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Federal Register / Vol. 86, No. 52 / Friday, March 19, 2021 / Rules and Regulations values. To ensure that all subject waters will be protected by the aluminum criteria, EPA recommends the State have either protective default input values for DOC, default criteria magnitude values, or procedures for how to calculate criteria values for waters for which there are insufficient data to adequately characterize sitespecific conditions in the water body.
EPA recommends that pH values be directly measured rather than estimated, given the variability of pH in the environment and the sensitivity of criteria calculations to differences in pH. EPA solicited comment in the preamble to the proposed rulemaking on whether it should promulgate default criteria values for aluminum to ensure protection of the aquatic life designated use when available data are insufficient to characterize a site. EPA agrees with comments that while default values may be needed in some situations, it is preferable to collect the needed ambient data and use the calculator to calculate criteria values. Commenters supported the use of default ecoregional criteria values for situations when data for more than one input parameter are unavailable, but requested that the final rule not include promulgation of default criteria values. In consideration of these comments, EPA has elected not to finalize default criteria procedures or values in this rule.
Although Oregon is not required to identify default input parameters or default criteria values for aluminum, the State is required to protect the designated uses of the waterbodies within its jurisdiction. As described in more detail below, EPA has elected to provide the procedures for developing default criteria values and default DOC
inputs in the docket to this rulemaking.
These procedures are available to Oregon to use at the States discretion, in the event the State does not yet have sufficient site-specific ambient data upon which to rely for a particular location. EPA expects that the State will provide publicly available default procedures or values so that the public and implementing entities will be aware of how all of the States fresh waters subject to the rule will be protected by the criteria when available data are insufficient to characterize a site.
Per commenters suggestions, this final preamble briefly describes a suggested procedure for calculating default ecoregional criteria, but does not include a table of pre-calculated values.
Comments supported the option of ecoregional criteria default values based on the 10th percentile of the distribution of calculator outputs calculated within an ecoregion, which is
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similar to the approach that EPA
suggested in the preamble to the proposal and described in a technical analysis included in the docket Analysis of the Protectiveness of Default Ecoregional Al Criteria Values Docket ID: EPAHQOW20160694
0114. In this procedure, EPA calculated ecoregional default aluminum criteria values based on publicly available data from each of Oregons Level III
Ecoregions.9 To calculate ecoregional default criteria values, 1 EPA
identified paired measurements of the three calculator input parameters where available, and 2 where paired measurements of the three calculator input parameters were unavailable, EPA
identified paired ambient data measurements for available input parameters along with estimated DOC
and/or total hardness estimated from measured Total Organic Carbon TOC
and specific conductivity, respectively as needed. EPA then calculated the 10th percentile CMC and CCC and other percentiles for each ecoregion from the distributions of calculator outputs.
Finally, depending on the ecoregion and data censoring method, EPA selected the 5th or 10th percentile as a statistic that represents a lower bound of spatially and temporally variable conditions that will be protective in the majority >90% of cases. This procedure is available for the State to use to generate default criteria values for areas for which the Aluminum Criteria Calculator v.2.0 will be used and there are insufficient site-specific ambient data. The State may also use another scientifically defensible procedure to generate default criteria values.
In addition to soliciting comment on including default ecoregional criteria, EPA also solicited comment on whether the final rule should include default DOC input values. Among the input parameters, ambient DOC data are the least likely to be available out of the three input parameters. DOC influences aluminum toxicity unidirectionally.
Higher levels of DOC provide more mitigation of aluminum toxicity. For water bodies for which sufficient pH
and total hardness data are available, but sufficient DOC data are not available, Oregon may develop default DOC input values to use with ambient pH and total hardness data, as an 9 USEPA.

2013. U.S. Environmental Protection Agency, 2013, Level III ecoregions of the continental United States: Corvallis, Oregon, U.S.
EPANational Health and Environmental Effects Research Laboratory, map scale 1:7,500,000, http
www.epa.gov/wed/pages/ecoregions/level_iii_iv.h.
Omernik, J.M. 1987. Ecoregions of the conterminous United States. Annals of the Association of American Geographers. 77:118125.

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alternative to using default criteria values. Comments supported the use of default DOC inputs when DOC input parameter data are unavailable.
Commenters requested the final rule afford the State the discretion to develop its own DOC defaults, including a comment requesting that the State be able to use its own DOC default inputs from its copper BLM criteria rule.10 EPA has elected not to finalize default DOC inputs for this aluminum rule so that the State may use its discretion to develop or apply its own.
Per commenters suggestions, EPA
briefly describes a possible procedure for calculating default DOC input values. One such approach would be to mirror the approach EPA described in the preamble to the proposed rulemaking, which also is described in technical support materials associated with EPAs proposed rulemaking and included in the docket to this rulemaking Analysis of the Protectiveness of Default DOC Options Docket ID: EPAHQOW20160694
0116. In that analysis, EPA analyzed the States DOC default procedures for its copper water quality standard and found that in most of the ecoregions, the default values those procedures would generate would be protective as default inputs for aluminum as well, with some exceptions and considerations. EPA
derived its suggested default DOC input values as the 15th or 20th percentile of the distribution of data from a compilation of high quality data available for Oregons georegions aggregated ecoregions with similar water quality characteristics.
Depending on the ecoregion and the data censoring method, EPA selected the 5th, 15th, or 20th percentiles as lowend percentiles of georegional DOC
concentrations that represent a lower bound of spatially and temporally variable conditions that will be protective in the majority of cases. EPA
encourages the State to continue refining its DOC default input procedures to ensure the calculated aluminum criteria values will be protective for all of Oregons fresh waters subject to this rule.
C. Implementation of Final Freshwater Acute and Chronic Aluminum Criteria in Oregon EPA understands that states have certain flexibilities under 40 CFR part 131 regarding how each implements water quality standards, such as todays 10 Oregon Administrative Rules, Copper Standard Implementatoin Chapter 340, Division 041, Section 0033, https www.oregon.gov/deq/wq/Pages/WQStandards-Copper.aspx.

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