Salem Creek Dye Traces: Dodge/Olmstead (sic) Counties, Minnesota October 8, 2004

Abstract

This dye trace study of the highly Karst Salem Creek Valley on the border of Dodge and Olmstead County in southeastern Minnesota was done to classify surface/near-surface connectivity along with a specific case study of a contaminated drinking well within the study area. The study deals with speeds and trends of subsurface flow, conduit flow, and how this flow can contaminate ground water aquifers on the order of hours if the water is given a flow path through the aquitard such as a failed well. Four fluorescent dye traces were conducted along a five mile section of the creek using sulforhodamine B, fluorescein/uranine, erythrosine, and eosin. The dyes were introduced through sinkholes, a stream sink, and around a well collar. Water samples were collected from Salem Creek using both direct water samples and activated charcoal detectors. The samples were measured for fluorescence using a spectrofluorophotometer and analyzed using a peak fitting program to characterize the resulting curves. Breakthrough curves (where applicable) showed that groundwater flow between sinkholes and the Salem Creek on the order of meters/hour. The private drinking well was also contaminated in less than two hours by dye introduced in a sinkhole approximately 100 meters away. The results show extremely fast subsurface conduit flow between the sinkholes and Salem creek. Nutrients and bacteria from the surrounding agriculture fields and feed lots can reach Salem Creek quickly and efficiently. The contamination of the private well also shows how surface recharge waters can penetrate down 400 ft or more through a failed well to contaminate otherwise clean drinking water.