2010-08-23_INSPECTION - C1981019

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August 18, 2010 C-1981-019/Colowyo Coal Mine e__? JRS control in the East Pit area, below the South Taylor Pit and the Taylor Tributary permanent drainage. Approved Map 41, Watershed Boundaries for Hydrologic Modeling, last revised with MR-90, 11/26/2007, shows the location and length of each approved ditch to be constructed in the post-mining topography in the East and West Pits (this map does not include the South Taylor area). - The inspection began in the East Pit at the Prospect Ditch at the location of a sump used to trap water and sediment from reclaimed and unreclaimed portions of the Prospect Ditch subwatershed of the East Pit. This sump was discussed as a part of NOV CV-2008-004. The operator constructed this sump to prevent and minimize water and sediment delivery to the Prospect Pond. During this inspection, the sump held only a small amount of water and had minimal capacity. It was not evident that the sump had been cleaned or maintained at any time in the recent past. Contour ditches were also established following the issuance of NOV CV-2008-004 and generally appeared to function as anticipated. One area where erosion and erosional problems commonly occur is where these contour ditches enter the main riprap channel. Flow from the contour ditches does not enter the armored portion of the channel, but instead flows along the side of the channel for some distance downslope prior to re- entering the channel. This concentrated flow downcuts into the unprotected slope causing gullies and channelized erosion adjacent to the channel, commonly referred to as "side-cutting". In the future, the operator should carefully construct these critical ditch intersections and inspect, repair and maintain these areas to prevent problems like this before they become larger concerns. The inspection should occur as part of the mine's annual rill and gully inspection. (**See Picture 1 - side cutting in contour ditch below sump on Prospect Ditch**) - The North Tributary of the East Pit Ditch has been constructed within the 2009 East Pit reclamation block from station 0+00 to approximately station 12+00 as shown on proposed Map 12, Hydrology, (submitted with Technical Revision 87, P.E. certified 8/9/2010). The approved location of this ditch is shown on Map 41, Watershed Boundaries for Hydrologic Modeling, (last revised with MR-90, 11/26/2007). Approved Map 41 shows the North Tributary Ditch entering the East Pit Ditch at approximately station 0+00 of the East Pit Ditch. However, field inspection confirms that the ditch was NOT constructed as shown on approved Map 41, and enters the East Pit ditch at approximately station 5+50, some 550 feet upstream from the approved location. The operator explained that this was done as a "field fit" due to steep slopes and concerns about using equipment on steep slopes. The portion of the ditch that was "field fit" is not controlled by the topography but instead serves as a contour ditch until it meets the Final East Pit ditch. Given that this ditch is the lower 500 feet of a ditch planned to be 3,450 feet in length, it is imperative that the ditch be located where function is controlled by the permanent post-mining topography, as approved by the Division. The operator has failed to construct the lower 500 feet of the North Tributary, East Pit Ditch in accordance with the approved plan with regard the location of the ditch. This ditch segment is included in NOV CV-2010-004. (**See Picture 2 - 21 June 2010 aerial showing North Tributary, East Pit Ditch and Final East Pit Ditch**) The channel design for the North Tributary, East Pit Ditch can be found in Appendix Exh7-14N, July 2006 of the approved Colowyo permit application. The design calls for a trapezoidal ditch cross section with 3H:1 V side slopes and a minimum depth of 4 feet. The channel will be protected by riprap averaging 18 inches. (**See Picture 3**) Field inspection and the above photograph found that the constructed North Tributary, East Pit Ditch (2009 portion) has no discernable trapezoidal shape nor does it have the required depth, including freeboard of 4 feet. Riprap is considerably larger than the approved 18 inches on average and seems to impede flow in the poorly defined channel. The operator has failed to construct the 2009 portion of the North Tributary, East Pit Ditch in Number of Partial Inspection this Fiscal Year: 2 Number of Complete Inspections this Fiscal Year: 0 Page 3 of 14