Application of remote sensing and GIS techniques for environmental geologic investigation, northeast Iowa

Northeast Iowa, where many localities of shallow groundwater contamination are known to occur, was selected for investigation of remote sensing and geographical information system techniques to address environmental geologic questions. The questions include: What is the spatial correlation among the structural factors, bedrock lithology, and sinkholes? How can the susceptibility to groundwater contamination of the study area be categorized? What is the spatial relationship between drainage network and sinkholes?; Landsat multispectral scanner and thematic mapper imagery proved to be useful in defining and delineating regional landforms, drainage basins, and lithological units based on the tones/colors, textures, drainage patterns, and topographic expressions. Digital image processing of the MSS and TM imagery provided a method for enhancing their spectral signatures. Spatial filtering techniques were especially useful for enhancing the subtle signatures of structural lineaments, which are difficult to delineate through conventional field investigations because of soil and glacial drift cover over the bedrock. Interpretation of enhanced imagery allowed better delineation of the lithological units and structural lineaments than the preliminary interpretation.; In analyzing and interpreting the Precambrian basement structural features, statistical transformation of gravity and aeromagnetic data provided an important method for removing local isolated anomalies and delineating regional high anomaly gradient trends. The latter can be related to the basement lineaments.; Computer-assisted geographical information system (GIS) was used for manipulation and integration of the geological, remote sensing, and geophysical data in this investigation. The result of the GIS analysis quantitatively verified that areas of high sinkhole density are located in areas of high lineament density and Ordovician carbonate bedrock where the Quaternary sediment cover is thin or absent. The relative susceptibility to groundwater contamination in the study area was classified into 6 classes, based on the quantitative relationship of these geologic factors. In order to reveal the correlation between drainage network and sinkholes, multiple buffering and overlay operations were performed. The result indicated that more sinkholes occur near streams of group level 3.; Through this study, it is concluded that the combination of remote sensing and GIS techniques provided a comprehensive approach for integrating environmental information.