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Surface Water Quality

Surface Water Quality Criteria and Standards

Water quality criteria are U.S. Environmental Protection Agency (EPA) recommended maximum concentrations for pollutants in ambient waters. The values are calculated, using primarily laboratory data, to protect most of the species most of the time, on a national basis. State agencies incorporate EPA’s water quality criteria or other state-approved site-specific criteria into legally enforceable water quality standards.

These state standards consist of designated uses for each specific body of water and maximum water quality concentrations for individual chemicals that will be protective of the uses specified. State standards also include a policy concerning anti-degradation, that is, whether standards can ever be revised so as to be less stringent. State agencies use water quality standards in establishing water quality-based permit limits, which are incorporated into permits issued under the National Pollutant Discharge Elimination System (NPDES). This process of setting water quality-based permit limits may be associated with development and allocation of a total maximum daily load (TMDL). The TMDL must be completed for a water body listed by the state as “impaired,” that is, not meeting water quality standards for one or more pollutants.

API’s Clean Water Issues Group addresses issues pertaining to federal water quality criteria and state standards. These issues include setting technically sound and achievable criteria for nutrients such as nitrogen and phosphorus, selenium, and other pollutants; determining whether mixing (dilution) zones should be allowed in calculating permit limits for pollutants that bioaccumulate; developing appropriate procedures for determining designated uses for individual water bodies and for determining whether those uses are in fact attainable; determining how to implement water quality criteria that are based not on pollutant concentrations in water but in fish tissue, etc.

Effluent Guidelines

Effluent guidelines are EPA limits on specific constituents in effluents from industries in a number of industrial categories, including Petroleum Refining and Oil and Gas Extraction. Effluent guidelines are based on the performance of treatment technologies available to the industry category. API, through the Clean Water Issues Group, addresses industry issues associated with effluent guidelines. For example, API participated in a recent regulatory investigation of the refinery effluent guidelines, to assess whether technical revisions were warranted. API provided detailed data demonstrating the refining industry’s exemplary record in addressing water quality concerns on a site-specific basis as they arise.

Total Maximum Daily Loads (TMDLs)

Total Maximum Daily Loads (TMDLs) are “budgets” setting the amounts of pollutants that waters can receive and be considered by EPA as safe for various designated uses, such as fishing, swimming, drinking, etc. The designated uses are established by the states as part of their process of setting water quality standards for waters that do not meet the use requirements.

The TMDL analysis should examine the chemical and biological condition of the water body, determine all of the inputs to the system, including both point and non-point sources, and ascertain the resilience of the system to those inputs. Based on the scientific data, the TMDL would then determine the maximum acceptable quantities of any chemicals or other materials that could limit the designated use. The total loadings thus determined are allocated among the inputs previously identified. Those allocations are then used in establishing limits for discharge permits.

The following are some of the publications resulting from the efforts of the Clean Water Issues Group:


The following API reports pertaining to surface water quality, effluent guidelines, NPDES permits, and other water issues:

  • Publication 4782 – Petroleum Refining Industry Contribution to Nationwide Surface Water Nutrient Loadings
  • Publication 4665 – Mixing Zone Modeling and Dilution Analysis for Water-Quality-Based NPDES Permit Limits
  • Publication 4656 – Bioaccumulation – How Chemicals Move from the Water into Fish and Other Aquatic Organisms
  • Publication 4701 – Bioaccumulation: An Evaluation of Federal and State Regulatory Initiatives
  • Publication 4694 – Laboratory Analysis of Petroleum Industry Wastewaters – Arranging for Analysis and Understanding Laboratory Reports
  • Publication 4695 – Understanding and Preparing Applications for Petroleum Facility NPDES Discharge Permits
  • Publication 4721 – Analytical Detection and Quantification Limits: A Survey of State and Federal Approaches
  • Publication 4736 – Identification of Key Assumptions and Models for the Development of Total Maximum Daily Loads
  • Publication 4756 – Interim Permitting Manual – Navigating NPDES Permit Issues on Impaired Waters
  • Publication 4783 – Water Management and Stewardship in Midstream, Downstream, and Delivery Operations in the Oil and Gas Industry
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