Performance Optimization of LNAPL Three Phases Extraction by Prefabricated Vertical Wells (PVWs)

Abstract

The use of petroleum products has sometimes been implemented with inadequate storage and disposal practices, which led to widespread contamination of the subsurface environment. Liquid petroleum products having a density less than water are referred to as Light Non Aqueous Phase Liquids (LNAPL), and are commonly found at the interface of unsaturated and saturated zones. LNAPL fluctuate with groundwater table and form a ‘smear zone’ occupied by ganglia. Remediation of these residual ganglia is extremely challenging even with today’s advanced technology. Research presented herein is focused on investigating the extraction of multiphase subsurface organic contamination using in situ approach termed Well Injection Depth Extraction (WIDE). The research encompasses field and modeling studies. The field study, performed at a former air force base in Ohio, included monitoring system performance, in terms of extracted liquid and gas phases, over 185 operating hours on 38 separate days. The modeling study consisted of three parts: i) groundwater modeling, ii) contaminant transport modeling, iii) multiphase flow and transport modeling. The modeling study attempted to characterize phase transfer mechanism as a function of air permeability and suction head, study the mechanics involved with controlled lowering/raising of groundwater table through system optimization, and investigate effect of subsurface hydrogeologic parameters (permeability, porosity) on the ability to extract LNAPL source and the magnitude of the residual phases. Modeling results were also used in an optimization scheme to investigate schedules for lowering of groundwater table and extraction efficiency. The results from this study document field data on system performance for extraction of LNAPLs in a subsurface with lenticular morphology. The field results were used to calibrate the models used in the analytical studies. Results from the analytical studies explained phenomena related to various phase extraction based on well spacing, and impact of subsurface parameters on residual LNAPL distribution and preferential phase for extraction. The optimization analyses provided a framework for establishing a process for systematic lowering of groundwater table to target residual phase with volatilization, and optimize well spacing for maximum removal of contaminant mass.