HYDROGEOLOGICAL DECISION-ANALYSIS .2. APPLICATIONS TO GROUNDWATER CONTAMINATION

Two case studies are presented as examples of a decision-analysis approach to engineering design for projects in which the hydrogeological environment plays an important role. This approach to design involves quantifying benefits, costs, and risks for each design alternative under consideration. Risk, which is defined as the expected costs of failure, reflects both performance uncertainties and failure costs. Probabilities of failure are estimated by coupling stochastic ground-water flow and solute transport models with uncertainty models that represent input parameters as random variables. The case studies that are used to describe the approach involve (1) selecting a pumping rate for an extraction well to capture an existing contaminant plume, and (2) designing a leachate collection system for a soil remediation facility. The examples illustrate that the decision-analysis approach can be accomplished using relatively simple analytical models to simulate the behaviors of hydrogeological environments and engineering components. The results identify how the preferred design alternative depends upon the regulatory, hydrogeological, and economic environments in which the decision is made. For the extraction well example, the preferred alternative is relatively insensitive to the costs of failure but is dependent upon the expected dimensions of the contaminant plume. For the soil remediation example, the preferred design alternative depends upon the anticipated costs of failure and the regulatory standard for ground-water contamination. Reducing the variance or uncertainty in dispersivity values by a factor of 3 had a relatively small effect on the overall design of the leachate collection system.