SECTION 330.337. Special Liner Design Constraints

(a) At the discretion of the executive director, owners or operators of Type IV landfill excavations that extend below the seasonal high water table may be required to meet one or more provisions in this section.

(b) The owner or operator of a Type I landfill shall demonstrate that the liner system will not undergo uplift from hydrostatic forces during its construction by using one or more of the following methods:

(1) providing calculations satisfactory to the executive director that the weight of the liner systems, including any ballast, is sufficient to offset by a factor of 1.2 any otherwise unbalanced upward or inward hydrostatic forces on the liner;

(2) incorporating an active or passive dewatering system in the design to reduce upward or inward hydrostatic forces on the liner by a factor of 1.2 and by providing calculations satisfactory to the executive director that the dewatering system will perform to adequately reduce those forces;

(3) providing evidence satisfactory to the executive director that the soil surrounding the landfill is so poorly permeable that groundwater cannot move sufficiently to exert force that would damage the liner; or

(4) providing evidence that the seasonal high water table is below the deepest planned excavation.

(c) The owner or operator shall ensure that the liner is stable during the filling and operation of the landfill through a suitable combination of dewatering and/or ballast, if determined to be required in subsection (b) of this section. These methods shall not be used without prior approval of the executive director.

(d) Any required leachate collection system shall be designed to handle both the leachate generated and the groundwater inflow from materials beneath and lateral to the liner system. The maximum volume of groundwater inflow shall be calculated based on determination of the permeability and potentiometric conditions of the liner system and of the materials surrounding the liner system.

(e) Prior to excavating any unit below the seasonal high water table, the owner or operator shall perform a preliminary foundation evaluation satisfactory to the executive director. The foundation evaluation shall consider stability, settlement, and constructability.

(f) The liner quality control plan as required in §330.339 of this title (relating to Liner Quality Control Plan) shall include the following information for landfills to which subsection (b) of this section is applicable:

(1) the methods and tests to be used to verify that the liner will not undergo uplift during construction and until ballast placement, if required, is complete; and

(2) the measures and tests that will be used to verify that any required ballast meets the criteria established, including, but not limited to, inspections, compaction, weight and density of material, thickness, and top elevations.

(g) Any dewatering systems used to ensure liner stability during construction and filling shall be operated until the executive director determines that such systems are no longer required.

(h) The executive director may determine on a site-specific basis that waste can be used as ballast. If so, the facility operating plan for the landfill shall contain the following requirements.

(1) The first five feet or the total thickness of the ballast, whichever is less, placed on the liner system shall be free of brush and large bulky items, which would damage the underlying parts of the liner system or which cannot be compacted to the required density.

(2) If waste is used for ballast, a wheeled compactor having a minimum weight of 40,000 pounds, or equivalent equipment, shall be properly utilized to reach a compaction density of at least 1,200 pounds per cubic yard. For purposes of determining the required ballast thickness, a density of compacted waste of 1,200 pounds per cubic yard shall be used. The weight of the liner system, including any ballast, must be sufficient to offset any unbalanced upward or inward hydrostatic forces on the liner by a factor of 1.5 when waste is used for ballast.

(3) The liner quality control plan shall also include the method(s) to be used to verify that compaction of waste used for ballast is to a density of not less than 1,200 pounds per cubic yard. If a compactor having a minimum weight of 40,000 pounds is used, no compaction density verification will be required.

(4) If waste is used for ballast, the ballast evaluation report shall also include verification that a compactor having a minimum weight of 40,000 pounds was used or, if not, that compaction was at least 1,200 pounds per cubic yard.

(i) The seasonal high water table shall be adjusted upward, if necessary, as additional data become available after a permit is issued.

(j) If ballasting or dewatering is used, the owner or operator shall submit a ballast evaluation report in a format specified by the executive director in duplicate to the executive director when the owner or operator determines that ballasting or dewatering is no longer necessary. If the executive director provides no response within 14 days of the date of receipt, the owner or operator may discontinue dewatering or ballasting operations. The ballast evaluation report shall include:

(1) verification that the liner did not undergo uplift during construction, using the method identified in the liner quality control plan;

(2) certification that ballast met the criteria established in this section and in the liner quality control plan; and

(3) signature and seal of an independent licensed professional engineer performing the evaluation and signature of the facility operator or his authorized representative.

Source Note: The provisions of this §330.337 adopted to be effective March 27, 2006, 31 TexReg 2502