Reactive treatment cells (RTCs) are described in combination with sediment capping systems as a means for environmental remediation. RTCs include an impermeable housing defining an interior, a permeable ceiling and floor typically including filtration materials such as geotextiles, and at least one interior compartment for treatment reagents. One RTC includes a gabion-like cage structure retaining a geomembrane-supported geosynthetic clay liner (GM-GCL) housing, while a second embodiment includes a hard, cylindrical shell as a replaceable reagent cartridge. RTCs may be employed in initial capping system installations or retrofitted into existing capping systems. RTCs may include optional baffles, flow restrictors, floating discs, sensor probes, and two or more serial reagent zones or compartments.
