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Combining physical containment with optimal withdrawal for contaminated groundwater remediation

1987; Elsevier BV; Volume: 10; Issue: 4 Linguagem: Inglês

10.1016/0309-1708(87)90029-7

1872-9657

David P. Ahlfeld, John M. Mulvey, George F. Pinder,

Reservoir Engineering and Simulation Methods

Two common techniques for remediation of groundwater plumes of toxic solute are physical containment and groundwater withdrawal. Both methods utilize existing technology and are applicable to aquifers with widely different characteristics. Both methods are also expensive, so that care must be taken in designing systems for their use. This paper considers the use of both methods at a single site and describes an analysis methodology for evaluating the tradeoff between the costs involved in the two methods. The methodology combines containment transport simulation modelling with a nonlinear optimization formulation which finds the optimal groundwater withdrawal pumping strategy given a specific physical containment configuration. Physical containment of contaminated groundwater typically involves the construction of a low permeability barrier (e.g,, slurry wall or grout curtain) in the subsurface designed to surround the contaminated groundwater 1. The ground surface bounded by the barrier is covered with an impermeable cap which prevents further leaching from the contaminated soil and forestalls any increase in water level by precipitation in the contained area. The costs of such a system are related to the length and depth of the barrier structure and the surface area covered by the cap. Withdrawal methods require the removal of contaminated groundwater from the aquifer by pumping. The design elements in a withdrawal system are the location of the wells and the magnitude of pumping at each well. Careful design of a withdrawal system may include the use of both injection and extraction walls to induce velocity fields which facilitate efficient plume contraction and removal. Because of the ability of a withdrawal system to affect velocity fields over large distances, this method is better suited than containment for large dilute plumes. The costs in a withdrawal system are related to the amount of pumped fluid and to the concentration of the extracted water. Case histories of groundwater withdrawal and physical containment systems have been reported in the literature, for example, McBride 2, and Water Well Journal 3. Methods for determining optimal withdrawal strategies for containment or avoidance of solute plumes which combine flow or solute modelling with optimization techniques have been proposed by Molz and BelP, Gorelick et al. 5 and Colarullo et al. 6. Methods for