History of the Queen Creek Landfill (QCLF)

The Queen Creek Landfill (QCLF) is a former municipal solid waste landfill (MSWLF) located at 20224 East Riggs Road in Queen Creek, Arizona. The site for the QCLF occupies approximately 80 acres of land owned by Maricopa County, and is currently managed by the Maricopa County Environmental Services Department (the County). The deepest part of the waste is believed to extend to approximately 60–70 feet (ft) below ground surface (bgs) from the top of the landfill, which has an elevation of approximately 1,420 ft above mean sea level (amsl).

County records indicate that the QCLF began operations in 1972 and wastes were accepted at the QCLF from 1972 through 1990. The facility was operated under an intergovernmental agreement between the County and the Town of Queen Creek, with landfill operations subcontracted to Allied Waste Industries, Inc. from 1994 through 2007. The waste acceptance is believed to have doubled in 1997 when waste from the City of Chandler was added to the existing waste stream received at the QCLF. Waste at the north end of the landfill is believed to be the oldest. The majority of the landfill disposal area is unlined. The total disposal capacity of the QCLF is estimated to be between 3,000,000 and 4,250,000 tons of waste.

The facility ceased accepting waste in 2007, and was formally closed in 2010. Closure activities were conducted as specified in an Arizona Department of Environmental Quality (ADEQ) - approved closure plan. The site has been graded for positive drainage over the entire disposal area. In addition, a final cover system consisting of an existing foundation soil layer, a 2-foot-thick infiltration barrier layer of low permeability soil, and a 1-foot-thick erosion control layer constructed primarily of clean, coarser-grained soils (sand and silt with low plasticity) above the infiltration barrier layer has been constructed. The QCLF has since been re-constructed for low-intensity public recreational use associated with the neighboring Horseshoe Park and Equestrian Center (HPEC). Park activities include walking paths, equestrian trails, and an overflow parking lot servicing the HPEC.

On January 14, 2021, the County received assessment monitoring results reporting a concentration of tetrachloroethene (PCE) in monitoring well MW-4s of 0.0067 mg/l (6.7 micrograms per litre (μg/L). A trend analysis indicated this detection was in exceedance of the Arizona Water Quality Standards (AWQS) for PCE set at 0.005 mg/l . Notice of the exceedance was placed in the operating record and provided to ADEQ by January 27, 2021. Consistent with the QCLF assessment monitoring program, the County proceeded with characterizing the nature and extent of the release by installing an additional monitoring well at the QCLF property boundary (MW-5s) and performing a round of groundwater monitoring and volatile organic compound (VOC) sampling to include the one new and four existing shallow aquifer monitoring wells. The two deeper aquifer piezometers (MW-1 and MW-4) that are used as observation wells and are not part of the groundwater monitoring system were also sampled. As this event coincided with semi-annual sampling, sampling and analysis for the full QCLF semiannual list was performed. Extraction wells located around the perimeter of the QCLF were also sampled for soil vapor impacted by landfill gas VOCs to characterize those concentrations in the subsurface.

Assessment is underway to determine the best way to accomplish remedial objectives (ROs):

1. Be protective of human health and the environment;
2. Attain the groundwater protection standard;
3. Control the source of releases to reduce or eliminate, to the maximum extent practicable, further releases of contaminants into the environment that may pose a threat to human health and the environment; and
4. Comply with regulatory waste management standards.

Maricopa County is committed to continuing characterization and remediation activities until they are no longer needed.