G-box Model for the Fate of Emerging Contaminants in Soil

• Main Author: Cranfield, Eileen
• Other Authors: Thibodeaux, Louis
• Format: Others
• Language: en
• Published: LSU 2014
• Subjects: Chemical Engineering
• Online Access: http://etd.lsu.edu/docs/available/etd-04112014-151802/

Pesticides applied to agriculture fields move and react into the soil system. The objective of this research was to develop a model that uses the natural soil processes (diffusion, advection, or reaction type processes in multiple phases) to track pesticides and other emerging contaminants (EMCONs) in the soil over space and time. The model separates the soil into a series of boxes with soil processes passing through and into the boxes. With a system of equations developed from these processes, the model produces a gradient concentration profile, hence the Gradient Box, or G-box Model. The model is first tested against a series of simple, one dimension known analytical solutions. The fixed concentration and zero flux boundary conditions analytical solutions are both steady state solutions that use the processes of diffusion and degradation. The semi-infinite slab and the finite quantity surface layer application gradient analytical solutions are both unsteady state solutions with diffusion as its only process. A steady state simultaneous diffusion with an up then down advection processes completed the final case. Upon successful outcome comparing G-box to the simple solutions, the soil column model was compiled. Nineteen total flux processes were selected and used to build the model. This included the soil column portion and an interface connection to atmospheric inputs. The model then examines several individual processes in the soil, such as dry deposition, wet deposition, diffusion, wind and water erosion, bioturbation, infiltration, and lateral flow. This exercise evaluated these individual processes separately, demonstrating their realistic and intuitively correct behavior patterns. Altering the processes from day-to-day is also tested by using a periodic quantity pesticide application process. A simulated single pesticide application and a seven-day application cycle, with and without reaction, are used to test the model. These positive simulation results on the effect these numerous processes displayed on the concentration behavior of pesticide in the soil supported the validity of the model.