Ground water pollution sensitivity assessment

Geological Sensitivity Assessment of Groundwater Systems: A Pilot Study for Scott County, Minnesota

Summary and Evaluation

H. O. Pfannkuch
Department of Geology and Geophysics
University of Minnesota, 1998

Report prepared for the Minnesota Department of Natural Resources


Geologic Groundwater Sensitivity Assessments were carried out in a Pilot Study for Scott County, Minnesota, according to DNR Guidelines' Level-1, -2, and -3 specifications. The first objective was to carry out a complete assessment for the entire county as a feasibility study. The second objective was to develop and to test various modifications to the basic guideline methodology. For the Level-1 assessment a modified version (Case #2) involving readily available well information and a surficial geology map is sufficient to meet the needs for a preliminary assessment of a county planning agency and more consistent and useful than the original Level-1 assessment. A modified Level-2 assessment (Case #10) based on more restrictive assumptions, simplified well log analysis, and rapid Geographic Information System (GIS) based areal map interpretation methods gives an internally consistent and conservative result without requiring an excessive investment in preparation time and effort. The third objective was to validate the methodology in general and the modifications in particular. Four methods are used: (1) statistical frequency analysis of relating process based physical-hydrologic decision variables or chemical analyses as dependent variables to areal map distribution of rating classes; (2) checks for internal consistency by an inter-parameter method of correlating and comparing decision variables to percentage occurrence in the sensitivity rating classes; (3) cross-correlation of groundwater chemistry analyses to sensitivity ratings and tritium age classes; (4) inter-parameter cross comparison between relative occurrence of sensitivity rating classes and tritium ages. The validation was carried out on results from 409 well records. The four methods of checking and validating showed the geologic groundwater sensitivity assessment methodology to be reliable, rationally based, and internally consistent.

Pilot study report [PDF/1.5MB]

Report maps (color) [PDF/1.4MB]

Report maps (black and white) [PDF/1.2 MB]