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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 />1. EXECUTIVE SUMMARY <br />1.1 Phase 1 Project Summary <br />At the request of the Cotter Corporation (N.S.L.) (Cotter), IRIS Mitigation and Design, Inc. (IRIS) has <br />prepared this Biological Assessment (BA) to identify and mitigate for temporary and permanent impacts <br />to the threatened and endangered (T &E) Preble's Meadow Jumping Mouse (Zapus hudsonius preblei) <br />(PMJM) species' habitat due to Phase 1 of the Ralston Creek Temporary Diversion Pipeline Project <br />(Project) in Jefferson County, Colorado (see Figures 1 and 2). A "proposed upstream concrete cutoff <br />wall" (cutoff wall) will be installed across Ralston Creek, and a proposed low flow bypass pipeline will <br />be installed along an approximately 3,500 linear stretch south of Ralston Creek through the <br />Schwartzwalder Mine and Vicinity (Site) (see Figure 3). This section of Ralston Creek has been <br />mapped by the U.S. Fish and Wildlife Service (USFWS) as critical PMJM habitat. <br />The proposed Phase 1 work includes installation of a cutoff wall with a thickness of up to 1.5 feet <br />upstream of the southern waste pile. The cutoff wall will be installed into bedrock and will span up to <br />125 feet across the valley. The cutoff wall has been located at an existing unpaved road crossing of <br />Ralston Creek where there are two existing culverts (see Figure 3). The project also includes <br />construction of a low flow bypass pipeline with a capacity up to 8 cubic feet per second (cfs) which will <br />divert Ralston Creek low flows and up- gradient alluvial groundwater forced to the surface by the cutoff <br />wall into an 18 -inch low flow bypass pipeline. The pipeline will have a pumped or gravity intake <br />upstream of the cutoff wall. Downstream of the cutoff wall, the pipeline will traverse along the north <br />side of the existing unpaved road through the Site with periodic anchoring and /or staking to prevent <br />excessive movement or rolling (see Figure 3). The low flow bypass pipeline will discharge below the <br />proposed location for the downstream cutoff wall planned in Phase 2. <br />During the 1960's, approximately 7 acres of the valley were filled to create a flat area for mine facilities <br />and operations (referred to as the Alluvial Fill Area). The cutoff wall and low flow bypass pipeline will <br />divert upstream low flows and alluvial groundwater through the Site and discharge back to the historic <br />alignment of Ralston Creek near the eastern boundary of the Site. The purpose of Phase 1 of the <br />Project is to isolate up- gradient surface and alluvial groundwater flows up to 8 cfs from potential areas <br />of contamination associated with historic uranium mining. <br />This BA addresses both temporary and permanent impacts to both PMJM riparian and upland habitat. <br />Impacted areas include previously disturbed and undisturbed PMJM riparian and upland habitat. This <br />Page 1 August 2011 <br />