MnDOT Potentially Acid Generating (PAG) Rock Implementation Project: Report on the Digital Map

Abstract

Environmental concerns exist surrounding the exposure of potentially acid generating (PAG) minerals to water and air and the subsequent aqueous products of their chemical weathering on the Earth’s surface. Such concerns have the ability to impact completion of infrastructure projects such as road building. A guidance manual, specifically written for the Minnesota Department of Transportation (MnDOT) and based on a detailed understanding of the geology of Minnesota, would help direct informed project task planning when PAG rock is anticipated to be encountered on a highway project. To complete a guidance manual, MnDOT must identify the geologic environments and/or formations where PAG rock may be encountered within future MnDOT right of ways. This Natural Resources Research Institute (NRRI) technical report describes the method and outcome of a new geology-based digital derivative map that combines geospatial information and produces a series of rankings on the likelihood of encountering PAG minerals throughout MnDOT Districts #1 and #2 (Fig. 1). The final map has four underlying ranked (from 0-low to 5-high) PAG components: bedrock geology, mineral occurrences, lithologic boundaries, and depth to bedrock that have been intersected and combined digitally using the Geographic Information System (GIS) ArcGIS.