An approach to validate groundwater contamination risk in rural mountainous catchments: the role of lateral groundwater flows.

Computer models dedicated to the validation of groundwater contamination risk in the rural environment, namely the risk of contamination by nitrate leachates from agriculture fertilizers, are frequently based on direct comparison of risky areas (e.g., cropland, pastures used for livestock production) and spatial distributions of contaminant (nitrate) plumes. These methods are fated to fail where lateral flows dominate in the landscape (mountainous catchments) displacing the nitrate plumes downhill and from the risky spots. In these cases, there is no connection between the spatial location of risky areas and nitrate plumes, unless the two locations can be linked by a contaminant transport model. The main purpose of this paper is therefore to introduce a method whereby spatio-temporal links can be demonstrated between risky areas (contaminant sources), actual nitrate plumes (contaminant sinks) and modeled nitrate distributions at specific groundwater travel times, thereby validating the risk assessment. The method assembles a couple of well known algorithms, namely the DRASTIC model [1,2] and the Processing Modflow software (https://www.simcore.com), but their combination as risk validation method is original and proved efficient in its initial application, the companion paper of Pacheco et al. [3].