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COLORADO DEPARTMENT OF HEATH, Wn(er Ounlit)~ Division Rmimm/e - Pnge 7, Perrnil No. CO-0043648 No. of Reported Previous No. of Parameter Reporting Concentrations Limitation Limitation Periods Avg/Min/Max Excursions. 30-day avg. 60 2.061/0.145/4.8 9.0 0 Daily max. 60 2.518/0.256/5.55 12.0 0 Potentially Dissolved Nickel, mg/l 30-day avg. 60 0.0218/0.0/0.059 0.274 0 Daily rnax. 60 0.0247/0.0/0.064 2.6 0 Oil & Grease, mg/1 60 NV/NV/NV 10 0 pH, s. u. 60 -/5.23/7.09 5.0-9.0 0 Total Mercury, tug/1 30-day avg. 60 0.0/0.0/0.0 0.00001 0 Daily tnnx. 60 0.0/0.0/0.0 0.002 0 NV menus "none visible" NA means "tto(applicnble 2. State Sampling: There are no recent state satnpling results available for this facility. B. Compliance With Terms and Conditions of Previous Permit Effluent Limitations: Occasional exceedances ofcertain permit limits have occurred since thepermit was issued. These have been, in general, one-time exceedences associated with the sporadically high ground water flows that follow large precipitation everts, or a series ofsuch events. In July of 1998, the single sample analyzed for TSS (nt 31 rng/l) exceeded the 30-day average and daily maximum limits nrrd the only sample analyzed for unionized ammonia (as N) (at 0.221 mg/1) exceeded the 30-day average limit. In September of 1998, the CNWAD concentrations slightly exceeded the 30-day average (0.025 v. 0.021 tug/1). All ofthe 1998 exceedances were associated with a series ofmajor precipitation events resazlting in a large amount ofprecipitation before the exceedances. CC&V's letters in August and October of 1998 explained the impact ofhigh runoffand flow thrrnrgla AG-01.5 associated with storm events and asserted an upset condition had occurred. In Mny, June, July, ar:d August of 1999, the CNWAO cortcentratiorts (0.037, 0.025, 0.022, and 0.025 ntg/l, respectively) at Outfal1001A exceeded the 0.021 mg/130-day average limit. The 30-day average copper limit was also exceeded in June 1999 (0.047 v. 0.039 rug/1). CC&V asserted that an upset condition: occurred with respect to all of the exceedences in 1999 that was attributable to a very large precipitation event, which caused ground water levels to rise in the bedrock surroundir:g the VLF. As n result, rrrore residual Carlton Mill tailing material may have been exposed to water that carried cyanide compounds (measured as total cymride) to the surface waters where the compowrds were converted to CNWAO in ca:centrations higher than permit limits. These conditions were reported and explained to the Division in a series ofletters submitted by CC&V in tlae latter hnlfof 1999 and early 2000. 77re aquatic life ofArequa Gulch, as demonstrated by studies conducted during this time in connection with t/ae Use Attainability Analysis (Chadwick, 1998 and Chadwick, 2001), remained protected. The Division, in a letter to CC&V dated March 13, 2000, concluded that "The complex nature ofthis site and the various theories as to the cause ofhigh CNWAD exceedences tnay not be identified but the heavy precipitation events likely had a sign cant influence. " 2. Other Pernnit Requirennents: CC&V appears to have complied with all other terms antd conditions of the pe»nit. YI. TERMS AND CONDITIONS OF PERMIT A. DetenninationofEffluentLimitations 1. Effluent Limitations -The following limits will apply and are discussed in Sections VI - A.2. a) "No Discharge"Limitation for the VLF Except as allowed under the exemptions described in the sections below, there shall be no dischargefrom the VLF, pursuant to federal effluent guideline regulations at 40 CFR, Part 440.104. This limitation does not apply to any flows from the ground water drainage systenn underlying the VLF, b) Annual Precipitation Exemption From "No Discharge" Limitation - Outfall OOSB