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Battle Mountain Resource • <br />January 25, 2000 <br />Page 4 <br />measurements taken during baseflow conditions will reflect the period of time when the water <br />quality in the Rito Seco is most influenced by contributions of flow from the alluvial groundwater <br />system. Tables 2 and 3 list the median and mean concentrations of dissolved manganese and <br />sulfate for the baseflow period of the water yeaz (October [o September). Concentrations are listed <br />for the available data record to provide a comparison of stream concentrations during all phases of <br />the San Luis project. Additionally, the comparisons presented in the following paragraphs assume <br />that the flow rate in the Rito Seco during baseflow conditions has not varied signifi~:antly over the <br />period of record. <br />The data in Table 2 show that the concentrations of dissolved manganese have declined over the <br />yeaz of record at RS-2 and RS-5. The improvement in Rito Seco water quality is readily appazent <br />with an approximate factor of 10 decrease in the concentration of manganese at both RS-2 and RS- <br />5. There is a possibility that naturally-occurring chemical reactions in the sediment; of the beaver <br />ponds, or some other natural source of manganese, contributes manganese to the Rico Seco, which <br />would confound any chemical signature associated wi[It seepage from the W~;st Pit. This <br />possibility is supported by [he values shown in Table 2 for RS-5 prior to 1996, which was the <br />period of time when there were no mining-related groundwater flows. In addition. water quality <br />measurements obtained from groundwater monitoring wells located in the unaffected portion of the <br />Rito Seco alluvial aquifer (M-26 and M-30) indicate that manganese occurs naturally in the alluvial <br />groundwater and there is likely an influence on stream chemistry from natural grouroiwater-surface <br />water interactions. <br />Sulfate concentrations also declined at RS-2 and RS-5 during 1999 as compared to the previous 2 <br />years of baseflow periods (Table 3). Sulfate concentrations decrease by a factor of approximately <br />four at both locations. <br />CONCLUSION <br />Overall, the initiation of the TR-26 water management plan, in conjunction wit:t the existing <br />seepage control system, has resulted in a decrease in groundwater levels in the W Est Pit and an <br />improvement in the water quality of the Rito Seco. <br />3801 Automation Way, Suite 100, Fort Collins, Colorado 80515 <br />Telephone (970) 223-9600 /FAX (970) 223-7171 <br />