WAC 173-306-450
Liner and final cap design and
construction standards. (1) Applicability. This section
applies to owners or operators of facilities that monofill
combined or separated special incinerator ash, except as WAC 173-306-400 provides otherwise.
(2) Liner design.
(a) Owners or operators who monofill combined or
separated fly ash and bottom ash shall comply with the
requirements of Design A, subsection (3) of this section.
(b) Owners or operators who demonstrate ability to
maintain the permeability requirements of Design B during an
eighteen-month demonstration period may seek approval to use
Design B following the demonstration period.
(3) Design A.
(a) General requirements. Owners or operators shall
comply with the liner inspection requirements of WAC 173-306-440 (4)(d) and siting and design requirements of WAC 173-306-440 (3) and (4). In addition, owners or operators
shall:
(i) Thoroughly compact ash residues. Owners or operators
shall compact ash residues thoroughly by using compaction
equipment.
(ii) Provide daily cover to prevent fugitive dust
emissions and run-on and runoff discharges. Cover material
may include high density polyethylene or any department
approved equivalent material.
(b) Liner design. The liner must be an engineered liner
of the following design from bottom to top:
(i) 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. The foundation slope must be a
minimum of two percent;
(ii) Next, a single composite liner consisting of an
engineered soil liner at least two feet thick that has
permeability of 1 x 10-7 cm/sec or the equivalent upon which a
synthetic liner of sixty mils high density polyethylene or
other material of equivalent mechanical strength and chemical
resistance is placed. Liner slopes must be a minimum of four
percent;
(iii) Next, a leachate detection system consisting of a
minimum of twelve inches of sand or equivalent material with a
permeability greater than or equal to 1 x 10-2 cm/sec with
drain pipes;
(iv) Next, a synthetic liner of sixty mils high density
polyethylene or other material of equivalent mechanical
strength and chemical resistance;
(v) Next, a leachate collection and removal system that
consists of a minimum of twelve inches of sand or equivalent
material with a permeability greater than or equal to 1 x 10-2
cm/sec with drain pipes; and
(vi) A fabric filter placed between the drainage layer
and the first lift of special incinerator ash.
(4) Design B. Owners or operators who monofill combined
or separated fly and bottom ash shall comply with these design
criteria.
(a) General requirements. Owners or operators shall
comply with the liner inspection requirements of WAC 173-306-440 (4)(d) and siting and design requirements of WAC 173-306-440 (3) and (4). In addition, owners or operators
shall:
(i) Compact ash residues to a permeability of 1 x 10-5
cm/sec. All ferrous material will be removed using magnetic
separation or an equivalent method approved by the department
so that the pozzolanic effect of compacted ash will not be
impeded.
(ii) Lifts will be tested for ash permeability using
guidance established by the department. Lift thickness before
compaction may not exceed one foot.
(A) Design B liner design may be used as long as lift
permeability tests at 1 x 10-5 cm/sec or less.
(B) If the ash permeability requirement cannot be
maintained, the owner or operator shall immediately close the
Design B cell according to the closure requirements of WAC 173-306-410 and subsection (5) of this section and resume
disposal activities using the Design A liner.
(iii) Provide daily cover to prevent fugitive dust
emissions and run-on and runoff discharges. Cover material
may include high density polyethylene or any department
approved equivalent material.
(b) Liner design. The liner must be an engineered liner
of the following design:
(i) 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. Foundation slope must be a minimum of
two percent;
(ii) Next, a single composite liner that consists of an
engineered soil liner at least two feet thick that has a
permeability of 1 x 10-7 cm/sec or the equivalent upon which a
synthetic liner of sixty mils high density polyethylene or
other material of equivalent mechanical strength and chemical
resistance rests. Liner slopes must be a minimum of four
percent;
(iii) Next, a leachate collection system that consists of
a minimum of twelve inches of sand or equivalent material with
a permeability greater than or equal to 1 x 10-2 cm/sec with
drain pipes; and
(iv) A fabric filter placed between the drainage layer
and the first layer of special incinerator ash.
(5) Final cap design. All owners or operators of special
incinerator ash monofills shall comply with the following
design requirements.
(a) The final cap shall maintain a surface slope between
two and five percent and side slope of no more than
thirty-three percent and shall consist, from bottom to top,
of:
(i) Two feet of ash, well graded (with ferrous material
removed and having proportional size distribution of ash
particles) and thoroughly compacted;
(ii) Next, a layer, system, or mechanism capable of
detecting cap failure;
(iii) Next, a fabric filter overlaid by at least two feet
of clay that has a permeability of 1 x 10-7 cm/sec upon which a
synthetic liner of sixty mils high density polyethylene or
other material of equivalent mechanical strength and chemical
resistance rests; and
(iv) Eighteen inches of native soil covered by six inches
of topsoil.
(b) Final cap inspections must be done in accordance with
the liner inspection requirements of WAC 173-306-440 (4)(d).
(c) In case of cap failure, immediately notify the
department with a plan for remedial action.
[Statutory Authority: Chapter 70.138 RCW. 00-19-018 (Order
00-17), § 173-306-450, filed 9/8/00, effective 10/9/00;
90-10-047, § 173-306-450, filed 4/30/90, effective 5/31/90.]