Maximum aqueous concentrations of six radionuclides (Sr, Np, U, Th, Pu and Tc) near a disposal site with a quartz sand or clay engineered barrier in a granitic environment, were calculated in a previous study by computer modelling. A sensitivity study has been carried out in order to assess the importance of three factors in determining the maximum concentrations likely to be found in solution: the maximum temperature reached, water salinity, and the dissolution constants used. In the circulating fluid, final concentrations for Pu, Tc and Th depend mostly on the final temperature. The solubility of Sr is influenced by the fluid salinity. The final concentration of Np is affected by the temperature of the waste disposal site. Uncertainty in the dissolution constants causes the greatest relative variation in calculated U concentrations.