Free Product Recovery of Non-aqueous Phase Liquids in Contaminated Sites: Theory and Case Studies

Abstract

Organic liquids with low water solubility are generally described as Non-Aqueous Phase Liquids (NAPLs). They penetrate the soil subsurface as oily liquids (free products), do not mix readily with water, and therefore flow independently from groundwater. They can be divided into two main classes: light NAPLs (LNAPLs), such as refined petroleum products, which are lighter than water; and dense NAPLs (DNAPLs), such as trichloroethylene, which are heavier than water. NAPLs may dissolve in the aqueous phase or evaporate in the gas phase. Due to their toxicity and widespread occurrence, they generate serious environmental and health problems. Most contaminants migrate when they are present as free-phase. Therefore, removing free products is of primary importance for the remediation of any contaminated site. Conventional NAPL remediation consists of pumping the free product until residual saturation is reached (i.e., no more NAPLs can be recovered). This residual saturation may impact gases (vapor phase) or groundwater (dissolved phase) for several years. Decreasing this residual saturation (i.e., increasing the recovery yield of free product) may contribute to reducing: (1) contaminants dissolved into water, (2) the duration of the remediation operation, (3) the extent of plumes and related contaminant concentration levels, and consequently, (4) remediation costs. In this chapter, we present conventional technologies for free product recovery from the practical and theoretical viewpoints: pump-and-treat, skimming, bioslurping, and recovery trenches. This chapter describes the advantages and limitations of these techniques, and discusses innovative technologies such as thermal and chemical enhancement (i.e., surfactants), which aim to increase free product recovery yields and rates.