Dilution dynamics of nonaqueous phase liquid (NAPL) source zone in subsurface

Abstract:

Characterizing and remediating nonaqueous phase liquids (NAPLs) in the subsurface represent grand challenges due to hydrogeologic complexity, uncertainties in NAPL distribution and dissolution, and associated high costs. The development of predictive models that can more accurately represent NAPL dissolution dynamics is desirable for evaluating source longevity, remediation efficiency and risk assessment. In this study, we develop a conceptual approach to relate NAPL dissolution to variations of groundwater flux in the NAPL source zone. The approach is based on the idea that the source zone NAPL mass discharge into the aqueous phase is directly related to the temporal variation of NAPL source zone groundwater flux. The NAPL source dynamics including source zone concentrations, reduction in the NAPL mass discharge to the aqueous phase, reduction in the NAPL mass in the source zone can be effectively related. We use power law and rational forms of NAPL source zone water flux to represent a range of potential variations of groundwater flux. The developed models can predict how NAPL source zone characteristics changes with time, which can be used in modeling subsequent fate and transport. The models developed have already taken into account the requirement of NAPL mass conservation. Based on the developed models, we discuss how NAPL source zone concentrations, NAPL mass discharge, and remaining NAPL mass in the source zone are inter-related.