Delineation of wellhead protection zones using analitical models and groundwater modelling Margarita aquifer, Cuba

Delineating capture zones plays an important role in the protection of drinking water wells. Analytical models can be used to delineate capture zones. However, because of the singularity and occasional inaccuracy of such methods, specially in the application to heterogeneous aquifers, their results are frequently uncertain. In such cases, groundwater flow modelling presents an alternative for the delineation of capture zones. In this paper, four analytical models and a groundwater model are compared to delineate traveltime-related capture areas of a well in the Margarita aquifer. The model presented here explicitly represents the capture zone desing problem using particle tracking analysis to determine flowpath trajectories and formalizes the desing procedures used by many government's agencies. Based on the case study, it is shown that numerical modelling provides more accurate protection zones than analytical models. The risk of delineation errors are discussed and the potential risks of over or under-protecting the well are presented. It appears that the analytical models do not accurately represents shallow, partially penetring wells, or heterogeneous and anisotropic sediments for the purposes of simulating contributing areas and traveltimes in complex groundwater systems. Particle tracking analysis can be used as an alternative to contaminant transport models in cases where they are not feasible due to budget constraints or the lack of chemical data.