Numeric Criteria Development

The information presented below gives a summary of state progress towards the development of numeric criteria. The information comes from EPA’s “State Adoption of Numeric Nutrient Standards (1998-2008)” report, current water quality standards, program activity measures, and nutrient criteria development plans. Links to the Colorado’s Nutrient Criteria Plan and state water quality standards are also provided.

• Existing Numeric Criteria
• Links to the Plan and Criteria
• Milestone Information

Existing Numeric Criteria

S = Statewide    W = For selected waterbody    N ⁄ A=Not Applicable

Note: See Statewide Criteria and Site-specific Criteria tabs for more information.

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Links to Numeric Nutrient Criteria Plan and Existing Nutrient Criteria

Plan:

• Nutrient Criteria Development Plan for the State of Colorado 2002

WQS: Colorado Water Quality Standards
Colorado Department of Public Health and Environment: Water Quality Control Commission Exit

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Milestone Information

Milestone information updated July 2012.

TN: Total Nitrogen; TP: Total Phosphorus

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Statewide Criteria

The information on this tab shows EPA-approved nutrient criteria for Colorado’s waterbodies. The language presented below comes directly from state water quality standards and applies to all waterbodies within the state (unless a waterbody type or designated use is noted). Criteria applicable to specific waterbodies within the state can be found on the “Site-specific Criteria” tab. For more information, refer to the Colorado water quality standards.

The following information reflects Colorado’s water quality standards posted to the Water Quality Standards Repository as of November 2010 (EPA-approved December 2005).

31.11 Basic Standards Applicable to Surface Waters of the State

All surface waters of the state are subject to the following basic standards; however, discharge of substances regulated by permits which are within those permit limitations shall not be a basis for enforcement proceedings under these basic standards:

(1) Except where authorized by permits, BMPs, 401 certifications, or plans of operation approved by the Division or other applicable agencies, state surface waters shall be free from substances attributable to human-caused point source or nonpoint source discharge in amounts, concentrations or combinations which:

(a) for all surface waters except wetlands;

(iii) produce color, odor, or other conditions in such a degree as to create a nuisance or harm existing beneficial uses or impart any undesirable taste to significant edible aquatic species or to the water; or

(v) produce a predominance of undesirable aquatic life; or

(b) for surface waters in wetlands;

(i) produce color, odor, changes in pH, or other conditions in such a degree as to create a nuisance or harm water quality dependent functions or impart any undesirable taste to significant edible aquatic species of the wetland.

31.16 Tables

* From Aquatic Life Use Attainment, Policy Statement 10-1:

31.13 STATE USE CLASSIFICATIONS

Waters are classified according to the uses for which they are presently suitable or intended to become suitable. In addition to the classifications, one or more of the qualifying designations described in section 31.13(2), may be appended. Classifications may be established for any state surface waters, except that water in ditches and other manmade conveyance structures shall not be classified.

(1) Classifications

(c) Aquatic Life These surface waters presently support aquatic life uses as described below, or such uses may reasonably be expected in the future due to the suitability of present conditions, or the waters are intended to become suitable for such uses as a goal:

(i) Class I - Cold Water Aquatic Life These are waters that (1) currently are capable of sustaining a wide variety of cold water biota, including sensitive species, or (2) could sustain such biota but for correctable water quality conditions. Waters shall be considered capable of sustaining such biota where physical habitat, water flows or levels, and water quality conditions result in no substantial impairment of the abundance and diversity of species.

(ii) Class 1 - Warm Water Aquatic Life These are waters that (1) currently are capable of sustaining a wide variety of warm water biota, including sensitive species, or (2) could sustain such biota but for correctable water quality conditions. Waters shall be considered capable of sustaining such biota where physical habitat, water flows or levels, and water quality conditions result in no substantial impairment of the abundance and diversity of specifies.

(iii) Class 2- Cold and Warm Water Aquatic Life These are waters that are not capable of sustaining a wide variety of cold or warm water biota, including sensitive species, due to physical habitat, water flows or levels, or uncorrectable water quality conditions that result in substantial impairment of the abundance and diversity of species.

Table II – Footnotes:

(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 100 ppm or less, and the NO₂-N content alone be limited to 10 ppm 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
(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)

(4) A combined total of nitrite and nitrate at the point of intake to the domestic water supply shall not exceed 10 mg/L.

Site-specific Criteria

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The information on this tab shows EPA-approved site-specific nutrient criteria for Colorado’s waterbodies. Criteria on this page apply only to the waterbodies listed below. Criteria applicable to all waterbodies within the state are found on the “Statewide Criteria” tab. For more information, refer to the Colorado water quality standards.

The following information reflects Colorado’s water quality standards posted to the Water Quality Standards Repository as of November 2010 (EPA-approved December 2002 for the Rio Grande Basin and EPA-approved March 2006 for the remaining basins).

Please refer to the “Stream Classifications and Water Quality Standards” table for the Arkansas River Basin (PDF) (16 pp, 238K) for numeric nitrite and nitrate standards.

The following information reflects Colorado’s 2006 water quality standards for the Upper Colorado River Basin and North Platte River posted to the Water Quality Standards Repository as of November 2010.

Please refer to the “Stream Classifications and Water Quality Standards” table for the Upper Colorado River Basin and North Platte River (PDF) (15 pp, 98K) for numeric nitrite, nitrate, and phosphorus standards.

The following information reflects Colorado’s 2006 water quality standards for the San Juan River and Dolores River Basins posted to the Water Quality Standards Repository as of November 2010.

Please refer to the “Stream Classifications and Water Quality Standards” table for the San Juan River and Dolores River Basins (PDF) (19 pp, 107K) for numeric nitrite and nitrate standards.

The following information reflects Colorado’s 2006 water quality standards for the Gunnison and Lower Dolores River Basins posted to the Water Quality Standards Repository as of November 2010.

Please refer to the “Stream Classifications and Water Quality Standards” table for the Gunnison and Lower Dolores River Basins (PDF) (92 pp, 477K) for numeric nitrite and nitrate standards.

The following information reflects Colorado’s 2003 water quality standards for the Rio Grande Basin posted to the Water Quality Standards Repository as of November 2010.

Please refer to the “Stream Classifications and Water Quality Standards” table for the Rio Grande Basin (PDF) (11 pp, 113K) for numeric nitrite and nitrate standards.

The following information reflects Colorado’s 2006 water quality standards for the Lower Colorado River Basin posted to the Water Quality Standards Repository as of November 2010.

Please refer to the “Stream Classifications and Water Quality Standards” table for the Lower Colorado River Basin (PDF) (11 pp, 90K) for numeric nitrite and nitrate standards.

The following information reflects Colorado’s 2006 water quality standards for the South Platte River Basin, Laramie River Basin, Republican River Basin, and Smoky Hill River Basin posted to the Water Quality Standards Repository as of November 2010.

Please refer to the “Stream Classifications and Water Quality Standards” table for the South Platte River Basin, Laramie River Basin, Republican River Basin, and Smoky Hill River Basin (PDF) (28 pp, 1MB) for numeric nitrite, nitrate, and phosphorus standards.

Cherry Creek*

The seasonal mean standard for chlorophyll a in Cherry Creek Reservoir is 18 ug/L based on July through September measurements in the upper 3 meters of the water column, with compliance required in 4 years out of 5.

Bear Creek*
The mixed layer seasonal mean value for chlorophyll a in Bear Creek Reservoir is 10 ug/L (for July through September). Compliance is required in four years out of five. The 10 ug/L chlorophyll a standard was adopted as a numeric replacement for the previous narrative standard. The previous narrative standard required shifting the Bear Creek Reservoir trophic state to a range of mesotrophic to eutrophic.

* Source: “EPA Action on Revisions to the Water Quality Standards for the South Platte River Basin” (March 2010).