Field scale longitudinal dispersivities estimation in a karstic aquifer
To simulate contaminant advective transport it is required to provide dispersivity values to the models, values that are unknown in many cases. In this paper a methodology is presented to estimate longitudinal dispersivities at field scale, based on the monitoring of groundwater quality at an unconfined aquifer that is below a waste disposal site with no liners for groundwater protection, and by applying a one–dimensional advective transport model. Chloride was used as a tracer, which is known to be present in dump site leachates. As part of the results, an equation was obtained that relates longitudinal dispersivity against the observation scale for the unconfined karstic aquifer of Yucatan, México. Some scenarios were employed for the longitudinal dispersivity estimation and for the solute transport simulation. In this way, a sensitivity analysis was performed to calculate the longitudinal dispersivities by varying the hydraulic conductivity and the hydraulic gradient. As a simulation exercise, a sensitivity analysis was also carried out to calculate the travel time that a particle would require to reach a certain distance depending on the longitudinal dispersivity value.
Keywords: groundwater quality, water quality monitoring, advective transport models, longitudinal dispersivity, observation scale, tracers, karstic aquifer, sensitivity analysis, hydraulic conductivity, hydraulic gradient, solute transport simulation, modelling, waste disposal sites, leachate, Mexico, water pollution