Bench-scale testing of an economical hollow-fiber membrane biofilm reactor (MBfR) that uses hydrogen for microbial nitrate removal has been conducted on four groundwater samples collected from California's Central San Joaquin Valley. The water sources had elevated levels of nitrate (three exceeding 14 mg-N/L) and varying concentrations of naturally occurring and anthropogenic chemicals. In all of the samples, nitrate was reduced to less than 0.5 mg-N/L. Other contaminants of concern, including arsenate, perchlorate/chlorate and dibromochloropropane (DBCP), were also reduced during the bench tests. The hydrogen-based MBfR is superior to heterotrophic biological denitrification processes, because hydrogen is the most economical reductant for microbial degradation, leaves no residual, and generates minimal excess biomass. In addition, the MBfR process eliminates costly and difficult waste disposal of salt streams from the competitive ion exchange and reverse osmosis processes. Information from the bench-scale testing is being directed toward engineering scale up evaluations for well-head pilotscale testing and eventual full-scale demonstration.