Closure with a Final Cover System

Section 845.750  Closure with a Final Cover System Closure Performance Standard When Leaving CCR in Place a)         The owner or operator of a CCR surface impoundment must ensure that, at a minimum, the CCR surface impoundment is closed in a manner that will: 1)         Control, minimize or eliminate, to the maximum extent feasible, post-closure infiltration of liquids into the waste and releases of CCR, leachate, or contaminated run-off to the ground or surface waters or to the atmosphere; 2)         Preclude the probability of future impoundment of water, sediment, or slurry; 3)         Include measures that provide for major slope stability to prevent the sloughing or movement of the final cover system during the closure and post-closure care period; 4)         Minimize the need for further maintenance of the CCR surface impoundment; and 5)         Be completed in the shortest amount of time consistent with recognized and generally accepted engineering practices. b)         Drainage and Stabilization of CCR Surface Impoundments.  The owner or operator of a CCR surface impoundment or any lateral expansion of a CCR surface impoundment must meet the requirements of this subsection (b) before installing the final cover system required by subsection (c). 1)         Free liquids must be eliminated by removing liquid wastes or solidifying the remaining wastes and waste residues. 2)         Remaining wastes must be stabilized sufficiently to support the final cover system. c) Final Cover System. If a CCR surface impoundment is closed by leaving CCR in place, the owner or operator must install a final cover system that is designed to minimize infiltration and erosion, and, at a minimum, meets the requirements of this subsection (c).  The final cover system must consist of a low permeability layer and a final protective layer.  The design of the final cover system must be included in the preliminary and final written closure plans required by Section 845.720 and the construction permit application for closure submitted to the Agency. 1)         Standards for the Low Permeability Layer.  The low permeability layer must have a permeability less than or equal to the permeability of any bottom liner system or natural subsoils present, or a hydraulic conductivity no greater than 1 x 10 ‑7 cm/sec, whichever is less.  The low permeability layer must be constructed in accordance with the standards in either subsection (c)(1)(A) or (c)(1)(B), unless the owner or operator demonstrates that another low permeability layer construction technique or material provides equivalent or superior performance to the requirements of either subsection (c)(1)(A) or (c)(1)(B) and is approved by the Agency. A)        A compacted earth layer constructed in accordance with the following standards: i)          The minimum allowable thickness must be 0.91 meter (three feet); and ii)         The layer must be compacted to achieve a hydraulic conductivity of 1 x 10 ‑7 cm/sec or less and minimize void spaces. B)        A geomembrane constructed in accordance with the following standards: i)          The geosynthetic membrane must have a minimum thickness of 40 mil (0.04 inches) and, in terms of hydraulic flux, must be equivalent or superior to a three-foot layer of soil with a hydraulic conductivity of 1 x 10 ‑7 cm/sec; ii)         The geomembrane must have strength to withstand the normal stresses imposed by the waste stabilization process; and iii)        The geomembrane must be placed over a prepared base free from sharp objects and other materials that may cause damage. 2)         Standards for the Final Protective Layer. The final protective layer must meet the following requirements, unless the owner or operator demonstrates that another final protective layer construction technique or material provides equivalent or superior performance to the requirements of this subsection (c)(2) and is approved by the Agency. A)        Cover the entire low permeability layer; B)        Be at least three feet thick, be sufficient to protect the low permeability layer from freezing, and minimize root penetration of the low permeability layer; C)        Consist of soil material capable of supporting vegetation; D)        Be placed as soon as possible after placement of the low permeability layer; and E)        Be covered with vegetation to minimize wind and water erosion. 3)         The disruption of the integrity of the final cover system must be minimized through a design that accommodates settling and subsidence. 4)         The owner or operator of the CCR surface impoundment must obtain and submit with its construction permit application for closure a written certification from a qualified professional engineer that the design of the final cover system meets the requirements of this Section. d)         This subsection specifies the allowable uses of CCR in the closure of CCR surface impoundments closing under Section 845.700.  Notwithstanding the prohibition on further placement in Section 845.700, CCR may be placed in these surface impoundments, but only for purposes of grading and contouring in the design and construction of the final cover system, if: 1)         The CCR placed was generated at the facility and is located at the facility at the time closure was initiated; 2)         CCR is placed entirely above the elevation of CCR in the surface impoundment, following dewatering and stabilization (see subsection (b)); 3)         The CCR is placed entirely within the perimeter berms of the CCR surface impoundment; and 4)         The final cover system is constructed with either: A) A slope not steeper than 5% grade after allowance for settlement; or B) At a steeper grade, if the Agency determines that the steeper slope is necessary, based on conditions at the site, to facilitate run-off and minimize erosion, and that side slopes are evaluated for erosion potential based on a stability analysis to evaluate possible erosion potential.  The stability analysis, at a minimum, must evaluate the site geology; characterize soil shear strength; construct a slope stability model; establish groundwater and seepage conditions, if any; select loading conditions; locate critical failure surface; and iterate until minimum factor of safety is achieved.