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INTEROFFICE MEMORANDUM <br />TO JANET BINNS <br />FROM: ROB ZUBER R. 9 2 <br />SUBJECT: COLOWYO PR-03 HYDROLOGY REVIEW - RESPONSE TO 9/29/11 SUBMITTAL FROM CCC <br />DATE: 10/5/11 <br />I have reviewed the hydrology sections of the September 29, 2011 submittal from Colowyo Coal <br />Company (CCC) regarding PR -03. This included a review of Exhibit 7, Item 23, which includes <br />the SEDCAD model inputs and results. <br />The primary changes to management of the surface water hydrology at the Collom site are: <br />• Removal of the Lower Clean Water Diversion (LCW) due to a lack of BLM consent. <br />This adds additional tributary area, flow and volume into the downstream sediment pond. <br />• A change in the plan for the sump. The water level in this impoundment will be kept at <br />least 6.5 feet below full to increase the capacity before storms (page Exh. 7- 23B -1). In <br />the previous submittal, the plan was to keep it at least 4.0 fget below full. <br />The SEDCAD model was not changed for reduced disturbance in the basin due to lease issues. <br />This is a conservative assumption and an appropriate modeling practice; therefore it is acceptable, <br />in my professional opinion. <br />I did not find any significant problems with the surface water hydrology portions of the submittal. <br />I did find a typographical error. On page Exh. 7- 23B -1, on the fourth line of the fifth paragraph, <br />the elevation is listed as 7730.5. I believe it should read 6730.5. <br />If this project is constructed as detailed in this latest submittal, it will be important for DRMS to <br />monitor the operation of the sump to ensure that CCC is indeed keeping the water level at or <br />below the elevation that they state on page Exh. 7- 23B -1. <br />