As a collaborative effort between MWH and Northwestern University (NWU), the objective of this research was to investigate the application of a novel hydrogen-fed hollow-fiber membrane biofilm reactor (MBfR) for the removal of perchlorate. During initial testing, it was discovered that a bench-scale MBfR was effective in reducing 50 to 1,000 ug/L perchlorate to below the previous California Department of Public Health Services Advisory Action Level of 18-ug/L. At pilot-scale, the objective was to evaluate the application of a pilot-scale MBfR system to biologically reduce low-concentration perchlorate-contaminated water from an active groundwater well to below the current 4 ug/L CaDHS Action Limit. Includes tables, figures.