Sensitivity of contaminant travel time to the combined effect of porosity and hydraulic conductivity
An approach is developed to analyze sensitivity of advective contaminant travel time to porosity and hydraulic conductivity and their dependence. The approach is applicable in situations when groundwater specific discharge can be calculated from an available groundwater flow model that has already been developed. The groundwater specific discharge results allow estimate of advective contaminant travel time together with porosity values for all grid cells in the groundwater flow model. This is particularly useful when a full contaminant transport model is not available. In this study, a sensitivity index is developed based on the covariance between the advective contaminant travel time and grid cell porosity and its relationship with hydraulic conductivity. The spatially variable sensitivity index provides a quantitative measure of the combined effect of porosity and hydraulic conductivity on the sensitivity of advective contaminant travel time. The index can be used to identify the most influential region to reduce uncertainty of predicting advective contaminant travel time, which in turn helps to facilitate field characterization to reduce uncertainty and to aid the design of monitoring networks. Three theoretical examples are presented and discussed to illustrate the approach. However, the approach can be easily applied to more complex aquifer domains where advective contaminant travel time can be calculated based on simulated flow results from available groundwater flow models.