Low-pressure Polymer Immobilization Methods to Reduce Contaminant Leaching from Deep Vadose Zone Sands

This study aimed to assess the extent of iodide immobilization provided by soil freezing and grouting by creating cured solid monoliths and measuring the diffusivity of model contaminants. Variables analyzed were freezing, moisture content (1.6%, 5%), iodide dosage (0.9- 0.28 wt.%), and accumulated pressure conditions (101.3-2289.1 kPa). The iodide leaching as cumulative fraction leached (CFL), diffusivity, and leachability index (LI) were evaluated per ANSI/ANS-16.1. Iodide concentrations were measured with an iodide ion selective electrode probe. CFL on grouted centrifuge tube test samples decreased (from 0.83 to 0.52) by moisture content reduction (from 5% to 1.6%). Iodide dosage increase (from 0.1 to 0.3 wt.%) led to a decrease of 0.2 in LI values (from 6.5 to 6.3). Lower moisture content significantly reduced the iodide mobilization during injection on acrylic chamber tests (from 37.9% to 0.3%) but did not reduce the extent of leaching. Freezing does not have a significant impact on iodide immobilization under the moisture contents investigated in this study. High pressure due to CO2 gas accumulation within the acrylic cells apparently inhibited the polymerization reaction. Using soil freezing and fracture grouting as immobilization technology can reduce the leaching of iodide (CFL from 0.45 to 0.66).