Low pressure injection of guar gum stabilized microscale zerovalent iron particles: a pilot study

In the framework of the research project AQUAREHAB (FP7 - G. A. Nr. 226565), a pilot injection test of guar gum stabilized microsized zerovalent iron (mZVI) was designed and performed under low pressure in a CAHs contaminated site in Belgium. Since the injection regime of iron slurries depends on subsurface geotechnical parameters, aquifer hydraulic conductivity, and fluid properties, a specifically designed injection well was installed and a monitoring set-up developed in order to achieve high discharge rates and radii of influence, and a likely homogeneous distribution of the iron particles through low pressure injection. The injection well was designed and sealed in order to sustain average to high discharge rates, preventing the daylighting of the product. Moreover it was hydraulically tested by means of innovative water and guar gum step rate injection tests in order to determine the most suitable injection rate for the iron slurry. A subsequent injection of 50 kg of microsized iron particles (BASF, Germany), dispersed in 5 m3 of a 2 g/l guar gum suspension, was performed at a discharge rate of 1.5 m3/h. The monitoring of the process was conducted measuring injection rate and pressure as well as iron concentration by means of a magnetic susceptometer. After the injection, the iron distribution in the subsurface was determined through liners extraction and the iron concentration measured both via non-invasive magnetic susceptibility measurements and chemical analysis. The field test was specifically designed to inject in a permeation regime, or on the threshold between permeation and fracturing. A radius of influence in the order of 1 m was obtained. The presence of mZVI particles was detected up to 1.7 m from the injection point.