Pilot-scale results from the City of Boulder's 63rd Street Water Treatment Plant showed that while only weeks were required to achieve steady-state concentrations of attached biomass for a low-ozone dosed influent, acclimation with respect to MIB & geosmin removal at a 20 ng/L influent concentration was on the order of months. For the first month of the study, percent removals for these compounds were less than 12%. By the fourth month, results for a 13 min empty bed contact time (EBCT) yielded up to 65% removal even though biomass values had not significantly increased. Results also indicated that shorter EBCTs (less than 8 min) often found in higher rate filters, may not be long enough for T&O control. A major issue with controlling MIB and geosmin is the highly varying source water concentration. The pilot results showed a lag in the performance when the influent concentration was increased from 20 ng/L to 80 ng/L. The full-scale biofilter (pre GAC) results at the Greater Cincinnati Water Works (GCWW) showed that MIB & geosmin could be removed (32% to 96%) under varying influent concentrations (2 to 398 ng/L MIB), with the lower removals associated with low influent concentrations and low temperatures. Other acclimation and biofilter performance factors include the impact of media-type and impact of acclimation source. In this study, biologically active carbon (BAC) filters outperformed sand media filters and media acclimated off-site (at the GCWW) showed similar percent removals of MIB and geosmin after being relocated and exposed to changes in influent water quality. MIB and geosmin removals recorded during this study are compared to two other pilot studies (Table 7) and six other fullscale biofilters (Table 2, Figures 5, 6, and 7).