ANALYTICAL EXPRESSIONS TO ESTIMATE THE FREE PRODUCT RECOVERY IN OIL-CONTAMINATED AQUIFERS

Petroleum products, such as gasoline, leaked from an underground stora ge tank can be recovered successfully by two-pump operations. The succ ess of the recovery effort depends on the accurate placement of the re covery well at the spill site. An effective recovery operation can min imize the remaining contamination mass in the subsurface. Therefore, a careful evaluation and determination has to be made as to where to lo cate the recovery well. The location of the well can be decided based on an estimation of the extent and thickness of free product on the wa ter table. Such an estimation should be based on analysis of governing mechanisms. In this study we present analytical solutions to estimate the recovery of oil from an established oil lens. These solutions are obtained by applying the Laplace transformation to averaged linear pa rtial differential equations governing the phenomenon. The governing e quation for the free product thickness is derived by averaging the oil phase mass balance equation along the free product thickness and subs tituting the boundary conditions at the oil/water interface and oil su rface. The analytical solutions estimate the temporal and spatial dist ribution of free product thickness on the water table for a number of recovery scenarios. Results are presented for the temporal and spatial variation of the free product thickness, temporal variation of the fr ee product Volume recovered, and recovery efficiency based on the read ings at the monitoring wells. Since they can be utilized without a gre at deal of data, analytical solutions are quite attractive as screenin g tools in two-pump free product recovery operations.