2013-08-30_REVISION - C1992080 (3)

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GoFF_� NGINEERINGSURVEYING INC Office 970.'247.1710 rax 970.247.171Q 126 RUCK POI.NT DRIVE I'0 BOX 97 DURANGO. COLORADO 81302 www.goffengineering.coni August 27, 2013 Ms. Marcia Talvitie, P.E. RECEIVED Environmental Protection Specialist Colorado Division of Reclamation, Mining and Safety AUG 3 0 2013 Coal Program — Durango Field Office 701 Camino Del Rio, Room 315 DIVISION OF RECLAMATION Durango, CO 81301 MININGANDSAFETY Re: Technical Revision 17 Application to the Carbon Junction Mine permit (CDMG permit C -92 -080) addressing Notice of Violation (CV- 2013 -005) Dear Ms. Talvitie: Oakridge Energy, Inc. is submitting this technical revision to the Carbon Junction Mine permit to address the Notice of Violation dated May 23, 2013. The technical revision includes the following items required from the abatement steps listed in the Notice of Violation: I. As -built information of the Carbon Junction Permanent Diversion configuration. 2. Updated post- mining topography map. 3. Map of Carbon Junction drainage area. 4. Channel Improvement Plan for the reestablishment of the Upper Carbon Junction Channel and un -named tributary entering from the east, and reclamation and stabilization of the Carbon Junction Temporary Diversion and gully erosion. Carbon Junction Permanent Diversion (Abatement Step #1) As -built topographic information for the Carbon Junction Permanent Diversion was obtained from 2012 aerial mapping provided by the City of Durango. The aerial topography consists of a 2 foot contour interval. The 2011 aerial topography and mine permit boundary are shown on Exhibit C1.0. The Carbon Junction drainage basins are shown on Exhibit C1.1. The as -built configuration of the Carbon Junction Permanent Diversion and associated cross sections are shown on C1.3 and C1.4. It was noted in the DRMS inspection report dated April 30, 2013 that the Carbon Junction Permanent Diversion was stable but was not constructed as designed in TR -11. Specifically, the channel gradients were different than design gradients, the rip rap armoring was frequently coarser than what was required, and the culvert crossing of the haul road used (2) -66" corrugated metal culverts instead of a single pipe arch culvert. As -built topography indicates that grades for the as -built channel are slightly different from the design grades, generally ±1%. A profile of the as -built channel is shown on map C1.3. The design rip rap for the channel ranged from a D50 =12" to D50 =30 ". From a field investigation of the as- constructed channel, it appears that the rip rap may be larger than designed, however, it is difficult to determine the actual D50 without a proper geotechnical analysis. Page l