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To: Mn Iletcr l a�s <br /> Page 22 <br /> — Cell 1 —West side <br /> — Cell 2—West side <br /> — Cell 3 —North side <br /> The pit inlet weirs are low, flat, rip rap or vegetated crests to the pit inlets that serve to <br /> spread out flows entering the pits, and to prevent flows from entering the pits in a <br /> concentrated fashion. These weirs help to reduce local shear stresses and assist in <br /> preventing the river from permanently establishing a new flow path through the pits. <br /> The flattening of the pit wall slope on the south side of Cell 1 has effectively reduced shear <br /> stresses in the area 250-300 feet east of the southwest corner so that peak shear stresses <br /> are less than 2.1 lb/ft2 for all flow rates less than 9,000 cfs. Therefore,it is our opinion that <br /> adequate erosion control in this area can be achieved by grassy revegetation and that hard <br /> armor is not required. <br /> Comment 6 <br /> Please explain the apparent discrepancies between pages 6 and 7 in terms of the sequence <br /> of flooding of the three cells. The table on page 6 suggests that flooding of Cell 2 occurs <br /> during smaller storm events than flooding of Cell 3;flooding of Cell 2 starts at 2000 cfs <br /> and flooding of Cell 3 starts at 4000 cfs. The discussion on page 7 states that flooding of <br /> Cell 2 and flooding of Cell 3 begin with approximately the same storm, approximately the <br /> 8-year event. <br /> Response 6 <br /> Please see the revised 2D HEC-RAS model and Attachment 14 for updated hydraulics.The <br /> control of flows into the pits has changed slightly from the previous submittal. As stated in <br /> Attachment 14, water begins to enter: <br /> • Cell 1 during river flows of approximately 1,000 cfs(peak flow rate of—4-year <br /> event) <br /> • Cell 2 during river flows of approximately 3,000 cfs (peak flow rate of—10- <br /> year event) <br /> • Cell 3 during river flows of approximately 8,000 cfs (peak flow rate of—70- <br /> year event) <br /> Comment 7 <br /> The last page of the Inlet Protection Calculations (page 7) states that "riprapped inlet <br /> weirs were sized and included in Exhibit C of the mine plan. " Can you be more specific <br /> where this is in the application? <br /> 20220209 1045_DRMS Adequacy ReviewResponse_MASTE <br /> R.docx TELEST© <br />