DESIGN FACTORS FOR IMPROVING THE EFFICIENCY OF FREE-PRODUCT RECOVERY-SYSTEMS IN UNCONFINED AQUIFERS

Free-product recovery system designs for light hydrocarbon recovery we re investigated to evaluate the effects of multiple-stage pumping, del ayed startup, and uncertainty of key residual oil saturation input dat a using a vertically integrated three-phase flow model, ARMOS. The res ults obtained from a single well recovery system subjected to a given well location and uniform soil properties suggested that multiple-stag e water pumping can enhance the recovery and provide optimal design co nditions if cost and recovery oil volume are the targets. However, if containment of the spill area with simultaneous recovery is the target , then single-stage pumping still provides the optimal design. Delayed startup of the operation from the initial site characterization can c ause substantial plume movement during the lag period making predictio ns made with zero time lag invalid. Allowance should be made in the de sign to account for this time delay. Uncertainty of maximum residual o il saturations in both saturated and unsaturated zones may cause consi derable differences in predicted results. Careful attention should be paid to obtaining these data for accurate remediation design.