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<br />Proposed Decision and Findings of Compliance July 2018 <br />Permit Renewal No. 7 P a g e | 16 <br />4.8 Ground Water Hydrology <br /> <br />Ground water information is found in Sections 2.04.5, 2.04.7 (Volume 1 for the East Pit, West Pit, <br />Section 16 Pit, Facilities Area and Gossard Loadout; Volume 12 for South Taylor Pit; Volume 15 <br />for Collom Pit) and Exhibit 7 of the PAP, as well as in Colowyo’s Annual Hydrologic Reports. <br />Ground water occurs as isolated, perched aquifers in interbedded and lenticular sandstones and <br />coals and within isolated alluvial aquifers. Base flow in the four perennial streams in the general <br />area (Good Spring Creek, Wilson Creek, Collom Gulch and Jubb Creek) comes mainly from <br />ground water discharge from alluvial aquifers in the stream valleys. Stratigraphically, the Trout <br />Creek Sandstone is the major regional aquifer in the area. It is approximately 800 feet beneath the <br />lowest coal seam to be mined. The principal recharge area for the aquifer is to the south of the <br />permit area in the headwaters of Taylor and Good Spring Creeks. There is no continuous, regional <br />ground water system within the permit area above the flood plain of Good Spring Creek. No <br />saturation was encountered in any of the beds to be mined in test holes drilled by W.R. Grace and <br />Company and the USGS (information contained in the PAP and the Northwest Colorado <br />Environmental Impact Statement). <br /> <br />The Trout Creek Sandstone outcrops north of the permit area where ground water is discharged at <br />the surface. The Mancos Shale underlies the Iles Formation and forms the base of the regional <br />ground water system in the area. This shale is exposed at the surface north of the permit area in <br />the southern limb of the Axial Basin Anticline. Due to the impervious nature of the Mancos Shale, <br />ground water flow in either the deep bedrock units of the Williams Fork and Iles Formations or <br />the alluvial aquifers of Good Spring Creek, Wilson Creek, Collom Gulch and Jubb Creek is <br />discharged to the streams where they flow across the Mancos Shale. <br />4.9 Surface Water Hydrology <br /> <br />Surface water information is found in Sections 2.04.7 and 4.05 (Volume 1 for the East Pit, West <br />Pit, Section 16 Pit, Facilities Area and Gossard Loadout; Volume 12 for South Taylor Pit; Volume <br />15 for Collom Pit); Maps 11, 11A, 12, 12A, 12B, 12C, 32 and 37; and Exhibit 7 of the PAP. <br />Surface water information for the South Taylor and Lower Wilson areas can be found in Section <br />2.04.7(2) Surface Water Resource Information and Section 4.05 Hydrologic Balance in Volume <br />12 of the PAP. Table’s 2.04.7-30 to 36, Volume 12 of the PAP, also present surface water <br />information for the South Taylor and Lower Wilson areas as do Figures 2.04.7-22 to 32, again <br />found in Volume 12 of the PAP. Map 10A and Map 11A in Volume 14 of the PAP provide <br />monitoring and other hydrologic feature locations for the South Taylor and Lower Wilson areas. <br />The permit area is drained by four perennial streams: Good Spring Creek and Wilson Creek (East, <br />West, Section 16, South Taylor, and Collom Pit) as well as Collom Gulch and Jubb Creek (Collom <br />Pit). Taylor Creek, an intermittent stream located just inside and generally parallel to the west <br />boundary of the permit area and generally parallel to Wilson Creek, flows into Wilson Creek north <br />of the rail loadout. Several ephemeral drainages occur on the permit area, including the Streeter <br />Drainage, Little Collom Gulch, Straight Gulch, Morgan Gulch and the East and West Forks of <br />Jubb Creek. These drainages are tributaries to Milk Creek, which flows into the Yampa River <br />about seven miles north of the permit area.