Ground-water flow in the St. Peter-Prairie du Chien-Jordan aquifer was studied in a 700 square-mile area surrounding Rochester, Minnesota. The aquifer consisting of sandstone, limestone, and dolomite is locally confined by the Decorah-Platteville-Glenwood sequence of shales and limestones. Regional flow in the aquifer is from a ground-water divide on the western, southern, and eastern sides of the city toward various rivers. A 140-square-mile area of the aquifer is a source of water supply for the Rochester area.
A cone of depression in the potentiometric surface of the aquifer throughout most of the year is centered around high-capacity (greater than about 200 gallons per minute) wells in downtown Rochester. The cone covered an area of about 2.3 square miles in August 1988.
Most streams in the area gain water from the ground-water system. One reach of the South Fork Zumbro River, however, loses water to the system. This loss is probably caused by the pumping of nearby high-capacity wells.
A ground-water-flow model was used to simulate the effects of an extended drought near Rochester. Conclusions based on the simulations are that (1) reduced recharge and increased pumping, conditions that could exist during a 3-year drought, would probably lower water levels 5 to 10 feet regionally and more than 30 feet in the city; (2) pumping of six additional municipal wells on the perimeter of the city would lower regional water levels about 1 to 5 feet; and (3) that water levels would recover 1 to 18 feet if pumping from six municipal wells in downtown Rochester were discontinued.
The area encompasses five recharge zones that can be delineated on the basis of recharge rate. About 54 percent of recharge to the aquifer in the area contributing water to Rochester is from a zone along the edge of the Decorah-Platteville-Glenwood confining unit. About 10 percent of recharge in this contributing area is to the sewered area of Rochester.
