SUSTAINABILITY OF SHALLOW GROUNDWATER IN SOUTHEASTERN WISCONSIN

Because of growing concerns about water-quality issues and declining groundwater levels in a deep confined aquifer in southeastern Wisconsin, local communities are turning to shallow, unconfined aquifers for water supply. Shallow wells commonly provide adequate yield, but can significantly deplete nearby surface-water resources. In addition, communities using shallow aquifers can have an overall negative groundwater balance if wastewater leaves the community via surface water rather than returning to the local groundwater system through septic systems. Sustainable use of groundwater requires a balance between groundwater availability, human water needs, environmental requirements of surface-water resources, and wastewater disposal.

We have investigated the sustainability of shallow groundwater resources in southeast Wisconsin by constructing simple groundwater flow models for six demonstration areas that reflect the range of hydrogeologic properties found across the region. Development scenarios take into account lot size and wastewater-disposal method. We assessed impacts using three metrics: drawdown, baseflow reduction, and overall water balance.

Shallow wells can provide adequate water supplies for single-family homes on lots of 1 acre or larger over much of the region. However, all development scenarios have impacts on nearby water resources. Under the most aggressive development scenarios (1 acre lots, no return flow), simulated drawdowns beneath developed areas range from 1 to 27 ft, and baseflow reductions range from 20 to 40 percent. In general, impacts are inversely proportional to recharge rates and hydraulic conductivity. Even under the most aggressive development scenarios, most of the demonstration areas withdraw less than 40 percent of the local recharge. However, simulated withdrawals in areas having clayey soils and low infiltration exceed 100 percent of natural recharge for lots smaller than 5 acres. For sustainable development these results demonstrate that analyses of geology, groundwater, and baseflow impacts should be a standard part of development planning.