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Federal Register / Vol. 86, No. 52 / Friday, March 19, 2021 / Rules and Regulations
scientific consensus has been that the total recoverable method for aluminum potentially overestimates the biologically available fraction and that a method that better addresses concerns with including aluminum bound to particulate matter would be useful e.g., He and Ziemkiewics 2016; Ryan et al.
2019.6
In an attempt to address concerns with measuring total recoverable aluminum concentrations, researchers recently investigated new analytical methods to measure biologically available forms of aluminum Rodriguez et al. 2019.7 This approach does not digest the sample at pH of 0.05 to +0.7
but rather to pH 4 to better measure only the bioavailable fraction of aluminum.
Rodriguez et al. reported that sodium acetate buffer is added to the sample to reach the desired pH, followed by sample agitation for a specified period of time, and finally 0.45-mm sample filtration. The sample is then acidified with nitric acid before inductively coupled plasma-optical emission spectrometry analysis. These authors provided data that led them to conclude that their proposed method is better able to discriminate chronic toxicity effects attributable to bioavailable aluminum from mineralized nontoxic forms of aluminum compared with existing methods using total or total recoverable aluminum.
EPA expects that an analytical method that uses a less aggressive initial acid digestion that liberates bioavailable forms of aluminum including amorphous aluminum hydroxide, yet minimizes dissolution of mineralized forms of aluminum such as aluminosilicates associated with suspended sediment particles and clays referred to as a bioavailable analytical method, will better estimate the bioavailable fraction of aluminum in ambient waters. EPA is not prescribing use of any specific method and looks to further research and method standardization efforts to identify best practices.
For the reasons articulated above, EPA is including the option for Oregon
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6 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.
7 Rodriguez PH, Arbildua JJ, Villavicencio G, Urrestarazu P, Opazo M, Cardwell AS, Stubblefield W, Nordheim E, Adams W. 2019. Determination of bioavailable aluminum in natural waters in the presence of suspended solids. Environmental Toxicology and Chemistry. 388:16681681.

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to use a bioavailable analytical method for characterizing aluminum concentrations in ambient waters, except where measurements of total recoverable aluminum are required by Federal regulations e.g., NPDES permit limits for aluminum and compliance reports, by regulation at 40 CFR 122.45, 40 CFR 122.44, and 40 CFR 122.48, must be expressed as total recoverable aluminum and measured using analytical methods approved at 40 CFR
part 136. Doing so, particularly when testing ambient samples expected to contain significant amounts of colloidal, particulate, and clay-bound aluminum, will better approximate the fraction of aluminum that is available to aquatic life in Oregon waters. The footnote in the criteria statement that speaks to Oregons use of a bioavailable analytical method specifies that such a method may utilize a less aggressive initial acid digestion, such as to a pH of approximately 4 or lower, that includes the measurement of amorphous aluminum hydroxide yet minimizes the measurement of mineralized forms of aluminum such as aluminum silicates associated with suspended sediment particles or clays. Oregon may use such methods as scientifically appropriate and as allowable by State and Federal regulations. For more discussion on analytical methods considerations, refer to Section C.
Implementation of Final Freshwater Acute and Chronic Aluminum Criteria in Oregon of this preamble.
Comments Regarding Language Included in the Aluminum Criteria Table In addition to addressing comments pertaining to the use of analytical methods described above, EPA also addressed separate and unrelated comments regarding language included in the proposed criteria table. In the proposed rulemaking, the proposed criteria table included the following text: Calculator outputs shall be used to calculate criteria values for a site that protect aquatic life throughout the site under the full range of ambient conditions, including when aluminum is most toxic given the spatial and temporal variability of the water chemistry at the site. Commenters requested that the text be moved out of the criteria table because they suggested that it referred to implementation of the criteria and that the criteria regulation should only contain a reference to the 2018 national recommended criteria for aluminum. In response, the final rule removes the proposed text from the criteria table and instead includes a modification of EPAs statement as a
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footnote to the criteria table. The Agency is using Oregons adopted water quality criteria for the copper Biotic Ligand Model BLM as its guide, specifically Endnote N, Subpart 3a, which states that Oregon will apply the BLM criteria for Clean Water Act purposes to protect the water body during the most bioavailable or toxic conditions. 8
Commenters also requested that EPA
edit the above-referenced statement to avoid the implication that a static set of criteria values must be calculated for each site for CWA implementation purposes. EPA affirms that the State need not calculate static criteria values for each site and has revised the statement to provide that for CWA
purposes, criteria values based on ambient water chemistry conditions must protect the water body over the full range of water chemistry conditions, including during conditions when aluminum is most toxic. The intention of the statement is to reflect that sitespecific pH, DOC, and total hardness conditions vary both spatially and temporally and that the State must apply the criteria in a manner that ensures protection over the full range of variability.
The State may ensure protection over the full range of water chemistry conditions in different ways for different CWA implementation purposes. For example, for NPDES
permitting, the permit protects the water body during critical conditions and therefore under other foreseeable conditions. The State could use multiple outputs of the calculator to generate a static set of criteria values that would be protective for the range of ambient conditions at a site, and use these to calculate a water quality-based effluent limit WQBEL for an NPDES
permit for a water body. For assessment, the State could concurrently measure the aluminum concentration and the input parameters at the site. The calculator would generate instantaneous criteria values against which the concurrently collected aluminum monitoring data would be compared.
Comments Regarding Default Criteria Values Regarding the topic of default criteria values, Oregon will need to use ambient water chemistry data i.e., paired pH, DOC, total hardness as inputs to the calculator in order to determine protective aluminum criteria values when implementing the criteria, unless the State provides protective default 8 See Endnote N, https www.oregon.gov/deq/
RulemakingDocs/tables303140.pdf.

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