The Minnesota Pollution Control Agency on Wednesday said it has filed a response defending its proposed wild rice sulfate standard that in January was panned by a state administrative law judge.

PCA officials say their proposed sulfate pollution standard is a good compromise that protects wild rice in places where sulfate pollution might damage it, but also allows more sulfate pollution in lakes and rivers where it may not harm the plant.

The new, lake-by-lake standard would replace a long-standing but mostly unenforced statewide sulfate limit for wild rice waters that industry officials say is too restrictive and could cripple the state's taconite iron ore industry, as well as cost millions of dollars for municipal sewage plants to comply with.

Scientists say excess sulfate in some waters can spur the development of sulfides, which can starve wild rice of needed nutrients, damaging or even killing the plants.

The PCA response this week, filed with the state's chief administrative law judge, addresses concerns raised in the January decision by Judge LauraSue Schlatter, who said the PCA's proposed new sulfate rule failed to meet the definition of a state rule and failed to meet the federal Clean Water Act. Schlatter also said the PCA also didn't properly consider concerns raised by tribal groups.

Schlatter ruled against repealing the existing, statewide 10 parts-per-million limit due to the PCA's "failure to establish the reasonableness of the repeal, and because the repeal conflicts" with the federal Clean Water Act.

The judge said the PCA plan to develop "equation-based" limits for specific lakes and rivers that hold wild rice "fails to meet the definition of a rule" under state law "and is unconstitutionally void for vagueness."

Schlatter even rejected the PCA's preliminary list of 1,300 lakes and rivers where the agency believes viable wild rice stands exist, places where the new rules would have applied, because the list itself violated federal law.

PCA officials on Wednesday said the judge simply erred in applying the Clean Water Act, noting that using equations to determine limits is a common practice in rulemaking for pollution standards.

"We think the law judge misread the Clean Water Act," said John Linc Stine, PCA commissioner, in a conference call with reporters.

PCA officials say their response addresses most of the concerns raised by Schlatter in her January decision, and they are hopeful the chief administrative law judge will reconsider the decision and support the new sulfate rule with the changes made.

A decision is expected in the coming weeks.

But even if the chief judge reverses the January decision, the future of the proposed sulfate rule is in question. Several state lawmakers, pushed by the state's mining industry, are advancing legislation that would prohibit the PCA from enforcing the new or old sulfate pollution limits, saying their impact on industry, jobs and commerce would be devastating. One bill also calls for a wild rice task force that would address multiple issues that threaten wild rice, not just sulfate pollution.

Meanwhile, tribal and environmental interests have panned the PCA's effort as too lax on industry, saying there's no scientific basis for a lake-by-lake standard that would be confusing, hard to enforce and not as protective as the existing statewide standard for wild rice. They are calling for enforcement of the existing statewide sulfate limit.

Tribal entities could ask the federal Environmental Protection Agency to step in and decide the issue if they believe it's not protective of tribal pollution limits where they have regulatory authority, such as where rivers flow through reservations.

Scientists have found that sulfate - which can come from sewage effluent, mine discharges and other industrial processes - is converted to sulfides in the sediment of many wild rice lakes and rivers. The rate of that conversion changes depending on the amount of carbon and iron in the water (generally, more sulfides with high carbon, fewer sulfides with high iron). It's those sulfides that prevent wild rice from thriving in some areas; the proposed new rule would study the water chemistry of each wild rice lake and river to determine what sulfate pollution level they could handle and still grow wild rice.

The PCA says about 135 facilities are within 25 miles upstream of wild rice waters and would be the most likely ones affected by any sulfate rule enforcement.