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IRIS <br />MITIGATION AND DESIGN, INC. <br />SCHWARTZWALDER MINE PHASE 1 - UPSTREAM CUTOFF WALL AND LOW FLOW BYPASS <br />PIPELINE - BIOLOGICAL ASSESSMENT <br />5. EFFECTS OF THE ACTION <br />5.1 Upstream Cutoff Wall Construction and Impacts <br />The cutoff wall along Ralston Creek will have permanent and temporary impacts to both previously <br />disturbed and undisturbed PMJM riparian and upland habitat along Ralston Creek (see Figures 7 to <br />10). Installation of the cutoff wall will involve excavation of a trench with a maximum depth of <br />approximately 30 to 35 feet across the valley with an excavation top -width of approximately 100 feet <br />(see Figures 3 to 6). Top -width and length calculations are based on average depth to bedrock known <br />for the area from the EPP and will be further defined following detailed geotechnical investigations in <br />August 2011. <br />Once the cutoff wall area is excavated, the cutoff wall will be installed to bedrock, and the area east of <br />the cutoff wall will be backfilled. The unpaved road crossing will be restored, and the upland area <br />located east of the restored road crossing will be re- contoured to direct any flows that may overtop the <br />cutoff wall back down into Ralston Creek. Grouted boulders will be placed east and down - gradient of <br />the cutoff wall as show on Figures 3 to 6. A grouted boulder drop structure, boulder energy- dissipating <br />structure, and riprap will direct flows back into the creek. A riprap pad will be installed west of the <br />installed cutoff wall along Ralston Creek for scour protection and as a substrate for placement of the <br />intake for the low flow bypass pipe. An 18 -inch low flow bypass pipeline will be installed through the <br />cutoff wall and belowground in the location of the unpaved road crossing. The low flow bypass pipeline <br />will generally run aboveground along the northern edge of the access road through the Site. The low <br />flow bypass pipeline will discharge back to Ralston Creek below the proposed location of the <br />downstream cutoff wall (Phase 2). <br />5.2 Temporary Impacts <br />There will be approximately 0.99 acre of temporary impacts to both previously disturbed and <br />undisturbed PMJM upland habitat, riparian habitat and upland area that is not considered PMJM <br />habitat at the location of the cutoff wall (see Figures 7 and 8 and Table 8). Of this 0.99 acre of <br />temporary impact, 0.12 acre of impact will be to previously heavily- impacted upland area that is not <br />considered PMJM habitat. This area includes the existing unpaved access road and crossing of the <br />creek. The majority of temporary habitat impact will occur to previously disturbed and previously <br />undisturbed PMJM upland habitat totaling 0.65 acre. This impact will be due to the need for <br />construction access, BMPs installation, and trenching activities during cutoff wall construction. A <br />conservative buffer area of temporary upland impact was considered during the design process, and <br />Page 28 August 2011 <br />