§ 20360. SWRCB - Subsurface Barriers. (C15: s2545)
(a) Subsurface barriers are cutoff walls or grout curtains which are used in conjunction with natural geologic materials to assure that lateral hydraulic conductivity standards specified in Article 3 of this subchapter are satisfied. Paragraphs (b) and (c) specify conditions under which cutoff walls and grout curtains, respectively, are used.
(b) Cutoff walls.
(1) Cutoff walls are required at Class II Units where there is potential for lateral movement of fluid, including waste or leachate, and the hydraulic conductivity of natural geologic materials is used for waste containment in lieu of a liner. Cutoff walls shall be installed at Class III landfills as required by the RWQCB.
(2) Cutoff walls shall be:
(A) a minimum of two feet thick for clay materials; or
(B) a minimum of 40 mils (i.e., 0.040 ") thick for synthetic materials; and
(C) regardless of the option under ¶(b)(2)(A or B), shall be keyed a minimum of five feet into natural geologic material which satisfies the applicable hydraulic conductivity requirements in Article 3 of this subchapter.
(3) If cutoff walls are used, excavations for Units shall be keyed into natural geologic materials which satisfy applicable hydraulic conductivity requirements in Article 3 of this Subchapter.
(4) At closure of a waste pile or surface impoundment, all contaminated natural geologic materials present between the cutoff wall(s) and the waste shall be removed and disposed of at an authorized location, or the Unit shall be closed as a landfill.
(5) Cutoff walls shall have fluid collection systems installed upgradient of the structure. The systems shall be designed, constructed, operated, and maintained to prevent the buildup of hydraulic head against the structure. The collection system shall be inspected regularly, and accumulated fluid shall be removed.
(c) Grout Curtains.
(1) Grout curtains may be used as needed to prevent lateral waste movement through fractures in natural geologic materials that otherwise satisfy applicable hydraulic conductivity requirements in Article 3 of this Subchapter. Only fractures that are at or near the surface and are of limited vertical extent may be grouted.
(2) The acceptability of grout curtains for a Unit shall include consideration of:
(A) depth and nature of fracturing; and
(B) fracture orientation.
(3) Grout characteristics shall not be adversely affected by fluid, including waste and leachate, or natural conditions.
(4) Optimum grouting pressure and the placement of grout holes shall be determined by test grouting.(1. New section filed 6-18-97; operative 7-18-97 (Register 97, No. 25).)
Note: Authority cited: Section 1058, Water Code. Reference: Sections 13172 and 13360, Water Code; and Section 43103, Public Resources Code.
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