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Instream Numeric Standards (CWQCC 33) <br />The Seneca 11 Mine discharges surface runoff and spoil leachate into Segment 13b (Fish Creek <br />and tributaries) of the Yampa River in CWQCC's Region 12 of the Yampa River Basin. The <br />Seneca II Mine is required to monitor 17 of the parameters in Segment 13b per CWQCC and <br />CDRMS. A review of the statistical summary of the water quality data provided in Seneca II <br />Mine's Annual Hydrology Reports and specifically for the past three years was conducted for the <br />mine's NPDES Outfall (NPDES8) and stream sites SSB12 (Bond Creek above the confluence <br />with Fish Creek), SSF 11 (Fish Creek above the confluence with Bond Creek), and SSF 13 (Fish <br />Creek downstream of the confluence with Bond Creek). <br />The total recoverable iron standard, 1.0 mg/l, was exceeded a total of seven times at Sites SSFI I <br />and SSF13 from 2011 to 2013. No exceedances of the iron standard occurred at SSB12 or <br />NPDES8; therefore the exceedances are not likely caused by runoff from the Seneca II Mine. <br />The nitrite standard, 0.05 mg /1, was exceeded one time at Site SSF 13 with a value of 0.06 mg /1. <br />The nitrite value at Site SSFI 1, SSB12 and NPDES8 were below the 0.05 mg/l value. Therefore, <br />the exceedance at Site SSF13 was not likely caused by runoff of the Seneca II Mine. <br />Based on a review of the water quality data, no sites exceeded the sulfide standard of 0.002 mg/1, <br />the aquatic life ammonia standard detection limit of 0.05 mg/l or the drinking water standard (2 <br />ug/1) and aquatic life standard(0.01 ug/1) for mercury. Based on the NPDES renewal, the <br />CDPHE performed a reasonable potential analysis on NPDES8 and determined that there was no <br />reasonable potential for the outfall to exceed the mercury limit; as -such, mecury monitoring is no <br />longer required at the NPDES8 outfall. <br />Five out of thirty six samples from NPDES8 exceeded the chronic selenium standard of 4.6 ug/l, <br />with values between 5.9 and 17 ug/l. The potentially dissolved method is the method that is <br />required for NPDES compliance and the dissolved selenium method is used for assessing stream <br />compliance. No selenium exceedances occurred at any monitored surface sites downstream of <br />NPDES8. <br />For NPDES8, the five exceedances of the selenium standard noted were not NPDES permit limit <br />exceedances. The permit limit for NPDES8 associated with selenium is to "Report" only. Sites <br />SSB12 and SSF13 downstream of NPDES8 are in compliance with the receiving stream standard <br />for selenium. The CDPHE uses the 85th percentile of dissolved selenium values over the past <br />five years to determine stream attainment of the selenium standard. At Site SSF 13, the sample <br />data value is 0.5 ug /1 and Site SSB12 is at 3.91 ug/1. <br />The Seneca II Mine contains one monitored spoil spring (SSPG9), which is located upstream of <br />and flows into permanent Pond 008 (NPDES8). Due to the fact that the post- mining land use for <br />the Seneca II Mine has been approved as grazing and wildlife habitat, a review of the water <br />quality data was compared to the CWQCC surface water agricultural standards. One standard <br />was exceeded for the past three years. The manganese standard was exceeded once with a value <br />2 <br />