2012-11-27_REPORT - C1994082 - Laserfiche WebLink

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This summary indicates that only two CDPHE surface water agricultural use standard were exceeded. The manganese standard was exceeded at six sites. However, as indicated in the recently revised CDPHE Regulation 31, the standard of 0.2 mg /l, applies to plants grown in acidic ( <6.0 pH) soils. In alkaline soils, as are found in the Seneca II region, a more appropriate (EPA) standard would be 10 mg /l. The maximum manganese value for any surface water site observed this year was 0.88 mg /l. Premining manganese values often exceeded the 0.2 mg /l standard. NPDESI3 exceeded the selenium agricultural use standard, 20 ug /l, with a value of 25.5 ug /l (potentially dissolved). Two other forms, dissolved and total recoverable, were also analyzed, as we are investigating differences in the method. This excursion occurred after a short duration thunderstorm. The flow at the time of sampling was only 2 gpm. The next time the pond discharged (March 9, 2012), the selenium value was only 1.1 ug /l (potentially dissolved). Table 13 shows the CDPHE receiving stream standards for Sage and Grassy Creeks (Yampa Segment 13e, Reg. 33, January 2009). These aquatic life standards were based on the presence of fish in the lower portions of the creeks. However, the upper portions that the Yoast Mine discharges into have no fish present. Table 14 provides a comparison of those standards to water quality data collected this year from NPDES and stream sites in the Sage and Grassy Creek basins. Standards that were exceeded are: Parameter # of Sites 1 # of Excursions Iron, Total Rec. 2/4 Selenium, Pot. Diss. 3/7 The total recoverable iron standard (1.0 mg /1) was exceeded four times this year. Excursions were normally related to high suspended solids. No NPDES excursions for this iron standard occurred this year. This strict aquatic life standard was exceeded in 380 of the premining stream samples. 12