Water Protection Program fact sheet
Division of Environmental Quality Acting Director: Steve Feeler


This fact sheet outlines and clarifies how Missouri facilities might be affected by recent changes to Section 316(b) of the Clean Water Act, which requires National Pollutant Discharge Elimination System (NPDES) permits to ensure the location, design, construction and capacity of cooling water intake structures reflect the best technology available to minimize harmful environmental impacts associated with the use of these structures. Over half of all water withdrawn each year from waters of the United States is for cooling purposes. By far, the largest industrial use of cooling water is for thermoelectric generation.

Section 316(b) of the Clean Water Act accords the U.S. Environmental Protection Agency broad authority to protect waters of the U.S. from adverse environmental impacts associated with cooling water intake structures, including adverse effects to federally-listed threatened and endangered species and designated critical habitat. Section 7 of the Endangered Species Act (1973) requires federal agencies to consult with the U.S. Fish and Wildlife Service to ensure actions they fund, authorize, or carry out do not jeopardize the continued existence of a listed species and do not destroy or adversely modify designated critical habitat. A planning tool is availble online to find out which species or critical habitat under Fish and Wildlife Service jurisdiction may be present in your area.

The ruling in 2014 established best technology available standards to reduce impingement and entrainment of fish and shellfish at existing facilities that are designed to intake more than 2 million gallons per day (MGD) of water and use at least 25 percent of their intake exclusively for dissipating waste heat from industrial processes. The finalized requirements are included in the NPDES permit regulations, which can be found in 40 CFR 122 and 125 Subparts I, J and N. Because Missouri is not concerned with offshore facilities, and the number of new facilities will be minimal, this document discusses only Subpart J of Section 125 (§125.)

Nothing in this ruling authorizes the take of threatened or endangered species of fish or wildlife. Such take is prohibited under the ESA unless it is exempted pursuant to 16 U.S.C. 1536(o) or permitted according to 16 U.S.C. 1539(a). Once the Missouri Department of Natural Resources receives all applicable permit application materials, the department is required to transmit them to the appropriate Fish and Wildlife Service field office for a 60-day review to ensure listed species have been accurately identified as present and to review the measures proposed to reduce adverse environmental impacts.

Definitions and Acronyms

NPDES Permit Requirements and Information

Operators are required to submit basic information such as but not limited to: contact information, facility location and process details, and a list of all permits applied for or received. Most facilities are also required to provide source water data [§122.21(r)(2)], source water baseline biological data [§122.21(r)(4)], cooling water intake structure data [§122.21(r)(3)], cooling water system data [§122.21(r)(5)], and operational status [§122.21(r)(8)]. Specific information can be found in 40 CFR 122.21. In accordance with the 2014 ruling on Clean Water Act §316(b), operators must also submit additional information when applying for NPDES permits. This information is discussed in more detail below.

All Existing Facilities [§122.21(r)(1)(ii)(A)]
In addition to the information previously outlined, applicants for existing facilities must now also submit the following at the time of permit renewal:

The department will review all application materials, including any further materials required due to facility size or the construction of new units, and establish best technology available standards for entrainment for each intake on a site-specific basis. Once a final permit establishing entrainment requirements has been issued, the facility must comply with impingement mortality standards and entrainment standards as soon as practicable. The factors considered during this evaluation are described in the Entrainment Best Technology Available Standards section of this document. The department may establish interim compliance milestones for both standards in the permit.

Large-Scale Existing Facilities [§122.21(r)(1)(ii)(B)]
Along with the information required of all existing facilities, large-scale existing facilities (those with an actual intake flow of at least 125 MGD) must also submit:

New Units at Existing Facilities [§122.21(r)(1)(ii)(D) and (E)]
Applicants for existing facilities with new units must submit the information required of all existing facilities along with identification of the chosen method of compliance with impingement mortality standards for each new unit, along with an impingement technology performance optimization study if required [§122.21(r)(14)].

If the new unit increases the total design intake flow capacity of the existing facility to more than 2 MGD, the applicant must submit all information required of facilities of that size with their permit application. If the new unit increases the total capacity of the existing facility to more than 125 MGD actual intake flow, the applicant must also submit the information required of facilities of that size.

Operational Status Report [§122.21(r)(8)]

A description of the operational status of each process unit that uses cooling water must include:

In addition, power and steam generating units must include capacity utilization rate for the previous five years, describing any extended or unusual outages that might affect flow, impingement, entrainment, or other data, and identification of any operating unit that uses less than eight percent of its capacity when averaged over two years. Units not used for power or steam generation must submit seasonal operation data, including any extended or unusual outages that might affect flow, impingement, entrainment, or other data, and any plans or schedules for decommissioning or replacing any process units or lines.

Entrainment Performance Study [§122.21(r)(7)]

Any previously conducted studies or studies obtained from other facilities addressing technology efficacy, through-facility entrainment survival, and other aspects of entrainment must be submitted as part of the permit application, along with a description of each study, its underlying data, and a summary of conclusions and results. In the case of studies more than 10 years old or those obtained from other facilities, the application must include an explanation as to why the data is relevant.

Entrainment Characterization Study [§122.21(r)(9)]

Entrainment characterization studies must include at least two years of data, collected during typical operational conditions, representative of the entrainment at the cooling water intake structure. The conditions and frequency of data collection must be identified along with the methods for data collection and analysis. The data must include the following:

Comprehensive Technical Feasibility and Cost Evaluation Study [§122.21(r)(10)]

The comprehensive technical feasibility and cost evaluation study must be evaluated for each potential entrainment control technology, and can be broken into two portions. The department reserves the ability to require evaluations of entrainment control technologies not identified as candidates by the applicant.

Technical Feasibility
An evaluation of the technical feasibility of closed-cycle recirculating systems, a screen with a mesh size of 2 mm or less, and either water reuse or alternate cooling water sources must be submitted, along with the following:

Cost Evaluation
The cost evaluation includes engineering cost estimates of all entrainment control technologies considered, discussed separately as compliance and social costs, along with any supporting documentation.

Compliance costs include the costs of the permit application; any costs associated with construction and operation of each technology along with any facility modifications necessary to support such construction and operation; those associated with any additional construction or operation permits; and a discussion of the costs and explanation for all reasonable attempts to mitigate detrimental effects identified in the non-water quality environmental and other impacts study.

Social costs are those imposed on the economy as society reallocates resources away from other production activities to attempt to balance the value of the goods and services lost as a facility complies with permit requirements.

Benefits Valuation Study [§122.21(r)(11)]

This study evaluates the benefits of each potential entrainment control technology in one or more of three ways: a qualitative discussion of environmental effects, a quantified analysis expressed in physical or biological units, and a monetized benefits analysis in which dollar values are applied to the quantified analysis. When possible, benefits should be quantified and monetized. The benefits valuation study must include:

Non-Water Quality Environmental and Other Impacts Study [§122.21(r)(12)]

This study entails a detailed site-specific discussion of any changes in non-water quality environmental impacts and other impacts as attributed to each potential entrainment control technology. It must include the following:

Peer Review [§122.21(r)(13)]

Each study from sections 122.21(r)(10) through 122.21(r)(12) must be submitted to a peer for review. The review of the reports must also be submitted with the application materials.

Entrainment Best Technology Available Standards [§125.98(f)]

After reviewing all of the application information, the department must establish site-specific best technology available standards for entrainment controls that reflect the maximum reduction in entrainment after considering the factors below:

The weight given to each factor is to be determined by the department based upon each facility’s circumstances. However, it is the facility’s responsibility to propose each technology considered to the department.

Impingement Mortality Best Technology Available Standards [§125.94(c)]

Existing facilities in Missouri must comply with one of the six technologies listed below, indicating whether for the entire facility or for each cooling water intake structure, submitting the necessary information to demonstrate compliance. Additional requirements to protect shellfish and fragile species may be imposed as necessary.

Impingement Technology Performance Optimization Studies [§122.21(r)(6)(i) and (ii)]

If the chosen method for reducing impingement mortality is either the operation of modified traveling screens [§125.94(c)(5)] or the adoption of a system of technologies [§125.94(c)(6)], the applicant must also submit a study demonstrating that the compliance method has been optimized to best reduce impingement mortality. The use of modified traveling screens need only be supported by an impingement mortality study. For facilities employing a system of technologies, the performance optimization study must include an impingement mortality study, data on rate of impingement, flow reduction data, a total system performance evaluation, and must document how and to what extent each element of the system contributes to its overall performance. Impingement technology performance optimization studies must also describe the data collection approaches used.

Impingement Mortality Study
Impingement mortality studies must include, at minimum, the following:

Rate of Impingement
If impingement mortality is reduced in part by a decrease in impingement, the applicant must provide an estimate of how the rate of impingement is credited towards reduced impingement mortality along with any supporting documentation. The estimated rate of reductions must be based on a comparison to a once-through cooling system with a traveling screen having a withdrawal point at the shoreline of its source water body. Data must be collected, at a minimum, on a monthly basis for two years.

Flow Reduction
If impingement mortality is reduced in part by flow reductions, the applicant must document how this flow reduction results in impingement reductions, and in turn how reduced impingement results in reduced impingement mortality. This must be supported by two years of daily intake flow data and a description of the extent to which flow reductions are seasonal or intermittent.

Total System Performance
Facilities employing a system of technologies, operational measures, or management practices must document the percent impingement mortality reflection optimized operation and all supporting calculations. Total system performance is the combination of impingement mortality performance reflected by the impingement mortality study, rate of impingement data, and flow reduction data.

Monitoring and Reporting [§125.96 and §125.97]

Several of the impingement standards have specific monitoring requirements, whereas the monitoring requirements for entrainment will be determined on a site-specific basis. Inspections to ensure that any technologies required for compliance are being appropriately operated and maintained must be conducted weekly, either visually or via remote monitoring devices.  Additional monitoring may be required, especially where the department has determined that additional measures are necessary to protect federally-listed species.

As part of the monitoring requirements, the owner or operator of any existing facility must submit the following information to the department:

Reports including results of any required monitoring will be submitted yearly at a minimum, or otherwise according to the schedule established in the permit. Records of all report submissions must be retained until the subsequent permit is issued. All records supporting the department’s determination of best technology available for entrainment must be retained until the department revises the determination of best technology available for entrainment in the permit.

Alternative Requirements

Applicants have the ability to request alternative schedules or requirements where applicable. When the applicant requests an alternative or exemption, the burden lies with the applicant to demonstrate the need for the alternative or exemption. The department is authorized to request additional information as well as impose additional requirements or conditions as necessary.

Reduced Requirements

Alternative Schedules and Requirements


This flowchart provides a rough framework to help evaluate which requirements apply to the various types of facilities. This does not account for any exemptions or inclusions which may be required by the department.