Concentration variations of nonaqueous phase liquids (NAPLs) in the subsurface source zone

Abstract:

The dissolution of nonaqueous phase liquids (NAPLs) into groundwater is a highly complex process due to the heterogeneous subsurface hydrogeology and NAPL distribution. The objective of this study is to relate the temporal variations of groundwater flux in the NAPL source zone to the NAPL dissolution dynamics. The main idea is that the temporal variation of NAPL source zone groundwater flux is directly related to the source zone NAPL mass discharge into the aqueous phase. By incorporating this new idea, 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. In this study, we developed new models that could be used to predict the source zone strength. In illustrating the new model development, we use a functional form of NAPL source zone water flux with a range of rate change to accommodate a range of potential variations of water flux. These models simply predict how the NAPL source zone characteristics changes with time, which can be easily used in modeling subsequent fate and transport. The models developed have already taken in 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. Comparison with field data demonstrates that the models are capable of capturing source zone NAPL discharge dynamics estimated from field experiments.