A Simulation Study of Surfactant/Foam Processes in Shallow Subsurface Remediation: Using Foams for Mobility Control vs. Blockage

Many shallow ex-situ and in-situ remediation treatments come from the contamination of underground soils and groundwater sources by organic hydrocarbon components called non-aqueous phase liquids (NAPLs). These contaminants, if leaking, can impose long-term threats causing environmental and health concerns. One of the versatile in-situ remediation techniques is using surfactant/foam processes that can overcome subsurface heterogeneity and improve NAPL removal. This simulation study investigates surfactant/foam processes, especially focusing on two different roles of foams during the treatment: foams for “mobility control” vs. foams for “blocking”. The first is based on the actual operations carried out in the pilot-test site for 23 days (i.e., 20 days of surfactant followed by 3 days of foam injection, in a line-drive pattern with 3 injection wells and 3 extraction wells), while the second is to evaluate the potential of blocking foams by placing foams downstream (i.e., foam injected into the downstream extraction wells, but surfactant is still injected into the upstream injection wells). The results show that (i) the use of mobility-control foams together with surfactant injection can improve and accelerate oil removal from the site (about 91.9 % oil recovery in this particular case investigated), and (ii) based on 24 scenarios, the use of blocking foams is as efficient as, or more efficient than, mobility-control foams, exhibiting the oil recovery up to near 94.9 %. This outcome of this study is believed to help design an improved way of applying surfactant/foam processes.