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~. <br /> <br />in that the berms would likely be eroded by water. Ditches would be cut subgrade into bank <br />or compacted material, whereas berms would be loose, porous material which could become <br />saturated and fail. Unless OCM has additional information which would demonstrate that the <br />berms would be more effective than ditches, DMG does not believe they are the best <br />technology currently available, and accordingly could not approve of their use as OCM has <br />proposed. <br />18. The pos[mine plan calls for "low maintenance dry crossings" where ditches cross roads. Please <br />provide design information for each crossing which demonstrates that water will be contained <br />in the crossing. <br />l9. The application narrative and data (pp 2.04-39f and -39g) indicate that the 6 ephemeral <br />drainages which could be affected by the West Valley Fill have not exhibited flow since <br />January 1995. Were the drainages visited during or shortly after rainstorms? If not, OCM <br />needs to obtain data during precipitation events to determine whether and how much the <br />drainages would flow in response to precipitation. Regazdless, the monitoring data should be <br />annotated to indicate weather conditions at the time of each observation. <br />The application states, on page 2.04-39e that the flow data aze presented on pages -39g and <br />-39h. The data aze presented on -39f and -39g. <br />20. A worksheet in Appendix C shows the calculations used to size the haul road ditches. From <br />where did OCM ascertain the 3.9 cfs flow value? We are unable to locate any supporting <br />information for the value. <br />21. OCM proposes to add another 24" culvert at the Second Drainage, where diverted water from <br />above the fill is carried. Please provide design information for the culvert, and include its <br />location on Maps E-3211 and E-3214. <br />22. The worksheets in Appendix C for two culverts, Existing RR Culvert and Additional Second <br />Drainage West Culvert, aze for circulaz channels. DMG is not familiar with calculations for <br />circular channels or with the Flowmaster program. We attempted to verify the proposed <br />culvert sizing with the culvert sizing utility in SEDCAD+'TM, and using the culvert nomography <br />in the Handbook of Steel Drainage and Highway Construction Products, and found that both <br />methods resulted in the requirement for considerably lazger diameter culverts than [hose <br />proposed. Inputs were identical to those used in OCM's worksheet, with the exception of <br />assumptions we made for two unknowns, headwater and culvert length. Even varying the two <br />unknowns, our results were consistently larger diameters. Please provide additional <br />information and supporting details for OCM's calculations. <br />23. OCM has designed ponds which will contain the 10-year, 24-hour precipitation event, and will <br />be manually dewatered. An indicator should be installed in all ponds which shows the <br />maximum water level which can be accumulated while still allowing ample capacity for the <br />10-yeaz event. <br />2.05.6 Mitiigation of the Impacts of Minine Oaerations <br />2.05.6(31 Protection of the hydrlo¢ic balance. <br />24. Pages 2.05-41 and -41a discuss the mitigation of impacts of mining with the additional <br />facilities and refuse pile proposed in this technical revision. There is no mention of any <br />impacts to surface water. OCM should include a discussion of what, if any, impacts aze <br />anticipated, and propose appropriate mitigation measures. <br />Bill Carter 3 May 6, 1997 <br />