Understanding 316(b)

The proposed EPA rule applies to power plants that withdraw at least 2 million gallons a day of cooling water and use at least 25 percent of that water for cooling. Roughly 670 power plants may meet this threshold. Here’s what it could mean.

By John A.D. Burnett and Thomas L. Englert, Ph.D., P.E., HDR, Inc.

Owners and operators of electric power generating stations have waited more than four years to see the U.S. Environmental Protection Agency’s (EPA’s) revised version of the Clean Water Act §316(b) Phase II rule for cooling water intake structures at existing power plants. The revised rule will determine what modifications power plant owners will have to make to their intakes and operations to minimize losses of organisms. In April 2011, EPA published a draft revision of the rule and is committed via a settlement agreement with environmental groups to issue a final version by July 27, 2012. EPA is currently reviewing public comments on the draft.

A Brief History

Section 316(b) is an offshoot of the 1972 Clean Water Act, which introduced the National Pollutant Discharge Elimination System (NPDES) permit program. NPDES regulates point sources of pollution, including power plants with thermal and other point-source discharges. Most states have permit programs approved by EPA. These states issue State Pollutant Discharge Elimination System (SPDES) permits that include state and federal requirements. Facilities with NPDES or SPDES permits are subject to §316(b) which requires that the location, design, construction and capacity of cooling water intake structures reflect the best technology available for minimizing 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 might 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.

Section 316(b) was enacted into law in 1972 (Figure 1). In 1976, EPA published §316(b) regulations, which were successfully challenged by a group of utilities. In 1979, EPA formally withdrew the regulations and states adopted their own cooling water intake regulations, varying widely in scope and rigor. In the mid-1990s, a coalition of environmental groups filed suit against EPA over failure to re-enact §316(b) regulations. In October 1995, the U.S. District Court Southern District of New York entered a Consent Decree between the parties, directing EPA to take final action. EPA then developed §316(b) regulations in three “phases.”

Issued in December 2001, the Phase I rule covers new facilities and mandates the use of closed-cycle cooling. The Phase II rule, issued in July 2004, covered existing electric generating plants that withdraw at least 50 million gallons of cooling water a day. This rule included waterbody-based performance standards for reducing organism loss due to entrainment and impingement relative to a baseline intake and flow condition. The Phase III rule, issued in June 2006, covers other existing facilities and new offshore and coastal oil and gas extraction facilities that have design intake flow thresholds of greater than 2 million gallons a day. Implementation of this rule was broadly based on a case-by-case, best professional judgment approach.

In January 2007, the Phase II rule and the portion of the Phase III rule dealing with existing facilities, were remanded to EPA for reconsideration as a result of legal proceedings. The proposed §316(b) rule for existing facilities issued in April 2011 and the subject of this article is EPA’s response to the remand and combines Phase II and the existing facility portion of Phase III into one rule. The proposed rule also removes the restoration-based compliance alternative from the Phase I rule.

Provisions for Existing Facilities

The proposed rule, which was published in the Federal Register on April 20, applies to existing power plants and industrial and manufacturing facilities that withdraw at least 2 million gallons per day of cooling water and use at least 25 percent of that water exclusively for cooling purposes. EPA estimates that roughly 1,260 facilities meet this threshold, 670 of them power plants.

Under the revised rule, plants would be subject to an upper limit on the percentage of impinged fish. This approach differs from the performance standards approach contained in the suspended Phase II Rule, which required 80 to 95 percent reductions in impingement mortality relative to a baseline condition. As a result, under the proposed rule there is no need to establish a baseline against which impingement reductions can be measured. Facilities would also have an alternative means of meeting the requirement to reduce impingement mortality that would require they reduce through-screen velocity to 0.5 feet per second or less, allowing most fish to safely swim away from the screens and thus avoid impingement.

If the first option is chosen, the facility operator must monitor for impingement mortality and demonstrate that the annual average mortality is 12 percent or less and the maximum monthly average is 31 percent or less. If the second option is chosen, the facility must verify that through-screen velocities meet the rule requirements.

With respect to entrainment, the proposed rule requires that the permitting authority maximize entrainment protections. Facilities that withdraw large amounts of water, at least 125 million gallons a day, are to conduct studies to help their permitting authority determine what site-specific controls, if any, would be required to reduce entrainment mortality.

The Rights and Wrongs

As currently written, the proposed rule gets some things right, but other aspects are unrealistic or impracticable. What does it get right? It does not mandate closed-cycle cooling retrofits at all facilities. In a recent Power Engineering blog by Associate Editor Brian Wheeler — “EPRI discusses possible implications of 316(b),” — Doug Dixon, a technical executive with the Electric Power Research Institute, said that if there were a national requirement for closed-cycle cooling, the cost to the nation to build the towers would be approximately $100 billion. The proposed rule also appropriately allows site-specific considerations when determining appropriate entrainment protections at each facility.

What does the proposed rule get wrong? It has an inflexible impingement compliance approach that disallows cost-effective fish protection at many facilities. For example, it gives no credit to facilities that have already installed alternate protections systems that may actually be more effective than those credited by the proposed rule. It also lumps small-withdrawal facilities (flows from two to 50 million gallons per day) in with larger withdrawal facilities, meaning that in some cases, facilities operating with closed-cycle cooling are regulated in the same manner as those using once-through cooling.

Available Compliance Technologies

There are typically tens of technology types and hundreds of technology combinations facilities can consider as cost-effective solutions for protecting fish. However, as a result of their review of candidate technologies, EPA proposed only two approaches to minimize impingement mortality: modified traveling screens equipped with fish buckets, a low-pressure wash and a fish return system, or reducing through-screen velocity to less than 0.5 feet per second.

Based on this limited purview, we summarize some technologies that are expected to gain the most attention should the rule be finalized as written.

If modified traveling screens (photo 1) are selected for compliance, the proposed rule requires that the annual average and monthly maximum mortality of impinged fish be no more than 12 and 31 percent, respectively. If this technology is paired with fine-mesh screens, entrainment protection may also be achieved. Variants on the traveling screen that may also warrant consideration include dual-flow screens that can reduce through-screen velocities, and drum screens and Geiger screens that can reduce screen carry over.

Photo 1. A modified traveling screen. All photos courtesy HDR.

Fixed panel screens (Photo 2) with sufficient screen surface area to achieve a through-screen velocity of less than 0.5 feet per second can be used to satisfy the reduced intake velocity requirement. Retrofitting fixed panel screens at most facilities involves significant modifications to the cooling water intake. Fixed screens with smaller mesh sizes may also be used to reduce entrainment.

Photo 2. A fixed panel screen used during a dewatered intake project.

Wedgewire screens (Photo 3) 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 slot size needs to be small enough to block passage of the smallest life stage to be protected. The through-slot velocity needs to be low enough to minimize potential impingement of weak swimmers, yet sufficient “sweeping” speed must be present in the source water body to carry excluded organisms safely away from the screen. This technology would achieve impingement compliance by reducing through-slot velocities to less than 0.5 feet per second and potentially provide entrainment protection by using narrow slot wedgewire.

Photo 3. A wedgewire screen system used during a screen installation project.

Barrier nets (Photo 4) are constructed of wide-mesh fabric panels and configured to completely surround the cooling water intake structure. Their mesh sizes are typically relatively large (3/8 inch) and they have had the most success in locations where seasonal migrations create high impingement events. 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.

Photo 4. A barrier net system.

Aquatic filter barriers such as the Gunderboom Marine Life Exclusion System (Photo 5) are water-permeable barriers that reduce both impingement and entrainment by completely surrounding the intake structure and preventing organisms from entering. 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 would achieve impingement compliance by reducing through-fabric velocities to less than 0.5 feet a second and provide substantial entrainment reductions to the extent early life stages are excluded from entering the intake.


Photo 5. The Gunderboom Marine Life Exclusion System.

Closed-cycle cooling (Photo 6) may have limited application as a full or partial retrofit depending on the existing configuration, repowering projects, and many other factors. These are closed-cycle, recirculation systems, which typically use 2 to 5 percent of the water used in a once-through system. The closed-cycle cooling option is not recognized explicitly by the proposed rule; however, if 0.5 feet per second through-screen velocities are achieved as a result of the reduced water use, impingement compliance would be assured and the reduced intake flows would also reduce entrainment.

Photo 6. Closed-cycle cooling.

Operational Measures

The list of potential operational measures to be considered for compliance is smaller than that for technologies but also worthy of mention. 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 optimization and targeted outages may also be considered to the extent they provide impingement and entrainment protections that will be recognized by permitting authorities. Operational measures may become more important as EPA refines the proposed rule before finalizing it.

The extent to which a particular technology or suite of technologies and operational measures may be appropriate for a facility will depend on the permit director’s objectives for entrainment reductions as well as site-specific biological and engineering considerations. For some technologies, performance in terms of impingement and entrainment reductions can be largely driven by the robustness or fragility of specific species subject to withdrawal at the facility and the extent of debris loading and biofouling. Costs will be driven by these same site-specific factors, as well as the existing intake configuration, space availability and potentially many other factors. Other technologies and combinations of technologies and operational measures may be worthy of consideration depending on how the final rule differs from what EPA has proposed.

Preparing for Compliance

When the final rule goes into effect (scheduled for no later than July 27, 2012) technologies to meet impingement requirements would need to be implemented as soon as possible but within eight years; that is, no later than 2020. Existing electrical generation facilities with a design intake flow of 50 million gallons per day or more would be on an expedited compliance schedule, presumably because EPA believes these former Phase II facilities already performed certain related studies based on requirements in the 2004 version of the rule. Of particular interest to these facilities is the large number of application requirements due within six months of rule promulgation. All other facilities, including electrical generation facilities that withdraw between 2 and 50 million gallons per day, have a more lenient schedule of three years. Also important is the requirement that all existing facilities with actual intake flows of 125MGD and greater perform additional entrainment studies.

The proposed rule has important implications for power plant owners and managers. Available compliance strategies for impingement mortality require either costly upgrades of traveling screens to include fish protection, or reducing through-screen velocity to less than 0.5 feet per second. The latter could be achieved by expanding the intake or installing one of a number of screen or barrier options discussed above, all of which can be very costly and in many cases not feasible. The approach plant owners should take toward planning for compliance will depend to a large extent on their individual permitting authority’s approach, given that entrainment requirements are based on the permit director’s best professional judgment.

If they haven’t done so already, facility owners should be talking with their permitting authorities and developing compliance strategies, considering the economic and operational impact of the alternatives. They should keep in mind that even if the final rule is challenged by lawsuits from utility and environmental groups, the process could take years. In the meantime, they will have to comply with the rule’s requirements, including timely submission of required reports, and implementing studies and selected technologies to maintain compliance with their NPDES and SPDES permits.

Authors: John Burnett and Dr. Thomas Englert are the §316 Practice Leaders for HDR Inc.

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