Changing federal standards for a chemical left behind after the cleanup of TCE and TCA from south-side groundwater could force the city - and water customers - to spend millions of dollars on a new treatment plant.

Removing trichloroethylene, or TCE, and trichloroethane, or TCA, from groundwater leaves behind a chemical called 1,4 dioxane, which was used to prevent the breakdown of TCA.

Although the massive federal Superfund site on the south side is able to strip out the TCE and TCA, the 1,4 dioxane does not evaporate and stays in the water.

To get under the current federal standards of 3 parts per billion for 1,4 dioxane in drinking water, Tucson Water mixes the treated water from the south side with other water that isn't contaminated by the chemical, lowering the level in Tucson's Water supply to 1.15 parts per billion, Tucson Water Director Jeff Biggs said.

But Tucson Water was notified two weeks ago that new federal drinking water standards will likely be issued in the wake of a new Environmental Protection Agency risk assessment for 1,4 dioxane showing the cancer potency factor of the chemical is nine times higher than the agency previously thought.

How low the new standard could fall hasn't been identified, but Biggs said it's likely to be below the level that Tucson Water now achieves. He also noted that, as differing degrees of contaminated water move through the treatment plant, there is no guarantee that the city can continue to hit the 1.15 standard it now achieves.

Because word of the likely change is so new, city officials have no estimate on how much the plant will cost - beyond that it will be in the millions - or exactly when it will be required.

TCE and TCA are industrial solvents used to clean airplanes and parts at Tucson International Airport, Hughes Aircraft Co. - now Raytheon Missile Systems - and elsewhere on the south side dating back 50 to 60 years. In addition to stabilizing TCA, 1,4 dioxane is used in many products such as shampoos, cosmetics and lotions.

Water contaminated with the chemicals was allowed to soak into the ground and spread through the groundwater table for years, before it was discovered in the early 1980s, prompting thousands of south-side residents to file lawsuits over illnesses that may have resulted from exposure to the chemicals. The lawsuits resulted in multimillion-dollar settlements.

"You're concerned when a new risk assessment comes out, because it will lead to a new drinking-water standard," Biggs said. "When a new standard is developed, we will most likely have to have a treatment plant."

In addition to the multimillion-dollar construction costs, Biggs said, it would cost hundreds of thousands of dollars a year to operate. "It's a very expensive treatment process," Biggs said, adding that Tucson Water is doing "pilot testing" now to determine which technology would be most cost-effective and still treat the water properly.

Money for the treatment plant will have to come from ratepayers, Biggs said.

Biggs and other city officials emphasized that current drinking water is safe, and they especially wanted to make that clear to south-side residents who were scarred by the TCE incident.

Under the current standard, a person would have to drink two quarts of the affected water a day for 70 years to get a 1-in-a-million exposure risk for cancer, according to the EPA. The new EPA standards will lower those amounts, although Biggs said it won't necessarily be lowered by nine times - the cancer potency increase determined by the EPA.

Councilwoman Regina Romero said the city needs to get the message out to make sure that people aren't afraid to drink tap water.

The levels are minuscule, said Councilman Steve Kozachik, adding that he was concerned about headlines in the paper saying the water is unsafe. "Too often these things get so hyped," he said.

Deputy City Manager Richard Miranda said he grew up on the south side and knows the lack of confidence and understanding the community had in the authorities who oversaw the TCE incident. He said there are still hard feelings, because "people did get sick and die."

"We'll we working diligently to make sure that mistakes . . . won't happen again," Miranda said.

Contact reporter Rob O'Dell at 573-4346 or