Rio Nuevo

Landfill Stabilization Project

The Rio Nuevo project includes construction of the Interpretive Center, Convento, and Chapel with gardens and grounds at the eastern base of "A" Mountain. To the north, the project includes the new University of Arizona Museum building, and the new State Historical Society building. The developments will all be located on the San Agustin Mission Site that includes the mission footprint and three retired municipal landfills (Nearmont, Congress, and A-Mountain) with a total area of 54 acres.

In 1999, City of Tucson Environmental Services (ES) proposed to perform a landfill stabilization pilot project at the Nearmont Landfill, within the project area footprint, using an aerobic biodegradation process. The process is similar to composting only it is performed on the waste in-place and will accelerate the decomposition rate of the refuse in the landfills to 2 to 3 years instead of the normal 100-year period. The aerobic biodegradation process decomposes the waste to the point where it is inert and can no longer produce methane gases. The process uses injected air and applied water to increase microbial activity in the waste to accelerate the biological degradation. This process will allow the decomposed refuse to remain as below the surface on the site or be removed as inert compost as opposed to municipal waste which would be hauled to an active landfill for disposal. It was agreed the aerobic biodegradation process will allow timely construction of the Rio Nuevo Project and eliminate the need to remove the majority of the 1.0 million tons of waste below the Interpretive Center footprint. Additionally, allowing the waste to stay in place or hauled as inert compost will save an estimated $50 million in construction costs for the Rio Nuevo Project.

Approval for the proposed landfill stabilization project was granted in September 2000 and the Nearmont Landfill pilot test of a 50-foot by 50-foot plot was planned for, permitted, and constructed. The aerobic biodegradation process began at the site in June 2001 and the project ran through to completion in February 2002. The pilot project was successful and accelerated decomposition rates were realized at the end of the pilot test.

Based on the success of the Nearmont pilot test, the next phase of the landfill stabilization project was planned for and the equipment was installed at the 2-acre Congress Landfill site. The Congress aerobic biodegradation process began in January 2003 and ran until March 2007. The project was interrupted for a year between June 2004 and June 2005.. Site samples obtained in July 2005 has allowed COT-ES to determine that the 2-acre Congress bioreactor site is completed. Design for the 17-acre full scale project began in May 2006 with construction completed in December 2006. The site began operation in February 2007. A site map is attached for reference.