The concept of the technology involves the emplacement of a permeable barrier containing reactive materials
across the flow path of the contaminated groundwater to intercept and treat the contaminants as the
plume flows through it under the influence of the natural hydraulic gradient. Since the invention of PRBs
in the early 1990s, a variety of materials has been employed to remove contaminants including heavy
metals, chlorinated solvents, aromatic hydrocarbons, and pesticides. Contaminant removal is usually
accomplished via processes such as adsorption, precipitation, denitrification and biodegradation. Despite
wide acknowledgment, there are still unresolved issues about long term-performance of PRBs, which
have somewhat affected their acceptability and full-scale implementation. The current paper presents
an overview of the PRB technology, which includes the state of art, the merits and limitations, the reactive
media used so far, and the mechanisms employed to transform or immobilize contaminants. The paper
also looks at the design, construction and the long-term performance of PRBs.