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iii iiiiuiiniu iii STATE OF COLORADO DIVISION OF MINERALS AND GEOLOGY Dcpanmenl ni Natural Rcsowce5 131 5 Sherman 51 . Ruom 215 Dcnvor. Colorado 80203 Phoni•' 1.10'1) 866-7567 FAX' 1 SO SI 832-81 U6 September 4, 1998 Michael G. Altavilla Seneca Coal Company P.O. Drawer D Hayden, CO 81639 Re: Seneca II Mine (Permit No. C-80-005) TR-32 - Postmine Drainage & Topography; Adequacy Review Deaz Mr. Altavilla: ~~~ DEPARTMENT OF NATURAL RESOURCES Roy Romer Governor lames s in~nneah Ereiueve Direoor ntichael a Lang Division Director The Division has reviewed Seneca Coal Company's (BCC's) responses to our adequacy letter dated June 5, 1998 regazding the above-referenced technical revision. The responses are accepted as submitted and generally deemed adequate. However, the Division has the following additional comments/concerns regazding specific SCC responses. 1.-5. Responses accepted. 6. Response accepted; however, use of a more conservative curve number may be appropriate to reduce the likelihood of accelerated erosion in the reclaimed channels. Erosional stability of the channels will continue to be monitored in the field. 7.-8. Responses accepted. 9. Response accepted. Refer to item #6 above for comment concerning use of a more conservative curve number. 10.-16.Responses accepted. l7. Response accepted; however, the Division cautions that proper filter layer installation is important to riprap channel function. If used, fabrics must be properly keyed to avoid undermining of the installation. Additionally, the fabric and entire channel cross section must be covered with the appropriate rock thickness, with no gaps in the rock along the channel. Use of a gravel filter layer may prove more effective than use of filter fabrics at the channel reconstruction areas.