Carbonate Aquifer Recharge in Western Lucas County, Northwest Ohio

Because the carbonate aquifer in much of northwestern Ohio is the principal water resource, understanding the avenues of recharge and resulting pathways of solute transport are crucial to the assessment of water resource availability, water quality and contaminant transport. This study uses estimates of evapotranspiration, measurements of piezometric heads and calculations of groundwater fluxes to investigate carbonate aquifer recharge from a small basin within the carbonate aquifer recharge area 2 km south of Whitehouse, OH. Of the 0.240 m of soil moisture surplus, approximately 43% runs off by way of drain tiles, ditches, and streams leaving 0.135 m as potential recharge for the deeper carbonate aquifer. Direct recharge to the 2% of the carbonate aquifer that is covered by less than 2 m of overburden accounts for a small percentage of the total recharge. Large amounts of radial flow from this shallow bedrock area suggest contributions from sources other than direct recharge or shallow lateral flow. The only remaining possible source of excess recharge in the shallow bedrock area is recharge contributed by streams through vertical fracture zones. Even where the glacial till is thick and vertical permeability is low, large vertical gradients over large areas induce significant bedrock recharge. Because direct recharge is derived from soil moisture surplus and surface water contributions in the area of shallow bedrock, the aquifer is most susceptible to contamination from these sources during the wet seasons. Conversely, even though recharge through the glacial till is maintained throughout the year, threats of contamination due to this vertical recharge are diminished.