The flow equation is solved using a node-centered finite difference method. Pathlines and isochrones for steady-state flow fields are computed by Euler integration. Sources can be either permanent or instantaneous.
Transport is based on a steady-state flow field.
The aquifer can be heterogeneous and anisotropic. Options are available for time-varying pumping and injection rates in wells, temporally and spatially variable recharge, permanent or instantaneous solute injection, and infiltration of exfiltration of surface water. The model supports a grid of up to 80 X 80 cells, includes a detailed water balance, and provides utilities for comparison of measured and computed heads, and generation of stochastic hydraulic conductivity or transmissivity distributions. The program includes various on-screen graphical options including head contours, concentration distribution, velocity vectors, pathlines, isochrones, breakthrough curves, parameter distributions, and imported DXF files. ASM is distributed on DOS-formatted disks containing source codes, runtime version, and example files.