Wastewater solids disposal at the Sacramento Regional Wastewater Treatment Plant (Regional Plant) site has evolved over the past decade into a large-scale system whereby all solids produced at the 136 million gallon per day (mgd) oxygen activated sludge treatment plant are processed and disposed on site. There has been no solids taken off-site since the Regional Plant began operation in 1982. Before that time the County’s Central Treatment Plant disposed of sludge at the site. The Central Treatment Plant disposal system over the period 1973 to 1982 was, in essence, a prototype for the expanded system now used at the Regional Plant.