REV95387

• Permit No: M1988112
• IBM Index Class Name: Revision
• Doc Date: 11/16/1998
• Doc Name: BMRI SAN LUIS MINE PN M-88-112
• From: BATTLE MOUNTAIN GOLD
• To: DMG
• Type & Sequence: TR15
• Media Type: D
• Archive: No

i
quality data indicate an average TDS concentration of 408 mg/1 and sulfate concentrations of
121 mg/l (Table A-4 of Appendix A). Generally, the principal cation present in the water was
calcium, with an average concentration of 79.2 mg/1. The pH of the Rito Seco alluvium is
generally slightly alkaline (average value of 7.4 su.). There have been fluctuations in TDS and
sulfate concentrations in the Rito Seco alluvium, however, they appear to be random and not
seasonally related.
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on:
anta Fe Format
re-mining water quality data from M-1, completed [n the Santa Fe
' Formation, indicates a similar water quality to data obtained from the Rito Seco alluvial wells.
inin
data indicates an avera
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e TDS a
lf
t
ti
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t
f 380
l
ll
d 135
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mg/l, respectively (Table A-7 of Appendix A).

Significant water quality changes occurred in the Santa Fe Formation in the vicinity of the
' West Pit during the mining phase. Average TDS concentrations increased from 380 mg/1
during the pre-mining phase to 565 mg11 during the mining phase (Table A-7 of Appendix A), i,.
' while sulfate concentrations increased from 135 mg1L to 202 mg/L and bicarbonate alkalinity
increased from 199 mg/L to 318 mg/L.
' During the last part of the mining phase, an additional Santa Fe Formation well (SF-1) was
' installed downgradient of the West Pit, and water quality data began to be toll@cted from this
well. The average TDS concentration during the mining phase at SF-1 was 447 mg/1,
compared to a value of 565 mg/1 at M-1. Similarly, the sulfate concentration at SF-1 during
the mining phase averaged 44 mg/I, while the average sulfate concentration ae M-1 was 202
mg/I. This indicates a variability in water quality in the Santa Fe Formation over a very small
' distance.
' Pre-Cambrian Rock: Pre-mining water quality in the pre-Cambrian bedrock was variable,
with lower-ion concentration water observed in the vicinity of Rito Seco and higher-ion
' concentration water observed at the higher elevations north of Rito Seco. Pre-mining average
TDS and sulfate concentrations at the upgradient pre-Cambrian bedrock well (87-86) were
' quite high, compared to Rito Seco alluvial and Santa Fe Formation values. The average TDS
and sulfate concentrations at well 87-8b for the pre-mining period were 1,100 mg/1 and 530
mg/1, respectively (Table A-9 of Appendix A).
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