THE RELATIONSHIP BETWEEN LAND USE, GROUND WATER FLOW AND NON-POINT SOURCE CONTAMINATION IN THE UPPER MAD RIVER WATERSHED

The Mad River is an exceptional cold water habitat stream that overlies an extensive outwash-filled buried valley. Located in west-central Ohio, the Mad River has the highest base-flow of any stream in Ohio. The strong ground water surface water interaction in this highly agricultural area has led to extensive nitrate contamination in the outwash aquifer. Urbana, the county seat of Champaign County, has had well documented nitrate problems in their north well field. The City of Urbana has experienced steadily increasing nitrate levels in their north well field. These increases have forced the city to publish nitrate level alerts and ultimately remove the well field from service. The Division of Water is working on a 2 ½ year study to look into the nitrate contamination in the capture zone for Urbana's north well field.

This project is using a multi-faceted approach to identify critical regions that may contribute disproportionately large quantities of nitrate to the ground water flow system. Synoptic water level measurements have been taken on a quarterly basis to construct detailed potentiometric surface maps. Nitrate sampling along and near flow-paths are being used to define the nitrate plume. Geographic Information Systems are being used to categorize land use and define crop rotations. Stable isotopes (15N and 18O) are being used to define the source of the nitrate. The enriched portion of the nitrogen isotope of Nitrate (NO3) will indicate the source of the nitrate. Potential sources of the nitrogen are from the atmosphere, human and animal waste, or synthetic fertilizer.

During July, 2005, the Division of Water and Ohio EPA Division of Drinking and Ground Water (Ohio EPA DDAGW) personnel worked together on the installation and sampling of 2 multi-port monitoring wells. Each well has a total of 6 screened sampling ports set at predetermined intervals. Water quality data was collected by Ohio EPA DDAGW from the 12 ports and additionally 9 wells selected from our quarterly data set. These samples were analyzed for major cations, anions, nutrients, metals, Volatile Organic Carbons (VOC) and herbicides.

A ground water flow model is being constructed using USGS Modflow and Modpath (3-D finite difference model) to refine and confirm the flow paths and nitrate source areas defined by the other methods used in this study.