Hassayampa Landfill

Description and History

The Hassayampa Landfill Superfund site is geographically situated approximately forty miles west of Phoenix and approximately three miles north of Arlington, in Maricopa County Arizona. The Hassayampa Landfill is a portion of a seventy-seven acre property owned by Maricopa County, in which forty-seven acres were used for disposal of municipal and domestic solid waste, including a ten-acre former Hazardous Waste Disposal Area located in the northeast section of the landfill. The landfill lies within the drainage area of the ephemeral Hassayampa River, which is located 3/4 mile east of the landfill, but outside of the 100-year floodplain. Several water-bearing geologic units have been identified beneath the site with a general groundwater flow of south-southwest.

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 site until the landfill was closed. 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 [down slope] residential well is about 1,000 yards south of the hazardous waste area. Future residential land use of the landfill property is considered unlikely in the future.

Maricopa County began operating Hassayampa as a municipal landfill beginning in 1961. During an eighteen month period from 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

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 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.

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.

A Record of Decision (ROD) for the Hassayampa Superfund site was signed on August 6, 1992 and detailed EPA’s selected cleanup remedy. The selected remedy for the contaminated groundwater at the site set forth by the ROD included: pumping the 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 ROD also identified the removal and treatment of contaminated vapor present in the soil through the use of Soil Vapor Extraction (SVE) vents, and a treatment system that was determined during the remedial design. The soil vapor cleanup standards were to be established by the EPA and 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.

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.

Following the Consent Decree, the Hassayampa Steering Committee PRPs have 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 was completed and has been in operation since March 1994. To date, this system has pumped and cleaned over 25 million gallons of contaminated groundwater. A soil vapor extraction system was constructed and began operation in 1996, and has since treated (using thermal oxidation methods) approximately 3,700 pounds of VOCs.

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. In 2001, 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 are protective of human health and the environment. A protectiveness determination for the soil vapor extraction and treatment portion of the vadose zone remedy was not be made at that time. When EPA makes a determination that a remedy is protective, this means that 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 Five Year Report was completed in September 2006 and is available for reviewing at the Buckeye Library. A finding was made that the remedy was protective in the short term but studies were need to be completed to make a determination of the protectiveness in the long term. New soil vapor extraction well are operating at the site with emphasis currently being made on vapor concentrations beneath the basalt layer. The studies have also identified that the basalt layer is not as laterally continuous as believed and the site conceptual model is being revised.

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

Fact Sheets
	12/01/01	U.S. EPA Completes Cleanup Remedy Review
	11/01/03	EPA Work on McCleur Tailings will Protect Community
	01/01/06	U.S. EPA BEGINS HASSAYAMPA REMEDY REVIEW PROPOSES RESUMING SOIL VAPOR EXTRACTION ACTIVITY

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Community Involvement

Public Meetings:

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Public Information Repositories

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Additional Links

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Contacts

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