2020-06-24_REVISION - C1981035 (2)

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ENVIRONMENTAL ASSESSMENT Surface Water Resources Surface water resources within the area encompassed by the King II Mine and its associated CIAA for water resources include drainages classified as ephemeral and intermittent by OSMRE (2017). Ephemeral streams flow only in response to precipitation events or snow melt and include East and West Alkali Gulch which cross the King II Mine underground workings and are tributary to Hay Gulch below Mormon Reservoir. The Gulch parallels the western boundary of the permit area and separates the King II mine workings from the Project Area to the west. The Gulch is an intermittent stream with a portion of the stream drainage below the water table, allowing for flow in a segment of the stream over part of the year derived from groundwater. Because of the lack of perennial streams in the Project Area and the CIAA, quantification of surface water is limited to storm events or flow in irrigation ditches (OSMRE 2017).The Hay Gulch Ditch is a year-round diversion from the La Plata River and showed a range in flow rates from 0.28 to 1.5 cubic feet per second (cfs) during the period from April 2016 to March 2017. The typical flow rate was on the order of 1.0 cfs (OSMRE 2017). To date,there are no water quality data on storm water runoff.The Hay Gulch Ditch water is sodium/calcium bicarbonate water with a pH of 8.2,total dissolved solids(TDS)of 100 to 700 mg/L(RHS 2017); most constituents are below drinking water standards(RHS 2017).Water in the Mormon Reservoir is calcium/magnesium sulfate water with a pH of 7.8, and a TDS ranging from 1,000 to 1,500 mg/L due to evapo-concentration (OSMRE 2017). Ground Water Resources Groundwater in the Project Area and the CIAA is found in the alluvium of Hay Gulch and in bedrock geologic units in the Cliff House Sandstone, the Menefee Formation, and the Point Lookout Sandstone members of the late Cretaceous Mesa Verde Group. Alluvial Groundwater Alluvial groundwater is present in the Hay Gulch alluvium and in some of the unconsolidated alluvial sediments that fill topographic lows in the ephemeral stream systems. Hay Gulch has groundwater that is sufficient in quantity for agricultural and stock water use during the summer months. Groundwater in the alluvial aquifers is generally unconfined (RHS 2016a). Groundwater in the La Plata River alluvium along the eastern margin of the CIAA is tapped by hundreds of domestic wells that yield up to 65 gallons per minute (gpm) (RHS 2016a). Groundwater in the Hay Gulch alluvium is found in the upper 100 ft of the alluvium and yields water on a seasonal basis for agricultural and stock water use at variable rates generally below 30 gpm. Groundwater in the alluvium of The Gulch exhibits spatially limited saturation and is highly variable depending on seasonal precipitation. Groundwater in the alluvium of Cherry Creek along the eastern margin of the CIAA yields water to domestic wells at rates up to 30 gpm (OSMRE 2017). Alluvial groundwater quality has been monitored for several years by GCCE along Hay Gulch and varies both spatially and temporally. In general, the pH of alluvial water is in the range of pH 7.0 to 8.0. TDS is highly variable and generally ranges from 400 to 800 mg/L but can be as high as 1,480 to 1,580 mg/L in the Wiltse Well (RHS 2016b; 2017). Sulfate can range from 400 to 800 mg/L. Most alluvial water samples exceed the drinking water standard of 500 mg/L for sulfate but have trace metals within drinking water standards (RHS 2017). Dunn Ranch Area Coal Lease by Application COC-78825 and Mine Plan Modification EA 3-13