Can HRC be used in the vadose zone?
We do not recommend using conventional HRC in the vadose zone. For certain sites with compact, well-defined contaminant mass, we may recommend (after a thorough technical evaluation) use of HRC primer. HRC primer is a low viscosity, free flowing version of HRC. A key difficulty with using conventional HRC (a thick, viscous, honey-like material that slowly releases lactate upon contact with water) in the vadose zone is obtaining sufficient HRC coverage to create anaerobic conditions in the typically aerobic and unsaturated vadose zone. In contrast, HRC primer rapidly releases lactate, is liquid enough to flush the contaminated area, and can quickly create an anaerobic treatment zone. For HRC primer treatment in the vadose zone, closely spaced injection points must be used and additional irrigation may be necessary. For these reasons, use of HRC primer in the vadose may be economically unfeasible. For vadose zone sites with large, highly contaminated plumes in shallow areas that are easi
