PESTAN - pesticide transport model; transport of organic solutes through the vadose zone to ground water PESTAN Categories: flow models - unsaturated zone, solute transport models - unsaturated zone PESTAN DescriptionIntroduction to PESTAN PESTAN, Pesticide Transport, is a U.S. EPA program for evaluating the transport of organic solutes through the vadose zone to ground water. PESTAN uses an analytical solution to calculate organic movement based on a linear isotherm, first-order degradation and hydrodynamic dispersion. Input data includes water solubility, infiltration rate, bulk density, sorption constant, degradation rates, saturated water content, characteristic curve coefficient, saturated hydraulic conductivity and dispersion coefficient. PESTAN includes the source code, executable version, user's manual, and technical support. The PESTAN model is a computer code for estimating the transport of organic solutes through soil to ground water. The model is based on a closed-form analytical solution of the advective-dispersive-reactive transport equation. The model has been tested under field and laboratory conditions. PESTAN utilizes extended memory and is menu driven. The vertical transport of dissolved pollutants through the vadose zone is simulated in PESTAN as a "slug" of contaminated water that migrates into a homogeneous soil. The concentration of the chemical slug equals the solubility of the pollutant in water, and the thickness of the slug is conceptualized principally as the volume of pore water required to dissolve the total available pollutant mass at the solubility of the pollutant. The total available mass is defined as that mass existing at the time of recharge. When no lapse of time occurs between the application and recharge, the total mass available will equal the applied mass. However, when a significant time lapse occurs between the application and recharge events, there will be a loss of mass due to solid-phase decay which begins at the time of application, and the total available mass will be less than the applied mass. The slug begins to enter the soil at the first precipitation event at a rate equal to the pore water velocity. PESTAN assumes steady flow conditions through the soil domain. Only the slug enters the soil; the pollutant transport is influenced by sorption and dispersion. Mass of the pollutant can be lost via liquid-phase decay or via migration out of the soil domain. The following assumptions apply to the model:
The PESTAN model presents results for the specific input values without accounting for any parameter uncertainty. Results should be compared for a series of simulations using a range to obtain an estimate of potential uncertainty. PESTAN input data includes:
The new WHI UnSat Suite includes a powerful graphical user interface for the PESTAN model. Click here for information. PESTAN Overview |
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PESTAN
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