In a recent pilot-scale study with contaminated groundwater at Glendale, CA, two weak-base anion exchange (WBA) (Duolite A-7 and SIR-700) resins exhibited at least one order of magnitude higher capacity than strong base anion exchange resins for Cr (VI) removal in presence of significantly high concentrations of competing anions like chloride, sulfate, etc. Comparison with earlier studies suggested, in addition to anion exchange, presence of other mechanism(s) is responsible for such high chromate removal capacity. It was also observed that there was a significant simultaneous removal of copper that was present in the groundwater along with chromate ions. Such a simultaneous removal of copper and chromate ions by the WBA resin also indicated a possible presence of polymeric ligand exchange phenomenon along with ion exchange. A series of laboratory investigations involving fixed bed column runs and other characterization studies were undertaken to find out the exact mechanism behind such a high chromate removal capacity. The results showed that there was an increase in pH associated with chromium removal by the resin. Also, the WBA resins pre-loaded with copper ions did not show any preference towards ligands like arsenates and phosphates over other common anions, thereby negating possibility of any polymeric ligand exchange. Further studies on exhausted WBA resin showed presence of Cr(III) species inside the ion exchanger, indicating reduction of influent Cr(VI) ions to Cr(III). Other ion exchange column runs and comparative FTIR studies of the virgin, exhausted and oxidized resins confirmed a structural change in the organic polymer phase of the resins. The results of the study revealed a new mechanism of reactive ion exchange. First, chromate ions are removed from the solution through anion exchange at the functional groups of the resin. Subsequently, chromate ions are reduced to form insoluble Cr(III) species within the resin beads. The redox reaction results in a renewal of the positively charged functional groups of the resin for further ion exchange and subsequent redox reaction. Redox reaction is a slower process than ion exchange and therefore, is the rate limiting step in the removal process. Interruptions in the column runs proved the presence of a rate limiting process with characteristics different from the usual intra-particle diffusion process. The presentation shall discuss the findings of multi-faceted studies carried out to investigate the mechanism of reactive ion exchange leading to high capacity of the WBA resins for chromate removal.