Contribution to the evaluation of solute transport properties in a karstic aquifer (Yucatan, Mexico)

In the process of solute transport, dispersivity and hydrodynamic dispersion coefficients are important factors that define the distribution and migration of dissolved salts in the aquifer. Tracer tests were carried out in wells located in the northeast coast of Yucatan, Mexico, whereby only the freshwater thickness of the aquifer was analyzed. Sodium chloride (NaCl) was used as a tracer. Groundwater flow velocity was estimated with the Drost dilution point method. To analyse the solute transport, the analytical model for instantaneous injection was chosen, which is derived from the advection-dispersion equation, and the dispersivity and longitudinal dispersion coefficients were determined. The results indicate that the longitudinal dispersivity and hydrodynamic dispersion of the aquifer vary from 2.56 to 2,500 m and between 1 x 10(-3) and 1 x 10(-2) m(2)/s, respectively. In the areas of Telchac Puerto, Dzilam Bravo and San Felipe, advection is the most important solute transport mechanism, while El Cuyo has lower velocity ranges than other locations in the study area and salts tend to disperse. Groundwater flow velocity varies between 3.1 x 10(-7) and 8.65 x 10(-5) m/s, associated with the flow in the karstic aquifer matrix, with maximum values of 1.5 x 10(-4) m/s, associated with the karstification of the aquifer. Groundwater flow velocity increases towards the coast, which is consistent with the fact that the aquifer discharges to the sea. It is observed that in the first 10 m of aquifer, the velocities are higher than those determined in deeper layers, up to an order of magnitude.