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DNR considers changing phosphorus standards for 3 lakes

MADISON — State environmental officials are considering changes to phosphorus regulations on three south-central Wisconsin lakes, a move that could cost wastewater treatment plants across the upper Wisconsin River basin millions of dollars over the coming decades.

The Department of Natural Resources is proposing loosening phosphorus restrictions on Petenwell and Castle Rock lakes in Adams, Juneau and Wood counties while tightening standards on Lake Wisconsin in Columbia County. The agency’s board is scheduled vote Wednesday on a scope statement outlining the plan.

Approval would give the department permission to begin working on regulatory language. The changes would ultimately need approval from the U.S. Environmental Protection Agency before they could go into effect.

Scientists believe phosphorus runoff contributes to algae blooms that can sicken people and kill animals. Phosphorus can enter lakes and rivers through runoff from farms and lawns as well as industrial waste and sewage. Petenwell and Castle Rock lakes and Lake Wisconsin all are on the DNR’s 2018 list of impaired waters due largely to phosphorus pollution.

DNR staff wrote in a May 21 memo to board members that statewide phosphorus standards are more restrictive than needed to preserve Petenwell and Castle Rock lakes for recreational use but too lax to protect Lake Wisconsin.

The department’s plan calls for raising phosphorus limits on Petenwell Lake from 40 micrograms per liter to 53 micrograms per liter and raising phosphorus limits on Castle Rock Lake from 40 micrograms per liter to 55 micrograms per liter. The memo said higher phosphorus concentration in those two lakes typically produces less algae than in other Wisconsin lakes.

The limit on Lake Wisconsin, meanwhile, would drop from 100 micrograms per liter to 47 micrograms per liter. The lake is essentially a wide spot in the Wisconsin River and doesn’t retain phosphorus for long, the memo said, but the area still responds to phosphorus loading like a lake.

The memo notes that the changes would affect most of the Wisconsin River basin north of Lake Wisconsin, a 9,000 square-mile swath of the state that includes 21 counties, 85 municipalities and nearly 110 individually permitted wastewater plants.

Most of those facilities are already installing equipment capable of meeting the limits or are already meeting the limits and likely won’t feel much of an economic impact. However, 36 facilities — 29 municipal plants and seven industrial facilities — likely will see their bottom line shift dramatically. Two dozen facilities will likely save a total of $180 million over the next 20 years. The remaining 12 will likely spend about $16.5 million in compliance over the next two decades, the memo estimated.

Improved water quality in Lake Wisconsin could convey economic benefits from tourism, the memo notes.

The plan doesn’t impose any new requirements on non-point phosphorus sources or factory farms.

Messages left Tuesday with the Petenwell and Castle Rock Stewards and the Lake Wisconsin Alliance — groups that work for improved water quality on their respective lakes — weren’t immediately returned Tuesday. A message left at the League of Wisconsin Municipalities also wasn’t immediately returned.