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<br />3.4 SURFACE WATER <br />' Monitoring of the Rito Seco has continued post-mining at stations RS-1, RS-2 and RS-5. <br />These sites are monitored on a quarterly basis. RS-1 has shown no significant change from <br />1 pre-mining to post-mining. However, during a careful review of the stream data after the <br />exceedance of TDS in Well M-11R, an increase in TDS and sulfate was noted in the RS-2 and <br />RS-5 readings beginning in the fall of 1997. TDS values at RS-2 increased from generally <br />below 100 mg/I to 256 to 422 mg/l. Sulfate values increased from generally below 10 mg/I <br />' to 98 to 173 mgfl. RS-5 values are generally somewhat lower than RS-2 values, but have also <br />seen an increase since late in 1997. Tables A-1, A-2, and A-3 in Appendix A shows selected <br />water quality data for these stations over the period of monitoring. It should be noted that at <br />' no time have the in-stream values exceeded the stream standards for the Rito Seco. <br />' 3.5 SEEPS AND SPRINGS <br />' On October 27`", BMRI initiated an in-stream survey of conductivity valuey to determine <br /> where the higher TDS values were entering the stream. The survey concentrated in the <br />' vicinity of the West Pit backfill. Immediately downhill from the location of well PW-1 a seep <br /> flowing at approximately 10 gallons per minute was noted exiting the bank albove the Rito <br /> Seco and flowing into the stream. This seep had a conductivity measurement of 1500 uhms. <br />' Within 24 hours BMRI contracted with a backhoe to dig a collection trench to collect and <br /> contain the flows and pump them back to the West Pit area. BMRI also contacted the Division <br /> and the Colorado Department of Public Health and Environment within 24 hours of noting this <br /> seep. <br />' <br /> Since that time an interim measures system has been installed as described in the following <br />' section. <br />' 4.0 INTERIM MEASURES <br /> Interim response actions to collect and pump back seepage water observed along the Rito Seco <br />' downgradient of monitoring well PW-1 have been implemented as previously discussed in <br /> Section 1.0. Work on this system began immediately upon discovery on October 27, 1998. <br /> <br /> 15 <br /> <br />