This slide presentation outlines information on Haloacetic Acid removal using granular activated carbon, focusing on biofilm community structure. Three approaches are outlined: adsorption, isotherm tests for carbon adsorption capacity; biofilm development, polymerase chain reaction (PCR) amplification of intergenic spacer region; and, mature biofilm, HAA degradation by biological active carbon (BAC). Conclusions included: the intergenic spacer region analysis revealed that the microbial diversity diminished and stabilized along the filter run; bacterial community diversity may be correlated with HAA degradation; hydrogenophaga palleronii (PCR identified bacterium) did not degrade any HAAs tested; and, isolate MC5 from enrichment cultures expressed higher degradation rates and affinity to ClAA than to Cl2AA. Includes figures.