Coal Tar – Yesterday’s Nuisance, Today’s Problem
OTO’s work includes a lot of remediation projects.in Massachusetts and Connecticut. One of the things we run into on occasion is coal tar, a viscous, black, smelly product of our industrial heritage. Coal tar is not one of the more common challenges encountered at MCP sites in Massachusetts, with gasoline, fuel oil, chlorinated VOCs and metals all coming up more often. It is, however, a complex and challenging mixture of contaminants. Thanks in part to the unfortunate experience with the Worcester Regional Transit Authority’s redevelopment project on Quinsigamond Avenue in Worcester, or the recent proposal to cap tar-contaminated sediments in the Connecticut River in Springfield, coal tar is back in the news after a period of relative obscurity.

Coal tar is a challenge for three main reasons.

First, it can be a widespread problem. Most coal tar encountered in the environment is a legacy of the coal gasification plants that supplied Massachusetts’s cities and towns with heating and lighting gas before natural gas became available via pipeline in the 1950s. Virtually any city or substantial town before 1900 had a gasworks, and some towns had several. Gasworks were often historically built on the ‘wrong side of the tracks’ due to their historically noisome character—their smell and constant racket beggared description. Where such “city gas” plants were not available, mill or factory complexes like the Otis Mills Company in Ware often had their own private gas plants, some of which also sold surplus gas to local residents for gas lights and stoves, and in some cases essentially became the town’s gas company.

As byproducts of making gas out of coal, these plants produced coal tar, cyanide-laden spent purification media, and much else of a dangerous nature. Some coal tar could be refined into waterproofing pitch, paving materials, industrial solvents, and even the red, foul-tasting carbolic soap that nobody who has ever seen “A Christmas Story” will ever forget. Massachusetts was also home to several plants that reprocessed tar into these plants, some of which later became all too well known, like the Baird & McGuire site in Holbrook, MA or the Barrett plant in Everett and Chelsea.

In addition to historically releasing wastes to the environment at the gasworks, gas companies also historically created off-plant dumps for their wastes, creating hazardous waste sites that might be located miles from the gasworks, or even in a different town.
EPA historically kept a sharp eye out for coal gasification plants, and during the 1980s listed over a dozen coal tar sites in Massachusetts on CERCLIS. Many of the sites that most alarmed MassDEP in the ‘80s were also related to MGPs—for example, Costa’s Dump in Lowell or the former Commercial Point gasworks in Boston. In recent years, however, regulatory attention has taken on an increasingly narrow focus towards other concerns, most notably vapor intrusion from chlorinated VOCs.

The second important consideration about coal tar is that it is pretty dangerous stuff, and poses both cancer and noncancer risks. Coal tar is typically a heterogeneous mixture of something like 10,000 distinct identifiable compounds, ranging from low molecular weight, highly volatile compounds like benzene and styrene to massive “2-methyl chickenwire” asphaltene compounds. From an environmental and toxicological perspective, coal tar is most conspicuous for its high concentrations of polycyclic aromatic hydrocarbons (PAHs), as much as 10% PAHs by weight, which make it significantly more toxic than petroleum. Two of the coal tar’s signature PAHs are benzo [a] pyrene and naphthalene; some coal tar can be up to 3% naphthalene alone, which accounts for the distinct, penetrating ‘mothball’ odor at MGP remediation sites.

Coal tar was associated with occupational diseases ranging from skin lesions to scrotal cancer even during the mid-19th Century, and was the first substance to be conclusively shown to be a carcinogen (by the Japanese scientist Katsusaburo Yamagiwa in 1915). The British scientist E.L. Kennaway subsequently proved that benzo [a] pyrene was itself a carcinogen in 1933, the first individual compound to be so categorized. Coal tar also contains concentrations of lesser-known PAHs, some of which may have significantly greater carcinogenic potential than benzo [a] pyrene. Coal tar is also a powerful irritant; remediation workers and others exposed to it can expect hazards including painful irritation of the skin, and respiratory or vapor intrusion hazards including high levels of benzene and coal tar pitch volatiles.

The third consideration is that coal tar is very persistent in the environment; tars and other gasworks wastes are highly resistant to geochemical weathering (and also to many remediation technologies, such as in-situ chemical oxidation), and do not break down in the environment like gasoline and most fuel oils do, so that tar contamination can still create problems over a century after the material was released.

So, coal tar is still with us, and will be for a long time. On the bright side though, with effort and careful planning, these challenges can be overcome. Many of the “wrong side of the tracks” locations of former gasworks are now prime downtown real estate, and a number of Massachusetts gasworks have been redeveloped as shopping plazas, transportation hubs, and biotech research facilities. As land prices, urban real estate availability, and government incentives continue to drive brownfield redevelopment, hopefully most of the Commonwealth’s former gasworks will see a new life.