2018-09-04_GENERAL DOCUMENTS - C1980007

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42 acre feet in water year 1977. Water in the North Fork has a neutral to alkaline pH, and is a sodium-bicarbonate type with total dissolved solids generally less than 100 mg/l. Streams in the northern part of the West Elk Mine permit area are Sylvester Gulch, Lone Pine Gulch, and Gribble Gulch. These three streams flow directly to the North Fork. Lone Pine and Gribble Gulches have ephemeral flows. No flow has been observed in Lone Pine Gulch for several years. Sylvester Gulch is ephemeral in its upper section, but has perennial flow in its lower section due to a spring. Sylvester Gulch has a drainage area of 4.25 square miles. The hydrologic yield of Sylvester Gulch is small for its size compared to other area watersheds due to its lower elevation and gentler slopes. Raven Creek crosses the northeastern corner of the permit area over a distance of approximately 2,000 feet. This perennial stream and its riparian zone are protected from undermining and subsidence by a buffer zone of 660 feet (1/8 mile) on either side of the stream, as stipulated in Lease COC-67011. Mining approved by PR-11 will terminate to the south of Raven Creek because of that buffer zone. A major contributor to flow in Raven Gulch is Deep Creek, a perennial stream that drains the southeastern part of the permit area. Flows in Deep Creek historically have been in the 0.1 to 0.5 cfs range during most of the year, as indicated by MCC’s monitoring data from 2000 through 2005. Springtime flows exceed 30 cfs. Alluvium in the Deep Creek watershed is too thin to serve as a ground water supply source. Most of the southern part of the permit area is in the Minnesota Creek watershed that was approved for mining in PR-10. This major watershed covers approximately 53.5 square miles. Tributaries to the mainstem of Minnesota Creek include Horse Creek, South Prong, Lick Creek, Dry Fork, and East Fork. The mainstem of Minnesota Creek enters the North Fork of the Gunnison near the town of Paonia. Based on streamflows measured in water year 1978, prior to mining, the water yields from these drainages are nearly an order of magnitude greater than the yield from Sylvester Gulch. The evaluation of flow within the Minnesota Creek drainage is considered only an approximation due to infiltration and seepage losses, seasonal variations in precipitation and potential evaporation and sampling difficulties. MCC estimates that more than 80% of the South of Divide mining area is in the Dry Fork drainage. MCC also describes the Dry Fork drainage as having minimal yield, but its stream channel annually conveys approximately 720 acre-feet of water imported from Little Gunnison Creek via the Deep Creek Ditch (based on Office of the State Engineer records for 1970 through 2002). The average annual flow of the East Fork of Minnesota Creek is approximately 19,920 acre-feet.