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ambient water quality criteria for the protection of freshwater aquatic life. The data evaluation <br />and screening level human and ecological risk assessments resulted in the following conclusions: <br />• Manganese concentrations have increased in the Rito Seco adjacent to and <br />downstream of the West Pit of the BMRI facility. However, manganese <br />concentrations have periodically exceeded the secondary MCL throughout the surface <br />water monitoring program at stations RS-2 and RS-5, even prior to mining as well as <br />at station RS-3 on the tributary upstream of the mine operations (1988 to 1999). <br />• Although manganese concentrations consistently exceed the secondary MCL at <br />locations above (e.g., the RS-3 tributary) and below the Site, manganese does not <br />pose a human health risk because this criterion is based on staining and taste <br />problems associated with manganese, not toxic effects. <br />• Agricultural water use for irrigation is not expected to result in adverse effects to <br />crops or soil conditions because the neutral to alkaline soil and water conditions will <br />limit the solubility and bioavailability ofmanganese. <br />• HQ calculations for terrestrial wildlife and free-range cattle indicate no significant <br />potential for adverse effect to growth or reproduction. <br />• Comparisons of the chronic and acute AWQC for the protection of aquatic life <br />indicate no significant potential for toxic effects. <br />• The natural alkalinity of the waters associated with the alluvial and Santa Fe <br />Formation deposits effectively mitigates the potential for toxic effects in aquatic <br />organisms from the observed concentrations ofmanganese. <br />• The only potential impairment of beneficial uses of the Rito Seco is associated with <br />the potential for staining and unpleasant taste associated with manganese and sulfate <br />which may influence a potential receptor's (human and wildlife) desire to drink the <br />water in the Rito Seco. Based on this analysis, a more quantitative assessment of <br />potential toxic effects and risks is not warranted. <br />• <br />Battle Moun(ain Resources. Inc. <br />pa/001671reportslmarchrptlvl6wtrmngfmarch.doc 62 March 11. /999 <br />