The treatment and disposal of perchlorate-laden concentrates can often be complicated and costly. Therefore, due to their ability to convert perchlorate to innocuous chloride and oxygen, biologically based processes may play an increasingly important role in the treatment of drinking water contaminated with perchlorate. A six-month pilot study at the Castaic Lake Water Agency has demonstrated that perchlorate-reducing biological reactors can be acclimated using organisms indigenous to the Saugus aquifer, that perchlorate can be removed to below detection using reasonable contact times, and that effluent water from these processes is of fairly high quality. Ultimately, the results of this project will be used to evaluate the feasibility and costs associated with treating perchlorate-laden Saugus aquifer water using both fixed- and fluidized-bed biological reactors.