QUALITATIVE GROUNDWATER TRACING IN A KARST AQUIFER, HIAWATHA NATIONAL FOREST, UPPER PENINSULA, 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 on the Forest to demonstrate that the technique worked there to prepare for future dye tracing efforts. Prior to dumping the dyes, charcoal packets were placed downstream of the expected resurgence locations to act as blanks and to ensure there was no dye already present. Approximately 2.5 weeks elapsed between dumping 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 the sinkhole. 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 of the 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 the sinkhole. 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 the dye tracing is effective in the area and serves as a bridge for future efforts in the area. The main future goals are to: conduct a more detailed and focused survey along the Carp River to check for where exactly the dye is coming from, and map all of the springs along it; and to conduct a qualitative trace in the Biscuit Sink / Spring system to begin determining rate of groundwater movement in the area.