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Disposal in an Engineered Waste Rock Pile <br />There are currently two engineered waste rock piles (WRPs) at the site, a South WRP (on the south side <br />of the creek) and a North WRP (on the north side of the creek). Both WRPs are located hydrologically <br />upgradient (west) of the alluvial fill pad. It may be technically possible to add additional waste rock to <br />one or both of the existing WRPs. Another potential option would be to build a new repository in an <br />alternate hillside location above groundwater regimes associated with Ralston Creek. Although formal <br />engineering assessments are beyond the scope of this report, conceptual considerations with respect to <br />long -term protection of public health and the environment, along with logistical /scheduling considerations <br />in a context of current overall reclamation plans for the site are assessed below. <br />Because engineered WRPs are located above ground, they are subject to physical, chemical, and <br />biological forces associated with the active surface environment. Gravity, water and wind erosion, <br />oxidation, geochemical leaching, and disturbance by biological systems and anthropogenic activities are <br />all potential mobilization and transport mechanisms that any repository design must effectively mitigate. <br />Despite these challenges, properly engineered waste rock piles can provide effective long -term isolation <br />and stabilization of such material (ITRC, 2011). <br />The International Atomic Energy Agency has outlined some basic principles with respect to permanent <br />management of uranium mine wastes (IAEA, 2002) which can be summarized as follows: <br />1. Maximize the use of natural materials and site features for containment. <br />2. Maximize the placement of waste material below ground level, or in some cases under water. <br />3. Minimize impacts on the surrounding environment. <br />4. Minimize waste relocation requirements for placement in management facilities. <br />5. Minimize the need for long -term surveillance, maintenance and institutional controls. <br />With the possible exception of waste relocation requirements, each of these principles favors underground <br />disposal of mineralized waste rock in the mine workings from which they originated, though a new <br />engineered waste rock repository may offer a viable alternative. There are no prescriptive regulatory <br />design criteria in Colorado or the United States for uranium mine waste rock repositories, though design <br />criteria guidelines have been developed in other countries (Rykaart and Caldwell, 2006). The U.S. <br />Department of Energy's Uranium Mill Tailings Remedial Action (UMTRA) Project, specifies that <br />uranium mill tailing covers should be designed to last for 1,000 years to the extent reasonably achievable, <br />and at minimum, last for at least 200 years. Design and performance criteria that would likely apply to a <br />new engineered repository for mine waste rock at the Schwartzwalder Mine site include the following: <br />• Generally stabilize and isolate the waste from physical and chemical attributes of the local surface <br />environment. <br />• Construct the disposal facility above the 100 -year floodplain. <br />• Minimize infiltration of precipitation and oxygen to inhibit oxidation and leaching potential. <br />• Effectively resist erosion by wind, precipitation, stormwater runoff. <br />• Resist degradation of cap integrity due to freeze /thaw cycles, shrink/swell soils, and biological or <br />anthropogenic disturbances. <br />21 <br />