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, and natural conditions. Minnesota has a water quality standard of 10 mg/L sulfate for wild rice waters. 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 facilities that are permitted to discharge to state waters 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 monitoring and new sulfate discharge limits in their National Pollution Discharge Elimination System/State Disposal System (NPDES/SDS) 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, implementing these treatment options may not be feasible at this time. With this understanding, the MPCA is considering the development of a sulfate multi-discharger variance (MDV) which ensures that sulfate levels from facilities will not increase while also requiring 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. It is time limited and an option under the Clean Water Act to work towards achieving compliance with the state’s water quality standard. 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 working through an engagement process to determine what factors and eligibility requirements are appropriate for a Sulfate MDV.
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.
Facilities that do not meet final eligibility requirements may still apply for an individual sulfate variance.
Outreach and information
The MPCA held an online informational meeting May 1 about a Sulfate multi-discharger variance.
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.