Statutes, codes, and regulations
Colorado Administrative Code
Department 1000 - Department of Public Health and EnvironmentDivision 1002 - Water Quality Control Commission (1002 Series)
Rule 5 CCR 1002-31 - REGULATION NO. 31 - THE BASIC STANDARDS AND METHODOLOGIES FOR SURFACE WATER
Section 5 CCR 1002-31.17 - NUTRIENTS

5 Colo. Code Regs. § 1002-31.17

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Current through Register Vol. 47, No. 20, October 25, 2024
Section 5 CCR 1002-31.17 - NUTRIENTS
(a) Overview

This section establishes interim numeric values for phosphorus, nitrogen and chlorophyll a and also sets forth provisions regarding the use of these numeric values for the adoption of water quality standards.

(b) Interim Phosphorus Values

Table 1 Interim Total Phosphorus Values

Lakes and Reservoirs, cold > 25 acres

25 µg/L1

Lakes and Reservoirs, warm > 25 acres

83 µg/L1

Lakes and Reservoirs < = 25 acres

RESERVED

Rivers and Streams - cold

110 µg/L2

Rivers and Streams - warm

170 µg/L2

1 summer (July 1 - September 30) average total phosphorus (µg/L) in the mixed layer of lakes (median of multiple depths), allowable exceedance frequency 1-in-5 years.

2 annual median total phosphorus (µg/L), allowable exceedance frequency 1-in-5 years.

(c) Interim Nitrogen Values (Effective December 31, 2027)

Table 2 Interim Total Nitrogen Values

Lakes and Reservoirs, cold > 25 acres

426 µg/L1

Lakes and Reservoirs, warm > 25 acres

910 µg/L1

Lakes and Reservoirs < = 25 acres

RESERVED

Rivers and Streams - cold

1,250 µg/L2

Rivers and Streams - warm

2,010 µg/L2

1 summer (July 1 - September 30) average total nitrogen (µg/L) in the mixed layer of lakes (median of multiple depths), allowable exceedance frequency 1-in-5 years.

2 annual median total nitrogen (µg/L), allowable exceedance frequency 1-in-5 years.

(d) Interim Chlorophyll a Values

Table 3 Interim Chlorophyll a Values

Waterbody type

DUWS

Lakes and Reservoirs, cold > 25 acres

8 µg/L1

5 µg/L3

Lakes and Reservoirs, warm > 25 acres

20 µg/L1

5 µg/L3

Lakes and Reservoirs < = 25 acres

RESERVED

5 µg/L3

Rivers and Streams - cold

150 mg/m22

Rivers and Streams - warm

150 mg/m22

1 summer (July 1 - September 30) average chlorophyll a (µg/L) in the mixed layer of lakes (median of multiple depths), allowable exceedance frequency 1-in-5 years.

2 summer (July 1 - September 30) maximum attached algae, not to exceed.

3 March 1 - November 30 average chlorophyll a (µg/L) in the mixed layer of lakes (median of multiple depths), allowable exceedance frequency 1-in-5 years.

(e) Use of Interim Phosphorus Values for Standards Adoption

Prior to December 31, 2027 the values set forth in subsection (b) above will be considered for the adoption of water quality standards for specific water bodies in Colorado in the following circumstances.

(i) Waters located upstream of
(A) all permitted domestic wastewater treatment facilities discharging prior to May 31, 2012 or with preliminary effluent limits requested prior to May 31, 2012,
(B) cooling tower discharges, and
(C) any non-domestic facility subject to Regulation #85 effluent limits and discharging prior to May 31, 2012.
(ii) Circumstances where the Commission has determined that adoption of numerical standards is necessary to address existing or potential nutrient pollution because the provisions of Regulation #85 will not result in adequate control of such pollution.
(f) Chlorophyll a Values for Standards Adoption

Prior to December 31, 2022, the values set forth in subsection (d) above will be considered for the adoption of water quality standards for specific water bodies in Colorado in the following circumstances.

(i) Waters located upstream of
(A) all permitted domestic wastewater treatment facilities discharging prior to May 31, 2012, or with preliminary effluent limits requested prior to May 31, 2012,
(B) cooling tower discharges, and
(C) any non-domestic facility subject to Regulation #85 effluent limits and discharging prior to May 31, 2012.
(ii) Discretionary Application of the Values for Direct Use Water Supply (DUWS) Lakes and Reservoirs. The Commission may determine that a numerical chlorophyll standard is appropriate for specific water bodies with this sub-classification after consideration of the following factors:
(A) Whether the public water system using the lake or reservoir as a raw water supply experiences impacts attributed to algae on an intermittent or continual basis;
(B) Whether there are lake or reservoir use restrictions in place that recognize the importance of the reservoir as a water supply;
(C) Whether application of this value appropriately balances protection of all classified uses of the lake or reservoir;
(D) Other site specific considerations which affect the need for a more protective value.
(iii) Circumstances where the Commission has determined that adoption of numerical standards is necessary to address existing or potential nutrient pollution because the provisions of Regulation #85 will not result in adequate control of such pollution.
(g) Use of Interim Nitrogen Values for Standards Adoption

After December 31, 2027, the values set forth in subsection (c) above will be considered for the adoption of water quality standards for specific water bodies in Colorado in the circumstances identified in subsection (e)(i) and (ii) above.

(h) Phase 2 Application of Numeric Standards

After December 31, 2022, the values set forth in subsection (d) will be considered by the Commission when applying numeric standards to individual segments. After December 31, 2022, the values set forth in subsections (b) and (c) for lakes and reservoirs will be considered by the Commission when applying numeric standards to Direct Use Water Supply (DUWS) reservoirs and lakes or lakes and reservoirs with public swim beaches that meet the definition of natural swimming areas in C.R.S. § 25-5-801. After December 31, 2027, the values set forth in subsection (b) and (c) will be considered by the Commission when applying numeric standards to individual segments where total phosphorus and total nitrogen standards have not yet been adopted.

For each individual segment where numeric standards for total phosphorus, total nitrogen, and chlorophyll a have not yet been adopted, numeric standards will be adopted by the Commission where necessary to:

(i) protect the assigned use classifications, and
(ii) comply with the Colorado Water Quality Control Act and the Federal Act.
(i) Site-Specific Flexibility to Consider Alternatives to the Interim Values

In accordance with the preceding subsection, both before and after December 31, 2027, in considering adoption of numeric standards for specific water bodies in Colorado, the Commission may review relevant site-specific factors and conditions in determining what numeric standards are most appropriate, and may adopt standards, either more or less stringent than the 31.17(b)(c) and (d) interim values.

(i) Where evidence demonstrates that an alternative numeric standard would be more appropriate for the protection of use classifications, the Commission may consider assigning ambient quality-based standards or site-specific criteria based standards as outlined in 31.7(1)(b)(ii-iii).
(ii) Where it has been demonstrated that interim values are not feasible to achieve, the Commission may consider modifying the use classification as outlined in Section 31.6(2).
(iii) Where the conditions established in Section 31.7 are met, the Commission may consider granting a temporary modification.

5 CCR 1002-31.17

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