Preferential Flow Paths in Heterogeneous Glacially-Deposited Aquitards

Preferential flow paths allow for faster movement of fluids than the surrounding matrix due to their hydraulic properties and connectivity. These paths are important to both groundwater flow and contaminant transport, but are difficult to detect and quantify. The main contribution of this research will be to determine the nature of preferential flow paths in heterogeneous glacially-deposited aquitards and how they affect groundwater flow and transport. This is significant as previous studies in glacially-deposited aquitards have focused on flow through the aquitard, but not considered flow within the aquitard. Flow paths will be delineated using multiple-point geostatistics. This geostatistical method uses a training image, instead of a variogram, to represent the general features of the subsurface. A training image maintains geologic structure and connectivity, features not easily captured by the traditional variogram method. A combination of well log data, geophysics, drilling, and measurements of hydraulic conductivity will be used to create and compare a variogram model and numerous three-dimensional hydrostratigraphic models of a representative site using multiple-point geostatistics. These models will be imported into groundwater flow and transport models to quantify and assess the connectivity of preferred paths in the flow system. The representative site is located in Outagamie County, Wisconsin, where a bedrock valley has been filled with a thick sequence of low conductivity sediment that occasionally contains sand lenses of unknown extent and continuity. These sand lenses provide water for many private wells and may provide recharge to bedrock aquifers used by municipalities. An additional research objective is to demonstrate the use of multipoint geostatistics, to determine whether or not our flow and transport models can benefit from this technique. A secondary and applied goal is to better understand the flow system in Outagamie County, which will be useful to both the municipal and private well owners.