PREDICTION OF SOLUTE-DISPERSION IN HETEROGENEOUS POROUS-MEDIA - EFFECTS OF ERGODICITY AND HYDRAULIC CONDUCTIVITY DISCRETIZATION

The performance of a stochastic numerical modelling procedure to simul ate dispersion of a conservative solute in two-dimensional heterogeneo us hydraulic conductivity fields is investigated in a series of numeri cal experiments, the results of which are compared with theoretical pr edictions. Random hydraulic conductivity fields are generated with a p rescribed statistical structure, a finite difference model is used to obtain the flow field and particle tracking reproduces the dispersive properties. For comparison between stochastic numerical methods and st ochastic theories for solute transport, fulfilment of the ergodic requ irement is necessary, consequently aspects of simulated solute plume b ehaviour are investigated with respect to ergodicity. Application of n umerical stochastic methods is hampered by the large associated comput ational burden, which is affected by a range of factors, not least the level of discretisation of the hydraulic conductivity field. The expe riments detailed here investigate the effects of hydraulic conductivit y discretisation and the effects of initial solute source area for a r ange of log-permeability variances. An increasing deviation from Dagan 's linear theory is observed for increasing coarseness of discretisati on. A tendency to ergodic conditions is found for a smaller initial so urce area than previously reported.