One of Minnesota’s leading environmental groups has sued the state, charging that top regulators are doing too little to protect Lake Pepin from the pollution discharged by sewage treatment plants, a violation of the federal Clean Water Act.

The suit centers on a new plan that would allow five of the largest metro-area water treatment plants to discharge 175 tons of phosphorus annually into the Mississippi River and Lake Pepin, which is one of Minnesota’s most scenic recreation spots and drains water from two-thirds of the state.

Although the plants are currently below that ceiling, on average, the new plan would not result in cleaner water downstream, said Kris Sigford, water quality director for the Minnesota Center for Environmental Advocacy (MCEA), which filed the suit Thursday.

The suit also says the state’s prediction for water quality in Lake Pepin optimistically presumes that thousands of farmers upstream on the Minnesota River will adopt sweeping changes in land management to reduce phosphorus discharges.

“You can’t just expect a miracle and base your limits on that,” Sigford said.

PCA assumptions

John Linc Stine, commissioner of the state Pollution Control Agency, said his staff must base any plan on assumptions, including some that reflect expectations about land use changes in the future.

He also pointed out that the Metropolitan Council has made enormous strides in reducing phosphorus discharges from its water treatment plants — voluntarily achieving reductions of 70 percent or more in recent years to bring the discharges well below their legal limits. He expects that performance to continue, he said.

But Stine also said he welcomes the debate because “it is focused on what our goals are for the water.”

The lawsuit raises the increasingly contentious question of whether Minnesota can clean up its lakes, rivers and streams without tackling problems caused by chemically intensive farming in the state’s largest watersheds.

Phosphorus, a nutrient that causes foul and sometimes toxic algae blooms in lakes and rivers, is one of the most common water pollutants. It comes from homes, pets, lawns, and stormwater runoff. But in Minnesota’s major rivers, most of it results from fertilizers used in agriculture.

In Lake Pepin and a stretch of the Mississippi just below its confluence with the Minnesota River, phosphorus levels are often well above 100 parts per billion, the state’s legal standard. State regulators have been working for years on a massive plan to reduce both phosphorus and the rising levels of sediment in Lake Pepin, and the permits under challenge are part of that plan.

In a novel step, the state agreed to issue one “umbrella” phosphorus permit for all the largest sewage treatment plants. Pooling the discharges would give the Met Council flexibility in reducing overall loads, Stine said.

But MCEA argues that the new permit would allow a 35 percent increase, on average, above what the plants are discharging now. It’s unlikely they would ever bump up against the ceiling, Sigford said, but even on paper the state has an obligation to reduce discharges into water that’s already polluted.

Cutting discharges from the plants even further is feasible, said Betsy Lawton, an attorney with MCEA. A handful of cities in other states have done so, and setting a lower ceiling would give the Met Council an incentive to do the same, she said.

Met Council officials declined to comment Thursday, saying they have not seen the lawsuit.

Predictions questioned

Perhaps even more troubling, Sigford said, is that in setting ceilings for the treatment plants, the state makes highly optimistic predictions about what farmers are willing to do. The phosphorus goals for Lake Pepin will be achieved only if other polluters produce additional, much larger reductions. And that would require, for example, that 20 to 30 percent of the land in the Minnesota River watershed be covered with grasses and forests instead of crops and pavement, and that soil erosion from sandy ravines be cut by 30 to 40 percent.

Even if all those assumptions were to “magically” come to pass, Sigford said, Lake Pepin would still meet water quality goals for phosphorus in only nine out of the next 22 years.

In documents, the PCA said it does not dispute that. But, while phosphorus in Lake Pepin may exceed the standard from time to time, on average it will be within limits.

Stine said his agency has to consider future changes on the landscape that will be driven by a growing understanding of what’s driving water pollution.

But, he said, the state cannot regulate farmers, “and if [MCEA] is concerned about the sources we don’t regulate, I don’t think this lawsuit is the way to get at it.”