After two years of construction, a plant to filter out potentially toxic groundwater contaminants from Pima County’s only Superfund site is expected to be fully operational at the end of the month.
The plant, which cost $18 million, is an innovative effort by Tucson Water to keep drinking water at the federal standard for about 50,000 people in the west-central and northwest service areas.
Located at the northwestern tip of a groundwater contamination plume at Irvington and 1-19, the plant is notable partly because the water it treats lies within a federally designated Superfund site near Tucson International Airport.
“We’re one of the few cities in the country where water from a Superfund site is actually put back into the distribution system for consumption,” said Fernando Molina, a spokeswoman at Tucson Water.
A Superfund site is an area where the Environmental Protection Agency has determined to have uncontrolled or abandoned hazardous waste and is in need of evaluation and cleanup, since it may be affecting the local population or ecosystems.
The new Advanced Oxidation Process water treatment facility, which aims to treat 1,4-dioxane, was built adjacent to the Tucson Airport Remediation Project. Completed in 1994, the project has been filtering trichloroethylene (TCE) and other contaminants out of the groundwater for 10 years.
According to Molina, 1,4-dioxane moves differently than TCE through the water and the soil. It’s much slower, which is why it wasn’t found at the facility until 2007.
In order to keep the amount of 1,4-dioxane below the health advisory level, Tucson Water used to run the water through the facility to remove the TCE. It was then blended in water from other non-contaminated sources to dilute it until it was below the health-advisory level.
However, in 2012 the Environmental Protection Agency revised its toxicological evaluation of 1,4-dioxane, finding that it was more likely to cause cancer than was previously estimated. The agency lowered the health level from 3 parts per billion (ppb) to 0.35 ppb.
“The reason we built the plant was that we knew the levels of 1,4-dioxane were rising, and because of that, we knew this solution process would not be sustainable in the long run,” Molina said.
According to Martin Zeleznik, the E.P.A.’s Tucson International Airport Superfund Site Manager, 1-4 dioxane is semi-volatile, which means it’s harder to treat than normal organic compounds because it needs more oxygen to be broken down.
TARP currently uses air stripping and carbon fibers to filter water. However, the advanced oxidation facility will use hydrogen peroxide and ultraviolet light to treat water. The new plant has three main sections: a main building that holds the ultraviolet reactors used to remove the dioxane through oxidation; two rows of giant white tanks called GAC contactors which remove hydrogen peroxide left in the water; and a GAC backwash tank. The two treatment facilities are projected to purify eight million gallons of water a day.
Groundwater contamination in Tucson began to become noticeable during the 1940s and continued through the 1970s when industries around Tucson International Airport improperly disposed of their waste. After testing the groundwater there, the E.P.A. classified the area near Tucson International Airport as a Superfund site in 1983.
The Superfund site covers approximately 10 square miles and is divided into seven project areas. The main contamination plume, which is approximately one half-mile wide and five miles long, stretches from the airport to Irvington Road and I-19.
“The parties which were held responsible for the groundwater contamination are the ones that are paying for the operation and maintenance of these facilities,” said Molina.
The E.P.A. has identified several potentially responsible parties. Tucson Water may be overseeing the cleanup of the contamination, but is doing so on behalf of the City of Tucson, Raytheon, the U.S. Air Force, McDonnell Douglas Corporation, Tucson Airport Authority, and General Dynamics Corporation for the Airport Property and TARP.
In order to keep all potentially responsible parties and concerned citizens aware of the progress with the cleanup, a Unified Community Advisory Board was formed. Made up of about 20 members from different parts of the community, the board meets quarterly to discuss the progress of the cleanup and community concerns.
“When I met and interviewed with the community individually, I didn’t hear that there was a lot of concern,” Zeleznik said. “They just want to be informed and kept apprised of the progress.”
While the tract near the airport is the only Superfund site in Pima County, there are four other sites in southern Arizona.
“We’re still kind of finalizing the construction of the new AOP plant,” Molina said. “We’re undergoing some testing on some of the equipment. As far as the plant being fully operational, I think we’ll be looking at the end of February in terms of bringing the plant back up into operation and start using the advanced oxidation process to remove the dioxane.”
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