Code of Colorado Regulations
1000 - Department of Public Health and Environment
1002 - Water Quality Control Commission (1002 Series)
5 CCR 1002-31 - REGULATION NO. 31 - THE BASIC STANDARDS AND METHODOLOGIES FOR SURFACE WATER
Section 5 CCR 1002-31.59 - STATEMENT OF BASIS, SPECIFIC STATUTORY AUTHORITY AND PURPOSE; JUNE 14-15, 2021 RULEMAKING; FINAL ACTION AUGUST 9, 2021; EFFECTIVE DATE DECEMBER 31, 2021
Current through Register Vol. 47, No. 17, September 10, 2024
The provisions of C.R.S. 25-8-202(1)(a), (b) and (2); 25-8-203; 25-8-204; and 25-8-402; provide the specific statutory authority for adoption of these regulatory amendments. The commission also adopted in compliance with 24-4-103(4) C.R.S. the following statement of basis and purpose.
BASIS AND PURPOSE
I. EPA DISAPPROVALS AND ACTION LETTERS
On December 8, 2011, EPA disapproved the Use Protected default for effluent-dependent or effluent-dominated waters provision at 31.8(2)(b)(i)(C) because Use Protected designations are to be based on water quality, not a default assumption regarding the impact of effluent on water quality. In the 2016 Regulation No. 31 rulemaking hearing, the commission adopted a sunset date of 12/31/2019 for this provision to resolve the disapproval. In this hearing, the commission deleted the repealed antidegradation provision at 31.8(2)(b)(i)(C).
To adequately protect aquatic life in Colorado, the commission, following guidance from the Temperature Technical Advisory Committee (TAC) deleted the air temperature, low-flow, and shoulder season excursions in Regulation No. 31 at Table I Footnote 5(c). In the 2016 Regulation No. 31 rulemaking hearing, the commission adopted a warming event provision. However, there was no technical basis for the joint adoption and application of both the warming event and excursions concepts.
On August 17, 2016, EPA wrote a letter to the commission citing concerns that the materials developed by the division to support its proposal did not align with the decision made by the commission. In addition, EPA requested additional information supporting joint application of the excursions and warming event allowance, as EPA did "not currently have a basis for approval." In its October 2, 2017 action letter regarding its review of the commission's 2016 changes to Regulation No. 31, EPA took no action on these standards changes. While EPA did not issue a formal disapproval, EPA's rationale for no action was that "a technical analysis has not been submitted which supports the revisions." Subsequent analysis by the division and TAC found that application of both the warming event and excursions is not biologically protective and recommended deleting the air temperature, low-flow, and shoulder season excursions and retaining only the warming event allowance.
During the 2016 Regulation No. 31 rulemaking hearing, some stakeholders voiced concern that deletion of the excursions would result in an unacceptable increase in 303(d) temperature impairment listings. Analysis of over 500 temperature sites across the state indicate that the warming event and excursions are approximately equal in resulting in an assessment decision of impairment or attainment for a waterbody; therefore, deletion of the excursions is not likely to result in an increase in temperature 303(d) listings, given the similar practical outcomes of these provisions. Regarding impacts to permitting, the air temperature, low-flow, and shoulder season excursions in Table I Footnote 5(c) have never been incorporated into permit effluent limits, and deletion of these excursions will not affect permit effluent limit calculations.
On December 8, 2011, EPA disapproved the point of application footnote for nitrate in Table II Footnote 4 that allowed the nitrate standard to not be implemented in discharge permits if no actual Water Supply use was identified and only applied the nitrate standard to the point of intake. The provision was disapproved because the standards are intended to protect classified uses, regardless of whether they are set to protect actual or future uses. During the 2016 Regulation No. 31 rulemaking hearing, a sunset date of 12/31/2022 was adopted for this provision to resolve the disapproval. The commission did not take any action regarding this provision in the current rulemaking hearing. However, Table II Footnote 4 at 31.16 was revised to clarify that the commission intended to retain the condition that the sum of nitrate and nitrite will not exceed the standard of 10 mg/L. The commission restructured the footnote to separate this condition from the portion of the footnote that expires on 12/31/2022.
II. REVISIONS OF CRITERIA IN LIGHT OF NEW INFORMATION
The commission adopted revised acute and chronic Aquatic Life water quality standards of 3 µg/L for acrolein, based on the EPA 304(a) criteria updated in 2009. The commission also adopted new acute and chronic Aquatic Life water quality standards of 2.1 µg/L for carbaryl, based on the EPA 304(a) criteria published in 2012.
The commission declined to adopt EPA's revised 304(a) Aquatic Life criteria for selenium, ammonia, and aluminum at this time; however, the division is committed to evaluating these new criteria. Studies are currently underway for each parameter to improve understanding of these criteria in the context of water quality conditions in Colorado and how these criteria may be adopted and implemented in Colorado in the future.
EPA has also released updated criteria or guidance for several other parameters, including copper (Aquatic Life), E. coli (Recreation), cyanotoxins (Recreation), and the human health risk exposure assumptions. However, the division does not recommend adopting EPA's recommendations for these parameters at this time, as these items are not included on the division's 10-Year Water Quality Roadmap.
III. ANTIDEGRADATION STATUTE ALIGNMENT
As part of the June 2020 Regulation No. 38 rulemaking hearing (final action August 10, 2020), the commission raised questions about a potential misalignment of the Use Protected regulatory provisions in Regulation 31.8(2)(b)(ii) that considered the reversibility of existing pollution, with the statutory language in the Water Quality Control Act that limits the water quality test for the Use Protected designation to existing quality.
SUNSET 31.8(2)(b)(ii) Effective December 31, 2031
Having considered the evidence and statements submitted in this rulemaking, the commission believes that it is appropriate to move forward toward revision or deletion of the discretionary water quality-based antidegradation test at 31.8(2)(b)(ii). While the late stages of this rulemaking helped to advance the discussion regarding options for Use Protected designations based on the presence of substantial pollution for parameters other than those listed in section 31.8 , it was not possible within the constraints of this rulemaking to subject these issues and options to the robust public process that they deserve. This included the division's compromise option presented as part of its consolidated proposal -Option B, which proposed to add clear and relevant factors for the commission to holistically consider the overall characteristics of a waterbody when determining antidegradation designations in the limited circumstances where the 12 parameters test may not be sufficient. Since the issues are complex and there remains much controversy at the time of the rulemaking hearing, the commission adopted the division's alternative compromise proposal - Option A and repealed the antidegradation provision at 31.8(2)(b)(ii) with a delayed effective date of December 31, 2031. It is the intention of the commission to retain the current provision until that date but maintain its focus on Use Protected designations based on the 12 parameters test.
This action preserves division resources already fully allocated to criteria development and implementation efforts as identified in the 10-Year Water Quality Roadmap (Roadmap) through 2027 and allows adequate time for the division to conduct a separate, comprehensive stakeholder process on antidegradation following completion of the Roadmap and prior to the expiration of 31.8(2)(b)(ii). The commission intends that the division will engage in this comprehensive stakeholder process to consider options to delete the test at 31.8(2)(b)(ii) or revise that test with criteria that holistically evaluate the overall characteristics of a waterbody in a manner consistent with state and federal requirements. The commission also intends to revisit the provisions at 31.8(2)(b)(ii) through a rulemaking action no later than 2031. Revisiting this provision in the future would have the added benefit of providing an opportunity to also consider other aspects of Colorado's antidegradation rule, such as a lack of explicit "Tier 1" antidegradation review for existing uses as noted by EPA. If this stakeholder process is delayed due to unforeseen circumstances, it is the commission's intent that a limited extension of the sunset date will be adopted to allow time for the stakeholder process and rulemaking hearing prior to deletion of 31.8(2)(b)(ii). The commission also deleted the word "/or" to align with the federal antidegradation rule at 40 CFR 131.12(a)(2) and the Colorado Water Quality Control Act at 25-8-209(4).
Prior to 2021 the commission has only considered the presence of substantial pollution for parameters other than those listed in Section 31.8 in the context of antidegradation designations in rare circumstances throughout the history of the antidegradation program in Colorado. The commission selected the 12 parameters listed in 31.8(2)(b)(i)(B) because they are effective indicators of water quality for antidegradation designation purposes. Accordingly, as the commission's past practice has reflected, the water quality-based tests set out in 31.8(2)(b)(i) will ordinarily suffice to determine whether waters' existing quality warrants a Reviewable or a Use Protected designation.
If proposals based on 31.8 are advanced prior to 2031, the commission will thoroughly and holistically consider the physical, chemical, and biological characteristics of a waterbody, social and economic impacts throughout the segment and on downstream waters and users, environmental justice and health equity principles, and ensure that the public has adequate notice and time to engage and comment on proposals.
It is also important to note that under the tests at 31.8(2)(b)(i), the commission may determine that those waters with exceptional recreational or ecological significance should be undesignated, and deserving of the protection afforded by the antidegradation review provisions of section 31.8(3).
Future Considerations
At this time, the commission believes that it would be appropriate for it to revisit the option of a discretionary test for use in the limited circumstances where the 12 parameters test may not be sufficient, so long as that test (1) includes clear factors established in the regulation for making Use Protected antidegradation determinations that are consistent with state and federal law and (2) is based on a finding of substantial pollution for parameters outside those included in the 12 parameters test. Without presuming to limit the options available to future decision makers and based on its experience in this rulemaking, the commission recommends that the following issues should be addressed in a future stakeholder and rulemaking process to revisit section 31.8(2)(b)(ii) . The issues include, but are not limited to, thorough and holistic consideration of all of the following:
The commission further recommends that the future stakeholder and rulemaking process should address the broader aspects of the antidegradation program noted above (e.g., explicit Tier 1 antidegradation review).
IV. DISCHARGER-SPECIFIC VARIANCES
The commission revised the discharger-specific variance (DSV) provisions at 31.7(4) to improve the clarity and organization of requirements, reflect the commission's current practices, and align with the 2015 federal rule (40 CFR 131.14). The commission's criteria for DSVs have been utilized successfully to develop DSVs that have been approved by EPA and are resulting in water quality improvements. Overall, the commission determined that the requirements at 31.7(4) continue to be appropriate. The changes made during this hearing are not expected to substantively change the requirements for variances, but rather are intended to improve transparency and facilitate commission action and EPA approval.
Previously, the requirements for DSVs were included in three locations in the regulations, at 31.7(4) Granting, Extending and Removing Variances to Numeric Standards, at 31.9(5) Conditions on Discharger-Specific Variances, and in some of the basin regulations, which include reevaluation requirements for existing DSVs (e.g., 32.6(6)(a) and (b)). The commission centralized the DSV requirements in a single location at 31.7(4) to ensure that requirements are not overlooked.
The commission deleted the term "numeric" from 31.7(4) Granting, Extending and Removing Variances to Numeric Standards and 31.7(4)(a) to better align with the federal rule, which does not preclude the possibility of variances to narrative criteria. As with all variances, a DSV for a narrative standard would need to meet all Colorado and federal requirements and be supported by a comprehensive alternatives analysis demonstrating that there are no feasible pollution control alternatives that would allow for the regulated activity to proceed without a discharge that exceeds water quality-based effluent limits (WQBELs) for a given parameter(s) and an evaluation that there are no other regulatory options to achieve compliance. Therefore, a DSV must include identification of the pollutant(s) or water quality parameter(s) to be able to perform an alternatives analysis and a detailed demonstration of why it is not feasible to meet the narrative standard. The identification of the pollutant is a critical and crucial step of the DSV process whether the standard is narrative or numeric, because the treatment and control technologies can vary significantly based on the pollutant requiring removal. For example, feasible treatment technologies for removing organic carbon and ammonia may not be effective at removing zinc, cadmium, or sulfate.
There are several narrative standards in Regulation No. 31 with implementation tools that help determine numeric effluent limitations or quantifiable conditions in NPDES permits. For example, one of the narrative water quality standards listed in 31.11(1) specifies that waters should be free from substances that cause toxicity to humans, animals, plants, and aquatic life. The implementation tool used for aquatic life toxicity determinations is Whole Effluent Toxicity (WET) testing. WET tests directly measure the toxic effects on aquatic life due to the presence of one or more pollutants in the wastewater. Because WET testing is a control mechanism that measures, and limits, the combined toxic effect that the pollutants in the effluent have on aquatic life, it does not require the identification of each one of the pollutants in the effluent. The commission recognizes that each situation is unique, but in cases such as the one for toxicity described here, to qualify for a DSV, the discharger will need to identify the pollutant(s) or water quality parameter(s) that is/are causing non-compliance with the standard and/or failures with the implementation tool. The identification of the pollutant will serve two purposes during a DSV process: first, to determine if there are any pollution control alternatives that can feasibly achieve compliance with the narrative standard (in other words, whether or not the discharger qualifies for a variance); and second, to develop the alternatives analysis of feasible pollution control technologies that will provide incremental water quality improvements.
To align with the federal rule and ensure that a variance results in measurable progress towards attaining the underlying designated use, the commission will also adopt a quantifiable expression of the highest attainable condition for narrative standards. A quantifiable expression of the highest attainable condition can be expressed as numeric pollutant concentrations in ambient water, numeric effluent conditions, or other quantitative expressions of pollutant reduction. The preamble to the federal rule at 40 CFR 131.14 describes the quantifiable expression by providing the example of the maximum number of combined sewer overflows that is achievable after implementation of a long-term control plan. The commission believes such a quantifiable expression helps ensure measurable water quality improvements during the term of the variance, which is a key purpose of a variance.
Although this change acknowledges the possibility of DSVs adopted for narrative standards, the commission encourages potential proponents of DSVs for narrative standards to closely coordinate with the division before proposing such variances. At this time, the commission does not have a full understanding of all the circumstances under which DSVs for narrative standards may be warranted. Similarly, no guidance yet exists for developing and implementing alternative effluent limits (AEL) for narrative standards that protect the highest attainable condition.
In 31.7(4), the commission changed the requirement to reevaluate DSVs "every three years" to "during each basin triennial review for the segment, unless the Commission requires a more frequent review when adopting the variance" to be consistent with current commission practice. Because the DSV reevaluation occurs across multiple hearings (Issues Scoping Hearing, Issues Formulation Hearing, and Rulemaking Hearing), the term "triennial review" better captures the process and timing of DSV reviews. This revision also provides flexibility to conduct more frequent reviews if it is required by the variance.
In 31.7(4)(a)(ii), the commission changed the requirement to obtain a DSV from being a preferable matter of policy when the conditions for granting a temporary modification are not met, to requiring evaluation of whether other regulatory tools are appropriate to obtain feasible WQBELs within the required timeframe. This change reflects the commission's practice of granting a DSV only in instances where there has been an evaluation of other regulatory tools, such as compliance schedules or a Use Attainability Analysis (UAA), to determine whether these tools may result in WQBELs that are feasible for the discharger to achieve within the required timeframe.
The required timeframe to evaluate the potential use of other regulatory tools is based on site-specific conditions; however, a reasonable timeframe for such determinations usually does not exceed a few years. For example, if a discharger is expecting more stringent WQBELs in a future permit, or has a compliance schedule and is considering a variance because it will not be able to achieve its WQBELs at the end of the compliance schedule, the discharger should use this time to evaluate other regulatory tools. A UAA can be evaluated if there is a potential to change the classified uses or standards on the segment; while uses and standards are required to be reviewed at least once every three years, and future changes are possible, DSVs are definitely temporary. In the past, UAAs to support removal of the Water Supply use where there are no current or future water supplies have been effective for several dischargers. This type of analysis can generally be completed within months. It is important to evaluate the potential use of other regulatory tools first, as it is the commission's intent that DSVs are to be used only in cases where the compliance problem cannot be solved using other regulatory tools.
In 31.7(4)(b), the commission adopted revisions to both the definition and selection of AELs to improve clarity and align with the federal rule. The commission clarified that the AEL selection process should be based on (1) implementation of the best feasible alternative(s) to achieve WQBELs over the longer term, (2) achieving the highest attainable condition throughout the term of the variance, and (3) protecting the existing water quality conditions at the time of the adoption of the variance unless necessary for restoration activities.
The commission renamed the two options for AELs to reflect what each option represents. The AEL must be either (i) an effluent-based (numeric) limit expressed as an effluent concentration, load, pollutant percent removal, or other quantifiable expression of effluent quality and quantity, or (ii) an action-based (narrative) limit with a quantifiable expression of the specific pollution control requirements to be completed by the discharger and the adoption and implementation of a Pollutant Minimization Program (PMP).
In addition, the commission revised its practice of only adopting AELs to be met by the end of the variance. Previously, the commission adopted only a final AEL, which established the required water quality improvement to be achieved once the selected alternatives had been fully implemented. To ensure that the DSV did not result in any lowering of the currently attained ambient water quality, the commission previously relied upon implementation requirements that directed the permit writer to develop "initial effluent limits" based upon the level of effluent quality currently achieved that applied from the beginning of the variance until the AEL was achieved. The permit writer would also develop "interim effluent limits" if the water quality improvements were planned in phases.
In order to align with federal requirements, the commission will instead adopt AELs that apply throughout the term of the variance. This will include an initial AEL that applies from the beginning of the variance and a final AEL based upon the expected water quality improvement to be achieved once the selected alternatives have been fully implemented. The purpose of the initial AEL is to ensure that the DSV does not result in any lowering of the currently attained ambient water quality. The purpose of the final AEL is to set requirements that represent the highest attainable condition that is feasible to achieve within the term of the variance. The commission may also adopt interim AELs to set requirements for variances with multiple planned phases of water quality improvement.
The commission strongly prefers adoption of effluent-based initial and final AELs, expressed as effluent concentrations, loads, or pollutant removal percentages. However, in cases where the commission determines that an action-based final AEL is appropriate, the commission may still adopt an effluent-based initial effluent limit. Action-based initial AELs with a quantifiable expression and a PMP will be considered only in extraordinary circumstances when it is not feasible for the discharger to comply with an effluent-based initial AEL. For instance, City of Pueblo's selenium DSV is a good example of a case where the permittee did not have sufficient control over pollutant concentrations at the onset of the variance and there was a high degree of variability and unpredictability that limited numerical characterization of the pollutant reductions achievable in effluent concentrations. This DSV, adopted by the commission in the 2018 Regulation No. 32 rulemaking hearing, included an action-based AEL (formerly known as a narrative AEL) that quantified the requirements of the DSV as a specific set of source control and optimization measures with a specific timeline (implemented as a PMP).
To be consistent with the federal rule, the commission revised the language to allow the adoption of an effluent-based (numeric) AEL or an action-based (narrative) AEL with a quantifiable expression and a PMP to ensure all feasible water quality improvements are implemented throughout the term of the variance. The commission described the effluent-based AELs as limits that can be expressed as an effluent concentration, load, pollutant percent removal, or other quantifiable expression of effluent quality and quantity. The commission described the action-based AELs as a quantifiable expression of the specific pollution control requirements to be completed by the discharger and the adoption and implementation of a PMP. The commission specified that the action-based AEL is only justified when there is no additional feasible control technology that can achieve a predictable, quantitative improvement in effluent quality, and therefore, will also require adoption and implementation of a PMP to specify the actions that need to be taken to achieve maximum pollutant reduction with existing control technologies. For the effluent-based AEL (numeric), the commission stated that it may also adopt a PMP at its discretion. These requirements are consistent with the nine DSVs adopted by the commission to date.
A PMP is a comprehensive source control measure described in 40 CFR 131.14 that will prevent and reduce the pollutant loadings to the receiving waterbody. A PMP is particularly essential for variances where the requirements are adopted as actions to be completed by the discharger, rather than effluent quality. Based upon experience with the DSVs previously adopted by the commission, a PMP provides a clear set of expectations and timeline for implementation, which makes it straightforward for both the discharger and the commission to determine compliance with the requirements. Without a PMP, there is a risk of the discharger and the commission having different expectations about the DSV requirements and whether compliance has been achieved. A PMP may be a short document, and the development of a PMP should not be an onerous requirement. Previously, it has been an extremely useful document to the discharger (particularly to the plant operator) after the variance has been adopted.
The Conditions on Discharger-Specific Variances section was moved from 31.9(5) to 31.7(4)(c) to facilitate consolidation of DSV requirements in a single location. Section 31.9(5) was deleted. Section 31.7 was revised to avoid redundancy with Section 31.7 . The commission also included language to state that the discharger should be in compliance with the initial AEL when the variance is implemented in the permit and that the permit writer determines the compliance schedule(s) of the interim (if any) and final AELs. The commission also clarified the language to allow the permit writer to set interim milestones to achieve the final AEL, if appropriate.
The commission moved Section 31.7 to 31.7 because it governs the division's permitting implementation rather than a requirement for the selection of AELs. The previous regulatory language in this provision also gave direction to the permit writer regarding DSV implementation; however, the language was confusing. Therefore, the commission clarified the language in 31.7(4)(c)(iv) to state that the effluent limits for the point source discharge in the variance should be based on either WQBELs based on the underlying standard for the receiving waterbody or the AEL, whichever is less stringent. This is applicable in situations where a discharger's WQBELs increase, for example, due to an increase in dilution in their discharging segment.
In 31.7(4)(b), the commission revised the language that described the variance as a standard "which represents the highest degree of protection of the classified use that is feasible within 20 years" to instead state that variances shall include AELs "that reflect the greatest pollutant reduction achievable throughout the term of the variance". While it is important to consider the potential for attaining standards on a long time horizon (i.e., approximately 20 years), in practice, there is often a great deal of uncertainty regarding the timeframe over which it may be feasible for the permittee to achieve WQBELs based upon the underlying standard. Adopting a variance with a shorter timeframe and a more certain AEL would allow for water quality improvement in the short-term, while retaining the ability to reconsider long-term feasibility during the reevaluation of the variance or at the end of the term of the variance.
Section 31.9 was clarified to note that compliance schedules are authorized when appropriate and necessary to meet interim and final AELs for variances.
The commission made several revisions to 31.7(4)(d). First, the commission changed the requirements for the duration of a DSV and included language to account for the planning, implementation, and monitoring of the activities planned to achieve better water quality. Previously, 31.7(4)(c) stated that the duration of the DSV will be determined on a case-by-case basis, based upon all relevant factors, including the potential for achieving more protective effluent levels. This was not entirely consistent with the federal rule, which states "The term of the WQS variance must only be as long as necessary to achieve the highest attainable condition." For each of the DSVs that the commission has adopted to date, the duration was based upon the time needed to achieve the highest attainable condition. The commission revised this section to align with the federal rule and reflect current commission practice.
Second, the same requirements included in the basin regulations (such as 32.6(6)(a) and (b)) regarding the reevaluation of DSVs were added to 31.7(4)(d). These requirements were not included in Regulation No. 31 previously. The requirements include conducting a reevaluation of the variance during the triennial basin review when the term of the variance is longer than five years, and more frequently if needed, and submitting the results of its reevaluation to EPA within 30 days of the date the commission completes its reevaluation, as is required by federal rule.
Third, to better align with the federal rule, the commission added that it would incorporate a more stringent AEL if, as part of the reevaluation process, it determines that a more stringent AEL or higher attainable condition than originally required by the variance is achievable. The commission added that if the commission determines a less stringent AEL is necessary, a revised variance must be submitted to EPA.
Lastly, the commission changed the language from "extending" to adopting "a subsequent variance" in order to better align with the federal rule, and clarified the requirements for adopting a subsequent variance.
V. LAKE TEMPERATURE AND DISSOLVED OXYGEN FOOTNOTE
The commission adopted Footnote 5(c)(i) to Table I, which states:
Lakes and reservoirs: When a lake or reservoir is stratified, the mixed layer may exceed the applicable temperature criteria in Table I provided that an adequate refuge exists in water below the mixed layer. Adequate refuge means that there is concurrent attainment of the applicable Table I temperature and dissolved oxygen criteria. If the refuge is not adequate because of dissolved oxygen levels, the lake or reservoir may be included on the 303(d) List as "impaired" for dissolved oxygen, rather than for temperature.
This footnote previously existed in Regulation No. 31, but was deleted in the 2016 Regulation No. 31 rulemaking hearing. In 2016, the commission declined to adopt the division's statewide temperature proposal for lakes to adjust the Table Value Standards (TVS) for temperature based on elevation. The proposal would have resulted in an increase in the allowable temperature for many lakes. A component of the proposal was also to delete Footnote 5(c)(iii) to Table I, which allowed for surface temperatures to exceed standards as long as concurrent attainment of dissolved oxygen (DO) and temperature existed in a profile of the reservoir. The commission did not adopt this proposal; however, Footnote 5(c)(iii) was still deleted, in error. The footnote deletion should not have been adopted because deletion of the footnote was directly coupled to the elevation-based temperature standards proposal.
The division provided evidence in this hearing showing that lake surface temperatures are widely subject to exceedances and correlated with elevation, and that Table I Footnote 5(c)(iii) should be reinstated. The reinstatement of Footnote 5(c)(iii), modified for clarity, will allow for lakes to have surface or mixed layer temperature exceedances (a naturally occurring condition) and assessments to consider 303(d) and M&E listings for DO where DO and temperature are not concurrently attained.
VI. LONGEVITY PLANS FOR SITE-SPECIFIC STANDARDS
The commission considered but did not adopt a proposal to revise section 31.7 and 31.7 to incorporate a longevity plan requirement for all ambient quality-based, criteria-based, and narrative site-specific standards. The commission determined that, at this time, a regulatory change is not needed for longevity plans to continue to be adopted with site-specific standards.
The purpose of longevity plans is to ensure that site-specific standards can be reviewed during subsequent triennial reviews, as required by federal and state rule (Federal Clean Water Act Section 303(c)(1) and Colorado Water Quality Control Act Section 25-8-202(f)). Consistent with past practice, the commission will continue to thoughtfully consider the expected longevity of each site-specific standard and identify the types, extent, and timing of information needed to facilitate future reviews of the standards. The commission will continue to adopt longevity plans as needed to guarantee the collection and analysis of information that will be necessary to ensure that a site-specific standard is maintained over time, continues to be scientifically sound, protects the beneficial uses, and can be updated or revised as needed.
The commission intends that longevity plans will continue to be developed in collaboration with the division and other interested parties. In addition, the commission intends that longevity plans will be implemented by the parties proposing site-specific standards; in some situations, longevity plans may be implemented by multiple parties. Longevity plans should include plans for collection of evidence necessary to support review of the site-specific standards in subsequent rulemaking hearings, taking into account the expected longevity of the site-specific standards, the conditions on which the site-specific standards were based, the time horizon in which those conditions are expected to change, and the resources required to collect, analyze, and report on data and other information. The purpose of collecting such information is to ensure the commission can determine whether the basis and assumptions used to support the initial adoption of the site-specific standards are still valid or if there has been a significant change in conditions. Depending on the type of site-specific standard (ambient-based, criteria-based, or narrative), this may include collection of instream and effluent water quality data (and, as appropriate, the flow and loading of effluent) to characterize existing quality; aquatic life community information; updates to toxicity databases; analysis of data; investigation of treatment technologies, treatment alternatives, and/or other controls to determine if further improvements to water quality are feasible; land use or habitat evaluations; or collection of other relevant site-specific information.
For example, longevity plans for site-specific standards based on the copper Biotic Ligand Model have included continued collection of the water quality data required to run the model; longevity plans for site-specific standards based on the recalculation procedure have included investigations of new toxicity data, reporting on changes to instream chemical, physical, or biological conditions, and additional biological and water quality data collection; longevity plans for site-specific standards based on natural or irreversible ambient conditions have included ongoing biological and water quality data collection.
When the division has identified an existing site-specific standard as a priority for review in an upcoming rulemaking hearing, the division will conduct outreach with potentially impacted entities as early as possible to identify data and other information needs and collaborate on data and information collection as needed. The division shall notify potentially impacted entities in consideration of a timeline that allows them adequate notice of the division's intent for review and allow participation in the routine approach to stakeholder participation in basin reviews.
The commission expects that longevity plans will result in the collection of evidence that is of the right type, quality, and quantity to be useful for future evaluations of the site-specific standard, recognizing that the type(s) of data collection is dependent on conditions unique to the site, and that a longer time horizon (beyond a single triennial review period) for the frequency of data collection may be warranted for certain sites. For some situations, it may be appropriate to require certain activities only if certain types of changes occur; for example, water quality data collection may only be necessary if changes to land use or flow are observed. Because every site-specific standards situation is unique, so too will be the components, review elements, and review timing of every longevity plan. In addition, the commission anticipates that individual longevity plans may be revised in future reviews to account for site-specific circumstances.
In addition, the commission encourages the division to begin evaluating the basis of all existing site-specific standards. Where the basis or validity of an existing site-specific standard cannot be confirmed with available data or other information, the commission encourages the original proponents of existing site-specific standards (including the division), and/or other dischargers whose permit compliance relies on the site-specific standards, to begin working with the division, EPA, CPW, and other interested parties to develop a plan to collect the necessary information and provide an update to the commission at the soonest possible triennial review for the waterbody at issue. Because most existing site-specific standards do not have a longevity plan, and in many cases, sampling is not occurring, the commission anticipates it will take time for representative data and/or information required for a comprehensive review of each site-specific standard to become available, and that progress will be incremental during routine basin review cycles. The division will compile and store information about all site-specific standards in a publicly available site-specific standards library; this library will house information about the basis and review history for each site-specific standard and will be used to prioritize site-specific standards for future review.
VII. TEMPORARY MODIFICATIONS
The commission adopted changes to the temporary modification provisions at 31.7 and 31.9 to reflect current commission practice and better ensure that temporary modifications are adopted only when necessary and eliminated in a timely manner. Changes were also adopted to ensure that facilities receiving regulatory relief through a temporary modification take measures to, at a minimum, maintain status quo and manage effluent quality at the best level reasonably achievable under the term of the temporary modification. These changes are described in more detail in the following sections.
Section 31.7(3) was also reorganized slightly for clarification and a definition for the term "status quo" was added to 31.5(40). The commission considers division Policy 13 Permit Implementation Method for Narrative (Current Condition) Temporary Modifications to be consistent with this regulatory definition.
Predicted Non-compliance
The commission made several substantive and editorial revisions to 31.7(3)(a). The commission clarified that temporary modifications may be granted for numeric water quality standards. Additionally, the commission clarified at 31.7(3)(a) that non-attainment of the underlying water quality standard in the waterbody is an explicit requirement for justifying a temporary modification. This requirement for a temporary modification is set forth at 31.7(3), namely that "Where non-attainment of underlying standards has been demonstrated or predicted the Commission may grant a temporary modification...". However, this requirement was not previously raised again explicitly at 31.7(3)(a). Furthermore, the commission added clarification that the appropriate scope of temporary modification application to a waterbody is only where demonstrated or predicted waterbody non-attainment and compliance problems co-occur (i.e., the temporal and spatial application should be appropriately narrow). For example, if a compliance problem or non-attainment is only observed in the summer, it may not be appropriate to grant a year-round temporary modification. These changes recognize current practice and are not meant to change that policy, only to clarify and expressly approve its use. The commission recognizes that evaluations of co-occurrence of non-attainment and non-compliance can vary depending on the situation and intends to consider site-specific information in determining the appropriate spatial and temporal extent of a temporary modification.
Additionally, the commission added language at 31.7(3)(a)(ii) to clarify how predicted compliance problems are justified. It was specified that temporary modifications are only justified in situations where, in addition to significant uncertainty and non-attainment, there is either a demonstrated or predicted problem complying with a water quality-based effluent limit (WQBEL) on a timescale such that, absent a temporary modification, the discharger would face unreasonable consequences. For purposes of temporary modifications, unreasonable consequences are defined as situations where it can be demonstrated that the timing of the anticipated permit limit (considering any potential compliance schedules or other permitting flexibility) would not provide sufficient time to resolve the uncertainty prior to requiring significant investment in design or construction of facility infrastructure. As such, the commission further defined predicted non-compliance as a problem complying with a WQBEL with which the discharge must comply within the next five years (i.e., within five years of the effective date of the temporary modification). Another example situation that would qualify for a temporary modification is where a discharge has a predicted problem complying with a WQBEL in more than five years, and evidence shows significant investment in facility infrastructure would be required before the uncertainty is resolved. For the purposes of temporary modifications, significant investment can be equated to any measures beyond low cost options for maintaining the best effluent quality reasonably achievable, such as example activities provided at 31.9(4).
These changes provide clarity regarding the appropriate use of prediction in determining whether compliance problems exist in the context of temporary modifications. The commission expects that, when time allows, progress to resolve the uncertainty (e.g., derivation of an appropriate site-specific standard or DSV) will occur in coordination with the division and other stakeholders outside of a temporary modification. This will allow for optimal use of resources and help to ensure that the scope of a temporary modification is appropriately narrow and the term is appropriately short.
The commission revised 31.7(3)(b) and 31.7(3)(c) to clarify what supporting information is required for temporary modification adoption and extension, respectively. To support an extension of a temporary modification, the commission added a requirement to provide justification as to why the time allotted under the previous temporary modification term was not sufficient to resolve the uncertainty. This information will help the commission judge whether the reasoning behind the need for extension is justified and avoid granting temporary modification extensions where the need for extension results from lack of sufficient effort to eliminate the need for the temporary modification.
The commission also added an explicit provision to 31.7(3)(b) and (c) requiring a characterization of the status quo of the waterbody and effluent, or, absent sufficient data, a plan to collect data to characterize the status quo as soon as possible. This characterization will ensure that the commission can use these data points to compare to future characterizations of ambient and effluent conditions when a temporary modification is reviewed or when it is proposed to be modified or extended, to verify that status quo has been maintained. As such, the commission also adopted revisions to 31.7(3)(e) that explicitly list consideration of the maintenance of the status quo when making a decision as to whether a temporary modification should be removed or extended. Additionally, a statement was added to the review criteria to clarify that an extension of the temporary modification shall not be granted in cases where the basic reporting requirements (i.e., providing annual updates and supporting documentation to the division) have not been met over the prior term of the temporary modification. All of these actions are aligned with the current intent of the regulatory language and reflect current commission practice. The commission recognizes that, during the temporary modification, permitted dischargers' effluent quality may be marginally changed and variability in effluent quality may occur; however, the commission also expects that dischargers take measures to ensure that effluent quality is maintained at the best level reasonably achievable, in a manner consistent with the provisions of 31.9(4), under the term of the temporary modification, as discussed below. There may also be situations where the waterbody quality status quo has not been maintained due to causes outside of the discharger's control (e.g., hydrological modifications of the waterbody upstream of the discharge point). Under these circumstances, justification that the waterbody degradation was not due to the effluent in question should also be provided and considered, as specified in 31.7(3)(c) and 31.7(3)(e).
The commission also made changes to 31.7(3)(b) to clarify the expectations for the required plan to resolve uncertainty that accompanies each temporary modification. The commission clarified that, for each type of uncertainty identified, the plan should include an adequately detailed, site-specific approach, including sampling plans where appropriate, to resolve the uncertainty. Plans should also include timelines for key deliverables and annual reporting of progress to the division. Furthermore, the commission added a requirement for plans to include activities to ensure that, at a minimum, status quo is maintained and effluent quality is maintained at the best level reasonably achievable. This is not only aligned with existing provisions at 31.9(4), but also with previous commission intent documented in the Statement of Basis and Purpose at 31.44 and existing commission practice to adopt plans that include low-cost activities that would result in water quality improvements under the term of the temporary modification. Such activities may include optimization-like activities such as pretreatment, source identification, and evaluations of source control and treatment options. Nonpoint source implementation of strategies for improving waterbody quality can also be considered, as appropriate. These activities also serve to help eliminate the uncertainty regarding the extent to which conditions are natural or irreversible. Except where justified otherwise, it is the commission's intent that efforts to resolve each type of uncertainty occur in parallel, rather than in sequence, such that the need for the temporary modification is eliminated as expeditiously as possible.
The commission removed the requirement for temporary modification operative values to "protect existing uses" at 31.7(3)(d). This requirement is not consistent with the intent of temporary modifications, which focuses on maintaining status quo. Thus, the requirement to "protect existing uses" was replaced with a requirement that the temporary modification operative values, at a minimum, ensure that status quo is maintained. The commission also aligned the language at 31.7(3)(d)(i) and (ii) to clarify that characterization of status quo is the requirement for both numeric and narrative operative values.
The commission added clarifying language at 31.7(3)(e) to better specify appropriate considerations when setting the term of temporary modifications. In circumstances where there is uncertainty pertaining to the justification for the temporary modification and further data are being gathered to support the justification (e.g., where there is some uncertainty whether waterbody non-attainment exists), a shorter term for the temporary modification may be warranted. The commission also clarified that the term granted shall be the shortest possible to sufficiently resolve the uncertainty. The reasoning for the length of term selected should be clearly justified in the plan to resolve uncertainty for the temporary modification. Additionally, the commission clarified that, when evaluating extension of a temporary modification, the situation must still qualify for a temporary modification under 31.7(3)(a) and substantial progress towards resolving the uncertainty must have been made under the previous term of the temporary modification. The commission will evaluate the adherence to planned activities scheduled in the plan to resolve uncertainty, as well as the justification (newly required at 31.7(3)(c)) as to why the time allotted under the previous temporary modification duration term was not sufficient to resolve the uncertainty.
The commission revised 31.7(3)(f) to expand the scope of temporary modifications included in the temporary modifications public rulemaking hearings from those expiring within the subsequent two years to all temporary modifications, so that the commission is able to better ensure that timely progress is being made on all temporary modifications, regardless of the expiration date. The commission also modified the minimum routine schedule for temporary modifications public rulemaking hearings from annually to biennially. The commission expects that proponents of temporary modifications will supply annual updates for all temporary modifications to the division, which the division will review to ensure that temporary modifications are still justified and timely progress is being made to resolve uncertainty. However, formal temporary modifications public rulemaking hearings will only occur routinely on a biennial basis. The need for a public rulemaking hearing in off years will be assessed after updates are received and hearings can be scheduled as needed.
Section 31.9 was reorganized slightly for clarification. The commission also added a new section (31.9(4)(ii)) that clarifies how numeric and narrative operative values for temporary modifications should be implemented in permits. Where a permit is issued for an existing discharge to a waterbody where a temporary modification applies, whether numeric or narrative, permit effluent limits applicable under the term of the temporary modification should be developed to ensure that, at a minimum, status quo is maintained.
Additionally, the commission removed the statement at 31.9(4) that specified that "The Division, where necessary and within a reasonable period of the expiration of a temporary modification, shall reopen any permit for a discharge to that segment and include a permit condition to attain limits based on the underlying standard". This was removed because it does not reflect current permitting practices.
The commission also added language at 31.9(4)(iii) to reemphasize that inclusion of low cost optimization in permits, which includes activities such as pretreatment, source identification, and evaluation of source control and treatment options, is authorized and may be an effective permitting tool for ensuring that effluent quality is maintained at the best level reasonably achievable without requiring significant investment in facility infrastructure under the term of the temporary modification, as well as resolving uncertainty regarding the extent to which ambient conditions resulting from the effluent in question are reversible.
Finally, the commission revised the language in 31.9(4) that pertains to implementation of temporary modifications for expanding and new discharges. The commission added clarification that, when considering expanding discharges to a waterbody where a temporary modification applies, permits should not only protect downstream uses, but unless specifically decided otherwise by the commission, should, at a minimum, ensure that status quo is maintained. The commission revised the expectations for permits for new discharges to waterbodies where temporary modifications apply from establishing limits that protect downstream uses to establishing limits based on the underlying standard, unless the commission has established a specific limit or value for new dischargers for a particular temporary modification or set of modifications. An example of such a case is the operative value assigned to new discharges by the commission for arsenic temporary modifications, which also considers arsenic control and treatment limits. This revision for new discharges aligns with the commission's intent at 31.53(IV), which states that "Specifically, the Commission added references to "existing discharges" to clarify that effluent limits based upon temporary modifications only apply to existing discharges, and that effluent limits for new and expanded discharges must generally be set to the underlying standard." The commission considers division Policy 13 Permit Implementation Method for Narrative (Current Condition) Temporary Modifications to be consistent with this regulatory revision.
VIII. CLEANUP, CORRECTIONS, AND CLARIFICATIONS
The commission added additional instructions for using the chloride-based nitrite standards for aquatic life in Table II Footnote 3 at 31.16 to clarify that sensitive fish species include salmonids, channel catfish, logperch and brook stickleback. The "sensitive species" are defined in the 1986 Nitrogen Cycle Committee of the Basic Standards Review Task Force document. This footnote was also edited to clarify that either total or dissolved chloride data may be used in these equations. About half of the available chloride data in Colorado is reported as "total" and the remainder is reported as dissolved. Whether or not a sample was filtered should not impact the concentration of chloride, because chloride is completely soluble at concentrations well above 40 mg/L. As more nitrite data become available and nitrite standards are assessed and implemented more frequently, it is expected that there may be more interest in adopting the equation-based standards from Regulation No. 31 in the basin tables on a site-specific basis. The proposed clarifying edits are intended to make this option as straightforward as possible.
The following changes were made to the hardness-based table value standard equations in Table III at 31.16 to improve compatibility with Excel:
* Acute and chronic aluminum, chromium III, copper, lead, manganese, nickel, silver, uranium, and zinc: the first bracket was replaced with the symbol * and the second bracket was deleted from the equation.
* Chronic aluminum: a missing parenthesis was added to the end of the equation.
* Acute and chronic lead: brackets and an extra parenthesis were deleted from the conversion factor in the equation.
* Acute silver: 1/2 was replaced with 0.5* in the equation. These changes were also made in Regulation Nos. 32-38.
The commission revised the footnote to the Radionuclide Standards table (Table A) in 31.11(2) to state that all of the radionuclide standards listed should be applied as chronic 30-day average health-based standards. Colorado's radionuclide standards (with the exception of americium 241) were adopted in 1979 using the 1976 National Interim Primary Drinking Water Regulations, which included maximum contaminant levels for radionuclides that are based on annual dose exposures and maintaining a body burden below harmful levels. In 1996, revised plutonium and new americium standards were adopted with the footnote specifying that they are 30-day averages. However, because all of the radionuclide standards in Table A are based on long-term risk exposure assumptions, the footnote was modified to specify that all should be implemented as chronic 30-day average standards.
31.16 Table II: (acute) was added to the agriculture nitrate standard and (chronic) was added to the asbestos standard to clarify the durations of the standards.
31.16 Table III: The word "chronic" was added to the column headers for the Agriculture, Water + Fish, and Fish Ingestion standards, and the phrase '30-day' was removed from cells in those columns to clarify the durations of the standards.
31.16 Tables II and III: In columns that include both acute and chronic standards, the duration is noted in the cell with each standard. To clarify the duration of the standards, the phrase "1-day" was replaced with "acute" and the phrase "30-day" was replaced with "chronic".
Footnote 6 was added to Table II and Footnote 18 was added to Table III at 31.16 to clarify that fluoride, asbestos, antimony, barium, beryllium, and thallium standards should be applied on a site-specific basis in accordance with 31.7(1)(b) and 31.7(2). Since their initial adoption, these standards have not been adopted broadly into the basin regulations (Regulation Nos. 32-38), and the footnote was included to encourage adoption of protective criteria, where appropriate.
The sulfate standard at 31.11(6)(ii) and in Table II at 31.16 was edited to clarify that the standard applies to dissolved sulfate concentrations. This change was also made in Regulation Nos. 32 38. As an ion, sulfate is found in water only in the dissolved state; therefore, either unfiltered or filtered samples may be used to determine sulfate concentrations. In addition to clarifying that sulfate is a dissolved parameter, Footnote 7 was added to Table II to clarify that sulfate can be assessed and implemented using data from unfiltered or filtered samples.
The commission revised the term "total" in Table III and the associated Footnote 6 to the term "total recoverable" mercury to align with the basin regulations and clarify the confusion caused by the use of two different terms that refer to the same fraction of mercury. The term currently used to describe the mercury standard in Table III is "total" to denote that the standard is based on all forms of mercury, not just methylmercury. It is also meant to denote that the standard is based on the "total" (unfiltered) fraction, rather than dissolved (filtered) fraction of mercury. However, in the basin regulations (Nos. 32-38), the term "total recoverable" is used to refer to the same fraction and all forms of mercury.
The term "total recoverable" comes from the analytical protocols used to analyze heavy metals, including mercury, and requires a pre-digestion step. This pre-digestion step does not provide quantification of any additional fraction of mercury in the sample. It simply serves as a sample preparation step for high turbidity samples to facilitate determination of mercury (all forms) present in the sample. Although both "total" and "total recoverable" terms are used in the literature to define results from analytical methods that include a pre-digestion step of unfiltered samples, "total recoverable" is technically the more correct term.
The commission also revised Table III Footnote 6 to clarify that mercury data analyzed and reported as "total" or "total recoverable" using EPA approved total mercury analysis methods listed in 40 CFR 136.3 are considered equivalent.
The commission revised Table III Footnote 5 to improve the clarity of the footnote, which directs the implementation of the trivalent (III) and hexavalent (VI) chromium standards when data for the individual valence states are unavailable. Chromium data are infrequently reported for chromium III and chromium VI individually. Instead, data are typically reported as the total of all valence states of chromium present in the sample. This is primarily due to the difficulty of accurately measuring chromium III concentrations and the instability of chromium when the sample is acidified for analysis of the total recoverable fraction. While chromium III and chromium VI are the valence states most often found in natural waters, chromium is unstable and can convert between forms in water and in the bodies of humans and aquatic life. However, chromium VI is more water soluble and a known carcinogen. Depending on the classified use, the chromium VI standards are the same as or more stringent than the chromium III standards (Table III). Therefore, when data for individual chromium species are unavailable, the use of the chromium VI standards to assess data reported as total chromium (i.e., the total of all valence states of chromium) will ensure protection of human health and aquatic life. In addition, Footnote 5 was modified to clarify that neither the sum of the concentrations of chromium III and chromium VI (when reported individually) nor the total chromium concentration (i.e., the total of all valence states of chromium) should exceed the Water Supply standards of 50 µg/L for chromium III and chromium VI in water bodies with a Water Supply use classification. This change was also made in Regulation Nos. 32-38.
The commission revised the definition of existing quality for temperature at 31.5(20) to distinguish between the calculations used to determine standards attainment and the calculations used in permits implementation. Standards attainment in the context of 303(d) assessment allows for a short duration of temperature exceedance as defined by the biological warming event in units of degree-days and was developed in the 2017 303(d) listing methodology. The warming event and degree-days concept was added to Table I Footnote 5(c)(ii). Permits implementation requires ambient upstream temperatures in seasonal or monthly maxima to calculate effluent limits and for reasonable potential analysis.
The method for calculating permits implementation was developed in the 2016 Regulation No. 31 rulemaking hearing at 31.53(A) to incorporate an allowable exceedance frequency for monthly determination of effluent limits. This method is being added to the definitions section of Regulation No. 31 and clarified by adding "seasonal or monthly maxima" to make clear that permits has the flexibility to implement seasonal or monthly based effluent limits. The commission expects the division to continue to engage with stakeholders regarding permits implementation of temperature and explore whether the warming event assessment method may be considered in the permitting context through workgroups and other appropriate means.
'Table A' was added to the title of Radionuclide Standards at 31.11. 'Table B' was added to the title of Basic Standards for Organic Chemicals at 31.11.
The following edits were made to improve clarity and correct typographical errors:
* The word "frequent" was removed from the definition of primary contact recreation at 31.5(33) to better reflect the commission's past practice. This change also aligns with E. coli's exposure risk assumptions and EPA's definition of primary contact recreation in the federal Recreational Water Quality Criteria.
* Letter references to 31.16(3) in Table I and Table II were changed to superscript to improve clarity and consistency.
* In order to reflect a previous change to the Stream Classifications and Water Quality Standards Tables, the reference to the 'Temporary Modifications and Qualifiers' column at 31.7(3) was replaced with language that specifies the presence of a temporary modification will be indicated in the appropriate water quality standards basin regulation.
* All variations of E. coli were edited to display a consistent format throughout the regulation. This change was also made in Regulation Nos. 32-38.
* References to "tot.rec." in Table III were replaced with "total recoverable". References to "dis" were replaced with "dissolved".
* Footnote 1 to Table II was modified to clarify that the "T" in the chronic ammonia equations stands for temperature. This change was also made in Regulation Nos. 32-38.
* The fluoride Water Supply standard in Table II included a reference to Footnote 3, which is the nitrite footnote. This reference was deleted to correct a previous error.
* Footnote 19 was added to Table III to provide clarity regarding the application of the chronic(trout) equation for silver.
* Tables and footnotes were formatted for consistency and clarity.
* Other minor edits were made to improve clarity and consistency.
