5 Colo. Code Regs. § 1002-36.51
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
Pursuant to the requirements in the Basic Standards (at 31.7(3)), the commission conducted its biennial review of the status of all temporary modifications to determine whether the temporary modifications should be modified, eliminated, or extended.
There are currently no temporary modifications for standards other than arsenic.
The Water Quality Control Division (division) provided an update to the commission on progress being made in implementing its plan to resolve uncertainty for the chronic arsenic temporary modification. This temporary modification applies to segments with an arsenic standard of 0.02 µg/L (to protect the Water + Fish use) and dischargers with demonstrated or predicted water quality-based effluent limit (WQBEL) compliance problems. The temporary modification was first adopted in 2011 (38.79), adopted more broadly throughout the state in 2013 (36.33), and extended in 2019 (36.44) to expire 12/31/2024.
Based on evidence that met the 31.7(3) requirements to support extension of temporary modifications, the commission extended the temporary modification by five years, to expire 12/31/2029. No changes were made to the temporary modification operative values at 36.6(2)(c). Therefore, for discharges existing on or before 6/1/2013, the temporary modification remains at As(ch)=current condition and numeric effluent limits will be implemented by the division using the division's Clean Water Policy 13, Permit Implementation Method for Narrative (Current Condition) Temporary Modifications. For new or increased discharges that commence(d) on or after 6/1/2013, the temporary modification remains at 0.02-3.0 µg/L (total recoverable).
To support this extension, the division demonstrated continued instream non-attainment of the underlying standard and demonstrated or predicted WQBEL compliance problems with permit limits based on the underlying standard. The division also demonstrated the need for additional time to resolve the remaining uncertainty regarding the appropriate arsenic standard to protect the use and the extent to which existing quality is the result of natural or irreversible human-induced conditions.
The division provided a revised, multifaceted plan to resolve uncertainty (division Prehearing Statement Exhibit F-5) that included details regarding ongoing investigations and information needed to resolve the uncertainty and derive a revised standard by 12/31/2029. The plan includes: evaluating results from the division's 2020-2023 field study to investigate the proportion of inorganic (versus total) arsenic in the tissue of fish collected from Colorado waters; deriving a Colorado-relevant bioaccumulation or bioconcentration factor for arsenic; characterizing ambient levels of arsenic statewide; gathering facility data for permittees discharging to temporary modification segments and collection of additional arsenic effluent data to better understand the extent of arsenic compliance issues throughout the state; conducting outreach regarding progress on standards revisions; and awaiting the finalization of EPA's Integrated Risk Information System (IRIS) toxicological assessment for arsenic.
Consistent with the requirements of 31.7(3), the division will also provide annual updates on progress related to the temporary modification and the commission will review this progress as part of the biennial reviews of the temporary modification and include efforts from other states. Additionally, the division will pursue avenues of outreach to engage relevant stakeholders, including, but not limited to, the division's Water Quality Roadmap Workgroup quarterly meetings, Feasibility and Implementation subgroup meetings, Technical Advisory Committee meetings, permit webinars, or other relevant stakeholder meetings as needed. In addition, the division will consult with the department's Toxicology and Environmental Epidemiology Office to ensure consideration of impacts to human health statewide is thoroughly evaluated. Additionally, input from potentially impacted Coloradans is essential, especially when considering the disproportionate impacts in some communities from arsenic along with other environmental stressors.
The division will continue implementing permit requirements to gather targeted data from facilities benefiting from the arsenic temporary modification. Effluent arsenic concentration data from facilities throughout the state demonstrate that many facilities will likely have issues meeting effluent limits based on the anticipated revised arsenic water quality standard to protect human health. As a result, there continues to be a widespread need to make progress in understanding sources of arsenic and options for source control and treatment. To ensure such progress is made, when implementing the "current condition" temporary modification in permits, the division will continue to include additional permit Terms and Conditions (T& Cs; division Consolidated Proposal Exhibit F-6 (FINAL)), which may include requirements for additional monitoring, source identification, characterization of source control and treatment options for reducing arsenic concentrations in effluent, and implementation of reasonably achievable effluent quality improvements to control sources of arsenic or reduce arsenic effluent concentrations. Although not required per 36.6(2)(c), new or expanding dischargers are also encouraged to implement the T&Cs.
In 2013, a value of 3 µg/L was identified by the commission as a "reasonable technologically achievable value for arsenic" that could be used as a point of reference until the uncertainty in the underlying standard is resolved. This value is also used as the temporary modification operative value for new or expanding facilities and as a value to categorize facilities for implementation of permit T&Cs. However, it is important to note that arsenic treatment feasibility can vary from facility to facility and is a topic that requires further investigation by the division, dischargers, and stakeholders. In addition, the future revised arsenic standard is anticipated to be at least as stringent as the current standard of 0.02 µg/L. Therefore, when evaluating arsenic treatment options, facilities are encouraged to investigate options that will reduce arsenic as low as possible and not assume 3 µg/L is the limit of technology in all cases. The commission recognizes that various factors, such as influent concentration, financial capacity, and influent competing ions, affect the effluent quality that is feasible for individual facilities to achieve.
The commission recognizes that, while arsenic occurs naturally in soil, sediment, and groundwater, there are also man-made sources of arsenic and anthropogenic activities can increase concentrations in the environment.Additionally, arsenic conditions may vary from watershed to watershed, and the relative contributions of point and nonpoint sources may be an area of further study to determine if conditions can be improved by means other than treatment, including source identification and controls. An additional practical consideration is the challenge related to laboratory analysis of arsenic at very low concentrations; specifically, sufficiently sensitive analytical methods to detect arsenic at very low levels such as 0.02 µg/L are not currently available. Thus, the certainty we have when identifying sources of arsenic is limited by the sensitivity of current analytical methods and arsenic may be not detected in water even though the standard has been exceeded. The division will routinely evaluate whether any advances in analytical capabilities have been made, and will provide updates to the commission as information becomes available.
Since 2020, T&Cs have been implemented in some permits that were reissued or modified. To ensure progress continues, when permits that already have the T&Cs are next reissued or modified, additional T&Cs may be added, such as implementation of reasonably achievable effluent quality improvements to control sources of arsenic or reduce arsenic effluent concentrations. Ultimately, the additional T&Cs will benefit facilities by requiring initial steps towards arsenic reduction during the temporary modification. By beginning preliminary investigations while the temporary modification is in place, facilities will have more time to plan for future permit limits, data to inform selection of source reduction and/or treatment options, evidence to identify appropriate future regulatory pathways, and data to assist the division and facilities in resolving the uncertainty for arsenic per 31.7(3)(a)(iii)(B). The additional T&Cs are consistent with the commission's rule at 31.9(4)(a)(iii), are reasonable, and will not cause undue economic burden for facilities. These requirements will ensure that progress is being made toward future attainment of the underlying standards and protection of the classified uses.
Arsenic is a known human carcinogen (e.g., of the bladder, lung, skin, liver, and colon) that is present at levels of concern in many Colorado waterbodies that are classified as water supplies. Despite the human health risks posed by arsenic, the commission has adopted arsenic temporary modifications since 2011 (38.79) to allow for feasible discharge permit requirements while the uncertainty regarding the standard necessary to protect the Water + Fish use and the extent to which arsenic levels are irreversible is resolved.
However, the commission's intent is for temporary modifications to be temporary; in 2021, the commission adopted rule changes at 31.7(3) and 31.9 to "better ensure that temporary modifications are adopted only when necessary and eliminated in a timely manner" (31.59(VII)). For example, the changes require a detailed, site-specific approach expected to result in sufficient information to resolve each type of uncertainty within the term of the temporary modification. Accordingly, the commission's intent is that the division and dischargers prepare for implementation of WQBELs following expiration of the temporary modifications on 12/31/2029. It is important for facilities to determine the degree to which effluent quality can be improved and on what timeline the improvements can be achieved.
The commission is determined that Colorado's temporary modification program will be a tool that encourages and facilitates progress, and not an impediment to achieving water quality improvements. Successful and timely implementation of all components of the Clean Water program is required by state and federal laws, and is necessary to assure continued EPA approval of Colorado temporary modifications.
The commission reviewed the basis, available information, and progress toward achieving the alternative effluent limits (AELs) and implementing Pollutant Minimization Program (PMP) for the discharger-specific variance (DSV) in Regulation No. 36.
The commission also adopted non-substantive revisions to the format of this DSV in Section 36.6(6) to provide clarity.
Alamosa River/La Jara Creek/Conejos River Segment 12 (CORGAL12): There is currently a DSV for acute nitrate, which is implemented as acute total inorganic nitrogen (TIN), and applies to the Town of La Jara (CO0020150; DSV expires 12/31/2025). See section 36.48(B). The commission reviewed La Jara's progress toward achieving the AELs, La Jara's most recent economic feasibility data, and alternatives analysis from 2022. The commission determined that the AELs continue to represent the highest attainable water quality that is feasible for La Jara to achieve. Therefore, the commission determined that the DSV is still appropriate and does not require revision at this time.
La Jara will continue to implement its DSV and revised pollutant minimization program (PMP) (division 2024 Prehearing Statement Exhibit H-4). The revised PMP includes improvements to the collection system, conducting an alternative analysis for TIN treatment, and monitoring treatment progress through regular progress reports. The commission will next review and reevaluate the DSV prior to its expiration on December 31, 2025. The commission expects that La Jara will submit annual reports to the division describing the progress made on DSV implementation until the end of the DSV and engage with the division and interested stakeholders in the years leading up to the expiration of the DSV regarding whether compliance with WQBELs (calculated from the underlying standards) are feasible for the city, or if the city plans to propose a subsequent DSV.
Site-specific criteria-based standards are adopted where alternate criteria are shown to be protective of the classified uses. Site-specific ambient-based standards are adopted where natural or irreversible human-induced conditions result in pollutant concentrations that exceed table value standards. Feasibility-based ambient standards are adopted where water quality can be improved, but not to the level required by the current numeric standard. Information is currently being gathered to better understand the basis of all existing site-specific standards and determine what information is needed to review each standard in future basin reviews. The commission made no revisions to any site-specific standards at this time.
The commission reviewed the Aquatic Life, Recreation, Water Supply, and/or Agriculture use classifications and standards applied to each segment to determine if the appropriate use classification(s) and full suite of standards necessary to protect each use applies. The commission did not adopt any changes at this time.
As part of the triennial review process, the commission must decide whether to adopt EPA's Clean Water Act 304(a) criteria recommendations (division Prehearing Statement Exhibit A). 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.
The following edits were made to the regulation and Appendix 36-1 to improve clarity and correct typographical errors:
* The segment descriptions in Appendix 36-1 were reviewed and minor revisions were made to several segments to correct grammar, punctuation, and typos, improve sentence structure, and add details to increase accuracy of the description.
Rio Grande: 4b, 15, 18, 20b, 21a, 21b, 30, 31, 35
Alamosa River/La Jara Creek/Conejos River: 2, 9, 10, 21
Closed Basin - San Luis Valley River Basin: 2b, 11
* The segment description of Rio Grande Segment 16 (CORGRG16) was revised to remove the statement "excluding the specific listing in segment 12". This exclusion is unnecessary, as CORGRG16 contains tributaries to the Rio Grande, while CORGRG12 contains a portion of the mainstem of the Rio Grande.
* To be consistent with other segment descriptions, wetlands were added to the descriptions of the following segments:
Rio Grande: 7
Alamosa River/La Jara Creek/Conejos River: 2, 21
Closed Basin - San Luis Valley River Basin: 2b, 11
* Existing site-specific temperature standards were reformatted in the Appendix 36-1 tables to provide clarity and consistency for the following segments:
Rio Grande: 21b
Closed Basin - San Luis Valley River Basin: 12b, 19
* The aluminum standards for CORGAL03a, CORGAL03b, CORGAL03c, CORGAL03d, and CORGAL08 were clarified to show they are total recoverable "Aluminum(T)". These aluminum standards are site-specific standards and are based on the total recoverable fraction.
5 CCR 1002-36.51