QUALITATIVE GROUNDWATER TRACING IN A KARST AQUIFER, HIAWATHA NATIONAL FOREST, UPPER PENINSULA OF MICHIGAN

Fluorescent dyes have been used to track groundwater movement in karst aquifers for a long time; however, this has never been done in the Eastern Unit of the Hiawatha National Forest, Upper Peninsula, Michigan. The underlying geology is Early Silurian dolostones, which host significant epikarst, namely grikes, alvar, sinkholes, and springs. No known solutional caves are in the forest, though there are many littoral caves associated with previous lake levels. Two qualitative dye traces were conducted in the forest to demonstrate that the technique worked there and to prepare for future dye tracing efforts. Prior to introducing the dyes, charcoal packets were placed downstream of the expected resurgence locations to act as blanks and to ensure that no dye was already present. Approximately 2.5 weeks elapsed between introducing the dye and collecting the charcoal packets.

The first dye trace was conducted at Petey's Sink, a sinkhole on the western edge of the forest. Two pounds of fluorescein, pre-dissolved in water, were added to the sinkhole and carried in with the water flowing into it. Charcoal packets were set out along the Carp River (approximately 750 meters away) to determine where the water was discharging. Dye was observed at two locations along the river.

The second dye trace was conducted at Biscuit Sink, a sinkhole near the Mackinac-Chippewa County line. Two pounds of eosine, pre-dissolved in water, were added to the sinkhole and carried in with the water flowing into it. A charcoal packet was set up in Biscuit Spring (approximately 400 meters away), and dye was observed there after the trace.

This work allows us to demonstrate that dye tracing is effective in the area and serves as a bridge for future efforts. The main future goals are to: 1) conduct a more detailed and focused survey along the Carp River to determine exactly where the dye is emerging and map all of the springs along it; and 2) conduct a qualitative trace in the Biscuit Sink/Spring system to begin determining the rate of groundwater movement in the area.