Who is Tom Barbas from A Civil Action and what is their importance?

Tom Barbas has worked in the paint shop at Grace Chemical and testifies that he, as well as many others, used TCE on a regular basis, accumulating a gallon or two of waste everyday. As late as the 1970's, he was told by supervisors to dump the waste in a gully near the back door of the plant. The testimony of Barbas, as well as other Grace employees, is key in the initial verdict against Grace.