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One sediment settling pond or sump will be located within the central processing area to capture <br /> stormwater runoff from the processing area, see Map C-2. A schematic cross-section of the <br /> processing area stormwater capture berm is shown in Figure 3. A second sediment settling pond <br /> or sump will be located at the base of the dump slope to collect stormwater flows from the slope <br /> of the dump (Map C-2; Figure 5). This sump will have the capacity to contain 100 year 24-hour <br /> rain events and will be surrounded by 9 foot tall seeded earthen berms. Therefore, no stormwater <br /> or process water will leave the site and all runoff from a 100 year 24-hour rain event will be <br /> trapped on site and waters will infiltrate the pit floor within 72 hours. The calculated available <br /> storage volume of the processing area sump is able to hold three back-to-back 100-year storm <br /> events. The calculated available storage volume of the dump sump with hold two back-to-back <br /> storm events. Therefore, both sumps will be capable of holding 100-year event stormwater from <br /> their drainage areas in addition to other moisture also temporarily captured for less than 72 hours <br /> in either sump. <br /> Natural drainages from unmined portions of the mesa will be diverted around the mining and <br /> processing areas either through drainage ditch relocations or construction of isolation berms. <br /> Fine sediment will be removed as needed from the sumps throughout the site. Material removed <br /> from the sumps will be placed in the mining strip that is actively being filled at that time. <br /> Although the sump will be lined with fines that will periodically require removal after <br /> accumulation,the lack of consistent precipitation in the area paired with the known low rain <br /> values will ensure that captured water either evaporates or will infiltrate the very porous ground <br /> surface. Additionally, all sumps will be emptied of sediment build-up periodically to ensure <br /> infiltration of water through the base of the sump. Additional calculations for the <br /> stormwater/sediment settling pond are presented in Exhibit G - Water Information. <br /> 4. Topsoil and Overburden Handling <br /> Topsoil ranges from 0 to 12 inches thick on site, 6 inches is the anticipated average. Both topsoil <br /> and overburden are used on site for reclamation of mined out areas. In the event that the <br /> Bradford Mesa Quarry needs to store topsoil, overburden, or waste fines in a berm, material piles <br /> will be either within the foot print of the current pit or along the western perimeter of the site. <br /> Topsoil stockpiles will be constructed to 2H:1 V slopes and overburden piles will have 2H:1 V <br /> Bradford Mesa Quarry <br /> January 2020 D-19 <br />