3.1 Mass Loss Expressions for Individual or Multiple Concurrent Loss Routes

The processes that can cause contaminant mass (or activity) to be lost from the source zone are assumed to be first-order radioactive decay/degradation within the source zone and horizontal leaching of the contaminant from the source zone along with the flowing groundwater.  Hence, the overall instantaneous rate of change of contaminant mass in the source zone for contaminant i is given by



This section discusses the theory developed to describe the individual terms of the right-hand side of Equation 3.4.