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RULE §336.1129Technical Requirements

(a) By-product material handling and disposal systems must be designed to accommodate full-capacity production over the lifetime of the facility. When later expansion of systems or operations may be likely, capability of the disposal system to be modified to accommodate increased quantities without degradation in long-term stability and other performance factors must be evaluated.

(b) In selecting among alternative by-product material disposal sites or judging the adequacy of existing sites, the following site features which would assure meeting the broad objective of isolating the tailings and associated contaminants without ongoing active maintenance must be considered:

  (1) remoteness from populated areas;

  (2) hydrogeologic and other environmental conditions conducive to continued immobilization and isolation of contaminants from usable groundwater sources; and

  (3) potential for minimizing erosion, disturbance, and dispersion by natural forces over the long term.

(c) The site selection process must be an optimization to the maximum extent reasonably achievable in terms of these site features.

(d) In the selection of disposal sites, primary emphasis must be given to isolation of the by-product material, a matter having long-term impacts, as opposed to consideration only of short-term convenience or benefits (e.g., minimization of transportation of land acquisition costs). While isolation of by-product material will also be a function of both site and engineering design, overriding consideration must be given to siting features.

(e) By-product material should be disposed of in a manner such that no active maintenance is required to preserve conditions of the site.

(f) The applicant's environmental report must evaluate alternative sites and disposal methods and shall consider disposal of by-product material by placement below grade. Where full below grade burial is not practicable, the size of retention structures, and size and steepness of slopes associated with exposed embankments must be minimized by excavation to the maximum extent reasonably achievable or appropriate given the geologic and hydrologic conditions at a site. In these cases, it must be demonstrated that an above grade disposal program will provide reasonably equivalent isolation of the by-product material from natural erosional forces.

(g) To avoid proliferation of small waste disposal sites and thereby reduce perpetual surveillance obligations, by-product material from in situ extraction operations, such as residues from solution evaporation or contaminated control processes, and wastes from small remote above ground extraction operations must be disposed of at existing large mill tailings disposal sites; unless, considering the nature of the wastes, such as their volume and specific activity, and the costs and environmental impacts of transporting the wastes to a large disposal site, such offsite disposal is demonstrated to be impracticable or the advantages of onsite burial clearly outweigh the benefits of reducing the perpetual surveillance obligations.

(h) The following site and design requirements must be adhered to whether by-product material is disposed of above or below grade:

  (1) the upstream rainfall catchment areas must be minimized to decrease erosion potential by flooding that could erode or wash out sections of the by-product material disposal area;

  (2) the topographic features must provide good wind protection;

  (3) the embankment and cover slopes must be relatively flat after final stabilization to minimize erosion potential and to provide conservative factors of safety assuring long term stability. The objective should be to contour final slopes to grades that are as close as possible to those that would be provided if by-product material was disposed of below grade. Slopes must not be steeper than 5 horizontal to 1 vertical (5h:1v), except as specifically authorized by the agency. Where steeper slopes are proposed, reasons why a slope steeper than 5h:1v would be as equally resistant to erosion shall be provided, and compensating factors and conditions that make such slopes acceptable shall be identified;

  (4) a full self-sustaining vegetative cover must be established or rock cover employed to reduce wind and water erosion to negligible levels;

  (5) where a full vegetative cover is not likely to be self-sustaining due to climatic conditions, such as in semi-arid and arid regions, rock cover shall be employed on slopes of the impoundment system. The agency may consider relaxing this requirement for extremely gentle slopes, such as those that may exist on the top of the pile;

  (6) the following factors must be considered in establishing the final rock cover design to avoid displacement of rock particles by human and animal traffic or by natural processes, and to preclude undercutting and piping:

    (A) shape, size, composition, gradation of rock particles (excepting bedding material, average particles size must be at least cobble size or greater);

    (B) rock cover thickness and zoning of particles by size; and

    (C) steepness of underlying slopes.

  (7) individual rock fragments must be dense, sound, and resistant to abrasion, and shall be free from cracks, seams, and other defects that would tend to unduly increase their destruction by erosion and weathering action. Local rock materials are permissible provided the characteristics under local climatic conditions indicate similar long-term performance as a protective layer. Weak, friable, or laminated aggregate may not be used;

  (8) rock covering of slopes may not be required where top covers are very thick (on the order of 10 m or greater); impoundment slopes are very gentle (on the order of 10h:1v or less); bulk cover materials have inherently favorable erosion resistance characteristics; there is negligible drainage catchment area upstream of the pile; and there is good wind protection;

  (9) all impoundment surfaces must be contoured to avoid areas of concentrated surface runoff or abrupt or sharp changes in slope gradient. In addition to rock cover on slopes, areas toward which surface runoff might be directed must be well protected with substantial rock cover (riprap). In addition to providing for stability of the impoundment system itself, overall stability, erosion potential, and geomorphology of surrounding terrain must be evaluated to assure that there are no ongoing or potential processes, such as gully erosion, which would lead to impoundment instability;

  (10) the impoundment must not be located near a capable fault that could cause a maximum credible earthquake larger than that which the impoundment could reasonably be expected to withstand; and

  (11) the impoundment should be designed to incorporate features that will promote deposition. Design features that promote deposition of sediment suspended in any runoff which flows into the impoundment area might be utilized. The object of such a design feature would be to enhance the thickness of cover over time.

(i) The following groundwater protection requirements and those in subsections (j) and (k) of this section and §336.1133 of this title (relating to Maximum Values for Use in Groundwater Protection) apply during operations and until closure is completed. Groundwater monitoring to comply with these standards is required by subsections (bb) and (cc) of this section.

  (1) The primary groundwater protection standard is a design standard for surface impoundments used to manage uranium or thorium by-product material. Unless exempted under subsection (i)(3) of this section, surface impoundments (except for an existing portion) must have a liner that is designed, constructed, and installed to prevent any migration of wastes out of the impoundment to the adjacent subsurface soil, groundwater, or surface water at any time during the active life (including the closure period) of the impoundment. If the liner is constructed of materials that may allow wastes to migrate into the liner during the active life of the facility, impoundment closure shall include removal or decontamination of all waste residues, contaminated containment system components (liners, etc.), contaminated subsoils, and structures and equipment contaminated with waste and leachate. For impoundments that will be closed with the liner material left in place, the liner must be constructed of materials that can prevent wastes from migrating into the liner during the active life of the facility.

  (2) The liner required by paragraph (1) of this subsection must be:

    (A) constructed of materials that have appropriate chemical properties and sufficient strength and thickness to prevent failure due to pressure gradients (including static head and external hydrogeologic forces), physical contact with the waste or leachate to which they are exposed, climatic conditions, the stress of installation, and the stress of daily operation;

    (B) placed upon a foundation or base capable of providing support to the liner and resistance to pressure gradients above and below the liner to prevent failure of the liner due to settlement, compression, or uplift; and


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