Enhanced remedial reagents delivery in unsaturated anisotropic soils using surfactant foam

Homogeneous delivery of solution of oxidant in unsaturated soils is limited by soil anisotropy and gravity. An innovative injection strategy using foam was developed to improve in situ delivery. Primary foam injection before oxidant solution enhanced both the lateral and uniform delivery of reactant in isotropic and anisotropic (permeability, contamination) soils. The oxidant spread isotropically through the foam water network. This sequential injection heavily improved the delivery radius of influence (ROI), while limiting contact between surfactant and solution of oxidant in order to preserve the selective oxidation of petroleum hydrocarbons contaminant (TPH). Prior foam injection allowed uniform delivery of the solution of oxidant across the region occupied by the foam, regardless of the soil permeability contrast (1:18), whereas poor ROI were observed for the direct injection of oxidant. Experiments in contamination contrasted soils showed that foam was able to propagate in highly TPH contaminated soils (max 60% velocity reduction for 22 g.kg(dry soil)(-1)). As for permeability contrast, foam is expected to enhance reagents delivery in such contexts. This novel strategy was proven to be efficient, even for complex anisotropic conditions, and should allow to cut field costs and uncertainties associated to poor reagents delivery. (C) 2018 Elsevier Ltd. All rights reserved.