NPL sites are sites that are initially discovered by local and State agencies, businesses, EPA, the U.S. Coast Guard, and the public. If the risk to human health is significant enough, based on the number and toxicity of substances discovered at the site and its ability to affect surrounding populations, then the site is placed on NPL. NPL is a published list of the most hazardous waste sites in the country that are eligible for extensive, long-term cleanup under the Superfund program. The list of NPL sites used to monitor improvement was “frozen” in the baseline year. Additional sites may be added to the database during the decade, but will not be included in monitoring progress for this objective. Progress will be measured by the number of sites on the baseline year list that are “delisted”; delisting indicates a successful cleanup and reduction of health risk.