NAPL remediation by vacuum-enhanced recovery: Laboratory and model evaluations

Abstract

This dissertation presents an innovative methodology in the form of two papers for the feasibility assessment and optimization of Vacuum Enhanced Recovery (VER) to remediate non aqueous phase liquids (NAPLs) in the vadose zone. The first paper demonstrates the use of a pilot-scale two-dimensional laboratory soil cell and an automated dual-energy gamma ray attenuation system for the feasibility assessment of VER to remediate free-product NAPL spills. The investigations were conducted in a 1.5 x 1 x 0.08 meter cell filled with heterogeneous soils for the simultaneous and continuous measurement of NAPL and water saturations at 96 programmed locations. The dynamic laboratory method determines the spatial distributions of three-phase fluid saturations of an oil spill simulation from the surface as it migrates through the vadose zone during the sequential stages of infiltration, redistribution and VER. Contour plots of observed NAPL and water saturations identify the distribution of NAPL as entrapped liquid in heterogeneous soils unavailable for free-product recovery by VER. The accuracy of the methodology used for the measurement of NAPL retention in soil was illustrated by a NAPL retention measurement precision analysis. A mean difference of 0.97% was achieved by comparing gamma system measured NAPL retention volumes in the soil with that derived by the VER system. The second paper utilizes the pilot-scale laboratory results for a comparative analysis with model simulations to calibrate a three-phase model and optimize the design of VER systems for free-product NAPL remediation in heterogeneous soils.