AT123D is based on an analytical solution for transient one-, two-, or three-dimensional transport of a dissolved chemical or radionuclide or heat in a homogeneous aquifer with uniform, stationary regional flow. The program assumes a stationary flow field parallel to the X-axis and allows for retardation (based on reversible instantaneous linear equilibrium sorption isotherm) and first-order decay. Longitudinal, and horizontal and vertical transverse dispersion can be input indepen- dently. The program calculates the concentration distribution in space and time in mg/l (ppm) or pCi/l or the temperature distribution in degrees Celsius. The aquifer can be bounded (finite extent) or of infinite extent in the Y- and/or Z-direction. It is of infinite extent in the positive X-direction.

AT123D models transport caused by a single source starting release of heat or solute at time T=0. It handles various source configurations and boundary conditions. It can simulate a point source, a line source parallel to the X-, Y-, or Z-axis, an area (patch) source in the X-Y, X-Z, or Y-Z direction, and a volume source. The source release may be instantaneous, continuous, or finite step-wise duration (up to 15 steps) and is assumed to be equally distributed over the source area.

The IGWMC version of AT123D includes a shell program for data input and editing, program execution, and post-processing. The program facilitates calculation of results in a grid of up to 20 * 20 nodes horizontally and up to 10 layers.

The AT123D package consists of DOS-based programs that run in low (convential) memory on PC-type of computers. They run also under various Windows versions. The programs do not contain graphics and can run in any graphic environment.

Program History:

AT123D was originally developed at Oak Ridge National Laboratory, Oak Ridge, Tennessee. Dr. Yeh is currently at Pennsylvania State University, Dept. of Civil Engineering, University Park, PA 16802.

This version of AT123D has been prepared by the International Ground Water Modeling Center (IGWMC). It includes improvements and corrections made by the author since its original release in 1981. The last changes by the author were incorporated in this program in 1987. Since, minor modifications have been made by IGWMC to improve output layout. The current version of AT123D is version 1.22, released by IGWMC in June 1993. Changes made in the AT123D package after release of version 1.22 of the AT123D code pertain only to PREAT123.

IGWMC has modified the I/O calls in the original version to facilitate interaction with the shell program and to allow easy post-processing. In porting the code to the microcomputer environment, the size of some of the arrays, especially the various source rate array, was reduced. The calculation grid was expanded to 20 x 20 x 10 and the relevant arrays resized. The original code included a call to an external math subroutine, which was replaced with an internal subroutine. Finally, the original code listed the units for time as [hour]. The IGWMC version uses [day] as time unit.

IGWMC Verification:

The IGWMC version of the AT123D model has been checked against independently programmed analytical solutions including SOLUTE, PLUME2D, and PLUME, available from the IGWMC. Generally, differences were small (1-10%), occurring primarily near the plume's edges.

As the IGWMC replaced the math library call for the error function in the original source code with a newly programmed subroutine, the user will notice small differences between the results generated with the IGWMC version and the results published in the documentation. These differences occur primarely for relative low values at the edges of the plume. It may be argued that such differences are not important considering the uncertainties in the assumptions the user has to make to justify the use of analytical solutions and the uncertainties in the data.

Sometimes, problems occur when using the three-dimensional mode with multiple area (patch) sources and multiple time steps. All other option work without a problem.

SYSTEM REQUIREMENTS

• Intel 80i86 based computer
• 640 Kb RAM
• DOS 2.1 or higher
• about 1 Mb free disk space for code and examples
• math coprocessor
• CGA, EGA or VGA graphics

Developer: Author: G.T. Yeh (Oak Ridge National Laboratory)