This report describes modifications to a
U.S. Geological Survey (USGS) threedimensional
solute-transport model (MODFLOWGWT),
which is incorporated into the USGS
MODFLOW ground-water model as the Ground-
Water Transport (GWT) Process. The
modifications improve the capability of
MODFLOW-GWT to accurately simulate solute
transport in simulations that represent a nonzero
flux across an aquifer boundary. In such
situations, the new Boundary Flux Package
(BFLX) will allow the user flexibility to assign
the flux to specific cell faces, although that
flexibility is limited for certain types of fluxes
(such as recharge and evapotranspiration, which
can only be assigned to the top face if either is to
be represented as a boundary flux). The approach
is consistent with that used in the MODPATH
model. The application of the BFLX Package was
illustrated using a test case in which the Lake
Package was active. The results using the BFLX
Package showed noticeably higher magnitudes of
velocity in the cells adjacent to the lake than
previous results without the BFLX Package.
Consequently, solute was transported slightly
faster through the lake-aquifer system when the
BFLX Package is active. However, the overall
solute distributions did not differ greatly from
simulations made without using the BFLX
Package.
