This report depicts potentiometric surfaces and groundwater- level changes in three aquifers that underlie the seven-county Twin Cities Metropolitan Area. Approximately 350 groundwater levels were measured in wells from the three aquifers-the Prairie du Chien-Jordan, the Franconia-Ironton-Galesville, and the Mount Simon-Hinckley aquifers-in March and August of 2008. The report presents maps, associated data tables, and 22 geographic information system datasets. The maps presented in this report show the potentiometric surfaces in March and August of 2008 for all three aquifers, groundwater-level changes from March to August 2008 for each aquifer, and revised potentiometric-surface contours for the winter of 1988-89 for the Prairie du Chien-Jordan and the Mount Simon-Hinckley aquifers, and the estimated long-term (winter of 1988-89 to March 2008) groundwater-level changes for the Prairie du Chien-Jordan and Mount Simon-Hinckley aquifers. This report documents the methods used to construct the maps and provides a context for the period of the measurements.
Although withdrawal demand is increasing in the Twin Cities Metropolitan area, particularly in the Prairie du Chien-Jordan aquifer, year-to-year changes in withdrawals can be substantial, and the relation between potentiometric surfaces in the major aquifers and year-to-year withdrawals is not well established. The estimated long-term (19-year) groundwater-level changes for the Prairie du Chien-Jordan and Mount Simon-Hinckley aquifers have not been large based on data and maps produced during this study, despite the large seasonal fluctuations shown by the March and August 2008 synoptic measurements.
