Mobility, Toxicity and Volume of Coal Tar at a Former Manufactured Gas Plant Site

Abstract

Prior to the widespread construction of interstate natural gas pipelines in the 1950s, gas manufactured from coal, petroleum or other hydrocarbon feedstock was produced for lighting and heating purposes by local utilities in cities and towns across the United States. By-products and wastes generated at these plants were commonly disposed of on site. Major wastes and by-products included tar and oil residues, spent oxides and ash materials. These materials can be a continuing source of pollutants threatening both groundwater and surface water bodies. Pollutants include a complex mixture of hundreds of volatile organic compounds (VOCs), polynuclear aromatic hydrocarbons (PAHs), heavy metals and cyanides. A former manufactured gas plant (MGP) is located in downtown Clayville, Georgia, on the south bank of the Indian River. Facility and geographic names have been changed to protect the privacy of the parties involved. By-products from the plant were estimated at 14,000 tons of coke and 22,000 gallons of tar in 1929. Disposal practices at smaller MGP sites typical of the subject facility included landfilling of purifier (oxide) wastes, tar sludge, ammonia recovery wastes, ashes, clinkers, coke wastes, building material wastes, etc. Based upon available data from the public record, and the history of this and other former MGP sites, the mobility, toxicity, and volume of free-phase coal tar in the subsurface has been estimated along with its associated environmental contamination. Results indicated that up to 300,000 gallons of free-phase liquid coal tar may remain in the subsurface soils and aquifer. The residual tar and other MGP contaminants have resulted in groundwater contamination exceeding the Georgia drinking water standards. Groundwater under the site is hydraulically connected with the adjacent major river with possible movement of contaminants into the local ecology.