Emissions, Policy & Regulation, Policy & Regulations

316(b): A New Technical and Implementation Challenge for Power Plants

Issue 10 and Volume 118.

By Douglas A. Dixon and David E. Bailey, Electric Power Research Institute

Editor’s note: This is the first of a two-part series on the U.S. Environmental Protection Agency’s 316(b) rule, which will affect more than 500 power plants in the U.S.

Section 316(b) of the Federal Water Pollution Control Act (aka Clean Water Act; hereafter the Act) of 1972 states:

Any standard established pursuant to section 301 or section 306 of this Act and applicable to a point source shall require that the location, design, construction, and capacity of cooling water intake structures reflect the best technology available for minimizing adverse environmental impact.

Section 316(b) of the Act contains five lines of text, 43 words, and 252 characters yet it has figuratively yielded separate institutional libraries for related legal documents and research results since the Act was passed in 1973! These “libraries” are still a valuable resource because while provisions of the regulation offer flexible compliance options for industry, many permit applicants will be challenged – technically, financially, and by schedule – as they strive to complete the required biological, engineering and economic studies to indentify Best Technology Available (BTA) options for both impingement and entrainment control. Those challenges will continue once BTA is determined and those technologies must be installed, properly operated and monitored. Part I of this article briefly reviews the Rule and the implementation challenges permit applicants will have to meet. Part II of this article will discuss the Technical Challenges.

Clean Water Act §316(b) Rule for Existing Facilities

On Aug. 15, 2014 the U.S. Environmental Protection Agency (EPA) issued its final regulation implementing this section of the Act for existing plants with cooling water intake structures (CWIS). The regulation is effective on October 14, 2014. Plants in scope of the rule include those that are capable of withdrawing more than 2 million gallons of water per day (MGD) design intake flow (DIF) from water’s of the U.S., have or require a National Pollution Control Discharge Elimination System (NPDES) permit, and of which 25 percent or more is used for cooling. The EPA rule affects over 500 existing power plants and an additional 500+ industrial facilities (e.g., iron and steel, pulp and paper, chemical manufacturing) that have CWIS. The regulation is intended to reduce the adverse environmental impact to fish and shellfish that is considered in the rule to be caused by CWIS impingement (entrapment of organisms on intake screens) and entrainment (passage of early life stages of organisms through intake screens into the cooling system). .

EPA Compliance Standards

All facilities withdrawing > 2 MGD DIF are in scope for both impingement and entrainment compliance control; however, only facilities withdrawing >125 MGD actual intake flow (AIF) are required to complete entrainment studies to determine entrainment BTA. Entrainment study requirements and BTA determination for facilities withdrawing ≤ 125 MGD AIF are subject to the discretion of Permit Directors [herein called “Directors”]. Facilities required to do the entrainment studies will determine entrainment BTA compliance first, after which and as soon as practical, the impingement compliance will be determined. This provision is a major change from the proposed Rule of 2011 and eliminates the possibility that an installed technology for impingement BTA would have to be abandoned or replaced because entrainment studies required a different control technology.

Species Protected – for entrainment compliance, all life stages (egg, larvae, and juvenile) of fish and shellfish, subject to Director’s discretion, are in-scope for protection. It does not include members of the infraclass Cirripedia in the subphylum Crustacea (barnacles), green mussels (Perna viridis), or zebra mussels (Dreissena polymorpha). The Director may determine that “all life stages of fish and shellfish” do not include other specified nuisance species. Shellfish includes shrimp, lobster, horseshoe and blue crab, and the motil larval stages of mollusks (clams, oysters, mussels, squid and octopus). For impingement compliance, EPA has developed a list of 14 fragile species that can be excluded (e.g., gizzard shad, bay anchovy, alewife, menhaden), subject to Director’s approval, from impingement protection. These species were identified based on their survival of less than 30 percent when collected on traveling water screens. Additional species may be identified as fragile by demonstrating survival rates of less than 30 percent on a site-specific basis. Non-fragile species of fish (survival > 30 percent) must be protected as well as shellfish, marine mammals and sea turtles. There are special provisions for the protection of threatened and endangered (T&E) species as discussed below.

Side-by-side testing of different screens was funded by EPRI and performed at Alden Research Laboratory in Worcester, Mass. Photo Courtesy: EPRI
Side-by-side testing of different screens was funded by EPRI and performed at Alden Research Laboratory in Worcester, Mass. Photo Courtesy: EPRI

Entrainment Mortality – Facilities using >2 MGD DIF are also subject to reducing entrainment mortality, however, only facilities withdrawing >125 MGD AIF must submit a Entrainment Characterization Study, a Comprehensive Technical Feasibility and Cost Evaluation Study (to evaluate entrainment reduction technologies), a Benefit Valuation Studay, and a Non-water Quality and Other Environmental Impacts Study. The technology evaluation must include a assessment of the feasibility of a closed-cycle re-circulating system (CCRS), fine mesh/narrow slot screens, and the use of “grey,” reclaimed, and process water. Compliance is determined by the permitting authority on a “case-by-case” basis using best professional judgment (BPJ) (see below for mandatory and optional factors Directors must consider). The determination could range from the existing cooling water intake structure (CWIS) being deemed BTA to a requirement to retrofit with a CCRS.

Impingement Mortality – facilities using > 2 MGD DIF have seven options to achieve BTA for impingement mortality reduction:

  • Option 1 – operate a CCRS
  • Option 2 – demonstrate the maximum design through-screen velocity does not to exceed 0.5 feet per second (fps) during minimum source water levels and periods of maximum head loss across the screens
  • Option 3 – demonstrate through daily monitoring that the actual through-screen velocity is ≤0.5 fps under all ambient conditions, including during minimum source water levels and periods of maximum head loss across the screens (Permit Director may issue waivers for brief periods during unusual conditions)
  • Option 4 – have an existing (minimum 800 feet offshore) velocity cap with exclusion bars for marine mammals and sea turtles
  • Option 5 – install modified traveling water screens with a fish return and optimize performance for non-fragile species in a two-year biological study
  • Option 6 – install an integrated system of technologies, practices, and operational measures that are optimized for non-fragile species in a two-year study and demonstrate biological performance is comparable to that required in the following Option 7, and
  • Option 7 – demonstrate that impingement mortality is reduced to no more than 24 percent annually based on a minimum of monthly latent mortality monitoring.

Entrapment (meaning the condition where impingeable fish and shellfish lack the means to escape the cooling water intake – complete definition at §125.92(j)) – the EPA dropped the 2011 proposed Rule requirement for special protection of entrapped fish; however, a facility that entraps fish must count the entrapped fish as impingement mortality (i.e., during optimization studies for Compliance Options 5 and 6 and as part of monthly monitoring of fish and shellfish survival to determine annual survival in Compliance Option 7.) Furthermore, when entrapment of shellfish is a concern, Directors may establish additional requirements, such as the seasonal deployment of barrier nets.

Waivers/Exemptions/Special Requirements – in addition to the impingement compliance options, compliance requirements can be waived or modified by the Permit Director if the applicant can demonstrate (1) impingement is de minimis, (2) if the capacity utilization rate is less than 8 percent averaged over a 24-month contiguous period, and (3) if the intake is located on a manmade lake or reservoir and the fishery is managed (but does not include any Federal T&E species or their critical habitat). Relative to the latter waiver for fishery managed water bodies, only the “r” studies (i.e., permit application study requirements – see below) can be waived; however, applicants are still required to comply with the Rule. This latter waiver also applies to the required “r” studies for entrainment.

There is also a special exemption for nuclear facilities. If compliance with the Rule conflicts with a safety requirement established by the Nuclear Regulatory Commission, the Department of Energy or the Naval Nuclear Propulsion Program, the Permit Director must make a site-specific BTA determination that would not result in a conflict with safety requirements.

New Units at Existing Facilities – these units would need to comply with the compliance standards in the EPA New Facility Rule which was issued in 2001. This requires them to employ use of CCRS or a technology that is equivalent to closed-cycle cooling (achieves an entrainment reduction within 90 percent of that achieved by a CCRS).

A cooling water intake structure at Alabama Power's Plant Barry. EPRI is testing and optimizing the Hydrolox molded polymer screen at this plant.
A cooling water intake structure at Alabama Power’s Plant Barry. EPRI is testing and optimizing the Hydrolox molded polymer screen at this plant.
Photo Courtesy: EPRI

Threatened & Endangered (T&E) Species Protection

The EPA delayed release of the final Rule for nearly a year until the U.S. Fish and Wildlife Service (FWS) and the National Marine Fisheries Service (NMFS) completed their consultation and Biological Opinion (FWS/NMFS 2014). The Services initially concluded, after review of the proposed regulation, the draft final regulation, EPA’s biological evaluation, and other available information, that the proposed action would likely adversely affect T&E species and designated critical habitat. EPA, therefore, modified the final Rule to include special information requirements and requirements for the Director to insure their protection and address the Services concern. As a result of the changes, the Services modified their determination to one of “no jeopardy” for the EPA regulation action. As part of the Source Water Baseline Biological Characterization Study, applicants must now provide information on all T&E species potentially affected by impingement and entrainment, existing incidental take permits and any information used to obtain the permit(s). Directors are also required to submit all permit application material to the FWS (and NMFS if anadromous species are involved) who then have 60 days to provide recommendations to insure T&E species protection. Permit Directors may also require 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 (e.g., spawning and nursery areas or prey base).

Ovivo Inc. contributed a fine-mesh traveling band screen to EPRI for testing at Alden Lab. Photo courtesy: EPRI
Ovivo Inc. contributed a fine-mesh traveling band screen to EPRI for testing at Alden Lab. Photo courtesy: EPRI

Information Requirements

The rule contains extensive information submittal requirements outlined within §122.21(r)(2) through (12) (see table for details).


EPA dropped the requirement for a peer review of the Entrainment Characterization Study Plan as the EPA believed it would be reviewed when review of the latter (§122.21(r)(10-12) documents is conducted. However, applicants should consider conducting a peer-review of their entrainment data collection plan as a prudent risk-management practice. Negative review(s) of the latter three studies, particularly if it is found that they are all based on a problematic entrainment characterization study, could set applicants compliance planning back multiple years at significant costs. State Permit director requirements

The EPA Rule also provides considerable flexibility or discretionary authority to Permit Directors. Directors may add EPA-designated fragile species to the non-fragile list and they can similarly include species not explicitly designated by EPA as fragile species. They can require additional protection for shellfish and interim measures for impingement and entrainment control until a final BTA is installed. The ultimate decision on entrainment BTA will be based on the Director’s BPJ. In accomplishing this, the Director has a number of mandatory factors (§125.98(f)(2)) that must be considered, including:

  1. Number and species of organisms entrained, including federally listed T&E species and designated critical habitat
  2. Impact of changes in particulate emissions or other pollutants associated with entrainment technologies
  3. Land availability as it relates to technology feasibility
  4. Remaining useful life of facility, and
  5. Quantified and qualitative social benefits and costs of available technologies when such information is sufficient to make a decision.

The following factors are optional for consideration and also weighted at the discretion of the Director (§125.98(f)(3)):

1. Entrainment impacts on the waterbody
2. Thermal discharge impacts
3. Credit for reductions in flow associated with retirement of units occurring within 10 preceding years
4. Impacts on reliability of energy in immediate area
5. Impacts on water consumption, and
6. Availability of process water, grey water, waste water, reclaimed water, or other waters of appropriate quality and quantity for reuse as cooling water.
Bilfinger Technologies contributed its fine-mesh rotary multi-disk pilot screen to EPRI for testing at the Alden Lab. Photo courtesy: EPRI
Bilfinger Technologies contributed its fine-mesh rotary multi-disk pilot screen to EPRI for testing at the Alden Lab. Photo courtesy: EPRI

Monitoring requirements

As part of the permit application, the following is required:

  • All facilities will have to describe the fish and shellfish community and critical habitat of T&E species in the area of the plant’s intake via existing data or by sampling
  • Facilities withdrawing >125 MGD AIF will have to conduct a two-year entrainment characterization study, and
  • Facilities that install modified traveling water screens or an integrated system of technologies will have to conduct a two-year impingement technology performance optimization study.

During permit compliance, the following monitoring will be required:

  • Entrainment mortality verification monitoring will be determined on a case-by-case basis depending on the compliance method
  • Facilities that use a CCRS or existing velocity cap for impingement mortality reduction must monitor intake flows and CCRS blowdown daily. Those using an actual velocity not to exceed 0.5 fps must monitor intake velocity daily
  • Facilities that optimize their modified traveling water screens and fish return systems or integrated system of technologies will have to monitor the parameter values that may result from the optimization study based on conditions included in the final permit, and
  • Facilities that select the impingement mortality criteria compliance option will have to collect non-fragile fish and shellfish on a monthly basis and hold them in tanks for 18 to 96 hours to assess latent impingement mortality.


Facilities with permits expiring after 45 months from the effective date of the Rule (60 days from publication in the Federal Register) will start the process in accordance with regular permit renewal (application information is due 180 days before the permit expires). Plants with permits expired or expiring within 45 months of the effective date of the Rule can set a schedule for compliance activities with their Permit Director. There is no fixed date by which entrainment or impingement mortality reduction technologies must be installed but for both, the Rule states it should be “as soon as practicable.” The existing NPDES permit remains in effect until a new one is issues, as long as the renewal process and deadlines are followed.


Douglas A. Dixon is a Technical Executive and Program Manager of EPRI’s Fish Protection Research.

David E. Bailey is a Senior Technical Leader managing EPRI’s closed cycle cooling retrofit research and 316(b) compliance support.

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