The Ohio Department of Natural Resources, Division of Water is responsible for collecting, researching, interpreting and disseminating hydrologic and ground water resource information for the State of Ohio. One important component of this program is the characterization of Ohio’s ground water resources through monitoring and evaluating long-term trends and fluctuations in ground water levels throughout the state’s numerous aquifer systems.

Ground water level data are collected from a series of observation wells located throughout the state. Observations wells are drilled and constructed in the same way a water supply well is drilled and constructed; the only difference is that an observation well is used to keep track of water levels in an aquifer and is not used to provide a source of water. Additional information on Ohio’s network of ground water observation wells can be found at: www.dnr.state.oh.us/water/waterobs/default.asp.

Ground water data from each observation well are typically compiled over long periods of time and summarized on a chart called a hydrograph. The figure below is part of a hydrograph from an observation well in Harrison, Ohio.

Hydrographs diagram the fluctuation of ground water levels during a given period of time and provide a way of comparing levels from year to year. The most prominent feature on many hydrographs is the annual cycle, a fluctuation of ground water levels in response to variations in climatic conditions. Represented within the annual cycle are the aquifer recharge and discharge periods (A and B respectively on the figure above). Aquifer recharge (rising ground water levels) typically occurs in the late fall through early spring, a period when precipitation usually exceeds evaporation from soils and plants. Aquifer discharge (falling ground water levels) usually occurs in the summer and early fall when the demand for water from growing plants, and evaporation from soils are both high.

The Division of Water has many observation wells located near municipal well fields and mining operations. With proper interpretation, data from these wells can be used to identify the availability of ground water locally within an aquifer, potential overuse of the resource, and other aquifer related technical information.

Water supply managers, ground water consultants, well drillers, planning agencies and many others use observation well data to answer questions about local groundwater resources. Since 42 percent of Ohioans depend on ground water for their drinking water, and about 85 percent of the public water supply systems rely on ground water as their water source, it is important to continue monitoring our aquifers with observation wells.