5 Colo. Code Regs. § 1002-32.72
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 (32.51), and extended in 2019 (32.63(B)) 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 32.6(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 32.6(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.
There are three discharger-specific variances (DSVs) in Regulation No. 32. Because the commission reviewed these DSVs in October 2023 (32.71(A)), there was not a need to review them as part of this triennial review.
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.
While the commission made no revisions to any site-specific standards in this rulemaking hearing, a review of the site-specific standards on three specific segments in Regulation No. 32 was conducted to meet longevity plan requirements.
Upper Arkansas River segments 8a, 8b, and 9 (COARUA08a, COARUA08b, and COARUA09): Resurrection Mining Company (Resurrection) provided an update to the commission on the results of implementing its longevity plan for the site-specific cadmium and zinc standards on Upper Arkansas River segments 8a, 8b, and 9. When these site-specific standards were adopted by the commission in 2019, a longevity plan was included that required Resurrection to provide information to facilitate the commission's review of the standards in future triennial reviews (32.63(A)). Resurrection is successfully implementing its longevity plan and the commission made no changes to the plan or site-specific standards at this time.
The longevity plan requires Resurrection to determine if recent cadmium and zinc toxicity studies are available that should be used to recalculate the site-specific standards. Resurrection conducted a comprehensive literature review and discussed the results with the division, CPW, and EPA. While new toxicity studies were found, there was little to no change to the standards when the new studies were included in the site-specific cadmium and zinc toxicity databases and calculations. Therefore, no changes were proposed. The longevity plan also requires Resurrection to report on the chemistry and volume of any discharges to Iowa Gulch pursuant to Resurrection's discharge permit. Because there have been no discharges since the site-specific standards were adopted, there was no need to conduct follow-up sampling to evaluate whether instream chemical, physical or biological conditions have changed. Consistent with its longevity plan, Resurrection will provide another update in advance of the next Regulation No. 32 triennial review (currently planned for 2028).
In addition, the commission adopted new site-specific standards for temperature on one segment:
Middle Arkansas River Segment 2 (COARMA02): The commission adopted site-specific ambient-based temperature standards for Middle Arkansas Segment 2 for July through December. Ambient quality-based standards are adopted where a comprehensive analysis has demonstrated that elevated existing water-quality levels are the result of natural conditions or are infeasible to reverse, but are still adequate to protect the highest attainable use. The commission recognized that it is not feasible for this segment to attain the Cold Stream Tier II (CS-II) table value standards in all months of the year due to the irreversible thermal effects of Pueblo Reservoir and Dam. Prior to the construction of Pueblo Dam, this section of the Arkansas River was populated entirely with warmwater fish species. Due to cool water releases from Pueblo Dam, the Arkansas River below Pueblo Dam now supports populations of rainbow trout, brown trout, and longnose sucker, in addition to warmwater species.
The Arkansas River downstream from Pueblo Reservoir exceeds CS-II temperature standards from July through December. Water from Pueblo Dam is released to the Arkansas River from deep in the reservoir. The water released from the dam is cooler than the natural water temperature in the Arkansas River in the summer (but not cold enough to attain CS-II standards) and warmer than the natural water temperature in the Arkansas River in the fall and winter. The thermal impact of CPW's Pueblo Hatchery was evaluated and determined to be minor, with a median thermal impact of +0.06 °C and a maximum thermal impact of +1.34 °C. CPW did not identify any other measurable sources of anthropogenic heat loads to Segment 2.
The adopted site-specific standards are a combination of ambient-based upstream of the hatchery (Upper Reach) and modeled ambient-based below the hatchery (Mid Reach and Lower Reach). The Upper Reach site-specific standards are based on measured temperatures between the dam and hatchery outfall, while the Mid Reach and Lower Reach site-specific standards were developed using a heat-load model that fully subtracts the thermal effects of the Pueblo Hatchery downstream of the hatchery outfall.
To capture the spatial and temporal gradient of ambient temperatures in the segment, the commission adopted monthly site-specific standards (for July through December) and defined assessment reaches at 32.6(4). The Upper Reach is defined as the Arkansas River from Pueblo Dam to the Pueblo Hatchery outfall and the standards are based on data from the USGS gage ARKPUECO and upstream of the Pueblo Hatchery. The Mid Reach is defined as the Arkansas River from the Pueblo Hatchery outfall to the end of the hatchery's mixing zone (38.264213, -104.708524) and the standards are based on data from the end of the Pueblo Hatchery mixing zone. The Lower Reach is defined as the Arkansas River from the end of the hatchery mixing zone to the confluence with Wildhorse/Dry Creek Arroyo, and the standards are based on data from sites near the Valco Ponds and Wildhorse.
All available data on temperature, hydrology, hydro-modification, canopy cover, groundwater influence, point and nonpoint thermal sources, and other relevant information were reviewed to develop these site-specific standards. Some of these factors are implicitly included in the heat-load model using actual downstream data, while others, such as the hatchery impacts, are explicitly modeled.
Temperature data collected at any location within the applicable reach is suitable for assessment of the standards of that reach. The site-specific standards should be assessed using a typical 1-in-3 year allowable exceedance frequency, consistent with 31.16 Table I Footnotes 5(a) and 5(b). Because the site-specific standards are ambient, and not biologically-based, the biologically-based "warming event" is not applicable for evaluating existing quality (31.5(20) and 31.16 Table I Footnote 5(c)(ii)). For permitting purposes, existing quality shall be determined consistent with 31.5(20) and the standards applicable to the reach where the discharge is located shall be used, as this is consistent with the protection of downstream waters.
The proposal was supported by a longevity plan, thermal modeling report, and temperature data collected at five locations. CPW will continue to monitor temperature and other factors as described in its longevity plan. CPW intends to provide updates at the Issues Scoping Hearings in 2027, 2032, and 2037, but may adjust this schedule if there is a need to revise the standards due to changes in the conditions or assumptions on which the site-specific standards are based.
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. Some segments assigned an Aquatic Life, Recreation, Water Supply, and/or Agriculture use classification were missing one or more standards to protect that use or the incorrect standards to protect the use were in place. The commission adopted revisions to standards for the following segments:
Upper Arkansas River: 14d (COARUA14d; full suite of aquatic life use standards); 14e (COARUA14e; acute and chronic ammonia standards for Aquatic Life); 14f (COARUA14f; full suite of Aquatic Life use standards)
Middle Arkansas River: 4d (COARMA04d; acute mercury standard for Water Supply); 11b (COARMA11b; chronic arsenic standard for Water + Fish); 15 (COARMA15; full suite of Aquatic Life use standards)
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 32-1 to improve clarity and correct typographical errors:
* The qualified discharger table at 32.5(4) was updated to accurately reflect the location of facilities in segments COARUA05a, COARUA14b, COARFO04c, COARFO04d, and COARFO04e. Permit CO0021181 (Fort Carson WWTF) was added to the table in COARFO04d. In addition, Permit COG589020 (Academy Water and San Dist WWTF) was deleted from the table, as this permit was terminated in 2021.
* The segment descriptions in Appendix 32-1 were reviewed, and minor revisions were made to several segments to correct grammar, punctuation, and typos, and improve sentence structure. The purpose of these changes was to improve clarity and consistency of the segment descriptions.
Upper Arkansas River: 1b, 2a, 3, 5a, 12b, 13, 14b, 15a, 15b, 21b, 29, 31, 33, 39, 41
Middle Arkansas River: 4e, 7b, 13b, 13c, 15, 18b, 25
Fountain Creek: 1b, 3b, 4d, 4e, 5a, 11
Lower Arkansas River: 3b, 5a, 5b, 5c, 6a, 8, 9a, 9b, 10, 18
Cimarron River: 1, 2
* To be consistent with other segment descriptions, wetlands were added to the descriptions of the following segments:
Upper Arkansas River: 6
Fountain Creek: 1b, 3b
Lower Arkansas River: 2c, 3b, 3c
* Existing site-specific temperature standards were reformatted in the Appendix 32-1 tables to provide clarity and consistency for the following segments:
Upper Arkansas River: 4a, 14c, 30
* The aluminum standards for COARUA11 and COARUA22a were clarified to show they are total recoverable "Aluminum(T)". While these aluminum standards were adopted as site-specific standards (see 32.24(11) and 32.28(4), respectively), they were based on information in the EPA 1988 304(a) aluminum criteria document, which was implemented in Colorado as total recoverable.
* The total copper standard for Lower Arkansas River Segment 3b (COARLA03b) to protect the Agriculture use was corrected from acute to chronic.
* The segment descriptions for Upper Arkansas River segments 13 and 14b (COARUA13, COARUA14b) were revised to remove an erroneous exception for Upper Arkansas River Segment 12b, which is upstream.
* The segment descriptions for Upper Arkansas River segments 15b and 25 (COARUA15b, COARUA25) were revised to include an exception for waterbodies in Middle Arkansas River Segment 1 to eliminate overlaps in segmentation.
* The segment description for Lower Arkansas Segment 8 (COARLA08) was revised to remove "lakes and reservoirs" from the description. Lakes and reservoirs were split from stream segments in 2013 to accommodate the addition of temperature standards. The correct segment for tributary lakes and reservoirs to Segment 8 is Lower Arkansas Segment 18.
5 CCR 1002-32.72