EFFECTS OF FRACTURES ON GROUNDWATER FLOW TODAY

Joints and fracture planes within crystalline bedrock controls groundwater flow in most of Central Wisconsin. Prior work conducted on three bore holes in the area around Pittsville, WI, has shown that interconnected fractures might control groundwater flow in that region. The data collected from those bore holes include (a), major and minor open joints or fractures, (b), partially open joints or fractures, (c), filled fractures or joints, (d), bedding, banding, or foliation planes, and (e), induced fractures. We are using the borehole data for this project. The goals of this project are to identify parent and daughter fractures, if present, determine how the dominant fracture orientation patterns might change with depth, and, find any lines of intersection which might create pathways for groundwater flow. We are also investigating regional stress directions based on the fracture orientation data in the study area.

We are analyzing fracture orientation data from the studied three bore holes using stereographic projections and gamma logs to investigate how the orientations of different types of fractures might have changed with depth, and also to determine whether the orientations of joints and fracture planes were influenced by pre-existing structures in any way. We are also using three-dimensional visualization tools within the ArcScene® software program to create a model of the fracture planes, and to identify existing fracture network patterns, if any. We are using the T-Tecto® software package to investigate regional stress directions.

Preliminary data shows that dominant fracture orientation patterns change with depth in each of the three bore holes, and that the changes in fracture orientation can roughly be correlated with presence of spikes on the borehole gamma log, possibly indicating that lithologic changes might have played a role in controlling fracture formation. Each of the three bore holes show unique fracture orientation patterns, and little or no similarity in how those orientations change with depth. Some of the fractures show evidence of past fluid flow in the form of veins. Since some of the fractures are not filled, this might indicate multiple episodes of fracture formation. Here we present our data, and discuss the implications in terms of present day groundwater flow.