South-Central Minnesota Groundwater Monitoring of the Mt. Simon Aquifer – Phase 2

This Phase 2 report is the final of two reports covering groundwater investigations for the Mt Simon and Mt. Simon-Hinckley aquifers in southern and central Minnesota. The Phase 1 report published in June 2011 reported on work accomplished in Martin, Watonwan, Brown, Nicollet, and Sibley counties. Both investigation phases included observation well installations, water level monitoring, groundwater chemical analysis, and aquifer capacity testing to determine recharge pathways and sustainable limits for this aquifer. Most data collected for this Phase 2 study are derived from 16 wells installed at 10 locations to depths of 100 to 695 feet in McLeod, Wright, Hennepin, Sherburne, Anoka, and Isanti counties. In the southern part of the study area (Phase 1 area) hydrograph and geochemical residence time data (14C and tritium) show relatively isolated conditions with groundwater ages ranging from 6,000 to 30,000 years for the Mt. Simon aquifer. In the northern portion of the study area (Phase 2 area) chemical residence time indicators from the Mt. Simon aquifer indicate groundwater ages less than approximately 1,000 years in eastern Wright and Sherburne counties and northern Isanti County. These relatively young groundwater ages are consistent with water level and stratigraphic information that indicate both direct and indirect connection of surface water to the Mt. Simon- Hinckley aquifer through localized focused recharge. This project has shown that the most critical recharge area for the Mt. Simon-Hinckley aquifer and Minneapolis-St. Paul metropolitan area water supply includes portions of Wright, Sherburne, and Isanti counties. Protection of this region from water pollution should be a high priority for all levels of government. Continued monitoring of wells installed for this investigation will create a long term record that can be used to interpret changes in local and regional water supply due to water use or climate changes.