To manage the potential risks to the Twin Port Interchange project budget and schedule, Braun Intertec, on behalf of the Construction Manager/General Contractor team, prepared a hydrogeologic model of groundwater for key construction features. Braun Intertec began the model by conducting a series of field groundwater pump tests. The first round used paired temporary pumping and sentinel wells in four proposed construction areas. The initial pump tests were followed by open test trench drawdown tests to mimic field construction conditions. The results of the field test provided a range of hydraulic conductivities for each tested feature. The features were correlated with geologic information to provide estimated hydraulic conductivities for various hydrogeologic settings.    

Each of the major proposed excavation areas were modeled using Theim and Hvorslev equations to simulate drawdown areas and groundwater pumping velocities. A geographic information systems (GIS) model was used to overlay the hydrologic information with the contaminant concentrations to provide a range of estimated groundwater contamination concentrations for each construction feature. The resulting information was used to size the groundwater treatment system, and in successful permit applications for discharge of contaminated water to the local POTW (WLSSD) and MPCA Industrial Groundwater Pump-out Permit to the St. Louis River Bay of Lake Superior.