Section 316(b) of the Clean Water Act requires NPDES permits to ensure that the location, design, construction, and capacity of cooling water intake structures reflect the best technology available to minimize adverse environmental impact. Such impacts include death or injury to aquatic organisms by impingement (being pinned against screens or other parts of a cooling water intake structure) or entrainment (being drawn into cooling water systems and subjected to thermal, physical or chemical stresses). EPA divided this rulemaking into three phases. Phase I for new facilities was published in December 2001. Phase II, for existing electric generating plants that use at least 50 MGD of cooling water, was published in July 2004. Phase III addresses other existing facilities, as well as new offshore and coastal oil and gas extraction facilities that are designed to withdraw at least two MGD. Any facility not covered by these national categorical rules will continue to be subject to 316(b) requirements set by the NPDES Permitting Director on a case-by-case, best professional judgment basis.