Water Quality Assurance Revolving Fund (WQARF) Site

Silverbell Jail Annex Landfill

Community Involvement Activities Public Health Impact Site Hydrogeology
Contacts Public Meeting Calendar Site Map
Contaminants Public Notice Calendar Site Status Update
Online Information Repository Site History

The Silverbell Jail Annex Landfill site is located in west Tucson, Arizona and is bounded approximately by Sweetwater Drive on the north, Interstate 10 on the east, Grant Road/Ironwood Hill Drive on the south and Silverbell Road on the west.

The plume geographic boundaries depicted on the site map represent the Arizona Department of Environmental Quality’s (ADEQ) interpretation of data available at the time the map was constructed. The map is intended to provide the public with basic information as to the estimated extent of known contamination as of the date of map production. The actual extent of contamination may be different. Therefore, the plume boundaries may change in the future as new information becomes available.

The Silverbell Jail Annex Landfill - A closed
municipal solid waste landfill
The Silverbell Jail Annex Landfill - A closed
municipal solid waste landfill

Site Status Update:

In August 2015, City of Tucson (COT) issued a Request for Proposal for design/build/operation of the P+T system to remove volatile organic contaminants of concern released from the Silverbell Jail Annex Landfill. The treated water will be delivered for reuse by the nearby City golf courses, parks, and Sweetwater Recharge Facility (instead of being disposed via injection wells as originally envisioned in 2010). Proposals are to be submitted in the fall of 2015.

As of June 2015, Kinder Morgan Energy Partners has extracted approximately 317,541 pounds (approximately 51,717) of gasoline from the soil beneath the SWR site. Previously, approximately 48,112 gallons of hydrocarbons were removed through a free product recovery system that was terminated (with ADEQ approval) in 2007. These hydrocarbons (gasoline) were released when the pipeline ruptured in 2003.

Community Involvement Activities:

COT involved the community throughout the remedial investigation/feasibility study (RI/FS) process. However, if the proposed remedial action plan (PRAP) is significantly modified, additional public comment will be solicited.

Site History:

1960 - 1978: The University of Arizona operated a solid waste landfill in the area east of the Santa Cruz River and south of Fort Lowell Road. The COT-managed Silverbell Jail Annex Landfill is made up of two landfill cells, approximately 40 acres in total size, which received wastes between 1966 and 1977. Neither cell accepted hazardous waste, although landfill access was not strictly controlled. The South Cell has been covered with soil, and the North Cell underlies a portion of the Silverbell Golf Course.

1983 - 1985: In fall 1983, groundwater contamination was discovered at the Tratel Mobile Home Park Production Well located east of the site. Also in 1983, COT began conducting subsurface investigations, and ADEQ began conducting groundwater investigations in 1985.  VOCs were identified in the groundwater at concentrations exceeding Aquifer Water Quality Standards (AWQS). 

1995: In June, COT completed an interim final remedial action proposal (RAP). The approved RAP proposed a P+T system utilizing air stripping treatment and a carbon filter to capture exhaust from the air stripper. Treated water would be reinjected into the aquifer and/or reused at Silverbell Golf Course. Although this groundwater remedy was not implemented, COT evaluated several groundwater remedial pilot projects and installed an air injection/soil vapor extraction (SVE) system.

Also in June, ADEQ closed the University of Arizona’s West Campus Agricultural Center site. Data and information collected and available as of June 1995 did not show that this site was a source of PCE and trichloroethene (TCE) contamination in the groundwater.

1996 - 1998: ADEQ approved COT’s request to conduct a pilot study to evaluate the effectiveness of a recirculation well to replace or enhance the approved P+T remedy.

1999: The site was placed on the WQARF Registry in April with an eligibility and evaluation score of 51 out of a possible 120.

The COT’s Bioremediation and Soil 
Vapor Extraction System
The COT’s Bioremediation and Soil
Vapor Extraction System

1999 - 2005: From October 1999 to September 2005, COT operated an SVE system to mitigate the source. This system removed a total of 2,061 pounds of VOCs. The system has remained off since achieving cleanup goals, but has operated occasionally to control methane migration.

In July 2003, a pipeline operated by Kinder Morgan broke resulting in the release of gasoline to an area near the site. Cleanup of the gasoline contamination is being conducted under ADEQ’s Voluntary Remediation Program (VRP) and the site has been named the (SWR) site. The gasoline contamination and the existing PCE and TCE plume emanating from the Silverbell Jail Annex Landfill are being monitored.

The COT has evaluated monitored natural attenuation with enhanced bioremediation for the source areas. A pilot test using sodium benzoate to stimulate indigenous microbes began in June 2003.

In 2004, Kinder Morgan identified the presence of VOCs in the soil vapors within the Silver Creek residential subdivision. ADEQ believed these soil vapors were unrelated to the gasoline pipeline rupture. ADEQ conducted additional soil vapor testing in early October 2004 to confirm and expand upon the Kinder Morgan data. With that data, the Arizona Department of Health Services conducted a Health Consultation to evaluate whether soil vapors from VOCs in the subsurface at the Silver Creek subdivision posed any health risks to residents. The report, released in June 2005, concluded that the observed concentrations of compounds in soil vapors pose no apparent public health hazard. In July, COT expanded the pilot test by constructing an automatic mixing and delivery system for the north cell area, and changed the added nutrient to sodium lactate.

2006: In May, COT included the south cell in the pilot test. Based upon the pilot test results, sodium lactate was shown to be a suitable nutrient to stimulate anaerobic bioremediation and has reduced PCE concentrations within both the north and south cells. However, COT has determined that use of this remedial technology for the final remedy would be cost-prohibitive.

2007: In August, Kinder Morgan began operating an SVE remediation system to clean up contaminated soil beneath the site.

2008: The COT Environmental Services, with assistance from Tucson Water, developed a groundwater fate and transport model for the site. The COT has been evaluating a P+T system for plume containment using this model to prevent further off-site migration.

2009: As of December, Kinder Morgan Energy Partners has extracted approximately 172,300 pounds (approximately 28,000 gallons) of hydrocarbons from the soil beneath the site.

2010: In January, COT submitted to ADEQ its revised RAP Implementation Evaluation of remedial alternatives report for review. In this report, COT proposed the installation of a groundwater P+T system to address the central part of the landfill with the highest VOC concentrations. The plan includes four extraction wells, an air stripping treatment plant with granular activated system to capture VOCs in the vapor phase, and four injection wells.  One potential complication not addressed by the plan is the commingling of the Kinder Morgan plume with the Silverbell Landfill PCE plume. 

In the fall, ADEQ provided COT with conditional approval of the plan as an ERA, but asked COT to further define the extent of the plume to the northeast. COT installed two shallow- and intermediate-zone well pairs between the Silverbell Jail Annex Landfill and the Miracle Mile WQARF sites. These wells were sampled during the fall groundwater monitoring event which was coordinated with Tucson Water, ADEQ, and Kinder Morgan so that the well water gauging for the Sweetwater Recharge Facilities, the Miracle Mile site, and the Kinder Morgan site were conducted during the same period.

2011: COT hired a contractor to review the most recent field data (including data from the more recently-installed wells), revise the conceptual site model (CSM), and update the modeling study. The model was to be updated to reflect revisions in the CSM and to account for the data collected from 2006-2011. To maximize contaminant removal by COT’s proposed groundwater P+T system, the contractor also was tasked with evaluating additional extraction and injection well arrangements and pumping rates. This work was completed in the fall. The ERA system will focus on removal of the contamination from the “shallow” part of the aquifer, which contains most of the contaminant mass, and reduction (to the extent feasible) of the migration of the most contaminated groundwater towards COT’s Sweetwater Recharge Facilities (located downgradient) extraction wells.  

2012: Prior to finalizing its conceptual design for the proposed groundwater P+T system, COT is having its contractor perform additional modeling to predict when the SWR site contaminants-gasoline additives methyl tertiary-butyl ether (MTBE) and tert-butyl alcohol (TBA) will reach COT’s proposed groundwater treatment system, (Benzene is also a contaminant of concern at the SWR site).  

2013: With the additional modeling of SWR site contaminants complete, COT has determined that the Kinder-Morgan gasoline release would reach COT’s proposed groundwater extraction wells within approximately eight years of pumping. Kinder-Morgan is planning on expanding their existing SVE system to continue to remove the remaining mass of gasoline contamination, and installing a groundwater treatment system to extract and treat gasoline contaminated groundwater by mid-2014. Additionally, COT has determined that injection of treated water from their groundwater extraction system will not be feasible and is undertaking an engineering study to determine how and where to discharge treated groundwater.

2014: COT evaluated options for handling the discharge water from COT’s proposed P+T system and decided that part of the treated water will be used for irrigation at a golf course lake and part of the water will be put into Tucson Water’s Sweetwater Recharge Facilities reclaimed water system.


The current contaminants of concern in groundwater include PCE, TCE, cis-1,2-dichloroethene (cis-1,2-DCE) and vinyl chloride. Contaminants of concern at the site may change as new data becomes available.

Public Health Impact:

No one is known to be drinking contaminated water from this site. However, if you are drinking water from a private well within the boundaries of the site, please contact the ADEQ Project Manager. COT is the main municipal water provider at this site.

Site Hydrogeology:

The site is located within the Tucson Basin. The basin is a broad, northwest sloping alluvial valley surrounded by mountain ranges and can be divided into four geologic units: the Pantano Formation, Tinaja Beds, Fort Lowell Formation, and recent alluvial deposits. The Santa Cruz River is an ephemeral stream that flows as a result of seasonal storm events and runs adjacent to the landfill cells.

The regional aquifer is encountered approximately 145 feet below ground surface. Flow direction in the aquifer is generally to the northwest.


Name Phone/Fax E-mail
Wendy Flood, ADEQ Community Involvement Coordinator (602) 771-4410*/(602) 771-4236 fax [email protected]
Gretchen Wagenseller, ADEQ Project Manager (520) 628-6708*/(520) 628-6745 fax [email protected]
ADEQ Silvercroft Wash Release Site Contact
Joey Pace ADEQ Project Manager (602)-771-4818*/(602) 771-4236 fax [email protected]

*In Arizona, but outside the Tucson area, call toll-free at (888) 271-9302.

Online Information Repository:

Interested parties can review site information here on this page and at the ADEQ Record Center located at 1110 W. Washington Street, Phoenix, Arizona. Please contact (602) 771-4380 or (800) 234-5677 ext. 6027714380 for hours of operation and to schedule an appointment. To review site information at a location near you, please contact the designated Community Involvement Coordinator.

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