Project Number:
DNR-194
Funding Year:
2006
Contract Period:
Funding Source:
DNR
Investigator(s) and affiliations:
Abstract:
Groundwater in the Fox River valley, Wisconsin has been of significant interest for the past several decades due to concerns about groundwater availability in rapidly growing metropolitan areas such as Green Bay, Appleton, Menasha, and Oshkosh. The water used by many municipalities, industries, and private residents in the Fox River valley is pumped from carbonate and sandstone rocks known as the Cambrian–Ordovician aquifer system. These rocks lie on top of relatively impermeable Precambrian crystalline bedrock and dip eastward toward the Lake Michigan basin. Shale of the Maquoketa Formation, dolomite of the Sinnipee Group, and/or fine-grained glacial sediment cap the Cambrian– Ordovician aquifer system. Where present along the eastern margin of the Fox River valley, the Maquoketa shale and the Sinnipee dolomite act as aquitards, confining the aquifers below. Recharge to these aquifers is traditionally understood to occur west of the Maquoketa shale and Sinnipee dolomite subcrop. However, a thick sequence of fine-grained glacial sediment covers large parts of this area and may act as an additional regional aquitard. The presence of this unit might shift the areas of recharge farther to the west than is currently assumed.
Objectives
Given the importance of groundwater reserves in the Fox River valley, this study was aimed at understanding vertical groundwater flow through the fine-grained glacial deposits to deeper bedrock aquifers.
Methods
To characterize the sediment sequence, two boreholes were drilled to collect continuous core and install multilevel wells. Representative samples of the core were used to determine physical properties of the sediment, including hydraulic conductivity. To evaluate vertical groundwater flow across the sediment sequence, multilevel wells were installed in each borehole to determine the distribution of hydraulic head. Pore water was also extracted from core subsamples to evaluate its relative age using stable isotope of oxygen (δ18O) and hydrogen (δ2 H).