The biological iron removal process uses naturally occurring bacteria to catalyze the oxidation of dissolved iron. Chemical oxidants, such as chlorine or potassium permanganate that are traditionally used in conventional iron removal processes, are eliminated. Reported advantages of the biological process when compared with conventional chemical oxidation processes include reduced chemical use, higher filtration rates, and the ability to efficiently treat source waters that contain high concentrations of iron (greater than 6 milligrams per liter [mg/L]). The City of Florence (City), Oregon, has chosen the biological iron removal process for expansion of its existing water treatment plant facility. The City currently practices conventional chemical oxidation to reduce dissolved iron levels in its source water from about 7 mg/L to below the secondary maximum contaminant level of 0.3 mg/L. Prior to selecting the biological iron removal process as its preferred treatment approach, the City conducted a five-month pilot study of the process to assess its feasibility, performance and economics. Parameters of particular interest during the pilot study included iron removal efficiency, filtration rates, bacteriological water quality of the treated water, and process stability. Testing was conducted with filtration rates ranging from about 3 gallons per minute per square foot (gpm/sf) to 12 gpm/sf with dissolved oxygen levels being maintained at levels from 1 mg/L to about 7 mg/L. Results showed the process to be stable and capable of achieving greater than 95 percent iron removal at all filtration rates tested. No adverse effects on the bacteriological quality of the water were noted. An economic evaluation of the process showed that while capital costs of the biological process are greater than those of conventional chemical oxidation, long term savings would be realized because of reduced chemical use. Includes 2 references, tables, figures.