Hydrogeological modeling constraints provided by geophysical and geochemical mapping of a chlorinated ethenes plume in northern FranceContraintes pour la modélisation hydrogéologique fournies par une cartographie géophysique et géochimique d’un panache d’éthènes chlorés dans le Nord de la FranceLimitaciones del modelado hidrogeológico provistas por el mapeo geofísico y geoquímico de una pluma de etenos clorados en el norte de Francia法国北部氯化乙烯污染羽地球物理和地球化学填图中的水文地质模拟限制条件Limitações da modelação hidrogeológica obtida por mapeamento geofísico e geoquímico duma pluma de eteno-clorados no norte de França

A methodological approach is described which combines geophysical and geochemical data to delineate the extent of a chlorinated ethenes plume in northern France; the methodology was used to calibrate a hydrogeological model of the contaminants’ migration and degradation. The existence of strong reducing conditions in some parts of the aquifer is first determined by measuring in situ the redox potential and dissolved oxygen, dissolved ferrous iron and chloride concentrations. Electrical resistivity imaging and electromagnetic mapping, using the Slingram method, are then used to determine the shape of the pollutant plume. A decreasing empirical exponential relation between measured chloride concentrations in the water and aquifer electrical resistivity is observed; the resistivity formation factor calculated at a few points also shows a major contribution of chloride concentration in the resistivity of the saturated porous medium. MODFLOW software and MT3D99 first-order parent–daughter chain reaction and the RT3D aerobic–anaerobic model for tetrachloroethene (PCE)/trichloroethene (TCE) dechlorination are finally used for a first attempt at modeling the degradation of the chlorinated ethenes. After calibration, the distribution of the chlorinated ethenes and their degradation products simulated with the model approximately reflects the mean measured values in the observation wells, confirming the data-derived image of the plume.