CHARLESTON - Tours were held Wednesday at the cavernous tent structure under which a former manufactured gas plant will be excavated starting today.

Property owner Ameren Illinois Utilities is having contaminated soil and residues removed from the site northeast of Washington Avenue and Third Street, where the plant operated from 1906 to 1928.

The $2 million project is being conducted in cooperation with the Illinois Environmental Protection Agency through its voluntary site remediation program.

"You can't see it, but it is there below ground," IEPA spokesman Stanley Black said of the contaminants, which include benzine.

Donald Richardson, a consulting environmental engineer with Ameren, said Environmental Operations Inc. of St. Louis will dig about 10 feet at the deepest in the tent-covered project area.

Contaminated materials will be removed with earthmoving equipment and dump trucks following the same techniques as a typical construction site, Richardson said.

"We are more concerned about the dust and odor than a construction site would be," Richardson said.

Richardson said air from inside the tent, made of an impervious fabric, will be blown through a carbon filter before it is released outdoors. He said contaminated groundwater will be pumped through a carbon filter and treated on site before being released into the sanitary sewer system.

Jack Gardner, a section chief for air quality services with Philip Service Corp. of Columbia, said his crews will monitor air quality at all hours during the project to ensure safety inside and outside of the tent.

Richardson said neighbors may smell a mothball-like odor from the tent, but the odor is not a health risk. He said the project will be completed by Oct. 31 at the earliest and Dec. 25 at the latest.

Brad Rucker, a project manager with Environmental Operations, said he has tested groundwater in the surrounding neighborhoods and not found any contaminants. He said a hard level of silt is located about 12 feet below the former plant.

"I saw no impacts below that," Rucker said.

rstroud@jg-tc.com|348-5734.