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COLORADO DEPARTMENT OF HEATH, Water Qun(iq~ Division Rationale - Prtge l 1, Permit No. CO-0043648 below the limit is demonsn~nted at which time CC&V cmt request a reduced monitoring frequency. ii) Other Metals and Inorganic Parmneters Past monitoring data presented in Table V-1 indicate that the respective assimilative capacities for ammonia, copper, mzd cyanide have been exceeded and the assimilative capacity for cadmium has been approached (6.0 pg/1 vs. 6.2 pg/1). Effluent limitsbasedonafndingofreasonablepotentinlwillbeincludedinthepermitforthoseparameters. Monitoring for these parmneters will also be maintained at a once per week frequency until consistent compliance at a level reasonably below the limit is demonstrated at which time CC&V can request a reduced monitoring frequency. Required effluent mercury monitoring tests have not detected effluent mercury concentations at 0.2 microgram per liter detection limit. Until recently there has not been an effective rnethadfor monitoring low-level mercury concentrations in either the stream or the facility effluent. To determine whether the discharge has reasonable potential to cause or contribute to nn exceedance ofthe water quality standard for mercury, for the term ofthis permit, CC&V will be required to monitor total mercury concentrations at OO]A and in Arequa Gulch at AG 2.0. This data will be used to determine reasonable potential nr:d to assess the impact of the discharge on Cripple Creek, respectively. A cornparisort of the mnximurn measured cortcentrntions oftotal recoverable iron, lend, and nickel in Table V-1 indicates that there is no reasonable potential for the discharge from Outfal1001A to cause or contribute to an exceedance of a water quality starrdardfor these parameters. Monitoring at a reduced frequency ofonce per month for total recoverable iron will be included in the permit and monitoring for nickel and lead will be reduced to quarterly based ort effluent concentrations well below the calculated nssirnilative capacity. Monitoring for nitrate will be dropped froth the permit based on the lack of an applicable water quality standard. c) Applicable Federal Effluent Guidelines and Standards: Federal Effluent Limitation Guidelines are not applicable to the discharge from Outfall OOIA as this discharge is not comprised, in whole or in part, of mine drainage. Far Outfal1005B, Effluent Limitation Guidelines ("ELGs') for TSS, lead, mercury, cndmiu»t, zinc, and pHwill be applied. Monitoring for other parameters for Outfall OOIA that are limited or for which monitoring at OO]A is required shall be monitored at OOSB in the event of n discharge. It should be noted that there are exemptions provided far the limits at this outfall, provided that the applicable exemption requirements are met. d) Special Notes For several parmneters, the analytical methods used in the definitior7 of effluent limits are different than those used in the defnition of the corresponding stream standard. For cyanide, the TVS standard for the receiving stremn is based upon "free" cyanide concentrations, which is less than the 'free" cyanide detection limit. While the limit will beset equal to the stream statdards, the pernit will include a provision allowing zero to be used in the calculation of reporting values whenever nn analytical result is less than the detection limit. For metals with dissolved standards, monitoring to determine compliance with the corresponding effluent limits shall be conducted using the potentially dissolved method of analysis. 3. Antidegradation Arequa Gulch (Segment 22a ofthe Upper Arkansas River), is designated as being "Use Protected "Therefore, for this segment, an antidegradation review is not required pursuant to, Section 31.8 of The Basic Standards and Methodologies for Surface Water (5 CCR 1002-31). 4. Whole Effluent Toxicity (WET) Testing CC& V conducted Whole Effluent Toxicity ("WET') testing in 1996 in accordance with the permit monitoring requirements for Outfall OOlA. CC&V submitted results to the Division, and subsequently requested a waiver of WET testing. The Division agreed with that request and waived WET testing requirements in a letter dated May 7, 1998. This waiver was based on the completion of a Toxicity Identification Evaluation (TIE) that demonstrated that high concentrations of alurnirrurn were responsible for previous WETfailures. CC& V subsequently conducted a UAA to support changes in Arequa Cntlch stream standards. The UAA demonstrated that indigenous aquatic life species in Arequa Gulch are adequately protected at the ambient water quality and the Water Quality Control Commission adopted site-specific metal standards for aluminum, manganese, and zinc in Arequa Gulch in September 1998- The final metals standards for aluminum were bused on recalculation of aquatic life