RECHARGE CHARACTERISTICS OF THE FRACTURED DOLOMITE AQUIFER IN NORTHEAST WISCONSIN: OBSERVATIONS, CONTROLS, AND IMPLICATIONS FOR AQUIFER VULNERABILITY

Understanding recharge processes is fundamental to protecting water quality in karst aquifers as recharge is the process by which contaminants move from the ground surface into the groundwater system. Historic studies of recharge to karst aquifers have usually measured variations in spring or seep discharge along with concurrent changes in water chemistry to gain an understanding of the recharge characteristics in an aquifer. In this talk, we use long-term records of water-level and chemical variations from several wells to determine recharge characteristics of the fractured-dolomite aquifer.

In northeastern Wisconsin, the fractured-dolomite aquifer has a long history of water-quality problems in areas with thin soil cover (< 20 feet). Using water-level and chemical data collected from several projects over the last two decades, we observe the following recharge characteristics for this aquifer. 1) Recharge varies seasonally and rarely occurs during the growing season. Rather recharge occurs within 1 to 2 days of snow melt events or significant (> 0.5-inch) rain events. 2) In some locations, recharge water can quickly penetrate 100's of feet into the saturated zone. 3) Water-level fluctuations alone are not good indicators of recharge reaching a well. 4) Monitoring fluid conductivity along with other chemical parameters provides a more complete understanding of recharge to wells and also a given well's vulnerability to contamination from near-surface sources.

Carbonate aquifers are an important, but vulnerable source of water supply in the eastern United States. While our data provide information on the timing and characteristics of recharge to the Silurian dolomite aquifer in NE Wisconsin, the methods used provide an inexpensive means of characterizing recharge and assessing a well's vulnerability to surface contamination in other carbonate aquifers.