2023: Contracting and equipment procurement for the advanced oxidation upgrade to the South Shannon Well treatment system was completed. Construction of the system upgrade was initiated. Operation of the South Shannon Well wellhead treatment system and regular groundwater monitoring continued throughout the year. 

2022: Final design of the advanced oxidation upgrade to the South Shannon Well treatment system was completed. Operation of the South Shannon Well treatment system and regular groundwater monitoring continued throughout the year. 

2021: Preliminary design of an Early Response Action (ERA) to increase the pumping rate of the South Shannon Well based on 2020 groundwater modeling was completed. The ERA was designed to upgrade the well’s treatment technology from carbon to advanced oxidation, allowing the well owner/operator to exceed the previous pumping rate which was limited by mass balance during downstream blending. Operation of the South Shannon Well wellhead treatment system and regular groundwater monitoring continued throughout the year.

2020: Groundwater modeling to determine the South Shannon Well’s plume capture at different pumping rates was completed. The results of the modeling indicated that recent pumping rates were suboptimal for hydraulic control and plume capture. Operation of the South Shannon Well wellhead treatment system and regular groundwater monitoring continued throughout the year.

2018 – 2019: Operation of the South Shannon Well wellhead treatment system and regular groundwater monitoring continued throughout the year.

2017: In July, the site Feasibility Study (FS) Report was issued.  Operation of the South Shannon Well wellhead treatment system and regular groundwater monitoring continued through the year.

2016: Operation of the South Shannon Well wellhead treatment system and regular groundwater monitoring continued through the year.

2015: The Remedial Investigation (RI) Report was finalized in April. ADEQ’s contractor conducted a data gap investigation including depth-specific groundwater sampling and developed a preliminary evaluation of remedial alternatives that appeared appropriate for the site in preparation for conducting a FS.

2014: The Draft Final RI Report was completed in March 2014. The El Camino del Cerro Landfill treatment system resumed operation.

2013: By the end of June 2013, the Metropolitan Domestic Water Improvement District (Metro Water) South Shannon Wellhead Granular Activated Carbon (GAC) treatment system had treated 1,337 million gallons of water and removed approximately 272 total pounds, or 123.5 kilograms, of volatile organic compounds (VOCs). The new extraction well at El Camino del Cerro Landfill remained inoperable for much of the year due to electrical difficulties. 

2012: The extraction well for the Shallow Tray Air Stripper treatment system was replaced with a new extraction well located closer to the landfill.

2011: By September the extraction well at the former El Camino del Cerro Landfill had shut down due to scaling problems.  By the end of September, the treatment system had pumped 131 million gallons of water and removed approximately 37.5 pounds or 16.6 kilograms of VOCs.

2010: Metro Water continued to operate the GAC treatment system at the South Shannon Well and the Pima County Solid Waste Division continued to operate the Shallow Tray Air Stripper treatment system at the former El Camino del Cerro Landfill. By the end of the year, Metro Water had pumped 851 million gallons of water and removed approximately 174.5 pounds or 79.2 kilograms of VOCs.  Also by the end of the year, Pima County had pumped 124 million gallons of water and removed 36.5 pounds or 16.6 kilograms of VOCs.

2009: On June 30th, Pima County Solid Waste Division began operation of a Shallow Tray Air Stripper treatment system at the former El Camino del Cerro Landfill.  The pump and treat system was expected to remove the bulk of the potential continuing source to the rest of the plume area. By the end of September, the treatment system had removed approximately 14.9 pounds or 6.7 kilograms of VOCs.

2008: Four additional monitor wells were installed in January. These wells were designed to more fully define the extent of contamination and to replace some wells that had gone dry.  Three of the new monitor wells also served as “sentinel” wells for monitoring possible contaminant migration toward Metro Water wells. Data gathered from these new wells were used to complete the RI of the site. Also in January, ADEQ discontinued operation of the SVE system at the former E.C. Winter property, due to declining extraction rates. 

2007: Five new monitor wells were installed at the site in the early summer. A soil removal action was completed at the former Arizona Wrecksperts/AMRI Oil facility in the spring and summer. A total of 1,600 tons of lead-contaminated soil were removed from the eastern portion of the former Arizona Wrecksperts/AMRI Oil and Western Trailer Park properties. In addition, a number of soil samples were collected on the western portion of the former Arizona Wrecksperts/AMRI Oil property that previously contained waste oil pits in order to complete a human health risk assessment. This risk assessment indicated that no unacceptable risk was associated with the soils at the former Arizona Wrecksperts/AMRI Oil property.

2004 – 2006: RIs were conducted by Pima County in the vicinity of the El Camino del Cerro Landfill and northeast of Interstate 10. The RIs included characterization of the nature and extent of groundwater contamination, evaluation of aquifer characteristics near the landfill, and characterization of the composition of the landfill gas. Available data showed that there was a single plume and supported the combining of the El Camino del Cerro and Shannon Road-Rillito Creek WQARF sites into one site. The El Camino del Cerro and Shannon Road-Rillito Creek WQARF sites were administratively combined into one site, the Shannon Road/El Camino del Cerro WQARF site, in the fall of 2004.

An ADEQ study to determine the vertical extent of the groundwater contamination within contaminated wells at the site was conducted. The data gathered were used to develop future monitor well designs.

An extensive passive soil gas survey was conducted south of Rillito Creek along the east side of I-10 to screen for potential sources of the groundwater contamination. The survey did not indicate that a significant source for the groundwater contamination exists in this area.  Additional active soil vapor investigations at the former E.C. Winter Oil and Arizona Wrecksperts/AMRI Oil properties were also completed because these properties had the highest passive soil gas results. The data gathered from these investigations were analyzed to determine the significance of these potential source areas and any risks they may pose.  In June 2006, a soil vapor extraction (SVE) system was installed at the former E.C. Winter Oil property and began operating to remove VOCs in the soil. The system was expected to operate for one to two years alternating on and off for six month periods.

The effectiveness of the treatment system at Metro Water’s South Shannon Well was diminishing as VOC concentrations increased in the well water. A study to evaluate upgrading the system was performed. The treatment system was shut down from April 2004 through June 2006 and upgraded with two large GAC filters. Five additional groundwater monitor wells were installed in winter 2006 to further evaluate the groundwater on the Arizona Wrecksperts/AMRI Oil property.

2001: In February, lead-contaminated soil was found in the southeast corner of Western Trailer Park property, formerly part of AMRI Oil property. The lot was unoccupied, so there was no risk to residents. Additional soil and groundwater tests were conducted to further determine the extent of the contamination and any potential risks it may pose.

A site investigation of the former E.C. Winter Oil property was completed and an engineering evaluation/cost analysis was issued in June. In the fall, ADEQ excavated surface and near-surface contaminated soil for disposal in a permitted landfill. Also, the Acacia Gardens Well was abandoned. The mobile home park is currently being supplied water from the City of Tucson (COT).   

1995 – 2000: In June 1995, the Pima County Health Department tested residents on the Arizona Wrecksperts property, formerly the AMRI Oil facility for lead. The children on site had elevated blood lead levels, and the residents moved off site until April 1996. From February to April 1996, ADEQ's Site Assessment Unit conducted an initial investigation and a soil removal action at the Arizona Wrecksperts/AMRI Oil property, after a black, tar-like substance was found on the property. Soil contaminated by lead and waste oil was removed and replaced with clean backfill. Additional investigations were conducted to monitor the residents’ lead levels and to determine if the contamination impacted groundwater.

In 1995, Acacia Gardens Mobile Home Park was connected to COT Water. In 1997, the owners of Acacia Gardens installed a wellhead treatment system for their well and operated their system until December 2000.

In September 1996, Pima County began the operation of a pilot landfill gas mitigation system flare. This system utilized a series of gas extraction wells that removed landfill gasses from the El Camino del Cerro Landfill to a flare where they were burned off.

In May 1997, ADEQ completed the installation of five soil vapor monitoring wells in the area of the El Camino del Cerro Landfill. In June 1997, Metro Water completed the installation of a wellhead treatment system for the South Shannon Well.

In December 1997, Pima County completed the El Camino del Cerro Study Area Landfill and Groundwater Operable Unit FS reports. Addendums to the reports were issued by Pima County in 1999. Subsequent landfill cleanup utilized vapor extraction wells and the extracted gas was piped to a biomass filter. Between 20 and 40 pounds of VOCs were removed each week when this system was operating. The system eventually reached a state of ineffective mass removal and Pima County shut down the system to let the landfill soil gas return to equilibrium.

The El Camino del Cerro site was placed on the WQARF Registry in August 1998 with a score of 71 out of a possible 120. In April 1999, the Shannon Road-Rillito Creek site was placed on the WQARF Registry with a score of 53 out of a possible 120. 

1994: VOCs were detected in Metro Water's South Shannon Well and in the Acacia Gardens Mobile Home Park Water Supply Well. Metro Water designated the South Shannon Well as a backup well, and the water drawn from it was blended with the water from two other wells prior to distribution. 

1993: VOCs were detected in the COT Z-006A Water Supply Well, and this well was taken out of the COT Water distribution system. This well is currently used as a monitor well.   

1950s – 1974: The E.C. Winter Oil property was a used oil recycling facility from the 1950s until 1974. The property has been a mixed use (industrial/commercial/residential) property since the cessation of the E.C. Winter operation.