Aside from PCBs that are occasionally discovered during facility upgrade projects in small sealed or previously untested specialized equipment, most of the PCB and PCB-contaminated equipment left on our system is the result of cross-contamination occurring during manufacturing or maintenance activities prior to or shortly after the adoption of the Toxic Substances Control Act Legacy Manufactured Gas Plant Projects In the late1800s until the mid-1900s, gas was manufactured using coal, oil and petroleum.