Laserfiche WebLink
d. Is the 7600 cfs base flow for the river based on the 10 year / 24 hour event for the entire water shed that <br />will contribute drainage to the river? Please ensure all flow event calculations use the entire contributing <br />drainage area. <br />e. DRMS calculations indicate that the minimum pipe diameter to allow a design flow of 5,000 gpm, <br />11.14cfs at 20.43ft/s exit velocity is 15 inches minimum. The Sediment Pond Discharge Detail indicates a <br />10" diameter discharge pipe. Please provide calculation details demonstrating that a 10 inch diameter pipe <br />will be adequate, or revise the details to indicate the appropriate sized pipe. <br />9. Response acceptable. <br />10. DRMS accepts the commitment to provide engineering details and stability analysis for the dike rebuild. <br />a. Please indicate the 100 year 24 hour delineation for the river. The sediment pond is a temporary feature, <br />so it can be designed to remain stable for a 10 year / 24 hour event. However, the dike is a permanent <br />feature and must be designed to remain stable and adequately handle the 100 year / 24 hour event. Please <br />ensure all flow event calculations use the entire contributing drainage area. <br />11. Response acceptable. <br />12. Response acceptable. <br />13. Please indicate how irrigation ditches will be redirected to maintain the wetland hydrology in the parcel that lies <br />between the river and Phase 3, especially near the final phases of mining when most irrigated land has been <br />excavated. Please contact the Army Corps of Engineers if proposed plans fall within their jurisdiction. <br />ADDITIONAL COMMENTS <br />14. The Reclamation plan map specifies an armored discharge channel for the lake, but the outlet detail only specifies <br />vegetation stabilization. Please clarify. <br />15. Please provide a longitudinal cross-section for the lake outlet and address the stability of each section with respect to <br />the grade of the channel. <br />16. DRMS recommends that any vegetation stabilization utilized for the lake outlet consist of a dense mat forming <br />vegetation. Because the pond outlet is a permanent feature, please indicate a more diverse seed mix to be used to <br />stabilize this outlet. <br />17. What is the invert elevation of the channel in comparison to the bottom of the lake elevation? <br />18. The Background and Mine Plan sections of the revised permit pages needs to be corrected. Amendment No. 1 in <br />2000 clarified that the south parcel is 26.13 acres and then added 115 acres for a total of 141.13 acres. Please adjust <br />the acreages in the permit accordingly. You may also want to state that barring any appeals of the DRMS decision <br />to approve Acreage Reduction No. 1, on December 28, 2007 the majority of the instream portion of the mine site, <br />31.2 acres, will be release from the permitted acreage. The resulting permitted area will total 109.97 acres. <br />19. Please remove the statement in paragraph two of the Reclamation Plan Revisions that states, "As of the technical <br />revision of September 2007, the backfilling of this area is accounted for in the bond." This statement couldn't be <br />further from the truth. <br />20. Please revise the Current Extents delineation on cross-section A-A' to reflect the current near vertical highwalls.