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• s <br />Addendum to Rational for Approval Recommendation Page 6 <br />Application for Stone Gravel Pit <br />Permit No. M-97-089 <br />February 17. 1998 <br />Applicant plans to stabilize the reconstructed drainage channel by constructing a 28' wide <br />channel, 3' deep, with 3H:1 V vegetated side slopes. The side slopes and channel bottom <br />of the 48' section of 33% slope, and 25' of the 1.5% channel immediately below the base <br />of the backfilled highwall, are planned to be rock lined or rip-rapped to control erosion and <br />ensure channel stability. Applicant has indicated that channel bottom of the 1.5% gradient <br />section will be stable without vegetative cover. <br />DMG recommended stabilizing the channel bottom with vegetative cover. However, <br />additional options exist to the applicant to ensure stability of the channel bottom. <br />Regardless of the method selected by the applicant, channel stability is a performance <br />requirement of Rules 3.1.5(3) and (10), and 3.1.611) and (3). Straw bale sediment filter <br />and/or silt fence will be installed at the outlet of the reconstructed drainage channel to <br />ensure that affected area drainage is treated for sediment prior to leaving affected lands. <br />The sediment filters will remain until the operator has demonstrated that the reconstructed <br />drainage channel is stable and satisfies all applicable performance requirements. The <br />applicant's financial warranty can not be released until all applicable performance <br />standards have been met. <br />Objections not related to the Technical Revision and nQt addressed previously in the <br />Proposed Pre-Hearing Conference Order <br />6. New issues not included in the scope o/ this comment period and not known before the pre- <br />hearing conference may include, but are not /invited to the information related to the angles of <br />repose, the proposed upgrades to the BLM right-of-way that is proposed as access to the <br />applicant's operation, rerouting of the access road to the south to avoid cultural resources, <br />and other changes that may be necessitated by discovery and analysis of the cultures sites in <br />the affected area. <br />Angle of repose is defined by Horace K. Church, Excavation Handbook, copyright 1981 by <br />McGraw-Hill, Inc., as the minimum angle of plane, measured from the horizontal, along <br />which coarse particles in the material begin to fall under the influence of gravity. Angle of <br />repose is the natural slope angle formed by a pile of material and can be utilized to <br />estimate stable slope angles for various materials. Angle of repose appears in the Stone <br />Gravel Pit application in the engineering evaluation, required by Rule 6.4.19, for fence lines <br />and BLM access roads located within 200' of affected lands. <br />Proposed upgrades to the BLM right-of-way that is proposed as access to the applicant's <br />operation are defined under the application for driveway installation, approved on 12/12/97 <br />by Montezuma County Road Department District Foreman, and under the road maintenance <br />agreements between BLM and the applicant. Applicant has characterized the road <br />