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EXHIBIT 7, ITEM 23, PART B <br />SPOIL PILE COLLECTOR DITCHES <br />This section addresses the design of a system of collector ditches around the toe of the temporary <br />spoil pile. Locations of the ditches are shown on Exh. 7-23B Figure B1 and the associated ditch <br />profiles are provided on Exh. 7-23B Figure B2. Dimensions, lining type, and flow <br />characteristics for all ditches are included in the SEDCAD output for the sedimentation pond <br />system described in the following Part C. This information is also summarized in Exh. 7-23B, <br />Table 1 below. <br />Designs of these are based on the 10 year, 24 hour storm event. Generally, trapezoidal ditches <br />with 12 foot bottom width and 2H:1 V side slopes with a depth of 4 feet. <br />For the West Side System there are three collector ditches, although two of them are further <br />broken out into an upper and lower section due to gradient changes. The uppermost ditch, which <br />is also the longest at 5,774 feet, is the D-1 Upper Ditch, which flows around the southern and <br />western sides of the temporary spoil pile and empties into the Section 26 Sidehill Pond. It has a <br />slope that is mild enough to allow the ditch to be designed as a vegetated channel. Below the <br />Sidehill Pond is the D-1 Lower Ditch which flows into the Section 26 West Pond. It is steeper <br />and is a rip -rap lined channel with D50 stone size of 9 inches. Collecting runoff from the <br />western half of the north face of the temporary spoil pile is the D-2 Ditch. The upper reaches of <br />this ditch, which account for about 85% of the ditch's overall length, has a mild slope of 2.2%, <br />allowing the use of a vegetative lining. The bottom approximately 400 feet of this ditch is <br />steeper at 30.6% and requires a rip -rap lining with a D50 stone size of 6 inches. <br />For the East Side System there are three ditches. The uppermost is the D-5 Ditch which collects <br />runoff from the south and east faces of the temporary spoil pile, ultimately reporting to the <br />Section 36 East Pond, the uppermost pond in the East Side System. It is a relatively flat gradient <br />of 2% and has been designed as a vegetated channel. The northeast face of the temporary spoil <br />pile reports directly to the Section 36 Middle Pond without requiring a collection ditch. The <br />eastern portion of the north face of the pile is collected in the D-4 Ditch which routes it westerly <br />toward the lowermost sediment pond, the Section 25 North Pond. This ditch is steep enough at <br />12% to require a rip -rap lining. The D50 stone size required for this ditch is 6 inches. Finally, <br />the central portion of the northern face of the spoil pile is collected in D-3 Ditch, which collects <br />and routes that runoff easterly toward the Section 25 North Pond. <br />For consistency in design and construction, all of the rip -rap lined ditches will use a standardized <br />D50 stone size rounded upward to 9 inches. <br />All vegetated segments have 10 year flow velocities lower than the limiting velocities specified <br />in the SEDCAD model. All flow depths are well below 3 feet, thereby providing at least one <br />foot of freeboard when discharging the 10 year design flow. Riprap sizes are defined by the <br />SEDCAD model, as described in more detail the Introductory Text of Volume 2D in the <br />document entitled "Methodologies And Assumptions For Sedimentation Pond Design <br />Evaluations". <br />Exh. 7-23B-1 Revision Date: 3/08/15 <br />Revision No.: PR -04 <br />