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Exhibit 7, Item 18 <br />Gulch A Small Area Exemption Demonstration <br />As shown on Map 41, the Gulch A Pond watershed encompasses 635.3 acres of the East Pit <br />reclamation and native areas adjacent to the East Pit. Within the reclaimed areas in this <br />watershed, all but 2.9 acres have been Phase II released as of November of 2018. This <br />demonstration provides the necessary justification to confirm that the Gulch A Pond is no longer <br />necessary for sediment control, and a grass filter will serve for sediment control for the <br />remaining 2.9 acres of disturbance that has not achieved Phase II bond release within the Gulch <br />A watershed. <br />The small area exemption for the remaining 2.9 acres within the Gulch A watershed that has not <br />achieved Phase II bond release is shown on Figure Exh. 7-18A-1. This area is located at the <br />farthest upper reach of the watershed to the west of the Gulch A Pond. Within this area, the <br />remaining 2.9 acres, the area was topsoil and seeded in 2018. <br />One hydrology model is presented within the exhibit. For the model demonstration, SEDCAD's <br />grass filter routine has been used to demonstrate that runoff from this area will meet the effluent <br />standards of 0.5 ml/l in accordance with Rule 4.05.2(7) (US EPA, 40 C.F.R. §434.52). <br />Sedimentology parameters and curve numbers used are defined in Exhibit 7 Methodologies and <br />Assumptions for Sedimentation Pond Designs Evaluations. <br />For the 2.9 acre small area exemption a curve number of 80 was used to reflect the topsoil and <br />seeded condition of the contributing watershed with a ground slope of 1.5%. <br />This demonstration utilized the Manning's roughness coefficient of 0.0054, and a stem spacing <br />of 0.86 inches. These inputs are intended to reflect that the vegetation cover density adjacent to <br />the small area exemption. The 1.16 cfs flow was then run through a native grass filter <br />approximately 3,041 feet in length and 10 feet in width (direction of the flow through the grass <br />filter). <br />As shown in the attached SEDCAD output file, the calculated resulting peak settleable <br />concentration released and the 24 -hr weighted settleable solids concentration is 0.00 ml/l, which <br />is well below the effluent standards of 0.5 ml/l. <br />Exh. 7, Item 18, Page 1 Revision Date: 12/3/18 <br />Revision No.: TR -130 <br />