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2011-08-31_REVISION - M1977300
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2011-08-31_REVISION - M1977300
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Last modified
8/24/2016 4:42:48 PM
Creation date
11/8/2011 12:46:45 PM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
M1977300
IBM Index Class Name
REVISION
Doc Date
8/31/2011
Doc Name
Phase 1 Biological Assessment.
From
IRIS Mitigation and Design, Inc.
To
Cotter Corporation
Type & Sequence
TR18
Email Name
DB2
Media Type
D
Archive
No
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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 />Temporary impacts to the riparian area will total 0.06 acre, with 0.02 acre occurring in previously <br />disturbed riparian area and the remaining 0.04 acre occurring in previously undisturbed riparian area <br />(see Table 9). The proposed low flow bypass pipeline will cross the edge of several riparian areas on <br />its route (3,500 linear feet) to the discharge location downstream to the east. The pipeline will cross <br />into 0.04 acre of previously undisturbed riparian area in its downstream location, as shown on Figures <br />7, 9, and 10. The 18 -inch low flow bypass pipeline will return flows back to Ralston Creek in this <br />location adjacent to the creek, whereby flows will be directed into a filter bag treatment system as <br />needed to removal sediment from discharges (see Attachment E of the PCN — SWMP /GESC Plan). <br />Once the low flow bypass pipeline is no longer needed, it will be removed, and the area will be restored <br />to preexisting conditions. (Please see mitigation section in this report.) <br />5.5 Summary of Impacts <br />Phase 1 proposed work will have both permanent and temporary impacts to both previously disturbed <br />and previously undisturbed PMJM riparian and upland habitat. Impacts are considered permanent for <br />this project where placement of concrete, boulders, or riprap, or a significant change in existing grade <br />is planned. Permanent impact includes engineered structures, such as the cutoff wall, and grouted <br />boulders which may remain onsite after Phase 3 of the project is completed. <br />The only permanent impacts for Phase 1 construction will occur during cutoff wall installation and will <br />affect previously disturbed PMJM riparian and upland habitat (0.22 acre). There will be no permanent <br />impacts to previously undisturbed upland or riparian areas in this proposed Phase 1 work (see Figure <br />9). Permanent impacts to previously disturbed uplands will be mitigated entirely onsite just upstream of <br />the cutoff wall location (see Figure 11, Table 11, and the Mitigation Section of this report). Half of the <br />permanent impacts to previously disturbed riparian areas will be mitigated onsite just upstream of the <br />cutoff wall (see Figure 11, Table 11, and the Mitigation Section of this report), and half will be mitigated <br />for at the end of Phase 3 when flows to Ralston Creek are restored. <br />Page 31 August 2011 <br />
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