NAMEmocdense - A two-constituent solute transport model for ground water having variable densityABSTRACTThis model simulates solute transport in flowing ground water. It is applicable to two-dimensional, cross-sectional problems involving ground water with constant or variable density. The model computes changes in concentration over time caused by the processes of advective transport, hydrodynamic dispersion, mixing or dilution from fluid sources. The concentrations of two independent solutes can be modeled simultaneously. Temperature is assumed to be constant, but fluid density and viscosity are assumed to be a linear function of the first specified solute. If a second solute is specified, it is assumed to be of a trace amount such that it does not affect the fluid density or viscosity. The aquifer may be heterogeneous and anisotropic. The model has been used mostly in studies of either saltwater intrusion or dense contaminant plumes. The model was documented by Sanford and Konikow (1985). For a documentation of the numerical method used, see the report by Konikow and Bredehoeft (1978).METHODThe model couples the ground-water flow equation with the solute- transport equation. The digital computer program uses an iterative strongly-implicit procedure to solve a finite-difference approximation to the ground-water flow equation. The model uses the method of characteristics to solve the solute-transport equation. This incorporates a particle-tracking procedure to represent advective transport and a two-step explicit finite-difference procedure to solve equations that describe the effects of hydrodynamic dispersion and fluid sources. This explicit procedure has several stability criteria associated with it, but the consequent time-step limitations are automatically determined by the program.HISTORYVersion 3.2 1995/01 - Most current version. This version includes several upgrades and fixes to minor bugs from earlier versions. Version 1.0 1985 - Original version released.DATA REQUIREMENTSInitial conditions, boundary conditions, aquifer properties at every node, grid descriptors, and linear equation parameters that relate fluid density and viscosity to solute concentration.OUTPUT OPTIONSSee documentation.SYSTEM REQUIREMENTSMOCDENSE is written in Fortran 77 with the following extensions: use of integer*2 declarations and use of the $ format descriptor. 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 and 4 mb of memory.DOCUMENTATIONSanford, W.E., and Konikow, L.F., 1985, A two-constituent solute transport model for ground water having variable density: U.S. Geological Survey Water-Resources Investigations Report 85-4279, 89 p.REFERENCESKonikow, 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.TRAININGOne-day introduction during the class Modeling 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 MOCDENSE software can be retrieved are, respectively: http://water.usgs.gov/software/mocdense.html --and-- /pub/software/ground_water/mocdense See http://water.usgs.gov/software/ordering_documentation.html for information on ordering printed copies of USGS publications.SEE ALSOmoc(1) - Two-dimensional method-of-characteristics ground-water flow and transport model modflow(1) - Modular three-dimensional ground-water flow model 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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