2025-10-31_GENERAL DOCUMENTS - C1981019

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Section 16 Pit,Facilities Area and Gossard Loadout; Volume 12 for South Taylor Pit; Volume 15 for Collom Pit) and Exhibit 7 of the PAP, as well as in Colowyo's Annual Hydrologic Reports. Ground water occurs as isolated, perched aquifers in interbedded and lenticular sandstones and coals and within isolated alluvial aquifers. Base flow in the four perennial streams in the general area (Good Spring Creek, Wilson Creek, Collom Gulch and Jubb Creek) comes mainly from ground water discharge from alluvial aquifers in the stream valleys. Stratigraphically,the Trout Creek Sandstone is the major regional aquifer in the area. It is approximately 800 feet beneath the lowest coal seam to be mined. The principal recharge area for the aquifer is to the south of the permit area in the headwaters of Taylor and Good Spring Creeks. There is no continuous, regional ground water system within the permit area above the flood plain of Good Spring Creek. No saturation was encountered in any of the beds to be mined in test holes drilled by W.R. Grace and Company and the USGS (information contained in the PAP and the Northwest Colorado Environmental Impact Statement). The Trout Creek Sandstone outcrops north of the permit area where ground water 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 Good Spring Creek, Wilson Creek, Collom Gulch and Jubb Creek is discharged to the streams where they flow across the Mancos Shale. 3.4 Surface Water Hydrology Surface water information is found in Sections 2.04.7 and 4.05 (Volume 1 for the East Pit, West Pit, Section 16 Pit, Facilities Area and Gossard Loadout; Volume 12 for South Taylor Pit; Volume 15 for Collom Pit); Maps 11, 1113, 11C, 12, 12A, 32 and 37; and Exhibit 7 of the PAP. Surface water information for the South Taylor and Lower Wilson areas can be found in Section 2.04.7(2) Surface Water Resource Information and Section 4.05 Hydrologic Balance in Volume 12 of the PAP. Table's 2.04.7-30 to 36, Volume 12 of the PAP, also present surface water information for the South Taylor and Lower Wilson areas as do Figures 2.04.7-22 to 32, again found in Volume 12 of the PAP. Map l0A and Map 11 in Volume 12 of the PAP provide monitoring and other hydrologic feature locations for the South Taylor and Lower Wilson areas. The permit area is drained by four perennial streams: Good Spring Creek and Wilson Creek (East, West, Section 16, South Taylor, and Collom Pit) as well as Collom Gulch and Jubb Creek (Collom Pit). Taylor Creek, an intermittent stream located just inside and generally parallel to the west boundary of the permit area and generally parallel to Wilson Creek, flows into Wilson Creek north of the rail loadout. Several ephemeral drainages occur on the permit area, including the Streeter Drainage, Little Collom Gulch, Straight Gulch, Morgan Gulch and the East and West Forks of Jubb Creek. These drainages are tributaries to Milk Creek, which flows into the Yampa River about seven miles north of the permit area. Precipitation averages 18 inches annually on the property and runoff is limited. Flows in the drainages are mainly in response to snow melt or intense thunderstorm events. Water sampled from the drainages is quite hard, dominated by calcium and magnesium cations and bicarbonate and sulfate anions. The relatively high alkalinity and pH of the system impedes the solubility and transport of heavy cations, thus minimizing potential toxicity problems associated with heavy metals or acid drainage. 17 Permit Revision No.5(PR-05),C-1981-019