| 1894 | First wastewater discharged to Santa Monica Bay |
| 1925 | Screening plant in operation |
| 1950 | Modern Hyperion Treatment Plant begins operation; 265 mgd capacity primary and "high rate" full secondary treatment; sludge dried and sold as soil amendment |
| 1957 | Ocean disposal of sludge begins; plant expanded to 420 mgd primary capacity and converted to 100 mgd capacity conventional secondary activated sludge process |
| 1975 | LA/OMA Project sludge study begins |
| 1980 | Consent Decree between Los Angeles and EPA to end ocean disposal of sludge |
| 1981 | Energy recovery sludge management system recommended for Hyperion |
| 1983 | Construction of energy recovery system begins |
| 1987 | Amended Consent Decree - Sludge out by end of 1987, full secondary by 1998; design of full secondary treatment facilities underway; chemical addition to improve primary treatment solids capture efficiency began; beginning of long term commitment to a cooperative effort with environmental groups |
| 1987 | First energy produced in co-generation power system; secondary treatment system capacity boosted to 130 mgd; ocean discharge of sludge halted in November |
| 1988 | Old internal combustion engines shut down and replaced by gas and steam turbines; air emissions from Hyperion cut by 80 percent; interim odor improvements completed; off-site beneficial reuse of sludge initiated; construction of new primary treatment and full secondary treatment facilities initiated; new digester gas flare system installed; secondary treatment capacity boosted to 200 mgd |
| 1989 | Energy recovery system in full-scale operation, beginning of 100% beneficial reuse of sludge and cessation of landfill disposal; Plant began meeting all 1998 Full Secondary Treatment Standards except BOD, nine years ahead of schedule |
| 1991 | Additional primary treatment in operation; one million tons of sludge have been beneficially reused; first phase of construction begins for phase 1 of full secondary treatment facilities and dewatering centrifuge expansion |
| 1992 | Begin Digester Expansion construction |
| 1993 | New headworks in operation, North Outfall Replacement Sewer completed and in operation |
| 1994 | First modules of new secondary treatment facilities in operation; first phase of dewatering centrifuge facility begins operating; first phase of co-generation expansion begins construction |
| 1997 | Expanded Digester Facilities begins operation |
| 1998 | Secondary treatment provided to all Hyperion flows; Second phase of dewatering centrifuge facility starts up |
