In Situ Fluidization for Solids Addition to Permeable Reactive Barriers

Abstract: This study concerns in situ fluidization (ISF), a new remediation method, in which an air/water jet is lowered from the ground surface into a contaminated, sandy soil, to produce an in situ fluidized zone [1]. NAPL removal takes place by the buoyant release of NAPL droplets and composite NAPL-soil particles, whilst metals are removed by the washing of fine particles from the soil [1-4]. The aim of the present study is to report recent work on the application of ISF for the in situ emplacement of zero-valent iron (ZVI), for low-cost construction of permeable treatment barriers. Experiments were conducted on a 240 µm sand in a tank, into which ZVI of was added during fluidization. It was found that the addition of increments of ZVI, as the jet was withdrawn, was successful for the in situ emplacement of layers of ZVI within the sand matrix. A schematic diagram of ISF is included in Fig. 1. Fluidization of the soil medium- as distinct from in situ flushing- has the advantage that it ruptures the soil matrix, releasing NAPL and fine contaminants which would otherwise remain trapped within the soil. Laboratory experiments indicate that very high reductions in NAPL concentrations (up to 99.9 % diesel) may be achieved, consistently over a wide range of initial NAPL levels (10,000 to 150,000 mg/kg) [1,3]