County staff and Illinois State Water Survey researchers on Sept. 12 reported interim results of a shallow-groundwater sustainability study for Kane County, highlighting areas of stress in Mill Creek and concerns about local spikes in chloride concentrations tied to road salt.

A county staff presenter summarized base-flow modeling that compares historical predevelopment and recent conditions, saying Mill Creek shows the largest proportional decline in base flow and is the county watershed “most impacted” by shallow‑aquifer pumping. The presenter said other watersheds (for example, the Fox River) receive enough treated wastewater effluent that modeled base flow aligns better with measured base flow there.

Researchers and staff told the committee they input more than 500 chloride observations into the model, including 290 readings supplied by county communities. The model generally matches lower chloride readings but underestimates some observed peak chloride concentrations at individual wells — “we’re not getting good comparison between our modeling results and actual field data” at the high end, a staff presenter said. The committee heard that the primary source of chloride is road salt, with smaller contributions from water softeners and fertilizer.

Committee members asked whether the model’s projection to 2050 is reliable. Staff said the model shows many utilities that had added wells between 1990 and 2020 are not planning additional withdrawals through 2050; that stabilizes modeled base flow in most watersheds but does not erase existing localized stress. The modeling team is refining calibration to better reproduce observed chloride peaks and is installing additional monitoring wells in a phased, real‑time network.

Staff emphasized that calibration improvements and additional monitoring wells (phase 2 planned for Hampshire and Carpentersville areas) are the next steps; a final report is expected after the team’s November meeting with the committee. The presenter said the study’s goal is to identify sensitive shallow‑aquifer areas and inform chloride‑management practices such as targeted road‑salt best management practices in hotspots.

Why it matters: localized chloride peaks can degrade drinking water taste and corrode plumbing, and sustained shallow‑aquifer pumping can reduce base flow in streams, harming aquatic ecosystems. The committee requested maps of vulnerable areas and said it wants monitoring results and revised calibration before recommending countywide policy changes.