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Negotiating Higher NPDES Permit Limits Strategies for Optimizing Technology and Water Quality-based Effluent Limit Calculations for Petroleum Refining

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The Clean Water Act is generally considered to be one of the most successful environmental statutes in terms of measurable progress towards pollutant reduction goals. This success is largely due to the National Pollutant Discharge Elimination System (NPDES) program, which regulates the control of pollutant discharges from point sources to waters of the United States. The NPDES program relies upon a system of permits comprised of effluent limitations and monitoring, record keeping, and reporting requirements. Through the self-monitoring program non-compliance is reported to regulatory agencies and made available to the public.

NPDES permit holders are required to submit a permit renewal application at least once every five years. At that time the effluent limitations are reviewed and revised as necessary to meet current regulatory requirements and water quality management objectives, as well as reflect changes to facility operations and discharges. The Clean Water Act is a strict liability statute, meaning that permit holders are held liable for violations even if there was neither negligence nor any intent to violate. Not only can violations result in criminal and civil penalties, but citizens can also sue the NPDES authority or permit holders in the event of ongoing noncompliance. Therefore, it is imperative that the primary objective of any NPDES permit renewal be to obtain effluent limitations that are achievable. The “anti-backsliding” provisions of the Clean Water Act do not allow limits to be increased in future permit renewals; therefore, a permit holder has only one opportunity to claim the effluent limit allocations that are available based upon the information provided in the application at the time of permit renewal.

Facility compliance can be improved by planning for permit renewal and using strategic approaches when developing the permit renewal application. Given an understanding of the methodology, data, and assumptions used in development of effluent limitations, the application can be developed to provide the most favorable presentation of data and facilitate development of the highest possible limits allowed under the regulation. This paper provides an overview of strategic approaches that can be employed to optimize effluent limitations for petroleum refineries.

Effluent Limitations

Effluent limitations must be developed in accordance with the requirements of Title 40 of the Code of Federal Regulations (40 CFR)Part 122.44. The permit writer must provide a regulatory and technical basis for all permit conditions and limitations. This permit rationale is published in a Fact Sheet that is made available for public review and comment as part of the permitting process. Limits may be either technology-based effluent limitations (TBELs) or water qualitybased effluent limitations (WQBELs).

Technology-based Effluent Limitations

Technology-based effluent limitations are established in accordance with federal regulations for minimum treatment standards. Treatment standards are established for industrial discharges as effluent limitation guidelines (ELGs) by the industrial sector. The effluent guidelines establish levels of treatment technology based on industry-specific consideration of the pollutants of concern, treatability, and economic factors. Limits are related to some measure of operation, such as production or effluent flow. The Petroleum Refining ELG, found at 40 CFR Part 419, was initially promulgated in 1974 and was subject to considerable litigation before final promulgation in 1985. Most ELG directly calculate limits very simply as the product of an effluent limitation factor times a measure of operation: the petroleum refining guidelines for process wastewater were based on complex models that related flow to production for five subcategories of processes. Effluent limit allocations are determined for specific processes according to the following formula:

Effluent limit = effluent limitation factor x size factor x process factor x refinery feedstock rate

The size factor is based on the refinery feedstock rate, which is defined as the largest of any of the crude process feedstock rates. The process factor is based on process configuration. Process configuration is calculated for each subcategory by multiplying the ratio of process feedstock rate relative to refinery feedstock rate times a weighting factor. The total refinery process configuration is the sum of the process configuration values for each subcategory. Process wastewater effluent limitations are the sum of the allocations for each subcategory. Final effluent limitations also include allocations for ballast water and contaminated stormwater that are developed by multiplying wastestream flow rate by effluent limitation factors.

Water Quality-based Effluent Limitations

In addition to authorizing discharges under the NPDES program, the Clean Water Act requires the regulatory authority to conduct certain water quality management activities, such as establishment of water quality standards, water quality assessment, reports to congress on the status of the nation’s waters, and establishment of Total Maximum Daily Loads (TMDLs) for pollutants that are impairing the use of waterbodies. These water quality management programs affect permits through the inclusion of WQBELs where the TBELs are not adequate to protect water quality and support attainment of standards. Discharges to water quality-limited receiving waters may require limitations for pollutants that are not regulated by the ELG or that are more stringent than the TBELS and may not be attainable using any known treatment technology.

The regulatory agency is required to establish that there is reasonable potential for the discharge to cause or contribute to a violation of state water quality standards in order to impose the more stringent WQBELs. EPA has published technical guidance for the reasonable potential analysis and development of water quality-based effluent limits; however, states are free to develop their own approaches.

The WQBELs are developed from wasteload allocations that are designed to support attainment of state water quality standards in-stream. On impaired streams where a TMDL is required, the development of a Wasteload Allocation (WLA) may involve a complex model with multiple point or nonpoint sources of pollutants. Where there is no TMDL, the wasteload allocation is developed by solving a simple, complete mix, conservative mass balance model for effluent concentration, given that the in-stream waste concentration cannot exceed the most restrictive
applicable numeric water quality criteria (see Figure 1).

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