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 213-acre Nineteenth Avenue Landfill is located in an industrial area of Phoenix, Maricopa County, Arizona. It has been estimated that the landfill contains approximately nine million cubic yards of refuse. The site is geographically situated just 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 landfill, 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 landfill were within the estimated 100-year flood plain of the Salt River. Flows in the Salt River at the landfill location result from controlled releases at dams more than thirty miles upstream as well as 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. However, during periods of flow in the adjacent Salt River, the groundwater table rises and is 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 water distribution system. The municipal system 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.
SITE HISTORY: In 1955, the 19th Avenue Landfill site was relatively undisturbed except for a shallow 20-acre excavation in the northwestern portion of Cell A. In 1957, the City of Phoenix extended an existing lease with the landowner to operate a municipal landfill. 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 below land surface. 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.
The landfill was operated by the City of Phoenix from 1964 until 1979, but was closed by a cease and desist order issued by the Arizona Department of Health Services (ADHS), predecessor to the Arizona Department of Environmental Quality (ADEQ), in February 1979. The City of Phoenix and ADHS entered into a consent agreement in June 1979. The consent order was amended in December 1979. To comply with the first amended consent order, the City covered the site with fill material, stockpiled soil for final capping, installed 18 groundwater monitoring wells, built berms around the boundary of the landfill, installed a methane gas collection system, and provided a 24-hour security guard until November 30, 1996. The guard was no longer required once the site was secured by a permanent fence with secured access points.
Nature and Extent of the Problem: Parts of the landfill were covered with water by at least one flood event during 1965 and intermittently during the 1970s. Liquid waste disposal pits were breached at least once during these events. River flow and surface water run-off events in May 1978 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. This scenario is not likely to occur since the Salt River Channel has now been 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.
The landfill was placed on the EPA's National Priorities List on September 8, 1983 (48 Fed. Reg. 40,658). A Remedial Investigation/Feasibility Study (RI/FS) was voluntarily conducted by the City in accordance with the requirements of CERCLA and SARA and was completed in June 1988. In 1988, EPA agreed to assign the lead oversight responsibility for the site to ADEQ. The City of Phoenix completed the Remedial Action Plan (RAP) in June 1989, and it was approved by ADEQ in September 1989. EPA concurred with the chosen remedy set forth in the RAP in the Record of Decision, signed in September 1989. The City of Phoenix entered into a Consent Decree with the State of Arizona in June of 1992 for the remedial action (design and construction) and all cleanup costs.
The final remedy for the Nineteenth Avenue Landfill site, completed in February 1997, provides for containment of the landfill wastes on-site with the collection and flaring of landfill generated gases. Landfill gases that are generated are managed by separate gas collection and flare systems which operate independently in each cell of the landfill. The City of Phoenix is required to monitor the methane at the landfill boundaries and perform other methane monitoring to ensure the system is preventing off-site migration of landfill gas. Groundwater monitoring is being performed at the site and the City of Phoenix is now operating under a Groundwater Contingency Plan (the Plan). Should groundwater quality standards in the Plan be exceeded at or downgradient of the landfill boundary, the City of Phoenix 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 of Phoenix 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).
EPA proposed delisting 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). Operation and maintenance activities will continue to be implemented by the City of Phoenix, and Five-Year reviews will always be required..
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, although this risk cannot be quantified. Again, with the channelization and stabilization of the Salt River Channel, this scenario is unlikely to occur in the future. The surface water concern is based on the potential for surface water run-off to contact refuse and transport this material to the Salt River, as has occurred in the past during periods of heavy river flow, thereby potentially increasing the risk for a surface water exposure pathway and a sediment exposure pathway. A more likely potential risk to public health and the environment could occur as the result of a rising water table which saturates a greater volume of refuse and releases additional leachate. The risk to the environment resulting from additional leachate generation by this mechanism is unknown and cannot be precisely quantified, although leachate may impact the quality of groundwater and thereby increase the risk for the human groundwater exposure pathway. 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 there is minimal resultant contamination of the groundwater. The Groundwater Contingency Plan for this site, explained in more detail in the next section, ensures continued monitoring of the groundwater in the vicinity of the landfill to evaluate and remediate potential degradation of the groundwater from the landfill. Exposure to groundwater from a shallow drinking water well, assuming such a well were drilled on or near the landfill boundary and used as a drinking water source, represents the only quantifiable potential public health risk.
Investigation and Cleanup Activities
The Arizona Department of Environmental Quality was assigned the oversight lead at this site in 1988. The City of Phoenix completed the Remedial Action Plan (RAP) in June 1989, and it was approved by ADEQ in September 1989. EPA concurred with the chosen remedy set forth in the RAP in the Record of Decision, signed in September 1989. The City of Phoenix entered into a Consent Decree with the State of Arizona in June of 1992 for the remedial action (design and construction) and all cleanup costs.
The site wide cleanup project was completed in nineteen months at a final construction cost of $22,500,000. The final remedy for the Nineteenth Avenue Landfill site, completed in February 1997, provides for containment of the landfill wastes on-site with the collection and flaring of landfill generated gases. Landfill gases that are generated are managed by separate gas collection and flare systems which operate independently in each cell of the landfill. The City of Phoenix is required to monitor the methane at the landfill boundaries and perform other methane monitoring to ensure the system is preventing off-site migration of landfill gas. Groundwater monitoring is being performed at the site and the City of Phoenix is now operating under a Groundwater Contingency Plan (the Plan). Should groundwater quality standards in the Plan be exceeded at or downgradient of the landfill boundary, the City of Phoenix 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 of Phoenix 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).
Immediate Actions: Earthen berms were constructed on the site to limit access. The site was covered with sand, gravel, and stones. In 1981, the City installed a system to collect methane gas and installed monitoring wells to sample the groundwater. There is a fence around the perimeter of the site to prevent unauthorized access.
Entire Site: In 1989, the EPA and ADEQ selected a remedy to clean up the landfill by installing a gas collection and treatment system, covering the landfill with a clay soil cap to prevent water from coming in contact with the buried materials, and constructing bank protection levees between the river and the landfill to prevent erosion. In 1990, the City of Phoenix began designing the technical specifications to clean up the site. Design activities were completed in May 1995.
Cleanup Complete: The City’s construction contractor started work on the bank protection system on August 14, 1995. By the end of August, work had started on the grade control structure and site grading for the capping system. On December 14, 1995, Explanation of Significant Difference (ESD) #1 was signed by ADEQ. ESD #1 changed the perimeter drainage lining material from Gunite to Armorflex. Also in December, areas of site grading were completed and work on the capping system was started. By March 1996, the bank protection system and grade control structure were completed, and work on the gas collection system was started. The installation of the Armorflex channel and sedimentation pond lining system was started in May 1996. The site landscaping was started in July 1996. The capping system and site landscaping were both completed by the end of November 1996.
The gas collection system and the two flare stations were completed in October 1996. The emissions testing for the flare stations at Cell A and Cell A-1 were performed on October 16-18, 1996 and were satisfactory. An air permit was subsequently issued to the City. The landfill gas collection system has been operational and functional since February 1997.
Containment of landfill wastes and minimization of infiltration by precipitation or any liquids is achieved by the construction of a compacted clay-soil cap with surface drainage structures to channel precipitation off of the cap. Construction of levees along the landfill cells that border the Salt River will prevent erosion and overtopping from the Salt River. The original earthen channel for storm water drainage along the eastern boundary of the site was replaced by a subsurface pipe with backfill to prevent erosion undercutting along the east boundary of the landfill
The Preliminary Close-Out Report (PCOR) was completed in February of 1998, documenting construction completion, and the Remedial Action Report was approved in September 1998. The landfill gas treatment system, soil cap, and levee system will continue to be operated and maintained by the City of Phoenix.
Site Studies: 1,1-dichloroethylene (1,1-DCE) contamination detected in the groundwater above the aquifer water quality standards at the landfill monitoring wells were studied by the City of Phoenix, ADEQ, and EPA in 1998. It was determined by EPA and ADEQ in January of 1999 that the 1,1-DCE contamination is originating from an upgradient source, and that the Nineteenth Avenue landfill is not contributing. Therefore, under the Consent Decree, the City of Phoenix is not responsible for addressing this contamination. The existing 1,1-DCE groundwater contamination will be considered for further investigation under ADEQ's Water Quality Assurance Revolving Fund (WQARF) or "state Superfund" program. The wells at the landfill continues to be monitored as part of the Groundwater Contingency Plan (described above).
The first Five-Year Review for the Site was conducted from January 2000 through June 2000 by ADEQ and approved by EPA September 2000. The Five-Year Review is required by CERCLA Section 121 (c) due to the fact that hazardous substances, pollutants, and contaminants remain at the site at levels that preclude unlimited land use. A review of the protectiveness of this remedy is required no less frequent than every five years. The start of construction activities on August 14, 1995 triggered the deadline for this review.
The Five-Year Review consisted of the following activities: a review of relevant documents; interviews with appropriate operations staff, state and local federal agencies, local government officials, and concerned community members; applicable, relevant, and appropriate (ARAR) review of current standards to the remedy; and a site inspection. In addition, a public notice regarding the completion of the review was placed in the local newspaper, and a copy of the completed report has been made available at the ADEQ file room and the local site repository (City of Phoenix public library).
The primary findings of the review were that a protectiveness determination for the remedy could not be made until additional data is obtained. However, several deficiencies were noted, which had the potential to affect current protectiveness. A follow-up report was required to investigate the deficiencies and determine whether the remedy is protective. The Follow-up report was completed in September 2001, and concluded that the remedy does remain protective of human health and the environment. However, additional recommendations were made to ensure protectiveness in the future. The most significant deficiencies in the Five-Year review requiring action are as follows:
- Methane recovery--Due to high methane levels in certain methane probes at the landfill, the City of Phoenix (COP) was required to conduct monthly surface monitoring measurements in those areas according to an approved plan, and enhance the methane recovery systems to ensure the methane is not allowed to migrate beyond landfill boundaries at both cells. The COP has completed construction on the enhancements of the methane gas collection and treatment system and installation of new methane monitoring probes. The project construction was completed in August 2002, and system operations have reduced methane levels at the boundary of the landfill to safe levels.
- Groundwater quality standards--Several groundwater monitoring standards outlined in the Groundwater Contingency plan were not longer protective, and new standards needed to be implemented. The groundwater quality at the landfill however, was not exceeding any of the new groundwater standards, therefore no specific action was required by the COP. ADEQ and EPA updated the Record of Decision (ROD) through an Explanation of Significant Differences (ESD) in to update the groundwater monitoring program requirements in September 2003.
The second Five-Year Review for the site was initiated by ADEQ in February 2005 and completed in September 2005. (See the requirement and purpose of the Five-Year Review in the section above.) The review determined that the remedy was protective of human health and the environment. Recommendations of this report identified deficiencies such as routing maintenance, repair and record keeping issues. These were completed and resolved by the City of Phoenix by May 5, 2006. The review also identified that there is no institutional control in place restricting future land use and recommended a Declaration of Environmental Use Restriction (DEUR) be placed on the Site, which has since been completed (see next section).
The third Five-Year Review for the site was completed by ADEQ in September 2010. The 2010 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 and institutional controls 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. The DEUR recommended for the site in the 2005 Five Year Review was placed on the site in 2006 during this review period.
Cleanup Complete: An Explanation of Significant Differences to the remedy was completed by ADEQ and EPA in June 2006 identifying the appropriate institutional controls (ICs) for the site. ICs ensure long-term protectiveness of the remedy in the event the property is sold or other land use changes occur. The specific ICs mechanisms identified were the Declaration of Environmental Use Restriction (DEUR) and the Arizona Department of Water Resources (ADWR) requirements. The DEUR controls the use and access to the landfill property and ADWR restricts groundwater well site location, construction, and use that could impact the remedy. The DEUR was attached to the property deed by the City (landowner) in July 2006. 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.
EPA and ADEQ completed a Final Close Out Report on August 3, 2006 documenting that the site is eligible for "site completion", signifying the end of all response actions at the site. No further Superfund response is required to protect human health and the environment. Operation and maintenance activities will continue to be implemented by the City of Phoenix, and Five-Year reviews will always be required. EPA proposed deletion of the site from the NPL on August 14, 2006. Public comments were accepted in writing through September 13, 2006. EPA finalized the deletion on September 25, 2006. A Responsiveness Summary to public comments was prepared, and is available in the public record.
Cleanup Results to Date
Pre-final inspections were conducted to determine the substantial completion of the project. A pre-final inspection of the gas collection system and flare stations was performed on December 4 and 5, 1996. Inspections for the other features of the project, including the completed levees and channelization of the Salt River, were conducted on December 6 and 12, 1996. Based on the results of the inspections, the project was determined to be substantially complete on December 6, 1996. Based on the results of two additional inspections conducted on January 7 and February 13, 1997, final project acceptance, by the City to the construction contractor, was made on February 28, 1997.
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 Nineteenth Avenue Landfill 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. ADEQ issued written approval of completion of the remedial action in accordance with the Consent Decree on June 30, 1997 which activated the groundwater contingency plan.
The remedy uses permanent solutions and alternative treatment technologies to the maximum extent practicable for this site. The collection and flaring of gas and the activation of a groundwater contingency plan are significant components of the remedy; however, the size of the landfill and the volume of landfill wastes preclude a remedy in which contaminants could be effectively excavated and treated.
As this remedy will result in hazardous substances remaining on-site above health based levels, a review will be conducted by ADEQ and EPA at least every five years after commencement of remedial action to ensure the remedy continues to provide adequate protection of human health and the environment. Three Five Year Review Reports have been completed. The first Review in September 2000, the second in September 2005, and the third in September 2010.
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
101 South Central Ave., 2nd Floor
Phoenix, AZ 85004
After Hours (Emergency Response)