Laserfiche WebLink
• Sedimentation Ponds 008 through 014 Design Parameters <br />In accordance with 4.05.2 and NPDES regulations, WFC will use Ponds 008 through 014 to <br />prevent, to the extent possible, additional contributions of sediment fo stream flow or runoff outside <br />the permit area due to mining disturbance. Ponds 008, 009 and 014 are as-built designs, 010 <br />through 013 have yet to be constructed. The pond designs and or run-off calculations for 008, 009 <br />and 010 - 014 are found in Attachments 2.05.3(3)-4, 2.05.3(3)-5, 2.05.3(3)-6 and 2.05.3(3)-11. <br />Map 2.05.3(3)7-1 shows the locations of the as-built and yet-to-be built ponds. <br />Pond 014 is the post-mine conversion of the pre-mine SAE #2. The drainage area is 4.4 acres, but <br />a contour ditch that drains to Pond 009 crosses the Pond014 drainage and reduces the effective <br />drainage for sediment control purposes to 2.1 acres. The contour ditch dimensions will be about <br />two feet wide at bottom and the downslope side will be about two feet high with a 2:1 slope. The <br />contour ditch is to remain as a permanent part of the reclamation landscape. Pond 014 is in the <br />bottom of apre-mining topographic depression, The land where this pond is located will remain as <br />a permanent topographic depression with its currently existing contours, after the pond removal <br />requirements of the DMG rule 4.05.2(2) are met. <br />The sedimentation pond is designed, constructed, and maintained as follows: <br />• a) Pond 010 has been designed to provide storage for the runoff or inflow entering the pond as <br />a result of a 10-year, 24-hour precipitation event and to meet all applicable State and Federal <br />regulations for all effluent limitations before discharge from the permit area. Ponds 008, 009, 011, <br />012 and 013 have been designed to contain the 25 year 24 hour event with no discharge from the <br />emergency spillway. Pond 010 design includes routing the 25 year event through the emergency <br />spillway. The pond 014 excavation has been designed fora 100-year 24-hour event with no <br />discharge. Due to its small drainage area and completely incised impoundment, there is no <br />embankment to fail and so only run-off volume calculations have been pertormed. Only b) below <br />pertains to Pond 014 and volumes were determined using SEDCAD4 instead of SurvCADD <br />software . <br />b) The sedimentation ponds are designed to provide adequate sediment storage volume in <br />compliance with the CDMG regulations. The actual designs are based on 3 year sediment volumes <br />based on USLE calculations. Actual construction may cut more volume below the dam level <br />(incised storage) to lessen expensive cleanout during the operation. <br />• (Revised ~/zooaJ 2.05.3(3) -13 <br />