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Waste Programs Division: Hazardous Waste Management: University of Arizona - Page Trowbridge Ranch Landfill (PTRL)

University of Arizona - Page Trowbridge Ranch Landfill (PTRL)

U.S. EPA ID No: AZD 980 665 814

Facility Location

North of State Highway 77, approximately seven miles west of Oracle and 30 miles north of Tucson.
Southern half of Section 27 and the northern half of Section 34, Township 9 South, Range 14 East of the Gila and Salt River Base and Meridian, Pinal County, Arizona.

Facility Description

The University of Arizona (UA) manages the Page Trowbridge Ranch Landfill (PTRL), a closed hazardous waste landfill located north of State Highway 77, approximately seven miles west of Oracle and 30 miles north of Tucson. A site location map is shown in Figure 1. The PTRL is located in Township 9 South, Range 14 East, Gila and Salt River Base and Meridian, and includes the southern half of Section 27 and the northern half of Section 34. Land to the north and northeast of the PTRL is owned by the State of Arizona and is used as open range grazing land. The UA owns and uses the land to the north, northwest and east for agricultural research. Property owned by Robson Ranch Mountains, L.L.C., a developer, to the southwest, south, and southeast of the PTRL is used for residential development. There are currently approximately 100 homes and a clubhouse constructed in the Saddlebrooke Resort Community.

UA used the PTRL to dispose of low-level radioactive material and chemical waste generated at UA, Northern Arizona University, Arizona State University, and the Veterans Hospital in Tucson from the early 1960s through 1986. The chemical waste primarily consisted of solvents, ignitables, acids, bases, heavy metals, pesticides, and photographic compounds.

The landfill site occupies a total of 3.25 acres and consists of two areas: Area A (northern unit, 200 feet by 200 feet) and Area B (southern unit, 200 feet wide by 500 feet long) as shown in Figure 2. In both areas, wastes were placed in individual cells (pits) that were approximately 15 feet deep. A final cover system was constructed over each area to prevent percolation through the landfill. It includes a final earthen cover on top that supports native grass vegetation. The landfill is surrounded with a six-foot-high chain-link fence with barbed wire along the top. Culverts and storm water channels were installed to divert rainwater from the surface of the site to minimize percolation into the subsurface soil.

A solar-powered soil vapor extraction (SVE) system was installed at the landfill and has been operating since June 2006 between Areas A and B (Figure 2). The system is used as a soil vapor monitoring system to detect potential releases from the landfill areas. If a release is detected, actions will be taken in advance of any contamination reaching ground water, which is at approximately 640 feet below ground surface (bgs). The system injects air into the soil through one well (SGD-Well) at a rate of approximately 43 feet3/min and a depth of approximately 435 to 605 feet bgs, while soil vapor is extracted from another well (SGS-Well) at a rate of approximately 90 feet3/min from a depth of approximately 98 to 225 feet bgs. The vapor is then directed through an activated carbon treatment system (two 2,000-pound units) where air emissions monitoring is conducted weekly, using a photoionization detector (PID), and samples are collected monthly to check for breakthrough of the granular activated carbon to determine when it needs to be replaced and to monitor the mass removal of any Volatile Organic Compounds (VOCs) from the subsurface. A photograph of the system is shown in Figure 3.

In addition to the SVE wells, there are four active ground water wells used for monitoring chemical and radionuclide contaminants, as well as vapor monitoring points to measure VOCs. The ground water monitoring wells and soil vapor monitoring points are located within the fenced enclosure surrounding the two landfill areas and finished with protective steel casings installed in cement with locking well head covers (Figure 4). Ground water monitoring wells MW-2, MW-3, MW-4, and MW-5 are approximately 800 feet bgs. For sample collection, a submersible pump was installed in each well, with power supplied by a generator. Six on-site soil vapor monitoring points, SGS-WELL, SGS-SP, SGD-WELL, SGD-SP, SGD-MP, and SGD-DP cover soil vapor monitoring intervals across a range of 75 to 600 feet bgs. In order to also use MW-2 and MW-5 as soil vapor monitoring points, inflatable packers were installed with soil vapor monitoring intervals extending to the ground water table. A well construction drawing example of MW-2 is shown as Figure 5. Ground water and soil vapor sampling will be conducted semi-annually.

The facility is not located in a 100-year floodplain.

UA PTRL Permit Application (latest submittal dated 04/27/2012)

The UA PTRL was originally permitted by ADEQ in 2001. In July 2011, the UA submitted a permit application for renewal of their hazardous waste post-closure permit.

Draft Hazardous Waste Post-Closure Permit Renewal

Based on the Permit Application submitted by the UA PTRL, a Draft Permit was prepared by ADEQ. A public notice was issued and a public comment period was held from May 06, 2012 through June 21, 2012.

Upon the final Permit decision, ADEQ issued a Response to Comments Summary. The summary responded to all significant comments submitted by the general public during the public comment period.

Hazardous Waste Post-Closure Permit

On June 29, 2012, ADEQ issued to UA PTRL a renewal to its Hazardous Waste Post-Closure Permit. The UA PTRL was originally permitted by ADEQ in 2001. Ground water quality at PTRL has been compliant with State and Federal standards for over twenty years with controls that are in place at PTRL to verify future compliance and protect human health and the environment. The hazardous waste rules provide for expansions to the groundwater monitoring program in the event of detections. If detections of constituents are noted in groundwater, the Permittee would be required to undertake Compliance Monitoring. Further detections of constituents in groundwater may lead to Corrective Action and a groundwater remedy. Soil vapor concentrations are also monitored to detect contaminant movement well before groundwater is impacted. If the concentrations exceed the soil vapor trigger concentrations specified in Permit Attachment G, Table G-8, additional actions will occur.

In accordance with R18-8-270.A (40 CFR 270.50) the Permit has a term of ten years and expires on June 29, 2022. A thirty year post-closure period began upon issuance of the Permit.

Contents of the Permit:

  • Part I - General permit conditions required by Arizona Administrative Code (A.A.C.) R18-8-270 A and L and 40 CFR 270.30.
  • Part II – Post-closure facility conditions required by A.A.C. R18-8-264.A and 40 CFR §§ 270.32 and 264, Subpart H.
  • Part III - Specific conditions related to the ground water monitoring and soil vapor monitoring. These conditions are authorized by A.A.C. R18-8-264.A and 40 CFR § 264.100.
  • Part IV - Specific conditions regarding corrective action for solid waste management units, also referred to as the Corrective Action Schedule of Compliance (CASOC) required by A.A.C. R18-8-264.A and 40 CFR 264.101.

Arizona Hazardous Waste Management Act Permit

Groundwater and Soil Vapor Monitoring

Groundwater and Soil Vapor is monitored at the PTRL on a semi-annual basis. Groundwater monitoring reports are submitted to ADEQ within 90 days of completion of the groundwater monitoring event. Historic groundwater monitoring results are available in Appendix H of the UA PTRL Hazardous Waste Permit Application.

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