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The pit bottom will serve as the containment basin for the operation. All water will be contained <br />from a 100-year event and allowed to evaporate or seep out during a 72-hr period. The drainage <br />basin area during mining is the entire permit area. The precipitation of a 100-year event is 3.2 <br />inches. The isolation berms surrounding the site will be 3 feet in height with 2H:1 V slopes, with <br />a primarily flat pit floor. This will provide more than sufficient storage for a 100-year event. <br />Because the pit will contain all runoff from a 100-year storm, no discharge permit is required. <br />Berms will also be built to isolate the grass lined channels which are being built in the valley fill <br />areas. During construction of the valley fills, an isolation berm will be built at the mouth of the <br />each valley. This berm will stop the sediment flow from leaving the permit area. <br />5. Maior Stormwater Channels <br />Two drainage channels will need to be constructed on the site due to two valleys being filled. <br />Valley Fill Area #1 watershed (29.5 acres) area is much larger and drains a watershed twice as <br />large as Valley Fill Area #2(13.5 acres). For ease of design and construction both channel <br />designs will be based on the Valley Fill Area #1. <br />Valley Fill Area # 1 <br />Stormwater from above the site will need to pass through the permit area, while maintaining <br />isolation from the disturbed area of the pit. This area is 29.5 acres based on USGS maps for the <br />drainage area. Due to a gully being filled at the landowner's request, the original natural drainage <br />will be buried. The valley fill will be discussed later. This will cause stormwater to flow across <br />the main pit area during mining and after reclamation in the middle of the irrigated field. If left <br />uncontrolled stormwater would readily erode the valley fill material. The stormwater channel <br />will be divided into two regions: Grass Lined and Grouted Rip-Rap. The Grass Lined Channel <br />#1 begins at a small pond near the gas well formed by a road installed before the current <br />operation. This pond will be removed with the 2009 amendment. The grass lined channel will <br />direct water along the mild slope (2%) to the southeast. The steeper sloped (50%) portion of the <br />channel will be grouted 12" rip-rap. Due to different channel widths a grouted 12" rip-rap funnel <br />will be built between the two sections. Below are the calculations performed in SurvCAD to <br />determine the channel characteristics. Initially, a Time of Concentration calculation was <br />performed to provide input for the Peak Flow calculation. From the Peak Flow calculation, an <br />Cugnini Pit, November 2009 D-8