Feb. 16--It's a dirty job, but somebody has to do it.

Work was completed Friday on a project to remove contaminants from the soil at the site of an old manufactured gas plant on Creston's south side.

Interstate Power and Light Company (IPL), an Alliant Energy Company, conducted the environmental cleanup after previous investigations by Alliant and Black and Veatch Corporation showed contamination in the area, which is just north of the Bill Sears Memorial Complex near the intersection of Union and South Cherry streets.

History

The contamination stemmed from a manufactured gas plant that operated on the land between 1907 and 1946. Gas from the plant, also known as town gas, was used for lighting, cooking and heating, but was replaced by natural gas when interstate pipelines came to the Midwest.

When the plant shutdown, it left significant amounts of byproduct, like tar, in the soil and in underground storage structures on the land now owned by IPL.

"When they shut the plant down, whatever was there, was there," said Dean Hargens, IPL senior environmental engineer. "Back in those days, they didn't keep track of those sorts of things as good as we do."

Although the contaminants posed no immediate threat to people or wildlife, there were concerns over leaving the soil in that state.

Excavation was done to prevent long-term exposure as the tar and contaminants continued to leach out of the structures and into the soil, potentially into ground water, said Gordon Abell, Black and Veatch project engineer.

Preparations for the project began last October with the demolition of an on-site building and pouring of a concrete pad.

DCI Environmental Incorporated assembled a thermal desorption system and began excavation work in November.

"We had done previous investigations to see the extent of the contamination in the soil and ground water," said Abell. "We based our excavation on those investigations."

According to Hargens, this meant excavating the entire property.

Process

The excavation process is really quite simple.

Workers dug and tested until they reached noncontaminated soil, at times up to 22 feet, and then piled the dirt near the desorption system. It is then sifted to separate large and small pieces; large pieces are crushed.

Once everything is an appropriate size, the material can be treated through thermal desorption.

This two-step process starts with the dirt being heated to vaporize the contaminants. Then the vapors are burned in a high temperature furnace to create clean air.