SILICATE REACTION KINETICS IN THE PAJARITO PLATEAU, NEW MEXICO

Reactions and reaction rates within aquifers are fundamental components of critical hydrological processes. However, reactions simulated in laboratory experiments typically demonstrate rates that are much slower than those observed in the field. For this reason, it is necessary to conduct more reaction rate analyses in natural settings. Here, we present a preliminary study of geochemical reactions in the regional aquifer in the Pajarito Plateau near Los Alamos in northern New Mexico. Groundwater geochemistry shows marked evolution along flow paths, which we attribute to precipitation, dissolution, and ion exchange reactions. We particularly studied one flow path, and performed preliminary inverse mass balance modeling and calculated the mass transfer along segments of the flow path. Preliminary X-ray diffraction and Field Emission Gun Scanning Electron Microscopy of drill cuttings and outcrop samples were used to identify possible reactants and products. SEM data show that sediment grains are commonly covered with a coat of clay minerals about 5-8 microns thick. Our initial interpretations can be further refined by considering the mineralogy of the aquifer and saturation indices for the regional water properties. This study combines modeling with petrographic assessment to further knowledge and understanding of complex natural hydrologic systems.