2019-03-11_REPORT - C2009087 (2)

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sites in part come from Scotchman's Gulch, which is in contact with Lewis Shale soils. Lewis Shale soils have contributed to the high selenium values observed in many of the streams in this area. However, there is a temporary modification (expires December 31, 2018) of the selenium standard as "current conditions". Therefore, this excursion is not considered a standard exceedance. The sulfide MDL is 0.20 mg/l. All test values this year were less than the MDL. The sulfide standard is 0.02 mg/l. Table 16 in Appendix A shows the CDPHE receiving stream standards for Lower Grassy Creek (Yampa Segment 13j). This new segment came into effect December 31, 2014. Table 17 provides a comparison of those standards to water quality data collected this year from NPDES and stream sites in the Grassy Creek basin. No standards were exceeded in 2018. The mercury MDL is 0.20 ug/l. All test values this year were less than the MDL. The mercury standard is 0.01 ug/l. NPDES Effluent Criteria (Permit No. CO -0048275). No excursions of effluent limits occurred this year. Surface Water Summary. Water discharged from the PSCM is not used directly for irrigation. No irrigation exists on Grassy Creek or Cow Camp Creek below the PSCM. Indirectly, although, water discharged from the mine is significantly diluted by water from either Fish Creek or the Yampa River before it is diverted and used for irrigation. Due to the relative amount of dilution by additional water from both sources, the ambient water qualities of Fish Creek and the Yampa River are the dominant factors in determining their suitability for irrigation. Water discharged from the PSCM is, however, used for livestock watering. Of the 15 surface water features monitored, 13 are exhibiting increasing TDS trends, and two display decreasing trends. 19