5 Colo. Code Regs. § 1002-38.104
The provisions of C.R.S. 25-8-202(1)(a), (b) and (2); 25-8-203; 25-8-204; and 25-8-402; provide the specific statutory authority for adoption of these regulatory amendments. The commission also adopted in compliance with 24-4-103(4) C.R.S. the following statement of basis and purpose.
BASIS AND PURPOSE
The commission deleted subsections 38.6 (a) and (b), which described the regulatory basis and implementation of discharger-specific variances, because this information was revised and consolidated into 31.7(4).
38.6(2)(b)(ii) was edited to clarify that the sulfate standard applies to dissolved sulfate concentrations. As an ion, sulfate is found in water only in the dissolved state; therefore, either unfiltered or filtered samples may be used to determine sulfate concentrations.
The following changes were made to the hardness-based table value standard equations at 38.6(3) to improve compatibility with Excel and align with corrections made to Regulation No. 31:
* Acute and chronic aluminum, chromium III, copper, lead, manganese, nickel, silver, uranium, and zinc: the first bracket was replaced with the symbol * and the second bracket was deleted from the equation.
* Acute and chronic cadmium: extra spaces were removed.
* Acute and chronic lead: the brackets were deleted and a parenthesis was moved within the conversion factor.
* Acute silver: 1/2 was replaced with 0.5* in the equation.
The commission revised Footnote 6 of the Table Value Standards table to improve the clarity of the footnote, which directs the implementation of the trivalent (III) and hexavalent (VI) chromium standards when data for the individual valence states are unavailable. Chromium data are infrequently reported for chromium III and chromium VI individually. Instead, data are typically reported as the total of all valence states of chromium present in the sample. This is primarily due to the difficulty of accurately measuring chromium III concentrations and the instability of chromium when the sample is acidified for analysis of the total recoverable fraction. While chromium III and chromium VI are the valence states most often found in natural waters, chromium is unstable and can convert between forms in water and in the bodies of humans and aquatic life. However, chromium VI is more water soluble and a known carcinogen. Depending on the classified use, the chromium VI standards are the same as or more stringent than the chromium III standards (Table III). Therefore, when data for individual chromium species are unavailable, the use of the chromium VI standards to assess data reported as total chromium (i.e., the total of all valence states of chromium) will ensure protection of human health and aquatic life. In addition, Footnote 6 was modified to clarify that neither the sum of the concentrations of chromium III and chromium VI (when reported individually) nor the total chromium concentration (i.e., the total of all valence states of chromium) should exceed the Water Supply standards of 50 µg/L for chromium III and chromium VI in water bodies with a Water Supply use classification.
The following edits were made to improve clarity, correct typographical errors, and improve consistency across the basin regulations (Regulation Nos. 32-38) and with Regulation No. 31:
* All variations of E. coli were edited to display a consistent format in the regulation and appendix tables.
* At 38.5(2) 'Table B' was added to the reference to organic standards at 31.11 to align with changes to Regulation No. 31.
* At 38.6(1), text was added to clarify that the tables in Appendix 38-1 only show the most stringent standards, and that additional, less stringent standards may be found in Regulation No. 31.
* The reference to the 'temporary modification and qualifiers' column at 38.6(2)(c)(i) was replaced with 'Other' to align with a previous change to the appendix tables.
* References to "Trec" were replaced with "total recoverable" or "T".
* Footnote 4 of the Table Value Standards table was modified to clarify that the "T" in the chronic ammonia equations stands for temperature.
* Other minor edits were made to improve clarity and consistency.
5 CCR 1002-38.104