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STATE OF COLORADO RiCHnRD D. ~. Gov c.~m III III III III IIII III <br />DEPARTMENT OF NATURAL RESOURCES 999 <br />D. Monte Pascoe, Executive Director <br />MINED LAND RECLAMATION <br />423 Centennial Building, 1313 Sherman Street <br />Denver, Colorado 80203 Tel. (30~) 839-3567 <br />David C. Shelton <br />Director <br />MEMORANDUM <br />T0: Mike Savage <br />FROM: R.A. Domingue <br />RE: Walden Coal Company's Bourg Strip Application <br />File No. C-021-81 <br />Hydrologic Concerns: <br />1. Maps: The area of several of the watersheds feeding sediment ponds <br />on the site extends beyond the area covered in the maps provided by W.C.C. <br />During the life of the permit the contributing area to each of the ponds <br />may change and new structures are to be built at various eras of the <br />permit period. Several of the watersheds delineated on plate 17 conflict <br />with the apparent natural drainage. <br />WCC must: <br />a. provide a map showing the entire areal extent of watersheds <br />contributing to their sediment ponds and collection ditches; <br />b. provide maps showing contributing areas and proposed structures <br />for each mining stage when the sediment control system is changing; <br />c. delineate watersheds according to topography existing at the time. <br />2. USLE Calculations: The value of 0.05 given to the CP(Z) factor for <br />undisturbed areas is very low and unverifiable with data provided. <br />Using vegetative cover figures given in the vegetative studies appendix <br />I was unable to justify the figure. WCC must explain how they arrived <br />at this value. <br />3. Water Storage: In the section on Water Information (Section I) WCC <br />describes the use of sediment pond H as a water supply reservoir. The <br />storage volume is given as 1.66 Ac ft. WCC uses a simple routing <br />technique to insure inflow volume to pond C will not exceed the spillway <br />capacity during the 25 year event. However, it is apparent that the process <br />ignores the storage of the 1.66 AC ft. mentioned above. WCC must provide <br />a stage area chart which is highly legible for pond H and route the 25 <br />yr. flood volume through the pond with the pond storing 100Y of the sedi- <br />ment volume and all of the aforementioned 1.66 Ac. ft. of water storage. <br />