Hydrogeological Investigation of the Carbonate Bedrock Aquifer to Evaluate Impact High-Yielding Wells, Ottawa County, Ohio

A groundwater investigation of the carbonate bedrock aquifer was initiated in May 2011 by the ODNR Division of Soil and Water Resources at the request of local homeowners in Harris Township, Ottawa County, Ohio. The purpose of the investigation was to evaluate the impact of high-yielding irrigation wells on ground water levels in the nearby domestic water supply wells.

Previous work completed in this area confirms that the carbonate bedrock aquifer of northwestern Ohio contains a number of flow zones. The well completion diagram for the Luckey homestead farm well shows the extent to which the flow zones occur in the subsurface. Drilling data shows that the carbonate bedrock aquifer is anisotropic and heterogeneous in its configuration. This gives rise to a number of concerns that need to be considered before long-term pumping rates can be accurately calculated and the data used to design water supply systems.

Pumping test data shows that the transmissivity of the aquifer is not uniform throughout the aquifer. It can vary both in the vertical and horizontal directions, and may vary over short distances within the carbonate bedrock aquifer when there are significant variations in permeability as well as fracturing. This helps to explain major changes in yield over short distances in both the vertical and horizontal directions.

Field data obtained for this project shows that the pumping of the high-yielding water wells can have an impact on the local water supply wells. The degree of impact depends on the location of the water well relative to the pumping center and the pumping rate. It also depends on the flow zone from which the water well produces. A deeper high-yielding well can impact water supply wells completed in the upper flow zone in the carbonate bedrock aquifer.