2019-01-18_REVISION - M1974086 (16)

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4. The slide area located in the northwest part of the permit area,between the quarry hillside and the Ralston Reservoir. The quarry will serve as a sufficient sediment trap for all runoff entering it. The processing area drains to a collection ditch along the south side of the area, which then drains into a sump north of the access road, that then drains into a larger sediment pond south of the road. This sediment pond does not discharge. The slide area has stormwater control systems designed and installed for it. See Maps C-2 and C-4. Slide Area Stormwater Control The slide area stormwater control systems have all been designed to handle the 10-YR 24-HR 2_3 storm event. This is due to the short-term nature of the disturbance in this area.No mining is taking place in this part of the site, so the only activity is regrading and reclamation earthwork. All of the stormwater improvements for this area will be removed promptly following successful revegetation. Based on Asphalt Paving Co. experience on the site, the slide area should be ready for release in the next few years. 2.3.1 Stormwater Runoff Calculations and Improvement Designs Two areas of disturbance will require stormwater handling in the slide area: the North and South Areas. The North Area consists of the repaired slide areas themselves, which drains to the west. The South Area consists of the waste rock embankment of slide material and the topsoil stockpiles adjacent to the embankment. Maps C-2 and C-4 show these areas. For each area,the Stormwater controls are outlined below. The 10-YR, 24-HR runoff was used for all stormwater designs as the disturbance activity will be temporary, with revegetation taking place promptly. In general,the soil hydrology was assumed to be that of recently regraded land despite the presence of vegetated areas in the drainage basins. Ralston Quarry CM l.ewicki and Associates,Pt LC January 2019 G-2