Idaho Administrative Code › Title IDAPA 58 - Environmental Quality, Department of › Rule 58.01.02 - WATER QUALITY STANDARDS › Section 58.01.02.054 - BENEFICIAL USE SUPPORT STATUS

Current through August 31, 2023
In determining whether a water body fully supports designated
				and existing beneficial uses, the Department shall determine whether all of the
				applicable water quality standards are being achieved, including any criteria
				developed pursuant to these rules, and whether a healthy, balanced biological
				community is present. The Department shall utilize biological and aquatic
				habitat parameters listed below and in the current version of the "Water Body
				Assessment Guidance," as published by the Idaho Department of Environmental
				Quality, as a guide to assist in the assessment of beneficial use status.
				Revisions to this guidance will be made after notice and an opportunity for
				public comment. These parameters are not to be considered or treated as
				individual water quality criteria or otherwise interpreted or applied as water
				quality standards. The Department shall employ a weight of evidence approach in
				evaluating a combination of water quality data types (including, but not
				limited to, aquatic habitat and biological parameters), when such a combination
				of data are available, in making its final use support determination.
				(3-31-22)
01.
Aquatic Habitat
			 Parameters
. These parameters may include, but are not limited to, stream
			 width, stream depth, stream shade, measurements of sediment impacts, bank
			 stability, water flows, and other physical characteristics of the stream that
			 affect habitat for fish, macroinvertebrates or other aquatic life.
			 (3-31-22)
02.
Biological
			 Parameters
. These parameters may include, but are not limited to,
			 evaluation of aquatic macroinvertebrates including Ephemeroptera, Plecoptera
			 and Trichoptera (EPT), Hilsenhoff Biotic Index, measures of functional feeding
			 groups, and the variety and number of fish or other aquatic life to determine
			 biological community diversity and functionality. (3-31-22)
03.
Use of Data Regarding pH,
			 Turbidity, Dissolved Oxygen, and Temperature
. In making use support
			 determinations, the Department may give less weight to departures from criteria
			 in Section 250 for pH, turbidity, dissolved
			 oxygen, and temperature that are infrequent, brief, and small if aquatic
			 habitat and biological data indicate to the assessor that aquatic life
			 beneficial uses are otherwise supported. Unless otherwise determined by the
			 Department, "infrequent" means less than ten percent (10%) of valid,
			 applicable, representative measurements when continuous data are available;
			 "brief" means two (2) hours or less; and "small" means conditions that avoid
			 acute effects. Subsection
			 054.03 only applies to use of
			 this data for determination of beneficial use support status. Subsection
			 054.03 does not apply to or
			 affect the application of criteria for any other regulatory purpose including,
			 but not limited to, determining whether a particular discharge or activity
			 violates water quality standards. (3-31-22)
04.
Natural Conditions
. There is
			 no impairment of beneficial uses or violation of water quality standards where
			 natural background conditions exceed any applicable water quality criteria as
			 determined by the Department, and such natural background conditions shall not,
			 alone, be the basis for placing a water body on the list of water quality
			 limited water bodies described in Section
			 055. (3-31-22)
05.
Rigor, Quality and Relevance of
			 Data
. In making any use support determination, the Department shall
			 consider the scientific rigor associated with the collection of samples or data
			 (e.g., the scientific methods used to collect samples or data); the quality of
			 measurements and/or analysis of the samples (e.g., methodology,
			 instrumentation, accuracy, precision, and limits of detection where
			 applicable); and the relevance of the data (e.g., the relationship to a water
			 quality standard, beneficial use or cause of impairment, and how representative
			 the samples or data are of the water body in question). (3-31-22)