Performance and longevity of colloidal silica gel in blocking vertical water flow and contaminant transport in the annuli of long-screened wells: Laboratory and numerical evaluation.

This laboratory-based study evaluated the performance and long-term (months) stability of colloidal silica (CS) gels in blocking vertical water flow and controlling chemical transport in subsurface applications, especially in the well annuli of long-screened wells. Laboratory-scale rheological tests demonstrated the injectivity of CS suspensions in expected field applications. Laboratory column, sandbox experiments and numerical modeling were used to assess the efficacy of CS gel in reducing hydraulic conductivities of the well annulus system. Further, a contaminant diffusion test was applied to evaluate the performance of CS gel-sand pack in mitigating transport of contamination. Rheological analyses highlighted the shear-thinning behavior of modified CS suspensions, facilitating more efficient injections in field applications. Hydraulic conductivity (K) tests revealed notable K reductions following CS gel injection, confirming its effectiveness in blocking vertical water flow. Diffusion tests demonstrated that no hexavalent chromium (Cr(VI)) migrated through CS gel-grouted sand barriers in 6 months, suggesting their strong potential as containment solutions for hazardous contaminants. Numerical simulations validated experimental data to reinforce the performance assessment of CS gels as barriers. The findings underscore CS gel's promising applications not only in long-screened well annular systems, but also in subsurface remediation, groundwater protection, and contaminant containment, providing critical insights for field-scale implementations.