After construction is completed, the site is monitored to make sure no waste is leaking into the air, soil, surface water, or groundwater. The site (or parts of the site) are deleted from the National Priorities List once the state and the EPA determine that the site poses no significant environmental or health risk. As of May 2009, 332 sites have been deleted from the NPL. Superfund is a unique program because it makes polluters responsible for paying part of the cleanup cost. Superfund starts by identifying polluters, called Potentially Responsible Parties (PRP)