Boone County officials hear 3‑D geologic mapping data to guide groundwater and stormwater planning

Dan Cain, the county’s geologic mapping presenter, told the Committee of the Whole on April 2 that new three-dimensional maps of Boone County show subsurface detail officials can use to make targeted stormwater and groundwater decisions. Cain said the mapping highlights the Troy bedrock valley, zones of sandy aquifer material and shale layers that act as aquitards, and that those features change how water infiltrates and recharges deeper aquifers.

“This data will tell us where very specifically we can take steps to be proactive in assessing our water supply and our groundwater needs,” Cain said during his slide presentation, which included cross-sections, ground-truth borings and seismic points. He told the committee the mapping resolves where recharge is likely and where stormwater practices can be most effective.

Cain outlined near-term steps: installing continuous data loggers in monitoring wells drilled last summer, using those records to measure recharge and water-table fluctuation, and funding a year‑two program to build three‑dimensional groundwater models. He said modeling and monitoring are needed to estimate sustainable withdrawal rates and to design stormwater controls that enhance infiltration where appropriate.

Board members pressed Cain on regional pressures. Several members cited large withdrawals in the Joliet area and asked whether data centers there are “sucking us dry.” Cain said the Joliet region has experienced deep aquifer drawdown and that gravity-driven flows can move water from surrounding areas. He emphasized the county cannot stop regional drawdown but can use local data to protect Boone County’s supply: prioritizing recharge areas, stronger stormwater infiltration in sensitive places and careful septic and development siting.

Members and staff discussed cooling strategies for large water users, including closed‑loop cooling and reuse of effluent rather than direct aquifer withdrawals. Cain and planning staff said the mapping will be integrated into the county’s stormwater management plan update and the stormwater technical committee’s monthly work.

Cain and staff stressed the study is the first step; funding and additional technical work will be required to convert the mapping into enforceable policies and to develop a predictive groundwater model. The committee did not take a formal vote on this study but requested staff follow-up on monitoring and funding options for the modeling phase.