Wisconsin's Role in Great Lakes Restoration - American Water ...

15. Preliminary Hydrogeologic Characterization Mink River Estuary – Water Chemistry
and Flow
Maureen A. Muldoon, Department of Geology, University of Wisconsin Oshkosh, Oshkosh,
WI, muldoon@uwosh.edu
Jack Borski, Department of Geology, University of Wisconsin Oshkosh, Oshkosh, WI,
borskj88@uwosh.edu
Kenneth R. Bradbury, Wisconsin Geological and Natural History Survey, Madison, WI,
krbradbu@wisc.edu
The Mink River Estuary, located in northeastern Door County, is one of the most pristine
freshwater estuaries in the country. Groundwater quantity and quality are critical to the health
of the estuary, but to date there has been little investigation of groundwater inputs to the
system. The objectives of this project are to 1) establish a groundwater monitoring network
around the estuary, 2) gather preliminary information on the groundwater system, and 3)
evaluate mixing between the Mink River and Lake Michigan.
During the summer of 2010 a survey of surface-water chemistry revealed a distinct mixing
pattern between groundwater discharging in discrete spring complexes and Lake Michigan
waters. Stream discharge measurements and in-stream mini-piezometers yielded mixed
results concerning groundwater/surface-water interactions. In the northwest arm of the Mink
River, both stream discharge and mini-piezometer data collected in May suggest that
groundwater discharges from discrete springs near the edges of the marsh but that the Mink
River does not gain flow along significant reaches. In contrast, mini-piezometers installed in
the northeast arm in August 2010 showed consistently upward hydraulic gradients. Heatpulse
flow logs from three bedrock monitoring wells indicate upward flow from fractures near
the base of the wells (~90 ft. depth) to fractures near the bedrock surface (~depth 20 - 40 ft.).
We are collecting continuous water-level measurements from both bedrock wells and stilling
wells in the estuary. Quarterly samples of both surface and groundwater were collected in
November and February.
41