The MPCA has started a study intended to understand and document the variation in naturally occurring sulfate levels across the state.
The MPCA will consider the occurrence and significance of multiple human-caused and natural sources of sulfate, including geologic minerals, atmospheric deposition, mining-related operations, agricultural fertilizers and wastes, and industrial/municipal effluents. The magnitude of each source and its relative importance vary by geographic location across the state and, in some cases, vary across time as well.
The analysis will use available datasets to identify and remove human-caused sources of sulfate through statistical methods and characterize naturally occurring sulfate levels across the state.
Scientific review panel role
This study is being led by MPCA staff and will include external review by a scientific review panel.
The scientific review panel is a group of scientists, engineers, and government partners whose primary role is to provide technical expertise to the MPCA study team. Panelists will be sharing input throughout the project and will participate in a formal review of the study’s results.
Milestones and timeline
Data preparation – Winter to Spring 2026
The initial phase of this study was to produce statewide sulfate datasets for both surface water and groundwater. This study primarily uses data submitted to the MPCA’s Environmental Quality Information System (EQuIS) database, as well as publicly available databases including the federal government’s Water Quality Portal. Other data sources include the United States Geological Survey’s Long-Term Resource Monitoring program, monitoring results submitted by Wastewater Treatment Facilities as required by their NPDES permits, and the Environmental Information Management System containing Metropolitan Council’s water quality data.
The MPCA is reviewing the methods used to collect sulfate data and considering different approaches for addressing uncertainty surrounding specific methods, especially in the northeastern part of the state where sulfate concentrations upstream of permitted dischargers are low.
Data analyses – Spring to Summer 2026
The study team is evaluating what factors are driving differences in sulfate concentrations. To do this, the team is considering information on land cover, land use, geology, soil composition, upstream point sources, hydrological modifications, atmospheric sulfur deposition, and other potential human-caused sources and impacts associated with available sulfate data. These analyses will further our understanding of the patterns of sulfate levels with the goal of establishing natural background sulfate regions.
Review – Fall to Winter 2026
The scientific review panel will complete an evaluation of the data findings and conclusions of this study. The MPCA study team will then respond to their feedback, make modifications as appropriate and finalize the study results.
Outreach and public engagement will follow the completion of the study.
More about this study
This analysis is a scientific endeavor to estimate natural background concentrations of sulfate across the state, and while it may be used to inform future implementation decisions, there is no commitment to change the wild rice sulfate standard.
This study will not explore the relationship between wild rice and sulfate, nor will it examine the variables that may impact wild rice growth. As such, this effort does not evaluate the 10 mg/L sulfate water quality standard to protect wild rice, found in rule at Minn. R. 7050.0224, subp. 2.