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The state will soon start sucking gaseous contamination out of soil beneath an old dry-cleaning business north of Downtown.

The Arizona Department of Environmental Quality will use newly installed equipment to remove vapors of three toxic chemicals that sit in soils as deep as 173 feet beneath the old Oliver's Cleaners building at 300 E. Seventh St. The entire site targeted for cleanup is bounded by Fourth Street to the north, Fourth Avenue to the east, Eighth Street and the railroad tracks to the south and Ash Avenue to the west.

It will take two weeks to install the equipment and two years for it to remove all contamination from the soil at a total cost of about $150,000. The water table is about 173 feet deep there.

The most heavily concentrated pollutant in the soil is perchloroethylene (PCE), a common dry-cleaning solvent that was found at 26,000 parts per million in 1997 near underground storage tanks at the cleaners' site. Levels of trichloroethylene (TCE) and cis-1,2 dichloroethylene also exceed regulatory limits in the soil, according to an Arizona Department of Environmental Quality fact sheet on the contamination released in January 2006.

Oliver's Cleaners and other dry-cleaning businesses operated on the site from 1928 to 1989, when the Oliver's building was destroyed by fire. In 1991, authorities excavated seven underground storage tanks beneath the building — five with dry-cleaning solvent and two with heating and waste oil.

Groundwater near and beneath the site is also heavily contaminated with PCE and petroleum hydrocarbons at levels above drinking-water standards, said Steve Owens, the department's director. There's no specific timetable for a groundwater cleanup. But because no drinking wells lie nearby, there is no immediate threat to the water supply, Owens said.

"That's the good news," he said.

A groundwater cleanup can take a decade or longer. Just how long depends on the success of the soil-vapor extraction method for sucking gaseous pollution out of the soil, Owens said. The hope is that that getting the pollution out of the soil will prevent the water from becoming more polluted.

"PCE, the dry-cleaning solvent, persists for quite a long time in water," he said. "It doesn't break up naturally, the way gasoline does. This is one of those situations where we have to do a significant amount of pumping and treating before we're over.

"We will keep doing it until we can get it (the contamination) down to an acceptable level."

John Sedwick, director of the Fourth Avenue Merchants Association, said it's great that the state is cleaning up the site. He said the contamination doesn't pose an imminent threat because it's all covered by an asphalt parking lot

"This has been in the works for a long time," he said. "They've done a good job of planning."