5 Colo. Code Regs. § 1002-37.6

Current through Register Vol. 47, No. 11, June 10, 2024

Section 5 CCR 1002-37.6 - TABLES

(1)Introduction

The numeric standards for various parameters in this regulation and in the tables in Appendix 37 1 were assigned by the Commission after a careful analysis of the data presented on actual stream conditions and on actual and potential water uses. For each parameter listed in the tables in Appendix 37-1, only the most stringent standard is shown. Additional, less stringent standards may apply to protect additional uses and can be found in the tables in Regulation No. 31.

Numeric standards are not assigned for all parameters listed in the tables in Regulation No. 31. If additional numeric standards are found to be needed during future periodic reviews, they can be assigned by following the proper hearing procedures.

(2)Abbreviations:

(a) The following abbreviations are used in this regulation and in the tables in Appendix 37-1:

ac	= acute (1-day)
°C	= degrees Celsius
ch	= chronic (30-day)
CL	= cold lake temperature tier
CLL	= cold large lake temperature tier
CS-I	= cold stream temperature tier one
CS-II	= cold stream temperature tier two
D.O.	= dissolved oxygen
DM	= daily maximum temperature
DUWS	= direct use water supply
E. coli	= Escherichia coli
MWAT	= maximum weekly average temperature
OW	= outstanding waters
sc	= sculpin
sp	= spawning
SSE	= site-specific equation
T	= total recoverable
t	= total
tr	= trout
TVS	= table value standard
µg/L	= micrograms per liter
UP	= use-protected
WL	= warm lake temperature tier
WS	= water supply
WS-I	= warm stream temperature tier one
WS-II	= warm stream temperature tier two
WS-III	= warm stream temperature tier three

(b) In addition, the following abbreviations were used:

Iron (chronic)	= WS
Manganese (chronic)	= WS
Sulfate (chronic)	= WS

These abbreviations mean: For all surface waters with an actual water supply use, the less restrictive of the following two options shall apply as numerical chronic standards, as specified in the Basic Standards and Methodologies at 31.16 Table II and III:

(i) existing quality as of January 1, 2000; or

(ii)

Iron	= 300 µg/L (dissolved)
Manganese	= 50 µg/L (dissolved)
Sulfate	= 250 mg/L (dissolved)

For all surface waters with a "water supply" classification that are not in actual use as a water supply, no water supply standards are applied for iron, manganese or sulfate, unless the Commission determines as the result of a site-specific rulemaking hearing that such standards are appropriate.

(c) Temporary Modification for Water + Fish Chronic Arsenic Standard

(i) The temporary modification for chronic arsenic standards applied to segments with an arsenic standard of 0.02 µg/L that has been set to protect the Water + Fish qualifier is listed in the Other column in Appendix 37-1 tables as As(ch)=hybrid.

(ii) For discharges existing on or before 6/1/2013, the temporary modification is: As(ch)=current condition, expiring on 12/31/2024. Where a permit for an existing discharge is reissued or modified while the temporary modification is in effect, the division will include additional permit Terms and Conditions, which may include requirements for additional monitoring, source identification, and characterization of source control and treatment options for reducing arsenic concentrations in effluent.

(iii) For new or increased discharges commencing on or after 6/1/2013, the temporary modification is: As(ch)=0.02-3.0 µg/L (total recoverable), expiring on 12/31/2024.

(a) The first number in the range is the health-based water quality standard previously adopted by the Commission for the segment.

(b) The second number in the range is a technology-based value established by the Commission for the purpose of this temporary modification.

(c) 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.

(3)Table Value Standards

In certain instances in the tables in Appendix 37-1, the designation "TVS" is used to indicate that for a particular parameter a "table value standard" has been adopted. This designation refers to numerical criteria set forth in the Basic Standards and Methodologies for Surface Water. The criteria for which the TVS are applicable are on the following table.

TABLE VALUE STANDARDS

(Concentrations in µg/L unless noted)

Click to view image

TABLE VALUE STANDARDS - FOOTNOTES

(1) Metals are stated as dissolved unless otherwise specified.

(2) Hardness values to be used in equations are in mg/L as calcium carbonate and shall be no greater than 400 mg/L. The hardness values used in calculating the appropriate metal standard should be based on the lower 95 per cent 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 appropriate, a site-specific method should be used. In calculating a hardness value, regression analyses should not be extrapolated past the point that data exist.

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

(4) For acute conditions the default assumption is that salmonids could be present in cold water segments and should be protected, and that salmonids do not need to be protected in warm water segments. For chronic conditions, the default assumptions are that early life stages could be present all year in cold water segments and should be protected. In warm water segments the default assumption is that early life stages are present and should be protected only from April 1 through August 31. These assumptions can be modified by the Commission on a site-specific basis where appropriate evidence is submitted. The "T" in the chronic equations stands for temperature.

(5) 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.

(6) Unless the stable forms of chromium in a waterbody 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.

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

(8) 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.

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(4)Site-specific Standards, Assessment Locations, and Assessment Criteria

(a) White River Segment 13b Selenium Assessment Thresholds and Locations

Corral Gulch, Se(ch)=5.7 µg/L

Assessment location: Corral Gulch at the mouth.

Duck Creek, Se(ch)=7.9 µg/L

Assessment location: Duck Creek at the mouth.

Yellow Creek, Se(ch)=6.9 µg/L

Assessment location: Yellow Creek upstream from the confluence with Barcus Creek.

Greasewood Creek, Se(ch)=6.0 µg/L

Assessment location: Greasewood Creek at the mouth.

(b) White River Segment 13c Iron Assessment Threshold and Location

Yellow Creek, Fe(ch)=1625 µg/L

Assessment location: Yellow Creek at the mouth.

(c) Lower Colorado Segment 4e Iron Standards and Assessment

Unnamed tributary. Iron (chronic) = 3500 (T) µg/L, assessment location as follows:

* UT-2: Unnamed tributary, immediately downstream of the Tri-State Rifle Station discharge (39.519572, -107.729424)

Dry Creek and remaining tributaries and wetlands, Iron (chronic) = 5900 (T) µg/L, assessment location as follows:

* DC-2: Dry Creek, downstream of dry tributary channel entering from the east from the Garfield County Airport (39.523944, -107.73496)

(d) Lower Colorado River Segment 1: Temperature Standards

Lower Colorado River from the confluence with the Roaring Fork River to Elk Creek

DM = 21.2 and MWAT = 16.9 from 4/1 - 5/31

DM and MWAT = CS-II from 6/1 - 9/30

DM = 21.2 and MWAT = 16.9 from 10/1-10/31

DM and MWAT = CS-II from 11/1 - 3/31

All other locations DM and MWAT = CS-II

(e) Lower Yampa River Segment 3g: Iron Standards and Assessment Locations

Iron Standards:

* Collom Gulch from the source to the diversion structure at 40.333977, -107.860833:

March-May, Iron(chronic) = 1500 µg/L, median of all data

June-February, Iron(chronic) = 1000(T)

Iron Assessment Location:

* Collom Gulch at County Road 32: located at 40.323530, -107.877200

(5)Stream Classifications and Water Quality Standards Tables

The stream classifications and water quality standards tables in Appendix 37-1 are incorporated herein by reference.

The following is information regarding duration and measured form of standards in Appendix 37-1:

(a)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.

(b) All phosphorus standards are based upon the concentration of total phosphorus.

(c) 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.

(d) All mercury standards apply to the total recoverable fraction of all forms, both organic and inorganic, of mercury in water.

(e) All ammonia, nitrate, and nitrite standards are based upon the concentration reported as nitrogen.

5 CCR 1002-37.6

39 CR 03, February 10, 2016, effective 3/1/2016

39 CR 03, February 10, 2016, effective 6/30/2016

40 CR 03, February 10, 2017, effective 6/30/2017

41 CR 03, February 10, 2018, effective 6/30/2018

42 CR 04, February 25, 2019, effective 6/30/2019

42 CR 17, September 10, 2019, effective 12/31/2019

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

44 CR 05, March 10, 2021, effective 6/30/2021

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

45 CR 17, September 10, 2022, effective 9/30/2022

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