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The FRAMES source-term release module includes models for estimating constituent loss from three different types of source zones: contaminated aquifer, contaminated pond/surface impoundment, and contaminated vadose zone. In all types of constituent source zones, it is assumed that the constituents may be present in multiple phases (i.e., in aqueous solution, sorbed to solid particles, in vapor-filled pore space, or in a separate non-aqueous-phase liquid [NAPL] that is immiscible with water and air). The source-term release module contains models to determine which constituents in the problem scenario will partition into which phases, and to what degree. Depending on the type of source zone, it is assumed that the processes causing constituent release from the source zone to an environmental transport pathway could be leaching (groundwater pathway), wind suspension (atmospheric pathway), water erosion (overland/surface water pathway), overland flow (overland/surface water pathway), and/or volatilization (atmospheric pathway). In addition, constituents could be lost from the source zone by radioactive decay or degradation within the zone. The source-term release module contains models for simulating "baseline" (i.e., unremediated) scenarios for all three types of source zones. These same models can be used to simulate remediated sites (for all three types of source zones) if the remediation methodology can be represented merely by changing the magnitude of certain model parameters from their "baseline" values. In addition, for the vadose zone source zone, the source-term release module contains models that can calculate loss fluxes from vadose zones subjected to two types of remediation methodologies that require special theory: in situ vitrification (ISV) and in situ solidification (ISS).

The ultimate objective of the source-term release component is to calculate a "mass-budgeted" set of constituent flux versus time functions that describe the simultaneous loss of constituents from the source zone to a number of different routes. When multiple loss processes are assumed to occur simultaneously, the mathematical models implemented in the source-term release module account for their synergistic or antagonistic interaction. "Mass-budgeted" means that the inventory of each constituent is apportioned to each loss route (by the implemented physics-based theory) in a manner such that the sum of the calculated constituent losses to all routes is limited to 100% of the initial inventory. The source-term release module has been developed to allow the user flexibility in how the constituent release to different routes is simulated. If the user wishes to explicitly enter the constituent flux to one or more loss routes (based on known or assumed data, or the predictions of some other model), the source-term release component will use the supplied flux versus time function(s) until mass balance considerations dictate that the flux must go to zero (because cumulative constituent mass loss to all routes has removed 100% of the initial inventory). If the user cannot or does not wish to supply explicit constituent fluxes to any or all loss routes, the source-term release component contains models that will calculate the flux verses time functions (also according to mass balance considerations). If the user wants to analyze a scenario that assumes constituent release to only a subset of the possible loss routes for a given type of source zone, loss to undesired routes can be "turned off" by specifying a known flux of zero to those routes.

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