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Disturbances to the stream buffer zone in the vicinity of the HRG and Top Soil Pile #RR (TSRR) are <br />limited to a 72-inch culvert that is riprapped and placed in Dry Creek, HRG, TSRR and associated • <br />sediment control structures (berm and sump), and two small overland flow conveyance ditches (see <br />Exhibit 13-19.11A). The TSRR features an earthen berm around the base of the stockpile that conveys <br />runoff and suspended solids to the sump. The sump is designed to collect all runoff and sediment from <br />the stockpile, preventing contributions of additional suspended sediment to streamflow in Dry Creek. <br />Attachment 13-8 presents the design criteria used in calculating the sump sizes. Topsoil pile RR sump <br />was designed to contain the runoff as the result of the 10-year, 24-hour precipitation event. The <br />minimum storage capacity, as listed on Table 13-8-1B, is 1850 cubic feet. Both small conveyance <br />ditches (one on each side of HRG) are designed to adequately convey runoff from HRG without <br />contributing additional suspended solids to Dry Creek. The ditch along the southern edge of HRG <br />discharges to a culvert (Culvert G-1) that is riprapped immediately downstream, providing dissipation of <br />energy from runoff conveyed by this ditch (2.6 percent gradient). The ditch along the northern edge of <br />HRG features a much lower gradient within the stream buffer zone (0.1 percent), so no energy <br />dissipation was necessary at its outlet point. PWCC has placed stream buffer zone signs along the <br />southern edge of the HRG, near Culvert G-1, and at the western edge of TSRR within the permit <br />boundary to identify the stream buffer zone at this location. <br />Mining disturbances within the stream buffer zone of Sage Creek have been minimized to the extent. <br />practical. One disturbance of the stream buffer zone occurred along Sage Creek near the intersection <br />of the tie-across haul road and County Road 51 B. The disturbance was limited to construction of the <br />toe of the haul road embankment and removal of topsoil prior to the embankment construction. There • <br />was no disturbance of the main channel of Sage Creek. The stream buffer disturbance could not be <br />avoided because the County raised several objections to a proposed haul road alignment that would not <br />have intercepted a portion of the stream buffer area. The associated haul road ditches are properly <br />designed (will convey the runoff from a 10-year, 24-hour storm) to prevent water quality degradation in <br />Sage Creek as a result of the embankment disturbance. <br />Following reclamation grading, salvaged topsoil will be replaced and will be disked to partially tie in <br />with the adjacent undisturbed vegetation. Revegetation methods will follow those described in Tab 22, <br />Revegetation. Seed Mix No. 2, which contains a number of the native species found in the stream <br />buffer disturbance area as well as other <br />E <br />7a Revision 11/10/95