From 1816 to 1950 it is estimated that between 1,100 to 1,500 manufactured gas plants existed in the United States. These plants produced approximately 15 trillion cubic feet of gas resulting in the production of 11 billion gallons of by-product tars (Eng, 1985). These plant sites have largely been forgotten due to the passage of time and many are still unlocated. Due to the large number former gas plants sites and the amount of waste they represent, these plants sites are one of the largest generic sources of wastes in the United States (Eng, 1985).