5 Colo. Code Regs. § 1002-31.44
The provisions of sections 25-8-202; 25-8-203; 23-8-204; 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:
This rulemaking hearing addressed a number of potential revisions to this regulation that were identified in the November 2004 issues formulation hearing. Many of the revisions proposed for this rulemaking and ultimately adopted by the Commission grew out of the efforts of the Colorado Water Quality Forum's Basic Standards Work Group, which provided important input to the Water Quality Control Division as it developed its proposals for this rulemaking. Each of the major revisions adopted by the Commission is addressed below.
The Commission added definitions for E.coli, effluent-dependent stream, effluent-dominated stream, ephemeral stream, existing quality and primary contact recreation. These definitions are discussed more below.
The Commission has revised section 31.5 by adding a subsection (18), which defines "ephemeral streams." Ephemeral streams are characterized by surface water and groundwater hydrology. To determine whether a stream is ephemeral, visual observation or a rain gage should be used to determine whether water is present for only a short duration following precipitation or snowmelt. If water is present for more than just a short duration, then the depth of the groundwater should be monitored. If the groundwater and flow are not connected, then the system is ephemeral.
There has been confusion regarding how acute standards are to be set where natural or man-induced conditions justify ambient standards. This section was clarified to state that acute site-specific ambient quality-based standards should be set at a level equal to the 95th percentile of the available representative data. This approach avoids debate over "outliers" yet characterizes the high levels that have been recorded.
The Commission revised sections 31.7 that address the conditions for granting a temporary modification, the duration of temporary modifications and the procedures for granting, removing or extending temporary modifications. The Commission also revised section 31.14 that addresses implementation of temporary modifications in discharge permits.
It is anticipated that this approach to temporary modifications will ensure that a more thorough consideration is given to the causes and sources of non-attainment before temporary modifications are proposed. In many cases, the appropriate way to address non-attainment of underlying standards will be through the TMDL program, not through adoption of temporary modifications. This may be particularly true where there are no point-source discharges.
Where the Commission determines that the TMDL program is the vehicle to address "the need for additional information regarding the extent to which existing quality is the result of natural or irreversible human-induced conditions or regarding the level of water quality necessary to protect current and/or future uses", no temporary modification shall be assigned. Non-attainment of underlying standards shall be addressed through Listing and prioritization of TMDLs.
In cases where there are point source discharges on such segments, decisions on temporary modifications will be made on a case-by-case basis and may include consideration of the parameter of concern, whether that parameter is present in the discharge, what are the other sources of the parameter, and what are the plans to either return the water to full attainment or determine what are the appropriate underlying standards.
The Commission has clarified its intent for the use of temporary modifications, including their duration. In establishing the duration of a temporary modification, the Commission will be focusing on the length of time required to determine the appropriate underlying standard.
Given this priority, the Commission adopted new subsection 31.14 . The Commission has provided latitude in this section for the Division to consider circumstances under which the permittee may not be able to comply with limits based on the underlying standard during the term of the permit (e.g. where a renewal permit would expire shortly after the underlying standard takes effect).
The Commission adopted subsection 31.14 to allow permittees, discharging to segments where temporary modifications have been adopted pursuant to subsection 31.7 , to focus their available resources on addressing uncertainty with respect to appropriate water quality standards. The Commission finds this to be appropriate and has determined that schedules of compliance directing permittees to identify and implement facility improvements are not required until the appropriate underlying standard is adopted. That way, permittees will be able to develop proposals for meeting underlying standards knowing the underlying standard that will have to be attained. In order to ensure that the underlying standard is attained in a timely manner, the Commission is requiring that the Division reopen permits within a reasonable period after its adoption. In this regard, permits should normally be reopened within six to nine months of the adoption of the underlying standard. However, the Commission intends that the Division have flexibility in its interpretation of this provision so that situations, such as where a permit will expire in twelve months, can be taken into account.
Also, consistent with the Commissions expectation that progress be made to develop information to resolve temporary modifications, it added subsection 31.14 . This subsection provides explicit authority for the Division to require permit compliance schedules that include milestones and dates to ensure that information necessary to determine appropriate underlying standards is developed.
The Commission adopted subsection 31.14 in order to provide direction that, while temporary modifications are in place, water quality should be maintained at the best level that is practicably achievable. This provision allows the Division to exercise its discretion in determining the level of treatment that a facility can provide without significantly increasing costs such that water quality would be maintained or even improved. An example would be where the existing quality of the facility discharge is better than the level of the temporary modification or where relatively minor actions, such as adopting local pretreatment limits or low cost facility improvements, could be taken to improve the quality of the discharge.
Concern was expressed in the hearing that this provision could have a ratcheting down effect on permit effluent limits. In other words, there was concern that a reissued permit could be based on the actual performance of a discharger that has achieved effluent quality better than required by its permit limits. If effluent limits were tightened to reflect this better effluent quality, the discharger could then be required to improve its discharge quality even further in order to consistently stay in compliance with the new limitations. This is not the Commission's intent. Rather, the Commission intends that best professional judgment-based effluent limits would be set at a level intended to maintain existing effluent quality, not at a level to further improve effluent quality.
For new or expanding facilities, the Commission is requiring the Division to establish limits that will be protective of downstream uses. The Commission does not expect the Division or other party to conduct a use attainability-like analysis in these situations. However, a sensitivity analysis or other appropriate approach should be used to establish the magnitude of downstream pollutant concentrations to evaluate potential impacts to uses. The Commission recognizes that, in some situations, allowing an increase in loading to the stream may be appropriate or even beneficial.
The Commission recognizes that portions of the temporary modification provisions adopted in this rulemaking may be inconsistent with current provisions in Regulation No. 93. The Commission intends that the provisions adopted in this rulemaking will govern and that appropriate revisions will be adopted in Regulation No. 93 in the next rulemaking hearing reviewing that regulation.
One previously automatic basis for a use-protected designation was the existence of a class 2 aquatic life classification for the water segment. The record demonstrates that in fact there are segments with a class 2 aquatic life classification that have water quality better than the aquatic life and recreation use table value criteria. The revisions adopted eliminate the presence of a cold-water aquatic life classification as a basis for a use-protected designation. The Commission determined that there is no substantial evidence of a correlation between cold water class 2 aquatic life classifications and poor water quality.
For warm water class 2 streams, the Commission modified the provision regarding application of a use-protected designation. The presence of a warm water class 2 classification will still be a presumptive basis for applying a use-protected designation; however, that presumption can be overcome based on the provisions of new subsection 31.8 if the water quality test in that subsection is met. That is, if there is data showing better-than-table-value water quality for at least 10 of 12 indicator water quality parameters and the segment is not listed, and does not qualify for listing, for two or more pollutants for exceedance of chronic or 30-day standards, the aquatic life class 2 classification will not be a basis for a use-protected designation.
The Commission also revised the provisions of subsection 31.8 . This subsection provided that a segment would not be designated use-protected if its quality was maintained better than standards solely because a point source discharger was achieving treatment levels better than required by law. This provision was never utilized to apply a use-protected designation and discussions with interested parties indicated confusion regarding how the previous language was intended to be interpreted. The Commission revised this subsection to provide that "effluent-dependent" and "effluent-dominated" water segments generally will be designated use-protected. Because such waters are, by definition, those where the majority of the flow consists of treated wastewater for the majority of the time, the Commission has determined as a matter of policy that it is reasonable to assume that in most instances such waters will not maintain water quality significantly better than table value standards for the majority of pollutants. Of course, the quality of these waters will continue to be protected for their designated uses. The Commission added definitions of the flow regimes "effluent dependent stream" , "effluent dominated stream", and "ephemeral stream" in section 31.5.
The Commission anticipates that the revised 31.8(2)(b)(i)(C) generally will result in use protected designations for most effluent dominated and effluent dependent water bodies. Parties advocating that a segment should be use-protected because it is effluent dependent or effluent dominated will need to provide flow data that documents that one of these definitions is met. However, the Commission cannot conclude, based on the limited evidence presented in this rulemaking, that use protected designations are necessarily appropriate for all effluent-dependent and effluent-dominated waters. Instead, the Commission has determined that it is appropriate to allow flexibility to make decisions for effluent dependent and effluent dominated waters based on the water body's public resource value and ecological significance. The Commission expects to apply this provision considering factors such as representative existing water quality data, information regarding the effects of nonpoint sources on water quality, the extent to which existing point source loads are less than allowed under current discharge permits, existing uses of the water by the public, the location of the water body, and ecological attributes. The purpose of allowing this flexibility is to recognize that:
Finally, the Commission revised subsection 31.8 . This subsection was created to provide for the possibility of a use-protected designation where a segment may have poor water quality for parameters other than those considered in the 12-parameter test in subsection 31.8 . The Commission has revised this provision to clarify that if there is poor water quality for one or more of those 12 parameters in addition to poor water quality for other parameters, the cumulative water quality conditions can be considered in determining whether to apply a use-protected designation. The Commission also notes that a portion of the existing language in subsection 31.8 , which is not being changed in this rulemaking, provides that "substantial natural or irreversible human-induced pollution" may be a basis for a Commission determination that a use-protected designation is appropriate. The term "pollution" is defined in the Colorado Water Quality Control Act more broadly than the term "pollutant" and can include any "alteration of the physical, chemical, biological, and radiological integrity of water" . Therefore, the Commission intends this provision to allow non-chemical water quality conditions to be taken into account in a site-specific determination that the quality of particular waters does not "exceed levels necessary to support propagation of fish, shellfish, and wildlife and recreation in and on the water" and therefore does not warrant the extra protection provided by the antidegradation review process.
The Commission considered alternative proposals for revisions to the use-protected provisions submitted by the Littleton-Englewood Wastewater Treatment Plant. In view of uncertainties regarding application of the revisions proposed by Littleton-Englewood, and because the Commission believes that the provisions adopted provide appropriate flexibility in applying use-protected designations, the Commission declined to adopt the Littleton-Englewood proposals.
September 30, 2000 date for determining baseline water quality was established as the result of a July 2000 rulemaking hearing. In that hearing, the primary assumption was that increasing human development over time would result in increasing water quality impacts and that the September 30, 2000 date would establish the minimum water quality used as a baseline against which to gauge future impacts. In establishing that date for determining baseline water quality, the Commission did not consider the possibility that water quality might improve after September 30, 2000.
There is currently substantial interest in remediation efforts to reduce the water quality impacts from past contaminant releases in Colorado, e.g. from past mining operations. Where remediation is legally mandated and such efforts are successful, the Commission believes that it is appropriate to help assure continuing benefits from the completed remediation by using the resulting improved water quality as the baseline for future antidegradation reviews. Otherwise, the opportunity for any new discharger to fully consume any increased assimilative capacity resulting from remediation activities could effectively undermine the benefits of clean-up efforts. Note that by referring to "unpermitted" past contaminant releases the Commission intends that the term "remediation" in this provision not apply to improved treatment of ongoing, permitted releases, e.g. from a municipal wastewater treatment plant.
The Commission also recognizes that some remediation, including that associated with pollutant trading, is not legally mandated. This brings additional considerations into play. In such circumstances, the Commission intends that in determining whether to establish an alternative baseline to be used for antidegradation purposes, it will consider the site-specific circumstances, including but not limited to (1) the benefit of protecting improved water quality that results from remediation and (2) the benefit of encouraging voluntary clean-up efforts. In no event would the alternative baseline be water quality worse than that as of September 30, 2000. The Commission recognizes that in some circumstances it may be appropriate to use the water quality resulting from voluntary remediation as the new baseline, to help assure that the actions of one entity do not undo, without adequate review, the benefits of remediation performed by another entity. However, in other circumstances, entities could be discouraged from conducting voluntary remediation if the improved water quality could result in stricter requirements on future modifications to their own discharge. Any individual or entity, including those involved in the remediation efforts, may petition the Commission, at any time, to establish an alternative baseline, including prior to proceeding with a remediation project. Nothing in this rule revision is intended to in any manner interfere with or adversely affect either existing or future water pollutant trades that are consummated in a manner consistent with state policies or regulations regarding trades, including the use of pollutant credits or offsets generated.
When the Division becomes aware of waterbodies where remediation of impacts from past unpermitted releases has or will result in improved water quality after the September 30, 2000 baseline date, the Division will provide documentation of this in the Basin Rationale at the time of the next basinwide or site-specific rulemaking hearing encompassing the segment. In such circumstances, the Commission will also include a note in the Designation column in the basin tables to indicate that the September 30, 2000 default baseline date does not apply to the specific segment. For such waterbodies, the appropriate baseline date will be determined at the time that a new activity triggers an antidegradation review. It is anticipated that in most cases this will be the date upon which the antidegradation review commences. However, where the remediation is not yet complete or the water quality benefits of remediation have not yet been fully realized in-stream, verifiable evidence of future pollutant loading reductions may be utilized to establish a baseline date that extends into the future.
A footnote was added to the statewide radionuclide Standards that clarifies which parameters should be analyzed in the unfiltered fraction.
Aquatic-life based criteria for Tributyltin (TBT) were added to the Basic Standards for Organic Chemicals Table based on information from EPA's National Recommended Water Quality Criteria: 2002 (EPA-822-R-02-047).
In this rulemaking the Commission adopted revisions to the provisions in subsection 31.13 regarding recreation use classifications, and to section 31.16 Table I water quality criteria for recreation uses.
The revised regulation moves the definition of primary contact recreation to the definition section at 31.5 and establishes two subsets of primary contact recreation and one undetermined recreational use category and a "Not Primary Contact" use category.
Existing Primary Contact Use: The Commission intends that this classification receive the highest level of protection (with an anticipated risk level of 8 swimmer illnesses per 1000 swimmers). It is to be adopted where evidence has been presented that these waters are used for primary contact recreation or have been used for such activities since November 28, 1975 (per the Federal Regulatory definition of "existing uses"). This use category applies to a subset of waters previously classified recreation 1a.
Potential Primary Contact Use:The Commission intends that this classification be used where a reasonable level of inquiry has failed to identify any existing primary contact use, but a full scale Use Attainability Analysis has not been conducted, or such analysis shows that primary contact uses may potentially occur in the future. This classification will receive a slightly elevated numeric value (with an anticipated risk level of 10 swimmer illnesses per 1000 swimmers). This use category replaces the previous recreation class 1b.
Undetermined Use: The Commission intends that this classification be used where little or no effort has been undertaken to determine the level of recreational use of a waterbody. This classification will receive the highest level of protection (with an anticipated risk level of 8 swimmer illnesses per 1000 swimmers) and will be the default classification until the Commission has determined that another classification is appropriate.
Not Primary Contact Use: The Commission intends that this classification be used only where a Use Attainability Analysis has been conducted that demonstrates that there is not a reasonable likelihood that primary contact uses will occur in the waterbody within the next 20 years. This classification will receive the lowest level of protection (five times the existing primary contact use standard). This use category replaces the previous recreation class 2.
This revised classification system for recreation uses was established to address issues of documentation and inquiry, or lack thereof. A key aspect of this revised classification system is to distinguish different reasons for applying the highest level of bacteriological standards protection to water bodies. The previous "class 1a" designation was applied either because an existing primary contact use had been documented for a segment or as a protective default classification where no significant site-specific investigation of recreation uses had occurred. These different situations are clearly distinguished by the new set of classifications. In addition, the "undetermined use" category provides a useful option in those circumstances where there is good water quality and no objection to applying the more stringent standards, but there is concern about labeling state waters on private lands as "primary contact" recreation waters when landowners intend not to provide public assess to those waters.
These new recreation sub classes necessitated revisions throughout Regulation No. 31 to ensure that references to recreation classifications conformed to the new nomenclature.
The Commission revised the first sentence of subsection 31.7 to delete the words "acute or chronic" . The reason for this change is to assure that site-specific standards can be adopted for classified uses other than aquatic life. For example, site-specific standards may be appropriate for a segment with a Class E recreation classification where it is demonstrated that E.coli levels in excess of table values are present as the result of natural or irreversible human-induced sources.
The Commission intends that any revisions of existing recreation classifications and standards to apply the new classifications described above would occur through the normal rulemaking process. This would provide an opportunity for public review and comment on information supporting any new site-specific classifications and standards.
Although Colorado has historically used a fecal coliform standard, E. coli levels have been shown to be a better indicator organism of the risk of human illness. E. Coli standards were added to the Basic Standards in 2000 and the Commission proposes to complete the transition to E. coli by removing the fecal coliform table values. The Commission intends to implement this change by deleting fecal coliform standards from individual segment standards in the next round of basin reviews.
The Commission also added the definition of "E.coli" to section 31.5.
Having considered the evidence submitted in this rulemaking the Commission believes that it is appropriate to move forward toward revised temperature table values. However, since this is a very complex issue and there is still much controversy, the Commission adopted revised temperature criteria with an effective date of December 31, 2007. The intention of the Commission is to retain the current standards until that date. During the interim, the Commission encourages establishment of an expert panel to review the available data and provide input on technical and policy issues regarding appropriate temperature standards for Colorado. The Commission anticipates that a further rulemaking hearing will be held prior to December 31, 2007, to consider further revisions to the temperature table values.
The Commission recognizes that many participants in this rulemaking hearing are likely to disagree with various specific aspects of the temperature criteria now being adopted with a delayed effective date. The Commission acknowledges this disagreement and intends that the overall package of criteria now adopted help create an incentive for further analysis of appropriate temperature criteria.
The Commission also recognizes that, because proposals evolved throughout this rulemaking process, for several specific aspects of the criteria now being adopted there is limited information in the hearing record beyond the statements contained in the original proposed statement of basis and purpose. In particular, because the Division's proposal evolved, several aspects of the original proposal did not receive a full dialogue from all interested parties. Nonetheless, the Commission concluded that the reasoning expressed in the original proposed statement of basis and purpose provides the best explanation regarding the rationale for the specific criteria adopted in this rulemaking.
The Commission adopted revised temperature standards, as proposed by the Division in February 2005, in Table 1 and Section 31.14 . This proposal was developed based on a literature review of temperature effect data for fish species present in Colorado. The temperature standards adopted provide protection for the aquatic community from lethal and sublethal effects, and provide protection against abrupt changes in water temperatures that may lead to thermal shock.
The original Colorado temperature standards were first adopted by the Commission in 1978. Over the years, the basis for the original standards has become unclear, the standards have been inconsistently applied in permits, and there have been disagreements about how the attainment of these standards should be assessed.
In this rulemaking, the Commission adopted new temperature standards based on warm and cold-water use classifications and adopted two new qualifiers of cold water use classifications, "cutthroat trout" and "cool water". These new qualifiers were developed in recognition that the cold water classification covers a wide range of temperature regimes and aquatic life communities.
The cutthroat trout ("ct") qualifier was developed to provide protection for cutthroat trout, a Colorado threatened species. Cutthroat trout require somewhat lower temperatures than other trout species. The Commission intends that the "ct" qualifier will be adopted on a site-specific basis where evidence has been presented that cutthroat trout are present or are expected to be present in a water body.
The cool water ("cw") qualifier was developed to acknowledge that temperature regimes are a continuum and the transition between cold and warm is not abrupt. The Commission intends that the "cw" qualifier will be adopted on a site-specific basis where the downstream end of the segment adjoins a warm water segment and where there is either free passage for cold water fish to move upstream or adequate refugia within the segment. These decisions will be made on a case-by case basis and are not intended to prejudge or predetermine the work of the Aquatic Life work group that is working on refined aquatic life classifications.
Two types of criteria were adopted: Maximum Weekly Average Temperature ("MWAT") and Daily Maximum ("DM"). The MWAT provides protection against sublethal effects on metabolism, growth, and reproduction. The MWAT is defined as the mean of multiple, equally spaced, daily temperatures over a 7-day consecutive period. The DM provides protection against lethal effects that elevated temperature can cause. The DM the maximum temperature attained in any one day. The MWAT is calculated from the optimum and upper temperatures tolerated by a species:
The rationale for using the MWAT as a temperature standard is based on studies that show moderate temperature fluctuations can be tolerated as long as the upper incipient lethal temperature is not exceeded for extended periods of time. The basic assumption of this method is that optimum temperatures are not necessary or realistically attainable at all times to maintain healthy fish populations.
The temperature criteria (both MWAT and DM) were developed for warm, cold and cool temperature regimes based on review of the temperature toxicity data in the literature. Where multiple studies were conducted for each species, the average for each value above was calculated before entering them into the MWAT equation (e.g., an average upper optimum temperature was calculated from multiple studies). Species MWATs were ranked and the value was selected that protects 95 percent of the species. The DM was developed by calculating an average ultimate incipient lethal temperature for each species, ranking the species and selecting the value that protected 95 percent of the species.
The Commission determined that special consideration should be provided for cold water fish during spawning seasons when they are more sensitive to increased temperature. The temperatures during these periods must be protective of the offspring (eggs, and early life stages). The spawning criteria are to be applied on a seasonal basis in segments where habitat is suitable and spawning is expected to occur. This standard is to be implemented as the MWAT in CDPS permits just as the DO spawning is applied.
Due to the complexity of a temperature standard and the potential for natural systems to have temperatures exceeding the numeric standards, the Commission adopted a series of excursions. The following excursions will not be considered an exceedance of the temperature standards:
Air temperature excursion : ambient water temperature may exceed the criteria in Table 1 or the applicable site-specific standard when the daily maximum air temperature exceeds the 90th percentile value of the annual maximum air temperatures calculated using at least 10 years of air temperature data.
Low-flow excursion : ambient water temperature may exceed the criteria in Table 1 or the applicable site-specific standard when the daily stream flow falls below the acute critical low flow or monthly average stream flow falls below the chronic critical low flow, calculated pursuant to Regulation 31.9(1)
Lakes and reservoirs : When a lake or reservoir is stratified, the surface layer may exceed the Table 1 value as long as the lower levels meet the temperature and dissolved oxygen standards.
Natural hot springs: ambient water temperature in a water body may exceed the criteria in Table 1 or the applicable site-specific standard, when the temperature in that water body is influenced by a natural hot springs.
The Commission acknowledges that there may be a need to adopt site-specific temperature standards that differ from current temperature standards to provide adequate protection for specific segments during the interim period prior to the delayed effective date of the revisions approved today.
Thermal Shock: Thermal shock has lethal and sublethal effects that result from an abrupt change in stream temperatures. The Commission adopted the provision in 31.14 (14) that effluent shall not cause an abrupt change in temperature of a magnitude, rate and duration deemed deleterious to the resident aquatic life This is quantified as no more than a 1°C change over one hour not to exceed 12°C in 24 hours. Because the effects of thermal shock are dependent on many factors (acclimation and thermal history, fish body size, other stressors) a single thermal shock criteria is a simplification. However, the Commission believes that it is important to protect fish from anthropogenic thermal shock.
The rate of change of 1°C per hour was selected since experimental evidence suggests that most fish can tolerate temperature shifts of 15 to 18°C if exposure falls within the tolerance range of individual species. Further, daily temperature fluctuations (within 10 to 12 hours) in this range have been measured in small streams of low volume without apparent high mortality. This equates to 1.25 to 1.8°C per hour.
Other parties have suggested a rate of change based on the research approach called Critical Thermal Method (CTM) wherein fish are warmed at a constant rate to either a lethal temperature or a loss of equilibrium. The key in this approach is to select a rate of change that is rapid enough that fish do not acclimate while they are being tested but slow enough that the internal temperature does not lag significantly behind the water temperature. Many rates have been recommended for CTM experiments ranging from 18°C per hour (in studies by Beitinger and by Becker and Galaway) to 1.2°C per hour (in studies by Elliot and Elliot). The Commission decided that the upper range was inappropriate since at 15°C, heat shock proteins have been shown to form in the tissues of rainbow trout. A rate rounded to 1°C per hour was selected.
Natural Conditions:In adopting new numeric temperature criteria so as to ensure the continued protection of classified uses, the Commission became aware of the fact that there may be a significant number of segments where the numeric temperature criteria are being consistently exceeded, at least on a seasonal basis, in the absence of impacts from point source discharges or controllable nonpoint sources, yet the aquatic life use continues to be attained. In these cases of natural or irreversible human-induced exceedances of the numeric criteria, the Commission desired to identify an option to retain and protect the existing uses, but avoid the need for inappropriate section 303(d) listings. Thus, it adopted a footnote providing that a narrative table value criterion for temperature that can be applied in such situations to site-specific waters, where there is a demonstration that exceedance of numerical criteria results from natural or irreversible human-induced impacts. Implementation of this provision will be further addressed in the temperature standards guidance to be developed by the Division.
Implementation in Discharge Permits
Modifications were made to section 31.14 to record the Commission's intentions regarding how the Colorado temperature standards will be implemented in discharge permits.
The DM standard is to be applied so that there is attainment of the DM at the edge of acute regulatory mixing zone. The MWAT is to be applied so that there is attainment of the MWAT at the edge of the chronic regulatory mixing zone.
Spawning criteria are to be applied on a seasonal basis where the Division determines that the habitat that will be affected by the physical mixing zone is suitable for spawning by fish species that are expected to be present.
The Commission also determined that temperature effluent limits would not be required for discharges to dry streams that only have flowing water in response to precipitation (effluent dependent streams). This provision is only valid if there is no evidence that the aquatic life use may be negatively affected by the discharge. A definition of effluent dependent streams was added to section 31.5.
Determination of Attainment
The Commission intends that the temperature standard be evaluated against representative instream data. Temperature varies within a reach both spatially and temporally. Data should be taken from a location in the stream that is representative of the reach, not in locations that may be substantially warmer or cooler than the rest of the segment - e.g. backwater habitats, eddies, deep pools, or refugia. Temperature also varies throughout the day. Attainment of the DM standard is based on temperature readings taken from the warmest part of the day - typically in the afternoon. Attainment of the MWAT standard is based on equally spaced data throughout the day including the warmest part of the day.
The Commission adopted revised ammonia aquatic life criteria, based on EPA's 1999 Update of Ambient Water Quality Criteria for Ammonia. Colorado's previous table value criteria for ammonia were adopted in the late 1980's and have not been revised since. The new criteria are in the form of total ammonia rather than unionized ammonia and generally represent a less stringent criterion in cold-water segments but a more stringent criterion in warm-water segments.
After lengthy discussions between the Division and Colorado Water Quality Forum's Basic Standards Work Group of EPA's 1999 criteria and alternative approaches, the Division determined that the 1999 criteria would be appropriate for Colorado. Based on the evidence submitted in this hearing, the Commission agreed.
Acute Criteria - Salmonids Present (sp) or Absent (sa): The Commission intends that, generally, the acute criteria be applied along cold or warm water classification lines. On a case-by-case basis, where evidence has been presented, the Commission may decide that salmonids (trout) are present in warm water segments or absent in cold water segments.
Chronic Criteria - Early Life Stage Present (Elsp) or Absent (Elsa): The early life stages include the pre-hatch embryonic period, the post hatch free embryo or yolk-sac fry, and the larval period, during which the organism feeds. Juvenile fish, which are anatomically rather similar to adults, are not considered early life stages. Since ammonia is less toxic to juvenile and adult fish than at earlier life stages, a somewhat relaxed criterion is available for use when early life stages are expected to be absent from the aquatic ecosystem.
The Commission found that for cold water streams, early life stages could reasonably be expected in any month, therefore the default assumption will be that the chronic Elsp criterion will apply to cold water streams all year. This assumption can be modified on a site-specific basis where appropriate evidence is submitted.
For warm water streams, early life stages could reasonably be expected in March through August. The default assumption will be that the chronic Elsp criterion will apply from March 1 through August 31, and the Elsa criterion will apply from September 1 through February 29. This assumption can be modified on a site-specific basis where appropriate evidence is submitted.
The Commission acknowledges that there will be a substantial cost of compliance with the new criteria for some entities, once the criteria are adopted as standards in individual basins and implemented in discharge permits. Economic impacts on a per capita basis may be most significant for small communities located on warm water streams and currently using lagoon treatment systems.
Anticipating a potentially significant cost of meeting the EPA criteria, the Division and others have explored whether other scientifically valid approaches to ammonia criteria are available. However, all parties involved have been unable to identify any alternative for statewide criteria that would be less costly and meet the requirements of the federal and state law by assuring protection of aquatic life uses.
The Commission believes that it will be important for all involved to explore options to mitigate the economic burden of meeting the new ammonia criteria. In some instances, consideration of site-specific criteria may be appropriate, so long as any such criteria are consistent with federal and state requirements to protect existing aquatic life uses. It also will be appropriate when applying the new criteria as standards in the individual basins to consider the adoption of temporary modifications that provide a reasonable and adequate amount of time for affected municipalities to address the planning, financing and construction that may be needed for upgrading treatment facilities. We encourage the state legislature to explore the possibility of state grant funds to provide financial assistance, particularly to small communities faced with significant costs to meet the new ammonia criteria.
Several changes are adopted with respect to the metals table values set forth in Table III. The metals parameters that changed include aluminum, antimony, arsenic, cadmium, uranium and zinc.
Aluminum : A footnote was added to the chronic aluminum value to explain the application of the standard. Application of the 87 µg/l total recoverable aluminum chronic table value is based on toxicity studies with brook trout and striped bass. The studies underlying the 87 µg/l chronic value, however, were conducted at low pH (6.5-6.6) and low hardness (<10 ppm CaCO3), conditions uncommon in Colorado surface waters. A water effect ratio toxicity study in West Virginia indicated that aluminum is substantially less toxic at higher pH and hardness (although the relationship is not well quantified at this time). Further, field data indicate that many high quality waters in the U.S. contain more than 87 µg/l aluminum when either the total recoverable or dissolved aluminum is measured. Based on this information and considering the available toxicological information in EPA's Aluminum Criteria Document (EPA 440/ 5-86-008), the 87 µg/l chronic table value standard for aluminum will be implemented as follows: where pH is equal to or greater than 7.0 and hardness is equal to or greater than 50 ppm as CaCO3 in the receiving water after mixing, the 87 µg/l standard will not apply, and aluminum will be regulated based on compliance with the 750 µg/l acute standard. In situations where the 87 µg/l chronic standard applies, a discharger may propose a site- specific chronic standard based on a water effect ratio.
Arsenic: Arsenic table values for drinking water supply, W+F and FI were updated to reflect the classification of arsenic as a Class A carcinogen by EPA, in accordance with Policy 96-2. The Commission during the recent adoption of Basic Standards for Organic Chemicals for Regulations 31 and 41 has allowed for two drinking water supply standards. The same approach is being applied in this hearing to metals table standards. The first number in the range is a strictly health-based value, based on the Commission's established methodology for human health-based standards. The second number in the range is a maximum contaminant level (MCL), established under the federal Safe Drinking Water Act that has been determined to be an acceptable level of this chemical in public water supplies, taking treatability and laboratory detection limits into account. Control requirements, such as discharge permit effluent limitations, shall be established using the first number in the range as the ambient water quality target, provided that no effluent limitation shall require an "end-of-pipe" discharge level more restrictive than the second number in the range. Water bodies will be considered in attainment of this standard, and not included on the Section 303(d) List, so long as the existing ambient quality does not exceed the second number in the range. The Drinking Water Supply table values are applicable at the point of intake to a domestic water supply.
Water + Fish (W+F) and Fish Ingestion(FI) Table Values:
Table values for antimony are updated to reflect a revised relative source contribution for both W+F and FI. The antimony W+F standard was updated to reflect the change in increasing the fish consumption rate numbers adopted by the Commission on 9/14/2004 at the hearing regarding organics for Regulation 31.
Table values for copper, nickel, selenium, thallium, and zinc were updated to reflect water quality criteria developed under the CWA section 304(a) and published in EPA National Water Quality Criteria: 2002.
Cadmium: The Commission considered alternative revised acute and chronic aquatic life table values. Using the results from the most recent literature review, it adopted new hardness based equations for cadmium. This review resulted in two separate acute equations: one for waters that have trout and one for waters that do not have trout. The Commission also adopted a revised hardness based chronic equation that resulted from the most recent literature review. Although the revised acute and chronic equations differ slightly from EPA's national criteria, they more accurately reflect the current science and are protective for Colorado's waters.
Uranium: A drinking water supply table value for uranium was added, in accordance with Policy 96-2. Since there is no bio-concentration factor (BCF) available, no W+F or FI criteria are proposed. A conversion of pCi/L to mg/L was developed. The conversion factor of 670 pCi/mg natural uranium, which assumes secular equilibrium of U-234 and U-238, will be used to provide for consistent interpretation of data. When uranium activity units are used (e.g. pCi/L), they will be converted to milligrams by dividing by 670. The current uranium standard of 40 pCi/L or 59.7 µg/l (when divided by 670 pCi/mg) is greater than the new MCL (drinking water supply standard). As each individual basin regulation is reviewed, the uranium standard will be changed from 40 pCi/L to 30 µg/L in the basinwide standards at the beginning of each regulation.
Zinc: The Commission adopted alternative revised zinc aquatic life table value hardness-based equations. These differ slightly from EPA's national criteria. However, they more accurately reflect the current science by inclusion of acute and chronic data for sculpin and are protective for Colorado's waters. The Commission notes that more protective standards may be adopted on a site-specific basis when appropriate to protect sculpin.
Hardness footnote (footnote 3): The Commission clarified how hardness is to be determined for permit effluent limitations and for determining standards attainment.
Segment descriptions, unless specified by the Commission, are to mean that any boundary location means "immediately above" that reference, except when the boundary location is referred to as "source".
The Commission clarified the methodology to be utilized in assigning ambient quality based standards.
The Commission added a definition of "existing quality" to section 31.5. This is the same definition that can be found at 31.8(2)(a)(i). It was added to the definitions because it has broader applicability than merely the antidegradation provisions.
The Commission added a footnote to the pH standard, which addresses judging when attainment is achieved, and when the appropriate averaging period can be applied.
The provision at 31.14(9) that addresses PQLs was revised in light of the removal of PQLs from the Regulation for the State Discharge Permit System (Regulation No. 61). Generally applicable PQLs now reside in a Division policy document. In addition, site-specific PQLs can be developed in accordance with Division policy.
The Commission has modified Section 31.9 to address an issue regarding the methodology used to calculate monthly low flows for streams experiencing large seasonal variability in in-stream flows. That section now provides that, when requested by the discharger, a specific method for calculating low flows during such periods is to be used.
Currently, the Division uses a modified version of a low flow model, commonly referred to as the "DFLOW model," which was developed by the U.S. Environmental Protection Agency. The DFLOW model was developed by EPA to establish an empirical "biologically based" annual low flow. The model calculates a harmonic mean for each consecutive, forward rolling, 30-day period for the period of record being considered. An excursion procedure is applied to establish an annual low flow which is expected to occur at a frequency of no greater than once every three years (see EPA, 1986. Technical Guidance Manual for Performing Waste Load Allocations, Book VI, Design Conditions: Chapter 1 - Stream Design Flow for Steady-State Modeling, Appendix C - Office of Water Regulations and Standards).
The Division modified the EPA DFLOW model to calculate monthly low flows for use in determining monthly effluent limitations. In calculating monthly low flows, the Division assigns to a month of interest all harmonic means that include one or more days in that month. This procedure can result in the calculated low flow for the month in interest being unduly influenced by the flow data from the preceding or succeeding month.
In order to reduce the influence of flows outside the month of interest during seasons of highly variable flow, the Commission adopted a revised procedure. That procedure uses only those consecutive 30-day harmonic means which contain at least 15 days from the month of interest to determine the low flow for that month. The Commission also determined the 1986 EPA Technical Guidance Manual sets forth the most appropriate excursion procedure and that such procedure should be used by the Division, when requested by the discharger, in calculating the annual 30E3 low flow. Appendix A to Section 31.9 sets forth the excursion procedure and is derived from the 1986 EPA Technical Guidance Manual. The low flow for a month of interest is then set at either the lowest harmonic mean assigned to that month, or the annual low flow value (using the procedure set forth in Appendix A), which ever is greater.
The Commission concluded that the revised methodology will more accurately reflect average in-stream low flow conditions during transitional flow months.
The Division's current practice is to use the most recent ten years of flow data in establishing low flow conditions. The Commission recognized that, in most instances, the period of record (POR) of available data might be different than ten years. The Commission also recognized that the determination of low flows based on the most recent ten years of flow data could be biased by the predominance of wet or dry cycles within the ten year period, and that such bias could be reduced by the use of a longer period of record. Where the period of available flow data exceeds ten years, the Commission would expect the Division to consider using such POR. In such instances, the Commission would expect the Division to evaluate whether changes (for example, anthropogenic changes such as dams or diversion structures) have occurred in the stream system that would make it inappropriate to use such longer POR. The Commission also determined that, where ten years of data does not exist, the use of a period of record of less than ten years may be appropriate to establish low flow conditions, particularly where less accurate methodologies such as "similar basin" approaches would otherwise be used. Determination of the appropriate period of record for calculating low flow conditions outside the Division's normal practice will likely be based on a case-by-case request by the discharger. In these situations, the Commission would expect the Division to work with the discharger to determine the most appropriate period of record for calculating low flow conditions.
Section 31.10 , "Mixing Zones" in the Basic Standards Regulation (Regulation 31) provides the regulatory basis for defining and implementing mixing zones in discharge permits ("mixing zone rule"), Section 31.10 of the mixing zone rule entitled "Additional Constraints on Mixing Zones" includes the following provision:
In February 2002, the Water Quality Control Division issued the "Colorado Mixing Zone Implementation Guidance" (Water Quality Control Division, February 2002). Appendix IV, entitled "Mixing Zone Guidance for Water for Threatened and Endangered Species," describes the manner in which the Division will work with the EPA and the Service to provide compliance with the Endangered Species Act for permits to discharge to waters that include threatened or endangered species.
EPA's approval of the mixing zone rule (May 16, 2002) was subject to compliance with the Endangered Species Act, given that EPA determined that the rule may adversely affect Colorado pikeminnow, humpback chub, bonytail, razorback sucker, and greenback cutthroat trout, and may affect critical habitat of these species. By letter dated September 16, 2002, EPA requested a formal consultation with the U.S. Fish and Wildlife Service regarding approval of the mixing zone rule.
On August 11, 2003, the U.S. Fish and Wildlife Service issued a biological opinion based on its review of EPA's approval of Colorado's amended mixing zone rule (Exhibit 2). Seven conservation measures are identified in the August 11, 2003 biological opinion.
Conservation measure No. 2 acknowledges that there may be situations where there are no feasible alternatives that would entirely avoid adverse impacts to listed aquatic species. In these cases, the project applicant will be asked to implement a conservation plan to minimize anticipated impacts. In such cases, the Service provides that it will issue a supplemental biological opinion, acknowledging the unavoidable nature of the issue, acknowledging the implementation of the conservation plan, and authorizing take for that permit. Federal regulations also allow the Service to specify reasonable and prudent measures in a biological opinion to minimize incidental take (50 CFR 402.14).
Conservation measure No. 2 was not included as an option in the revised Mixing Zone Guidance developed by the Division, as the Guidance preceded the biological opinion. In addition, neither the guidance nor the biological opinion recognized other regulatory options that may be available under the federal Endangered Species Act, such as issuing a biological opinion with reasonable and prudent alternatives, or issuing a programmatic biological opinion dealing with more than one permit.
Conservation measure No. 7 also states that site-specific modifications to eliminate or minimize adverse effects can include:
- effluent diffusers,
- application of numeric standards at end of pipe, or
- relocation of the discharge and associated mixing zone.
Conservation measure No. 7 is recognized in the Mixing Zone Guidance document.
The Commission received requests from parties to the hearing to modify the mixing zone rule to address the terms of the biological opinion and other available regulatory options. Prior to the hearing, those parties and the Division agreed that the proposed modifications would be withdrawn and that it is appropriate to modify the Mixing Zone Guidance to incorporate provisions from the biological opinion, and provide for use of other federal regulatory options that may be available under the Endangered Species Act. The Commission supports this approach and recognizes that the Division will need to present it to the US Fish and Wildlife Service and EPA for their comment and make any appropriate changes prior to bringing a revised version of the Mixing Zone Guidance before the Commission for public comment.
PARTIES TO THE RULEMAKING HEARING
5 CCR 1002-31.44