Updates of the computer code associated with "Computer model of two-dimensional solute transport and dispersion in ground water"

                           GEOLOGICAL SURVEY
                           RESTON, VA. 22092

In Reply Refer To:                           March 4, 1986
WGS-Mail Stop 411


Subject:  GROUND WATER--Updates of the computer code associated
                        with "Computer model of two-dimensional
                        solute transport and dispersion in ground
                        water" by L. F. Konikow and J. D.
                        Bredehoeft (1978): U. S. Geological Survey
                        Techniques of Water-Resources Investigat-
                        ions (TWRI), Book 7, Chapter C2

Attached are "update notes" by Leonard F. Konikow that document
revisions made and verified since the previous update of October
12, 1983, to the subject solute-transport model.  Following are
brief descriptions of the updates:

June 10, 1985--Changes to the computer code are given that allow
the user to specify 16 particles per node.  This option can lead
to increased numerical accuracy in some cases.  The original
program allowed for the placement of 4, 5, 8, or 9 particles per

July 26, 1985--Changes to the code correct a programming error in
the routine to calculate changes in concentration caused by
dispersion.  For most problems, the difference in computed results
will be negligible.  However, if the problem being solved involves
dispersive fluxes large relative to the convective (advective)
fluxes, then the original program could have generated negative
mass-balance errors of up to several percent.

July 31, 1985--The solute-transport equations presented in the
TWRI include two terms that should have canceled out during the
derivation and expansion of the basic governing equation.  The
five equations that are affected are given in their correct form.
The corresponding changes to the computer code were given in the
August 26, 1981, update.

August 2, 1985--Changes to the computer code allow the model to
simulate a first-order irreversible-rate reaction and (or)
equilibrium-controlled sorption-desorption for a linear isotherm.

August 8, 1985--Changes to the computer code allow the user to
solve the transport equation within a secondary subgrid of the
primary finite-difference grid for the flow model.  This can
result in a great savings in computer calculation time and storage
requirements for problems in which the hydraulic gradients within
the area of interest for transport are influenced by hydraulic
stresses and (or) boundary conditions outside of the area in which
solute transport is occurring.

August 12, 1985--Changes to the computer code allow the user to
specify only one particle per node.  This will significantly
reduce the computer time required to solve a given problem, but
may adversely affect the numerical accuracy of the solution to the
solute-transport equation.  Hence, this option is recommended only
for test runs in which high numerical accuracy is not needed, such
as when the main objectives of the run are to check input data,
boundary conditions, or overall problem formulation.

Collectively, these changes improve the accuracy, efficiency, and
usability of the model.  Revisions can be implemented by following
the instructions in the updates.  Mr. Konikow advises that the
modified computer code will be available through SOFTEX (entry
ID=VAMWM00007) for U.S. Geological Survey users.

                                   (s) Charles A. Appel
                                   for Eugene P. Patten
                                   Chief, Office of Ground Water


WRD Distribution:  A, B, S, FO, PO