IDENTIFICATION OF GROUNDWATER RECHARGE AREAS IN WAUKESHA COUNTY, WISCONSIN FOR REGIONAL AQUIFER PROTECTION

Rapid urban sprawl in Waukesha County, Wisconsin, is increasing demand for potable water, causing serious declines in the region's groundwater supply. The most serious depletions have occurred in areas of Menomonee Falls, Brookfield and Pewaukee which have lost between 150 and 200 feet in water elevation from the deep sandstone aquifer since 1975. The decline in water levels indicates that much of the water has been withdrawn from storage and will continue to decline unless groundwater withdrawals are decreased and recharge areas are maintained. Location of groundwater recharge areas is important in developing groundwater management strategies to protect these areas from the negative impacts land-use can have on recharge. A Geographic Information System (GIS) based comparative methodology for quantitatively delineating groundwater recharge areas was created. An empirical method was developed for delineating groundwater recharge areas. The method presented here enhances an infiltration model by including surface runoff, potential evapotranspiration, and the root-zone water capacity (RWC) as additional recharge factors. The general hypothesis is that the less likely water will be lost to evapotranspiration and surface run-off, the more likely the water will infiltrate given the correct soil conditions. The dataset requirements of large-scale soil and land-cover maps, along with precipitation and temperature data, are used to produce three preliminary maps (percolation, surface runoff, and root-zone water capacity). Preliminary maps are ranked (1-10) according to their ability to enhance (10) or reduce (1) recharge potential. The ranking scheme (1-10) is designed to adapt to any study area and any set of groundwater protection principles. Addition of the three preliminary maps resulted in a final groundwater recharge potential map. Zonations of recharge areas in the final map are presented in a weighted index map at the scale of 1:40,000 with the minimum mapping unit of 5 acres. The final groundwater recharge indexes can be used for resource protection, providing planners with a decision making tool regarding location, type, and extent of new developments.