2016-08-08_GENERAL DOCUMENTS - C1981019

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PR-04, Colowyo Coal Mine C1981-019 21 August 2016 Sandstone is hydrologically isolated from disturbance associated with the Collom expansion by a laterally continuous smectite layer, two to three feet thick, which is identified as the “KM” and overlies the Trout Creek Sandstone by approximately 165 feet. This was formed from the deposition of volcanic ash and is of such low hydraulic conductivity (less than 1x10-12 m.s-1, or 2.8x10-7 ft/day), that it is essentially impermeable. The Trout Creek Sandstone outcrops north of the permit area, where groundwater is discharged at the surface. The Mancos Shale underlies the Iles Formation and forms the base of the regional ground water system in the area. This shale is exposed at the surface north of the permit area, in the southern limb of the Axial Basin Anticline. Due to the impervious nature of the Mancos Shale, ground water flow in either the deep bedrock units of the Williams Fork and Iles Formations or the alluvial aquifers of Goodspring Creek and Wilson Creek is discharged to the streams where they flow across the Mancos Shale. 3.2.9 Surface Water Hydrology Surface water information is found in the following within the PAP:  Sections 2.04.7 and 4.05 (Volume 1 of the PAP for the East Pit, West Pit, Section 16 Pit, Facilities Area and Gossard Loadout; Volume 12 for South Taylor; and Volume 15 for Collom expansion).  Maps 10A, 11, 11A, 12, 12A, 32 and 37  Tables 2.04.7-30 to 36 (Volume 12)  Figures 2.04.7-22 to 32 (Volume 12)  Exhibit 7. The permit area is drained by four perennial streams (from east to west): Goodspring Creek, Wilson Creek, Jubb Creek and Collom Gulch. Several intermittent and ephemeral drainages are also on the permit area. These drainages, all generally flowing from south to north, are tributaries to Milk Creek and Morgan Gulch, which flow into the Yampa River north of the permit area. Based on monitoring data from 2004 through 2006, water quality in the perennial streams was characterized as follows. Collom Gulch samples contained calcium-magnesium or calcium- sodium anions and bicarbonate-chloride-sulfate cations. Some Total Dissolved Solids (TDS) and manganese concentrations exceeded the United States Environmental Protection Agency (USEPA) secondary drinking water standards, but total recoverable iron standards did not exceed the USEPA aquatic life standard. TDS concentrations increase in the downstream direction. Water quality in the main stem of Jubb Creek is dominated by calcium-sodium anions and chloride-sulfate-bicarbonate cations. TDS concentrations exceeded the USEPA secondary