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<br />' increase in TDS at the downstream surface water stations was mostly related to increases in <br />calcium, bicarbonate, and sulfate concentrations, with calcium concentrations averaging 17 <br />mg/I and 22 mg/l, respectively. Bicarbonate concentrations averaged 83 and 95 mg/l, <br />respectively, while sulfate concentrations averaged 11 mg/l and 13 mg/l, respectively (Tables <br />A-2 and A-3 of Appendix A). Similar to RS-1, average pH values at RS-2 and RS-5 were also <br />slightly alkaline, with pH values of 7.6 and 7.7 standard units, respectively. <br />During the mining period, water quality remained relatively consistent compared to the pre- <br />' mining period. For example, the pre-mining average TDS, sulfate and pH values at RS-2 were <br />98 mg/I, 11 mg/1, and 7.6 std. units, respectively, compared to average concentrations during <br />the mining period for the same constituents of 94 mg/l, 8 mg/l, and 7.5 std. omits (Table A-2 <br />of Appendix A). <br />3.0 POST-MINING AND CURRENT CONDITIONS <br />' As previously discussed, the West Pit backfill and topsoil replacement was completed in <br />September of 1997. The site was then re-vegetated in October of 1997 to take advantage of <br />' winter moisture conditions. Water levels in the backfilled pit are taken on a ~montltly basis. <br />Quarterly water quality samples are collected in accordance with the approved TR-15. The <br />' following sections discuss the post-mining monitoring results as well as the actions taken by <br />BMRI since the July 1998 notification to the Division of a potential water qualGty exceedance <br />a[ Well M-11R. <br />3.1 GROUND WATER HYDROLOGY <br />' TR-18 included several predictions related to the recovery of the water table within the <br />' backfilled West Pit area. These predictions were developed based on a limited data set and <br />indicated that the water table would take between four and six years to fully recover. TR-18 <br />also predicted that the water table would stabilize at the level of the Rito Seco or <br />approximately 30 feet below the top of the backfill. The backfill elevation is approximately <br />' 8600 feet-msl; therefore the water elevation was predicted to be 8570 feet-msl. <br /> <br /> 11 <br /> <br /> <br />