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BATTLE MOUNTA/N RESOURCES /NC./BATTLE MOUNTAIN GOLD COMPANY <br />SAN LU/S PROJECT <br />FACILITY NUMBER: CO-0045675, COSTILEA COUNTY <br />Appendix 8 <br />Water Quality Standard-Based Mass Balance Calculations <br />and <br />Antidegradalion-Based WQS Mass Balance Calculations <br />The following calculations are for the WQS-Based Calculations and the Antidegradation-Based WQS Calculations jor the three <br />discharge levels, 400gpm (outfall001a), 250gprn (outfa110016), and /IOgprn (outfal[OOIc). <br />The water quality standard-based miss balance calculation is: <br />MiQi - H1rQr <br />M_, _ <br />Qz <br />Where: <br />Q, = Upstream low flow (/E3 or 30E3) jrorn Part 1lI.B.2 <br />Q1 = Average daily effluent flow (design capacity) <br />Q, = Combined dowrrstrearn flow (Q, + Q~ <br />Mr = Upstream background pollutant concentration from III. B./and Table VI-3 <br />Mr = Unknown; Marimum allox~able effluent pollutant concentration <br />M, = Marimum downstream allowable pollutant concentration (stream standard or antidegradation-bared <br />standard) <br />This mass balance equation is further discussed on page 13 ojthe BMR! rationale <br />The M2 calculated limits are shox•n in the following tables. However, in addition to these WQS calculations, anlidegradation- <br />based calculations of the WQS parameters roust be assessed. These calculations are in the last three tables following. <br />For the ambient background water quality data, MI in all the tables, this is based upon the mean (50" percentile) ojthe data <br />from Smtion RS-1. Most ojtlris is based upon the data from 1-1988 through 7-20-1999, <br />Baseline loading levels used jor the antidegradation evaluation for the Rito Seco are based upon t/re 85 '" % of t/re data from <br />station RS-5 jor the period from 1-11-1990 rhrouglr 616-1998, xlrich is the period from prernining up to the time just before an <br />increase x~as observed for certain parameters when the impact to ground water and the seep occrtrred. <br />The exception for determination ojMl values and the baseline loading slues are jor certain parameters, such as copper, lead, <br />selenium, silver, and sulfide, xere a specific period involved use oja lower minimum level of detection. !n these cases, dre <br />period with the lower detection levels was used. For ezarnple, the period from 12-9-1992 through 5-27-1994 was used ro <br />determine t/re MI value at the RS-1 station jor copper, lead, and selenium. <br />For the 10 % of the baseline loading evahration, this x~as determined by the following calculation. <br />M2A10 __ (MBSL X !.1)(031 - tMll(OIl <br />Q2 <br />For the IS % incremental increase evaluation, this seas determined as follows. <br />M3A/5 = (M2WQS - MBSL)(0.15) +MBSL <br />M2A15 = (M3A/51(031 - (Mll(O/1 <br />Q2 <br />