FINDING THE CONNECTION BETWEEN A TROUT STREAM AND A QUARRY WELL USING BOREHOLE GEOPHYSICS

Science plays an important role in defining and helping resolve societal conflicts over groundwater. When a pumping well in a quarry dewatered a nearby trout stream in Vernon County, Wisconsin, borehole geophysics and hydrogeology provided the information and framework needed for a solution that protected the stream and, at the same time, yielded enough water for the quarry operations. Use and acceptance of the science, communication, and cooperation among the quarry operator, the Wisconsin Department of Natural Resources, and the Wisconsin Geological and Natural History Survey were keys to a successful resolution.

In 2004, an existing quarry well was deepened from 350 feet to 550 feet to provide additional capacity for the quarry. This change in the well construction corresponded with a dewatering of the Class I trout stream and loss of spawning habitat while the pump was in operation. The well construction met Wisconsin code and the quarry operators were within their legal right to pump the well. It was clear that the stream and well were connected, but a workable, acceptable solution was unclear.

Borehole geophysics provided the data necessary to understand the connection between the stream and the well. Geophysical logs, including gamma, normal resistivity, caliper, spinner flowmeter, and fluid temperature and resistivity, were collected. The logs identified a large fracture at the same elevation as the trout stream headwaters. Groundwater entered the well through this fracture and flowed downward across an aquitard into an underlying sandstone aquifer at 90 gallons per minute. When the well was pumped, the flow rate from the fracture increased and the trout stream ceased to flow at its headwaters. With the problem clearly defined, the quarry operator was able to case the well across the fracture and below the aquitard to cut the connection between the well and the trout stream. This resulted in sufficient well capacity for quarry operations and increased flows to the trout stream, a successful outcome for all.