25 Pa. Code § 16.24 - Metals criteria

(a) Metals criteria are established to control the toxic portion of a substance in the water column. Depending upon available data, aquatic life criteria for metals are expressed as either dissolved or total recoverable. As information develops, the chemical identifiers for the toxic portion may be added, changed or refined. The criteria form one of the bases for water quality-based effluent limitations, which are expressed as total recoverable metal. When calculating equation-based metals criteria for determining effluent limitations, the criteria must be developed in accordance with § 93.8c (relating to human health and aquatic life criteria for toxic substances).

(b) Chemical translators are used to convert dissolved criteria into effluent limitations which are required by Federal regulations to be expressed as total recoverable metal. The default chemical translator used by the Department is the reciprocal of the conversion factor (listed in the Conversion Factors Table located in § 93.8b (relating to metals criteria)) that was used to determine the dissolved criterion. If an NPDES discharger performs a chemical translator study for a dissolved criterion, the study of this site-specific translator should be conducted in accordance with the EPA's "The Metals Translator: Guidance for Calculating a Total Recoverable Permit Limit from a Dissolved Criterion" (June 1996), as amended and updated.

(c) NPDES dischargers may request alternate effluent limitations by using site-specific water quality characteristics in a request to modify an existing water quality criterion, in accordance with § 93.8d (relating to development of site-specific water quality criteria). This may be accomplished through one or more of the following methods:

(1) Recalculating a water quality criterion in accordance with the EPA's "Interim Guidance on the Determination and Use of Water-Effect Ratios for Metals, Appendix B: The Recalculation Procedure" (February 1994), as amended and updated. The Recalculation Procedure accounts for corrections, update and additions to the original criterion dataset to create an appropriate dataset to calculate the site-specific criterion. If the optional deletion process is used to evaluate the taxonomic composition, this process should follow the EPA's "Revised Deletion Process for the Site-Specific Recalculation Procedure for Aquatic Life Criteria" (April 2013).

(2) Developing a water quality criterion by performing a Water Effect Ratio (WER) study, which is a factor that expresses the difference between the measures of the toxicity of a substance in laboratory water and the toxicity in site water. The WER provides a mechanism to account for that portion of a metal which is toxic under certain physical, chemical or biological conditions. WERs are applicable only to certain metals, which are listed by the EPA in "Interim Guidance on the Determination and Use of Water-Effect Ratios for Metals" (February 1994), as amended and updated. WERs should not be used for the development of site specific criteria for copper.

(3) Developing a water quality criterion by performing a Biotic Ligand Model (BLM) study for copper in freshwater systems. The BLM is a metal bioavailability model that uses receiving water body characteristics and monitoring data to develop site-specific water quality criteria. The BLM is used in evaluating the differences in the bioavailability and toxicity of metals. These differences occur as a result of variation in local water chemistry. The BLM may be used to derive site-specific criteria for copper in freshwater systems. The BLM incorporates the best available science for determining site-specific water quality criteria for copper and is therefore preferred by the Department. The Department will require use of BLM for copper in freshwater systems. Subject to Departmental approval of the testing and its results, the Department will evaluate the use of the BLM to establish alternate site-specific criteria. In the absence of available site data to run the BLM, estimates for missing water quality parameters may be developed using EPA's guidance, "Draft Technical Support Document: Recommended Estimates for Missing Water Quality Parameters for Application in EPA's Biotic Ligand Model," (March 2016), as amended and updated.

(4) Developing a water quality criterion using other guidance approved by the Department, which is based on other EPA-approved or scientifically defensible methodologies.

(d) Either the WER or BLM may be combined with a chemical translator study. The WER may also be used in combination with the Recalculation Procedures. If the Recalculation Procedure is selected, the procedure requires the recalculation of the existing criterion before the WER is applied. The BLM cannot be used in combination with the recalculation procedures or the WER.

Notes

25 Pa. Code § 16.24

The provisions of this § 16.24 adopted November 17, 1995, effective 11/18/1995, 25 Pa.B. 5067; amended November 17, 2000, effective 11/18/2000, 30 Pa.B. 6111; amended February 11, 2005, effective 2/12/2005, 35 Pa.B. 1223; corrected June 23, 2006, effective 2/12/2005, 36 Pa.B. 3117; amended May 15, 2009, effective 5/16/2009, 39 Pa.B. 2543; amended July 10, 2020, effective 7/11/2020, 50 Pa.B. 3485.