2018-02-05_REVISION - C1992081 (29)

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The majority of the permit area associated with the Loadout drains to Dry Creek. A small, northern portion of the railroad loop drains directly into the Yampa River. Three drainages: Stokes Gulch, Dry Creek, and Sage Creek, run through the permit area associated with the TAHR. The Walker irrigation ditch crosses the northern portion of the permit area. The Yampa River lies about one mile north of the permit area. Precipitation averages approximately 16 inches annually in the permit area and the volume of runoff is limited. Most runoff comes from snowmelt or intense thunderstorm events. Flows in Dry Creek have ranges from 0 to 126 cubic feet per second (cfs) upstream of the Loadout to 0 to 225 cfs downstream. Two sediment ponds control runoff at the loadout: the Truck Loop Pond usually discharges during spring snowmelt; the Rail Loop Pond has rarely discharged. Stream flow in Dry Creek generally increases downstream, although some sections are ephemeral. During the growing season, diversions from Dry Creek above the permit can significantly reduce and periodically eliminate streamflow in the vicinity of the Loadout, while at the same time return flows from surrounding irrigated fields can discharge small volumes of water to Dry Creek below the Loadout. The dominant cations in Dry Creek water are magnesium, calcium, and sodium. The dominant anion is sulfide. The pH is generally around 8.2. The concentrations of major cations, total dissolved solids and nitrate (possible due to agricultural return flow) increase during periods of low flow (baseflow). Total suspended solids (TSS) are higher downstream than upstream of the Loadout, with average values of 2,439 and 3,175 milligrams per liter (mg/1), respectively. Section B, Item III of this document includes a discussion of the probable hydrologic consequences (PHC) of the Loadout on surface water quantity and quality and a discussion of the surface water monitoring plan. Alluvial valley floors (AVF's) are discussed in Section B, Item XIV of this document. Ground Water Ground water information is located in Tabs 7, 13, 14, and 15 of the PAP. A summary of this information can be found in Section B, Item III of this document, along with specific findings related to ground water hydrology. The reclaimed coal storage and tipple area of the Loadout was situated on alluvial and colluvial materials overlying the Lewis shale. Waters from the Lewis shale are a primarily calcium and sodium bicarbonate type although sulfate type water also occurs in the Lewis shale. The potential source of sulfates is the reduction of sulfide materials and organic materials in shales. The Lewis shale has low hydraulic conductivity. It is generally considered to be an aquitard that retards transmission of surface water to the underlying regional aquifer, the Twentmile Sandstone. This low conductivity results in low well yields which, along with poor water quality characteristics, preclude the use of Lewis shale waters for use other than stock watering (Seneca II -W Permit Application, HGTI application Attachment 7-1). 7