Current through Register Vol. 54, No. 44, November 2, 2024
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.
This section cited in 25 Pa. Code §
290.408 (relating to storage
impoundments-scope).
