Pacific Southwest, Region 9: Superfund
Serving Arizona, California, Hawaii, Nevada, the Pacific Islands, and Tribal Nations
EPA #: AZD980735666
City: 40 miles west of Phoenix
Congressional District: 03
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Description and History
NPL Listing History
NPL Status: Final
Proposed Date: 06/10/86
Final Date: 07/22/87
The Hassayampa Landfill Superfund Site (Site) is geographically situated approximately forty miles west of Phoenix and approximately three miles north of Arlington, in Maricopa County, Arizona. The approximately 10-acre Superfund Site was used for disposal of hazardous wastes for an eighteen month period between 1979 and 1980. This former hazardous waste disposal area (Site) is located in the northeast section of closed sanitary landfill that was operated by Maricopa County. The entire property is seventy-seven acres, of which forty-seven acres were used for the disposal of municipal and domestic solid waste. The Site, the 10-acre hazardous waste disposal area, is part of the 47 acres used for disposal of municipal waste
The Site lies within the drainage area of the ephemeral Hassayampa River, which is located half a mile east of the Site, but outside of the 100-year floodplain. The Site is located in an alluvial-filled basin, which has been influenced by the nearby river and the Arlington Mesa. A regional aquifer consisting of basin-fill deposits underlies the Site and comprises the principal source of groundwater to wells in the area. The groundwater flow direction is general to the south-southwest. Approximately 350 people draw drinking water from private wells, and 2,800 acres of farmland are irrigated by wells within three miles of the site. The nearest downgradient residential well is about 1,000 yards south of the hazardous waste area.
Surrounding land use includes mostly desert (undeveloped) land with some cultivation (approximately one-sixth of the total surrounding land use). Vegetation is sparse and includes creosote and salt bushes. There are no residents living in the immediate vicinity of the Site, although there were several landfill employees who worked in the non-hazardous portion of the landfill until it was closed in 1997. Future residential land use of the landfill property is considered unlikely. There is some increase of residential development near the Site in recent years.
Maricopa County began operating Hassayampa as a municipal landfill beginning in 1961. During the period of April 20, 1979 to October 28, 1980, hazardous wastes were disposed in unlined disposal pits in a 10 acre area in the northeast section of the landfill. This disposal occurred under a manifest program operated by the Arizona Department of Health Services (ADHS) in response to an “extreme emergency” that resulted from an ADHS ban on the disposal of industrial waste at City of Phoenix landfills. When landfills along the Salt River were closed to industrial waste disposal due to flooding, industrial waste was transported and disposed of at the Hassayampa Landfill site. Under this program, a wide range of hazardous wastes were approved by ADHS for disposal at the Hassayampa Landfill, including up to 3.28 million gallons of liquid wastes and 4,150 tons of solid wastes. Manifests were used to document the volume and type of wastes and the names of the generators and transporters. The landfill pits were subsequently covered with native soil and restored to grade at the end of the eighteen month period. Disposal of wastes at the municipal portion of the Hassayampa Landfill ceased in June, 1997.
Contaminants and Risks
- Soil and Sludges
Contaminants of Concern (COCs) detected at Hassayampa which exceeded the Federal Maximum Contamination Levels (MCLs) for groundwater include: 1,1-dichloroethene; trichlorotrifluoroethane (Freon 113); 1,1,1-trichloroethane; 1,1-dichloroethane; trichloroethene; tetrachloroethene; trichlorofluoromethane (Freon 11); 1,2-dichloroethene; 1,2-dichloropropane; and toluene.
Ambient air contained very low levels of volatile organic compounds (VOCs) prior to the landfill being capped in 1996. Soils beneath the capped waste pits contain VOCs, heavy metals, pesticides, and lime wastes. Risk assessment results indicated that potential health risks may exist for individuals who ingest the contaminated groundwater or come into direct contact with hazardous wastes present in several of the trenches. Currently, there does not appear to be any potential for adverse health effects due to inhalation of VOCs in the air or direct contact because of the construction of the cap over the wastes.
Who is Involved
The Hassayampa Steering Committee (HSC) is a group of companies that comprise the potentially responsible parties (PRPs) for the Site. The HSC is responsible for the cleanup and long-term operation and maintenance activities at the Site. EPA is the lead regulatory agency, with technical support provided by Arizona Department of Environmental Quality (ADEQ).
Investigation and Cleanup Activities
In 1981, ADHS constructed three groundwater monitoring wells at the Hassayampa Landfill. Samples collected from one of these wells were found to be contaminated with volatile organic compounds (VOCs). In 1984, ADHS conducted a site inspection of the Hassayampa Landfill and surrounding area. In response to ADHS findings, EPA proposed adding Hassayampa to the Superfund National Priorities List (NPL) on June 10, 1986. The site was added to the NPL on July 22, 1987, thereby making it eligible for Superfund cleanup.
Shortly after disposal at the hazardous waste disposal area (Site) ceased, investigations were commenced in 1981. Results of sampling and analysis conducted during the remedial investigation, as well as additional investigations conducted later, indicated that soil and groundwater in the hazardous waste area of the landfill were contaminated by VOCs and semi-volatile organic compounds (SVOCs). Several disposal pits were identified within the hazardous waste portion of the landfill, with elevated levels of VOCs and SVOCs present in waste, soil, and soil gas, especially beneath Pit 1. Substantial downward percolation of these compounds was also discovered in this area. Metals (including chromium, copper, and lead) were detected in waste and soil beneath several pits with concentrations of chromium and copper exceeding State hazardous waste regulatory levels. Groundwater samples from several monitoring wells indicated that groundwater in the uppermost water-bearing unit beneath portions of the hazardous waste area were contaminated with VOCs and SVOCs. Additionally, groundwater monitoring wells installed south of the hazardous waste area indicated a southerly VOC and SVOC contaminant migration away from the area.
On August 6, 1992, EPA signed a Record of Decision (ROD) for the Hassayampa Superfund Site that described EPA’s selected cleanup remedy. The remedy in the ROD included: pumping the contaminated groundwater; treating the contaminated water using an air stripping system; reinjecting the treated water back into the groundwater in the vicinity of the site; and performing continued groundwater monitoring to measure the ongoing effectiveness of the remedy. EPA selected the federal and state MCLs as cleanup standards for the groundwater. MCLs indicate the maximum level of a contaminant EPA considers safe in drinking water. For those contaminants for which MCLs had not been established, proposed MCLs or Health Based Guidance Levels (HBGLs) identified by the Arizona Department of Environmental Quality were selected as groundwater cleanup levels. HBGLs were developed by the ADHS and represent human ingestion levels in water which are unlikely to result in adverse health effects during long-term exposure.
The 1992 ROD also identified the removal and treatment of contaminated soil vapor present in the soils through the use of a Soil Vapor Extraction (SVE) extraction and treatment system. The ROD allowed selection of the treatment system for the soil vapor to be determined later during the remedial design phase. It also allowed the selection of soil vapor cleanup standards to protect groundwater quality to be established later by EPA. Finally, the ROD called for a protective cover (landfill cap) meeting federal requirements to be placed over the entire ten acre hazardous waste portion of the landfill. A landfill cap was selected to reduce infiltration of rainwater, thereby limiting continued movement of soil contaminants to groundwater and also improving the efficiency of the soil vapor extraction system. The selected remedy also included the use of deed and access restrictions to control future use of the property. The cap and access restrictions were also chosen to prevent people from coming into contact with contaminated soils and soil vapor at the site.
In 1994, following EPA and the HSC signing a Consent Decree, the HSC began construction on the remedy for the Site. The cap was constructed in 1994 to prevent erosion and infiltration of contaminants into the groundwater. In March 1994, a pump and treat Groundwater Remediation System (GRS) was completed to clean up groundwater contamination in the upper aquifer (Unit A). This extracted groundwater is treated by air stripping to remove the VOCs and the treated groundwater is re-injected back into the deeper aquifer (Unit B) of the aquifer. The GRS has been operating continuously since 1994. As of January 2016, this system had removed an estimated 380 pounds of VOC contamination from the groundwater.
In 1996, the HSC constructed a soil vapor extraction (SVE) system using thermal oxidation treatment system to treat the VOCs present in the contaminated soil vapor. The initial SVE system included eleven monitoring/extraction wells drilled into the coarse grained, upper vadose zone, eleven monitoring/extraction wells drilled into the fine-grained, lower vadose zone, and eight dual-completion passive injection wells. In 1996, the HSC also completed Performance Monitoring Verification Plans for both groundwater and soil vapor which incorporated the selected cleanup standards for the Site.
In 1997, once the HSC completed the construction phase of the remedy, EPA completed a Preliminary Close-Out Report (PCOR). Then, EPA issued a certificate of completion of construction for the remedial action in April 1998.
In 1999, the thermal oxidation treatment system for the soil vapor was shut down after the system failed several compliance tests for destruction efficiency. During the period 0f 1997-1999, when the system was in operation, approximately 3,700 pounds of VOCs in soil vapor were removed and treated. By the mid-2000s, after the SVE system had been shut down for a few years, soil vapor monitoring data indicated upward trends in VOC concentrations in the vadose zone soils. There also was an unexpected increase of groundwater contamination in an upgradient groundwater monitoring well (MW-11UA) due to vapor migration. In 2006, an investigation was conducted to determine the source of these migrating subsurface soil vapors at the Site. Additional groundwater and soil vapor monitoring wells were installed. Sampling results indicated the presence of soil vapor concentrations exceeding 900,000,000 ug/kg total VOCs beneath a deep basalt layer (approximately 90 feet below ground surface) near the liquid disposal pit, Pit 1.
In 2006, in response to the dectection of these high vapor concentrations, the SVE system was re-started. At that time, the soil vapor treatment system was changed from thermal oxidation to a proprietary cryogenic technology. This new technology involved extraction of the vapors, pressurization of the vapors, cooling of the vapor stream, and a polishing step. During the high pressure and low temperature treatment steps, the majority of VOCs changed from a vapor to a liquid phase (condensation step). The liquids were then treated with granular-activated carbon as the polishing step prior to disposal at an EPA-approved disposal site. This cryogenic treatment system operated continuously from 2006 through 2015. As of 2015, approximately 15,000 pounds of VOCs were extracted and treated by the SVE system on an annual basis.
In 2009, EPA signed an Explanation of Significant Difference (ESD) #1 to update EPA’s soil vapor remedy to include the change from thermal oxidation to the proprietary cryogenic system, and also include flexibility to change solely to a granulated activated carbon treatment system when feasible. The ESD also revised the soil vapor performance standards (SVPSs) that were originally established in the 1994 through site-specific analytic computer modeling. The 2009 revised SVPSs were based on Arizona Minimum Groundwater Protection Levels (GPLs) and the EPA methods used to develop site-specific Soil Screening Levels (SSLs). After allowable total soil concentrations were developed for the Site, additional calculations were performed to convert the soil concentrations to soil vapor concentrations at equilibrium conditions.
In May 2016, EPA signed an ESD #2 to update the SVPSs again, as a result of development of a new site-specific model that took into consideration the potential impact of soil vapor migration on the groundwater. ESD #2 also clarified the Remedial Action Objectives (RAOs) for the Site. The new SVPSs were developed as a joint effort between EPA, DOE modeling experts and the HSC. The HSC also changed the soil vapor treatment system to granulated activated carbon in mid-2016. The HSC is responsible for the long-term operation and maintenance of the Site’s groundwater and soil vapor treatment systems.
Cleanup Results to Date
After adding this site to the NPL, the EPA performed preliminary investigations and determined that the Hassayampa Landfill site does not pose an immediate threat to public health or the environment while cleanup activities are being designed and built at the site.
The selected remedy is protective, meets Applicable and/ or Relevant and Appropriate Requirements (ARARs), is effective for the long-term, and is permanent. The State of Arizona has concurred with the EPA’s selected remedy.
A Preliminary Close-Out Report (PCOR) was completed in September 1997 and EPA certification of the completion of remedial action was issued to the PRPs in April of 1998. The PRPs continue to operate the remediation systems at the site.
Every five years EPA evaluates the performance of its on-going cleanup remedies and issues a report of its findings in a document called a Five-Year Review (FYR) Report. FYR Reports have been completed for the Site in 2001, 2006, 2011, and 2016. The fourth FYR completed in 2016 concluded that the remedy was protective in both the short-term and the long-term, and is currently being operated effectively. The next FYR will be conducted in 2021.
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.
In 1987, the EPA sent Special Notice Letters informing 108 individuals and companies of their potential responsibility for wastes contaminating the Hassayampa Superfund site. In February 1988, nine of the major potentially responsible parties entered into a Consent Order with the EPA in which they agreed to conduct the remedial investigation/feasibility study (RI/FS) under EPA oversight. After the ROD was signed in July 1992, Special Notice letters for remedial design/remedial action (RD/RA) were issued to 121 parties on September 30, 1992. A Consent Decree (CD) for RD/RA was filed in U.S. District Court on September 2, 1994 with twelve of the PRPs responsible for sending large amounts of waste to the Site to design, construct and operate the remedy. This group, known as the HSC, consists of Maricopa County (the owner at the time of disposal), Bull, DEC, Honeywell, Alcatel, General Instrument, AT&T, Shell, Arizona Public Service Co., Intel, National Can, and Reynolds Metals. The CD, valued at $10.5 million, requires the HSC to reimburse EPA for all its past and future response costs at the Site. Seventy seven PRPs responsible for sending smaller amounts of waste to the site (referred to as “de minimis parties”) are obligated by the Consent Decree to make cash payments directly to the twelve major settling PRPs. The size of the cash payment required from the seventy seven de minimis parties is based on the volumetric share of the waste sent to the Site by each of these PRPs. The de minimis settling parties are not responsible for conducting any of the remedial work at the Site. This action represented the first ever de minimis party settlement finalized by EPA.
Documents and Reports
Public Information Repositories
The public information repositories for the site are at the following locations:
310 North 6th Street
Buckeye, AZ 85326
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
14818 W. 6th Avenue
Golden, CO 80401
After Hours (Emergency Response)