CURRENT TRENDS IN GROUNDWATER USE IN SOUTHEASTERN WISCONSIN ARE NOT SUSTAINABLE

The most intensive use of groundwater in Wisconsin occurs in rapidly urbanizing areas in the southeast part of the state. Suburban areas west of Milwaukee rely completely on groundwater and currently withdraw more than 33 million gallons per day from the sandstone aquifer system. These groundwater withdrawals from municipal and industrial wells have created a regional cone of depression, which, when combined with that of the Chicago region to the south, represents one of the largest cones of depression in North America. Water levels in the deep aquifer have dropped about 500 ft since the early 1900s and continue to decline at about 6 ft/yr.

A new groundwater flow model created for the seven counties that make up the Southeastern Wisconsin Regional Planning Commission region helps quantify the effects of long-term pumping on the natural circulation and replenishment of that area's groundwater. The model simulates groundwater movement through the entire geologic section, extending from shallow glacial and dolomite units near the land surface to sandstone units at depths of more than 2,000 ft. By incorporating all known municipal and industrial wells operating now and in the past into transient runs, the model illustrates the evolution of groundwater levels and flows between 1864 and 2000 and allows predictions of future conditions. If historic consumption trends continue, pumping will increase by as much as 40 percent between 2000 and 2020; the model shows that this increased use will produce over 100 ft of additional drawdown at the center of the cone.

The current trends of increased pumping and consequent increased drawdown in the sandstone aquifer are not sustainable over the long term. Consequences of continued drawdown include progressively higher and higher energy and infrastructure costs, reduced aquifer yield, and declining groundwater quality. Along with increased drawdown, pumping has reduced groundwater discharge to springs, lakes, and wetlands, has shifted groundwater divides, has increased flow from the shallow to the deep parts of the aquifer system, and has redirected groundwater flow lines.

Long-term sustainability for water supply in the region will require a regional approach to water management, improved hydrogeologic and water-use data, optimal well placement and operation, and trade-offs between groundwater and surface-water supplies.