Breakthrough Curve Separation Using Applied Solute Tracers

The separation of advection and dispersion from the breakthrough curve of a potentially reactive solute can help determine if reactive transport mechanisms occurred. This is typically done by solving the advection–dispersion equation and fitting the breakthrough curve of an applied non-reactive solute tracer by adjusting groundwater velocity and the dispersion coefficient; the values of velocity and dispersion are then applied to the breakthrough curve of the potentially reactive solute, and any residuals can be fitted with the appropriate reactive transport mechanisms. A simpler approach is to plot the dimensionless relative concentrations of the non-reactive and reactive solutes on the same breakthrough curves; thus, any differences between the two curves can be attributed to reactive transport. The method proposed here can allow for separating advection and dispersion from the breakthrough curve of a potentially reactive solute based on data only, as opposed to model-derived fitting of groundwater velocity and dispersion, all while preserving the true concentration, as opposed to the dimensionless relative concentration, of the potentially reactive solute. A new measure of overall solute reactivity is also introduced that summates relative temporal moments to quantify and rank the reactivity of a suite of solutes. The method is described and applied to numerical model simulations and field tracer data to demonstrate its utility for combined visual–quantitative breakthrough curve separation to better characterize reactive solute transport in applied tracer studies.