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The Arizona Department of Environmental Quality is assisting the city in cleaning up contaminated groundwater under the city's Police and Fire departments' headquarters Downtown, the agency said Tuesday.

A written statement issued by ADEQ Director Steve Owens said the state's involvement means the city will be eligible to receive up to $500,000 in state funds to help pay for the cleanup.

ADEQ said it determined the cause of the contamination was five storage tanks located between the Police and Fire departments — which were removed in 1993 — and that gasoline from those tanks likely contaminated the groundwater with benzene.

"Everybody agrees this is the release site," said Nancy Petersen, deputy director of Tucson's Environmental Services Department.

The chemicals are not in the aquifer from which drinking water is drawn, and officials said there is minimal chance they will migrate there. Petersen said the city found benzene in high concentrations in the "perched aquifer" about 60 feet below ground.

There is a perched aquifer at that depth throughout Downtown, she said, adding that the regional drinking-water aquifer is 120 feet below ground. There are no drinking wells in the Downtown area, she said.

The benzene was found in five wells drilled in the area.

In two wells, the city found actual petroleum on top of the water in the perched aquifer. Those wells were in between the police and fire stations, and in a well under the Tucson Convention Center parking lot.

In three other wells near the police and fire headquarters, the benzine had dissolved into the water, Petersen said. Those wells had benzene 380 times, 174 times and 56 times the maximum level allowed by state and federal environmental standards.