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Page COLORADO DEPARTMENT OF HEALTH, Water Quality Control Division Rationale -Pape 9 Permit Na. CO-0045675 I PR I 60 I Median 7.0 15.58.14••# 16.5/9.0 I N/A I 0 I See discussion in text Pot. Dis. means the potentially dissolved fraction, as defined in the Basic Standanls acid < =less than Methodologies for Surface Water (Regulation No. 31). Table V-1 (Cont.) "The range of effluent pH measurements includes all analytical laboratory reported pR values during the period October 13,1999 to July 18, 2000. Prior to January 16, 2000, the reported pR values were determined by the analytical laboratory and were subject to potential analytical bias associated with carbon dioxide /ormafion and pH reduction during transport and storage. Since that date all reported analy8cal pH values have been based on field measurements to eliminate the carbon dioxide bias in accordance with EPA policy and guidance. Although the reported analytical pH value during the period October 13, 1999 through January 16, 2000 was biased by the carbon dioxide interference, field pH measurements have been collected for the enfire period October 13, 1999 through July 18, 2000 and at no a'me has the effluent discharge field pH measurement (alien outside the Daily Maximum trigger level range of 6.5 to 9.0. # Initially, the reported laboratory pH values which were below the 6.5 s. u. trtgger level were 5.8 (11-1999), 6.2 (11.99), 6.3 (12- 1999), and 5.9 s. u. (1-2000). This occurred during and immediately following the ini8al startup period (October 1999) for the treatment system. All field pN values 1ha1 have been reported have been greater than 8.5 s.u. The two field measured pH values for January 2000 were 6.98 and 7.3 s.u. Also, field pH data at the downstream stations RS-2 and RS-5 were well in compliance with the pH standard (RS-2 values were 795 s.u. to 8.5 s. u. durng 10-1999 through 1-2000; and RS-5 pH values ranged Irom 8.05 to 8.4 s. u. during 10-1999 through 1-2000). Since the time just after the initial start up period (or the treatment system (November 1999 through July 2000), all pH values in the discharge have been in compliance with the pH m'gger level range. Since all the reported samples for mercury and silver are below the minimum level of detection, these values are not considered exceedances of the chronic limits for these parameters. All consb'tuent effluent concentrations reported as less than the analytical detection level were assigned the value o(zero (0) in preparing the Mean Effluent Concentration calculation. This assignment is cronsistent with the CDPHE Notice o/ ViolafioNCease and Desist Order, Amendment Number 1 and the draft CPDS permit. B. En/orcement History On August 20, 1999, the Division of Administration o(the Colorado Department of Public Health and Environment issued to Battle Mountain Resources, Inc. and Battle Mountain Gold Company a Notice o/Violation and Cease and Desist Order ('NOV/CDO~. In this NOV/CDO, BMRI was notified that the (acts described in items 22 through 27 of the 'Findings o(Fact constitute violations of § 258-501(1), C.R.S., which provides in pertinent part: 'No person shall discharge any pollutant into any state water from a point source without first having obtained a permit from the division for such discharge.' 22. TR-26 iodinates that "The balance of Ne groundwater flow mixes in Ne alluvial aquifer and a portion of the Mxture flows past the groundwater well M-11R. The Increase in concentrations of sulfate and TDS recorded in groundwater at M-11 R is mnsislent with the downgradient migration of groundwater outflow from the West Pit Elevated concentrations of sulfate and TDS observetl at M-11 R depend on the geodtemicel processes that influence the release of sulfate from the backfill material and on the groundwater travel time between the location of groundwater Bow from the West Pit and M-11R' 23. TR-26 indudes a lengthy disassion of the geodtemistry of the materials that were used to backfill Ne West Pit. The disassion mncludes that sulfate and manganese are leaching from the badrfiYed materials in the West Pit and that groundwater centaining elevated levels of sulfate and manganese is migrating from the West Pit into the Rito Seco alluvial aquifer. 24. BMRI and BMGC are persons as defined by § 25103(13), C.R.S. 25. The discharge of manganese, sulfate and inorganic mnsdtuenfs from the seeps into the Rito Sece, as described in paragraphs 13 and 14, above, constitutes a discharge of pollutants as defined by § 25-&103(3) 8 (15), C.R.S. 26. The discharge of manganese and sulfate that are leadting from bte baUdill materials in the West Pll into the Rito Sem alluvial aquifer, as tlesaibed In paragraphs 22 and 23, above, constitutes a discharge of pollutants as defined by § 25& }03(3) 8 (t5), C.R.S.