Stockholm Hopes Microbes Will Gobble Goo, Speed Cleanup at Old Gasworks Site

Engineers will let billions of hungry microbes loose on tar-like waste left by an old gasworks in hope of quickly cleaning up the mess in three years, rather than the 1,000 years nature would need if left to itself.

The goo is on a site called Blekholmstorget, in the shadow of the gold-tipped brick tower of Stockholm City Hall, where an apartment and office center is planned.

Biotreatment of Cardiff, Wales, developed the use of microbes to break down ground pollution, and the technique has been used in Britain and West Germany. This is the first use in a major cleanup that does not involve hauling away the contaminated soil.

Chief engineer Hans Kronberg said the goal is to purge potentially cancer-causing grit from about 1.2 acres on the bank of Lake Klara, a channel in Stockholm’s interlocking chain of lakes. Dozens of pleasure boats now dock there.

A gas and coke factory was built on the site in 1852 and operated for about 70 years. Most recently, the site was a parking lot for the nearby central railway station.

Kronberg said it took scientists nine months to identify specific microbes that attack the pollutants involved. Bacteria were taken from the site and fed oxygen and nutrients to help them multiply.

When the project begins in May, the plan is to filter microbe-enriched water through the soil, which is soaked with creosote, breaking down the tar-like waste.

Grids of pipes spaced a few yards apart cover the site. Enriched water will seep from one set of pipes and be collected by another 10 feet below. The water will be pumped to a container for analysis, treated with nutrients and recycled into the pipes.

“As of this moment, we can’t say if it will work or not,” City Inspector Viveka Ehd-Falander said. “We have never done this in Sweden before.”

Stockholm officials and federal environmental authorities see the biological cleanup as a pilot project for opening hundreds of polluted acres in the city to development.

Kronberg, who works for the Skanska construction company, said the creosote at Blekholmstorget was not a problem while it was buried under the parking lot asphalt, but would become a threat under a major housing development.

Engineers fear the creosote would release harmful gases and construction work would allow some of it to seep into the lake water.

Authorities are withholding some building permits until the area is safe. Kronberg said the cleanup project adds about $6 million to construction costs.

“If we didn’t clean it up, the pollution would still be there in 100 or 200 years when they rebuild this area again,” the engineer said.

Land reclamation normally involves excavating polluted earth and taking it to a safe dump. About 26,000 cubic yards of contaminated soil would have to be removed from Blekholmstorget, enough to bury a football field nearly 10 feet deep.

“There are a lot of places in Stockholm where we’d like to build,” Ehd-Falander said. “This is not the only place with dirty soil. It’s hard to dig everything up. We don’t have places to put it.”