DESC Overview Clause Samples

DESC Overview. The (DESC) model dynamically simulates fate and transport of chemical pollutants in surface water. DESC is capable of simulating water quality in a multiple watershed setting by routing flow from upstream to downstream while simulating the transformation of in-stream water quality constituents. The DESC model is composed of two major components: C simulation of pollutant transport and C simulation of selected chemical reactions using MINTEQ computational codes (EPA, 1991). The model includes advective and diffusive transport equations that are solved using a numerical solution of the explicit finite difference method. The chemical equilibrium solutions are solved using the ▇▇▇▇▇▇-Raphson approximation method to solve mass balance (linear) and mass action equations (nonlinear) as in MINTEQ. The model can simulate various chemical reactions as long as thermodynamic data is available to the model. The MINTEQ database contains information for more than 5,000 chemical reactions. If a targeted chemical reaction is not available in the database, it can be added by the user. For the pollutant transport routine, the DESC utilizes time series or constant total chemical concentrations and flow and the physical characteristics of the stream as inputs. The transport routine assumes one-dimensional trapezoidal stream cross-sections with in-stream concentrations equally distributed throughout each segment. Time series average depth data from the watershed model is used to estimate time series flow. The model fully connects all chemical reactions with the transport routine and pollutants are routed from upstream to downstream allowing for loading inputs from landuses. The model supports all major chemical reactions and some kinetic reactions that need to be considered in the mining-affected stream. Examples of these reactions include: C Adsorption of metals onto iron oxide included on the surface of clay or other soil particles C Adsorption of metals onto aluminum oxide C Saturation calculations with dissolved and precipitated conditions within the water column and sediment C Kinetic photo iron reduction C Microbial iron oxidation C Homogeneous oxidation processes