Temporal Dynamics of NAPL Source Zone Strength: Relationship between Groundwater Flux and Contaminant Mass Discharge

Abstract:

Use of contaminant mass discharge (CMD) or mass-flux measurements to characterize site conditions and assess remediation performance of nonaqueous phase liquid (NAPL) is becoming popular. The main objective of this study is to determine how groundwater flux variations in the source zone can affect NAPL dissolution dynamics. In particular, we develop interplays among groundwater flux variations, NAPL aqueous concentration, NAPL CMD and other source strength dynamics. The developed analytical models can capture a wide range of NAPL source zone dynamics encountered in real-world applications. The results demonstrate the significance of groundwater flux variations in influencing the NAPL source dynamics. If groundwater flux decreases with time, the CMD declines initially at higher rate but the rate decreases at later stages. On the other hand, when groundwater flux increases with time, the NAPL CMD exhibits a slower decline initially and faster decrease at later stage. When groundwater flux in the source zone increases with time, the reduction in CMD (CMDR) increases slower than the NAPL mass reduction (MR), leading to a concave downward CMDR versus MR curve. If groundwater flux decreases with time, the CMDR versus MR curve is convex upward. When the groundwater flux does not change with time, CMDR versus MR follows a 1:1 linear relationship.