Perchlorate was detected in the Concord River in August 2004. Initially, it was believed that explosives used in road and building construction were the source of this pollutant. However, an investigation by the town of Billerica eventually determined that the source was a local company that produced surgical and medical materials. The company was using 220 gallons per month of perchloric acid in a bleaching process, and rinse water was being discharged into the sewage system. After the company was identified, it voluntarily shut down until ion exchange equipment could be installed in accordance with environmental guidelines.