NAMEmoc3d - Three-dimensional method-of-characteristics ground-water flow and transport modelABSTRACTThis model 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 model can also simulate ground-water age transport and the effects of double porosity and zero-order growth/loss.METHODThe 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. Particle tracking is used to represent advective transport and explicit finite-difference methods are used to calculate the effects of other processes.HISTORYVersion 3.01 1999/07/08 - Bug fixed in double porosity routine. Version 3.0 1999/03/24 - Added capabilities to simulate age transport, double porosity exchange, and simple reactions. The simple reactions include cell-by-cell terms for decay and zero- order growth/loss. Decay and growth coefficients can change in time at the beginning of each flow model stress period. Version 2.02 1999/03/08 - Added the elapsed transport time to the header information for particle output files. Version 2.01 1999/01/25 - Altered the replacement scheme for particles entering the subgrid to fix distribution problems for weakly divergent flow fields near subgrid boundaries. Version 2.0 1998/11/16 - Added implicit dispersive transport algorithm, rearranged main.f file to call a MOC3D control module (moc_main.f), added new output option for printing concentrations in "table" style, FHB package added, added printing of time step and stress period in MOC3D output file, fixed velocity calculation bug (KSTP>1, ISS=0), corrected calculation of subgrid face counter, fixed bug in mass balance calculation for decay, fixed sign in saturated thickness calculation, corrected check for porosity vs. storage terms, typographical errors fixed. Version 1.2 1998/05/01 - Output control for particles (NPNTPL) fixed; automatic initialization for retardation factor (RF) fixed, bug in crch5.f fixed, single header line for CNCA and VELA files, test for rounding error in move.f fixed, HFB1 and DE45 packages added, mass balance loop error fixed, some output formats changed. Version 1.1 1997/05/14 - Minor bug fixes affecting a format statement and output of initial condition data to observation well file. Version 1.0 1996/11/08 - Initial releaseDATA REQUIREMENTSInitial conditions, boundary conditions, aquifer properties at every node, and grid descriptors.OUTPUT OPTIONSSee documentation.SYSTEM REQUIREMENTSMOC3D is written in Fortran 77 with the following extensions: use of variable names longer than 6 characters, use of more than 19 continuation lines, and a common block with character and noncharacter variables. By default, the software is dimensioned for use with models having up to 20,000 cells and 200,000 particles. MOC3D requires that file names required for the simulation be defined prior to execution. Two Name Files (MODFLOW and MOC3D) must be used for this purpose. The format of these is described in the documentation. Generally, the program is easily installed on most computer systems. The code has been used on UNIX-based computers and DOS-based 386 or greater computers having a math coprocessor.DOCUMENTATIONGoode, D.J., 1999, Age, double porosity, and simple reaction modifications for the MOC3D ground-water transport model: U.S. Geological Survey Water-Resources Investigations Report 99-4041, 34 p. Kipp, K.L., Jr., Konikow, L.F., and Hornberger, G.Z., 1998, An implicit dispersive transport algorithm for the U.S. Geological Survey MOC3D solute-transport model: U.S. Geological Survey Water-Resources Investigations Report 98-4234, 54 p. Konikow, L.F., Goode, D.J., and Hornberger, G.Z., 1996, A three- dimensional method-of-characteristics solute-transport model (MOC3D): U.S. Geological Survey Water-Resources Investigations Report 96-4267, 87 p. The basic MODFLOW documentation is contained in the following three reports: McDonald, M.G., and Harbaugh, A.W., 1988, A modular three- dimensional finite-difference ground-water flow model: U.S. Geological Survey Techniques of Water-Resources Investigations, book 6, chap. A1, 586 p. Harbaugh, A.W., and McDonald, M.G., 1996, User's documentation for MODFLOW-96, an update to the U.S. Geological Survey modular finite-difference ground-water flow model: U.S. Geological Survey Open-File Report 96-485, 56 p. Harbaugh, A.W., and McDonald, M.G., 1996, Programmer's documentation for MODFLOW-96, an update to the U.S. Geological Survey modular finite-difference ground-water flow model: U.S. Geological Survey Open-File Report 96-486, 220 p.RELATED DOCUMENTATIONKonikow, L.F., Granato, G.E., and Hornberger, G.Z., 1994, User's guide to revised method-of-characteristics solute-transport model (MOC--Version 3.1): U.S. Geological Survey Water-Resources Investigations Report 94-4115, 63 p. Goode, D.J., and Konikow, L.F., 1989, Modification of a method-of- characteristics solute-transport model to incorporate decay and equilibrium-controlled sorption or ion exchange: U.S. Geological Survey Water-Resources Investigations Report 89-4030, 65 p. Konikow, L.F., and Bredehoeft, J.D., 1978, Computer model of two- dimensional solute transport and dispersion in ground water: U.S. Geological Survey Techniques of Water-Resources Investigations, book 7, chap. C2, 90 p.TRAININGModeling Transport of Ground-Water Solutes (GW2080TC), offered annually at the USGS National Training Center.CONTACTSOperation and Distribution: U.S. Geological Survey Hydrologic Analysis Software Support Program 437 National Center Reston, VA 20192 h2osoft@usgs.gov Official versions of U.S. Geological Survey water-resources analysis software are available for electronic retrieval via the World Wide Web (WWW) at: http://water.usgs.gov/software/ and via anonymous File Transfer Protocol (FTP) from: water.usgs.gov (path: /pub/software). The WWW page and anonymous FTP directory from which the MOC3D software can be retrieved are, respectively: http://water.usgs.gov/software/moc3d.html --and-- /pub/software/ground_water/moc3d See http://water.usgs.gov/software/ordering_documentation.html for information on ordering printed copies of USGS publications.SEE ALSOmfi(1) - A preprocessor for MODFLOW moc(1) - Two-dimensional method-of-characteristics ground-water flow and transport model modflw96(1) - Modular three-dimensional finite-difference ground- water flow model modflow-gui(1) - Preprocessor and postprocessor graphical-user interfaces for preparing MODFLOW-96 and MOC3D input data and viewing model output for use within Argus Open Numerical Environments (Argus ONE) Modflowp(1) - Parameter-estimation version of the modular model sutra(1) - Saturated and (or) unsaturated, constant or variable-density fluid flow, and solute or energy transport (2-dimensional finite-element code) vs2di(1) - A graphical software package for simulating fluid flow and solute or energy transport in variably saturated porous media

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