Sulfate, wild rice, and wastewater
Sulfate is a naturally occurring chemical and can be found at varying concentrations in surface and groundwater across the state. Sulfate can move from groundwater to surface water, and vice versa, as a result of domestic consumption and other human activities. Sulfate is also produced through various industrial processes.
Sulfate is commonly found in wastewater across Minnesota, and the effluent concentration varies based on human activity, treatment methods, natural conditions, and drinking water sources. Minnesota has a water quality standard of 10 mg/L sulfate for waters used for the production of wild rice. This standard was established to protect wild rice because elevated levels of sulfate can have a negative impact on its growth. More information on the standard, permitting questions, and impairment listings can be found on the Protecting wild rice waters web page.
The vast majority of wastewater treatment facilities are upstream of a wild rice water.
For facilities that discharge to surface waters and have reasonable potential to cause or contribute to an exceedance of the sulfate standard in downstream wild rice waters, MPCA is including new sulfate discharge limits in their NPDES permits.
While some facilities can currently attain their sulfate discharge limits, most are unable to meet their limits at this time. Solutions exist to reduce sulfate concentrations in water discharges but for many facilities, these treatment options are logistically difficult to implement. With this understanding, the MPCA is developing a sulfate multi-discharger variance (MDV) which requires incremental progress towards compliance with sulfate permit limits.
Wild rice producing waters
This online search tool will assist in identifying waters used for production of wild rice, as well as in identifying facilities that require a permit review because they are located in a watershed upstream or partially upstream of such waters.
What is a multi-discharger variance (MDV)?
A water quality variance is a temporary change in a state's water quality standard for a specific pollutant and its relevant criteria, allowing deviation from meeting a permit limit for a particular discharger for a set amount of time. An MDV is a single variance that applies to several facilities unable to attain water quality-based effluent limits for the same reason, sometimes termed “eligibility factors.” Like an individual variance, an MDV must be applied for and has specific requirements that facilities must adhere to in order to reduce pollutant loading in their discharge.
What is the basis for the sulfate MDV?
There are six eligibility factors in which U.S. EPA (40 CFR 131.10(g)) and MPCA (Minn. R. 7050.0190 and 7052.0280) outline conditions for a variance to be approved. MPCA is pursuing the Sulfate MDV under the factor stating that permittees must show they cannot meet an established permit limit because “human-caused conditions or sources of pollution prevent attainment of water quality standards, and the conditions or sources cannot be remedied or would cause more environmental damage to correct than to leave in place."
Additionally, all variances require an alternatives analysis, a study that evaluates a range of practicable alternatives that would prevent or reduce the discharge of the pollutant. The alternatives analysis is a driving factor in determining both the applicability of utilizing a variance and the eligibility for an MDV. The MPCA is still determining eligibility requirements for the MDV.
Facilities that do not meet final eligibility requirements may still apply for an individual sulfate variance.
Learn more and provide input
Early public engagement will help shape the program’s structure, while exploring alternative protective measures for wild rice.
MPCA will be hosting a series of meetings to provide information on the Sulfate MDV and to solicit input on its implementation. A virtual kickoff meeting will be held at 3 p.m. on May 1, 2025, to provide introductory information.
As part of the formal variance approval process, the MDV will undergo a formal public notice period with associated comment period and a public meeting.
Additionally, the MPCA will host virtual listening sessions for target groups of permittees, environmental staff and members of Tribal Nations, and watershed practitioners to provide input to MPCA during these early stages. These listening sessions are by invite only. Other informal input can be directed to WQSvariances.MPCA@state.mn.us.
Alternatives for sulfate treatment
The report "Analyzing alternatives for sulfate treatment in municipal wastewater" (2018) presents potential treatment options for reducing sulfate in municipal wastewater discharges.