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Federal Register / Vol. 86, No. 52 / Friday, March 19, 2021 / Rules and Regulations aluminum should provide more accurate quantification of the toxic fraction of aluminum. EPA has included a footnote to the final criteria statement specifically noting that for characterizing ambient waters, Oregon may utilize, as scientifically appropriate and as allowable by State and Federal regulations, analytical methods that measure the bioavailable fraction of aluminum. The States use of such a method would need to comply with other requirements in the States own program, for example, any applicable Quality Assurance/Quality Control requirements. For assessment and listing purposes, ambient field measurements analyzed using a bioavailable analytical method may be compared directly to the criteria because both represent the toxic fraction of aluminum.
EPA recognizes that in some circumstances, assessing waters using the total recoverable analytical method could result in the listing of some waters i.e., those with high amounts of total suspended solids as impaired even though the elevated aluminum measurements could be largely attributed to non-bioavailable forms of aluminum. EPAs existing regulations do not require use of analytical test methods promulgated at 40 CFR part 136 in the implementation of CWA
Section 303 programs, including assessment and listing of waters, nor in the determination of the need for a WQBEL. However, EPAs regulations require that states assemble and evaluate all existing and readily available water quality-related data and information for use in developing their CWA Section 303d lists. 40 CFR
130.7b5. The requirement to assemble and evaluate all data and information for assessment and listing purposes includes situations where only total recoverable aluminum data and information are available. However, in those circumstances, the State is not required to rely on that data for listing purposes as long as it provides a technical, science-based rationale for not using the data and information. 40
CFR 130.7b6iii. This technical, science-based rationale documenting the States consideration of existing and readily available data and information is referenced in the additional footnote language to the criteria statement, which speaks to Oregons ability to use analytical methods that measure the bioavailable fraction of aluminum for characterizing ambient waters as scientifically appropriate. For example, the State may be able to demonstrate that total recoverable aluminum
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samples are not representative of water quality conditions because non-toxic, non-bioavailable forms of aluminum are leading to an exceedance above the criterion. When data and information are available for both total recoverable and bioavailable aluminum, the State must evaluate all of it, but need not rely on all of it for assessment and listing purposes. Applicable regulations do not prohibit the State from assigning more weight to data and information about bioavailable aluminum than total recoverable aluminum for assessment and listing purposes.
For developing TMDLs and load allocations, field measurements analyzed using a bioavailable method also may be used as the basis for identifying allocations for TMDLs, both wasteload allocations WLA for point sources and load allocations LA for nonpoint sources. For implementing a WLA, the associated WQBEL must be assessed for NPDES compliance purposes using total recoverable methods just as would be the case for other NPDES applications consistent with permitting regulations NPDES
permit limits for aluminum and compliance reports, by regulation at 40
CFR 122.44, 40 CFR 122.45, and 40 CFR
122.48, must be expressed as total recoverable aluminum and measured using analytical methods approved at 40
CFR part 136. For implementing a LA, a bioavailable analytical method could be used to measure nonpoint source contributions because significant solids with colloid and clay-bound aluminum could be present He and Ziemkiewics 2016; Ryan et al. 2019,13 and should not contribute to the measured aluminum for comparison to a LA.
The contexts where use of an EPA
approved method is required are: 1
Applications for NPDES permits, specifically, measurements of effluents, 2 reports required from dischargers, and 3 certifications issued by states under CWA Section 401. 40 CFR
136.1a. NPDES permit limits for metals must be expressed as total recoverable metals with the exception of circumstances that would not apply for the aluminum criteria in this rule. 40
CFR 122.45c.
D. Incorporation by Reference The regulatory text incorporates an EPA document by reference, 13 He YT, Ziemkiewicz PF. 2016. Bias in determining aluminum concentrations: Comparison of digestion methods and implications on Al management. Chemosphere 159:570576; Ryan AC, Santore RC, Tobiason S, WoldeGabriel G, and Groffman AR. 2019. Total recoverable aluminum:
not totally relevant for water quality standards.
Integrated Environmental Assessment and Management. 156: 974987.

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specifically, EPAs Final Aquatic Life Ambient Water Quality Criteria for Aluminum2018, December 2018
EPA822R18001. The 2018
national recommended criteria document is an update to the 1988
recommended aluminum aquatic life ambient water quality criteria, in accordance with the provisions of CWA
Section 304a directing EPA to revise criteria from time to time to reflect the latest scientific knowledge. The criteria for aluminum that protect aquatic life in fresh water depend on a sites water chemistry parameters. Using those inputs, users can enter a sites pH, DOC, and total hardness into the aluminum criteria calculator or use the lookup tables in the criteria documents appendix. Incorporating this document by reference will allow the State to access all of the underlying information and data EPA used to develop the 2018
national recommended criteria for aluminum. With access to this information, the State will have the flexibility to create its own version of the calculator built upon the underlying peer-reviewed models. EPA has made, and will continue to make, this document publicly available electronically through www.regulations.gov at the docket associated with this rulemaking and at www.epa.gov/wqc/aquatic-life-criteriaaluminum.
IV. Critical Low Flows and Mixing Zones To ensure that the final criteria for aluminum are applied appropriately to protect Oregons aquatic life uses, EPA
recommends Oregon use critical low flow values consistent with longstanding EPA guidance 14 when calculating the available dilution for the purposes of determining the need for and establishing WQBELs in NPDES
permits. Dilution is one of the primary mechanisms by which the concentrations of contaminants in effluent discharges are reduced following their introduction into a receiving water. During a low flow event, there is less water available for dilution, resulting in higher instream pollutant concentrations. If criteria are implemented using inappropriate critical low flow values i.e., flow values that are too high, the resulting ambient 14 USEPA. 1991. Technical Support Document For Water Quality-based Toxics Control. U.S.
Environmental Protection Agency, Office of Water, Washington, DC EPA/505/290001. http
www3.epa.gov/npdes/pubs/owm0264.pdf.

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