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C- 2010 -089 PAR Part 1 <br />New Horizon North Mine <br />23- Dec -2010 <br />Page 15 of 21 <br />detailed hydrology designs and maps were prepared by or under the direction of a registered <br />professional engineer. <br />4. As required under Rule 2.05.3(4)(a)(i)(B) and Rule 2.10(2), please provide certified cross <br />sections of each sediment pond, oriented both lengthwise and widthwise and which include <br />each primary discharge structure. <br />5. Map 2.05.3(3) -1, "Surface Water Hydrology ", has several depictions that are not explained, <br />either on the map or in the map legend. Such depictions include the black, blue, dark orange <br />and magenta colored lines, as well as the mine plan year numbers 2013 through 2018. <br />Under Rule 2.05.3(3) and (4), please add labels on the map or explanations in the map <br />legend that describe what the depictions represent. <br />6. On Map 2.05.3(3) -1, "Surface Water Hydrology", the green lines that depict the collection <br />ditches are obscured in some areas by the magenta lines. Also, the ditches' names are not <br />shown. Under Rule 2.05.3(3) and (4), please revise this map to show the full extent of the <br />collection ditches and the appropriate ditch names. <br />7. On the first and third pages of the pond memo found in Appendix 2.05.3(3) -1, there are two <br />references to design criteria of the Office of Surface Mining. Please change this to the <br />DRMS, since the DRMS has primacy in Colorado. <br />8. On the third page of the pond memo in Appendix 2.05.3(3) -1, it is stated that the design <br />capacity pond volume is the volume of the pond up to the emergency spillway. However, the <br />required design capacity volume of a pond is the pond volume measured from the lowest <br />discharge elevation up to the elevation of the emergency spillway. Please revise this page <br />accordingly to include this explanation. <br />9. In Table 2 of the pond memo in Appendix 2.05.3(3) -1, design capacities of the three <br />sediment ponds are listed. Each pond's listed capacity is the total pond volume up to the <br />emergency spillways. However, since a sediment pond cannot be dewatered below the <br />lowest discharge elevation of the discharge structure, a sediment pond's designed capacity <br />has to be able to contain the runoff from the 10 year -24 hour event as measured from the <br />elevation of the lowest discharge point up to the elevation of the emergency spillway. Please <br />provide demonstrations that the three ponds have sufficient capacity above the lowest <br />discharge elevation to contain the runoff from a 10 year -24 hour event and revise the <br />sediment pond design capacities in Table 2 accordingly. <br />10. The three sediment ponds each use a gated drop inlet primary discharge structure. However, <br />the Sedcad program cannot model pond volumes, discharges and sedimentology for a gated <br />pond to show compliance with Rule 4.05.6 and 4.05.9. The Sedcad designs that were <br />submitted use an un- gated, self - dewatering drop inlet structure. As a consequence, the <br />designs do not match the proposed construction and the designs may be confusing. For <br />example, the Sedcad designs show that runoff from the 10 year -24 hour precipitation event <br />will flow out of the emergency spillway, which is not allowed under Rule 4.05.9(2)(b). <br />Please provide sediment pond designs that demonstrate that the gated sediment ponds will <br />comply with Rules 4.05.6 and 4.05.9. The demonstration can rely on pond water and <br />sediment storage volumes without the pond discharging and without sedimentology <br />demonstrations. <br />11. In the first full paragraph on the fourth page of Appendix 2.05.3(3) -1, the first sentence <br />states that an emergency spillway with a height that is one foot below the top of the pond <br />