Initial development of the trickling filter/solids contact (TF/SC) process occurred at Corvallis, Oregon, in 1979 as a joint effort on the part of Brown and Caldwell and the city of Corvallis. The process continues to operate with outstanding effectiveness at Corvallis. Since 1979, this 9.7-mgd plant has consistently produced an effluent with monthly 5-day biochemical oxygen demand (BOD5) and suspended solids (SS) averages of less than 10 mg/l without advanced treatment.