"Prior to that I testified before the Senate subcommittee addressing mountaintop removal"

In this quote, Kevin Richardson is specifying that he had actually formerly offered testament in front of a Senate subcommittee concerning the issue of mountaintop elimination. This means that he had spoken to a group of senators about the practice of getting rid of the tops of mountains in order to extract resources such as coal. By utilizing the word "prior," Richardson is suggesting that this statement took place before a specific occasion or time. This quote suggests that Richardson has knowledge and experience in this topic and has actively participated in advocating for or versus mountaintop elimination.