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May Day/Idaho Mine - Chief Drainage Channel Reclamation Work Plan Comments <br />Page 2 <br />May 27, 2011 <br />one foot. Furthermore, based on the provided hydraulic input, the channel would need to <br />be 2.4 feet deep to convey the 210 cfs with no freeboard, not the 2-foot depth stated. <br />Please correct the calculations and statements, and note Comments # 9 and #10 regarding <br />the design presented in Figure 1. <br />Page 3, Site Preparation: <br />4. This bullet is unclear, please restate and clarify what is to be removed, and from where. <br />Page 4, Construction: <br />5. The first bullet includes "hay" bales for erosion/sediment control. Hay attracts deer, elk, <br />and other animals as a food source. The bales are damaged by these animals and fail as <br />erosion/sediment control BMPs. Please remove all references to hay bales in the work <br />plan. <br />6. The fourth bullet discusses segregating mine rock for use as riprap. It is not clear what <br />criteria are to be used to segregate the mine rock. DRMS requires a chemical analysis of <br />any mine rock used as riprap to demonstrate that it is non-acid generating material. In <br />addition, riprap intended for channel revetment is required to meet the following <br />specifications: <br />a. Shape: angular with the longest dimension not to exceed three times the shortest <br />dimension, <br />b. Density: the minimum dry specific gravity should be 2.5, 2.6 is preferred, <br />c. Durability: riprap shall be hard and durable, <br />d. Gradation: in order to provide adequate interlocking rock, the coefficient of <br />uniformity (Cu = D85/D15) shall be between 1.5 and 2.5, <br />e. Thickness: the layer of placed riprap shall be two times the D50, or 24 inches for <br />D50 = 12-inch riprap. <br />Finally, the riprap must be hand or machine placed such that segregation of sizes does not <br />occur as it would be if end-dumped from a truck. <br />7. The second open bullet discusses the use of filter fabric. The filter fabric shall be a non- <br />woven geotextile with a minimum weight of 12 oz/sq.yd. Please note that any channel <br />designed with a longitudinal slope of eight percent or greater will require a granular filter <br />in place of filter fabric. <br />Figures 1 and 2: <br />8. It is difficult to interpret the contours in Figure 1 because the existing grading and the <br />proposed grading have the same line weight and type. Please change the line type and/or <br />weight of the proposed grading contours so they can be easily differentiated from the <br />existing contours. Also add contour labels to the proposed grading. <br />9. There appears to be a discrepancy between the two-foot bottom width of the proposed <br />channel in the provided hydraulic input on page 3, and what appears to be about a 20-foot <br />bottom width in Figure 1. Please make corrections such that the design calculations are <br />consistent with the design drawing. Also clarify on the drawing (Figure 1) whether the <br />proposed contours are finished grade (i.e., top of riprap) or subgrade (i.e., top of <br />excavated surface on which the filter fabric is to be placed). <br />cAdocuments and settings\whe.naturenet\local settings\temporary internet <br />files\content.outlook\580z7cpc\ldg_wrkplnlcomments mem27mayll.docx