275-1 Long Term Monitoring of Groundwater Quality and Levels during and after the Transition from Agriculture to Solar in Central Wisconsin

Session: Advancing the Understanding and Management of Groundwater Pollution with Arsenic and Other Geogenic Contaminants Using Geospatial Tools, Machine Learning, and Data Science, Part II

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Abstract:

Changes in land use from agricultural to solar fields often come with questions and concerns about groundwater quality.  As a relatively new land use, implications of this change to solar are unknown, causing the local communities both concern and hope about the transition.  For example, while groundwater quality might be expected to improve as nitrate and pesticide use decreases, the timing needed to see that improvement is uncertain.  There is also a concern about potential contaminants, e.g. metals, leaching from the solar fields and associated storage batteries.  

This transition from agriculture to solar is occurring in central Wisconsin.  This region grows potatoes, vegetables, and corn with groundwater supplying crop irrigation and most homes with their water needs.  The aquifer is composed of sandy outwash and lake plain sediment with an approximate thickness of 80 feet located on top of crystalline bedrock.  In this region, a solar field with an area of 4 square miles (10.4 square kilometers) is currently under construction. In consultation with the Town of Plover and Portage County, we installed three well nests around the solar field, one upgradient and two downgradient.  Each well nest consisted of three wells, one screened across the water table, one screened across the middle of the aquifer, and the third screened just above the crystalline bedrock. Prior to construction, we sampled the wells and a stream for nitrate, common ions, and a suite of metals.  The sampling showed many of the wells have nitrate (NO₃-N) concentrations over 10 mg/l and metals concentrations reflecting the minerology of the sandy aquifer.

These background data will allow us to identify changes and set a baseline for the water quality before the construction and operation of the solar farm and battery storage. In addition, Portage County and the Wisconsin Department of Agriculture, Trade, and Consumer Protection plan to continue sampling for the next decade and beyond to provide a long-term record of the changes in water quality. The long-term plan will include nitrate, common ions, metals, and pesticides. This long-term study will provide data that indicates how this land use change affects groundwater quality in Wisconsin and could be a model in areas where similar transitions are occurring.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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