2014-12-19_REVISION - C1980005 (2)

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the confluence with Bond Creek). The total recoverable iron standard, 1.0 mg/l, was exceeded a total of seven times at Sites SSF 11 and SSF 13 from 2011 to 2013. No exceedances of the iron standard occurred at SSB12 or NPDES8; therefore, the exceedances are not likely caused by runoff from the Seneca II Mine. The nitrite standard, 0.05 mg /1, was exceeded one time at Site SSF13 with a value of 0.06 mg /1. The nitrite value at Site SSF 11, SSB12 and NPDES8 were below the 0.05 mg/1 value. Therefore, the exceedance at Site SSF 13 was not likely caused by runoff of the Seneca II Mine. Based on a review of the water quality data, no sites exceeded the sulfide standard of 0.002 mg/1, the aquatic life ammonia standard detection limit of 0.05 mg /1, nor either the drinking water standard (2 ug/1) nor the aquatic life standard (0.01 ug/1) for mercury. Based on the NPDES permit renewal, the CDPHE performed a reasonable potential analysis on NPDES8 and determined that there was no reasonable potential for the outfall to exceed the mercury limit; as -such, mercury monitoring is no longer required at the NPDES8 outfall. Five out of thirty -six samples from NPDES8 were greater than the chronic selenium standard of 4.6 ug/1, with values between 5.9 and 17 ug /1. The potentially dissolved method is the method that is required for NPDES compliance and the dissolved selenium method is used for assessing stream compliance. No selenium exceedances occurred at any monitored surface sites downstream of NPDES8. For NPDES8, the five samples of the selenium noted were not NPDES permit limit exceedances_ The permit limit for NPDES8 associated with selenium is to "Report" only. Sites SSB 12 and SSF 13 downstream of NPDES8 are in compliance with the receiving stream standard for selenium. The CDPHE uses the 85th percentile of dissolved selenium values over the past five years to determine stream attainment of the selenium standard. At Site SSF 13, the sample data value is 0.5 ug/l. At Site SSB12, the sample data value is at 3.91 ug /1. The Seneca II Mine includes one monitored spoil spring (SSPG9), which is located upstream of, and flows into, permanent Pond 008 (NPDES8). Due to the fact that the post- mining land use for the Seneca II Mine has been approved as grazing and wildlife habitat, a review of the water quality data was compared to the CWQCC surface water agricultural standards. One standard was exceeded for the past three years. The manganese standard was exceeded once with a value of 0.262 mg/l. However, as indicated in CWQCC Regulation 31, the standard of 0.2 mg/l applies to plants grown in acidic ( <6.0 pH) soils. In alkaline soils, as found in the Seneca II Mine Permit area, a more appropriate standard is 10 mg/l. Permit Requirements of the Colorado Discharge Permit System (CDPS) The Seneca II Mine maintains one outfall, Pond 008 (NPDES8), that is monitored under the CPDS Permit No. CO- 0000221. Sample data were collected and reviewed for all required parameters and sample analysis included testing for Whole Effluent Toxicity. Sample data have been reported on a quarterly basis in discharge monitoring reports filed with the CDPHE and the CDRMS. These DMRs indicate that no exceedances of permit limits have occurred in the past three water years.