Principals of Isotope Geochemistry and Applications to Groundwater Investigations

摘要

Isotope geochemistry has emerged as a formidable geochemical tool in groundwater investigations for coal combustion residuals (CCR). Specifically, isotopic 'fingerprinting' of dissolved metals such as boron (δ11B), lithium (δ7Li), and strontium (87Sr/86Sr), or of the water molecules themselves (i.e., δ2H, δ18O, or tritium), serves as a proxy for common contaminants of concern and provides powerful insights into several important topics, including (1) identification of alternate sources of contamination, (2) plume delineation, (3) contaminant migration over time, (4) site assessment, (5) attenuation predications, and (6) seepage rates. As water flows through a matrix (e.g., coal ash, soil, or rock), metals leach from particle surfaces and dissolve into the water. As a result, the water acquires the same diagnostic isotopic composition as the matrix that it flowed through or interacted with, regardless of the concentration, pH, or redox potential. Furthermore, inputs of less than 1% from a given source are often discernable using isotopic fingerprinting. A distinct advantage of using hydrogen and oxygen isotopes of water is that these isotopes are a property of the water itself and not subject to adsorption or retardation. Isotopes of the water molecule are sensitive indicators of both physical and chemical changes in water. This information can be used to evaluate groundwater age, flow paths, and relative proportions of groundwater, precipitation, and surface water in a groundwater sample.