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PDFWAC 173-304-430

Surface impoundment standards.

(1) Applicability.
(a) These standards are applicable to solid wastes that are liquids or sludges containing free liquids as defined in WAC 173-304-100 and applicable under WAC 173-304-015(2) and are stored or treated in surface impoundments;
(b) These standards are also applicable to sludges and septage stored or treated in surface impoundments; and
(c) These standards are not applicable to:
(i) Surface impoundments whose facilities and discharges are otherwise regulated under federal, state, or local water pollution permits; and
(ii) Retention or detention basins used to collect and store stormwater runoff.
(2) Requirements. All surface impoundments must be designed, constructed, and operated so as to:
(a) Meet the performance standards of WAC 173-304-460(2);
(b) Have an inplace or imported soil liner of at least two feet of 1 x 10-7 cm/sec permeability or an equivalent combination of any thickness greater than two feet and a greater permeability to protect the underlying aquifers or a thirty mil reinforced artificial liner placed on top of a structurally stable foundation to support the liners and solid waste and to prevent settlement that would destroy the liner; natural soils shall be recompacted to achieve an equivalent permeability. Owners or operators shall be allowed to use alternative designs, operating practices and locational characteristics which prevent migration of solid waste constituents or leachate into the ground or surface waters at least as effectively as the liners described in this subsection;
(c) Avoid washout including the use of an extended liner or dikes or restriction of flow in the one hundred year flood plain and to comply with local flood plain management ordinances and chapter 508-60 WAC, Administration of flood control zones;
(d) Have dikes designed with slopes so as to maintain the structural integrity under conditions of a leaking liner and capable of withstanding erosion from wave action;
(e) Have the freeboard equal to or greater than eighteen inches to avoid overtopping from wave action, overfilling, or precipitation;
(f) Have either a groundwater monitoring system, or a leachate detection, collection and treatment system, for surface impoundments having a capacity of more than two million gallons unless the jurisdictional health department and the department require either for smaller surface impoundments. For purposes of this subsection, capacity refers to the total capacity of all surface impoundments on-site (i.e., two, one million gallon surface impoundments on one site will trigger these monitoring requirements);
(g) Be closed in a manner which removes all solid wastes including liners, etc. to another permitted facility and the site returned to its original or acceptable topography except that surface impoundments closed with the waste remaining in place shall meet the requirements of WAC 173-304-407 and 173-304-130;
(h) A jurisdictional health department may require that the liner be inspected for wear and integrity and repaired or replaced by removing stored solid wastes or otherwise inspecting the liner or base at any time. The request shall be in writing and cite the reasons including valid groundwater monitoring or leachate detection data leading to such an inspection and repair;
(i) Surface impoundments containing septage will also be subject to the department's "criteria for sewage works design" used to review plans for septage surface impoundments; and
(j) Surface impoundments that have the potential to impound more than ten acre-feet of waste measured from the top of the dike and which would be released by a failure of the containment dike shall be reviewed and approved by the dam safety section of the department.
[Statutory Authority: RCW 70.95.215. WSR 88-20-066 (Order 88-28), § 173-304-430, filed 10/4/88. Statutory Authority: Chapter 43.21A RCW. WSR 85-22-013 (Order 85-18), § 173-304-430, filed 10/28/85.]
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