Liner Design Criteria for Existing CCR Surface Impoundments

Section 845.400  Liner Design Criteria for Existing CCR Surface Impoundments a)         An existing CCR surface impoundment is considered to be an existing lined surface impoundment if it has been constructed with either a composite liner that meets the requirements of subsection (b) or an alternative composite liner that meets the requirements of subsection (c). b)         Composite Liner 1)         A composite liner must consist of two components: the upper component consisting of, at a minimum, a 30-mil geomembrane liner, and the lower component consisting of at least a two-foot layer of compacted soil with a hydraulic conductivity of no more than 1 x 10 ‑7 centimeters per second (cm/sec).  The geomembrane liner components consisting of high-density polyethylene (HDPE) must be at least 60 mil.  The geomembrane liner or upper liner component must be installed in direct and uniform contact with the compacted soil or lower liner component. 2)         The composite liner 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 CCR or leachate to which they are exposed, climatic conditions, the stress of installation, and the stress of daily operation; B)        Constructed of materials that provide appropriate shear resistance of the upper and lower component interface to prevent sliding of the upper component, including on slopes; C)        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 D)        Installed to cover all surrounding earth likely to be in contact with the CCR or leachate. c)         Alternative Composite Liner 1)         An alternative composite liner must consist of two components: the upper component consisting of, at a minimum, a 30-mil geomembrane liner, and a lower component, that is not a geomembrane, with a liquid flow rate no greater than the liquid flow rate of two feet of compacted soil with a hydraulic conductivity of no more than 1 x 10 ‑7 cm/sec.  The geomembrane liner components consisting of high-density polyethylene (HDPE) must be at least 60 mil. If the lower component of the alternative liner is compacted soil, the geomembrane liner must be installed in direct and uniform contact with the compacted soil. 2)         The liquid flow rate through the lower component of the alternative composite liner must be no greater than the liquid flow rate through two feet of compacted soil with a hydraulic conductivity of 1 x 10 ‑7 cm/sec. The hydraulic conductivity for the two feet of compacted soil used in the comparison must be no greater than 1 x 10 ‑7 cm/sec.  The hydraulic conductivity of any alternative to the two feet of compacted soil must be determined using recognized and generally accepted methods. 3)         The liquid flow rate comparison must be made using the following equation, which is derived from Darcy's Law for gravity flow through porous media. Q/A = q = k ((h/t)+1) Where: Q = flow rate (cubic centimeters/second) A = Surface area of the liner (squared centimeters) q = flow rate per unit area (cubic centimeters/ second/squared centimeter) k = hydraulic conductivity of the liner (centimeters /second) h = hydraulic head above the liner (centimeters); and t = thickness of the liner (centimeters) 4)         The alternative composite liner must meet the requirements specified in subsection (b). d)         The hydraulic conductivity of the compacted soil must be determined using recognized and generally accepted methods. e)         The owner or operator of an existing CCR surface impoundment that has not completed an Agency approved closure before July 30, 2021 must submit an initial operating permit application under Section 845.230 that demonstrates whether the CCR surface impoundment was constructed with either of the following: 1)         A composite liner that meets the requirements of subsection (b); or 2)         An alternative composite liner that meets the requirements of subsection (c). f)         A CCR surface impoundment is considered to be an unlined CCR surface impoundment if either: 1)         The owner or operator of the CCR surface impoundment determines that the CCR surface impoundment is not constructed with a liner that meets the requirements of subsection (b) or (c); or 2)         The owner or operator of the CCR surface impoundment fails to document whether the CCR surface impoundment was constructed with a liner that meets the requirements of subsection (b) or (c). g)         All unlined CCR surface impoundments are subject to the requirements of Section 845.700. h) The owner or operator of the CCR surface impoundment must obtain a certification from a qualified professional engineer attesting that the CCR surface impoundment meets the requirements of subsection (a) and submit the certification to the Agency in the facility's initial operating permit application.