5 Colo. Code Regs. § 1002-31.5

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

Section 5 CCR 1002-31.5 - DEFINITIONS

See the Colorado Water Quality Control Act, section 25-8-101et seq., C.R.S., and the codified water quality regulations additional definitions.

(1) "ACT" means the Colorado Water Quality Control Act, section 25-8-101et seq., C.R.S..

(2) "ACUTE STANDARD" means the level not to be exceeded by the concentration for either a single sample or calculated as an average of all samples collected during a one-day period, except for temperature, which shall be based on the DM (see DM definition). As used in tables II and III, acute represents one-half of the LC-50 that protects 95 percent of the genera in a waterbody from lethal effects. The acute standard is implemented in combination with a selected duration and frequency of recurrence (section 31.9). In determining attainment of the applicable acute standard, the representative nature of the data must be considered.

(3) "ANTIDEGRADATION RULE" means the rule established in section 31.8.

(4) "BASIC STANDARDS" means those standards as established in section 31.11.

(5) "BENEFICIAL USES" means those uses of state surface waters to be protected such as those identified in the classification system.

(6) "BMP" (Best Management Practices) means a practice or a combination of practices that is determined by a governmental agency after problem assessment, examination of alternative practices, and appropriate public participation, to be the most effective, practicable (including technological, economic, and institutional considerations) means of preventing or reducing the amount of pollution generated by nonpoint sources to a level compatible with quality goals.

(7) "CHRONIC STANDARD" means the level not to be exceeded by the concentration for either a single representative sample or calculated as an average of all samples collected during a thirty-day period, except for temperature, which shall be based on the WAT (see WAT definition). As used in tables II and III, chronic represents the level that protects 95 percent of the genera from chronic toxic effects. Chronic toxic effects include, but are not limited to, demonstrable abnormalities and adverse effects on survival, growth, or reproduction. The chronic standard is implemented in combination with a selected duration and frequency of recurrence (section 31.9). In determining attainment of the applicable chronic standard, the representative nature of the data must be considered.

(8) "COLD WATER BIOTA" means aquatic life, including trout, normally found in waters where the summer weekly average temperature does not frequently exceed 20 ºC.

(9) "COMMISSION" means the Colorado Water Quality Control Commission.

(10) "COMPENSATORY WETLANDS" means wetlands developed for mitigation of adverse impacts to other wetlands (e.g. wetlands developed pursuant to section 404 of the federal Act).

(11) "CONSTRUCTED WETLANDS" means those wetlands intentionally designed, constructed and operated for the primary purpose of wastewater or stormwater treatment or environmental remediation provided under CERCLA, RCRA, or section 319 of the federal Act, if (a) such wetlands are constructed on non-wetland sites that do not contain surface waters of the state, or (b) such wetlands are constructed on previously existing wetland sites, to the extent that approval or authorization under section 404 of the federal Act has been granted for such construction or it is demonstrated that such approval or authorization is not, or was not, required. This term includes, but is not limited to, constructed swales, ditches, culverts, infiltration devices, catch basins, and sedimentation basins that are part of a wastewater or stormwater treatment system or a system for environmental remediation mandated under CERCLA or RCRA. Compensatory wetlands shall not be considered constructed wetlands. Constructed wetlands are not state waters.

(12) "CREATED WETLANDS" means those wetlands other than compensatory wetlands created in areas which would not be wetlands in the absence of human modifications to the environment. Created wetlands include, but are not limited to wetlands created inadvertently by human activities such as mining, channelization of highway runoff, irrigation, and leakage from man-made water conveyance or storage facilities. Wetlands resulting from hydrologic modifications such as on-channel reservoirs or on-channel diversion structures that expand or extend the reach of adjacent classified state waters are not considered created wetlands.

(13) "DAILY MAXIMUM TEMPERATURE (DM)" means the highest two-hour average water temperature recorded during a given 24-hour period.

(14) "DISSOLVED METALS" means that portion of a water and suspended sediment sample which passed through a 0.40 or 0.45 µm (micron) membrane filter. Determinations of "dissolved" constituents are made using the filtrate. This may include some very small (colloidal) suspended particles which passed through the membrane filter as well as the amount of substance present in true chemical solution.

(15) "DIVISION" means the Division of Administration of the Colorado Department of Public Health and Environment of which the Water Quality Control Division is a part.

(16) "E. coli" means Escherichia coli.

(17) "EFFLUENT-DEPENDENT STREAM" means a stream that would be ephemeral without the presence of wastewater effluent, but has continuous or periodic flows for all or a portion of its reach as the result of the discharge of treated wastewater.

(18) "EFFLUENT-DOMINATED STREAM" means a stream that would be intermittent or perennial without the presence of wastewater effluent whose flow for the majority of the time is primarily attributable to the discharge of treated water (i.e. greater than 50 percent of the flow consists of treated wastewater for at least 183 days annually, for eight out of the last ten years).

(19) "EPHEMERAL STREAM" means a stream channel or reach of a stream channel that carries flow during, and for a short duration as the result of, precipitation events or snowmelt. The channel bottom is always above the groundwater table.

(20) "EXISTING QUALITY" means the numeric value that represents the quality of a waterbody and is generally used for comparison with the water quality standard. Existing quality shall be calculated as:

* Total ammonia, nitrate, and the dissolved metals: 85th percentile

* Total recoverable metals: 50th percentile

* Dissolved oxygen in streams: 15^th percentile

* E.coli: geometric mean

* pH: the range between the 15th and 85th percentiles

* Temperature: For the purposes of determining standards attainment, existing quality is the seasonal maximum DM (acute) and WAT (chronic) which allows one warming event with a 3-year average exceedance frequency. For data records with less than or equal to 3 years, existing quality is equal to the maximum WAT and DM. For data records with 4-6 years, one warming event above the standard is permitted. The warming event allowance is described in Footnote 5(c)(ii) to Table I.

For the purposes of permits implementation, for data records with less than or equal to 3 years of representative upstream data, existing quality is equal to the seasonal or monthly maximum DM (acute) and WAT (chronic). For data records with 4-6 years, for monthly limits, the second highest monthly DM or WAT may be selected for one month in either winter or summer and the remaining months shall be the max DM or WAT.

(21) "FEDERAL ACT" means the Clean Water Act, U.S.C. Section 1251 et seq., as amended.

(22) "FIRST (1st) ORDER STREAM" means a stream that has no tributaries, based on USGS mapping at 1:100,000 scale.

(23) "FLOODPLAIN" means any flat or nearly flat lowland that borders a stream, a lake, or an on-channel reservoir and that may be covered by its waters at flood or high stage as described by the parameter of the probable maximum flood or probable maximum high stage.

(24) "HIGHEST ATTAINABLE USE" means the modified use that is both closest to the uses specified in section 31.13 and attainable based on the evaluation of the factors in 31.6(2)(b) that preclude attainment of the use and any other information or analyses that were used to evaluate attainability.

(25) "LC-50" means the concentration of a parameter that is lethal to 50% of the test organisms within a defined time period.

(26) "MAXIMUM WEEKLY AVERAGE TEMPERATURE (MWAT)" means the largest WAT in the period of interest. For lakes and reservoirs, the summertime MWAT is assumed to be equivalent to the maximum WAT from at least three profiles distributed throughout the growing season (generally July-September).

(27) "MIXED LAYER" means that part of a lake that is well-mixed by wind action and can be expected to have relatively homogeneous physical and chemical conditions. In a thermally stratified lake, the mixed layer corresponds to the epilimnion; in an unstratified lake, the mixed layer extends to the bottom. The vertical extent of the mixed layer usually is determined by inspection of a vertical profile of temperature.

(28) "MIXING ZONE" means that area of a waterbody designated on a case-by-case basis by the Division which is contiguous to a point source and in which certain standards may not apply.

(29) "NUMERIC VALUE" means the measured concentration of a parameter.

(30) "PARAMETER" means the chemical constituents or other characteristics of the water such as algae, E. coli, total dissolved solids, dissolved oxygen, or the magnitude of radioactivity levels, temperature, pH, and turbidity, or other relevant characteristics.

(31) "PERMIT" means a National Pollutant Discharge Elimination System (NPDES) permit, a Colorado Discharge Permit System (CDPS) permit, or other state water quality permit.

(32) "POTENTIALLY DISSOLVED METALS" means that portion of a constituent measured from the filtrate of a water and suspended sediment sample that was first treated with nitric acid to a pH of less than 2.0 and let stand for 8 to 96 hours prior to sample filtration using a 0.4 or 0.45 µm (micron) membrane filter. Note the "Potentially Dissolved" method cannot be used where nitric acid will interfere with the analytical procedure used for the constituent measured.

(33) "PRIMARY CONTACT RECREATION" means recreational activities where the ingestion of small quantities of water is likely to occur. Such activities include but are not limited to swimming, rafting, kayaking, tubing, windsurfing, water skiing, and water play by children.

(34) "REGIONAL WASTEWATER MANAGEMENT PLAN" means a water quality planning document prepared pursuant to section 208 of the federal Act, sometimes referred to as "208 Plans" or "Water Quality Management Plans."

(35) "REPRODUCTIVE SEASON" means the portion of the year when fish migration, spawning, egg incubation, fry rearing or other reproductive functions occur.

(36) "SALINITY" means total dissolved solids (TDS).

(37) "SECOND (2nd) ORDER STREAM" means a stream which begins downstream of the confluence of two first (1st) order streams and ends downstream of the confluence of two second (2nd) order streams, based on USGS mapping at 1:100,000 scale.

(38) "STANDARD" means a narrative and/or numeric restriction established by the Commission applied to state surface waters to protect one or more beneficial uses of such waters. Whenever only numeric or only narrative standards are intended, the wording shall specifically designate which is intended.

(39) "STATE WATERS" means any and all surface and subsurface waters which are contained in or flow in or through this state, but does not include waters in sewage systems, waters in treatment works of disposal systems, waters in potable water distribution systems, and all water withdrawn for use until use and treatment have been completed.

(40) "STATUS QUO", in the context of temporary modifications, means the numeric values representative of the conditions at the time of the original temporary modification adoption for:

1. the quality of a waterbody, for which a temporary modification is applied, and

2. the quality, and as appropriate the flow and loading, of effluent discharged into a waterbody, for which a temporary modification is applied.

Status quo shall be calculated as follows using data representative of quality at the time of the original temporary modification adoption, typically using data for the 5 years leading up to the temporary modification. Where such adequate, representative data do not exist, data representative of quality as close in time as practicable to the original temporary modification adoption shall be used.

For consideration of waterbody status quo:

* Total ammonia, nitrate, and dissolved metals (chronic): 85th percentile

* Total recoverable metals (chronic): 50th percentile

* Total ammonia, nitrate, total metals, and dissolved metals (acute): 95th percentile

* Temperature: seasonal maximum DM (acute) and WAT (chronic)

* Other parameters: As appropriate based on the duration and frequency for the water quality standard from Tables I, II, or III

* Or, in limited circumstances, as otherwise determined by the Commission on a case-by-case basis

For consideration of effluent status quo:

* Total ammonia, nitrate, and dissolved and total recoverable metals (chronic): maximum 30-day average

* Total ammonia, nitrate, and dissolved and total recoverable metals (acute): maximum daily maximum

* Temperature: seasonal maximum DM (acute) and WAT (chronic)

* Other parameters: As appropriate based on permit implementation approaches of the water quality standard from Tables I, II, or III

* Representative effluent flow and loading, as appropriate

* Or, in limited circumstances, as otherwise determined by the Commission on a case-by-case basis

(41) "TABLES" means tables I, II, and III, appended to this regulation, which set forth accepted levels for various parameters which will generally protect the beneficial uses of state surface waters.

(42) "THIRD (3rd) ORDER STREAM" means a stream which begins at the confluence of two second (2nd) order streams and ends downstream of the confluence of two third (3rd) order streams, based on USGS mapping at 1:100,000 scale.

(43) "TOTAL RECOVERABLE METALS" means that portion of a water and suspended sediment sample measured by the total recoverable analytical procedure described in "Methods for Chemical Analysis of Water and Wastes," U.S. Environmental Protection Agency, March, 1979, or its equivalent.

(44) "TRIBUTARY WETLANDS" means wetlands that are the headwaters of surface waters or wetlands within the floodplain that are hydrologically connected to surface waters via either surface or groundwater flows. The hydrologic connection may be intermittent or seasonal, but must be of sufficient extent and duration to normally reoccur annually. Tributary wetlands do not include constructed or created wetlands.

(45) "USE ATTAINABILITY ANALYSIS" means an assessment of the factors affecting the attainment of aquatic life uses or other beneficial uses, which may include physical, chemical, biological, and economic factors.

(46) "USES" see Beneficial Uses.

(47) "WARM WATER BIOTA" means aquatic life normally found in waters where the summer weekly average temperature frequently exceeds 20 °C.

(48) "WATER QUALITY-BASED DESIGNATION" means a designation adopted by the Commission for specific state surface waters pursuant to section 31.8 , to identify which level of water quality protection such waters will receive under the Antidegradation Rule in section 31.8 . Such designations are adopted pursuant to the Commission's authority to classify state waters, as set forth in section 25-8-203, C.R.S., and the procedural requirements for classifying state waters shall be applied in adopting such designations.

(49) "WATER EFFECT RATIO" means a ratio that is computed as a specific pollutant's acute or chronic toxicity value measured in water from the site covered by a standard, divided by the respective acute or chronic toxicity value in laboratory dilution water, as more specifically defined in 40 CFR. subsection 131.36(c) (1993).

(50) "WATER QUALITY STANDARD" see Standard.

(51) "WEEKLY AVERAGE TEMPERATURE (WAT)" means the average of daily average temperatures over a seven-day consecutive period, with a minimum of three data points spaced equally through each day. For lakes and reservoirs, the WAT is assumed to be equivalent to the average temperature of the mixed layer. The average temperature of the mixed layer is determined from a vertical profile of equally-spaced temperature measurements, separated by not more than one meter.

(52) "WETLANDS" means those areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions.

5 CCR 1002-31.5

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