The program was compiled with all FORTRAN REAL variables promoted to DOUBLE PRECISION. Experience with the RRCA Groundwater Model has shown that the mass balance error is much lower when using double rather than single precision floating point variables.
A modification to the program was made to check the percentage mass balance error when the solver fails to converge. When the mass balance error is less than one percent, the ICNVG variable is reset and model simulation continues. This occurs only in rare cases. However, this feature allows the simulation to complete with an acceptable mass balance, where the stock MODFLOW-2000 program would have stopped prematurely.