circuit Court said the spill raised special environmental concern because the site is bordered by lands owned by the National Park Service and Governor Knowles State Forest. The complaint also said the nationally protected river supports 95 species of fish and 41 species of mussels. Beaver, muskrat, otters, eagles, osprey and ducks nest along the river.

Mike Caron, a spokesman for Tiller, expressed regret over the leaking berm soon after it occurred.

"This is the last thing we'd ever want to happen at any of our facilities," he said at the time.

Judge Kenneth Kutz signed the order on Jan. 2.

Kevin Giles • 651-925-5037