The Millers Point Gasworks operated on parts of the Barangaroo site from 1841 and produced the gas which lit the first gas lamps outside Europe. It was decommissioned in 1921. The gasworks was a coal fired gas manufacturing plant that contained a range of structures during its operation including tar tanks, gasholders, gasholder annuli, coal stores and other manufacturing buildings. Waste products generated from the gas manufacturing process were stored in a variety of in-ground structures such as tanks, created in the sandstone bedrock, or in above-ground structures such as purifier beds. In addition, handling of waste materials was uncontrolled and may have been re-used as fill materials. When the gasworks ceased operation, above ground structures were demolished but waste products were either left within the in-ground structures or were used as fill materials in an uncontrolled manner.
More information is available on the NSW Environment Protection Authority (EPA) website.