The Silurian Aquifer provides potable water for many parts of Johnson County, Iowa, as well as other counties in eastern Iowa.

Final Version of Study

July 2026: Final U.S. Geological Survey (USGS) study released: Simulation of Groundwater Flow in the Silurian Aquifer, Eastern Iowa, 2020-45.

A layperson summary of the study will be added soon.

The USGS Publication Warehouse provides links to the final study in other formats and additional information (datasets, models, etc.).

Preliminary Study

The preliminary USGS Silurian Aquifer Study was presented and discussed at a Johnson County Board of Supervisors meeting held May, 14, 2025. Judith Coffman, groundwater and geophysics section chief for the USGS-Central Midwest Water Science Center, reviewed the findings and explained the model used to run predictions for the next 20 years. Coffman said the model indicates decreasing storage in the Silurian aquifer from 2020-2045. She added that limited availability of some data will continue to make it challenging to understand the aquifer conditions. The Board discussed how to address future water supplies in the county and its cities. 

Video of the May 14, 2025, aquifer study presentation and discussion begins at the 6 minute-mark.

Slides of the May 14, 2025, aquifer study presentation