Making MGP Wastes Beneficial
More than 11 billion gallons of coal tar were generated at MGP sites in the United States from 1816 to 1947. The types and quantities of waste discharged to surface waters from MGPs vary from site to site, and the disposition of several billion gallons is unknown and remains unaccounted for. Numerous locations in the United States have sediments and soils contaminated with wastes generated from former coal gasification operations. MGP wastes include polyaromatic hydrocarbons (PAHs), which are found in coal tar, a byproduct of gasification processes, and cyanide salts, which are found in iron oxide waste produced during purification of the manufactured gas. In addition to being a problematic soil and sediment contaminant, MGP solid waste frequently causes groundwater and surface water contamination with benzene, phenanthrene, anthracene, pyrene, and benzo(a)pyrene. These contaminants pose threats to human health to the extent that many MGP sites are listed on the Superfund National Priority List for cleanup and removal. The USEPA references a number of technologies acceptable for disposing of or treating MGP residues. In general, MGP waste is 1) stored on-site until a more suitable, permanent treatment option is developed, 2) moved to a hazardous material landfill, or 3) incinerated in a hazardous waste incinerator. However, each of these disposal or treatment options has at least one of the following significant drawbacks: high costs, low destruction capabilities, high emissions, and/or a residual waste (long-term liability) with questionable leaching characteristics that require disposal.