Modeling Aquifer Inhomogeneities With Analytic Elements With Application In A Model of Flow At The St. Croix Rest Area Storm Runoff Pond

The design for Interstate Highway 94, east of St. Paul, Minnesota included a dead-end storm water retention pond constructed by the Minnesota Department of Transportation (Mn/DOT), for the purpose of collecting highway runoff. Flow into the pond will discharge primarily through the pond bottom into the groundwater system. Concern for potential impacts to both local and regional groundwater levels prompted Mn/DOT to conduct a groundwater study using an analytical element computer model.

Presented in this report is a summary of the analytical aquifer modeling method, including basic theory, fundamental equations, and a brief description of how to access the computer program. As part of the study, an analytical element was developed to permit modeling of inhomogeneities in the aquifer hydraulic conductivity, thickness, and/or base elevation. Basic theory and equations for this element are discussed in the report.

Use of the model for the storm retention pond is described including hydrogeology, site description, and simplifying assumptions used in the model. Results of the model are presented, including contour plots of groundwater levels prior to construction of the retention pond, as well as predicted levels when the pond reaches a steady state.