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Cramer, Johanna <br />From: <br />Mathews, Dan <br />Sent: <br />Wednesday, August 04, 2010 8:30 AM <br />To: <br />Cramer, Johanna <br />Cc: <br />Brown, Sandy <br />Subject: <br />FW: Diversion Ditch 14A Removal <br />Could you please file this email in the Laserfiche file for Yeast. I suppose it would belong under General <br />Correspondence, since it is not associated with a particular revision. You should be receiving a letter from Roy Karo <br />today or tomorrow (dated August 2 and copied to Sandy) regarding "Diversion Ditch 14A Removal ", that should be filed <br />in the same category as my email. <br />I <br />From: Mathews, Dan <br />Sent: Tuesday, August 03, 2010 4:21 PM <br />To: Karo, Roy <br />Subject: Diversion Ditch 14A Removal <br />Roy, <br />I took a look at your letter dated August 2, 2010, which addresses hydrologic conditions associated with runoff and <br />sedimentation into Diversion Ditch 14A, which reports to Sediment Pond 14 at Yoast. The letter was prompted by our <br />conversation during my inspection last week, in which I indicated that required sedimentation demonstrations would <br />have to be submitted before Ditch 14A could be reclaimed /eliminated, since it is currently a part of the approved <br />sediment control system for the disturbed area at Yoast (certain reclaimed pit areas drain to the ditch, which reports to <br />Pond 14). <br />In the letter, you indicate that no runoff was ever expected from the watershed associated with Diversion Ditch 14, and <br />you include SEDCAD documentation showing that the 32.5 acre sub - watershed SWS2 would not generate runoff or <br />sedimentation as a result of a 10yr /24hr storm event. This is true, but it is not the whole story. <br />See Map Exhibit 13 -12.1. Sub - watershed SWS2 is designated "UNDISTURBED ". The SEDCAD modeling indeed indicates <br />that this 32.5 acre area of undisturbed aspen and mountain shrub would generate no runoff or sedimentation as a result <br />of the design storm event. However, Exhibit 13 -12.1 also shows that 44.0 acres of disturbed land labeled Sub - watershed <br />SWS1 ( "Pit /Pre- Strip ") drains into Ditch 14A. The Subwatershed Hydrology Detail on page 130 of Tab 13, Appendix 13- <br />12.1 shows that the design event was projected to generate a peak discharge of 26.37 cfs from the SWS1 Sub- <br />watershed. The Subwatershed Sedimentology Detail on the same page indicates that the design storm was projected to <br />generate a peak sediment concentration of 536,755 mg /I, with a peak settleable concentration of 217.44 ml /I. <br />I have to conclude that the letter and documentation you provided does not demonstrate that "the ditch was not <br />required during initial mining disturbance ". With the amount of flow and sediment projected from disturbed area sub- <br />watershed SWS1, the ditch would definitely have been required. The documentation you provided addressed only the <br />undisturbed portion of the watershed tributary to Ditch 14A, not the disturbed portion of the watershed. <br />In order to justify removal of the ditch, the same type of documentation would be required for the sub - watershed as <br />would be required to support sediment pond removal for an entire reclaimed watershed (see Rule 4.05.6(7), 4.05.2(1), <br />