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EXHIBIT 7, ITEM 20, PART PP—PROSPECT SEDIMENTATION POND <br /> The progression of mining in the East Pit was generally from east to west, climbing <br /> upward in topography and moving away from the Prospect Pond. As a result, the <br /> watershed tributary to the pond in the early years was intercepted by the inactive East Pit, <br /> and the watershed increased as backfilling and grading advance westerly. Currently, the <br /> entirey of the East Pit is reclaimed except a small portion at the headwaters of the <br /> watershed where a long term haul road exists. <br /> Ditch Design, overview <br /> As the reclamation in the East Pit advanced to the west, three permanent ditches were <br /> constructed to convey runoff form the disturbed and reclaimed lands southeasterly toward <br /> the Prospect sedimentation pond. From north to south these ditches are Prospect Ditch, <br /> North Tributary East Pit Ditch, and Final East Pit Ditch. Although the total drainage area <br /> tributary to Prospect Pond is 711.1 acres, the largest watershed for any single ditch is <br /> 153.3 acres, that being Prospect Ditch just before it releases into undisturbed lands. The <br /> ditches are therefore all designed for the 10 year-24 hour storm in accordance with Rule <br /> 4.05.3. <br /> The two southern ditches are rip rap lined for their entire length, while the re-established <br /> Prospect Ditch is rip-rap lined only in its lowermost reach. Minimum stone size (D50) for <br /> each ditch was determined in SEDCAD using the Simons/OSM model. The largest <br /> riprap size determined in SEDCAD for any ditch and design flow is D50 equal to or <br /> greater than 6 inches. All ditches are nevertheless designed with a minimum D50 of 12 <br /> inches. For channels with a vegetative erosion control lining (upper reaches of Prospect <br /> Ditch, uppermost reach of North Tributary East Pit Ditch) the maximum peak flow <br /> velocity for the design storm is 1.98 fps (Prospect Ditch). This velocity is well below the <br /> maximum allowable velocity of 5 fps for the vegetative cover lining. <br /> Stock Ponds <br /> In order to assure compliance with effluent requirements at the outlet of Prospect Pond, <br /> five stock tanks have be constructed near the re-established main drainage channels of <br /> Prospect Ditch, North Tributary East Pit Ditch, and Final East Pit Ditch. These stock <br /> ponds include PD1, PD2,NTEP1, EP1, and EP2 respectively. <br /> The stock ponds were designed and constructed in accordance with Fig. 2.05-6 "Stock <br /> Tank Plan/Profile — Typical Design". In many cases these stock tanks completely <br /> intercept the runoff from their tributary watersheds in the 10 year 24 hour design storm. <br /> Inlet and outlet details relating to tie-in to their respective ditches are presented on Figure <br /> Exh. 7-15R-8. The SEDCAD modeling shows the runoff volume from the 10 year, 24 <br /> hour storm to be 6.98 acre feet, and the modeled outflow from Prospect Pond is well <br /> Exh. 7-PP-1 Revision Date: 1/6/20 <br /> Revision No. TR-136 <br />