1a.Objectives (from AD-416):
Update the existing pesticide theoretical mathematics sub-module in SWAT for application to emerging contaminants. Specifically, (1) update the soil surface model, and (2) establish the foundation for developing a dynamic "air box" compartment to connect soil-surface processes to the atmospheric boundary layer as appropriate for emerging contaminants.
1b.Approach (from AD-416):
The Soil and Water Assessment Tool currently does not model the transport and fate of emerging contaminants, although it does model pesticides. Therefore, the Lavoisier mass balance (MB) approach for a single emerging contaminant will be used to provide the first principle approach. Each system to which the MB is applied will be carefully defined and will consider three phases in soil: solid particles, water, and soil gas. The three-layer soil structure presently in SWAT likely will be retained. Processes occurring within the individual micro-phases will reflect reaction, transport (diffusive and advection), and partitioning. Continuity of flux at interface concept will be used to connect transport between adjoining phases. Literature search on the latest mechanisms will be used to update process rate equations for reaction, transport, and partitioning.
A conceptual model of the fate of organic emerging contaminants, such as hormones and antibiotics, was developed. The model is similar to the pesticide model currently in SWAT (Soil and Water Assessment Tool). Soils with varying texture, organic matter, and pH were assembled to determine Kd (soil adsorption coefficient) and half-life (a degradation parameter) for several groups of emerging contaminants.