Draft Language for Temperature Assessments - Defining the ‘Warming Event’
Draft language for 2018 303(d) Listing Methodology (Section IV.A.3.iv pg. 2019 of revised draft)
For the assessment of chronic and acute temperature standards, one warming event above the standard is permitted for datasets with 4-6 years of data. No warming event is allowed for datasets with 3 4 or less years of data.
A warming event is defined as the maximum allowable extent of consecutive days above the standard, with the maximum exceedance defined in terms of degree-days. This concept integrates both the magnitude of temperatures above the standard as well as the duration (in days). The stream is allowed to exceed standards for a specific number of ‘degree-days’. However, if temperatures exceed the number of ‘degree-days’ specified in Table XX, the segment is placed on the 303(d) List as impaired for temperature.
The following degree-days are allowed for Cold and Warm streams:
Table XX. Allowable Degree Days for Defining aTemperature Warming Event
Acute / Chronic
Cold / 2.4 / 13.5
Warm / 3.8 / 35.5
*Degree-days were derived using a biological basis and represent cumulative temperatures where growth or lethal impacts to fisheries are expected.
To assess if the warming event has extended beyond its allowable extent, several calculations are performed. For any consecutive days where the WAT or DM exceeds the standard, the difference between the WAT/DM and the standard is calculated.Next, a running total of these differences iscompared against the ‘degree day’ values in table XX. If the running total does not exceed the ‘degree day’ value in table XX, then the segment is not considered impairedment.However, if the running total does exceed this value, then the timing of excursions is considered to evaluate impairment. If all of the remaining days over the standard have excursions,then the segment is not considered impaired. However, ifIfthe running total is above the allowed amount in Table XX and those exceedances do not have excursions,then the warming event has exceeded its allowable extent and the segment is considered impaired. When excursions are evaluated, the WAT’s for 6 days after the last identified excursion are not considered exceedances, thus removing the effect of the date with the excursion from the evaluation.
In summary, the warming event, when applicable, is applied to the dataset first. After the timing of the warming event has been identified, then the excursions are evaluated. Any data that is not covered by the warming event or an excursion will be used to support a listing decision.
If stream temperatures drop below the standard and then exceed the standard again (even if only one day later), this is considered a second warming event and the segment is considered impaired.If exceedances in the standard are identified in multiple years or multiple seasons, these exceedances are considered more than one event and therefore the segment is also considered impaired.
Discrete temperature measurements may be used to assess attainment of acute temperature standards. However, unless a minimum of three equally spaced measurements are collected throughout a 24 hour period over a seven day consecutive period, discrete data cannot be used to assess chronic temperature standards.All temperature measurements used for assessment purposes must be collected in accordance with the division’s temperature SOP (WQCD - Standard Operating Procedures for the Collection of Stream Water Temperatures Utilizing the Deployment of Temperature Data Loggers).
If the acute temperature standard is exceeded, excursions must be evaluated for those dates to justify a 303(d) listing. If the excursions have not yet been evaluated, or if there is insufficient data to evaluate excursions, the segment will be placed on the Monitoring and Evaluation List. A minimum of 2 exceedances from two different seasons or years is required for 303(d) listing.
To delist a segment that was placed on the 303(d) List due to exceedances of the acute temperature standard, a minimum of 5 samples is required from the same season and conditions that indicated initial impairment. Samples should be collected in the middle afternoon, when temperatures are expected to be highest.