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 1002-31.22 - STATEMENT OF BASIS AND PURPOSE (1987 REVISIONS)
Current through Register Vol. 47, No. 17, September 10, 2024
A. BACKGROUND
These amendments to the Basic Standards and Methodologies were made as a result of a February, 1983 triennial review hearing which revealed dissatisfaction with several elements of the regulation. The Commission organized a task force of three committees of selected scientific experts representing several points of view in early 1985:
Reports from the three committees were completed in early 1986. The recommendations of the Water Quality Standards and Methodologies Committee and the Nitrogen Cycle Committee formed the basis for the proposed revisions that were considered at this hearing. The Commission decided to take no action with respect to the recommendations of the Aquatic Life Committee in this hearing, because it felt that the recommendations advanced did not warrant proposing changes to the classification system at this time. Revisions of the aquatic life classification system may be considered at a later date.
At least one party recommended that a separate peer review process regarding the committee reports be held prior to taking action on revisions to the Basic Standards and Methodologies. The Commission believes that this hearing process provided an adequate opportunity to review those aspects of the reports relied on in the proposed revisions.
B. OVERVIEW OF REVISIONS
The revisions adopted by the Commission make a variety of changes in the system for establishing and implementing site-specific water quality standards in Colorado. The following are the major areas in which the Commission made or considered changes:
The Commission also has added to the regulation a statement of a second alternative approach to setting site-specific standards, referred to as site-specific-criteria-based standards.
The basis and purpose for each of these actions is discussed in the following sections of this statement of Basis and Purpose.
The July 31, 1988 effective date has been selected for several reasons. First, the Commission felt that it could reach a consensus on the revisions adopted herein. To delay final adoption of these revisions to a later date along with the other issues described below would have unnecessarily complicated new hearings with old issues and would have possibly required a total rehearing due to the turnover of membership on the Commission.
Second, certain technical issues (particularly relating to low flows) that the Commission had hoped to address in this rulemaking proceeding were not addressed as fully as the Commission had hoped during the hearing. The Commission hopes to address those issues in a new rulemaking hearing prior to the effective date of these revisions, so that any additional technical changes can become effective as part of one overall package, reducing the confusion and disruption that could result from two successive major sets of revisions of the regulation.
Third, EPA has raised several issues regarding the adequacy of the Basic Standards and Methodologies. The Commission intends to hold a rulemaking hearing regarding those issues sometime between December, 1987 and March, 1988. Therefore, the Commission again hopes that any changes to the regulations that may be determined necessary relating to the issues raised by EPA can become effective as part of one overall package, to avoid multiple revisions going into effect at different times.
Fourth, the Commission recognizes that a number of the revisions now being adopted are major. Because the range of options considered in this hearing was wide, it may be that there are aspects of the specific changes adopted which could usefully be further clarified. Therefore, between now and the effective date of these revisions the Commission may consider the adoption of further refinements of these changes if that appears appropriate.
The Commission gave extensive consideration to the public and private costs potentially associated with implementing a major overhaul of the State's water quality standards system. In several instances the Commission has attempted to minimize these impacts by minimizing the magnitude of the change. (E.g. the 85th percentile ambient quality-based standards methodology adopted is very similar to the previously-used mean plus standard deviation (Ji+ s) methodology, especially compared to the more stringent 50th percentile hearing proposal; the new table values for unionized ammonia are similar to existing values and the previous approach to setting site-specific ammonia standards has been ratified; proposed changes to domestic use classifications and agriculture table values were rejected.) In addition, the Commission hopes to minimize the dislocation caused by these changes by ratifying all existing site-specific standards and implementing the revised system on a basin-by-basin, segment-by-segment basis as adequate data becomes available. Adoption of these revisions to the Basic Standards and Methodologies in no way undermines the legitimacy or effectiveness of existing site-specific standards adopted under the previous system.
Generally, the Commission Contemplates that standards will be revised in conjunction with the triennial review of each basin's standards. The new provisions are being adopted because they represent an improvement and refinement of the existing system based on more recent information, not because the existing system is based on material assumptions that were in error or no longer apply. Therefore, this revision of the Basic Standards and Methodologies does not by itself create grounds for site-specific hearings pursuant to 25-8-207, C.R.S. However, the Commission may in its discretion hold hearings to revise site-specific standards in accordance with the new system prior to the next triennial review for a basin where exigent circumstances warrant.
The Commission intends that when considering revision of site-specific standards based on the new system, either all or none of the standards on a particular segment will be revised to conform with the new system, unless there is a compelling justification to vary from this procedure. This should mean that during the transition period of implementation of the new system, dischargers on any given segment are dealing with either the old system or the new system, not a mixture of both. In some instances, during the transition period it may be desirable to collect and analyze data for both total recoverable metals and dissolved metals. At least one party recommended that the Commission adopt a revised system as an alternative to the existing methodologies, without doing away with the existing system. The Commission rejected this approach because it believes it is important to move, over time, to a single, consistent standard-setting system. However, retaining existing site-specific standards and implementing the new system on a site-specific basis only when adequate data is available will ease the transition to the new system.
Although it is not feasible to predict the impact of implementing this new water quality standards system for each stream segment in the State, from the evidence submitted it is clear that certain site-specific standards may become more stringent while others may become more lenient. For example, the revised table values will result in some more stringent standards and some less stringent standards for various metals, depending on water hardness. The new table value acute standards generally will result in less stringent daily maximum effluent limitations in discharge permits. Basing standards on dissolved metals will result in lower in-stream metals standards in certain instances, but this is partly compensated for by corresponding changes in the methodology for analysis of discharge effluents.
The Commission finds that the revisions as a whole are economically reasonable because the new water quality standards system is more scientifically justifiable. Any practical water quality standards system must rely on simplifications and generalizations of the large variety of conditions that exist in nature. In general, the Commission finds that the revisions being adopted as scientific improvements in the system will minimize the potential for over-protection (saving the resources of dischargers) and minimize the potential for under-protection (reducing unwarranted impacts on the State's water quality resources). Therefore the revisions are justified by the need to base standards on the best scientific information available, to the maximum extent feasible.
C. ANALYTICAL TECHNIQUES FOR METALS (Sections 3.1.7, 3.1.14, Table III)
The shift to basing water quality standards on dissolved metals has been undertaken because the evidence indicates that it is the dissolved fraction that is principally responsible for impacts to aquatic life. EPA proposed reliance on an "acid soluble" method for establishing ambient criteria, but the Commission believes the evidence adequately supports reliance on the dissolved method. Generally, the dissolved method more accurately measures (compared to total or total recoverable analyses) the ionic form of metals that is toxic to aquatic life, while excluding less toxic complexed forms. The acid soluble method may overstate the metals that are biologically available to aquatic life.
In addition, dissolved ambient water quality data tends to be more "normally" distributed than total or total recoverable data. Therefore, dissolved data is better suited to the methodology adopted for setting ambient quality-based standards, including the use of Chauvenet's Criteria to screen potential outliers.
Adoption of the potentially dissolved method for effluent monitoring may overstate the availability of ionic metals in an effluent. However, the dissolved method would potentially understate the availability of ionic metals once an effluent has mixed with receiving waters. For example, this would occur where stream pH is lower than effluent pH, so that more metals would be released into solution after mixing with the lower pH receiving waters. To better ensure protection of aquatic life, the Commission has decided as a matter of policy to require the more conservative approach. Also, it is noted that a discharger has the option of using the dissolved method to monitor its effluent if it can demonstrate that the dissolved and potentially dissolved fractions in its effluent are not significantly different.
Because extensive in-stream metals data has not previously been generated, this shift in methodologies will result in additional monitoring costs for the State and the regulated community. However, in certain instances it may be possible to set new dissolved standards without extensive new in-stream data; for example, where table value standards are determined to be appropriate or where appropriate assumptions can be made to set dissolved standards based on existing total recoverable data.
As discussed in the "Overview of Revisions" section of this Statement of Basis and Purpose, current site-specific water quality standards (including metals standards not based on the dissolved method) remain in effect in spite of the adoption of these revisions to the Basic Standards and Methodologies until new site-specific standards are adopted. The Commission intends to move as quickly as feasible (generally through the triennial review process) to the adoption of site-specific dissolved metals standards throughout the State. All interested parties are encouraged to begin collecting and analyzing in-stream metals data using the dissolved method.
Finally, the Commission notes that using dissolved metals values for aquatic life in Table III while using total recoverable values for agriculture and domestic water supply could result in requirements for multiple analyses of water quality samples in some circumstances. It is the Commission's intention that the Division avoid or minimize this result in establishing discharge permit monitoring requirements to the extent feasible, by making appropriate assumptions regarding the relative levels of dissolved and total recoverable metals present.
D. AMBIENT QUALITY-BASED STANDARDS (Section 3.1.7)
For normally distributed data, the new 85th percentile methodology for setting chronic ambient quality-based standards is comparable to the mean plus standard deviation ( x + s) approach previously used. For data sets with a large standard deviation, the 85th percentile methodology will result in a more protective standard. (As discussed above, the shift to dissolved metals analysis will generally result in lower numeric ambient quality-based standards.)
In determining what is "representative data" for setting ambient quality-based standards, the Commission intends that the Division's established procedure for excluding outliers be applied. In order to retain appropriate site-specific flexibility in the process, the Commission decided as a matter of policy not to specify specific techniques for screening outliers in the regulation.
In adopting 85th percentile methodology, the Commission rejected a proposal to set chronic ambient quality-based standards equal to the 50th percentile of representative data and acute ambient quality-based standards equal to the 90th percentile. A shift to the 50th percentile for chronic standards would result in uniformly more stringent water quality standards and effluent limitations compared to the current system. The Commission does not believe that the evidence justifies this change or demonstrates that the 85th percentile methodology (which is generally comparable to the current x + s methodology) is insufficiently protective of state waters. Adoption of the 85th percentile methodology means that it is expected that 15 percent of the data for a given segment is expected to exceed standards set equal to the 85th percentile. Such exceedances do not constitute a violation of ambient quality-based standards.
There was evidence submitted that setting an ambient quality-based standard above the 50th percentile can result over time in a "creeping mean." In other words, since dischargers can discharge up to the standard, over time the mean water quality value may increase, justifying an upward revision of the standard, based on a new 85th percentile value. Other testimony indicated that this risk is largely theoretical, since dischargers must plan to routinely discharge at levels below established effluent limitations in order to assure that they remain in compliance. In addition, because permit limitations are based on low flows, during most of the year discharge levels should not result in a significant increase in ambient levels. Moreover, standards based on ambient quality generally are set factoring out the contribution of point source discharges. The Commission determined that the theoretical creeping mean is not likely to occur.
The revised regulation also explicitly provides for an additional alternative basis for establishing site-specific standards. Site-specific-criteria-based standards may be established when justified by the results of a bioassay or comparable scientific study. This provision essentially codifies previous practice and preserves flexibility in the standard-setting process. It provides a mechanism for taking the wide variation of conditions that exist in Colorado into account when adopting site-specific standards. For example, site-specific standards may be determined from a recalculation based on the species present at a particular location.
The Commission finds that in certain circumstances even substantial improvements in water quality will not result in any furtherance of the "fishable-swimmable" goal, as where factors other than water quality limit the diversity and abundance of aquatic life. Under such circumstances it would be unsound policy to require standards reflecting a need for substantial improvements in water quality.
E. REVISED TABLE VALUES FOR METALS (Table III)
The adoption of new tiered, acute and chronic table values for metals should result in more accurate protection of water bodies from short and long-term impacts. The values have been adopted using the current EPA water quality criteria, modified to apply to Colorado. Some parties testified that the new table values are inappropriately based on excessive, multiple safety factors. However, EPA testified that in certain respects the approach adopted by the Commission is not conservative enough. The Commission has decided as a matter of policy that the safety factors provided are not excessive. This conclusion is reinforced in part by the fact that the new chronic table values are partly more stringent and partly less stringent than the existing table values.
Moreover, the Commission feels that the safety factors reflected in the table values are appropriate and necessary because those values are intended to protect aquatic life over a wide range of conditions throughout the State. The conservative nature of the table values is tempered by the availability of alternative approaches to setting site-specific standards when justified by available site-specific information. Both ambient quality-based standards and site-specific-criteria-based standards are available alternatives in such circumstances.
For simplicity, the Colorado Final Chronic value (FCV) as described in the Water Quality Standards and Methodologies Committee report is referred to in the regulation as the "chronic" value. The Colorado Criterion Maximum Concentration (CMC) is referred to as the "acute" value. The Committee report also discussed a Colorado Final Acute Value (FAV), to be applied when more extensive monitoring is undertaken. The Commission considered but rejected the option of establishing alternative acute table values equal to the FAV.
Some parties testified that an acute (i.e. 24-hour average) standard based on the CMC is excessively stringent, since the CMC is equal to one-half of the FAV, which in turn represents the 96-hour LC-50 that should protect 95 percent of the genera from acute toxic effects. The Commission decided as a matter of policy that the more conservative CMC-based acute standards are appropriate. The Commission felt that an alternative acute standard equal to the FAV walks too close to the edge of potential impacts. In fact, it is a concentration expected to adversely impact 50 percent of the fifth percentile of the genera tested. Moreover, there was testimony that the costs of the increased monitoring that would be required to allow reliance on a more lenient alternative acute standard would be excessive so that dischargers would be unlikely to choose that option.
The majority of the new Table III metals values are based on equations that rely on ambient measurements of water hardness. The equations reflect the reduced toxicity of metals in higher hardness waters. The proposed revisions also provided that alkalinity values may be substituted for hardness in the equations. This would have been generally consistent with the Commission's previous practice of using the more stringent of available hardness or alkalinity data in determining the applicable "range" of metals values in Table III and setting site-specific standards based on that determination. The Commission felt that there was insufficient evidence justifying a direct substitution of alkalinity into equations developed based on hardness. The new table value equations are based on a data base that uses hardness data. For these reasons, the Commission deleted the alternative of substituting alkalinity into the Table III equations. Where appropriate site-specific evidence has been developed, alkalinity may be a factor in establishing site-specific-criteria-based standards.
Several parties testified that the proposed table values in certain instances unacceptably result in standards below detection limits associated with standard analytical techniques. However, the evidence generally was lacking in specific information to demonstrate that detection limits present a practical problem in implementing stream standards, although similar concerns had been raised in earlier hearings. One witness did propose adoption of a new set of definitions to address the concerns raised. Because this issue was not addressed in the notice for this hearing, and because the Commission feels that insufficient information was presented at the hearing to warrant new provisions regarding detection limits at this time, the Commission has not included any such provisions in the revisions being adopted. This issue may be addressed in a future rulemaking hearing if specific information and/or proposals submitted to the Commission warrant.
Footnote 5 to Table III states that standards based on these table values are not to be exceeded more than once every three years on the average. This provision is adopted based on evidence that aquatic life can recover from impacts if not exposed to exceedances more frequently than once every three years.
Finally, the Commission notes that the new acute metals table values adopted, once translated into site-specific acute standards, may in many instances result in less stringent short-term effluent limitations in discharge permits, as compared to the current system. Currently, daily maximum effluent limitations generally are established equal to twice the 30-day average effluent limitation. Because the new acute table values often are more than twice the corresponding chronic value, standards based on these numbers would result in less stringent daily maximum effluent limitations.
F. REVISED UNIONIZED AMMONIA TABLE VALUES (TABLE II)
The adoption of new tiered, acute and chronic table values for unionized ammonia should result in more accurate protection of water bodies from short and long-term impacts. The new acute table values for class 1 warm and cold water aquatic life are based on equations that take pH and temperature into account. The primary controversies regarding these equations centered on the extent of safety factors included and the appropriate universe of aquatic life on which to base the equations.
With respect to acute values, the Commission adopted an approach consistent with its adoption of new acute table values for metals. That is, the acute unionized ammonia values are based on one-half of the 96-hour LC-50 level that protects 95 percent of the genera. In general, the Commission believes that the safety factors present are not excessive.
With respect to species considered in developing the equations, the Commission decided as a matter of policy that the golden shiner and orangethroat darter should be included. Even though these species are present only in limited areas, they should be included in a statewide value intended to protect waters throughout the state. Under the alternatives provided in the revised regulation, site-specific-criteria-based standards (which may not be protective of these specific species) can be established in lieu of table value standards where warranted by available information.
Consistent with the methodology underlying the equations for new metals table values, the Commission determined that invertebrates should be included in developing the ammonia equations. Healthy invertebrate populations are essential to viable aquatic ecosystems. However, including some invertebrates in the calculations did not change the final table values.
The Nitrogen Cycle Committee proposed varying ammonia standards based on whether salmonids are present or absent, rather than on whether waters are cold or warm. Because this change would not result in a major difference in the standards applied to most state waters, the Commission chose to stay with the current system of basing distinctions on cold versus warm water. This will help minimize disruption of the current system.
The Class 1 cold and warm water, acute and chronic table values adopted conform with the recommendations of the Nitrogen Cycle Committee, based on EPA documentation (translating salmonid/non-salmonid values into cold/warm water values, respectively), with minor modifications. The acute values are based on EPA's criteria calculation procedures. The cold water acute value results specifically from data on the adult male rainbow trout. The warm water acute value results from using in the EPA equations available data for warmwater species found in Colorado.
The Class 1 cold and warm water chronic values are the same as those contained in the existing regulation. The Nitrogen Cycle Committee recommended values of 0.02 mg/l and 0.05 mg/l for cold and warm water segments, respectively. These values were calculated to correspond to the 95 percent protection level when the number of taxa in the calculation is 19. However, for several reasons the Commission decided not to lower the chronic value to 0.05 mg/l as proposed. There was evidence submitted that it is difficult to distinguish between aquatic life impacts resulting from 0.06 mg/l versus 0.05 mg/l unionized ammonia. Adoption of the 0.06 mg/l value has the benefit of minimizing disruption to the current standards-setting system. This is particularly appropriate when the lower 0.05 mg/l value could result in substantial additional costs for some dischargers, without necessarily resulting in identifiable environmental benefits.
The Class 2 cold and warm water acute and chronic table values are essentially the same as Class 1, except that a range of 0.06 to 0.10 mg/l is provided for chronic values, depending upon the aquatic life present or intended to be protected on a site-specific basis, and whether the waters have been adversely impacted by factors other than ammonia. The evidence demonstrated that values near the higher end of this range may not be protective of certain species, such as the Johnny darter. Therefore, the absence of such sensitive species should be demonstrated to justify a site-specific standard in the upper end of the range.
The adoption of the 0.06 to 0.10 mg/l range is based on a policy judgement regarding the appropriate degree of flexibility to vary precise protection levels and take into account site-specific circumstances when adopting site-specific standards. A level of 0.08 mg/l unionized ammonia represents the 90 percent protection level. Moreover, the Nitrogen Cycle Committee found that it is difficult to toxicologically differentiate between the 0.08 and 0.10 mg/l levels. Thus, the upper end of the range accepts some sublethal effects. One study of the South Platte River (entitled "Physical, Chemical, and Biological Characteristics of the South Platte River, Segment 15, in Relation to Classified Uses" , by William M. Lewis, Jr. and James F. Saunders III, dated November 13, 1985) found no identifiable differences in diversity or abundance of aquatic life for unionized ammonia levels in the range of 0.05 to 0.10 mg/l.
Finally, although the Committee report recommended that a chronic standard greater than 0.10 mg/l not be allowed, under the approach adopted by the Commission a higher site-specific standard could adopted for severely impacted segments where justified by an appropriate site-specific study in accordance with Section 3.1.7 (c) (iii) of the regulation. Such a study may consider whether factors other than ammonia reduce the diversity and abundance of species present.
G. REVISED NITRITE STANDARD FORMULA (Table II)
The revised aquatic life table values for nitrite are based on equations that take into account the buffering effects of chloride ions on nitrite toxicity. The City of Longmont testified that this approach included too many safety factors, while Denver Metro supported the proposal. The Commission has decided as a matter of policy that the safety factors included are appropriate. The Commission intends that existing nitrite standards will remain in effect until adequate chloride data is developed on a site-specific basis to allow application of the new formula.
The Nitrogen Cycle Committee also proposed revisions of the nitrite and nitrate table values for the agricultural use classification. No public comment was received regarding this proposal and the Commission has decided to make no change in the existing table values at this time.
H. DOMESTIC WATER SUPPLY CLASSIFICATIONS (Section 3.1.13(1) (d))
The Nitrogen Cycle Committee proposed subdividing the current domestic water supply classification for surface waters into two classifications, depending on the levels of total ammonia present and the need for standard or special treatment of waters prior to use. The hearing proposal for a new classification was similar, but not tied specifically to ammonia levels. Limited comment was received regarding this proposal. Because questions regarding the application and impact of this proposed new classification have not yet been fully examined, the Commission has decided to make no changes in the existing domestic water supply classifications at this time. In particular, the Commission was concerned that the proposal would have resulted in a new "priority to pollute" concept being added to Colorado water quality regulation, accepting the presence of pollution if an upstream discharge is established prior to a downstream water supply use.
I. LOW FLOW CRITERIA (Section 3.1.9(1))
As noted above, the Commission decided to make no change in the current low flow criteria at this time, pending analysis of additional information, including the results of a low flow study undertaken by Colorado State University. The Commission contemplates that this issue will be addressed in an additional rulemaking hearing prior to the effective date of these revisions.
J. DELETION OF SECTION 3.1.4
Section 3.1.4 of the Basic Standards and Methodologies, entitled "Implementation" , was repealed effective June 9, 1980, after a public hearing on March 3, 1980, but was not deleted from the Colorado Code of Regulations by the Secretary of State's Office. The Commission's action here merely ratifies that earlier action, so that the deletion will appear in the official published regulation.
FISCAL IMPACT STATEMENT
The most significant change embodied in these amendments is the use of dissolved metals standards dependent upon hardness levels instream, and the corresponding requirement of the potentially dissolved metals analytical test by dischargers. Since a relatively small ambient data base for dissolved metals exists compared to the total recoverable data base, it is unknown at this time whether this change in metal form will require additional treatment costs for dischargers of metals to state waters. However, it is likely that some relief in the form of relaxed discharge limits may be realized by adopting this new system since most metals in effluents are likely to be in the bound or total form.
Some site-specific standards may become more stringent as a result of these revisions and some less stringent (once the revisions are translated into new site-specific standards). Therefore, for some dischargers costs may increase while for others they decrease. More specifically, limitations may become more stringent for some that discharge to low hardness waters and less stringent for those that discharge to high hardness waters.
The use of acute and chronic standards with the corresponding two-tiered discharge permit limits will allow more flexibility to the discharger by not penalizing him for short-term excursions above a chronic limit. In many instances short-term effluent limitations under the new system will be less stringent than short-term effluent limitations under the previous system. This should result in less economic burden to dischargers of both metals and nitrogen compounds.
Since the ammonia table values are essentially identical to previous standards, no major additional economic consequences are anticipated from these revised provisions. In isolated circumstances, the new table values for Class 2 aquatic life classifications could result in more stringent ammonia standards on a site-specific basis. In such instances, the economic impact of such standards will be addressed in the site-specific hearings. The other changes to nitrogen parameters should have no substantial economic ramifications.
The recognition of tolerable excursion of these standards no more than once every three years should also provide some economic relief to dischargers since previously the level of tolerance was once every ten years.
These changes are all made in recognition of maintaining the beneficial uses of the state's waters. Preservation of the uses to the level maintained in the recent past represents an economic benefit to the citizens of the state. In general, the Commission finds that the revisions being adopted as scientific improvements in the system will minimize the potential for over-protection (saving the resources of dischargers) and minimize the potential for under-protection (reducing unwarranted impacts on the State's water quality resources).
PARTIES TO PROCEEDINGS
1. Adolph Coors Company
2. Castle Pines; Silverthorne/Dillon; and Purgatory
3. Larimer-Weld Regional Council of Governments
4. Cotter Corporation
5. The Colorado Association of Commerce and Industry (CACI)
6. The City of Boulder
7. The City of Loveland
8. The City of Longmont
9. AMAX Inc.
10. The Colorado Water Congress (CWC)
11. Eastman Kodak Company
12. Trout Unlimited
13. Colorado Mining Association (CMA)
14. Gulf & Western
15. Metro Denver Sewage Disposal District No. 1
