"Everybody says dirt is dirt. Dirt is not dirt," Daub said, meaning that everything an excavator handles must be tested to determine the kind of dirt it is. Then there's the search for hazardous wastes, which must be taken to special landfills.

Daub said he knows most of the kinds of soil in the St. Louis area - because he's probably worked there at one time.

"There may be 500 kinds of soil in the area," he said. "So when a soil doesn't look right, I know something's wrong."

One of the most common contaminants in the St. Louis area is gasoline, said Richard D. Laughlin, president of Midwest Testing, of Bridgeton.

Laughlin's company analyzes soil mechanics, which Laughlin said tells "how the earth behaves under loads," such as buildings of various sizes and heights.