IMPORTANCE OF POROSITY CORRELATION ON THE UNCERTAINTY OF CONTAMINANT TRAVEL TIME

Porosity of hydrogeologic formation is an important parameter in estimating contaminant travel time and its uncertainty in groundwater contaminant migration scenarios. An approach is presented to quantify sensitivity of advective contaminant travel time to porosities of hydrogeologic units (HGUs) along the flowpaths when the porosities of different HGUs are correlated. The focus is on the impact of porosity correlations on the sensitivity of advective contaminant transport time. Specifically, the importance of an HGU porosity is quantitatively assessed through the covariance between the overall advective travel time of contaminants and the portion that is contributed from an individual HGU porosity. Three sensitivity indices are introduced based on the decomposition of covariance between the advective contaminant travel time and individual input porosities of HGUs. When the input HGU porosities are correlated, the three sensitivity indices quantify the total, intrinsic and correlated contributions from each individual HGU porosity, which should be considered in order to determine the relative importance of the input HGU porosities contributing either independently or correlatedly. A simple one-dimensional flow example is presented to illustrate the approach. The approach can be easily applicable to more complex multi-dimensional cases where adevective contaminant travel time can be calculated based on simulated flow results from groundwater flow models.