| 1948 | Site used as quarry |
| 1952 | Site became private landfill under Operating Industries Inc.; Eventually, over 4000 companies, businesses and cities disposed of waste at the OII Landfill |
| 1954 | Disposal of waste liquids |
| 1964 | State of California buys 28 acres for Pomona Freeway |
| 1976 | Liquid waste continued to be deposited at 190-acre site by permit of Regional Water Quality Board |
| 1978 | Landfill gas control measures initiated; daily cover required |
| 1980 | Federal Superfund law enacted |
| 1983 | Liquid waste disposal stopped |
| 1984 | All waste disposal stopped; OII site closed |
| 1989 | First Consent Decree signed to address site control, monitoring and leachate management |
| 1990 | Landfill gas control measures defined by EPA in a Record of Decision (ROD) |
| 1992 | Third Consent Decree signed to address Gas Control, Landfill Cover, Surface Water Management |
| 1994 | Leachate Treatment Plant constructed on North Parcel and begins operation, treating and disposing of landfill liquids |
| 1995 | Five-year review plan prepared by EPA; Third Consent Decree Final Work Plan and pre design report introduced |
| 1996 | Long-term landfill remediation Record of Decision issued by EPA |
| 1997 | Cover design completed |
| 1998 | Design plan includes capping landfill with compacted soil and a vegetative layer for native plants |
| 1999 | Final design for Thermal Destruction Facility (TDF) approved; Construction of TDF completed, replacing existing flare station |
| 2000 | Construction of cover completed; TDF certified as providing 99.99% Destruction & Removal Efficiency; Final inspection on South Parcel conducted jointly by EPA, US Army Corps of Engineers, and DTSC; DTSC requests EPA accept the project as complete, EPA agrees |
| 2001 - 2003 |
Ongoing site maintenance, monitoring and compliance testing (approved by EPA) |
| 2004 | May – EPA directs, at NCI's request, to undertake North Parcel remediation; NCI continues to approach North Parcel remediation in a manner to assist City of Monterey Park in commercial development |
| 2005 | EPA conducts Five Year Review of South Parcel progress and operations. The Site marks five-year anniversary of South Parcel environmental cover installation. OII Custodial Trust discusses sale of North Parcel with developer selected by City of Monterey Park, Zelman Development and Home Depot. North Parcel land planned for retail center by City of Monterey Park. NCI collects and crushes 50,000 tons of on-site concrete debris for reuse in North Parcel redevelopment. |
| 2006 | May – OII Custodial Trust, Zelman Development and Home Depot negotiate on sale of North Parcel. Remedial design work for landfill area on North Parcel submitted to and approved by EPA, and "integrated" remedial work underway with NCI and Zelman Development, with revised plans for integration submitted to EPA for review. NCI imports 29,000 cubic yards of soil suitable for landfill cover from source provided by EPA. |
| 2007 | Sale negotiation between OII Custodial Trust, Zelman, and Home Depot continues. Remedial design for landfill closure on North Parcel is updated and submitted to EPA so that future development is accommodated. South Parcel site operations maintenance and monitoring continues. |
| 2008 | April – EPA approves the remedial design and directs the remediation for the North Parcel. May – Unable to reach agreement with Zelman and Home Depot after a multiple year effort, the OII Custodial Trust identifies other qualified developers and enters into an agreement for the sale of North Parcel with Monterey Park Realtors, LLC, a subsidiary of JMP Holdings. June – Mobilization and remediation of North Parcel is underway. NCI imports 10,000 to 25,000 cubic yards of clean soil suitable for landfill cover on the North Parcel from a Los Angeles area development project. |
OII Landfill circa 1969.