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COLORADO DEPARTMENT OF HEALTH, Water Quality Control Division Rationale -Page 19, Permit No. CO-0043648 Conversely, discharges that would be monitored at point OOIA would likely consist ojre-emergent groundwater seepage, which should be !ow in suspended solids. At point OOIB, discharges xnuld consist of the same type of seepage, plus stormwater runoff, for which there are no special 7SS effluent limitations or guidelines. Also, bath points OOIA and OO1B are the receiving stream, which may naturally carry a sign cant amount of sediment. Therefore, far points OOIA and OO1B, no 7SS Limit will be applied. Al[ discharges included in this section -those qual~ing for precipitation related exemptions or those monitored at points OOIA or 0018, will likely flow to Arequa Gulch, far which there are stream standards for pH, cyanide and metals. Therefore, inter quality based limiu for these parameters will be applied. Limits for pH will be applied to all discharges, being set equal to the stream standards. For cyanrde, existing WAD cyanrde concentrations measured at point AG-1.5, which is at the same location along Arequa Gulch as points OOIA and OOIB, indicate that it is possible that the free cyanide stream standard is currently being exceeded, at least on a periodic basis. This may be due to seepage from historic tailings, which will eventually be moved and placed in an area that is likely to produce less leachate. It should be noted, however, that data supplied by CC&V in the permit application shows that even the maxmium WAD cyanide concentration measured at point AG-1.5 is only 0.015 mg/l, which it less than the detection limit of 0.030 mg/! that will be used in the permit. It is assumed that this is because the laboratory doing the analysis is able to acheive a greater degree of precision than what the typical laboratory may be able m acheive. !n order to be consistent with other permiu, the WAD cyanide detection limit that will be used in the permit will be 0.030 mg/l. But, the permittee should insure that only approved methods are being used for cyanide analyses, and should perform asite-speck PQL study for WAD cyanide in order to verb that its lab is able to accurately detect WAD cyanide at the levels that have been reported. With respect to the spec cation of cyanide limits, since existing concentrations are below the 0.030 mg/l detection limit, it will not be necessary to include any interim limits for cyanide that might otherwise be necessary until the tailings can be moved. /nstead, the Jinal cyanide limit -which is equal to the stream standard, will be imposed immediately. With respect to any discharges qualhing for precipitation related exemptions, there is no need to delay the imposition ojcyanide limits, and they will become effective immediately. For metals, the existing quality measured ar point AG-1.5 shows instream concentrations are below standards. Therefore, limits equal to the standards will be applied immediately to all discharges listed in this section, except for lead and nickel acute limits, which are so high that they do not need to be included. It should be Hared that the permitree has indicated some concern about the possibility that metals concentrations in Arequa Gulch may rise through the movement of the existing tailings and a resulting decrease in pH levels. This may be an stream standards issue that the perrniaee will need to bring to the attention of the Water Quality Control Commission.