2020-08-20_PERMIT FILE - C2009087 (2)

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RULE 2 - PERMITS RN15-01 2.05-96 Revision 10/17 • Surface placement of coal (stockpiling) • Operation of drainage and sediment control structures • Discharge of mine water to surface drainages • Discharge of mine-affected groundwater to alluvial aquifers • Elimination of springs Operational measures that will be implemented to mitigate these impacts are discussed below. Areas both within and adjacent to the PSCM Permit Area were previously surface mined, have been reclaimed, and in most cases, have full or partial bond release. In general, contributions of suspended solids from these areas are similar to baseline conditions, however, spoil springs and outfalls receiving spoil groundwater contributions may continue to show elevated levels of dissolved solids and other constituents, above baseline conditions. Seasonal pulses of selenium above the 4.6 µg/L chronic aquatic life table value standard (TVS) have occurred at the PSCM outfalls. In 2012 the Water Quality Control Division (WQCD) issued PSCM a violation for the elevated selenium in the mine discharges. In response PSCM completed an extensive monitoring effort to evaluate the source and fate of selenium in these watersheds. Water quality and biologic monitoring were conducted in the receiving stream watersheds (Cow Camp Creek and Grassy Creek), as well as several adjacent watersheds. Biological surveys were completed to document fish and invertebrate populations and stream habitat quality and selenium tissue samples were collected to determine if aquatic species were adversely affected by the selenium discharges. Findings, as described in the Comprehensive Technical Report dated February 28, 2014, indicate elevated selenium in the PSCM discharges occur seasonally, usually during the spring snowmelt season, and are related to spoil groundwater contributions from historic mining, not PSCM operational activities. Selenium is typically in compliance with the chronic aquatic life selenium TVS at the receiving stream points immediately downstream of the outfalls. Selenium was found to be naturally elevated in this region as a result of the natural weathering of underlying seleniferous marine shales, such as the Lewis Shale Formation which is known to be a source of selenium that can be mobilized in surface water and shallow groundwater systems (Frankenberger et al., 1998; Lemly and Smith, 1987). This is evident in Scotchmans Gulch which is a tributary to Lower Grassy Creek downstream of the PSCM. Scotchmans Gulch does not receive drainage from PSCM but flows through the Lewis Shale Formation. Selenium has periodically exceeded the chronic TVS in Lower Grassy Creek as a result of the high selenium drainage contributions from Scotchmans Gulch. Results of the biologic surveys indicate that aquatic species, especially fish, are absent throughout Little Grassy Creek and the upper reaches of Cow Camp Creek. These drainages are ephemeral and the absence of aquatic species is a result of unsustained stream flow limiting available habitat, not selenium related effects from mine discharges. Fish are only present in the lowermost reach of Cow Camp Creek near its confluence with Fish Creek during the spring when water is present. Fish were present during the spring, summer, and fall in Grassy Creek downstream of the mine discharges. Selenium deformity rates are very low in these watersheds (< 0.2 percent) and are considered negligible based on the Lemely’s teratogenic deformity index. Selenium tissue concentrations are generally low and are within the EPA recommended whole body tissue criterion (8.5 mg/kg) at the biologic monitoring points immediately downstream of the mine discharges. PSCM has taken steps to mitigate elevated selenium including the use of an integrated system of permanent ponds and enhanced wetlands to