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_ 17 _ The surface facilities will be built on unconsolidated sediments, including colluvium and terrace deposits between the Colorado River and the Grand Hogback, and on exposed bedrock to the east and west. Surface runoff from the facilities will be totally contained within sediment ponds except for outslopes of the railroad and access roads. The total disturbance to alluvial material within the surface facilities is proposed as 6.4 acres. The surface facilities in the vicinity of the portal will include the shop and office area with parking. Coal preparation and storage facilities will also be present in this area. The mining process will produce both fine and coarse slurry which will be initially ponded on the colluvial terrace near the portal area. These ponds will be lined to restrict inflow into the underlying colluvial material. A thickener plant will be needed. This thickener plant will be a concrete structure precluding loss of water into the colluvium. A diversion ditch will be emplaced above the portal area and around the surface facilities to drain all natural runoff from the surface facilities area. All runoff from the surface facilities will be channeled into sediment ponds. These sediment ponds will be designed for total containment of the 10 year-24 hour storm. All excess runoff will be recycled into the hydraulic mining process. Accumulated sediment will be removed as necessary to ensure that the pond provides adequate storage at all times. An increased sediment yield will be experienced during construction of the railroad and access/haulroads. The outslopes of these areas will be revegetated. The potential for degrading of the hydrologic environment due to sediment generation will be short-term and any impact is expected to be minimal. A refuse embankment will be constructed in a small ephemeral drainage tributary to the Colorado River. The embankment will be underlain by the relatively impermeable Mancos Shale. The embankment will be formed of coarse refuse generated during the mining process and will impound the slurry refuse generated through the hydraulic mining process. The embankment will be designed to impound approximately 16,000,000 tons of refuse over an expected project life of 25 years. Construction will occur as a phased process where the embankment is always of sufficient height to hold the slurry and refuse from the mining process and to totally contain the probable maximum precipitation of the drainage area above the embankment. A sediment pond will be built downstream of the embankment, and will contain any runoff from the face of the refuse embankment occurring from storm events. This pond is designed to totally contain the 10 year-24 hour runoff event. This pond also serves a second function. Although the Mancos shale is relatively impermeable, a ground water investigation has shown that some element of ground water movement is present through the Mancos. A preliminary analysis by a consultant for the applicant indicates that seepage from the coal refuse impoundment will be about 50 to 60 gpm. This seepage is expected to surface in the channel downstream from the main coal refuse embankment. Pond B will be constructed to collect any seepage which may surface in the ephemeral channel. This seepage will be reused in the hydraulic mining process.