Oily ballast water from tankers is treated at the Valdez Marine Terminal's Ballast Water Treatment Facility (BWTF). The treatment reduces the oil concentrations to a few parts per million before the water is discharged into Port Valdez. Two effluent discharge permits are issued to Alyeska Pipeline Service Co. that allow treated tanker ballast water to be discharged into the port. These permits must be renewed every five years. The National Pollution Discharge Elimination System permit (NPDES) is issued by the Environmental Protection Agency (EPA), and the Mixing Zone permit is issued by Alaska Dept. of Environmental Conservation (ADEC). For more information on NPDES permitting concerning ballast water, see the Environmental Protection Agency's web pages regarding ballast water.