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Pacific Southwest, Region 9: Superfund

Serving Arizona, California, Hawaii, Nevada, the Pacific Islands, and Tribal Nations

Hassayampa Landfill

EPA #: AZD980735666

State: Arizona(AZ)

County: Maricopa

City: 40 miles west of Phoenix

Congressional District: 03

Other Names:

Bulletin Board


Description and History

NPL Listing History

NPL Status: Final

Proposed Date: 06/10/86

Final Date: 07/22/87

Deleted Date:

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 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. ADHS used a manifest system to screen and track industrial waste deliveries to the landfill during this period. 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 to the municipal landfill ceased in June, 1997.

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Contaminants and Risks

Contaminated Media
  • Groundwater
  • Air
  • 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 contains very low levels of volatile organic compounds (VOCs). Soils beneath the waste pits contain VOCs, heavy metals, pesticides, and lime wastes. Risk assessment results indicate 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.

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Who is Involved

This site is being addressed through federal, state, and potentially responsible party actions.

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Investigation and Cleanup Activities

In 1981, ADHS constructed three groundwater monitoring wells at the Hassayampa Landfill. Samples collected from 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.

On February 19, 1988, nine of the major potentially responsible parties (PRPs) for the Site entered into a Consent Order with EPA in which they agreed to conduct the Remedial Investigation and Feasibility Study (RI/FS) under EPA oversight. In addition, there were more than sixty other PRPs who contributed funds toward the completion of the RI/FS, which was completed in June 1992. There were about forty other PRPs, identified at the time, who did not participate in the RI/FS. On September 30, 1992, Special Notice letters for remedial design/remedial action (RD/RA) were issued to 121 parties.

EPA and the Arizona Department of Environmental Quality (ADEQ) are working together to clean up this site. EPA is the lead regulatory agency with technical support being provided by ADEQ.

Site Studies

In 1981, shortly after disposal at the hazardous waste disposal area (Site) ceased, investigations were commenced. 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 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.

Remedy Selected

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 that was determined during the remedial design. The soil vapor cleanup standards were to be established by the EPA to be protective of groundwater quality. 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. The cap system was chosen 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 deed and access restrictions were also chosen to prevent people from coming into contact with contaminated soil at the site.

On December 23, 2009, EPA signed an Explanation of Significant Difference (ESD) #1 to update the soil vapor remedy. The ESD modified the treatment technology for the SVE system from thermal oxidation to a proprietary cryogenic treatment system. The ESD also revised the soil vapor performance standards that were originally established in the 1994 through site-specific analytic computer modeling. The 2009 revised soil vapor performance standards are 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 concenrations were developed for the Site, additional calculations were performed to convert the soil concentrations to soil vapor concentrations at equilibrium conditions. These are the updated soil vapor performance standards for the Site in the 2009 ESD.

Remedy Design

Following issuance of the ROD, EPA commenced negotiations with over 89 PRPs toward a proposed settlement agreement, called a Consent Decree, under which the PRPs would implement the remedy selected in the ROD. Consent Decree negotiations were prolonged due to complications. As a result, EPA issued a Unilateral Administrative Order (UAO) on March 30, 1993 to eleven of the parties to conduct additional investigation activities and to begin remedial design (RD) and remedial action (RA) activities on the groundwater treatment system and soil cap while Consent Negotiations continued.

Cleanup Ongoing

Following the signing of the Consent Decree, the Hassayampa Steering Committee (HSC) has undertaken the majority of the work at Hassayampa. A soil cap was constructed in 1994 to prevent erosion and infiltration of contaminants into the groundwater.

A pump and treat Groundwater Remediation System (GRS) was completed and has operated continuously since March 1994. The GRS was designed to extract contaminated groundwater from four Unit A extraction wells. This extracted groundwater is then treated by air stripping to remove the VOCs and the treated groundwater is re-injected back into Unit B of the aquifer. In 2000, approximately 3 million gallons of groundwater were treated that year. To date, this system has pumped and cleaned over 30 million gallons of contaminated groundwater.

In 1996, a soil vapor extraction (SVE) system was constructed that used thermal oxidation methods to treat the VOCs extracted from the contaminated soils. The system included eleven SVE monitoring/extraction wells drilled into the coarse grained, upper vadose zone, eleven will drilled into the fine-grained, lower vadose zone, and eight dual-completion passive injection wells. It was shut down in March 1999, after the system failed several compliance tests for destruction efficiency the previous year. Approximately 3,700 pounds of VOCs were removed while it operated between 1996 and 1999.

After termination of the SVE system, monitoring data indicated upward trends in the concentration of the VOCs in the vadose zone soil vapor plume. In addition, there was an unexpected contamination of groundwater 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. Results from these new monitoring wells indicated 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.

Later in 2006, in response to these high vapor concentrations, a new SVE system was installed that changed the treatment system from thermal oxidation to a proprietary cryogenic technology. This new technology involves 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 change from a vapor to a liquid phase (condensation step). The liquids are then treated with granular-activated carbon as the polishing step prior to disposal at an EPA-approved disposal site. This system has been operating continuously since 2006. As of October 2010, approximately 114,000 pounds of VOCs have been recovered.

Cleanup Ongoing

A Preliminary Close-Out Report (PCOR) was completed in September 1997 and EPA certification of the completion of construction of the remedial action was issued in April of 1998. The groundwater extraction and treatment system and soil vapor extraction and treatment system will continue to be run by the PRPs until the groundwater and soil meet cleanup levels.

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 Report. In 2001, during the first Five-Year Review, EPA determined that the groundwater remedy, the soil cap portion of the vadose zone remedy (for the dry soils above the water table) and the deed and access restrictions were protective of human health and the environment. However, at that time, a protectiveness determination for the soil vapor extraction and treatment portion of the vadose zone remedy was not be made. EPA determines that a remedy is protective, when the various parts of the system are operating in such a way that contaminants are not coming into contact with people or other living systems.

The second Five Year Report was completed in September 2006. This Review concluded that the remedy was protective in the short term, but additional studies were need to be completed to make a determination of the protectiveness in the long term. To obtain more data, new soil vapor extraction wells were installed beneath the basalt layer near Pit 1 at the Site in 2006. The studies determined that the basalt layer is not as laterally continuous as previously believed and that VOCs have migrated downward below the basalt layer and migrated laterally away from the site. In response to these discoveries, a new SVE system was installed and restarted with a cryogenic treatment system, that now is capturing and treating the migrating soil vapors discovered in 2006.

The third Five Year Review commenced in early 2011 and a final report was signed on September 30, 2011. EPA is conducted the review with assistance from ADEQ. Both the operation and maintenance of the GRS system for groundwater and the SVE system were re-evaluated. An Optimization Analysis was conducted by the U.S. Army Corps of Engineers, as part of the process, to evaluate possible options for accelerating the cleanup of the contaminated groundwater and soil vapor at the Site. The Review concluded that the remedy is protective in the short term. However, to remain protective for the long term, the Site will need to be continually monitored and the soil vapor and groundwater contamination will need to be continually captured and controlled because of the high concentration of VOCs present in the soils.

Operation and maintenance of the groundwater treatment system and the soil vapor extraction system at the Site is on-going and is managed by the HSC (PRPs).

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, several potentially responsible parties entered into a Consent Order with the EPA in which they agreed to conduct the site investigation under EPA oversight. The Consent Decree was filed in U.S. District Court September 2, 1994. It required twelve of the PRPs responsible for sending large amounts of waste to the site to design, construct and operate the remedy selected in the 1992 ROD. The twelve major PRPs, known as the Hassayampa Steering Committee, 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 Consent Decree, valued at $10.5 million, required these twelve PRPs 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 represents the first ever de minimis party settlement finalized by EPA.

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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 will continue to operate the remediation systems at the site.

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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.

Online information about the PRPs for the site is not yet available.

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Documents and Reports

Show details for Fact SheetsFact Sheets
Show details for Records of DecisionRecords of Decision
Show details for Technical DocumentsTechnical Documents

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Community Involvement

Public Meetings:

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Public Information Repositories

The public information repositories for the site are at the following locations:

Buckeye Library
310 North 6th Street
Buckeye, AZ 85326
(623) 386-2778

The most complete collection of documents is the official EPA site file, maintained at the following location:

Superfund Records Center

Mail Stop SFD-7C

95 Hawthorne Street, Room 403

San Francisco, CA 94105

(415) 820-4700

Enter main lobby of 75 Hawthorne street, go to 4th floor of South Wing Annex.

Additional Links

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EPA Site Manager
Andria Benner
US EPA Region 9
Mail Code SFD
75 Hawthorne Street
San Francisco, CA 94105
EPA Community Involvement Coordinator
David Yogi
US EPA Region 9
Mail Code SFD
75 Hawthorne Street
San Francisco, CA 94105
EPA Public Information Center
State Contact
Sara Benovic
Arizona Department of Environmental Quality
1110 W. Washington St. mailcode: 4415B-1
Phoenix, AZ 85007
PRP Contact
Ben Costello
Hassayampa Steering Committee, Project Manager
14818 W. 6th Avenue
Suite 5A
Golden, CO 80401
Community Contact
Other Contacts
After Hours (Emergency Response)
(800) 424-8802

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