CANVAS is a composite analytical-numerical code for simulation of transport and fate of viruses in ground-water. The code provides transient transport taking into account advection and dispersion of viral particles in the unsaturated and saturated zones, adsorption, inactivation (die-off), attachment and detachment kinetics and colloidal filtration. CANVAS may also be used for delineation of ground-water pathlines and well capture zones. Both areal and line sources of various shapes in unconfined or confined aquifers can be accommodated. Typically, areal sources may be used to represent leaky septic tanks, cesspools, or areas of surface and subsurface disposal of waste water. Line sources may be used to represent leaky sewer lines or pipes. Barrier or stream boundary conditions that exist over the entire aquifer depth can be simulated.

CANVAS consists of various modules. The USCOL module simulates the flow of ground-water and the transport of viruses from a viral source to the water table. The viral breakthrough curve at the water table computed with this module is used as input for the LTG2D module. The USCOL module uses a semi-analytical technique to solve the one-dimensional, steady-state flow equation together with the Newton-Raphson method to find the non-linear roots of the equation. For the transport equation a numerical approximation is obtained using an upstream- weighted finite element method and linear elements. Time integration is performed using a central difference formulation.

SZFLOW computes steady-state, two-dimensional (areal) ground-water flow velocities within each (rectangular) finite element of the specified grid. This module also delineates ground-water flow pathlines and well capture zones. The module uses the Laplace Transform Galerkin (LTG) technique for solution of the flow equation.

LTG2D simulates two-dimensional transport of viruses in the saturated zone, using output of USCOL and SZFLOW as input. Steady-state transport is solved using the standard upstream-weighted residual finite element scheme.

In its present configuration the model handles up to 75x75 grid, 10 sources, 10 soil layers, 25 pumping wells, 5 recharging wells, and 10 forward-tracked and 10 reverse-tracked pathlines.

The preprocessor, PRECV, allows the user to efficiently enter and edit input data and includes the graphical construction of the finite element grid and the placement and removal of multiple sources and pumping and injection wells. The post-processor, CVGRAF, allows the graphic presentation of ground-water flow path-lines, viral breakthrough curves at the water table or at pumping wells, and ground-water pressures and saturations in the unsaturated zone beneath contaminant sources.

CANVAS is distributed on DOS-formatted disks containing executable versions and example data files. The user's manual consists of installation instructions and the program documentation prepared by HydroGeologic, Inc. for US EPA.

SYSTEM REQUIREMENTS

Intel 80386 based computer, 8 Mb RAM, math coprocessor, at least 5 Mb free disk space, VGA graphics, DOS 5.0, extended memory manager, and a Microsoft compatible mouse.