Advanced Environmental Interface

Review the diagrams in sequence to see the cleanup of the site of an old manufactured gas plant in Willimantic, CT.

1. Gas Holder 2. Tarry Soil 3. Controlling Odors
4. Cleaning Off Bedrock 5. Soil Disposal

1. Gas Holder:

From the late 1800's up until the 1940's (when natural gas pipelines came into much of Connecticut, gas for street lighting and heating was manufactured from coal. The gas was stored in cylindrical holders. At the bottoms of the holders there was an accumulation of tar from breaking down the coal. Sometimes the tar was sold for roofing or road work, but in many cases when the plants were demolished and the gas holders were removed, the tar was left behind -- in the foundation for the holder or in other deposits on the site. Those of course were times when the environmental consequences were not envisioned, and when that was a standard demolition practice. At this site, the tar was slowly migrating out of the holder foundation, and moving along the water table or bedrock surface to a nearby river.

2. Tarry Soil:

Demolition debris and soil had been plowed into the foundation of the gas holder, so that at about the 5-ft depth, stained soil was apparent. At the 10-ft depth, there were high concentrations of coal tar in the soil. Coal tar has several chemical constituents that are carcinogenic or that have other health implications. In addition, the odor is typically very strong. Like creosote, sun and heat make coal tar more chemically reactive. For all these reasons, excavation has to be done carefully, and workers protected.

3. Controlling Odors:

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Near the bottom of the excavation, which was on a bedrock ledge, the concentrations of coal tar in the soil were so heavy that any area not being actively worked was kept covered. This kept odors from migrating offsite, and cut down the exposure of workers in the excavation. If chemical exposures reached specific trigger levels, workers switched from respirators to self-contained breathing apparatus.

4. Cleaning Off Bedrock:

Coal tar is typically sticky and difficult to remove. The bedrock surfaces and the brick walls of the foundation of the holder were steam cleaned after all the contaminated soils was excavated.

5. Soil Disposal:

Contaminated soil excavated from the holders was held onsite in covered rolloffs, pending analysis results that determined the method of disposal. Most of the material went to asphalt plants. Many of the constituents in coal tar are also in asphalt.

See the slide show for a groundwater recovery system.