DEVELOPMENT OF GEOCHEMICAL SENSORS FOR THE DETECTION OF CARBON DIOXIDE IN GROUNDWATER

The injection and storage of anthropogenic carbon dioxide in deep geologic formations is being tested globally as a potential strategy to reduce elevated atmospheric carbon dioxide concentrations due to the use of fossil fuels. However, carbon dioxide buoyancy may lead to its migration away from a storage site and into the shallow subsurface and atmosphere if permeable pathways (such as well bores, fractures, or faults) are present. Subsurface pressure changes due to carbon dioxide injection may also cause brines to migrate out of storage formations and into other hydrologic units. The protection of groundwater quality, along with the development of groundwater-specific monitoring and mitigation tools, is necessary for the implementation of successful carbon dioxide storage. Previous work in our laboratory has shown that gel-immobilized redox- and pH-sensitive mineral species can be used to evaluate geochemical conditions in sediment porewaters and in the waters of flooded bituminous coal mines. In this study, we used the geochemical model MINTEQA2 to evaluate a wide variety of potential indicator compounds that would be expected to demonstrate increased solubility in groundwater upon the addition of carbon dioxide. The most promising of these compounds included a wide variety of metal oxides and carbonates. These were prepared and tested under controlled laboratory conditions simulating carbon dioxide-impacted brine and groundwater. A prototype field sensor based on the spectrophotometric analysis of gel-immobilized compounds in a multiwell plate format is presented.