Code of Colorado Regulations
1000 - Department of Public Health and Environment
1002 - Water Quality Control Commission (1002 Series)
5 CCR 1002-31 - REGULATION NO. 31 - THE BASIC STANDARDS AND METHODOLOGIES FOR SURFACE WATER
Section 5 CCR 1002-31.32 - STATEMENT OF BASIS, SPECIFIC STATUTORY AUTHORITY AND PURPOSE: OCTOBER, 1995 HEARING

A. Aquatic Life Table Values for Selenium

The aquatic life table value criteria for selenium are being changed from 135 ug/l acute and 17 ug/l chronic to 20 ug/l acute and 5 ug/l chronic respectively. These values, which are measurements of waterborne selenium, will serve as interim guidance for the Commission in establishing numeric standards for specific basins and individual stream segments. The new interim numeric criteria are based upon EPA's 1987 Selenium Criteria Document. The EPA selenium criteria values of 5 ug/l chronic and 20 ug/l acute are not expected to be the appropriate standards for each and every waterbody within Colorado. Appropriate site-specific standards may be different than these table value numbers. These numbers may no longer represent the latest scientific evidence for all cases. Bioaccumulation may occur at higher or lower water column concentrations of selenium depending upon a variety of factors. Nutrient enrichment, productivity of primary producers, selenium speciation, pond residence time and other factors influence bioaccumulation. Several parties argued that the EPA criteria are unnecessarily stringent to protect aquatic life in many Colorado streams, while the U.S. Fish and Wildlife Service urged the adoption of a chronic table value of 2 ug/l to assure adequate protection.

Information was presented at the rulemaking hearing that the field studies which support the EPA criteria may not be directly transferrable to Colorado streams and reservoirs. Certain Colorado segments currently have elevated selenium levels, yet there is no apparent evidence of adverse impacts upon aquatic life or wildlife. Selenium in the aquatic environment exhibits a strong association with particulate organic matter and, as a result, measurements of waterborne concentration can be an unreliable predictor of bioaccumulation and the subsequent potential for adverse biological effects. Some research indicates that particulate selenium (i.e. selenium associated with detritus sediment or suspended particulate matter) is a more reliable predictor of these effects. Pending further study, the table values are used as an interim guideline.

In accordance with Section 3.1.7 of the Basic Standards and Methodologies for Surface Waters, the selenium table values are intended to guide the Commission and others at site-specific standard-setting hearings. These values are generally considered to protect the beneficial use classifications, but are not presumptively applicable to site-specific stream segments prior to or during the course of subsequent triennial review or segment specific rulemakings. The site-specific standard-setting process is a more appropriate vehicle for identifying and weighing the many variables influencing selenium toxicity.

Given the potential for significant site-specific differences in bioavailability and subsequent effects, the naturally high concentrations of selenium in some Colorado water bodies, the lack of evidence of adverse impacts to Colorado ecosystems despite such elevated levels, and the difficulty in remediating selenium contributions from natural and nonpoint sources, the Commission has added a footnote to the TVS which explicitly states: "Selenium is a bioaccumulative metal and subject to a range of toxicity values depending upon numerous site-specific variables." This footnote recognizes the opportunity to develop ambient or site-specific water quality standards on a basin-by-basin or specific segment basis. This can be accomplished in a number of ways, including the adoption of ambient or site-specific standards under Section 3.1.7 , or pursuant to other scientifically defensible methods. No single appropriate site-specific method has been identified to date.

The Commission will reconsider this interim standard and the availability of site-specific standard setting methods in subsequent reviews of this regulation. In the meantime, the Commission strongly encourages statewide cooperative efforts to (i) define potential biological thresholds, (ii) consolidate fish population data bases, and (iii) provide specific Colorado guidance for the development of methodologies for derivation of site-specific standards. The Commission urges all participants in this hearing, including the U.S. Fish and Wildlife Service, to assist in this effort. It is apparent that the determination of appropriate water quality standards for selenium is an extremely complex technical issue that warrants a broad-based effort if an appropriate long-term resolution is to be achieved. The absence of guidance and/or methods for the development of site-specific standards shall be considered by the Commission during subsequent reviews in determining whether to retain this interim standard. The next triennial review informational hearing for this regulation is currently scheduled for July, 1996, with any subsequent rulemaking hearing likely to be scheduled 6 to 12 months later.

Site-specific standards may be based upon considerations of site-specific factors including, but not limited to, ambient selenium concentrations, selenium speciation, sulfate antagonism, sediment and water column interaction, food web structure, stream gradient and temperature, seasonal stream flows, geohydrology, hydrologic residence time and evaporation rates, selenium sensitivity of the aquatic life present or to be protected, the diversity and density of the aquatic life present, conditions conducive or not to bioaccumulation, presence of toxic effects, risk of sublethal effects taking into consideration habitat limitations or other water quality factors, and the availability, practicality, technical and economic feasibility of point and nonpoint source treatment techniques, as well as other factors enumerated in C.R.S. 25-8-204(4).

During the hearing, one party urged the Commission not to apply the new selenium table values to cold water aquatic life streams above 7,000 feet in Colorado but rather to retain the existing table value criteria for these waters. The Commission has decided as a matter of policy that these issues are better addressed in site-specific standard-setting hearings, rather than addressing them in a hearing on table value criteria. As indicated in the preceding paragraph, site-specific factors such as geology, stream gradient and temperature, ambient selenium levels and other conditions conducive to bioaccumulation can be considered in standard-setting hearings.

Extensive testimony was received concerning the natural, as well as nonpoint source nature of selenium loading of streams. These sources will necessitate long-term water quality planning processes. Testimony was presented on the need for Total Maximum Daily Load determinations and allocation of mass loading among point and nonpoint sources. This implementation process is separate from the setting of the standard and may require additional planning processes and efforts by the Commission and Division once standards are set.

Finally, the Commission notes that a selenium standard need not be adopted during the course of triennial review or segment specific rulemakings unless it is determined that the discharge or presence of selenium in the affected waters reasonably could be expected to interfere with the classified uses adopted for the affected waters. Where it is determined that the presence of selenium reasonably could be expected to interfere with classified uses, appropriate action shall be taken in conjunction with a site-specific or a basin-wide rulemaking hearing.

B. Agriculture Table Value for Selenium

The notice for this rulemaking also proposed that the current agriculture table value for selenium be changed from 20 ug/l to 50 ug/l based on levels needed for protection of livestock. However, in this hearing the Commission was not presented with substantial scientific information demonstrating that 50 ug/l of selenium would be protective of agriculture uses. Therefore, the Commission has declined to modify the current agriculture table value at this time.

PARTIES TO THE OCTOBER 11, 1995 HEARING