In many low-permeability aquifers, it is very diffi cult to construct well systems that can reliably inject reagents — the concentration of fl ow in silt and clay aquifers is often extreme, with thin lenses of conductive matrix embedded within much larger bodies of compressible material. It is often diffi cult to map the contaminant transporting strata and drilling tends to smear the lower-permeability soils across the borehole, blocking the fl ow conduits. Attempts to clear the smearing during well development are often unsuccessful, yielding reagent injection wells that are disconnected from the contaminant transport pathways. Flow-controlling reactive zone designs offer an alternative strategy to overcome the limitations on reagent distribution in low-permeability (silt and clay dominated) aquifers. They can also provide a cost-effective alternative to groundwater pumping, when fl ow containment is the primary objective.