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i w <br />S IAIF OF COI OftA nO 4u'n nRIIU M r•••v ~~~~r ~~ III III III III IIII III <br />DEPARTMENT OF NATURAL RESOURCES ~ 999 <br />D. Monte Pascoe, Executive Director <br />1191NEU LAND RE(:LA]11A'TION <br />423 Centennial Building, 1313 Sherman Street <br />Denver. Colorado 80203 Tel. (303) 839-3567 <br />David C. Shelton <br />Director <br />December 19, 1980 <br />TO: Mike Savage ~" <br />FROM: Bob Liddle ~~% /may" "~ ' <br />RE: Review of TBM Sediment Control <br />The following comments are directed at the TBM response to Carol Pahlke's <br />adequacy comments of September 8, 1980. My concerns must be addressed <br />before we can give approval of TBM's plan. <br />N6. To verify that the berm in the Pit HI area will be high enough to <br />prevent disturbed drainage. from entering diversion 22-D3, TBM will have to <br />show designs and cross-sections of this berm. In addition, TBM must <br />indicate what will prevent undisturbed drainage above ditches 22-DL and <br />22-D2 fiom flowing off the hill, through the buffer area and directly into <br />pond 22-P1. R small diversion will be needed above pond 22-P1 or else <br />the ponds must be sized to include aZZ undisturbed drainage. <br />{t8. TBM's use of a C Factor of 0.45 is unjustified. There are recent <br />studies indicating that regraded spoils decrease infiltration rates. (See <br />Westmoreland study by John Herrin, Pittsburgh and Midway Coal Company Study, <br />and Soil, Water, + Solute Movement in Montana Strip Mine Spoils by the University <br />of Montana.) In addition, the C factor from your referenced table 10 <br />assumes idle land that has not been disturbed and the cover at the surface <br />is grass, grasslike plants, decaying compacted duff, or litter at least <br />2 inches deep. Even the application of mulch would have little effect on <br />the C factor since the length limit of mulch for C valves is 50 feet on <br />30ss slopes. (See Table 9 of agricultural Handbook No. 537). <br />More representative C valves have been reported for mining conditions. <br />Utah State University recommends C valves from 1.30 to 0.90 depending on <br />conditions and time after disturbance. (See "Manual of Erosion Control <br />Principles and Practices", Hydraulics and Hydrology Series report No. N-78-002, <br />Utah Water Research Laboratory, 1978). Barfield and Naan ("Hydrology and <br />Sedimentology of Surface Mined Lands", University of Kentucky, 1979) recommend <br />(cont'd) <br />