Environmental Threat
Site Characterization
Man. Gas Processes
Plant Wastes
Contamination Threat Modes
Residuals - Components
Sources of MGP Liquid Effluent
FMG Plants in the US
Parallel MG Technologies
Think you've found a gas works?
Locating and Confirming a Site
Locations of US Gas Plants
FMGP In The News
FMGP In The Arts
Coal-tar Site Litigation
Related sites on the Internet
Literature of Manufactured Gas
Hatheway Harangues
Publications by Dr. Hatheway
Slide Shows by Dr. Hatheway
Slide Shows by others
Hatheway Bio
Hatheway Resume
Legal Considerations


 Coal-tar Residuals and the Environmental Threat

Former manufactured gas plants typically operated 24 hours a day, 365 days a year. The solid and liquid residuals generated each day were a profound concern for the management of the works. The gas was only briefly stored, then distributed off the plant site. The residuals also had to be move along or they would constitute a space burden, an obstacle to movement around the gas yard, and the liquids would obstruct operations even more profoundly. Owners, operators and managers of gas works had a variety of available options before them. Some residuals could be utilized or sold as by-products and some residuals patently were valueless wastes.

Today we are very much concerned about the gas making residuals that were deemed to be unsalable wastes by the works management. These wastes had particular physical and chemical characteristics that made them just as dangerous at the time of thei r creation as they are today. The smallest portion of the wastes were leaked and spilled in and around the works; the larger portion of the wastes that are found around the gas works today were subject to informed choices of disposition at the time of their creation, by the owners, managers and operators of each gas works.

  Nature of Coal-tar Residuals

Photo of congealed tar

Typical residual coal-gas tar, after many years of weathering in
the environment. (photograph by A.W. Hatheway)

Former Manufactured Gas Plants (FMGPs) produced toxic floaters, mixers, and sinkers, characterizing the variable density of the dominantly liquid wastes. Among these toxics were aromatic hydrocarbons, including the tar-acid phenols and cresols; the monocyclical aromatic hydrocarbons (MAHs) more commonly known as the BTEX series (benzene, toluene, ethylbenzene and xylene); the duocyclical aromatic hydrocarbons (DAHs) represented mainly by the base-neutral naphthalene; the polycyclical aromatic hydrocarbons (PAHs) represented by the medium and heavy oils (the "tars"), as well as various forms of cyanogens, sulfur, and some heavy metals concentrated from the trace metals of the coal and some of the enrichment oils.

Most coal-tar wastes are chemically labeled as "non-aqueous" because they do not have the high degree of solubility in water that has traditionally concerned chemists, who are not notably concerned about groundwater pollution. Taken from the standpoint of environmental protection, many of the wastes lie in the ppm range of solubility in water and, hence are chemicals of concern (COC) from the environmental standpoint.

Industrial chemical production, worldwide, was based on coal-tar as a source, from about 1854 (with Perkin's discovery of coal-tar dyestuffs) to the demise of coal as a routine domestic and industrial energy source, in the face of local municipal smoke and smog control ordinances (beginning in 1950s) and air pollution restrictions (1970 Federal Air Pollution Control Act). Certainly there are other factors, such as the rise of natural gas pipelines after the 1928 discovery of high-grade pipeline welding, the rise of petroleum refining as a source of road tar (after about 1940), and the general demise of our domestic steel industry (post-1965).


Gas Works No. 2 - Hannibal, Missouri
A semi-quaint Mississippi River coal gas plant at 1911 at Hannibal,
Missouri. This plant was built as a new replacement of the 1860 coal gas plant constructed at another location in Hannibal. Shown is the By-products Building, beginning, at street side, with the Condensing House, the Exhauster Room and the Ammonia Still House. Below-grade purifier boxes lay to the immediate right of the By-products Building. (Photograph by A.W. Hatheway)


Photo of gas plant as red sandstone ruins

Red sandstone was used to construct the 1870s coal gas plant at Ripley, Michigan, preserving the typical high arched windows typical of 19th century gas plants. (Photograph by A.W. Hatheway)

  Why coal-tar sites may go undetected until site exploration

Geologists, geological, geotechnical, engineer and land survey crews are often in the key position to detect the presence of coal-tar residuals. The current standard of practice is that sufficient literature and records search work should be performed to detect the presence and layout of gas works over their operating lives.

Sanborn Map  

(Click on Image for an enlarged image of the Sanborn Map) America's most famous prominent maker of fire insurance maps, the Sanborn Company, here visited the Mississippi River industrial and shipping community of Burlington, Iowa, in 1892 to depict its coal gas plant, built in 1856 by the future father-in-law of John D. Rockefeller. (From the Library of Congress collection)

  Generic FMGP Wastes

Gas works wastes had to be managed literally on the day of their creation, burned as fuel, stored, recycled (as with some box wastes), treated (such as distilling for tar-oil fractions, ammonia or sulfur), dumped, transported and dumped, or discharged to the ground. Gas works management had to make a choice of waste management fate, as required by their circumstances, and the choice literally due on the day the wastes were created. Here follows a selection of actual gas works solid wastes typical of what will predictably be found at the dump or dumps of each former manufactured gas plant.

Generic FMGP Hazardous Substances


Origin in Manufacturing

 Present-Day Environmental Implication


Residuum of coal-gas coal charge

Was always of value and could either be used ingeneration of carburetted water gas, for boiler or bench furnace heating, or sold to residents or businesses. May have sorbed contamination under certain FMGP conditions


Coal-Gas generation

Generally dissipated over post-operational decades, but could emerge to endanger those involved in excavation or whom enter gaining leaks to sewers


Clinker formed in retorts or gas generators

Required retort chiseling to remove, or back-draft carbonization in carburetted water gas plants; should not be sorptive of PAH residuals


Refractive portion of retort or generator feedstock

Low sorptive capacity for PAHs; Generally dumped around the plant or in off-site dumps


Fused refractive portion of retort or generator feedstock

Low sorptive capacity for PAHs; Generally dumped around the plant or in off-site dumps


Washwater effluent from cleansing

All forms tend to have dropped PAHs in tar form in surface watershed or subsurface aquifer matrix; Emulsions typically have a long, un-degraded life

Ammoniacal From coal-gas manufacture
Gas Liquor From carburetted water gas


PAH residue as a whole

Any of such, when in the groundwater environment have the capacity to further contaminate bodies of ground water entering into contact with these gas-house wastes 

Liquor Water decanted by gravity from tar
Tar PAH residue as a whole
Tar Sludge PAHs containing ash
Tar-Water Emulsion Carburetted water-gas tars made with inferior non-coke feedstock and/or heavy oil enrichment


Carbon sequestered from oil feedstock

Most common in oil-gas processes; Very typical of Pacific Coast Oil Gas process; can occur with carburetted water gas and oil-enrich water gas. Formed without PAHs but acts to sorb such contamination afterward

Scrubber Packing

Generally wood chips

Scrubbers commonly were packed with wood chips as a sorption medium

Box Waste  

Media from purifying boxes, as removed and disposed of from standpoint of being “spent” and no longer capable of purification

Always considered environmentally dangerous from standpoint of sorbed PAHs, cyanide, sulfur as well as arsenic and other heavy metals

Spent Lime
Spent Chips
Spent Oxide
Compiled by A.W. Hatheway for ASFE Newsletter
Copyright 2020-25 by Dr. Allen W. Hatheway    All rights reserved.
Individuals and organizations (Governmental, Corporate, Public Interest, Publishing Authors and The Media) wishing to make use of the contents, either for scholarly research, publication of any form, hardcopy or electronic, news media copy, and for various commercial purposes, such as website offerings of services, are herewith cautioned to make appropriate quotes of www.hatheway.net as the source of such materials, including the date upon which such materials were transferred to the above-stated personal or corporate use and to so inform Dr. Hatheway, electronically, as a courtesy.  Professor Hatheway's offerings, constituting this website, are further subject to the Copyright & Legal Considerations appearing on the webpage by that name. For further information on Former Manufactured Gas Plants and related topics, please contact Dr. Hatheway at allen@hatheway.net