2010-07-09_REVISION - C1981019 (3)

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Technical Revision No. 78 Permit No. C-1981-019 July 9, 2010 In the past several years the Division has reviewed and/or approved several revisions that influence the hydrologic analysis included in TR-78. TR-63 resulted in drainage designs for permanent ditches in the East Pit. TR-73 changed the approved hydrologic curve numbers for the various reclamation blocks. Two other revisions, TR-79 and TR-80, approved a more detailed schedule for backfilling and grading of areas of the West Pit and the East Pit at Colowyo, respectively. In addition to the materials submitted with TR-78, the Division reviewed the revised materials approved in these other revisions, the 2008and 2009 reclamation maps, the approved drainage profiles (Map 33 and Map 33A), and the approved permanent drainage plan shown on Map 41. The revised SEDCAD model proposed in TR-78 for the Prospect pond includes the internal ditches (A, B, and C) to divert a portion of the ungraded spoil runoff' to the East Pit, and the temporary sump. The sump is constructed in the spoil area adjacent to the completed section of the Prospect post-mining drainage, to assist in. handling and treating runoff from about 57 acres above the sump that includes both reclaimed and un reclaimed areas. Recently approved hydrologic input paranicters (from TR- 73) wcrc used in the proposed SEDCAD model to calculate flows into Prospect Pond with the internal ditches and sump in-place. The Division evaluated how the proposed model correlates with the backfilling and grading plan approved in TR-80. The Division evaluated the backfilling and grading plan (Map 29, revised and PE stamped 3/26/2009) to understand the sequence of reclamation at Colowyo, especially in the East Pit. The Division digitized the acreage for each area and put the acres in the table shown below. Since many of the reclamation blocks have a range of years for a given area rather than one specific year, the Division listed a minimum and a maximum number of acres by pit for each year. The number of acres scheduled for backfilling and grading in the East Pit is specified as follows. Year end Overall min Overall max East Pit min East Pit max East Pit Completed Overall Completed 2007 0 144.5 0 102.5 0.0 42.2 2008 0 391.5 0 102.5 0.0 -36.5 ( Sec. 16 redisturb) 2009 47 718.0 47 47 32 (plus some re-handled areas). 83.3 2010 36.5 707.5 36.5 36.5 2011 47.4 624.4 47.4 47.4 2012 35.0 612.0 35 35.0 2013 24.5 96 24.5 24.5 2014 0 71.5 0 0 2015 0 99.5 0 28 2016 0 599.5 0 28 2017 0 599.5 28 (if not done) 28 2018 0 949.5 0 0 2019 0 378 0 0 2020 0 378 0 0 2021 0 69 0 0 Obviously, there is flexibility built into the approved plan. However, by the end of 2012, according to the approved plan on Map 29, Colowyo must reclaim 790 acres, an average of 263 acres each year from 2010-2012. This total includes approximately 40 acres each year in the East Pit and much larger areas in the West Pit. 2