UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY RESTON, VA. 22092 In Reply Refer To: June 2, 1987 WGS-Mail Stop 411 OFFICE OF GROUND WATER TECHNICAL MEMORANDUM NO. 87.03 Subject: PUBLICATIONS--Release of two new reports documenting numerical models for the analysis of solute transport in ground-water systems The two subject reports are: 1. Kipp, Kenneth L., 1987, HST3D: A computer code for simulation of heat and solute transport in three-dimensional ground-water flow systems: U.S. Geological Survey Water- Resources Investigations Report 86-4095, 517 p. 2. Lewis, Frank M., Voss, Clifford I., and Rubin, Jacob, 1986, Numerical simulation of advective-dispersive multisolute transport with sorption, ion exchange and equilibrium chemistry: U.S. Geological Survey Water-Resources Investigations Report 86-4022, 165 p. Both reports document powerful numerical simulators that represent the state-of-the-art of documented computer models in the U.S. Geological Survey. As such, both computer models are intended are research endeavors, where use and interpretation of the code and results is primarily the responsibility of the investigator. The first report, the Heat- and Solute-Transport Program (HST3D) simulates ground-water flow and associated heat and solute transport in three dimensions. The HST3D program may be used for analysis of problems such as those related to subsurface-waste injection, landfill leaching, saltwater intrusion, freshwater recharge and recovery, radioactive-waste disposal, hot-water geothermal systems, and subsurface-energy storage. The three governing equations are coupled through the interstitial pore velocity, the dependence of the fluid density on pressure, temperature, and solute-mass fraction, and the dependence of the fluid viscosity on temperature and solute-mass fraction. The solute-transport equation is for only a single, solute species with possible linear-equilibrium sorption and linear decay. The HST3D code uses finite-difference techniques to discretize the governing equations using a point-distributed grid. The flow-, heat-, and solute-transport equations are solved, in turn, after a partial Gauss-reduction scheme is used to modify them. The modified equations are more tightly coupled and have better stability for the numerical solutions. Two techniques are available for solution of the finite-difference matrix equations. One technique is a direct-elimination solver, using equations reordered by alternating diagonal planes. The other technique is an iterative solver, using two-line successive overrelaxation. It is important to note that the computer storage and time demand of three-dimensional transport codes, such as HST3D, is significant and is much greater than most ground-water flow codes. The second report, known as SATRA-CHEM, simulates fully saturated two-dimensional transient or steady-state areal or cross-sectional constant-density ground-water flow and multisolute transport. The options for transport under the condition of local equilibrium are: (a) linear sorption and up to two aqueous complexations, and (b) binary ion exchange and a single complexation reaction involving one of the exchanging species. SATRA-CHEM is a modified version of the computer code SATRA, which itself is a simplified version of the flow and solute-transport model SUTRA (Voss, 1984). A finite-element Galerkin scheme is used for spatial approximations of the dependent variable and backwards finite- differencing for its time derivative. Hydraulic conductivities can be anisotropic and variable in direction and magnitude on an element wise basis. One copy of each report is being sent under separate cover to all District Offices and some Subdistricts in order that these powerful tools will be available. The HST3D code is available from the SOFTEX system on the Prime (ID# VAKLK00001), and SATRA- CHEM is available from Clifford Voss. As the physics, chemistry, and numerical techniques are nontrivial, a substantial time investment is required to use these tools appropriately. Thus, we do not envision the use of these tools in routine or short-term projects. Projects planning to use either of these models must be thoroughly planned and take into account the time required and the possibility (which exists in all research work) of unforeseen difficulties which may limit the use of these tools. (s) Thomas E. Reilly for Eugene P. Patten Chief, Office of Ground Water WRD Distribution: A, B, S, FO POPUBLICATIONS--Release of two new reports documenting numerical models for the analysis of solute transport in ground-water systems