About 30,000 tons of soil will be removed by the time Ameren Missouri crews finish the work.

A manufactured gas plant operated at the site from 1875 to 1932, leaving behind tars that can contain carcinogenic compounds.

Warren Mueller, the utility’s manager of environmental assessments, says the soil remaining at the site is the most contaminated. He says crews are working to remove an underground gas tank and the soil surrounding it.

The Columbia Daily Tribune reports (http://bit.ly/1hchHmm) Mueller said the extreme winter weather delayed the work, which is now expected to be completed by September.