Temporal Effects of Capture Zone Geometry in Fractured Rock

Capture zone delineation is a critical step toward sound wellhead protection plans ensuring groundwater safety where a community's sourcewater is groundwater. Well capture zone delineation is difficult where there is fractured rock in the subsurface, as the fractures transport the majority of the water and fracture location often includes substantial uncertainty. This study focuses on numerical modeling for a hand-pumped well, where the subsurface is fractured bedrock. Fracture density and fracture connectivity are critical to the transport of water in bedrock and are parameters of interest for this study. The geometry for five year, ten year, and infinite time capture zones was investigated. Results show that finite time period capture zones are most impacted by fracture density / connectivity and follow a discrete path along the fracture location. At infinite time scales, the low density capture zone geometry approaches a geometry characteristic of porous media.