Health & Safety

MGP Contaminants

The byproducts of MGP operations - coal tar, purifier waste and petroleum products used in the manufacturing process are typically the sources of contamination found around former MGP sites. The following is a description of the contaminants that can be found in these byproducts.

There are two major classes of chemical compounds found in coal tar:

  • Volatile organics, generally characterized by benzene, toluene, ethylbenzene and xylene, which are identified by their initials as the BTEX compounds. The BTEX compounds are widely associated with gasoline and are commonly encountered as contaminants surrounding leaking gasoline tanks or spills. Together, these compounds often represent only a small percentage of the mass of MGP tar. However, of all the contaminants found in coal tar, these are the most likely to dissolve in water and are thus the most likely to be dissolved in groundwater and move off-site. These are also the most volatile and thus the most likely to move through subsurface soils as vapors or soil gas.
  • Semi-volatile organic compounds, known as polycyclic aromatic hydrocarbons or PAHs, are present in many forms in the environment, most notably in asphalt and other petroleum products such as diesel fuel. Coal tar is still commonly used today as asphalt pavement sealer. While hundreds of PAH compounds have been identified in coal tar, the most important are the 16 listed below. These are recognized by the U.S. Environmental Protection Agency (EPA) as priority pollutants. They're the PAHs the most is known about and data concerning their presence are commonly used to evaluate levels of PAH contamination:
acenaphthylene anthracene
benzo(a)anthracene benzo(a)pyrene
benzo(b)fluoranthene benzo(g,h,i)perylene
benzo(k)fluoranthene dibenzo(a,h)anthracene.
chrysene fluoranthene
fluorene indeno(1,2,3-cd) pyrene
2-methylnaphthalene naphthalene
phenanthrene pyrene

Most PAH compounds do not readily dissolve in water, so they are not as easily transported in groundwater as are BTEX compounds. With the exception of naphthalene, most PAHs do not readily volatilize. Consequently, they are not as readily transported as soil gas. However, despite low solubility and volatility, PAHs may still migrate significant distances, because mobile tars or emulsions may move through the subsurface.

What Contaminants Are Typically Present in Purifier Waste?

Purifier waste often contains significant quantities of chemically complexed cyanide compounds. Some cyanide can leach from waste and contaminate groundwater, which can move through the subsurface away from the contaminant source area. Although some cyanide compounds are highly toxic, there is evidence that cyanide compounds typically leached from purifier waste are in a chemically complexed form which is significantly less toxic. The New York State Department of Environmental Conservation (NYSDEC) and the New York State Department of Health (NYSDOH) are continuing to collect data to evaluate this question.

In addition to containing complexed cyanide, water that comes into contact with purifier waste is often highly acidic. Concrete structures in contact with purifier waste may be corroded to some extent by the acid. If the acidic water discharges to a stream or other surface water body, it may cause harm to fish and wildlife.

Although purifier waste typically contains coal tar residue, this contamination is generally in a solid form, which does not migrate on its own or dissolve readily in water.