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Rule 4.05.9 - Impoundments <br />Map 157 shows water flowing from one dewatering pond to the next and <br />ultimately to the artificial wetlands and Last Chance Pond. The direction of flow <br />from pond to pond appears to maximize detention and treatment time. However, <br />there is no detail given regarding how the water will be conveyed from one pond <br />to the next. The provided cross-sections of the dewatering ponds do not show any <br />obvious spillway(s) in the pond embankments. Additionally, it is not clear how <br />the water will enter the next pond in the series. Please provide more detail on <br />both Map 157 and on page IV-38 regarding how the water will be conveyed <br />from one dewatering pond to the next and into the artificial wetlands. If <br />ditches will be used to convey the water from one pond to the next, please <br />include ditch designs for review. <br />9. On Map 157 BME shows numerous heavy blue lines (after the dewatering ponds) <br />in the artificial wetlands. Based on their placement, the Division is assuming that <br />they will be earthen berms, which will act as baffles to direct the flow of water <br />through the artificial wetlands. It also appears as though the final baffle will <br />direct water into the Last Chance Pond. Please provide a description of these <br />heavy blue lines both on Map 157 and page IV-37. Please describe how <br />water will flow through the artificial wetlands and into the Last Chance Pond <br />(overland, through a defined channel, etc.). Please include a description of <br />the assumptions BME used in designing the pond and wetlands system to <br />ensure that proper treatment and detention time will be achieved. <br />10. On revised page IV-37 BME has changed the value for the 100-year 24-hour <br />storm event from 2.6 inches to 2.1 inches. Based on the NOAA Precipitation <br />Frequency Atlas of the Western US, Figure 31 - Isopluvials of 100-Year 24-Hour <br />Precipitation, the 100-year 24-hour storm event for the Deserado Mine should be <br />2.4 inches. This is still less than the 2.6 inches used to model Deserado's ponds <br />and ditches. Please change the 100-year 24-hour storm event on revised page <br />IV-37 to 2.4 inches. <br />11. Pursuant to Rule 4.05.9(2), all "...spillway systems shall provide for either a <br />combination of principal and emergency spillways, or a single spillway <br />configured as required by 4.05.9(2)(a), designed to safely pass the applicable <br />design precipitation event specified...". BME has provided a cross-section of the <br />proposed dewatering ponds but there is no indication of a spillway in the pond <br />embankments. Map 157 shows the water flowing from the corner of each of the <br />dewatering ponds into the next pond but no spillway is shown. Please provide a <br />description and cross-section of the proposed spillway for each of the <br />dewatering ponds. Please provide a design for the spillway that will include <br />sizing for the maximum anticipated discharge as a result of the pumping of <br />water from the B-Seam. Please include a description of the assumptions used