The Isles of Shoals North Disposal Site (IOSN) is located approximately 24.5 kilometers (km) (15 nautical miles) east of Portsmouth, New Hampshire, in the Gulf of Maine. The IOSN is circular in shape and approximately 2.5 km in diameter. Water depths at the site range from approximately 77 to 104 meters (252 to 341 feet) with a bottom topography that slopes gradually and increases in depth from the western boundary to the eastern boundary of the site.

Additional information about the monitoring and management of IOSN, including the current Site Management and Monitoring Plan (SMMP), can be found on the EPA Region 1 Ocean Dumping web page.