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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 />BA also addresses proposed mitigation both during and after Phase 1 construction activities are <br />completed. <br />1.2 Overall Schwartzwalder Mine Clean -Up Project Summary <br />The ultimate purpose and need of the overall Project is to protect public health, safety, welfare and the <br />environment by meeting the Colorado uranium water quality standards for Ralston Creek. The Site is <br />located approximately two miles upstream of Ralston Reservoir, a public water supply owned and <br />operated by Denver Water. The Project will result in the hydrologic isolation of the Site's Alluvial Fill <br />Area, which will facilitate characterization, clean -up and reclamation activities identified in the <br />Environmental Protection Plan (EPP).. <br />A phased approach is necessary for the overall Project because additional characterization work is <br />needed to quantify areas of contamination and to formulate long -term reclamation plans for the Site. <br />Characterization and reclamation activities can be accomplished if the hydrologic connection between <br />Ralston Creek and the Alluvial Fill Area are controlled to allow excavation activities to occur in relatively <br />dry conditions rather than having to continually, actively manage groundwater in areas that may <br />potentially be contaminated. The Colorado Mined Land Reclamation Board (MLRB) and the Colorado <br />Division of Reclamation, Mining and Safety (DRMS)agree with Cotter's proposed approach. <br />The following paragraphs describe each of the three phases. This BA is submitted for proposed Phase <br />1 work only. <br />Phase 1: As fully detailed in this BA <br />Phase 2: Temporary Diversion Pipeline (100 cfs) and Downstream Cutoff Wall — Phase 2 of the <br />Project will involve construction of a 100 cfs Temporary Diversion Pipeline (pending authorization from <br />the applicable regulatory agencies). The pipeline will consist of 42 -inch diameter steel pipe and will <br />follow a largely aboveground alignment from the upstream cutoff wall through the Site, tying in to the <br />downstream cutoff wall and discharging near the downstream property boundary. The downstream <br />cutoff wall will be constructed to key into bedrock to contain residual groundwater (primarily direct <br />precipitation and flows entering the alluvial fill between the two cutoff walls) so that it can be collected <br />via the existing pump- and -treat system. The discharge from the Wastewater Treatment Plant (WWTP) <br />to Ralston Creek will be below the downstream cutoff wall. Energy dissipation measures will be <br />installed below the downstream cutoff wall to provide protection against erosion from the higher water <br />velocity occurring as flows up to 100 cfs exit the Temporary Diversion Pipeline. Phase 2 will also <br />Page 2 August 2011 <br />