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Privileged and Confidential-Attorney Client Communication Geosyntec C' <br /> consultants <br /> 2. CONCEPTUAL DESIGN AND SCHEDULE <br /> 2.1 Existing Infrastructure <br /> The water treatment system currently in place at the Mine consists of various pumps, <br /> pipes, and ponds as identified in Attachment 1. Starting from the Mine portal, an <br /> existing set of dual pipelines that are each 8 inches in diameter receive water from the <br /> Mine portal by gravity flow and convey the water to the Mine Water Pond (MWP). The <br /> MWP is a geomembrane lined pond. On the downgradient side of the MWP Outfall <br /> 001 A discharges to Sneffels Creek when in operation. There is also a pipeline <br /> discharge option from MWP that feeds into Pond#2. Pond #2 was designed as an <br /> upflow bioreactor that consists of a layer of crushed limestone on the bottom, a layer of <br /> peat on top of the limestone, and a layer of topsoil on top. Pond #2 is currently operated <br /> as an infiltration system with water pooling before seeping into the subsurface under <br /> Pond #2. Further east on the Mine site is Pond #3, which is currently serving as a <br /> stormwater detention pond. <br /> OSMI conducted a capacity analysis for the existing Mine ponds using survey data <br /> collected at the Mine in October 2017 and the results are included in Table 4. The <br /> volumetric capacities of Ponds #2 and #3 assume the ponds will be completely full of <br /> water/materials and during detailed design that assumption will be refined according to <br /> the pond construction requirements and freeboard requirements for storm events. In <br /> order to estimate the pore volume and calculate hydraulic residence times, a porosity <br /> value of 0.34 (EPA, Sept. 2008)was applied to Ponds #2 and #3. <br /> Table 4: Approximate Volumetric Capacity of Water System <br /> Future Conditions After Pond <br /> Current Conditions Expansion <br /> Estimated Estimated Pore Estimated Estimated Pore <br /> and Empty Bed Volume of Pond Empty Bed Volume of Pond <br /> Volume of Assuming 0.34 Volume of Assuming 0.34 <br /> Pond aI * Poros' * 'orosi al <br /> NA To be NA <br /> MWP 285,000 evaluated in <br /> the future <br /> Pond#2 683,200 232,000 928,000 316,000 <br /> Pond#3 239,000 81,000 803,000 278,000 <br /> *Information provided to Geosyntec by OSMI 2018; MWP was calculated using the approximate current <br /> surface area of the pond and an estimated depth of water—the reconfigured MWP will in the future have <br /> a different configuration and design basis that will be evaluated further as the design progresses <br /> Treatability Study Work Plan 6 February 8,2018 <br />