§ 290.410. Storage impoundments—design requirements.
Impoundments used to store coal ash must meet the following minimum design criteria:
(1) The liner system for a coal ash storage impoundment must include the following elements:
(i) The subbase, which is the prepared layer of soil or earthen material upon which the remainder of the liner system is constructed.
(ii) The leachate detection zone, which is a prepared layer placed on top of the subbase and upon which the liner is placed, and in which a leachate detection system is located.
(iii) The composite liner, which is a continuous layer of synthetic material over earthen material, placed on the leachate detection zone. The upper component is no more permeable than 1.0 x 10-7 cm/sec. based on laboratory testing. The composite component is no more permeable than 1.0 x 10-6 cm/sec., based on laboratory testing and field testing.
(iv) The protective cover and leachate collection zone, which is a prepared layer placed over the liner in which a leachate collection system is located.
(2) The bottom of the subbase of the liner system cannot be in contact with the water table without the use of groundwater pumping systems.
(3) The subbase must meet the following performance standards. The subbase must:
(i) Bear the weight of the liner system, coal ash, and equipment operating on the coal ash storage impoundment without causing or allowing a failure of the liner system.
(ii) Accommodate potential settlement without damage to the liner system.
(iii) Be a barrier to the transmission of liquids.
(iv) Cover the bottom and sidewalls of the coal ash storage impoundment.
(4) The leachate detection zone must meet the following performance standards. The leachate detection zone must:
(i) Rapidly detect and collect liquid entering the leachate detection zone, and rapidly transmit the liquid to the leachate treatment system.
(ii) Withstand chemical attack from coal ash or leachate.
(iii) Withstand anticipated loads, stresses and disturbances from overlying coal ash and equipment operation.
(iv) Function without clogging.
(v) Prevent the liner from puncturing, cracking, tearing, stretching or otherwise losing its physical integrity.
(vi) Cover the bottom and sidewalls of the coal ash storage impoundment.
(5) The liner must meet the following standards of performance:
(i) The liner must prevent the migration of leachate through the liner to the greatest degree that is technologically possible.
(ii) The effectiveness of the liner in preventing the migration of leachate may not be adversely affected by the physical or chemical characteristics of the coal ash or leachate from the coal ash storage impoundment.
(iii) The liner must be resistant to physical failure, chemical failure, and other failure.
(iv) The liner must cover the bottom and sidewalls of the coal ash storage impoundment.
(6) The protective cover must meet the following performance standards. The protective cover must:
(i) Protect the primary liner from physical damage from stresses and disturbances from overlying coal ash and equipment operation.
(ii) Protect the leachate collection system within the protective cover from stresses and disturbances from overlying coal ash and equipment operation.
(iii) Allow the continuous and free flow of leachate into the leachate collection system within the protective cover.
(iv) Cover the bottom and sidewalls of the coal ash storage impoundment.
(7) The leachate collection system within the protective cover must meet the following performance standards. The leachate collection system must:
(i) Ensure that free flowing liquids and leachate will drain continuously from the protective cover to the leachate treatment system.
(ii) Withstand chemical attack from leachate.
(iii) Withstand anticipated loads, stresses and disturbances from overlying coal ash and equipment operation.
(iv) Function without clogging.
(v) Cover the bottom and sidewalls of the coal ash storage impoundment.
(8) An onsite leachate storage system shall be part of each leachate treatment method used by the person. The storage system must contain impoundments or tanks for storage of leachate. The tanks or impoundments must have a storage capacity at least equal to the maximum expected production of leachate for a 30-day period. No more than 25% of the total leachate storage capacity may be used for flow equalization on a regular basis. Leachate storage capacity may not be considered to include leachate that may have collected in or on the liner system.
(9) Leachate may be collected and handled by one of the following:
(i) Onsite treatment and discharged into a receiving stream under a permit issued by the Department under The Clean Streams Law (35 P. S. § § 691.1—691.1001) and regulations thereunder, if the Department approves this method in the permit.
(ii) Direct discharge into a permitted publicly-owned treatment works, following pretreatment, if pretreatment is required by Federal, State or local law or by discharge into another permitted treatment facility.
(iii) Transport to an offsite treatment facility that is operating in compliance with The Clean Streams Law (35 P. S. § § 691.1—691.1001) and regulations thereunder, and is otherwise capable of accepting and treating leachate from the coal ash storage impoundment.
(10) Impoundments must be designed, constructed, operated and maintained in accordance with the following:
(i) An impoundment must have sufficient freeboard to prevent overtopping, including overtopping caused by the 24-hour precipitation event in inches to be expected once in 25 years. The freeboard may not be less than 2 feet.
(ii) The dike must have sufficient structural integrity to prevent failure. The liner system of the impoundment may not be considered in determining the structural integrity of the dike.
(iii) The inside slope shall be designed and constructed with sufficient protective cover to prevent wind and water erosion, and to preserve the structural integrity of the dike.
(iv) The dike must be capable of withstanding anticipated static and dynamic loadings with a minimum safety factor for the most critical failure surface of 1.5 for static loading and 1.2 for dynamic loading.
(v) The outside slopes of the dike may not exceed 25% unless the following requirements are met:
(A) A horizontal terrace with a minimum width of 10 feet is constructed at each 20-foot vertical rise of the slope, or the Department approves in the permit a terrace with different dimensions.
(B) Surface water on the terrace is collected and discharged so that it does not erode or otherwise adversely affect the stability of the dike.
(C) The final slope does not exceed 50%.
(vi) Dikes and berms must be free of burrowing mammals and plants with root systems capable of displacing earthen materials upon which the structural integrity of the dikes or berms is dependent.
(vii) An impoundment must be surrounded by structures sufficient to prevent surface runoff from a 25-year, 24-hour precipitation event from entering the impoundment.
Cross References This section cited in 25 Pa. Code § 290.408 (relating to storage impoundments—scope).
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