Preliminary evaluation of the ground-water-flow system in the Twin Cities Metropolitan area, Minnesota

Water-Resources Investigations Report 82-44

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A preliminary quasi-three-dimensional finite-difference ground-water-flow model of the seven-county Twin Cities Metropolitan area was constructed and used to evaluate parameter sensitivity and adequacy of available data. Fourteen geologic units that underlie the study area were grouped into nine hydrogeologic units and were incorporated into a five-layer model. The layers in the simulation model include the Mount Simon-Hinckley, Ironton-Galesville, Prairie du Chien-Jordan, and St. Peter aquifers and the drift. Sensitivity analyses were made for 19 parameter and boundary-condition specifications. Model results are most sensitive to recharge and withdrawal rates and hydrogeologic variations related to drift-filled bedrock valleys. Analyses of available data and results of steady-state simulations indicate that critical data needs for improving the simulation model include (1) spatial and temporal variations in ground-water withdrawals and potentiometric levels, and (2) hydraulic properties of the drift that fills or partly fills bedrock valleys. Areal distribution of calcium, sodium, sulfate, and chloride concentrations were analyzed to provide information on the hydrologic and geochemical relationships between aquifers. Ground water is generally of the calcium magnesium bicarbonate type. Concentration of dissolved solids in the Jordan Sandstone and Mount Simon-Hinckley aquifer generally decreases from southwest to northeast across the study area. This decrease probably reflects differences in the quality of recharge water and geochemical processes within the aquifers such as ion-exchange. (USGS)

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Preliminary evaluation of the ground-water-flow system in the Twin Cities Metropolitan area, Minnesota
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Water-Resources Investigations Report
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U.S. Geological Survey,
v, 65 p. :ill., maps ;28 cm.