Source Water Protection
Manganese in Minnesota’s Groundwater
Manganese is a naturally-occurring metal common to groundwater throughout Minnesota. The Health Risk Limit (HRL) for manganese is 100 micrograms per liter of water (ug/L), but manganese concentrations in Minnesota groundwater range from less than 50 ug/L to greater than 1,000 ug/L, and the pattern of occurrence is complex.
In 2012, the Minnesota Department of Health (MDH) Health Risk Assessment unit replaced past manganese guidance (last updated in 2008) with tiered guidance for two populations (infants, and children older than one year, plus adults). See:
Basic information about Manganese can be found at:
Pattern of occurrence of Manganese in Minnesota Groundwater
The Source Water Protection unit (SWP) coordinated with the health risk assessment effort by determining the pattern of occurrence for manganese in groundwater throughout Minnesota. To do this, SWP collated available chemical information from ten major data sources. The preliminary result is discussed here:
Similar information (in in poster presentation format) was presented to the combined Midwest Ground Water Conference/Minnesota Groundwater Association Conference in October 2012:
- Poster Presentation:
Preliminary Assessment of Naturally-Occurring Manganese in Minnesota Groundwater (PDF: 2.05MB/1 page)
The preliminary assessment concluded:
- Manganese distribution in Minnesota groundwater is highly variable but there are areas where concentrations are consistently less than 50 ug/L (southeastern Minnesota) or greater than 1,000 ug/L (southwestern Minnesota). The southwestern area of elevated concentrations roughly corresponds to the western flank and interior of the Des Moines Lobe till.
- Manganese concentrations in plastic-cased wells were twice those in steel-cased wells, consistent with a manganese-removal mechanism specific to steel-cased wells.
- For wells completed in water table settings, no correlation was determined between manganese concentration and screen placement below static water level.
- The manganese data were strongly spatially correlated.
- The best strategy for understanding manganese occurrence in Minnesota groundwater will be continued analysis of existing data combined with targeted geochemical assessments over restricted areas of interest where geology and hydrogeology are well-constrained.