Impact of Best Management Practices on Surface Runoff and Ground Water Quality in a Solutioned Limestone Area, Thompson Township, Seneca County, Ohio. March 1994.


In March 1990, the Seneca SWCD District Cooperative Extension Service, Seneca County Board of Health, and the Ohio Farm Bureau sponsored a county-wide well water testing program in Thompson Township. There were 87 residents of Thompson Township who voluntarily paid to have their wells tested for nitrates and 85 residents paid to have a bacteria test performed by the Seneca County Health Department. The samples were analyzed by the Heidelberg Water Quality Lab, primarily for nitrates, and Aqua Tech of Melmore for bacteria.

The average nitrate level for Thompson Township was 3.8 milligrams/liter (mg/1) compared to 1.67 mg/1 average for the county. Eleven of these wells (12.6%) exceeded the safe drinking water standard of 10 mg/1. The highest nitrate concentration was 16.9 mg/1. Twenty wells had 0 - 0.3 mg/1 nitrates, 31 wells had 0.3 - 3.0 mg/1, and 25 wells had 3.0 - 10 mg/1 nitrates.

Of the 85 bacteria samples taken, 30 (35.3%) were bacteriological unsafe. The acceptable safe water limits are less than 4 ppm for coliform bacteria.

High bacteria and nitrate concentrations have been found in a large percentage of the wells in the area, creating the need for a sewage system moratorium. This moratorium does not allow present landowners to build homes in the area, unless the septic system perimeter tiles can outlet directly into an open flowing stream. Many Thompson Township residents are concerned, and wonder what needs to be done to lift the moratorium and allow the present residents to have clean usable well water.

The main cause for the poor water quality is the more than 250 sinkholes that are mapped throughout the township (SC, 1980). These sinkholes allow the direct recharge of the ground water supply by surface water. Faulty or substandard septic systems and runoff containing fertilizers and pesticides from adjacent agricultural fields drain into these sinkholes.

In order to improve both surface and ground water quality, the Seneca Soil and Water Conservation District, Ohio Department of Natural Resources - Division of Water, Soil Conservation Service, Seneca County Health Department and the University of Toledo have joined forces to implement a USEPA Section 319 grant focusing on the use of management measures in karst (solutioned) limestone areas.

The main goal of the project was to reduce non-point source pollutants affecting ground water quality in Thompson Township. Objectives to meet this goal were:

  • Initiate a water quality education program that reaches all residents of the study area and promotes NPS pollution control.
  • Determine the hydrogeology of the study area so that proper ground water sampling points can be determined.
  • Monitor and document water quality improvement as the result of project implementation.
  • Reduce sediment load and NPS pollutants flowing into sinkholes and entering the ground water system by promoting and installing management measures.