EPA’s new water intake rule: what does it mean for power plants?

2 September 2014



The US Environmental Protection Agency finalised the long-anticipated Clean Water Act §316(b) rule for existing facilities on 19 May 2014. What does the rule require of power plants and what modifications are expected to be implemented as a result of the rule?
John A.D. Burnett and Thomas L. Englert, HDR, Inc, USA; Mark Gerath, ECT, Inc, USA


The new rule (http://water.epa.gov/lawsregs/lawsguidance/cwa/316b/upload/316b-prepub-preamble.pdf) applies to existing facilities that withdraw more than 2 million gallons per day (MGD) and use at least 25% for cooling purposes. The rule supersedes the Phase II rule, which regulated electrical generating facilities with large cooling flows until it was remanded in 2007, and the remanded existing-facility portion of the previously promulgated Phase III rule (see Figure 1 for a summary of the timeline).

EPA estimates that roughly 1065 existing facilities will be captured by the rule, including 544 power plants and 521 manufacturing facilities. The rule gives National Pollutant Discharge Elimination System (NPDES) permit directors (referred to as Directors in the following) significant authority, including the determination of Best Technology Available (BTA) for entrainment at each facility. This in turn conveys a large responsibility to facility owners who will be required to develop information that will be used by the Director to make a BTA determination for their facility.

Scope and requirements

Section 316(b) was enacted under the 1972 Clean Water Act, which also introduced the NPDES permit programme (see Figure 1). Facilities using cooling water with NPDES permits are subject to §316(b), which requires that the location, design, construction and capacity of cooling water intake structures reflect BTA for minimising adverse environmental impacts.

Cooling water intakes can cause adverse environmental impacts by drawing early life-stage fish and shellfish into cooling water systems, where the organisms may be harmed by heat, pressure, mechanical stress or chemicals used to clean the cooling system. This process is referred to as entrainment. Larger organisms may be harmed when they are trapped against screens at the opening of an intake structure. This process is referred to as impingement.

All facilities captured by the rule will be required to develop and submit technical material that will be used by the Director to make a BTA determination for the facility. The specific material required to be submitted is dependent on intake flow rates at the facility and the cooling system configuration, with a schedule that is based on permit renewal date. The rule also contains a new-to-§316(b) requirement that the Director subject all submitted material for review and comment by the National Marine Fisheries Service or US Fish and Wildlife Service (referred to as Services in the following).

As part of each facility's application for NPDES permit renewal, the rule requires submittal of as many as 12 reports, referred to as §122.21(r) permit application requirements, that are to be provided to the Director to support the evaluation of BTA at each facility. The Director retains significant best professional judgment (BPJ) authority, including the ability to add or waive submittal requirements under certain circumstances. Many submittal requirements require technically complex biological, engineering, and economic analyses, which need to be understood at the outset of the project. Refer to Table 1 for a summary of the 12 submittal requirements.

The actual intake flow (AIF) and design intake flow (DIF) at a facility determine what submittals will be required. As shown in Table 2, facilities with flow rates of 125 MGD and less will have fewer application submittal requirements and will generally be required to select from the impingement compliance options contained in the rule and provide a summary of potential entrainment impacts for the Director to review. Facilities with flows in excess of 125 MGD are required to address both impingement and entrainment and provide explicit entrainment studies which may involve extensive field studies. Facilities equipped with closed-cycle recirculating systems are not automatically exempt from these requirements.


The compliance schedule contained in the final rule is driven by NPDES permit renewal date with facilities falling into one of two categories depending on whether their NPDES permit renewal date is before or after 45 months after the effective date of the rule (assumed to be approximately March 2018 based on what is known today).

  • For NPDES permits expiring after approximately March 2018: facilities must submit to the Director the information required in all applicable provisions of §122.21(r) when applying for renewal of their permit (ie, 180 days prior to expiration).
  • For NPDES permits expiring before approximately March 2018: the facility may request the Director to establish an alternate schedule for submission of all applicable provisions of §122.21(r) when applying for a subsequent permit.

Importantly, any peer review, which is required for §122.21(r)(10)-(12), has to be completed within this same time frame. The compliance schedule also appropriately prioritises in time the evaluation of entrainment BTA followed by selecting from among the rule's impingement mortality control options (discussed in the next section). This order of priority is critical to achieving an efficient compliance process because entrainment controls will typically by nature also address impingement while impingement controls may not address entrainment.

The final rule gives existing facilities the following seven alternatives for meeting the BTA impingement standard:

  1. 1. Operate a closed-cycle recirculating system as defined by the rule (this includes cooling towers and certain impoundments).
  2. 2. Operate a cooling water intake structure that has a maximum design through-screen velocity of 0.5 feet per second (fps).
  3. 3. Operate a cooling water intake structure that has a maximum actual through-screen velocity of 0.5 fps.
  4. 4. Operate an existing offshore velocity cap that is a minimum of 800 feet offshore and has bar screens or otherwise excludes marine mammals, sea turtles, and other large aquatic organisms.
  5. 5. Operate a modified travelling screen system such as modified Ristroph screens with a fish handling and return system, dual flow screens with smooth mesh, or rotary screens with fish returns.
  6. 6. Operate any combination of technologies, management practices and operational measures that the Director determines is the BTA for reducing impingement. Or
  7. 7. Achieve a 12-month performance standard of no more than 24% mortality including latent mortality for all non-fragile species

Compliance options 1, 2 and 4 are essentially preapproved technologies requiring a minimal demonstration that the flow reduction and control measures are functioning as EPA envisions. Options 3, 5 and 6 require more detailed information to be submitted to the Director before they can be specified as the BTA to reduce impingement mortality. EPA expects that except for future technologies or innovations, few facilities will select the option 7 compliance alternative.

EPA has determined that there is no single technology that is BTA for entrainment at existing facilities. For existing facilities, the Director will establish BTA standards for entrainment for each intake on a site-specific basis. These standards will reflect the Director's determination of the maximum reduction in entrainment warranted after consideration of the following relevant factors:

  • Numbers and types of organisms entrained, including the numbers and species of Federally-listed, threatened and endangered species, and designated critical habitat (eg, prey base).
  • Impact of changes in particulate emissions or other pollutants associated with entrainment technologies.
  • Land availability inasmuch as it relates to the feasibility of entrainment technology.
  • Remaining useful plant life. And
  • Quantified and qualitative social benefits and costs of available entrainment technologies when such information on both benefits and costs is of sufficient rigor to make a decision.

Existing facilities with an actual intake flow of more than 125 MGD are required to submit information to characterise entrainment and assess the engineering feasibility, costs and benefits of installing various potential technological and operational controls (§ 122.21(r)(9)-(12)). Facilities must evaluate closed-cycle cooling, fine-mesh (<2.0 mm) screens, and reuse of water or alternate sources of cooling water in addition to any other technologies or operational measures requested by the Director. The rule requires that the § 122.21(r)(10)-(12) studies be subject to an external peer review.
For the Entrainment Characterisation Study required at §122.21(r)(9), facilities are to develop a study that includes a minimum of two years of entrainment data collection. Existing data may be used in lieu of collecting new data where it can be shown to be representative of current conditions.

Importantly, facilities with flows below the 125 MGD threshold are not automatically exempt from entrainment requirements. The Director may require entrainment studies or installation of entrainment controls at any cooling water intake structure.

As the rule was being finalised, EPA consulted with the Services under the Endangered Species Act. While the Services concluded that the rule is not likely to jeopardise the continued existence of listed species or result in the destruction or adverse modification of designated critical habitat, the rule includes a number of provisions that regulated facilities need to be aware of, including:

  • The final rule requires that facilities identify all Federally-listed threatened and endangered species and/or designated critical habitat that are or may be present "in the vicinity of impingement and entrainment at the cooling water intake structure." This extends to all listed species and not just fish and shellfish.
  • "The Director may establish in the permit additional control measures, monitoring requirements, and reporting requirements that are designed to minimise incidental take, reduce or remove more than minor detrimental effects to Federally-listed species and designated critical habitat, or avoid jeopardising Federally-listed species or destroying or adversely modifying designated critical habitat (eg, prey base)."
  • Measures or requirements established according to the preceding bullet may include those identified by Services' staff during established review and comment periods wherein the rule requires that the Director transmit all permit applications to the Services upon receipt and provide the Services 60 days to review the material.
  • The facility must comply with any such requirements included in the permit.

The rule contains a number of provisions (not detailed here) related to repowered units, capacity utilisation, planned retirements, facilities utilising impoundments, de minimis impingement and other factors that may allow a Director to waive certain submittal requirements. These concepts should be carefully evaluated by each facility that finds itself subject to complying with this rule.

Potential compliance technologies

There are tens of technology types and hundreds of technology and operational measure combinations that facilities can consider as cost-effective solutions for protecting fish at cooling water intakes. The following are summaries of some technologies expected to gain the most attention as facilities work to achieve compliance under the final rule requirements.

Modified travelling screens
If modified travelling screens (Photo 1) are selected for impingement compliance, the rule requires that a two year optimisation study be undertaken to maximise survival of impinged organisms. If this technology is paired with fine-mesh screens, the number of organisms entrained can be reduced. However, the excluded organisms become impinged on the screens and only those that survive impingement will actually contribute to the reduction in entrainment losses. Variants on the travelling screen that may also warrant consideration include dual flow screens that can reduce through-screen velocities, and drum screens, vacuum returns (eg, Beaudrey WIP Screen), and Geiger screens that can reduce debris carry over.

Wedgewire screens
Wedgewire screens (photo 2) are considered one of the more promising technologies available for reducing both impingement and entrainment. They have a "v" or wedge-shaped cross-section wire welded to a framing system that forms a slotted screen. The screen configuration needs to be developed with consideration of the specific life stages to be protected. Design features may include narrow slot sizes, through-slot velocities low enough to minimise potential impingement of life stages with underdeveloped swimming ability, and placement and orientation of the screen assembly that will result in sufficient "sweeping" velocities in the source water body (or through engineered velocities) to carry excluded organisms safely away from the screen. This technology would achieve impingement compliance by reducing through-slot velocities to 0.5 feet per second or less and potentially provide entrainment protection by using narrow slot wedgewire. Recent studies have indicated that in addition to physically excluding some entrainable size organisms, narrow slot sizes may increase screen avoidance by motile early life stages.

Barrier nets and aquatic filter barriers
Barrier nets are constructed of wide-mesh fabric panels and configured to completely surround the cooling water intake structure. Their mesh sizes typically are relatively large (3/8 inch) and they have had the most success in locations where seasonal migrations create high impingement levels. This technology would achieve impingement compliance by reducing through-net velocities to less than 0.5 feet per second, but would not generally protect against entrainment.
Aquatic filter barriers (Photo 3) are similar to barrier nets in that they completely surround the intake structure but have a smaller pore size (approximately 0.5 mm diameter or smaller) and thus prevent more organisms from entering the intake. A curtain formed by two layers of treated fabric is either suspended by flotation billets and anchored in place or integrated into existing shoreline intake structures. This technology could achieve impingement compliance by reducing through-fabric velocities to less than 0.5 feet per second and provide substantial entrainment reductions to the extent early life stages are excluded from entering the intake.

Closed-cycle cooling
Closed-cycle cooling (Photo 4) may have limited application as a full or partial retrofit depending on a facility's existing configuration, planned repowering projects and many other factors. Closed-cycle recirculation systems typically use 2-5% of the water used in a once-through system. The closed-cycle cooling option is recognised explicitly as an impingement compliance option by the proposed rule and the reduced intake flows would also reduce entrainment.

Operational measures
The list of potential operational measures to be considered for compliance is smaller than that for technologies. For example, if capacity factor reductions or unit mothballing results in through-screen velocities that are less than 0.5 feet per second, impingement compliance would be achieved and entrainment losses would be reduced. Variable speed drives, flow optimisation and targeted outages may also be considered to the extent they provide impingement and entrainment protections that will be recognized by permitting authorities.


The extent to which a particular technology or suite of technologies and operational measures may be appropriate for a facility will depend on the Director's objectives for entrainment reductions, as well as site-specific biological, economic, and engineering considerations. For some technologies, performance in terms of impingement and entrainment reductions can be largely driven by the fragility of specific species subject to withdrawal at the facility and the extent of debris loading and biofouling. Costs will also be driven by these site-specific factors, as well as the existing intake configuration, space availability and potentially many other factors.

Preparing for compliance

The new rule has important implications for owners and managers of impacted power plants and manufacturing facilities. It will determine what facility modifications will have to be made to intakes and operations in order to minimise losses of organisms. Available compliance strategies for impingement mortality will typically require either costly upgrades of travelling screens to include fish protection, or reducing of through-screen velocity to 0.5 feet per second or less. The latter could be achieved by expanding the intake or installing one of a number of screen or barrier options previously discussed; all of which can be very costly and in many cases not feasible. The approach owners and managers should take toward planning for compliance will depend on their individual permitting authority's approach as well as a variety of site-specific factors.

When listed species are present, we expect the Services to seek an active role in the review of the Directors' BTA decisions for both impingement and entrainment. Owners and managers should be developing compliance strategies that consider the economic and operational impact of the rule's alternatives. If the final rule is challenged, the process could take years. In the meantime, compliance with the rule would be required, including timely submission of reports, and implementation of studies and selected technologies to maintain compliance with NPDES permits.


John A.D. Burnett and Thomas L. Englert, HDR, Inc, USA; Mark Gerath, ECT, Inc, USA. This article first appeared in the June 2014 issue of Modern Power Systems

Figure 1. Timeline, how we got to the final rule Figure 1. Timeline, how we got to the final rule
Photo 1. Travelling screen Photo 1. Travelling screen
Photo 2. Wedgewire screen Photo 2. Wedgewire screen
Photo 3. Aquatic filter barrier Photo 3. Aquatic filter barrier
Photo 4. Closed-cycle cooling Photo 4. Closed-cycle cooling
Table 2 Table 2


Linkedin Linkedin   
Privacy Policy
We have updated our privacy policy. In the latest update it explains what cookies are and how we use them on our site. To learn more about cookies and their benefits, please view our privacy policy. Please be aware that parts of this site will not function correctly if you disable cookies. By continuing to use this site, you consent to our use of cookies in accordance with our privacy policy unless you have disabled them.