MINVAR and UNCCON, computer programs for uncertainty analysis of solubility calculations in geological systems ?
Computer simulations of different phenonmena have become increasingly important as computer time has become cheaper and computers have become faster. In some cases, it may be that simulation results are used instead of experiments, since experiments are expensive and require a great deal of time. One such example is the determination of solubilities of different elements under different conditions, e.g. different temperatures and water compositions. It is important when working with computer simulations, however, to remember that the result is a direct function of the input data, i.e. if input data are slightly uncertain, so will be the results. The main input data to solubility calculations are thermodynamic data, such as stability constants and enthalpies of reactions, and water composition data. The thermodynamic data have been discussed elsewhere, and the focus of this paper is thus on the water parameters. The uncertainties in water composition may originate from at least two different sources. Either the water composition at a certain location has been measured, thus making the main measurements uncertain, or the uncertainties in water composition arise from computed estimates of water composition on the basis of rock-water interactions. To investigate these different approaches, two programs, MINVAR and UNCCON, have been developed. The MINVAR program gives uncertainties in water composition caused by uncertainties in rock composition using the CRACKER code. These uncertainties or measurement uncertainties may then be transferred to the UNCCON program, which estimates the effect on the calculated solubilities. Both programs use the Latin Hypercube sampling technique.
uncertainty analysis solubilities latin hypercube sampling phreeqe