Revised On: Feb. 23, 2024 - 3:30 p.m.

2021: Rebound testing indicated that the soil vapor extraction (SVE) system objectives had been achieved. In June, the operation of the SVE system was discontinued. Removal of the system and demolition of supporting infrastructure began in October and was completed in February 2022.

2020: ADEQ continued operating the in-situ chemical oxidation groundwater treatment system ERA at the Broadway North Landfill and the soil vapor extraction system ERA at the Broadway South Landfill. ADEQ also conducted annual groundwater monitoring and sampling at the Site in May.

2019: ADEQ implemented three early response actions (ERAs) including construction of an asphalt cap within the dross (metal waste) area, construction and operation of an in situ chemical oxidation (ISCO) groundwater treatment system at the Broadway North Landfill (BNL), and construction of a soil vapor extraction (SVE) system at the Broadway South Landfill (BSL). ADEQ also conducted groundwater monitoring and sampling and finalized the Proposed Remedial Action Plan (PRAP). A soil remediation system was installed at BSL in April. An Operation & Maintenance (O & M) Plan for groundwater treatment was released for a 30-day public comment period, also in April. In June, the PRAP was made available and opened for a 90-day public comment period. The comment period was later extended to expire January 7, 2020.

2018: ADEQ conducted groundwater monitoring and sampling at the site.

2016 - 2017: ADEQ conducted groundwater monitoring and sampling and finalized the Feasibility Study (FS).

2015: Site-wide sampling was performed and much of the FS work was completed.

2014: The Landfill Operable Unit (LOU) Proposed Remedial Objectives (RO) Report was prepared and issued for public comment on March 5, 2014.

2013: During spring ADEQ completed the LOU Remedial Investigation (RI) field work which included deep soil gas testing at BSL and BNL (to assess whether there is a continuing release to groundwater), shallow subsurface soil gas testing at BSL and BNL (to assess onsite risk), shallow soil gas testing at three locations at the BSL boundary (to assess indoor air/vapor intrusion risk), installation of temporary boreholes within the BSL Gollob Park (to delineate vertical and horizontal extent of buried waste) and surface soil testing at BSL. All soil gas samples were tested for volatile organic compounds (VOCs) and soil was tested for metals, pesticides, and semivolatiles. Using these results and previously-obtained data, the LOU Draft RI report was produced and issued for public comment on Nov. 29, 2013.

2012: In January, ADEQ’s contractor began a modeling study to evaluate more cost effective operation of the Western Containment System (WCS) and various pumping scenarios were simulated.

ADEQ finalized the updated “Potential Historical Users of perchloroethene (PCE) and/or trichloroethylene (TCE) Technical Memo” in May. ADEQ finalized the groundwater RI report on June 1. The final groundwater RI report includes, as appendices, the Water Use Study, the final groundwater RO report, and ADEQ’s responses to public comments received on both the draft groundwater RI report and the proposed groundwater ROs report.

In Oct., ADEQ shut down the WCS because the concentrations of PCE coming into the WCS had continued to be non-detectable or well below the Arizona Water Quality Standards (AWQS) for many years. However, the WCS is being maintained in a state of readiness (including monthly exercising of the system) in case PCE concentrations increase to levels requiring resumption of WCS operation. Also, enhanced groundwater monitoring is being performed quarterly by the City of Tucson (COT) under the ADEQ/COT work share agreement.

2011: In the fall, ADEQ’s contractor began updating and revising the groundwater RI report to include site data and information produced since the draft groundwater RI was issued in 2007.

2010: ADEQ completed the groundwater modeling study in June. The study included a groundwater fate and transport model, preliminary simulations of possible final groundwater remedial actions, and simulations of different operational durations for the WCS. The results of this study will be used in the future groundwater FS. In July, ADEQ finalized the Human Health Risk Assessment (HHRA) for the potential shallow soil gas pathway from the BNL to adjacent residences. The HHRA determined that the potential risk was below the level requiring remediation. COT continued quarterly sampling of select wells. COT’s sampling results indicate that a small portion of the groundwater plume extends to Craycroft Road.

2009: In January, under an amendment to the ADEQ/COT work share agreement, COT completed installation of three groundwater monitor wells west/northwest of the WCS wells to delineate the downgradient edge of the PCE plume. COT also began quarterly sampling of key groundwater monitor wells near and downgradient of the WCS.

ADEQ also executed Prospective Purchaser Agreements (PPA) for nine BNL parcels. As a public benefit under the PPA, the property owner has agreed to prepare and record a Declaration of Environmental Use Restriction (DEUR) and associated engineering control plan for the maintenance of the landfill cover and methane gas mitigation system for each parcel.

2008: SVE rebound testing was performed at the BNL in January and the results continued to show negligible rebound of VOC concentrations in vadose zone soil gas. In March, ADEQ initiated the groundwater modeling study in preparation for the future groundwater FS. In May, a groundwater monitor well was installed at the northwestern edge of the BNL to more fully characterize that part of the site. The proposed groundwater RO report was issued for public comment in November. In December, ADEQ/COT amended the work share agreement for COT to install three groundwater monitor wells downgradient of the WCS, and ADEQ finalized a scope of work for completing the BSL RI field work.

2007: In November and December, ADEQ completed installation of a cluster of three groundwater monitor wells at a location approximately one-quarter mile downgradient from the BNL. Each well was screened at a different depth below the water table. The purpose of installing this well cluster was to help delineate the vertical extent of contamination and to allow for other groundwater testing needed for the groundwater FS. The draft groundwater RI report was issued for public comment, and the groundwater RO public input meeting was held in the spring.

2006: Two groundwater monitor wells were installed in the northeast part of the BSL in the spring to further delineate the groundwater contamination. At this time, it appears that the only groundwater contaminant of concern is PCE and the only exceedances of the AWQS for PCE are in the northern part of the BSL. ADEQ also installed deep nested soil gas monitor wells in the northern half of the BSL to assess whether an ERA would be warranted.

In the summer, ADEQ decided to separate the groundwater part of the RI from the landfill part of the RI to expedite the groundwater cleanup at the site. The landfill part of the RI is referred to as the LOU and it includes the BNL and BSL and the vadose zone beneath them. Rebound testing of the deep nested soil gas monitor wells at the BNL again showed insufficient rebound for bringing the soil vapor extraction/air injection (SVE/AI) system back on line.

ADEQ again collected shallow soil gas data along the southwest perimeter of the BNL and tested the samples for VOCs for use in evaluating the shallow soil gas/indoor air pathway at the BNL.

2005: Groundwater sampling events confirmed that the BSL PCE plume had merged with the BNL PCE plume. Therefore, ADEQ expanded the RI to include the BSL groundwater contamination.

In August, COT installed two groundwater monitor wells downgradient of the northwestern edge of the plume to help delineate this part of the plume and to evaluate the effectiveness of WCS capture. One sample from one of these wells contained PCE at 5.8 micrograms per liter (μg/L) during the initial sampling. Subsequent samplings of this well have shown the groundwater at that location to be either slightly above or slightly below the AWQS of 5.0 μg/L. All samples collected from the other well have contained PCE concentrations that were either less than the AWQS or non-detectable. The well water elevation data indicated that these two wells were not within the WCS capture zone.

2004: In November, groundwater monitoring results indicated that the BSL PCE plume might be merging with the BNL PCE plume.

ADEQ installed four new deep nested soil gas monitor wells at the BNL to provide additional sampling points for evaluation of BNL SVE/AI system rebound. Rebound testing of these and the original deep nested soil gas monitor wells at the BNL showed insufficient rebound for bringing the SVE/AI system back on line.

2003: In the spring, ADEQ and COT completed the installation of the WCS at the western edge of the plume. The WCS consisted of two extraction wells, granular activated carbon (GAC) treatment system, and two injection wells. On March 24th, the WCS began full operation. Analytical results showed that the treatment system was removing the PCE to non-detectable levels.

When the WCS was initially brought on line, the extraction rate was 1100 gallons per minute (gpm). However, in the summer, the injection capacities in the R-090A and R-091A injection wells decreased because of plugging so the WCS extraction rate was reduced to 800 gpm. Subsequently, both injection wells were rehabilitated/redeveloped and injection-specific capacities improved, but not to original levels. Back flushing of the injection wells would need to be performed regularly to maintain performance.

ADEQ conducted surface soil testing at the BNL in April. Thirty-five samples were collected from topographically low areas and locations where it appeared that a release of some substance(s) may have occurred previously. These samples were tested for semi-VOCs, metals, pesticides, and polychlorinated biphenyls. Twelve samples were collected approximately 25 feet beyond the dross site fence perimeter and tested for metals. For the constituents tested in these samples, none were found above the Arizona residential or non-residential soil remediation levels.

Rebound testing of the deep nested soil gas monitor wells at the BNL continued to show insufficient rebound for bringing the SVE/AI system back on line.

ADEQ again collected soil gas data along the southwest perimeter of the BNL and tested the samples for VOCs for use in evaluating the shallow soil gas/indoor air pathway at the BNL.

2002: In June, COT issued a groundwater RI report. This report documented the results of groundwater investigations conducted through 2000; however, additional investigation was needed to complete the groundwater part of the RI.

In November, ADEQ completed a focused investigation to determine whether an ERA was required to protect or provide for the use of the water from the two COT water supply wells located south of Broadway Boulevard and west of the BSL. Another aim of this investigation was to determine whether the BSL PCE groundwater plume was comingling with the BNL PCE groundwater plume. The data collected indicated that an ERA was not warranted and that the BSL PCE plume appeared to not be comingling with the BNL plume at that time; however ADEQ continued to monitor groundwater in the area. ADEQ installed eight groundwater monitor wells to be used for WCS performance monitoring and the groundwater RI report.

The BNL SVE/AI system was turned off in September to conduct rebound VOCs testing of nested soil gas monitor probes/wells. Results from the VOC testing indicated insufficient rebound for continued operation of the system. Over the approximately two years of operation, the SVE/AI had removed over 5,000 pounds of VOCs, including 1,200 pounds of PCE, from the vadose zone.

ADEQ collected shallow soil gas data along the southwest perimeter of the BNL and tested the samples for VOCs for use in evaluating the shallow soil gas/indoor air pathway at the BNL.

2001: COT completed the design of the WCS groundwater pump and treat and inject system with ADEQ oversight. In June, ADEQ and COT executed a work share agreement under which COT would construct, operate and maintain the WCS with ADEQ oversight, and ADEQ would reimburse COT for most of the costs. Under this agreement, ADEQ took over responsibility for operating the SVE/AI system. Also, with the execution of the work share agreement, ADEQ took over the further investigation and remediation of the site.

ADEQ installed four groundwater monitor wells needed to evaluate whether an ERA was needed for the two COT water supply wells located south of the BNL PCE plume. 

2000: In June, COT and Pima County completed installation of a deep SVE/AI system at the BNL. The SVE/AI worked as follows: Clean air was injected deep below the landfill, and contaminated soil gas was extracted and treated with GAC to remove the PCE. The purpose of this ERA was to prevent, to the extent practicable, additional PCE contamination of the groundwater. COT, with technical assistance from Tucson Water and the County, completed development and calibration of a groundwater model for the site to be used for conceptualization of a groundwater ERA.

Two COT water supply wells located south of the groundwater plume were put on restricted pumping "standby" status. COT installed the first groundwater monitor well at the BSL and the groundwater samples from this well were found to contain PCE above the AWQS.

In December, Home Depot completed a report regarding its investigation of properties located on, and immediately to the south of, the BNL which indicated that dross had been buried on these properties. Home Depot covered the dross site with soil and temporarily fenced off the part of the dross site not overlain by buildings and pavement. ADEQ later replaced the temporary fence with a permanent fence and warning signs.

1999: COT installed four additional groundwater monitor wells at the site to help with lateral and vertical delineation of the plume.

1998: In March, COT issued an RI report for the BNL. The report confirmed that the BNL was the major source of groundwater contamination at the site. However, the RI report did not contain a complete assessment of the shallow soil gas; thus, more work was needed to complete the landfill part of the RI.

ADEQ installed three groundwater monitor wells, including two wells upgradient of the St. Joseph's Hospital water production well. A fourth COT well (one of the wells designated "last-on, first-off," or LOFO, in 1994) was shut down because of PCE contamination. The groundwater contamination was found to extend approximately two miles to the west from the BNL.

The site was placed on the WQARF Registry in December with an eligibility and evaluation score of 48 out of a possible 120. 

1994 – 1997: In 1994, COT designated five COT water supply wells located close to the site groundwater plume as LOFO wells, thus restricting their usage.

PCE was detected in the St. Joseph's Hospital water supply well at levels below the drinking water standard in 1994, after which COT began monitoring the well. By September 1995, the PCE concentration in the well had increased to 4.9 μg/L. The well was shut down, and COT provided water to the hospital until a GAC system was installed on the well in 1997. The GAC system removed PCE to levels below the AWQS.  Also in 1997, COT installed shallow groundwater monitor wells at the western edge of the BNL.

1993: The City of Tucson, Pima County, and property owners formed a project management team to conduct a RI/FS of the site, with oversight provided by ADEQ.

1989 – 1991: In 1989 and 1991, two COT water supply wells at the site were shut down because of PCE contamination. In 1990-1991, COT installed groundwater monitor wells and began periodic monitoring of these wells to help delineate the extent of groundwater contamination.

1959 – 1972: The BNL, which is the major source of contamination at this site, was originally developed as a sand and gravel mining operation in the mid-1940s. In 1959, formal landfilling operations began on a portion of the BNL under the Sanitary District No. 1 of Pima County and lasted until 1968, when the district was dissolved. Pima County Department of Sanitation took over operation of this portion of the landfill, which was closed and capped by approximately 1973. The COT also operated on a portion of the BNL from approximately 1965 to 1971.

1953 – 1962: The BSL, which is a source of contamination at this site, was originally developed as a sand and gravel mining operation prior to 1953. From 1953 to 1956, the landfill was operated by Pima County, and, from 1956 to 1958, the landfill was operated by Sanitary District #1 of Pima County. In 1958, Pima County and the Sanitary District No. 1 of Pima County agreed to share interest in the landfill until it closed in 1962.