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Ms. L. Potter <br />April 22, 1999 <br />Page 4 <br />Appendix D, Table 5 <br />The CDPHE acute and chronic AWQC's listed on Table 5 were taken from CDPHE Regulation No. <br />31, "Basic Standards and Methodologies for Surface Water". RMC believes that the more <br />appropriate document is Regulation No. 36, "Classifications and Numeric Standards for the Rio <br />~~ t~ Grande Basin". Regulation No. 36 contains specific numeric standards for stream segment 28 of <br />the Rio Grande Basin, which is defined as the "Mains[em of the Rito Seco, including all tributaries, <br />wetlands, lakes, and reservoirs, f,~om the source to the eudet o/ Salazar Reservoir". Several <br />standards listed in Regulation No. 36 are lower than those used in Table 5. Specifically, Regulatior <br />No. 36 standards for the following parameters differ from those used in Table 5: <br />• Arsenic (0.05 mg/L for acute); <br />• Chromium (0.05 mgfL for acute); <br />• Iron (0.3 mg/L for chronic, as dissolved iron); <br />• Manganese (0.05 mg/L for chronic); <br />• Selenium (0.01 mg/L for acute, as total recoverable selenium); and <br />• Sulfate (250 mg/L). <br />Using the Regulation No. 36 standards, the maximum dissolved iron value at station RS-5 is in <br />exceedence; the minimum, maximum and mean manganese values at station RS-2 are in <br />exceedence; the maximum and mean manganese values at stations RS-3 and RS-5 are in <br />exceedence. <br />Note also that the detection limits for ammonia and WAD cyanide apparently exceed their acute <br />and chronic standards. Comparison of these two parameters to their respective numeric standards <br />can not be made using the existing data. <br />Aooendix D, Table 6 <br />The agricultural and drinking water quality criteria presented in Table 6 were apparently taken from <br />Table III of CDPHE Regulation No. 31. Note that the State of Colorado's primary and secondary <br />drinking water regulations contain water quality criteria that are different than those presented on <br />I' Table 6. Specific examples are: <br />• Aluminum has a SMCL of 0.2 mg/L; <br />• Barium has an MCL of 2 mg(L, not 1 mg/L; <br />• Chromium has an MCL of 0.1 mg/L, not 0.005 mg/L; <br />• Lead has an at the tap action level of 0.015 mg/L; <br />• pH range is 6.5 to 8.5, not 5 to 9; and <br />• Silver has a SMCL of 0.1 mg/L, not 100 mg/L. <br />Mean aluminum concentrations for RS-2 and RS-5 exceed the SMCL value. <br />