Surfactant/Foam Processes in Shallow Subsurface Remediation: Evaluation of Foams as a Blocking Agent

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. Motivated by an earlier study of successful implementation of surfactant/foam in-situ remediation processes, this simulation study investigates the next phase of the research, that is, (i) understanding two different roles of foams during the treatment: foams for “mobility control” vs. foams for “blocking” and (ii) evaluating 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). When twenty-four different scenarios are taken into consideration for the 23-days pilot test with 3 injection wells and 3 extraction wells, the results from the simulations reveal that using foams for blocking purpose is as efficient as, or more efficient than, foams for mobility-control purpose, exhibiting the oil recovery up to near 94.9%. Additional simulation efforts also show that foams as a blocking agent have a unique advantage over mobility-control foams because of less pressure buildup required and, therefore, less chance of displacing the contaminants out of the treatment area. This feasibility study of examining foams as a blocking agent focuses on vertical wells currently, which can be regarded as a stepping stone into the broader range of similar applications with horizontal wells located in hilly terrain.