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Attachment TP4UGD <br /> Page No.TP4UGD- 4 <br /> Permit No. CO-0044768 <br /> SGC is under no obligation to defend these estimates and they should only be used as an <br /> estimate using many assumptions to obtain. SGC does not represent that its mitigation <br /> project at this site will remove any specific percentage of metals loading from this site. the <br /> loading estimate contained herein does not form the basis for an enforceable permit <br /> obligation. <br /> Description of Project <br /> —Identifv the strike length where extension of the groundwater cutoff wall is technically and <br /> economically feasible through trenching to define bedrock contact and location of groundwater flows <br /> —Install impenneable barriers to impede groundwater flow on the bedrock contact in areas identified <br /> where groundwater flow is occurring and installation of an interception structure is feasible. <br /> —Install piping and drains where needed to capture flows and provide a drainage path to the existing <br /> lined up-land diversion ditch <br /> —Temporar\ sediment control structures will be used as necessary to minimize sediment transport <br /> from the site. Disturbed areas will be vegetated to minimize erosion and sediment transport in the <br /> long-term <br /> Analvsis <br /> Installation of strictures and control of drainage to minimize the potential for water to contact <br /> tailings and mine waste material is a Best Management Practice. Any reduction in contact of mine <br /> waste or tailings with flowing water has the potential for reduction in metals loading to the Animas <br /> River <br /> The original design and construction of Tailings Pond No. 4 was according to standards prevailing at <br /> the time N\hich did not include an underdram and liner system to assure separation of tailings and <br /> migrating water If any of the groundwater flowing on the bedrock contact surfaces at the contact of <br /> tailings-soil before passing under the tailings pond, it will contact tailings and the potential exists for <br /> an increase in metals loading to the receiving stream (ie. Animas River). Providing a drainage <br /> path\\a\ to nnininize contact of(lowing water with tailings material Nvill serve to reduce any metals <br /> loading that nna\ occur as a result of the contact Implenncntation of the work plan will not materially <br /> alter the land or create am land use changes or potential uses. <br /> Monitoring <br /> Due to the close prominitN to other Annnas River monitoring stations and the high flows that occur <br /> in the Amnnas RIN er. no additional monitoring is contemplated for this proiect Improvements would <br /> be reflected in the nnonthl monitoring results from A-68. <br />