VLEACH

One-Dimensional Finite-Difference Vadose Zone Leaching Model


VLEACH OVERVIEW

VLEACH, a One-Dimensional Finite-difference Vadose Zone Leaching Model, is a U.S. EPA program which describes the movement of an organic contaminant within and between three phases: (1) as a solute dissolved in water, (2) as a gas in the vapor phase, and (3) as an adsorbed compound in the solid phase. The leaching is simulated in a number of distinct, user-defined polygons vertically divided into a series of user-defined cells. At the end of the simulation, the results from each polygon are used to determine an area-weighted ground-water impact for the modeled area. VLEACH includes the executable, source code and technical support.

DESCRIPTION

VLEACH, A One-Dimensional Finite Difference Zone Leaching Model, is a menu-driven computer program for estimating the impact due to the mobilization and migration of a sorbed organic contaminant located in the vadose zone on the underlying groundwater resource.
VLEACH describes the movement of the organic contaminant within and between three different phases:
(1 ) as a solute dissolved in water,
(2) as a gas in the vapor phase, and
(3) as an adsorbed compound in the solid phase
Equilibration between the phases occurs according to distribution coefficients defined by the user. In particular, VLEACH simulates vertical transport by advection in the liquid phase and by gaseous diffusion in the vapor phase.
These processes are conceptualized as occurring in a number of distinct, user-defined polygons that are vertically divided into a series of user-defined cells. The polygons may differ in soil properties, recharge rate, and depth to water. However, within each polygon homogeneous conditions are assumed except for contaminant concentration, which can vary between layered cells. During each time step the migration of the contaminant within and between cells is calculated. Hence, VLEACH can account for heterogeneities laterally but is limited when simulating vertical heterogeneity.
Initially, VLEACH calculates the equilibrium distribution of contaminant mass between the liquid, gas, and sorbed phases. Transport processes are then simulated. Liquid advective transport is calculated based on values defined by the user for infiltration and soil water content. The contaminant in the vapor phase migrates into or out of adjacent cells based on the calculated concentration gradients that exist between adjacent cells. After the mass is exchanged between the cells, the total mass in each cell is recalculated and re-equilibrated between the different phases. These steps are conducted for each time step, and each polygon is simulated independently. At the end of the model simulation, the results from each polygon are compiled to determine an overall area-weighted ground-water impact for the entire modeled area.
For computational purposes, each polygon is divided vertically into a series of cells. When developing a model simulation, it is important to fully understand the implications of the VLEACH conceptualization.
VLEACH includes a preprocessor for creating/editing data files.

ASSUMPTIONS

The following assumptions are made in the development of VLEACH:

INPUT PARAMETERS Simulation Data

Polygon Data - (for each polygon)


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Incredible NetworksΤελευταία Ενημέρωση 27 Ιουλίου 2004 - Last Revised on July 27, 2004
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