Congress amended the Clean Water Act in 1996 to create section 312(n), captioned "Uniform National Discharge Standards (UNDS) for Vessels of the Armed Forces." Section 312(n) directs the EPA and DoD to establish national discharge standards for discharges incidental to the normal operation of a vessel of the Armed Forces in three phases of rulemaking. The discharges have the potential to impact the aquatic environment and/or human health. After the final phase is complete, these national standards will preempt State discharge standards for these vessels, though States may enforce the uniform national standards.

The EPA and DoD jointly promulgated Phase I of these regulations, 40 CFR part 1700, on May 10, 1999 (64 FR 25126)and concluded that 25 discharges from vessels of the Armed Forces would require discharge performance standards). Phase II of the rulemaking (joint EPA/DoD rule), is the development of the 25 discharge performance standards and is being done in three batches” of rulemaking. UNDS Phase II - Batch One performance standards were promulgated on January 11, 2017 (82 FR 3173). The UNDS Phase II - Batch Two was proposed on October 7, 2016 (81 FR 69753). The UNDS Phase II - Batch Two includes the following discharges:  catapult water brake tank & post-launch retraction exhaust; controllable pitch propeller hydraulic fluid; deck runoff; firemain systems; graywater; hull coating leachate; motor gasoline compensating discharge; sonar dome discharge; submarine bilgewater; surface vessel bilgewater/oil-water separator; and underwater ship husbandry. The EPA and DoD anticipate completing the UNDS Phase II Batch Two Final Rulemaking in the Fall of 2018.  The UNDS Phase II Batch Three will begin upon completion of Batch Two.