The Air Force Civil Engineer Center's environmental cleanup at the former Williams Air Force Base in Mesa, Ariz., is in its final stages.

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What's been done? What's left to do?
The environmental cleanup at the former Williams Air Force Base in Mesa, Ariz., is in its final stages. Cleanup decisions have been made and implemented at most of the sites identified at the former base. In addition to maintenance and monitoring of existing cleanup actions, the Air Force is modifying or establishing remedies for the remaining sites where needed. Site investigations are wrapping up for these sites and the Air Force anticipates selecting remedies in 2013.

Background
The 4,043-acre Williams was a flight training school in 1941. During its 52 years as a military aviation, training, supply and maintenance complex, several areas of the former base were environmentally impacted from industrial practices that were legal and commercially accepted at the time.

Contaminants from military operations include organic solvents and paint strippers, petroleum, metal plating waste, hydraulic fluids, pesticides, and radiological wastes. In 1983, the Air Force implemented the Department of Defense Installation Restoration Program to identify, investigate, and remediate sites at Williams.

Investigative and remedial activities have been underway at Williams since 1983. In 1989, the base was added to U.S. Environmental Protection Agency's National Priorities List as a Superfund site. This listing requires the Air Force to follow the EPA-regulated cleanup processes defined in the Comprehensive Environmental Response, Compensation and Liability Act.

Since then, the Air Force has continued the environmental cleanup at Williams with oversight from the U.S. EPA, the Arizona Department of Environmental Quality and the Arizona Department of Water Resources.

Williams Air Force Base closed in 1993 following the 1991 announcement from the Base Realignment and Closure Commission. The Local Reuse Authority, Phoenix-Mesa Gateway Airport, has turned the closed base into a thriving international aviation and aerospace center and educational complex.

Meanwhile, the Air Force continues its commitment to environmental cleanup and protecting human health and the environment at the former base.

To date, the Air Force has spent more than $93.54 million on the cleanup and millions more will be spent for ongoing monitoring and operation of groundwater treatment and soil cleanup systems, and for maintenance and monitoring of the former landfill site.
 
Groundwater
Cleanup of the groundwater is the most complex project remaining at Williams. Investigation to fully define the extent is nearly complete and the Air Force is studying different alternatives for completing the cleanup.

The contaminated water at Williams is not used for drinking. Drinking water is supplied by the City of Mesa, which tests the drinking supply in accordance with state and federal laws and regulations. Annual water quality reports are provided to customers, as required by law. In addition, the Air Force samples the water from many monitoring wells in the area to ensure no impact on drinking water supplies.

The groundwater contamination at Williams occurs in distinct plumes associated with three site areas. The Air Force plans to use several technologies to clean the groundwater, depending on the site geology and specific contaminants as described below.

LF004, a former landfill. This site was capped in 1995; however rising groundwater has mobilized some volatile organic compounds, or VOCs. Through a network of monitoring wells sampled quarterly, the Air Force determined the VOC concentrations are decreasing in the highest concentration areas, and that the plume is not spreading. The Air Force anticipates presenting a proposed plan for groundwater cleanup for public comment in late 2012, with a Record of Decision and implementation of a remedy to follow in 2013.

ST035, former base gas station and underground storage tanks. Contaminants of concern are petroleum hydrocarbons. Groundwater monitoring is ongoing and a soil vapor extraction, or SVE, system is actively removing VOCs from the soil above the groundwater. The Air Force anticipates installing in-well air strippers in late 2012 to remove contaminants from the groundwater.

ST012, the former liquid fuels storage area. Contaminants of concern are petroleum hydrocarbons. Groundwater monitoring is ongoing and a SVE system is actively removing VOCs from the soil above the groundwater. In October 2008, the Air Force conducted a pilot test using thermal enhanced extraction to remove petroleum hydrocarbons from soil and groundwater. The pilot test was successful. A proposed plan and public comment period are scheduled for late 2012. Implementation of the remedy would follow shortly thereafter. 

In addition, the Air Force is monitoring groundwater for the pesticide dieldrin at Site SS017, a former pesticide storage and paint shop. A soil removal action was completed in 2000 that addressed potential exposure to contaminated surface soil. Groundwater monitoring indicates no need for remedial action, but the Air Force and regulators are determining if restrictions and continued monitoring are necessary.

Soil Cleanup
The majority of contaminated soils at Williams have been cleaned up through dig-and-hauls, where the soil is excavated, tested and disposed of in an approved off-site facility. In most cases, this has resulted in the site being released for unrestricted use.

However, at some sites, such as the former skeet ranges and firing range, dig and haul is not an option because of current land use. One of the skeet ranges and the firing range are located at the end of the flight line, limiting access and development. Base housing was built atop the other former skeet range. The housing is a valuable resource for Arizona State University which operates a campus at Williams. Lead in soil at these sites near housing was excavated and a protective cap was installed. Deed and use restrictions that protect human health were implemented when the properties were transferred to the Phoenix Mesa Gateway Airport or ASU.

Soil cleanup to remove petroleum hydrocarbons using SVE continues to operate at site ST035, the former base gas station, and site ST012, the former bulk storage facility. Site sampling is planned at site FT002, a former fire training area, to determine if the cleanup objectives have been met and the site can have unrestricted use. The Air Force and regulatory agencies are determining if land restrictions and continued groundwater monitoring are necessary for site SS017, the former pesticide and paint shop. At site LF004, the former base landfill, maintenance and monitoring of the landfill cap is ongoing.

Monitoring & Review
An important component of the cleanup at Williams is ongoing monitoring and a 5-year review. The monitoring verifies, on a regular basis (from weekly to annual), that the program is working as intended.

The 5-year review is a comprehensive audit of cleanup remedies at the former base. It reviews the effectiveness of the cleanup, and the current knowledge about the contaminants and treatments to ensure the remedies remain protective of human health and the environment.

Lastly, the review provides recommendations for ongoing operations of the site remedies.

Community Involvement
Community involvement and acceptance is a key part of the Williams cleanup. The Air Force works with the Williams Restoration Advisory Board to provide a two-way exchange of information with the community. The RAB is composed of representatives from various stakeholder groups within the local community as well as regulatory agencies. The group meets quarterly to advise the Air Force and regulators about concerns and provide comments on Williams cleanup documents. The public is invited to attend the RAB meetings and notices of upcoming meetings are published in advance in local newspapers.