Section 316(b) Rules for Cooling Water Intake Structures

Section 316(b) of the federal Clean Water Act (33 U.S.C. section 1326) requires that the location, design, construction, and capacity of cooling water intake structures for facilities having National Pollutant Discharge Elimination System (NPDES) permits reflect the best technology available for minimizing adverse environmental impact. Three separate rulemaking efforts have been undertaken by U.S. EPA in order to implement this section of the Clean Water Act, and are defined as:

  • Phase I Rules - for new facilities
  • Phase II Rules - for existing facilities
  • Phase III Rules - for new off-shore oil and gas extraction facilities

Any industrial facility with an NPDES permit that withdraws cooling water from a surface water intake structure or purchases cooling water from a third-party supplier that utilizes a surface water intake structure may be subject to this rule.

Requirements for implementation of these rules are detailed in Part 40 of the Code of Federal Regulations (CFR), Chapter 125, Subparts I and J, and Chapter 122.21(r). Implementation of these rules may require considerable data collection, taking place over a period of a year or more. In addition, certain compliance alternatives will necessitate engineering studies, economic analyses, and/or development of a number of operational plans and monitoring plans.

It is recommended that NPDES permit holders determine the compliance requirements for their permitted facility(ies) and contact the Division of Surface Water as soon as possible to develop a plan to achieve compliance. Click on one of the three choices above for additional information and resources. Facilities with cooling water intake structures which are not classified specifically under Phase I, Phase II, or Phase III regulations will be evaluated for Section 316(b) compliance using best professional judgment (BPJ).

This document contains general guidelines addressing confidentiality of information submitted to Ohio EPA.


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Phase I Rules - for new facilities

U.S. EPA promulgated Phase I final rules for new facilities with cooling water intake structures on December 18, 2001, and these rules became effective on January 17, 2002. (Minor amendments of the Phase I rule have been promulgated and became effective on July 21, 2003.) New facilities, those commencing construction after the effective date of the rules (January 17, 2002), are subject to Phase I rules if:

  • the facility requires an NPDES permit;
  • the facility has a cooling water intake structure with a design capacity greater than or equal to two (2) million gallons per day (MGD); and
  • the facility uses at least 25 percent of the water withdrawn for cooling purposes.

Q&A Document [PDF 12K]What constitutes a "new facility" under the Phase I rules? Are facilities which have been constructed during 2002 subject to Phase I rules? Ohio EPA has included responses to these questions in the question and answer document.

A copy of the Phase I rules and guidance materials is available on U.S. EPA's website at:

Phase II Rules - for existing facilities (as defined in 40 CFR 125.92(k))

On August 14, 2014, regulations developed by the U.S. Environmental Protection Agency (U.S. EPA) to implement Section 316(b) were promulgated in the Federal Register for existing facilities. These rules became effective on October 14, 2014, and require NPDES permit renewal applications submitted on or after this date to include information demonstrating compliance with the new rules. NPDES permits that were renewed prior to this date and expire on or after July 18, 2018 must submit documentation to demonstrate compliance with the next NPDES permit renewal application.

Phase II Guidance Document
Ohio EPA has developed this guidance document for implementation of the Phase II rules. Although not intended as a substitute for the actual rules, it is designed to facilitate understanding of rule requirements, and permittees are encouraged to use the outline structure of the guidance document when compiling the necessary data.

Facilities subject to Phase II rules
***Please note that this document is in the process of being updated in accordance with the finalized rules.*** This document lists existing facilities located in Ohio, and provides the NPDES permit expiration date and the applicability to the Phase II rules.

A copy of the Phase II rules and guidance materials is available on U.S. EPA's website at:

For more information contact:

Cole Miller
(614) 782-3846


Chris Monroe
(614) 644-2007

Phase III Rules - for all other existing facilities not subject to Phase II rules

The final Phase III rules were published in the Federal Register on June 16, 2004. The Phase III rules apply to new off-shore oil and gas extraction facilities with a design intake threshold of greater than 2 million gallons per day (MGD) and that withdraw at least 25 percent of the water exclusively for cooling purposes.

A copy of the final Phase III rules and related information is available on U.S. EPA's website at: