Geologic Investigation for portions of the Twin Cities Metropolitan Area: I. Quaternary/Bedrock Hydraulic Conductivity, II. Groundwater Chemistry

This report summarizes work performed by the Minnesota Geological Survey (MGS) in partial fulfillment of work as described under contract 091037 between the University of Minnesota and the Metropolitan Council. The goal of this investigation was to provide datasets that would assist the Metropolitan Council with regional ground water planning. Specifically,hydraulic conductivity data for both unconsolidated and bedrock materials, along with historic ground water chemical and isotopic data were assembled into spatial databases that can be used in a geographic information systems (GIS) format. Wherever possible, depth of the sampled or tested material was included along with location information, so the three-dimensional distribution of these data could be queried and compared to ongoing Metropolitan Council planning projects. For hydraulic conductivity data, the focus was on glacial-related Quaternary deposits, because these are the data most lacking for current ground-water modeling investigations. Hydrostratigraphic attributes of fine-grained materials were evaluated based on a comparison of measured values with texture, depth, and a literature review of other midcontinent tills. For water chemistry, the goal was to display the distribution of chemical types (hydrochemical facies) as a means to illustrate possible ground-water flowpaths. A sample acquisition date was included so the database could also be used to assess changes in chemical composition with time. For both hydraulic conductivity data and water chemistry, attributes were also assigned to a regional dataset of regularly spaced grid points to facilitate importing the data into groundwater modeling programs.