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iii iiiiiiiiiiiii iii <br />STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />DrP~nmenl of Natural Resources <br />I.{ 17 Shcrntan $1., Room II S <br />Dcirvcr, Colorado RO?03 <br />Phone: (3071 866-3567 <br />FAC. (7031 872-A106 <br />September 3, 1998 <br />Michael G. Altavilla <br />Seneca Coal Company <br />P.O. Drawer D <br />Hayden, CO 81639 <br />Re: Seneca II-W Mine (Permit No. C-82-057) <br />TR-30 - Postmine Drainage & Topography; Adequacy Review <br />Dear Mr. Altavilla: <br />~~~ <br />DEPARTMEtVT OF <br />NATURAL <br />RESOURCES <br />Ror Romer <br />Governor <br />tames 5 Lxhhrad <br />Eterunvr Dvedor <br />•vlic hael B Lon,l <br />Dw~sinn D~rriuv <br />The Division has reviewed Seneca Coal Company's (BCC's) responses to our adequacy letter <br />dated June 5, 1998 regazding the above-referenced technical revision. The responses aze <br />accepted as submitted and generally deemed adequate. The Division has additional <br />comments/concerns regarding specific SCC responses as presented below. <br />1.-3. Responses accepted. <br />4. Response accepted; however, use of a more conservative curve number may be <br />appropriate to reduce the likelihood of accelerated erosion in the reclaimed channels. <br />Erosional stability of the channels will continue to be monitored in the field. <br />~.-6. Responses accepted. <br />Riprap channel installation technique is important to ensure long-term channel stability <br />and function. The Division has observed many channel failures over the years due to <br />improper keying of riprap, particularly at inlet and outlet portions of the channels. SCC <br />comments are acknowledged; however, the Division continues to recommend that inlet <br />and outlet installations be keyed more effectively than has been observed in recent field <br />inspections. <br />8.-10. Responses accepted. <br />11. Response accepted; however, the Division cautions that the steep channel section located <br />low in the drainage (for example, section 400 to 1000 on Exhibit 20-~.7) may be <br />