Changes in groundwater levels?

By Mike Ekberg, Manager for Water Resources Monitoring and Analysis

Groundwater levels in the aquifer beneath downtown Dayton fluctuate throughout the year. Locally, groundwater levels often peak in winter or spring and decline to their annual low in the fall. However, we’re seeing changes to the normal up-and-down cycle of groundwater in the aquifer in a couple of downtown wells.

Graphic of depth to groundwater

Groundwater levels fluctuate throughout the year. But the annual low groundwater level at the Apple Street and South Main Street observation well shows a decline over the past 25 years.

The annual low groundwater levels in two downtown observation wells are showing a distinct downward trend, declining as much as 25 feet over the past 10 years. In fact, recent groundwater levels at both wells tend to be below monthly normals for much of the year. What’s causing the drop?

Geothermal systems may be the reason
An increase in geothermal heating and cooling systems in Dayton may be the cause. In the last 15 years or so, several buildings in downtown Dayton installed open loop geothermal systems. Open loop systems pull groundwater from high-capacity wells —tied to the aquifer beneath Dayton—to create heat and air conditioning.

If too many geothermal systems draw water from the same area, that could cause a significant drop in average groundwater levels. That’s happening now in these two wells in downtown Dayton. And yet, these wells—and the Dayton area–still have plenty of groundwater

Water supply safe
Is the aquifer going to go dry? Not likely. The buried valley aquifer, which stores this region’s groundwater, holds 1.5 trillion gallons of water. That said, in areas where a lot of groundwater is pulled from the aquifer, it’s possible for one well to cause another well to go dry. This situation is most likely to occur during summer months when water demand for cooling systems peak.

MCD tracks groundwater levels at more than 100 monitoring wells in the region. The City of Dayton tracks groundwater levels at more than 300 monitoring wells throughout its well fields and within the aquifer. City officials say their well field areas are not impacted by the pumping of groundwater downtown.

Can geothermal systems continue to be a workable option for Dayton buildings? Yes, provided there’s a plan to balance the number of systems and well locations.

Better water planning prevents problems
Steps to ensure this balance include:

  1. Inventory high-capacity geothermal wells in the downtown area.
  2. Fully understand current groundwater levels throughout the area.
  3. Assess the potential impact of new geothermal wells on existing wells and storm sewers.
  4. Site wells strategically.

With these steps, Dayton—and other cities—can ensure existing geothermal systems will not be harmed by adding new systems, and all the systems will be sustainable.

 

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