There are presently more than 3,000 dams in Massachu-setts. Many of these dams are no longer used for their original purpose, and some are in disrepair. Contaminants bound to sediment trapped behind dams have the potential to affect the downstream environment in the event of a sudden release or dam failure. These sediments may also be an ongoing source of contaminants to overlying water and to organisms living on or in bottom sediment. In addition, dams do not entirely retain impounded sediment and associated contaminants. Such sediments are subject to scour, resuspension, and downstream redistribution during storm events.