MODELING SPATIAL DISTRIBUTION OF HYDROFACIES USING TRANSITION PROBABILITIES

A proper aquifer characterization is crucial in hydrogeology because heterogeneity and spatial variability are prevalent in natural formations. This is particularly important in solute transport by groundwater; solutes and contaminants tend to be transported along zones of high permeability, while lenses or layers of low permeability will retain contaminants and release them by diffusion. However, data scarcity prevents a detailed site characterization. In addition, hard data are difficult and expensive to collect. Soft data are sometimes more abundant but they are not easily related to quantitative representations. We outline an indicator geostatistical approach to model hydrofacies using lithologic records of water-wells applied to the hydrogeologic system in Mexico City. The lithologic categories are grouped into four hydrofacies: two hydrofacies in granular media (low and high permeability facies) and two hydrofacies in consolidated rocks (low and high permeability facies). The distribution of hydrofacies is modeled using a transition-probability indicator approach. Further work will include inverse modeling of pumping tests to assign hydraulic conductivity values to each hydrofacies.