Pacific Southwest, Region 9: Superfund
Serving Arizona, California, Hawaii, Nevada, the Pacific Islands, and Tribal Nations
Nineteenth Avenue Landfill
EPA #: AZD980496780
Congressional District: 04
Other Names: Salt River Landfills
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Description and History
NPL Listing History
NPL Status: Deleted
Proposed Date: 12/30/82
Final Date: 09/08/83
Deleted Date: 09/25/06
The Nineteenth Avenue Landfill Superfund Site (Site) is a 213-acre closed landfill, composed of two section, located in an industrial area of Phoenix, Maricopa County, Arizona. The Site contains approximately nine million cubic yards of refuse. It is located southeast of the intersection of Lower Buckeye Road and 19th Avenue, and is intersected by the Salt River Channel. An approximately 200 acre section of the Site is located on the northern bank of the Salt River and is referred to as Cell A. The remaining 13-acre portion of the Site, referred to as Cell A-1, is located on the southern bank of the Salt River.
Before the channelization of the Salt River was completed in March 1996, as a part of the final remedy, portions of the Site were within the estimated 100-year flood plain of the Salt River. Flows in the Salt River near the Site were caused by controlled releases at dams more than thirty miles upstream, rainfall, and local sources of discharge into the riverbed. The direction of groundwater flow is predominantly from the southeast to the northwest at the rate of one to eight feet per day. The average depth to groundwater at the Site is approximately 50 - 55 feet below ground surface (bgs). However, in the past during periods of flow in the adjacent Salt River, the groundwater table became elevated and was in contact with the landfill refuse.
The population within six miles of the Site is approximately 16,000 people. The nearest residence is 1/3 of a mile from the Site. The area's primary drinking water is provided by the City of Phoenix (City) water distribution system. The City's municipal water distribution system (the closest drinking water supply) draws water from groundwater and surface water sources over thirty miles away. The nearest drinking water supply well is over three miles away. An industrial well and a down gradient agricultural well are located 200 feet and 800 feet, respectively, from the Site. However, there is no known contamination of these wells at this time.
In 1957, the City extended an existing lease with the landowner to operate a municipal landfill. Prior to that date, the Site was relatively undisturbed. The landowner brought in another party to start sand and gravel mining at the Site to create the space needed for the landfill. The mining and landfill operations began shortly thereafter. Sand and gravel pits were generally excavated to a depth of approximately 30 to 35 feet, although some pits were excavated as deep as 50 feet bgs. The pits were then backfilled with municipal refuse from the Phoenix area. Solid and liquid industrial wastes were also deposited. Liquid wastes, including industrial wastes, were poured into unlined pits dug into areas of Cell A previously filled with refuse. In addition to the municipal and industrial wastes, some medical wastes and materials containing low levels of radioactivity were also deposited. The refuse was generally covered on a daily basis. A final soil cap was placed over the area once it was full of waste. From 1964 until 1979, the landfill was operated by the City.
During 1965 and intermittently during the 1970s, parts of the landfill were covered with water by flood events. Liquid waste disposal pits were breached at least once during these events. In May 1978, river flow and surface water run-off events washed refuse from the southwest portion of Cell A and the northern third of Cell A-1. The area in Cell A was then refilled with new refuse during the summer of 1978. The Cell A-1 area was refilled with construction debris in 1979. Early in 1979, the Salt River flooded again, raising the water table and filling several of the landfill pits. The high water also breached several dikes, opening landfill cells and causing refuse to wash directly into the river. Water infiltrated directly into the cells, increasing the potential for leachate generation and resulting in leachate contamination of groundwater. In addition, saturation of the waste generated excess amounts of methane gas.
In 1979, the Arizona Department of Health Services (ADHS) issued a cease and desist order for the landfill to be closed. Later in 1979, the City and ADHS entered into a Consent Agreement. To comply with the Consent Agreement, the City covered the Site with fill material, stockpiled soil for final capping, installed 18 groundwater monitoring wells, built earthen berms around the boundary of the landfill to limit access, covered the landfill with sand, gravel and stones, and provided a 24-hour security guard. In 1981, the City installed a system to collect methane gas and completed installation of groundwater monitoring wells to sample the water quality.
Contaminants and Risks
- Surface Water
- Soil and Sludges
During the remedial investigation (RI), the groundwater was found to contain very low levels of volatile organic compounds (VOCs), heavy metals including arsenic, barium, mercury, and nickel, and beta radiation. The only compound that is above drinking water standards (MCLs) is 1,1-dichloroethylene (1,1-DCE). Sampling of soil and refuse in the landfill during the RI had shown that the contents of the landfill are generally similar to those expected in municipal landfills, although refuse in the landfill also contains VOCs and pesticides. Soil contained VOCs, polychlorinated biphenyls (PCBs), heavy metals and pesticides. During the RI, the most frequently detected VOCs were ethyl benzene, 1,4-dichlorobenzene, xylenes and toluene.
Potential public health risks could occur if landfill material were washed out of the landfill as the result of flows in the Salt River. However, since the channelization and stabilization of the Salt River Channel, this scenario is unlikely to occur in the future. The surface water concern was based on the potential for surface water run-off to contact refuse and transport refuse to the Salt River. This may have occurred in the past during periods of heavy river flow due to increased risk of a surface water exposure pathway and a sediment exposure pathway. Another risk could be a rising water table that would saturate the refuse and release additional leachate. Additional leachate could impact the quality of nearby groundwater. Although the groundwater table is still in contact with refuse in the landfill during periods of flow in the adjacent Salt River, the existing monitoring network indicates that it results in minimal contamination of the groundwater.
The Groundwater Contingency Plan ensures continued monitoring of the groundwater in the vicinity of the Site to evaluate and remediate potential degradation of the groundwater from the landfill. Exposure to groundwater from a new shallow drinking water well, assuming such a new well were drilled on or near the landfill boundary and used as a drinking water source, represents the only quantifiable potential public health risk.
Who is Involved
The City of Phoenix, the potentially responsible party (PRP) for the Site, was responsible for the construction of the remedy and continues to be responsible for the long-term operation and maintenance of the Site. The Arizona Department of Environmental Quality (ADEQ), at the State-level, and EPA, at the federal level, provide oversight of the work.
In 1983, the Site was placed on EPA's National Priorities List (NPL). In June 1998, the City completed a Remedial Investigation/Feasibility Study (RI/FS) in June 1988. The same year, EPA agreed to assign the lead oversight responsibility for the Site to ADEQ. In 1989, the City completed and ADEQ approved a Remedial Action Plan (RAP) for the Site. In September 1989, EPA concurred with the chosen remedy set forth in the RAP in a Record of Decision.
In 1990, the City began design the Site remedy. In June 1992, the City entered into a Consent Decree with the State of Arizona for the remedial design/remedial action (RD/RA) and all cleanup costs. The City completed the design specifications in 1995. The selected remedy required completion of levees and channelization of the Salt River to prevent future potential flooding of the landfill refuse during storm events. It also required containment of the landfill wastes on-site, with the collection and flaring of landfill generated gases. Soil vapor gases (methane) generated in the landfill are to be managed by separate gas collection and flare systems operating independently in each cell of the landfill. Monitoring of the soil vapor at the Site boundaries and within the landfill is required to ensure the system is preventing off-site migration of soil vapor. The remedy also required long-term groundwater monitoring.
In August 1995, the City started work on the bank protection system and the grade control structure and site grading for the capping system, which was completed in December. Also, in December 1995, ADEQ signed Explanation of Significant Difference (ESD) #1 to change the perimeter channel drainage lining material from Gunite to Armorflex. In May 1996, the installation of the Armorflex channel and sedimentation pond lining system was started. The capping system and site landscaping were both completed by the end of November 1996. Flooding of the landfill is not likely to occur again in the future since the Salt River Channel was channelized to withstand a (estimated) 100-year flood event. In addition, the north and south river banks were strengthened with soil cement levees extending to 10 feet below the river channel.
In 1996, construction of the landfill gas remedy was also started. In October 1996, the gas collection system and two flare stations were completed. Maricopa County issued an air permit to the City for the landfill gas flare stations. In February 1997, the landfill gas collection system became fully operational.
In 1996, pre-final construction inspections and final inspections were conducted of the remedy. In February 1997, the City accepted final completion of the construction work by the contractor. The final Site remedy design and construction cost was $22,500,000. In June 1997, ADEQ issued written approval of completion of the remedial action in accordance with the Consent Decree. which activated the Groundwater Contingency Plan.
The Groundwater Contingency Plan requires the City to perform long-term groundwater monitoring. If water quality standards in the Plan are exceeded at or downgradient of the landfill boundary, the City is required to evaluate the potential source of the groundwater degradation. Should ADEQ determine that the landfill is the cause of the degradation, the City must evaluate, and potentially implement, measures to remediate groundwater. In the event that groundwater remediation would be required, the remedies proposed will be evaluated using the nine criteria specified in 40 CFR Part 300.430(e)(9)(iii).
In February 1998, EPA signed a Preliminary Close-Out Report (PCOR), which documented construction completion. In September 1998, EPA approved the Remedial Action Report for Construction Complete, prepared by the City, and previously approved by ADEQ.
In 1998, the City, with oversight by ADEQ and EPA, conducted some additional groundwater studies at the Site because groundwater contamination of 1,1-dichloroethylene (1,1-DCE) was detected above aquifer water quality standards in some monitoring wells. In January 1999, EPA and ADEQ determined that the 1,1-DCE contamination originated from an upgradient source, not the Site. Therefore, under the Consent Decree, the City is not responsible for addressing this contamination. The wells at the Site continue to be monitored as part of the Groundwater Contingency Plan (described above).
In 2002, the City completed construction on improvements to the landfill gas collection system, including installation of new methane monitoring probes after high methane levels were detected in some methane probes at the landfill. The City was also required to conduct monthly surface monitoring measurements in those areas of the landfill, under an approved plan, to ensure that methane does not migrate beyond landfill boundaries from either of the two cells.
In 2003, EPA signed ESD #2 to modify the remedy to update the maximum contaminant levels (MCLs) for specific chemicals to be consistent with EPA’s changes to those standards. The need to update the standards was identified during the Five Year Review conducted in 2001. No specific actions were required of the City because the groundwater quality at the Site was not exceeding any of the new groundwater standards.
In April 2006, EPA signed ESD #3 to incorporate into the remedy Institutional Controls (ICs) for the Site. The ICs included both a Declaration of Environmental Use Restriction (DEUR) administered by ADEQ and Arizona Department of Water Resources requirements. ICs ensure long-term protectiveness of the remedy in the event the property is sold or other land use changes occur. The DEUR controls the use and access to the landfill property. In July 2006, a DEUR was attached to the property deed by the City (landowner). The DEUR is a covenant that runs with the land and therefore, provides notification to future landowners of use restrictions to prevent human exposure to the landfill contamination. The Arizona Department of Water Resources (ADWR) ICs also restrict the placement, construction or use of a groundwater well near a contaminated Site that could impact the operation of the remedy.
In August 2006, EPA and ADEQ completed a Final Close Out Report documenting that the Site is eligible for "site completion", signifying the end of all response actions at the Site. The Report concluded that no further Superfund response is required to protect human health and the environment. As part of that determination, EPA proposed deletion of the Site from the NPL on August 14, 2006 (Federal Register Vol. 71, No. 156, page 46429) and finalized the deletion on September 25, 2006 (Federal Register Vol. 71, No. 185, page 55742). EPA also prepared a Responsiveness Summary to the public comments received on the delisting proposal, which are available for public review. The City of Phoenix continues to be responsible for long-term operation and maintenance activities. EPA will continue to conduct Five Year Reviews, which will always be required because contaminated waste is left in place at the Site.
Cleanup Results to Date
Based on the information gathered during the RI/FS and the quality of the construction of the final remedy, it is believed that the final remedy selected by ADEQ and EPA for the Site is protective of human health and the environment, is cost effective, and attains federal and state requirements that are applicable or relevant and appropriate
The remedy uses permanent solutions and alternative treatment technologies to the maximum extent practicable for this Site. The collection and flaring of gas and implementation of a Groundwater Contingency Plan are significant components of the remedy. The size of the landfill and the volume of landfill wastes preclude a remedy in which contaminants could be effectively excavated and treated.
As hazardous substances remain buried on-Site in the landfill above health-based levels, EPA will continue to conduct a Five Year Review (FYR) to ensure the remedy continues to be protective of public health and the environment. Four FYR Reports have been completed to date in 2000, 2005, 2010 and 2015. The most recent 2015 Five Year Review concluded that the site remedy is protective of human health and the environment. There are no environmental exposure pathways that result in unacceptable risks, and none are expected as long as the engineered controls and ICs selected in the decision documents continue to be properly operated, monitored and maintained, and the land use at the Site allows for the integrity of the remedy to continue.
Potentially Responsible Parties
Potentially responsible parties (PRPs) refers to companies that are potentially responsible for generating, transporting, or disposing of the hazardous waste found at the site.
The City of Phoenix is the PRP for the 19th Avenue Landfill.
Documents and Reports
Public Information Repositories
The public information repositories for the site are at the following locations:
City of Phoenix Public Library
1221 N. Central Avenue
Phoenix, AZ 85004
Arizona Department of Environmental Quality (ADEQ)
1110 W. Washington St.
EPA Site Manager
Mail Code SFD
75 Hawthorne Street
San Francisco, CA 94105
EPA Community Involvement Coordinator
Mail Code SFD
75 Hawthorne Street
San Francisco, CA 94105
EPA Public Information Center
1110 W. Washington St.
Phoenix, AZ 85007-2935
After Hours (Emergency Response)