VIII. DETERMINATION OF ATTAINMENT IN WATER BODIES The following section presents a procedure for determining whether a particular stream segment is attaining a site-specific temperature standard. Identification of an exceedance of a numeric temperature standard requires an exceedance of a site-specific numeric temperature standard, which has been adopted by the Commission and is based on physical data. A. Identification of Temperature as the Cause of Non-Attainment A waterbody can only be listed for temperature of the Commission has adopted a site-specific standard for that segment. Where site-specific standards have been adopted for a particular segment, the following criteria are considered: summertime maximum chronic criteria, summertime maximum acute criteria, a normal pattern of spatial fluctuation and a normal pattern of diurnal fluctuation. 1. Summertime Maximum Numerical Table Value Criteria The numeric, site-specific standards will be used to determine attainment. The Commission sets these standards. The numerical table value criteria in Table 1 of Regulation No. 31 may be used to establish these standards. Two summertime maximum numeric table values exist: 1. Chronic Attainment of the chronic numerical temperature standard is based on a Maximum Weekly Average Temperature (MWAT), unless specified otherwise in a site-specific standard. 2. Acute Attainment of the acute numerical temperature standard is based on a Daily Maximum (DM) water temperature, unless otherwise specified in a site-specific standard. 2. Normal Pattern of Spatial Fluctuation Temperature profiles will be gathered from multiple locations and habitat types along the reach being investigated. Comparisons will be made with the expected thermal regime. Significant deviation from the expected normal regime should be avoided. The normal pattern of spatial fluctuation can be evaluated through a comparison of the thermal regime from a representative stream with similar attributes. Similar attributes can include: basin, size, flow, elevation loss, and shade cover. 3. Normal Pattern of Temporal Fluctuation In order to determine whether the normal pattern of diurnal and seasonal fluctuations has been attained, an assessment must be provided that shows significant deviation from the expected condition. Where no actual measurements of the expected normal pattern are available, a modeled expectation is acceptable. The Division has developed (is working on) index patterns for a variety of streams in Colorado that could be used for this assessment. K:\Reg 31 2005\Temperature\2006 work\for 10-16\Temp guidance v2 attainmt 10.12.06.doc 1
The Division s index patterns discussed above shall include summertime diurnal fluctuation information as well as seasonal patterns. It is the Commission s intent that when the Division or interested parties evaluate whether a specific water body is meeting the normal seasonal fluctuation requirement, the pattern should be similar, but not necessarily identical to the index pattern. Summer Diurnal Patterns: The maximum hourly temperature change shall not exceed 3 C in addition to temperature changes caused by natural conditions. When evaluating a point source discharge, profiles above and below the discharge shall be compared. An upstream representative location shall be compared to a downstream location below the regulatory mixing zone. Seasonal Patterns: The monthly average MWAT change shall not exceed 3 C in addition to temperature changes caused by natural conditions. When evaluating a point source discharge, profiles above and below the discharge shall be compared. An upstream representative location shall be compared to a downstream location below the regulatory mixing zone. B. Temperature Data Requirements The representative instream data will be evaluated against the appropriate numeric standard, either the default value adopted from Table 1 or an alternative numeric value adopted for a sitespecific circumstance. Location: Temperature measurements should be taken from a location (or locations) in the stream that is representative of the reach. Locations such as deep pools or exposed riffles may not be typical of the entire reach. The monitoring location's characteristics will be used in the assessment to determine the extent of the attainment/impairment. Time: Ambient water temperature varies throughout the day. The maximumrecorded temperature for a given day will be compared against the appropriate DM standard. Determination of attainment of the MWAT standard relies upon multiple equally spaced, daily measurements over a seven-day consecutive period, with a minimum of three data points spaced equally through the day. The DM is defined as the highest instantaneous water temperature recorded during a given 24-hour period. Use of recording thermographs are encouraged, but not required. Temperature Data Requirements for lakes and reservoirs: Representative lake or reservoir data will be evaluated against the applicable temperature standard. Representative data are profile data collected from the deepest part of the lake or reservoir, near the dam and/or mid-lake, at 1 meter intervals. Near-shore data collected from a boat dock or dam are not representative data. Assessment of temperature will generally require that vertical profile data be developed for temperature. Vertical profile data for temperature will be used to determine thermal stratification. Profile data will be evaluated to determine depth of K:\Reg 31 2005\Temperature\2006 work\for 10-16\Temp guidance v2 attainmt 10.12.06.doc 2
mixed layer. A mixed layer mean will be calculated to be evaluated against the Maximum Daily Average (MWAT) standard. If more than one profile is collected on the same date, a mean of mixed layer means will be calculated to be evaluated against the standard. C. MWAT Comparison Example In order to determine whether the summertime maximum weekly temperature standard is attained, the mathematical mean of multiple, equally spaced, daily temperatures over a seven-day consecutive period is compared to the criterion. WAT are not to be overlapped, i.e. individual daily mean temperatures used in the calculation of one exceedance of an MWAT will not be used in any other exceedance calculation. Table 1 presents an example of the MWAT comparison. Water temperature for this example was collected twice a day at equally spaced time intervals. The daily averages for 28 days are presented here. In this example, the MWAT is exceeded fifteen times, but because the data has been overlapped they do not all count as exceedances. For consecutive days in which the MWAT is exceeded, only the first in seven days is counted. The next six are not applicable. In this example, there are only three MWAT exceedances of nonoverlapping data. In addition, this exceedance must be screened against the allowable excursion provisions to see if it represents non-attainment. Table 1: Example WAT Comparison Where 7-day Average Temperature Exceeds a MWAT Standard of 19.3 C Date Daily Mean WAT MWAT Criterion Exceed? # Exceedances 26-Jun-02 18.52 19.3 - na - 27-Jun-02 16.89 19.3 - na - 28-Jun-02 18.04 19.3 - na - 29-Jun-02 18.13 19.3 - na - 30-Jun-02 18.38 19.3 - na - 01-Jul-02 19.13 19.3 - na - 02-Jul-02 18.93 18.29 19.3 no 03-Jul-02 17.69 18.17 19.3 no 04-Jul-02 18.80 18.44 19.3 no 05-Jul-02 19.37 18.63 19.3 no 06-Jul-02 20.22 18.93 19.3 no 07-Jul-02 19.95 19.15 19.3 no 08-Jul-02 21.29 19.46 19.3 YES 1 09-Jul-02 21.75 19.87 19.3 - na - 10-Jul-02 20.11 20.21 19.3 - na - 11-Jul-02 20.87 20.51 19.3 - na - 12-Jul-02 20.86 20.72 19.3 - na - 13-Jul-02 19.54 20.62 19.3 - na - 14-Jul-02 20.56 20.71 19.3 - na - 15-Jul-02 20.65 20.62 19.3 YES 2 16-Jul-02 19.87 20.35 19.3 - na - 17-Jul-02 19.39 20.25 19.3 - na - 18-Jul-02 19.31 20.03 19.3 - na - K:\Reg 31 2005\Temperature\2006 work\for 10-16\Temp guidance v2 attainmt 10.12.06.doc 3
Table 1: Example WAT Comparison Where 7-day Average Temperature Exceeds a MWAT Standard of 19.3 C Date Daily Mean WAT MWAT Criterion Exceed? # Exceedances 19-Jul-02 19.63 19.85 19.3 - na - 20-Jul-02 19.36 19.82 19.3 - na - 21-Jul-02 20.40 19.80 19.3 - na - 22-Jul-02 18.82 19.54 19.3 YES 3 23-Jul-02 18.10 19.29 19.3 - na - Note 1: Column 1 is the date of the measurements Note 2: Column 2 is the arithmetic mean of equally spaced individual measurements taken on that date. Note 3: Column 3 is the weekly average temperature (WAT): the seven-day rolling average of the values in column 2. Note 4: Column 4 is the MWAT temperature criterion for the water body. Note 5: Column 5 is the logical test to see if the WAT (in column 3) exceeds the standard. Note 6: Column 6 is the number of independent exceedances of the MWAT (no overlap of individual daily mean temperatures). D. DM Comparison Example: In order to determine whether the summertime Daily Maximum ( DM ) temperature standard is attained, the maximum recorded temperature in a given day is compared to the appropriate daily maximum criterion. Table 2 presents an example of this comparison. In this example, the DM is exceeded twenty-two times. These exceedances must be screened against the allowable excursion provisions to see if they represent nonattainment. Table 2: Example DM Comparison Where daily maximum temperature exceeds a DM standard of 23.8 Date Maximum Temperature Criterion Exceed? 25-Jun-02 22.17 23.8 no 26-Jun-02 25.26 23.8 YES 27-Jun-02 22.84 23.8 no 28-Jun-02 24.73 23.8 YES 29-Jun-02 22.51 23.8 no 30-Jun-02 23.18 23.8 no 01-Jul-02 24.39 23.8 YES 01-Jul-02 24.39 23.8 YES 02-Jul-02 23.01 23.8 no 03-Jul-02 21.01 23.8 no 04-Jul-02 24.04 23.8 YES 05-Jul-02 24.04 23.8 YES 06-Jul-02 24.39 23.8 YES 08-Jul-02 25.78 23.8 YES 08-Jul-02 25.78 23.8 YES 09-Jul-02 26.66 23.8 YES 09-Jul-02 26.66 23.8 YES K:\Reg 31 2005\Temperature\2006 work\for 10-16\Temp guidance v2 attainmt 10.12.06.doc 4
Table 2: Example DM Comparison Where daily maximum temperature exceeds a DM standard of 23.8 Date Maximum Temperature Criterion Exceed? 10-Jul-02 23.53 23.8 no 11-Jul-02 26.48 23.8 YES 12-Jul-02 26.13 23.8 YES 13-Jul-02 24.73 23.8 YES 14-Jul-02 26.13 23.8 YES 15-Jul-02 26.48 23.8 YES 16-Jul-02 26.30 23.8 YES 17-Jul-02 25.60 23.8 YES 18-Jul-02 25.95 23.8 YES 19-Jul-02 25.95 23.8 YES 20-Jul-02 24.73 23.8 YES 22-Jul-02 22.51 23.8 no 23-Jul-02 22.00 23.8 no 24-Jul-02 26.48 23.8 YES E. Index Patterns The following is an index pattern for seasonal fluctuations of a cold water mountain stream. This data is taken from Gore Creek. Table 3 shows the monthly average weekly average temperatures and the range of variation from month to month. The monthly minimum and maximum vary from the average WAT anywhere from one to three degrees C. The graph shows an example of what the maximum downstream value could be to still maintain a similar pattern. Table 3: Index Pattern Gore Creek Range Monthly average WAT + - January 1.17 1.51-1.17 Feb 1.99 1.33-0.97 Mar 4.22 1.87-2.24 April 4.94 1.03-0.86 May 5.10 1.26-0.81 June 6.71 2.02-1.78 July 11.58 2.32-2.83 Aug 13.56 1.46-1.64 Sept 10.26 2.57-2.47 Oct 6.94 2.48-2.25 Nov 3.19 2.35-1.50 Dec 1.34 1.20-1.50 K:\Reg 31 2005\Temperature\2006 work\for 10-16\Temp guidance v2 attainmt 10.12.06.doc 5
Av Temp Values Gore Cr nr Minturn temp 18 16 14 12 10 8 6 4 2 0 1/1 3/2 5/1 6/30 8/29 10/28 12/27 date WAT Mo Av WAT Up Bound F. Allowable Excursions Regulation 31 provides three situations that are not to be considered excedances of the numeric table values. 1. Air Temperature Excursion. Ambient water temperature may exceed the daily maximum (DM) temperature criteria or the applicable site-specific daily maximum standard, when the daily maximum air temperature exceeds the 90 th percentile value of the annual maximum air temperatures calculated using at least 10 years of air temperature data. The maximum average weekly temperature (MWAT) may be exceeded when the maximum seven day average air temperature exceeds the 90 th percentile value of the annual maximum seven day average air temperatures calculated using at least 10 years of air temperature data K:\Reg 31 2005\Temperature\2006 work\for 10-16\Temp guidance v2 attainmt 10.12.06.doc 6
2. Low Flow Excursion. Ambient water temperature may exceed the DM temperature criteria or the applicable site-specific daily maximum standard, when the daily stream flow falls below the acute critical low flow calculated pursuant to Regulation 31.9(1). The MWAT may be exceeded when consecutive 7-day average stream flow falls below the chronic critical low flow (30E3) calculated pursuant to Regulation 31.9(1). 3. Natural hot springs: Ambient water temperature in a water body may exceed the criteria in Table 1 or the applicable site-specific standard, when the temperature in that water body is influenced by a natural hot springs. K:\Reg 31 2005\Temperature\2006 work\for 10-16\Temp guidance v2 attainmt 10.12.06.doc 7