See the latest EHS federal and state regulatory updates due to COVID-19

On May 19, 2014, the U.S. Environmental Protection Agency (EPA) released a final rule regulating cooling water intake structures at existing facilities under Section 316(b) of the Clean Water Act (CWA). As noted in the sidebar, the release of the final rule brings an end to a long history of legal proceedings and EPA setbacks which date back to 2004.

EQ Summer 2014_CWIS sidebarThere are three main components to the final rule:

  1. Existing facilities that withdraw at least 25 percent of their water from an adjacent waterbody exclusively for cooling purposes and have a design intake flow of greater than 2 million gallons per day (MGD) are required to reduce fish impingement
  2. Existing facilities that withdraw at least 125 million gallons per day are required to conduct studies to help their permitting authority determine whether and what site-specific controls, if any, would be required to reduce the number of aquatic organisms entrained by cooling water systems
  3. New units that add electrical generation capacity at an existing facility are required to add technology that achieves one of two alternatives under the national Best Technology Available (BTA) standards for entrainment for new units at existing facilities

The Rule regulates existing facilities and new units at existing facilities that withdraw cooling water from “waters of the United States” and have, or require, a National Pollutant Discharge Elimination System (NPDES) permit, issued under section 402 of the CWA.


CWIS Rule Requirements

Section 316(b) of the CWA requires that the location, design, construction, and capacity of CWIS reflect the best technology available (BTA) for minimizing adverse environmental impacts. Under the regulation, the term “cooling water intake structure” means the total physical structure and any associated waterways used to withdraw cooling water from “waters of the United States.”


For purposes of the final Rule, adverse environmental impacts include, but are not limited to, impingement and entrainment at CWIS, including adverse effects to federally-listed species (species listed as threatened or endangered under the ESA), designated critical habitats, and changes in flow regime, caused by the withdrawal of water.

Impingement is defined as the entrapment of any life stages of fish and shellfish on the outer part of an intake structure or against a screening device during periods of intake water withdrawal. Entrapment is defined as the condition where impingeable fish and shellfish lack the means to escape the cooling water intake. Entrainment is defined as any life stages of fish and shellfish in the intake water flow entering and passing through a cooling water intake structure and into a cooling water system, including the condenser or heat exchanger.

EQ Summer 2014_CWIS photo

BTA Standards for Impingement Mortality

Pursuant to 40 CFR 125.94(c), EPA requires owners or operators to comply with one of following BTA Standards for Impingement Mortality:

  1. Closed-cycle recirculating system and daily monitoring of actual intake flows
  2. Demonstrated ≤ 0.5 ft/sec through-screen design velocity
  3. Demonstrated ≤ 0.5 ft/sec through-screen actual velocity and daily monitoring of velocity
  4. Existing offshore velocity cap and daily monitoring of intake flow
  5. Modified traveling screens, optimized to minimize impingement mortality
  6. BTA** systems of technology, management practices, and operational measures
  7. 12-month impingement mortality performance standard and monthly monitoring (# fish killed/# fish impinged < 24 percent)

BTA Standards for Entrainment
Demonstrating to the permitting authority that they will operate and maintain technologies for the intake flow serving the new unit that demonstrate entrainment reductions equivalent to at least 90 percent of the reduction that could be achieved through compliance with intake flow commensurate with a closed-cycle system (i.e., 125.92(c)(1)). Reducing design intake flow for the new unit, at a minimum, to a level commensurate with that which can be attained by the use of a closed-cycle recirculating system for the same level of cooling for the new unit. The CWIS Rule requires the permitting authority to establish requirements that reflect the BTA standards for entrainment for each CWIS on a site-specific basis that must reflect the maximum reduction in entrainment warranted by section 125.98 of the Rule. The owner or operator of an existing facility must comply with BTA standards for entrainment, as determined by the permitting authority.

The owner or operator of a new unit at an existing facility must achieve the impingement mortality and entrainment standards by the following:

Exceptions are described in the Rule, and the permitting authority may establish alternative requirements or additional BTA standards for entrainment on a site-specific basis.


EPA has established monitoring requirements for some of the BTA Standards for Impingement Mortality. The owner or operator complying with the 12-month impingement mortality performance standard may request the permitting authority to reduce monitoring requirements after the first full permit term in which these monitoring requirements are implemented, if the facility’s CWIS does not directly or indirectly affect federally-listed species or designated critical habitat. To do so, the results of the monitoring to date must demonstrate that the owner or operator of the facility has consistently operated the intake as designed and is meeting the impingement mortality standard. In addition, the permitting authority will determine entrainment monitoring requirements on a site-specific basis, as appropriate, to achieve the maximum reduction in entrainment warranted.

The permitting authority may require additional monitoring for a variety of reasons as specified in section 125.96 of the Rule, including additional monitoring for federally-listed species. Where the permitting authority requires additional monitoring for federally-listed species or critical habitat, the owner/operator must implement such monitoring.


Reporting requirements include Monitoring Reports (Discharge Monitoring Reports or equivalent state reports) and results of all monitoring, demonstrations, and other information required by the permit sufficient to determine compliance with the permit conditions and requirements established under section 125.94(g), such as:

  • Status reports required by the permitting authority
  • Signed annual certification statement and report (indicating substantial modifications, if any)
  • Additional supplemental permit reporting, as determined by the permitting authority
  • Additional reporting required by the permitting authority regarding federally-listed species or critical habitat

In addition, the permitting authority may require supplemental recordkeeping, such as compliance and other monitoring or supplemental data collection required in the permit.

Incidental Take of Listed Species

The Rule does not authorize “take” of endangered or threatened species. EPA defines impingement as entrapment, and entrainment as entering or passing through a CWIS and into the cooling water system. The USFWS and the NMFS have interpreted these as examples of “trap,” “capture,” and “harass,” and have determined that any impingement or entrainment of federally-listed species constitutes take.

As cited in the Rule, incidental take of endangered species (and threatened species, as applicable, under 16 U.S.C. 1533(d)) is prohibited under the ESA, unless it is permitted or exempted by the USFWS or the NMFS. Absent such exemption or permit, any facility operating under the authority of the CWIS Rule must not take federally threatened or endangered species.

Permit Application

The content requirements for the CWIS permit application have been outlined by EPA under 40 CFR 122.21(r). Table 1 summarizes the requirements.

The permit issued by the permitting authority may include requirements for the protection of federally-listed species and designated critical habitat, including additional control measures, monitoring requirements, and reporting requirements that are designed to minimize incidental take, reduce or remove more than minor detrimental effects to federally-listed species and designated critical habitat, or avoid jeopardizing federally-listed species or destroying or adversely modifying designated critical habitat.

EPA requires the permitting authority to include the following language as a permit condition: “Nothing in this permit authorizes take for the purposes of a facility’s compliance with the Endangered Species Act.”

EQ Summer 2014_CWIS Table


As with every other newly promulgated rule, the CWIS presents new challenges for affected facilities that will require careful planning and selection of the optimum demonstration methods and technologies.

It will be interesting to see how public participation related to entrainment studies for site-specific controls is considered during permitting actions. It will also be interesting to monitor developments and interpretations on the reach of cooling water intake structures, instances of incidental take and resulting compliance costs.

Affected facilities may undertake the following actions to assure compliance with the rule requirements:

  • Evaluate and determine regulatory requirements based on type of system and intake volume
  • Select techniques and methods to comply with the applicable impingement and entrainment standards
  • Assess potential impacts on critical habitats or endangered/threatened species and plan accordingly
  • Evaluate impact of the rule on future expansion projects and plan for early compliance
For assistance with evaluating CWIS applicability and preparing for compliance, please contact Jose Orsini at (407) 982-2891 or