Interpreting TAR Patterns at Former Manufactured Gas Plants Check Access

At former manufactured gas plants (MGPs), both tars and oils are commonly found in soils. Tars are generally considered to have a density greater than water, therefore they can penetrate the water table as a dense nonaqueous-phase liquid; this makes tar releases capable of contaminating large aquifer volumes for long periods of time and difficult to remediate. MGP tar is often referred to as coal tar. Other manufacturing technologies did not use coal at all, or supplemented coal with other fuels. When petroleum was cracked and added to blue gas (generally made by spraying steam onto incandescent coke), it was referred to as carbureted water gas (CWG). The distinction between coal gas tar and CWG tar is important because CWG is more mobile in the environment, and it also comprises most of the tar in the ground at MGPs in the United States. In order to interpret tar patterns at former MGP sites several topics need to be addressed, namely: how tarry (viscous) MGP tar is; what the distances and timescales for tar motion are; how to interpret boring logs in terms of tar volume; and how to identify source locations at a site where tar has migrated.