Rising groundwater levels in Bitterfeld, Germany, will transport organic contaminants near the ground surface in the future, so that the construction of near-natural wetlands may present an effective remediation approach. A 2 × 6 m pilot plant was built to investigate the fate of monochlorobenzene (MCB), one of the main pollutants at the site, in a wetland system. MCB concentrations were reduced from ~10–15 mg l-1 at the inlet to ~1–3 mg l-1 after passage through the soil filter. A zonation in the vertical and horizontal direction was apparent for MCB, sulfate, iron(II) and pH. Aerobic MCB-degrading microbial communities were enriched from the pilot plant and showed degradation of MCB in microcosms down to oxygen-limited conditions of 0.5 mg O2 l-1. Volatilization may also constitute a significant process as indicated by the results of active and passive gas sampling at the surface of the soil filter. Overall, constructed wetlands have a high potential for the remediation of chlorinated solvents, but more research is needed to move away from a black box approach and understand the relevant attenuation processes.