Quarrying in limestone aquifers can interfere with groundwater flow paths. Quarries can pirate karst conduit flow by physically breaking into the conduits and changing the groundwater discharge points. Another mechanism of groundwater flow interference occurs as quarry dewatering lowers the water table changing groundwater flow directions. Dye tracing is an effective tool to evaluate and quantify these impacts. In Minnesota, tracing investigations have been conducted at two quarries. The Big Spring quarry near Harmony, Minnesota is in the Ordovician Galena Formation. The quarry is 500 meters from Big Spring, the headwater spring of Camp Creek, a Minnesota designated trout stream. Although the quarry is nominally above the water table, beginning about forty years ago, the quarry intercepted conduits carrying groundwater to the spring. Groundwater that formerly discharged from Big Spring now rises in the quarry then flows overland joining Camp Creek 100 meters downstream of Big Spring. About 90 percent of the mapped groundwater basin of Big Spring is now routed through the quarry. The Osmundson quarry is in the Devonian Lithograph City Formation at LeRoy, Minnesota. This sub-water table quarry requires seasonal dewatering at 1,000-3,000 liters/minute. When the quarry is being dewatered, Sweets Spring, approximately 300 meters to the southeast, stops flowing. Dye tracing has verified that the quarry pirates the flow to the spring. Both of these cases demonstrate the utility of using dye traces to determine the impact of limestone quarrying on groundwater flow paths. This information can be used to evaluate proposed quarry sites for their potential alterations of groundwater flow paths.
Funding for this research has been provided by the Legislative Commission on Minnesota Resources Environment and Natural Resources Trust Fund and by the Minnesota Department of Natural Resources-Division of Waters