Advective control of groundwater contaminant plumes using simulation and optimization
A new optimization formulation for designing groundwater contamination control systems is presented that uses particle tracking to simulate and constrain advective transport. The new model solves design problems in complex hydrogeologic domains with multiple candidate wells and multiple particles. The model explicitly represents the plume control design problem using particle tracking, formalizes the design procedures used by many practitioners, and represents a significant advancement in design capability over existing particle tracking-based models. In addition, designs obtained using the advective control model are more efficient at capturing plumes than designs obtained from hydraulic control formulations. ^ A two-step solution process is used to solve the model, which seeks the least cost steady-state control system that satisfies the two equivalent requirements that the contaminant plume be located within the capture zone (step 1) and that all particles representing contaminant solute travel to an extraction well (step 2). A new interior point algorithm for solving nonlinear optimization problems is developed to solve the advective control model. The solution algorithm is robust to a range of numerical characteristics that arise from different values used to parameterize the model. Monte Carlo stochastic modeling is performed to investigate the reliability of optimal pumping designs in the presence of uncertain aquifer heterogeneity. Although the optimal well location that is identified assuming homogeneous transmissivity is robust to heterogeneous conditions, uncertainty in the pumping rates needed to capture a plume increases as the variance and correlation length of transmissivity increase. ^ Pumping designs obtained using the advective control model typically require active extraction at the most downgradient well(s), indicating that the solution takes advantage of natural flow patterns. The model is demonstrated on several example problems that represent a variety of hydrogeologic conditions, including confined and unconfined aquifers, two- and three-dimensional flow regimes, and domains with homogeneous and heterogeneous hydraulic properties, recharge, rivers, and water supply wells. Example problems contain from two to six candidate wells and multiple particles representing the contaminant plume. The new advective control model is the first particle tracking-based formulation that can solve plume control design problems in complex domains with multiple wells and multiple particles.