For the first time in 16 years of testing, UA officials have found evidence that they say suggests an old landfill northwest of Oracle may be contaminating ground water.

Slightly more than 1 part per billion of the common industrial solvent toluene last month appeared in a monitoring well lying 650 feet underneath and just west of the Page-Trowbridge Ranch.

The ranch took UA's radioactive wastes, starting in the early 1960s, and hazardous wastes, starting in the middle 1970s. About 500 tons of wastes later, the university closed the 3-acre site in 1986 under pressure from residents.

The measured toluene amount is a fraction of the state's ground water quality standard of 1,000 parts per billion. It doesn't affect drinking wells.

The Arizona Department of Environmental Quality must verify the results. UA officials say the results may have other causes: contaminated pumping equipment or solvent vapor from the pump's diesel-fired generator.

Still, UA officials say the results may be significant because for the first time, they came in separate UA and DEQ samples.

In April 2000, authorities couldn't duplicate a single water sample containing 3.7 ppb toluene.

Until now, the university has said its studies have found that the area's deep ground water table, its low annual rainfall and its high evaporation rate would almost certainly shield that aquifer from contam- ination.

Skeptical residents last year issued an inch-thick study warning of pollution threats.

Now, area residents have a "very reasonable concern" that this contamination may signal future, higher test readings, said Steve Holland, UA's risk management director.

UA will re-sample the ranch's four wells in January and at least every three months afterward.

It will soon start drilling up to 100 feet deep to test soil between the ground surface and the aquifer, he said.

The results come just after Oracle residents submitted nearly 6,000 petition signatures to Pinal County seeking a referendum vote on a November county rezoning for 5,900 homes and three golf courses on the Falcon Valley Ranch north of the landfill.

By early January, the Pinal County Recorder's Office will determine whether residents submitted the 2,819 valid signatures needed for a referendum.

The Page Ranch likely will dominate a referendum campaign. Developer Robson Communities' consultants have agreed with UA officials that the odds of contamination were extremely unlikely.

In November, Robson executive Steve Soriano said that once the facts about the landfill are fully known, the referendum drive will be "toast."

Oracle activists contend that the development's pumping could suck contaminants into the aquifer.

An Oracle activist last week declined to say, "I told you so."

"My reaction is that finally, we get the university to admit this is a serious business, so testing is extremely important," Ann Woodin said. "I don't care what happened in the past. That doesn't get us anywhere."

Robson isn't commenting much on the test results until further tests occur, Soriano said Wednesday.

"I don't think it's evidence of anything yet," Soriano said. "It's so far below the maximum contamination limit."

DEQ spokesman Jim Fallin said the test results show that when the state signs off on a final permit for overseeing the closed landfill, continued monitoring will be necessary.

"The results are an indication that the monitoring system is working," he said. "It's also an indication of the commitment of ADEQ to continue to safeguard public safety."

Contact Tony Davis at 807-7790 or verdin@azstarnet.com.