EPA #: AZD009004177

Superfund National Priority List (NPL) Status: The EPA listed this site on Oct. 4, 1989

Location: The Motorola 52nd Street Superfund Site (the site) is located in Phoenix, Arizona within the general boundaries of 52nd Street on the east, Palm Lane on the north, Seventh Avenue on the west and Buckeye Road on the south. Due to its size and to better manage cleanup efforts, the site was divided into three areas called Operable Units (OUs). The operable units, from east to west, include OU1, OU2, and OU3.

The site consists of a large area of contaminated groundwater extending from the former Motorola facility at 52nd Street and other sources west of 52nd Street, including Honeywell, the former Joray Corporation, and Arizona Public Service. ADEQ, working in concert with the U.S. Environmental Protection Agency (EPA), is the lead agency for activities in OU1 and OU2 with the exception of the vapor intrusion/indoor air investigation. The EPA is the lead agency for OU3 and vapor intrusion/indoor air investigations.

Contaminants of Concern: Volatile Organic Compounds (VOCs), including trichloroethene (TCE), 1,1,1-trichloroethane (1,1,1-TCA) and tetrachloroethene (PCE), are the main contaminants of concern (COCs) for the site. Additional COCs may be identified in one or more of the remedial investigation/feasibility studies (RI/FS) currently in progress.

Public Health Concerns: There are currently no known exposures to COCs in excess of applicable health based screening levels at the site. This includes studies conducted to date for groundwater, soil (surface and subsurface) and soil vapor intrusion.

The main exposure pathway to the COCs is through ingestion of contaminated groundwater. In Phoenix, drinking water is provided primarily through surface water sources, with only limited groundwater use from areas located outside the Motorola 52nd Street Superfund site. Interim remedial measures are in place at OU1 and OU2 to clean up groundwater and reduce migration of COCs. Remedial activities include operation of two groundwater extraction and treatment systems (GETS): one located at the former Motorola facility (OU1) and the other located at N. 20th Street and E. Washington Street (OU2). These activities are designed to mitigate the risk of exposure to the COCs through groundwater.

The EPA has also been studying the possibility that soil vapor from contaminated groundwater has migrated into buildings and has impacted indoor air. VOCs are able to easily transfer from liquid to vapor phase. TCE and PCE vapor can travel up and into surface structures, such as residential homes and commercial buildings. This exposure scenario, known as vapor intrusion (VI), is currently being studied as a part of the RI/FS process within OU1 and OU2. Based on the detection of elevated TCE concentrations in soil vapor, vapor mitigation systems were installed at specific locations to reduce exposure risk.

Environmental Considerations: Within the site, there are no unique wildlife habitats or threatened or endangered species. Native vegetation is sparse, as the site is located entirely within urbanized areas of Phoenix. As such, there are no known elevated risks to the environment from COCs or from the mentioned interim remedial activities being conducted at OU1 and OU2.

The extracted groundwater, impacted with COCs, is being treated to the EPA drinking water standards or less. Most of the treated groundwater is beneficially reused and future plans are to have all of the treated groundwater beneficially reused.

Action Taken: Responsible parties have operated various soil vapor and interim groundwater treatment systems since the early 1990s that have reduced the extent of contamination. Vapor intrusion mitigation has been installed at 15 residences. The responsible parties, EPA, and ADEQ are in the process of gathering information from across the site to identify any new COCs and to develop final cleanup actions. This process will be completed over the next few years.

The OU1 and OU2 GETS have been effective in reducing the extent and concentration of COCs in groundwater across a large portion of the site. To date, the groundwater remedial actions at OU1 has removed and treated over four billion gallons of COC impacted groundwater and over 26,000 pounds of TCE. At OU2, groundwater remedial actions have removed and treated over 16 billion gallons of COC impacted groundwater and over 15,000 pounds of VOCs. In 2016, review of the interim remedies indicated the need to address several outstanding issues in order to define a final remedy. These issues included an ongoing source of contamination — dense non-aqueous phase liquid (DNAPL) that has seeped into bedrock fissures — and completing evaluation of the potential vapor intrusion pathway within OU1 and OU2.

In 2011, the EPA entered into an agreement with NXP USA, Inc. (NXP) (formerly Freescale Semiconductor Inc., an independent company that spun off from Motorola in 2004) to investigate the soil gas (vapor) to indoor air pathway within OU1. From 2011 to 2014, soil gas samples were collected and analyzed for TCE and PCE. Due to TCE concentrations in soil vapor above health-based screening levels, the EPA followed up with sub-slab and indoor air sampling at homes, apartment buildings, and commercial buildings within identified areas. Under EPA oversight, NXP sampled 115 residences, four schools and seven commercial buildings. NXP installed sub-slab depressurization systems at 15 residences and successfully reduced TCE concentrations to below two micrograms per cubic meter (µg/m3) in those homes/buildings. Although four locations refused mitigation, all remaining residences now have levels below current health-based screening levels.

In 2017, as part of the feasibility study, NXP implemented the Focused (TCE) Mass Reduction Field Scale Pilot Project at OU1. This pilot program included installation of test wells and the application of a mixture of agents to promote and enhance bio-degradation of TCE in groundwater.

Status:

OU1
Currently, OU1 is operating under an interim groundwater remediation system to contain and control COCs. NXP installed seven additional soil vapor monitoring wells in December 2015 and completed the OU1-wide vapor intrusion report in November 2017. Activities to complete the Remedial Investigation portion of the project are ongoing and the report is anticipated to be issued in 2021.

In 2018, NXP also began a TCE mass reduction pilot project in the Almeria neighborhood. The purpose of this pilot project is to determine the effectiveness of treating TCE and other COCs in groundwater using a chemical specific bio-agent and other bio-enhancing applications. To date, monitoring continues and preliminary results suggest that the needed biological conditions to promote bio-enhanced attenuation of TCE is not sustainable on a long-term basis.

OU2
Currently, OU2 is continuing to operate the 20th Street groundwater extraction and treatment system and monitoring the COC groundwater plume. An administrative order of consent (AOC) was signed to complete the remedial investigation and the feasibility study (RI/FS) for the final remedy. The final remedy is pending completion of the RI/FS. In late 2019, a work plan to enhance the groundwater extraction system was approved and is currently being implemented. Remedial investigation activities continue with soil gas monitoring for vapor intrusion, which is planned for completion in 2020.

Remedy evaluation continues for the Honeywell 34th Street site. An integrated focused human health risk assessment was submitted in November 2018. The annual groundwater monitoring report, submitted in 2019, indicated continued detection of TCE in groundwater above the action level.

The former Joray Corporation (Kachina) facility, located at 30th Street and E. Washington Street, continues to operate a soil vapor extraction (SVE) system that began in March 2013 to remove residual VOC concentrations (primarily PCE).  The soil vapor rebound testing performed in 2018 indicated significant concentrations of PCE accumulating in subsurface soil. As a result, the SVE system operates in a cyclical fashion to improve efficiency and cost effectiveness. A work plan to further investigate the soil vapor plume and the possible presence of DNAPL in bedrock was implemented in 2019 and work will continue through 2020.

OU3
Groundwater monitoring continues at OU3 on an annual basis. The OU3 Working Group completed an initial draft of the groundwater baseline risk assessment in September 2018 and a finalized version is expected by Spring of 2020. Currently the OU3 Working Group is in the process of revising the FS report.

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