Enhanced delivery of amendments in contaminated low-permeability soils by hydraulic fracturing

Abstract

In-situ remediation of contaminated low-permeability sites remains to be a critical challenge due to severe mass transfer limitations. This work developed an analytical model for enhanced in-situ remediation by hydraulic fracturing in low permeability sites, considering the mechanisms of convection, diffusion, adsorption, and degradation of amendments. In this model, amendment-filled fractures were conceptualized as mass release sources, with the release process controlled by a dissolution-diffusion equation. Combining the Laplace and Fourier-cosine transformation techniques, the semi-analytic solutions in the two-dimensional spatial domain were obtained and then validated by COMSOL Multiphysics 6.0. Based on this model, the influence range, effective longevity, degradability, amendment reserves, and fracture spacing design of reactive fractures were investigated. Results show that (1) three reaction zones with different degradability will potentially form around the reactive fractures; (2) a larger reservoir of amendments effectively increases the influence range and effective longevity of reactive fractures; (3) the synergy of multiple fracture systems outweigh the sum of individual fracture properties, but the reasonable spacing design is decisive; (4) ignoring adsorption in low-permeability site remediation may overestimate the influence range of reactive fractures, leading to remediation failure. This work comprehensively analyzed the properties of reactive fractures, providing practitioners with a reference for the enhanced remediation of low-permeability contaminated sites.