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RESPONSES TO 1999 ANNUAL HYDROLOGY REPORT REVIEW 1. The DtL1G notes that the CDPS sulfate limitation sects exceeded for discharges to Tro:rt Creek on ji~ur occasiats during 1999. These e.rceedances occurred in July, .9ugus/, and December crt Dh1P 00-1 and in December ut DMP 007. Based on review of data from stu•face seater moraila•ing sites TR-A, TR-B, TR-C. and TR- D, the numeric standard, jor sulfate for the n:ains7ern of Trout Creek (Segment lac of the }•ampa Rirer Sub-basin) u•ns not exceeded on any occasion during 1999. Therefore, there are no specific material damage issues to be addressed by the Division n! this time as u r•esrdt ofthe CDP,Ssulfute criteria erceedances. T{ter•e is a sigrti~cant increase in suljnte conc•etttration from the apstrecrm rnoni[oruag location on Trout Creek (TR-A) ro the downsn•earn monitoring point (TR-D). The highest concentration reported for TR-D in /999 is 660 nrg~/I mhich i.c svilhin the PHC predic•lion. The PHC prediction contained ha the PAP slates that sulfate concentrations in Trout Creek rnight be erpec•ted to reach an upper /irnit ojapprorimately 842 mg// at some time during the mining mad postanining era at [hc Edna tLline. Please note that DA1P 007 is not shown at the 6Y"ater Monitoring Loccrtiat A4ap (Exhibit Exhibit 4.6-26 has been revised to show the location of DMP 007 via Technical Revision 39. 2. On page 9 of the 1999.9 HR. PceM stcdes Hurt "ulthouglr elevated TDS concenn-ations have moved dox~nstremn in conjrrrrction with mining and reclamation nctivities, all values .for TDS are consisreru s+ith the probable hydrologic conseg:tences projections". /t is evident Ihal there hers been n signifrcant increase in TDS' concena•ation fran the upstream monitoring point on Trotrt G•eek (TR-•9) to the don nstream moni[a•ing point (TR-D) in cor:junctiorr with the mining cmd reclamation nctivities•. /t also crppeurs that the predicted post-mining menu annual concenn~atiaa of TDS irr Tray! Creek has been e.ceeded for the past several years n! the downstream monitoring point TR-D. The PHC• predictions presented in the PAP indicate that after mining the 6Vest Ridge crud Mgf/at Areas, the mean TDS conc•entrution in Trout Creek svadcl be expected [n increase to 330 rng/l. A4ortuorittg data reported in 1999 show t/tat dte mean unnunl TDS concernrution For TR-D was 420 mg/!. Please clcn~ifj• the stcrternent on page 9 that all values for TDS are consistent with [he PHC projections. Erceedances ol'PHC' predictions should be addressed in ftu:rre AHR's so that crny significant n•ends can be identified and catclusions regarding PHC' predictions can be rerifted. The statement on page 9 refers to the short-term analysis of TDS concentrations provided in Appendix 2.5-A. As discussed in the appendix, in the short-term, the mean TDS concentration value for Trout Creek is anticipated to be 442 mg/I (page Z.SA-7).