SUSTAINABLE PUMPING FROM REGIONAL AQUIFERS: QUANTIFYING WATER USE

In the regionally confined aquifer system of southeastern Wisconsin, pumping has caused groundwater levels to decline by several hundred feet. Public debate centers on balancing groundwater pumping with use of surface water from the Great Lakes. In response, water resource managers are developing water supply and conservation plans based in part on our regional-scale, three dimensional groundwater flow model. In principle, the model is well-suited to evaluate sustainable use of groundwater resources, but uncertainty in pumping rates affects the model calibration and the quality of simulations of future conditions. Pumping rates can be measured more accurately than aquifer parameters, but Wisconsin has no requirement to meter or report any private (non-municipal) groundwater withdrawals.

Our study of pumping rates in urban and rural areas of Wisconsin illustrates the fundamental importance of withdrawals to the water budget of highly developed regional aquifers. Based on land use information, well records and a survey of well owners, we estimate pumping in an area with extensive suburban and urban development exceeds previous estimates by 25 percent. In a predominantly rural region, pumping likely exceeds previous estimates by up to 300 percent. Not surprisingly, estimates of withdrawals are more accurate in densely populated areas because a higher percentage of pumping is from metered municipal wells. Our survey of high-capacity well owners (response rate of 43 percent) indicates self-supplied water is a significant component of total pumping in both study regions, even though 68 percent of well owners report pumping less water than we had estimated from available records. This study demonstrates that relatively simple improvements in tracking water use will reduce uncertainty in pumping rates and improve simulations with the regional flow model.