In the heart of downtown Dayton, a network of innovative open loop geothermal systems quietly works to cool 35 buildings and facilities. These systems pump groundwater from wells into heat exchangers, providing an energy-efficient way to cool buildings before discharging the water into the stormwater sewer system. This water eventually flows into the Great Miami River, contributing to the river's base flow during dry weather.
While these systems have been lauded for their energy efficiency, especially since they gained popularity over the last two decades due to clean energy incentives, their impact on the region’s aquifer is becoming a growing concern.
How Much Water Are We Talking About?
City of Dayton stormwater permit records reveal that during peak cooling periods, the combined pumping from these systems exceeds 40 million gallons of groundwater per day. To put that into perspective, Dayton’s public water system—the largest user of groundwater in the Great Miami River Watershed—supplies around 60 to 65 million gallons of water per day. This means that during the hottest parts of the year, downtown's geothermal systems alone account for about two-thirds of the city’s total daily water usage!
What’s Happening to the Aquifer?
The Buried Valley Aquifer system beneath Dayton is a critical resource, not only for drinking water but also for cooling systems and river health. However, data from observation wells maintained by the Miami Conservancy District (MCD), U.S. Geological Survey (USGS), and the Ohio Department of Natural Resources (ODNR) show troubling trends.
Groundwater levels in some downtown areas have dropped significantly over the past 15 years. Observation wells MT-6 and MT-426, which have records dating back to the 1940s, reveal a steady decline in annual low groundwater levels, typically recorded in September or October, after the summer cooling season.
Why Should We Care?
If groundwater levels continue to decline, some geothermal wells may eventually run dry during peak cooling seasons. A dry well would mean the associated building's cooling system could fail, potentially forcing occupant relocation during extreme heat—a costly and disruptive scenario.
Preventing this outcome requires proactive management. The goal? To ensure that the Buried Valley Aquifer can continue to support both human and environmental needs for years to come.
A Three-Pronged Approach: Monitor, Model, and Manage
By embracing this monitor, model, and manage strategy, Dayton can continue to enjoy the benefits of clean energy geothermal systems without compromising its most vital natural resource. The Buried Valley Aquifer is not just a cooling mechanism or a water source—it’s a lifeline for the city and the entire Great Miami River Watershed.
Proactive stewardship today will ensure its health and sustainability for future generations.
