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 1002-31.45 - STATEMENT OF BASIS, SPECIFIC STATUTORY AUTHORITY AND PURPOSE: January 2007 Rulemaking Hearing; Final Action February 12, 2007; Revisions effective July 1, 2007
Current through Register Vol. 47, No. 5, March 10, 2024
The provisions of sections 25-8-202(1)(b), 25-8-204; and 25-8-402, C.R.S., provide the specific statutory authority for adoption. The Commission also adopted, in compliance with section 24-4-103(4) C.R.S., the following statement of basis and purpose.
BASIS AND PURPOSE:
In this rulemaking, the Commission adopted new temperature criteria for Colorado's surface waters. The revisions to the regulation and definitions, revised table values and qualifiers, and revised implementation provisions. In this rulemaking, the Commission also adopted revisions to the basinwide temperature standards in Regulation Numbers 32 - 38.
Overview: As the Commission indicated in the 2005 Statement of Basis and Purpose, the basis of the original temperature standards had become unclear, the standards had been inconsistently applied in permits and there had been disagreements about how the attainment of these standards should be assessed. In adopting these revisions, the Commission has established criteria that are clear and can be consistently and fairly implemented by the Division. Section 31.14 was amended to establish general criteria to be followed by the Division in determining when effluent limits related to temperature are necessary in discharge permits. These criteria are intended to assure that effluent limits are imposed only when thermal discharges can reasonably be expected at a level such that the applicable standards would be threatened or exceeded.
Temperature standards will also be implemented in the context of determining attainment of standards in individual water bodies, for instance in the context of the biennial compilation of the "List of Impaired Water Still Requiring TMDLs" (the Section 303(d) List). Methods and process for determining of attainment of the temperature standards will be consistent with the Section 303(d) Listing Methodology as adopted by the Commission for that particular listing cycle.
Water Rights: Concerns have been raised regarding the potential impact of the proposed temperature criteria and standards on the exercise of water rights. The Commission included a reference to section 25-8-104, C.R.S. in the revised table value criteria. Section 25-8-104 states in part that "Nothing in this article [the Colorado Water Quality Control Act] shall be construed, enforced or applied so as to cause or result in material injury to water rights."
In cases where it is determined that the classified aquatic life use is adversely impacted by any pollutant, the Commission believes that it is appropriate to place the impacted segment on the Section 303(d) List. When a segment is placed on the 303(d) List for any reason, the Division (along with any interested parties) then investigates the source of the impairment. If the cause of non-attainment is deemed to be natural or irreversible man-induced, then a site-specific standard is appropriate. See Regulation 31.7 , 5 CCR 100-31, section 31.7 . In cases where a temperature standard exceedance is determined to be caused by the valid exercise of those water rights and the exceedance cannot be eliminated in a manner consistent with CRS 25-8-104, the Commission would consider that to be an irreversible man-induced condition, and thus would support adoption of a site-specific standard as provided in section 31.7(1)(b)(ii).
Similarly, Colorado's 401 certification regulation (Regulation No. 82.5(6)) provides that 401 Certification shall not be denied where the imposition of conditions or denial would result in material injury to water rights as prohibited under section 25-8-104, C.R.S. In such case, the Division, the project proponents, and any commenters are to examine and implement, where appropriate, any means to prevent, reduce, or mitigate water quality impacts identified during the permitting process and associated with the exercise of valid water rights. Where such means are found they may be included in the Division's certification determination. This process would apply to temperature standards in the same manner as other water quality standards.
Definitions: Definitions were added to section 31.5 for terms used in the context of revised temperature standards. Pre-existing definitions were renumbered.
Low-Flow Exemptions: Language was added to section 31.9 to clarify that for calculation of chronic temperature effluent limits for permits, a 7-day average low flow with an average once in three-year recurrence interval (7E3) will be used. This statistic is appropriate since the chronic temperature criteria (the MWAT) has a seven day averaging period and a once in three-year exceedance frequency.
New Temperature Table Values: One result of the 2005 Basic Standards hearing was a focused effort on developing a sound methodology, re-reviewing the laboratory-based temperature effect literature, and developing a new, more robust temperature database. The methodology for developing temperature criteria was the subject of an Administrative Action Hearing in April, 2006, that resulted in adoption of WQCC Policy 2006-1: Temperature Criteria Methodology. The Policy is intended as a general informational guide of the Commission's approach to the adoption of these criteria and standards. As stated in the Policy, it is not intended and should not be interpreted to limit any options that may be considered or adopted by the Commission in future rulemaking proceedings.
The new table values, adopted in this hearing, were developed using the laboratory-based studies of individual fish species' tolerance to elevated water temperatures. For each aquatic community, the tolerances were ranked and the 5th percentile was selected as the operative criterion, except in the case of coldwater aquatic life.
Cold Water Numeric Criteria: The cold water criteria were generated using laboratory generated thermal tolerance information for the following cold water species: Arctic grayling, brook trout, brown trout, cutthroat trout, mottled sculpin, longnose sucker, rainbow trout, and sockeye salmon. The lake trout and mountain whitefish are also present in Colorado, but insufficient thermal data were available to consider them in numeric criteria development. The fish species were grouped into two communities "Rivers and Streams" (all the species except lake trout and sockeye salmon) and "Lakes and Reservoirs" (see below). Other groupings, including east and west slope were investigated, however provided no significant difference in criteria. For "Rivers and Streams" the Policy 2006-1 methods, 5th percentile did not fully protect cutthroat trout (the most sensitive species). Since cutthroat trout are an ecologically important species in cold-water communities, and are the only native trout species in Colorado, the cold criteria were lowered to ensure full protection of that species. The Commission anticipates that as the Division and interested parties continue to collect thermal tolerance studies, the database will become more robust and these decisions will be revisited.
A specific large lake and reservoir category was created for lakes and reservoirs equal to or larger than 100 acres in size, which is consistent with CDOW's management regime where lakes and reservoirs are grouped into one of three size classes: < 100 acres, 100-500 acres, or > 500 acres. Lakes and reservoirs larger than 100 acres typically do not contain brook or cutthroat trout. The summertime criteria for this category are based on protection of rainbow trout. Site-specific standards can be applied to the few large lakes and reservoirs that do contain thermally sensitive fish, such as cutthroat trout, brook trout, sockeye or arctic grayling. The Commission believes that having two separate cold-water lakes and reservoirs standards will protect thermally-sensitive fish in their natural habitat and in small lakes and reservoirs where they may be stocked by CDOW while exempting larger lakes and reservoirs from overly restrictive temperature standards.
Warm water numeric criteria: The warm water numeric criteria were developed using laboratory-based temperature studies of fish species. As with development of the cold criteria, several community groupings were evaluated. With the current data, it was determined that criteria for four river and stream sub-classes and one lake class would be promulgated. The default "Rivers and Streams" criteria are based on information about the Arkansas darter, bigmouth shiner, black bullhead, bluegill, boneytail, brown bullhead, channel catfish, fathead minnow, golden shiner, green sunfish, hornyhead chub, longnose dace, orangespotted sunfish, plains killifish, plains minnow, plains topminnow, pumpkinseed, red shiner, roundtail chub, sand shiner, smallmouth bass, southern redbelly dace, speckled dace, spottail shiner, western mosquitofish, and yellow bullhead. The following species are also present in Colorado, but insufficient thermal data were available to consider them in numeric criteria development for rivers and streams: bluehead sucker, brassy minnow, Colorado pikeminnow, common carp, flannelmouth sucker, flathead catfish, flathead chub, freshwater drum, Iowa darter, quillback, Rio Grande chub, Rio Grande sucker, river carpsucker, smallmouth buffalo, and stonecat.
Three additional sub-classes (a, b, and c) of sensitive warm water species were created to protect thermally sensitive warm water species with similar thermal requirements or geographic distribution. Existing data for these species indicate that they are sensitive to chronic high temperatures, relative to other warm water fish. If these species were included with the other warm-water river and stream species, following Policy 2006-1, the resulting criteria are over protective for waters without these thermally sensitive species. Since the range of these species are known, the Commission decided that it was more appropriate and will provide flexibility to create a separate subclass rather than have interested parties outside the range of thermally sensitive species to have to go through the recalculation procedure. The Commission directs the Division to rely upon information from the Colorado Division of Wildlife for determining where thermally sensitive species are expected to occur at the site.
Where thermally sensitive species occur, or are expected to occur, the most protective applicable criteria will be used. Warm-water sensitive group a is the most thermally sensitive and includes the common shiner, Johnny darter, and orangethroat darter. The common shiner and Johnny darter specifically occupy the eastern slope transition zone. The orangethroat darter occurs only in the Republican River Basin. Warm-water sensitive group b includes only the razorback sucker that occurs on the west slope. Warm-water sensitive group c includes the brook stickleback, central stoneroller, creek chub, longnose dace, Northern redbelly dace, finescale dace and white sucker. The default warm-water table value will apply in segments that do not have, and are not expected to have, any of these thermally sensitive species.
The "Lakes and Reservoir" criteria are based on information about the bluegill, largemouth bass, northern pike, pumpkinseed, smallmouth bass, spottail shiner, striped bass, tiger muskellunge, walleye, white bass, and yellow perch. The following species are also present in Colorado lakes and reservoirs, but insufficient thermal data were available to consider them in numeric criteria development for lakes: black crappie, common carp, gizzard shad, sauger, wiper, and white crappie.
The Commission acknowledges that all of these fish species do not occur in all warm water locations. For instance, the white bass only occurs in east slope reservoirs, and channel catfish generally occur in warm water lakes, reservoirs, ponds, and moderate to large rivers. Neither of these may be appropriate in some locations on the western slope. However, rather than include all the combinations in Table 1, the Commission adopted table values for five subclasses. The revised regulation allows for refinement of criteria on a site-specific basis using the recalculation procedures in Policy 2006-1 without the burden of a Commission hearing. This provides the Division and interested parties the flexibility to develop site-specific solutions based on the species that are expected to occur at the site.
Occur at the Site: The Commission intends that the phrases "occur at the site" and "expected to occur at the site" have the same meaning as in WQCC Policy 2006-1 (see Section XII, Recalculation Procedures), and shall be determined on a site-by-site basis. The Commission requests that the Division consider further appropriate refinement of this concept in the development of implementation guidance, including but not limited to appropriate consideration of fish only temporarily present in transition segments.
Spawning/Reproductive Seasons: The Commission revised the provisions to protect spawning in order to broaden the consideration to all the reproductive functions. The consideration of reproductive season is to ensure that the thermal requirements for successful migration, spawning, egg incubation, fry rearing and other reproductive functions are met These particular life stages and behaviors warrant more protective criteria than those required for the young adult and adult life stages; however, there are many site-specific considerations. The Commission decided to provide protection for these life stages in combination with protection of seasonal patterns as discussed below.
Winter Criteria to Protect Reproductive Functions and Normal Pattern of Seasonal Fluctuation:
The original language of the temperature standard contained the requirement that "temperature shall maintain a normal pattern of seasonal fluctuation." This component is intended to preserve thermal cues necessary for protection of aquatic life cycles. After consideration of alternative means to protect seasonal patterns, the Commission chose an approach that links protection of the seasonal pattern with protection of reproductive functions. To this end the Commission added winter season table value criteria in Table 1. The default winter season for cold water river and streams was established from October to May, November to March for "not sensitive" cold water rivers and streams, and for warm water rivers and streams from December to February. The winter season for lakes and reservoirs for both cold and warm water was established from January to March.
Normal Pattern of Summertime Diel Fluctuation: The narrative provision contains the requirement that temperature shall maintain a normal pattern of summertime diel fluctuation. The addition of "summertime" represents a modification of the longstanding language in the Basic Standards. While it is clear that aquatic life need nighttime cooling during the summers, to allow recovery from daily afternoon high temperatures, it is not clear that this recovery period is necessary during the rest of the year. A single value to protect summertime diel fluctuation would not address the myriad site-specific conditions, and so the Commission is relying upon the narrative statement. The Division is directed to impose permit conditions where best professional judgment indicates such protection is necessary to protect the use.
Normal Pattern of Spatial Diversity: The narrative standard also contains the requirement that temperature shall maintain a normal pattern of spatial diversity. Spatial diversity is a concept that incorporates the importance of a distribution of conditions along the stream reach. Natural aquatic ecosystems have a range of temperatures available to organisms in microhabitats. This array of microhabitats makes it possible for a broader range of organisms and life-cycles to flourish in the aquatic system. Although spatial diversity is critical to a fully functioning aquatic community, the Commission does not see a way to quantify or define the lower threshold in regulation at this time. The Commission's intent is that the Division use its discretion to implement the narrative requirement for spatial diversity in situations where there is evidence that an activity does or will create spatial uniformity that will threaten or impair the aquatic life use.
Abrupt Changes / Thermal Shock: The thermal shock provisions were reviewed and revised. Even though there is a need to provide clear direction for implementation of the narrative prohibition of abrupt changes, the complexity of the phenomenon and the confusion over implementation indicate that Colorado is not yet ready for a numeric thermal shock criterion at this time. The Commission directs the Division to continue to explore means to protect aquatic life from anthropogenic thermal shock, with particular emphasis on an implementation strategy that is straightforward. The Commission expects to see a revised thermal shock proposal in the 2010 Basic Standards rulemaking proceedings. In the meantime, the Division is directed to impose permit conditions where best professional judgment indicates protection is necessary to protect the use from abrupt thermal changes.
Transition Zones: In 2005, the Commission adopted the cool water ("cw") qualifier to acknowledge that temperature regimes are a continuum and the transition between cold and warm is not abrupt. The Commission endorses recognition of the transition zone, but decided that rather than having separate criteria for the transition zone, it is more appropriate to wait for the results of the Aquatic Life Work Group's effort to propose refined aquatic life uses. To help assure a reasonable approach in the interim, the Commission believes that the flexibility provided by resegmentation, recalculation of standards at the time of permit renewal, and the tools available at 31.7(1) are adequate. On a case-by-case basis, appropriate standards can be established at the upper end of warm water segments and the lower end of cold water segments.
Implementation Overview: The Commission has identified an approach to the implementation of the temperature standards that attempts to strike a balance between:
(1) the goal of having temperature standards in place in Colorado that will protect beneficial uses of our surface waters, particularly for aquatic life; and
(2) the goal of minimizing the demands on internal and external resources in implementing temperature standards, in an effort to focus on instances where it is more likely that temperature may present a concern.
The Commission intends that implementation guidance will be developed by the Division to facilitate implementation of the narrative standard. However, the Commission does not intend that implementation of the new standard will be delayed pending finalization of such guidance.
Role of Numerical Temperature Criteria and Site-Specific Numerical Standards: The Commission has adopted numerical temperature criteria that have been included in Table I of these Basic Standards. These Table I criteria are established at levels that the record indicates will be generally protective of the beneficial use classifications. The Commission intends that the numerical table values will be used as the starting point for establishing segment-specific numerical standards for individual segments, while providing an opportunity for a demonstration that alternative site-specific standards are appropriate. Unlike pollutants that may occur at significant levels only rarely, such as beryllium or thallium, temperature is a parameter that can impact aquatic life in any waterbody. Therefore, the Commission anticipates that in the next round of triennial reviews, numerical temperature standards generally will be adopted for segments throughout the state.
Although the table value criteria adopted here will be used as the starting point for considering such standards, alternative site-specific standards may be appropriate. As outlined in the Basic Standards at section 31.7 , Ambient Quality-Based or Site-Specific Criteria-Based Standards may be adopted by the Commission. These situations include:
The Commission notes that the adoption of site-specific standard may require resegmentation in some instances, e.g. to appropriately match numerical standards with changes in species compositions. The Commission also notes that in the initial round of basin hearings considering site specific temperature standards, in circumstances where there is concern about whether table value criteria are attainable, but there is inadequate information available - e.g. regarding ambient temperature levels or expected species composition - the adoption of temporary modifications pursuant to section 31.7(3)(a)(iii) may be appropriate.
Attainment in Lakes and Reservoirs: The Commission determined that when a lake or reservoir is stratified, the average temperature in the mixed layer may exceed the temperature criteria provided that an adequate refuge exists in a lower level. Adequate refuge exists when the lower levels meet both the temperature and applicable dissolved oxygen standards.
If the temperature criteria is not met in the mixed layer, and there is no adequate refuge, the lake or reservoir may be included on the 303(d) list as impaired for dissolved oxygen rather than temperature. The Commission recognizes that dissolved oxygen standards are intended to apply to the epilimnion and metalimnion, while dissolved oxygen in the hypolimnion may be less than the criteria due to natural conditions, although no reductions in dissolved oxygen levels are allowed due to controllable sources. Reg. #31, § 31.16, Table 1, Footnote 9.
Implementation in Discharge Permits: The provisions in section 31.14 have been revised to provide clarification regarding how temperature standards are to be implemented in discharge permits. The Commission added language to this section to emphasize that the Division will impose temperature effluent limits in permits only when the thermal energy in the discharge presents a significant threat to the standards.
Two general provisions were added to section 31.14 that provide exclusions from the circumstances where the Division will establish effluent limitations for temperature. First, no temperature effluent limitation will be applied if a discharge is to an effluent-dependent stream and there is no evidence that the aquatic life use may be negatively affected by the discharge. The Commission has determined that this provision is appropriate since ephemeral streams have no continuous flow and limited associated aquatic life, such that no adverse impact to aquatic life is anticipated.
Second, no temperature effluent limitation will be applied to a discharge of water from a natural hot spring, provided that the discharge is in the vicinity of the hot spring's natural outflow. The Commission determined that discharges of natural hot springs water do not have reasonable potential to cause significant adverse temperature impacts because the hot springs would flow directly into rivers and streams as natural heat sources if they were not diverted and used. A discharge will be considered to be "in the vicinity" of the natural outflow if it is to the same stream that would have received the hot springs flow under natural conditions and in the same general area that would have been affected by the natural flow of the hot springs.
For discharges that are not excluded by these two general provisions, the Division will conduct a reasonable potential analysis, to identify discharges with a potential to cause significant adverse temperature impacts. If this analysis shows that there is no reasonable potential for such impacts, no temperature effluent limitations will be established.
During the rulemaking hearing, there was consideration of an exclusion from temperature effluent limitations where it is determined that a discharger:
The Commission agrees that it is generally appropriate to exclude this class of dischargers, including, e.g., many municipal wastewater treatment plant discharges, from temperature effluent limitations based on the Commission's conclusion that this group poses a relatively low risk of causing adverse temperature impacts to aquatic life uses. Such an exclusion would not apply to discharges that have not been in place long enough to provide a substantial "track record" , discharges (such as power plants) that cool heated water prior to discharge, discharges that frequently exceed the default values in Table 1, and discharges on segments that have been identified as impaired for aquatic life. Rather than include this exclusion in the Basic Standards Regulation, the Commission has directed that the Division include an exclusion such as this as part of its reasonable potential guidance. In such guidance, the Division would retain the authority to determine, pursuant to a reasonable potential analysis, that individual discharges that meet the criteria of this provision nevertheless pose a risk of thermal impact to aquatic life that warrants the inclusion of effluent limits in a permit.
The Commission decided not to adopt an exemption from temperature limits for discharges covered by general permits as requested by the Colorado Rock Products Association. The Commission found that there was not adequate information to provide a blanket exemption for the several classes of discharges covered by general permits and that the need for temperature limits for these operations is appropriately determined during the permitting process. However, the Commission assumes that there may be several categories of discharges covered under current general permits that pose no threat to temperature standards, particularly those discharges for which there is a fair amount of dilution in the receiving water. Therefore, the Commission expects the Division to identify those classes of activities covered by general permits for which temperature is not a pollutant of concern and/or conduct a "class-wide" reasonable potential analysis to confirm whether temperature limits may be required.
Where a reasonable potential analysis determines that there is a potential to cause significant adverse temperature impacts, several results are possible. Barring information suggesting that an alternative result is appropriate, the Division will establish permit effluent limitations for temperature using the applicable temperature standards (either the basin-wide temperature standards that are listed at the beginning of each basin regulation or site-specific temperature standards that have been adopted). If the Division or a discharger believes that the effluent limitations resulting from such standards do not provide the appropriate level of temperature protection in a particular instance, three options are available.
First, the Division or a discharger may bring forth the results of a site-specific recalculation procedure analysis that supports variation from the applicable standards. As noted above, the recalculation procedure would need to be completed in a manner acceptable to the Division. An acceptable procedure is set forth in the Temperature Criteria Methodology, Policy 2006-1. This demonstration can be made at the time of permit application or for a standards hearing. When conducted as part of the permit renewal, the resulting recalculated standard should then be considered for formal adoption in the next regularly-scheduled basin-wide water quality standards rulemaking hearing or in a separate site-specific rulemaking, as determined appropriate by the Commission.
Second, a discharger could request a "section 316(a) waiver" , in accordance with the provisions added to section 31.14 . This procedure has been established consistent with the provisions of the federal Clean Water Act and EPA's implementing regulations, to allow a discharge-specific waiver based on a showing that alternative effluent limitations will be protective of the classified aquatic life use. This provision applies to both domestic and industrial dischargers. The Commission anticipates that in the future, Regulation No. 61 may be revised to provide added detail regarding the requirements of this provision.
Third, the Division or a discharger may request that the Commission adopt a site-specific numerical or narrative standard that differs from the applicable temperature standard where it can be demonstrated that the alternative standard provides an appropriate level of protection of the classified aquatic life use. The showing required for this option would be similar to that for a section 316(a) waiver, except that the result would be a water quality standard that applies to a water segment as a whole, rather than a discharger-specific effluent limitation waiver. Such a standard could be considered in a regularly-scheduled basin-wide water quality standards rulemaking hearing or in a separate site-specific rulemaking, as determined appropriate by the Commission.
For discharges to lakes and reservoirs, since the location of the refuge cannot be predicted, the Division should develop permit limits assuming the appropriate temperature standard is in effect for the entire mixed layer. The daily maximum was retained to facilitate permitting thermal discharges to lakes and reservoirs.
Implementation in the Section 303(d) Listing Process: With respect to implementation in the section 303(d) listing process, the Commission will hold an Administrative Action Hearing in May 2007 to consider approval of the Listing Methodology for the development of a 2008 Section 303(d) List. The Commission's intent is that this Listing Methodology will provide that a segment's thermal condition will be evaluated based on the basin-wide temperature standards that are listed at the beginning of each basin regulation until such time as segment-specific standards are adopted in the course of the regularly scheduled triennial reviews or in a separate site-specific hearing.
Ongoing review and refinement: The Commission acknowledges that this temperature criteria and standards rulemaking has not answered all the questions regarding appropriate temperature standards for Colorado's waters and their applicability and implementation. More work needs to be done and as the Division and other interested parties gain experience with these provisions, the Commission anticipates that refinements to the system will be necessary. In particular, the Commission expects to see the results of the following in the course of the 2010 Basic Standards Rulemaking.
- Review and revision of Table Value criteria in recognition of newly available data.
- Consideration of numeric thermal shock provisions.
- Refined thinking regarding application of temperature standards to ephemeral and intermittent streams as they dry up.
- Reconsideration of how temperature standards are applied to transition zones.
- Review and reconsideration of the averaging period for the daily maximum.
PARTIES TO THE RULEMAKING HEARING
