Mapping the Base of the Cambrian Aquifer through Geophysical Modeling of Precambrian Topography, Southern Wisconsin

This project will address uncertainty in the topography and depth to the Precambrian basement that is the base of Wisconsin’s Cambrian sandstone aquifer. Basement topography exerts strong control on aquifer thickness, the volume of groundwater stored in the system, and the geometry of a “no-flow” boundary to the aquifer. Accurate interpretation of the aquifer thickness aids in accurately assessing effects of pumping on groundwater levels and surface water features, and it aids in accurate simulations of well-head protection areas. However, published maps of Precambrian basement topography are interpreted from sparse well data alone, and the restricted spatial distribution of this well data significantly limits accurate interpretation of the Precambrian surface elevation and structure. 3D modeling of gravity and aeromagnetic data integrated with well data allows improved estimation of the Precambrian basement topography relative to well data alone. We propose to estimate the topography of the Precambrian surface under south-central Wisconsin through 3D modeling of gravity and aeromagnetic data. Our project will leverage ongoing and completed geophysical modeling of the Precambrian topography of southern Wisconsin by incorporating and refining methods, insights, and conclusions derived from these prior and ongoing modeling efforts. Our findings will result in an internally consistent, geologically reasonable, 3D interpretation of Precambrian topography across an approximately 7,425 km2 area spanning three counties in south-central Wisconsin. Our results will be published in map format at a minimum 1:100,000 scale. Maps and accompanying report will be publicly available in PDF and GIS format. The published Precambrian topographic surface will provide constraint to modifications of existing and future groundwater flow models, thereby improving communities’ ability to plan wellhead protection, understand and respond to groundwater quality issues, and to better understand hydrologic resources and related issues of development and water use.