Current through Register Vol. 48, No. 38, September 20, 2024
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.
