Shear-thinning fluids for gravity and anisotropy mitigation during soil remediation in the vadose zone.

Surfactant foam has been proposed as an effective treatment fluid for in situ environmental remediation of soils. In the vadose zone, it could improve treatment homogeneity, but its use remains challenging. To better understand and predict foam formation and propagation in vadose zone, we studied them in 24 soils with wide range of properties (including permeability: 2 10-12 to 3.3 10-9  m2 ). Foam rheology showed to be complex and mostly influenced by soil permeability and grading. Below 2 10-11  m2 , foam propagation velocity was not influenced by permeability. Conversely, slight shear thinning to Newtonian behavior was observed for higher permeabilities. Benefits for remediation in anisotropic vadose zones and the injection strategies (mobility control agent or blocking agent) were discussed. Moreover, different methods of foam injection were compared over the range of soil permeability. It showed that "surfactant alternating gas" method was the most suitable for soil permeability lower than 5 10-10  m2 to avoid soil fracturing. Conversely, in higher permeability soils, pre-generated foam was required to get high viscosity foam. Foam and xanthan polymer solution behaviors were compared across the range of permeability studied. They show similarities, and the benefits of one among the other should be evaluated for each specific case.