5 Colo. Code Regs. § 1002-31.16

Current through Register Vol. 47, No. 20, October 25, 2024

Section 5 CCR 1002-31.16 - [Effective 12/31/2024] TABLES

(1)INTRODUCTION

The numeric levels for parameters listed in Tables I, II, III shall be considered and applied as appropriate by the Commission in establishing site-specific numeric standards, in accordance with section 31.7.

For the purposes of integrating these parameters into NPDES discharge permits, the duration of the averaging period for the numeric level is designated in the tables. Chronic levels and 30-day levels are to be averaged as defined in section 31.5(7). Acute levels and 1-day levels are to be averaged as defined in section 31.5(2).

Certain toxic metals for Aquatic Life have different numeric levels for different levels of water hardness. Water hardness is being used here as an indication of differences in the complexing capacity of natural waters and the corresponding variation of metal toxicity. Other factors such as organic and inorganic ligands, pH, and other factors affecting the complexing capacity of the waters may be considered in setting site-specific numeric standards in accordance with section 31.7. Metals listed in Table III for aquatic life uses are stated in the dissolved form unless otherwise indicated.

(2)TESTING PROCEDURES

Various testing procedures to determine that numeric values for water quality parameters may be appropriate to present to the Water Quality Control Commission at stream classification hearings. (See section 31.6(3)). These include:

(a) Standard Test Procedures

(i) Code of Federal Regulations, Title 40, Part 136;

(ii) The latest approved EPA Methods for Chemical Analysis of Water and Wastes;

(iii)Standard Methods for the Examination of Water and Wastewater (current edition), American Public Health Association;

(iv)ASTM Standards, Part 31, Water;

(v) EPA Biological Field and Laboratory Methods.

(b) Toxicity testing and Criteria Development Procedures:

(i) The latest EPA Methods for Chemical Analysis of Water and Wastewater; ASTM, Standard Methods for Examination of Water, Wastewater;

(ii)Interim Guidance on Determination and Use of Water-Effect Ratio for Metals, EPA-823-B-94-001, U.S. Environmental Protection Agency, February, 1994.

(iii) Other approved EPA methods.

(c) Other Procedures:

Other procedures may be deemed appropriate by either the Water Quality Control Commission and/or the Water Quality Control Division.

(3)REFERENCES

Capital letters following levels in the tables indicate the sources of the level; they are referenced below.

(A) EPA Quality Criteria for Water, July 1976, U.S. Environmental Protection Agency, U.S. Government Printing Office: 1977 0-222-904, Washington, D.C. 256 p.

(B) EPA Water Quality Criteria 1972, Ecological Research Series, National Academy of Sciences, National Academy of Engineering, EPA-R3-73-033, March 1973, Washington, D.C. 594 p.

(C) Davies, P.H. and Goettl, J.P., Jr., July 1976, Aquatic Life - Water Quality Recommendations for Heavy Metal and Other Inorganics.

(D) Parametrix Inc., Attachment II, Parametrix Reports - Toxicology Assessments of As, Cu, Fe, Mn, Se, and Zn, May 1976, Bellevue, Washington, 98005. submitted to Water Quality Control Commission by Gulf Oil Corp., Inc., 161 p.

(E) EPA National Interim Primary Drinking Water Regulations, 40 Code of Federal Regulations, Part 141.

(F) EPA, March 1977, Proposed National Secondary Drinking Water Regulation, Federal Register, Vol. 42 No. 62, pp 17143-17147.

(G) Recommendations based on review of all available information by the Committee on Water Quality Standards and Stream Classification.

(H) American Fishery Society, June 1978, A Review of the EPA Red Book Quality Criteria for Water, (Preliminary Edition).

(I) Section 307 of the Clean Water Act, regulations promulgated pursuant to Section 307.

(J) Final Report of the Water Quality Standards and Methodologies Committee to the Colorado Water Quality Control Commission, June 1986.

(K) Proposed Nitrogenous Water Quality Standards for the State of Colorado, by the Nitrogen Cycle Committee of the Basic Standards Review Task Force, March 12, 1986 (Final Draft).

(L)Quality Criteria for Water, 1986, and Updates Through 1989, U.S. Environmental Protection Agency, U.S. Government Printing Office, EPA 440/5-86-001, Washington, D.C. 20460.

(M) Level modified by Commission

(N) 1999 Update of Ambient Water Quality Criteria for Ammonia (1999 Ammonia Update), U.S. Environmental Protection Agency, Office of Water, EPA-823-F-99-024, Washington, D.C. 20460.

(O) Raisbeck, M.F., S. L. Riker, C. M. Tate, R. Jackson, M. A. Smith, K. J. Reddy and J. R. Zygmunt. 2008. Water quality for Wyoming livestock and wildlife. University of Wyoming AES Bulletin B-1183.

(P) Agency for Toxic Substances and Disease Registry, Toxicological Profile for Molybdenum, May 2020

TABLE I - PHYSICAL AND BIOLOGICAL PARAMETERS

TABLE I PHYSICAL AND BIOLOGICAL PARAMETERS
Parameter	Recreation			Aquatic Life			Agriculture	Domestic Water Supply
	CLASS E (Existing Primary Contact) and CLASS U (Undetermined Use)	CLASS P (Potential Primary Contact Use)	CLASS N (Not Primary Contact Use)	CLASS 1 COLD WATER BIOTA	CLASS 1 WARM WATER BIOTA	CLASS 2
PHYSICAL
D.O. (mg/L)(1)(9)	3.0(A)	3.0(A)	3.0(A)	6.0(2)(G) 7.0 (spawning)	5.0(2)(G)	5.0(A)	3.0(A)	3.0(A)
pH (Std. Units)(3)	6.5-9.0(B,M)	6.5-9.0(B,M)	6.5-9.0(B,M)	6.5-9.0(A)	6.5-9.0(A)	6.5-9.0(A)		5.0-9.0(A)
Suspended Solids(4)
Temperature (°C)(5)				Rivers & Streams: Tier Ia,g: June-Sept = 17.0 (ch), 21.7 (ac) Oct -May = 9.0 (ch), 13.0 (ac) Tier IIb,g: Apr-Oct = 18.3 (ch), 24.3 (ac) Nov-Mar = 9.0 (ch), 13.0 (ac) Lakes & Resh: Apr-Dec = 17.0 (ch), 21.2 (ac) Jan-Mar = 9.0 (ch), 13.0 (ac) Large Lakes & Resc,h: Apr-Dec = 18.3 (ch), 24.2 (ac) Jan-Mar = 9.0 (ch), 13.0 (ac)	Rivers & Streams: Tier Id: Mar-Nov = 24.2 (ch), 29.0 (ac) Dec-Feb = 12.1 (ch), 24.6 (ac) Tier IIe: Mar-Nov = 27.5 (ch), 28.6 (ac) Dec-Feb = 13.8 (ch), 25.2 (ac) Tier IIIf: Mar-Nov = 28.7 (ch), 31.8 (ac) Dec-Feb = 14.3 (ch), 24.9 (ac) Lakes & Res: Apr-Dec = 26.2 (ch), 29.3 (ac) Jan-Mar = 13.1 (ch), 24.1 (ac)	Same as Class 1
BIOLOGICAL:
E. coli per 100 ml	126(7)	205(7)	630(7)					630
Note: Capital letters In parentheses refer to references listed in section 31.16; numbers in parentheses refer to Table I footnotes.
Temperature Definitions a Cold Stream Tier I temperature criteria apply where cutthroat trout and brook trout are expected to occur. b Cold Stream Tier II temperature criteria apply where cold-water aquatic species, excluding cutthroat trout or brook trout, are expected to occur. c Large Cold Lakes temperature criteria apply to lakes and reservoirs with a surface area equal to or greater than 100 acres surface area. d Warm Stream Tier I temperature criteria apply where common shiner, johnny darter, or orangethroat darter, or stonecat are expected to occur. e Warm Stream Tier II temperature criteria apply where brook stickleback, central stoneroller, creek chub, finescale dace, longnose dace, mountain sucker, northern redbelly dace, razorback sucker, or white sucker are expected occur, and none of the more thermally sensitive species in Tier I are expected to occur. f Warm Stream Tier III temperature criteria apply where warm-water aquatic species are expected to occur, and none of the more thermally sensitive species in Tiers I and II are expected to occur. g Mountain whitefish-based summer temperature criteria [16.9 (ch), 21.2 (ac)] apply when and where spawning and sensitive early life stages of this species are known to occur. h Lake trout-based summer temperature criteria [16.6 (ch), 22.4 (ac)] apply where appropriate and necessary to protect lake trout from thermal impacts.

Table I - Footnotes

(1) Standards for dissolved oxygen are minima, unless specified otherwise. For the purposes of permitting, dissolved oxygen may be modeled for average conditions of temperature and flow for the worst case time period. Where dissolved oxygen levels less than these levels occur naturally, a discharge shall not cause a further reduction in dissolved oxygen in receiving water. (For lakes, also see footnote 9.)

(2) A 7.0 mg/liter standard (minimum), during periods of spawning of cold water fish, shall be set on a case by case basis as defined in the NPDES or CDPS permit for those dischargers whose effluent would affect fish spawning.

(3) The pH standards of 6.5 (or 5.0) and 9.0 are an instantaneous minimum and maximum, respectively to be applied as effluent limits. In determining instream attainment of water quality standards for pH, appropriate averaging periods may be applied, provided that beneficial uses will be fully protected.

(4) Suspended solid levels will be controlled by Effluent Limitation Regulations, Basic Standards, and Best Management Practices (BMPs).

(5) Temperature shall maintain a normal pattern of diel and seasonal fluctuations and spatial diversity with no abrupt changes and shall have no increase in temperature of a magnitude, rate, and duration deleterious to the resident aquatic life. These criteria shall not be interpreted or applied in a manner inconsistent with section 25-8-104, C.R.S.

a. The MWAT of a waterbody shall not exceed the chronic temperature criterion more frequently than one event in three years on average.

b. The DM of a waterbody shall not exceed the acute temperature criterion more frequently than one event in three years on average.

c. The following shall not be considered an exceedance of the criteria:

i. Lakes and reservoirs: When a lake or reservoir is stratified, the mixed layer may exceed the applicable temperature criteria in Table I provided that an adequate refuge exists in water below the mixed layer. Adequate refuge means that there is concurrent attainment of the applicable Table I temperature and dissolved oxygen criteria. If the refuge is not adequate because of dissolved oxygen levels, the lake or reservoir may be included on the 303(d) List as "impaired" for dissolved oxygen, rather than for temperature.

ii. A "warming event" is the maximum allowable extent of exceedances above the standard, in units of degree-days (°C-days). This concept integrates both the magnitude of temperature (°C) above the standard as well as the duration (in days) and represents the cumulative temperatures above which growth or lethal impacts to fisheries are expected. For all Cold Stream tiers the allowable degree-days are 2.4 (acute) and 13.5 (chronic). For all Warm Stream tiers the allowable degree-days are 3.8 (acute) and 35.5 (chronic).

(6) Deleted

(7)E. coli criteria and resulting standards for individual water segments are established as indicators of the potential presence of pathogenic organisms. Standards for E. coli are expressed as a two-month geometric mean. Site-specific or seasonal standards are also two-month geometric means unless otherwise specified.

(8) Deleted

(9) The dissolved oxygen standard applies to lakes and reservoirs as follows.

a. Recreation: In the upper portion of a lake or reservoir, dissolved oxygen shall not be less than the criteria in Table I or the applicable site-specific standard. In the lower portion of a lake or reservoir, dissolved oxygen may be less than the applicable standard except where a site-specific standard has been adopted. A site-specific dissolved oxygen standard will be established for the lower portion of a lake or reservoir where there is evidence that primary contact occurs within the lower portion.

b. Agriculture: In the upper portion of a lake or reservoir, dissolved oxygen shall not be less than the criteria in Table I or the applicable site-specific standard. In the lower portion of a lake or reservoir, dissolved oxygen may be less than the applicable standard except where a site-specific standard has been adopted. A site-specific dissolved oxygen standard will be established for the lower portion of a lake or reservoir where there is evidence that livestock watering or irrigation water is pumped from the lower portion.

c. Aquatic Life: In the upper portion of a lake or reservoir, dissolved oxygen shall not be less than the criteria in Table I or the applicable site-specific standard. In the lower portion of a lake or reservoir, dissolved oxygen may be less than the applicable standard as long as there is adequate refuge. Adequate refuge means that there is concurrent attainment of the applicable Table I temperature and dissolved oxygen criteria. A site-specific dissolved oxygen standard will be established for the lower portion of a lake or reservoir where the expected aquatic community has habitat requirements within the lower portion.

i. Fall turnover exclusion: Dissolved oxygen may drop 1 mg/L below the criteria in Table I in the upper portion of a lake or reservoir for up to seven consecutive days during fall turnover provided that profile measurements are taken at a consistent location within the lake or reservoir 7-days before, and 7-days after the profile with low dissolved oxygen. The profile measurements taken before and after the profile with low dissolved oxygen must attain the criteria in Table I in the upper portion of the lake or reservoir. The fall turnover exclusion does not apply to lakes or reservoirs with fish species that spawn in the fall unless there are data to show that adequate dissolved oxygen is maintained in all spawning areas, for the entire duration of fall turnover.

d. Water Supply: The dissolved oxygen criteria is intended to apply to the epilmnion and metalimnion strata of lakes and reservoirs. Dissolved oxygen in the hypolimnion may, due to the natural conditions, be less than the table criteria. No reductions in dissolved oxygen levels due to controllable sources is allowed.

TABLE II - INORGANIC PARAMETERS

TABLE II INORGANIC PARAMETERS
Parameter	Aquatic Life						Agriculture	Domestic Water Supply
	CLASS 1 COLD WATER BIOTA		CLASS 1 WARM WATER BIOTA		CLASS 2
Ammonia (mg/L as N) Total	chronic = elsp or elsa(1) acute = sp(1)(N)		chronic = Apr 1-Aug 31 = elsp(1) Sept 1-Mar 29 = elsa(1) acute = sa(1)(N)		Class 2 Cold/Warm have the same standards as Class 1 Cold/Warm(N)
Total residual Chlorine (mg/L)	0.019(L) (acute)	0.011(L) (chronic)	0.019(L) (acute)	0.011(L) (chronic)	0.019(L) (acute)	0.011(L) (chronic)
Cyanide - Free (mg/L)	0.005(H) (acute)		0.005(H) (acute)		0.005(H) (acute)		0.2(G) (acute)	0.2(B,D,M) (acute)
Fluoride(6) (mg/L)								2.0 (E) (acute)
Nitrate (mg/L as N)							100(2)(B) (acute)	10(4)(K) (acute)
Nitrite (mg/L as N)	TO BE ESTABLISHED ON A CASE BY CASE BASIS(3)				A CASE BY CASE BASIS(3)		10(2)(B) (acute)	1.0(2)(4)(K) (acute)
Sulfide as H2S (mg/L)	0.002 undissociated(A) (chronic)		0.002 undissociated(A) (chronic)		0.002 undissociated(A) (chronic)			0.05(F) (chronic)
Boron (mg/L)							0.75(A,B) (chronic)
Chloride (mg/L)							250(F) (chronic)
Sulfate, dissolved(7) (mg/L)							250(F) (chronic)
Asbestos(6) fibers/L							7,000,000 (5) (chronic)
Note: Capital letters in parentheses refer to references listed in 31.16(3); numbers in parentheses refer to Table II footnotes.

Table II - Footnotes

(1) Chronic:

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(2) In order to provide a reasonable margin of safety to allow for unusual situations such as extremely high water ingestion or nitrite formation in slurries, the NO3-N plus NO2-N content in drinking waters for livestock and poultry should be limited to 100ppm or less, and the NO2-N content alone be limited to 10ppm or less.

(3) Salmonids and other sensitive fish species* present:

Acute= 0.10 (0.59 * [Cl-]+3.90) mg/L NO2-N Chronic= 0.10 (0.29 * [Cl-]+0.53) mg/L NO2-N

[Cl-] = Chloride ion concentration; upper limit for Cl- = 40 mg/L Salmonids and other sensitive fish species* absent: Acute= 0.20 (2.00 * [Cl-]+0.73) mg/L NO2-N Chronic=0.10 (2.00 *[Cl-]+0.73) mg/L NO2-N

[Cl-] = Chloride ion concentration; upper limit for Cl- = 22 mg/L

*Sensitive fish species include salmonids, channel catfish, logperch and brook stickleback. Either total or dissolved chloride data may be used in these equations.

(4) The combined total of nitrate plus nitrite will not exceed 10 mg/L.

a. The§ nitrate limit shall be calculated to meet the relevant standard in accordance with the provisions of Section 31.10 of this regulation, unless the permittee provides documentation that a reasonable level of inquiry demonstrates that there is no actual domestic water supply use of the waters in question or of hydrologically connected groundwater. The combined total of nitrate plus nitrite at the point of intake to the domestic water supply will not exceed 10 mg/L as demonstrated through modeling or other scientifically supportable analysis. (This Footnote 4a is repealed effective 12/31/2022).

(5) Asbestos standard applies to fibers 10 micrometers or longer.

(6) Consistent with 31.7(1)(b) and 31.7(2), these table values will be applied on a site-specific basis.

(7) The dissolved sulfate standard may be assessed and implemented from either unfiltered or filtered samples.

TABLE III - METAL PARAMETERS

TABLE III METAL PARAMETERS (concentration in µg/L)
Metal(1)	Aquatic Life(1)(3)(4)(J)		Agriculture(2)	Domestic Water Supply(2)	Water + Fish(7)	Fish Ingestion(10)
	ACUTE	CHRONIC	CHRONIC		CHRONIC	CHRONIC
Aluminum	e(1.3695*In(hardness)+1.8308) (total recoverable)	87 or e(1.3695*In(hardness)-0.1158) (total recoverable)(11)			---	---
Antimony(18)				6.0 (chronic)	5.6	640
Arsenic	340	150	100(A)	0.02 - 10(13) (chronic)	0.02	7.6
Barium(18)				1,000(E) (acute) 490 (chronic)	---	---
Beryllium(18)			100(A,B)	4.0 (chronic)	---	---
Cadmium	Warm(17) = (1.136672-(ln(hardness)* 0.041838))*e(0.9789*ln(hardness)-3.443) Cold(17) = (1.136672-(ln(hardness)* 0.041838))*e(0.9789*ln(hardness)-3.866)	(1.101672-(ln(hardness)*0.041838))* e(0.7977*ln(hardness)-3.909)	10(B)	5.0(E) (acute)	---	---
Chromium III(5)	e(0.819*ln(hardness)+2.5736)	e(0.819*ln(hardness)+0.5340)	100(B)	50(E) (acute)	---	---
Chromium VI(5)	16	11	100(B)	50(E) (acute)	100	---
Copper	e(0.9422*ln(hardness)-1.7408)	e(0.8545*ln(hardness)-1.7428)	200(B)	1,000(F) (chronic)	1,300	---
Iron		1,000 (total recoverable)(A,C)		300 (dissolved)(F) (chronic)	---	---
Lead	(1.46203-(ln(hardness)* 0.145712))*e(1.273*ln(hardness)-1.46)	(1.46203-(ln(hardness)* 0.145712))*e(1.273*ln(hardness)-4.705)	100(B)	50(E) (acute)	-	---
Manganese	e(0.3331*ln(hardness)+6.4676)	e(0.3331*ln(hardness)+5.8743)	200(B)(12)	50 (dissolved)(F) (chronic)	-	---
Mercury		FRV(fish)(6) = 0.01 (total recoverable)		2.0(E) (acute)	-	---
Molybdenum			300(O)(15)	530(P) (chronic)
Nickel	e(0.846*ln(hardness)+2.253)	e(0.846*ln(hardness)+0.0554)	200(B)	100(E) (chronic)	610	4,600
Selenium(9)	18.4	4.6	20(B,D)	50(E) (chronic)	170	4,200
Silver	0.5*e(1.72*ln(hardness)-6.52)	e(1.72*ln(hardness)-9.06) Trout(19) = e(1.72*ln(hardness)-10.51)		100(F) (acute)	-	---
Thallium(18)		15(C)		0.5 (chronic)	0.24	0.47
Uranium(16)	e(1.1021*ln(hardness)+2.7088)	e(1.1021*ln(hardness)+2.2382)		16.8 - 30(13) (chronic)	---	---
Zinc	0.978*e(0.9094*ln(hardness)+0.9095)	0.986*e(0.9094*ln(hardness)+0.6235) Sculpin(14) = e(2.140*ln(hardness)-5.084)	2000(B)	5,000(F) (chronic)	7,400	26,000
Note: Capital letters in parentheses refer to references listed in section 31.16(3); numbers in parentheses refer to Table III footnotes.

Table III - Footnotes

(1) Metals for aquatic life use are stated as dissolved unless otherwise specified.

Where the hardness-based equations in Table III are applied as table value water quality standards for individual water segments, those equations define the applicable numerical standards. As an aid to persons using this regulation, Table IV provides illustrative examples of approximate metals values associated with a range of hardness levels. This table is provided for informational purposes only.

(2) Metals for agricultural and domestic uses are stated as total recoverable unless otherwise specified.

(3) Hardness values to be used in equations are in mg/L as calcium carbonate and shall be no greater than 400 mg/L. The exception is for aluminum, where the upper cap on calculations is a hardness of 220 mg/L. For permit effluent limit calculations, the hardness values used in calculating the appropriate metal standard should be based on the lower 95 percent confidence limit of the mean hardness value at the periodic low flow criteria as determined from a regression analysis of site specific data. Where insufficient site-specific data exists to define the mean hardness value at the periodic low flow criteria, representative regional data shall be used to perform the regression analysis. Where a regression analysis is not possible, a site-specific method should be used, e.g., where hardness data exists without paired flow data, the mean of the hardness during the low flow season established in the permit shall be used. In calculating a hardness value, regression analyses should not be extrapolated past the point that data exist. For determination of standards attainment, where paired metal/hardness data is available, attainment will be determined for individual sampling events. Where paired data is not available, the mean hardness will be used.

(4) Both acute and chronic numbers adopted as stream standards are levels not to be exceeded more than once every three years on the average.

(5) Unless the stable forms of chromium in a water body have been characterized and shown not to be predominantly chromium VI, data reported as the measurement of all valence states of chromium combined should be treated as chromium VI. In addition, in no case can the sum of the concentrations of chromium III and chromium VI or data reported as the measurement of all valence states of chromium combined exceed the water supply standards of 50 µg/L chromium in those waters classified for domestic water use.

(6) FRV means Final Residue Value and should be expressed as "total recoverable" mercury. The term "total recoverable" refers to the mineral acid digestion of an unfiltered sample to account for all forms of mercury present in water. Mercury data analyzed and reported as "total" or "total recoverable" mercury by using EPA approved total mercury analysis methods listed in 40 CFR 136.3 are considered equivalent.

Many forms of mercury are readily converted to toxic forms under natural conditions. The FRV of 0.01 µg/liter is the maximum allowed concentration of total mercury in the water. This value is estimated to prevent bioaccumulation of methylmercury in edible fish or shellfish tissue above the fish tissue standard for methylmercury of 0.3 mg/kg.

In waters supporting populations of fish or shellfish with a potential for human consumption, the Commission can adopt the FRV as the stream standard to be applied as a 30-day average. Alternatively, the Commission can adopt site-specific ambient-based standards for mercury in accordance with section 31.7. Site-specific water-column standards shall be calculated from the site-specific bioaccumulation factor, using measured water column concentrations of total mercury and measured fish tissue concentrations of methylmercury. Fish tissue data shall be collected from species of the highest trophic level present in the waterbody. Fish tissue samples should include older, larger individuals present in the waterbody. A bioaccumulation factor should be calculated separately for each species sampled, and the highest bioaccumulation factor should be used to calculate the site-specific water column standard in order to prevent the average fish tissue concentrations from exceeding 0.3 mg/kg for all species.

(7) Applicable to all Class 1 aquatic life segments which also have a water supply classification or Class 2 aquatic life segments which also have a water supply classification designated by the Commission after rulemaking hearing. These Class 2 segments will generally be those where fish of a catchable size and which are normally consumed are present, and where there is evidence that fishing takes place on a recurring basis. The Commission may also consider additional evidence that may be relevant to a determination whether the conditions applicable to a particular segment are similar enough to the assumptions underlying the Water + Fish ingestion criteria to warrant the adoption of Water + Fish ingestion standards for the segment in question.

(8) The use of 0.1 micron pore size filtration for determining dissolved iron is allowed as an option in assessing compliance with the drinking water standard.

(9) Selenium is a bioaccumulative metal and subject to a range of toxicity values depending upon numerous site-specific variables.

(10) Applicable to the following segments which do not have a water supply classification: all Class 1 aquatic life segments or Class 2 aquatic life segments designated by the Commission after rulemaking hearing. These class 2 segments will generally be those where fish of a catchable size and which are normally consumed are present, and where there is evidence that fishing takes place on a recurring basis. The Commission may also consider additional evidence that may be relevant to a determination whether the conditions applicable to a particular segment are similar enough to the assumptions underlying the fish ingestion criteria to warrant the adoption of fish ingestion standards for the segment in question.

(11) Where the pH is equal to or greater than 7.0 in the receiving water after mixing, the chronic hardness-dependent equation will apply. Where pH is less than 7.0 in the receiving water after mixing, either the 87 µg/L chronic total recoverable aluminum criterion or the criterion resulting from the chronic hardness-dependent equation will apply, whichever is more stringent.

(12) This standard is only appropriate where irrigation water is applied to soils with pH values lower than 6.0.

(13) Whenever a range of standards is listed and referenced to this footnote, 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, 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.

(14) The chronic zinc equation for sculpin applies in areas where mottled sculpin are expected to occur and hardness is less than 102 ppm CaCO3. The regular chronic zinc equation applies in areas where mottled sculpin are expected to occur, but the hardness is greater than 102 ppm CaCO3.

(15) In determining whether adoption of a molybdenum standard is appropriate for a segment, the Commission will consider whether livestock or irrigated forage is present or expected to be present. The table value assumes that copper and molybdenum concentrations in forage are 7 mg/kg and 0.5 mg/kg respectively, forage intake is 6.8 kg/day, copper concentration in water is 0.008 mg/L, water intake is 54.6 L/day, copper supplementation is 48 mg/day, and that a Cu:Mo ratio of 4:1 is appropriate with a 0.075 mg/L molybdenum margin of safety. Numeric standards different than the table-value may be adopted on a site-specific basis where appropriate justification is presented to the Commission. In evaluating site-specific standards, the relevant factors that should be considered include the presence of livestock or irrigated forage, and the total intake of copper, molybdenum, and sulfur from all sources (i.e., food, water, and dietary supplements). In general, site-specific standards should be based on achieving a safe copper:molybdenum total exposure ratio, with due consideration given to the sulfur exposure. A higher Cu:Mo ratio may be necessary where livestock exposure to sulfur is also high. Species specific information shall be considered where cattle are not the most sensitive species.

(16) When applying the table value standards for uranium to individual segments, the Commission shall consider the need to maintain radioactive materials at the lowest practical level as required by Section 31.11 of the Basic Standards regulation.

(17) The acute(warm) cadmium equation applies to segments classified as Aquatic Life Warm Class 1 or 2. The acute(cold) cadmium equation applies to segments classified as Aquatic Life Cold Class 1 or 2.

(18) Consistent with 31.7(1)(b) and 31.7(2), these table values will be applied on a site-specific basis.

(19) The chronic silver equation for trout applies in areas where trout are expected to occur. The regular chronic silver equation applies in areas where trout are not expected to occur.

TABLE IV - AQUATIC LIFE TABLE VALUE STANDARDS FOR SELECTED HARDNESS CONCENTRATIONS

TABLE IV AQUATIC LIFE TABLE VALUE STANDARDS FOR SELECTED HARDNESS CONCENTRATIONS (µg/L)
Mean Hardness in mg/L Calcium Carbonate
		25	50	75	100	150	200	250	300	350	400
Aluminum	Acute	512	1324	2307	3421	5960	8838	10071	10071	10071	10071
	Chronic	73	189	329	488	851	1262	1438	1438	1438	1438
Cadmium	Acute(cold)	0.49	0.94	1.4	1.8	2.6	3.4	4.2	5.0	5.8	6.5
	Acute(warm)	0.75	1.4	2.1	2.7	4.0	5.2	6.4	7.6	8.8	10
	Chronic	0.25	0.43	0.58	0.72	0.97	1.2	1.4	1.6	1.8	2.0
Chromium III	Acute	183	323	450	570	794	1005	1207	1401	1590	1773
	Chronic	24	42	59	74	103	131	157	182	207	231
Copper	Acute	3.6	7.0	10	13	20	26	32	38	44	50
	Chronic	2.7	5.0	7.0	9.0	13	16	20	23	26	29
Lead	Acute	14	30	47	65	100	136	172	209	245	281
	Chronic	0.5	1.2	1.8	2.5	3.9	5.3	6.7	8.1	9.5	11
Manganese	Acute	1881	2370	2713	2986	3417	3761	4051	4305	4532	4738
	Chronic	1040	1310	1499	1650	1888	2078	2238	2379	2504	2618
Nickel	Acute	145	260	367	468	660	842	1017	1186	1351	1513
	Chronic	16	29	41	52	72	94	113	132	150	168
Silver	Acute	0.19	0.62	1.2	2.0	4.1	6.7	9.8	13	18	22
	Chronic(trout)	0.01	0.02	0.05	0.08	0.15	0.25	0.36	0.50	0.65	0.81
	Chronic	0.03	0.10	0.20	0.32	0.64	1.0	1.6	2.1	2.8	3.5
Uranium	Acute	521	1119	1750	2402	3756	5157	6595	8062	9555	11070
	Chronic	326	699	1093	1501	2346	3221	4119	5036	5968	6915
Zinc	Acute	45	85	123	160	231	301	368	435	500	565
	Chronic(sculpin)	6.1	27	64	118	N/A	N/A	N/A	N/A	N/A	N/A
	Chronic	34	65	93	121	175	228	279	329	379	428
Shading indicates the aquatic life standards exceed drinking water supply standards.

5 CCR 1002-31.16

39 CR 11, June 10, 2016, effective 6/30/2016

39 CR 17, September 10, 2016, effective 12/31/2016

40 CR 03, February 10, 2017, effective 3/2/2017

40 CR 23, December 10, 2017, effective 12/30/2017

41 CR 01, January 10, 2018, effective 1/31/2018

43 CR 03, February 10, 2020, effective 6/30/2020

43 CR 11, June 10, 2020, effective 6/30/2020

44 CR 17, September 10, 2021, effective 12/31/2021

Renumbered from 5 CCR 1002-31.57 44 CR 17, September 10, 2021, effective 12/31/2021

Renumbered to 5 CCR 1002-31.5844 CR 17, September 10, 2021, effective 12/31/2021

46 CR 10, May 25, 2023, effective 6/14/2023

47 CR 18, September 25, 2024, effective 12/31/2024