Water Resources Investigations Report 96-4267 " A three dimensional method of characteristics solute-transport model (MOC3D)" by L.F. Konikow, D.J. Goode, and G.Z. Horberger       This report presents a model, MOC3D, that simulates three-dimensional solute transport in flowing ground water. The model computes changes in concentration of a single dissolved chemical constituent over time that are caused by advective transport, hydrodynamic dispersion (including both mechanical dispersion and diffusion), mixing (or dilution) from fluid sources, and mathematically simple chemical reactions (including linear sorption, which is represented by a retardation factor, and decay). The transport model is integrated with MODFLOW, a three-dimensional ground-water flow model that uses implicit finite-difference methods to solve the transient flow equation. MOC3D uses the method of characteristics to solve the transport equation on the basis of the hydraulic gradients computed with MODFLOW for a given time step. This implementation of the method of characteristics uses particle tracking to represent advective transport and explicit finite-difference methods to calculate the effects of other processes. However, the explicit procedure has several stability criteria that may limit the size of time increments for solving the transport equation; these are automatically determined by the program. For improved efficiency, the user can apply MOC3D to a subgrid of the primary MODFLOW grid that is used to solve the flow equation. However, the transport subgrid must have uniform grid spacing along rows and columns. The report includes a description of the theoretical basis of the model, a detailed description of input requirements and output options, and the results of model testing and evaluation. The model was evaluated for several problems for which exact analytical solutions are available and by benchmarking against other numerical codes for selected complex problems for which no exact solutions are available. These test results indicate that the model is very accurate for a wide range of conditions and yields minimal numerical dispersion for advection-dominated problems. Mass-balance errors are generally less than 10 percent, and tend to decrease and stabilize with time. Return to the Water Resources of Pennsylvania Home Page or go directly to: The URL for this page is http://pa.water.usgs.gov /abstracts/wrir_96-4267.html Please note our privacy statement and disclaimer Accessibility Answers to many common questions can be found on our Frequently Asked Questions (FAQ) page. Please direct content comments or questions to: Information Specialist U.S. Geological Survey 215 Limekiln Road New Cumberland, PA 17070-2424 Phone: (717) 730-6916 FAX: (717) 730-6997 Email: is_pa@usgs.gov or contact: Director, USGS Pennsylvania Water Science Center U.S. Geological Survey 215 Limekiln Road New Cumberland, PA 17070-2424 Phone: (717) 730-6960 FAX: (717) 730-6997 Email: dc_pa@usgs.gov Please direct web related comments to webmaster@pa.water.usgs.gov sdww50