Section 329IAC10-22-6. Final cover requirements for new MSWLF units or existing MSWLF units that have a composite bottom liner and a leachate collection system

   (a) The owner, operator, or permittee of an MSWLF containing new MSWLF units or existing MSWLF units that have a composite bottom liner system and a leachate collection system shall install a final cover system as defined in subsection (b) within one hundred eighty (180) days on any area in the MSWLF units as approved in the closure plan that:

(1) has received the final waste volume; or

(2) is filled to the approved final waste elevation;

or as approved under section 5(b) of this rule.

  (b) Final cover systems for new MSWLF units or existing MSWLF units that have a composite bottom liner system must consist of the following, starting from the top of the municipal solid waste mass (waste placement) to the top of the final cover system:

(1) A methane gas venting layer must be installed directly over the waste. This layer must consist of twelve (12) inches of drainage layer material that has a hydraulic conductivity of 1 × 10^-3 centimeters per second or more. Geosynthetic material (geotextile, geonet, both, or other material as approved by the commissioner) may be substituted for drainage layer material in the gas venting layer if equivalent or better performance is demonstrated. The owner, operator, or permittee must demonstrate that transmissivity and permitivity provide for the anticipated gas discharge quantity.

(2) A soil barrier layer must be installed over the methane gas venting layer. The soil barrier must consist of a lower component of twelve (12) inches of structural fill and an upper component of twelve (12) inches of compacted earthen material with a hydraulic conductivity of 1 × 10^-6 centimeters per second or less. The upper component must be soil of Unified Soil Classification ML, CL, MH, CH, or OH. Other suitable material approved by the commissioner may be used if it provides an adequate level of protection to human health and the environment. Grain size, Atterberg limits, and hydraulic conductivity tests as approved by the commissioner must be performed to confirm the quality of the final cover.

(3) A minimum thirty (30) mil geomembrane top liner must be installed directly in contact with the upper portion of the soil barrier layer. If the geomembrane is composed of high density polyethylene (HDPE), then it must be at least sixty (60) mil thick. The commissioner may require an increase in the thickness of the geomembrane if it is determined that increased thickness is necessary to prevent failure under stresses caused by construction equipment and waste settlement during the post-closure care period.

(4) A drainage layer must be installed over the geomembrane liner. The drainage layer must consist of twelve (12) inches of material that has a hydraulic conductivity of 1 × 10^-3 centimeters per second or more. If geosynthetic materials are used as a drainage layer, the effective transmissivity must be equivalent to twelve (12) inches of drainage layer with a hydraulic conductivity of 1 × 10^-3 centimeters per second or more.

(5) A top protective soil layer must overlay the drainage layer. This layer must consist of at least eighteen (18) inches of earthen material. If geosynthetic materials are used as a drainage layer, at a minimum, thirty (30) inches of earthen material must be placed on top of the geosynthetic materials. The protective soil layer material must be designed to not clog the drainage layer.

(6) A vegetative layer must overlay the top protective layer. This layer must consist of at least six (6) inches of earthen material capable of sustaining vegetation. In any case, a total thickness of earthen material over the geomembrane top liner must not be less than thirty-six (36) inches.

(7) The maximum projected erosion rate of the final cover must be no more than five (5) tons per acre per year.

(8) The final cover must have a slope no less than four percent (4%) or two and twenty-nine hundredths (2.29) degrees and no greater than thirty-three percent (33%) or eighteen and twenty-six hundredths (18.26) degrees.

  (c) The requirement in subsection (b)(1) may be waived by the commissioner if the following apply:

(1) The MSWLF has a permitted active gas recovery and extraction system in place.

(2) The permitted active gas extraction system at the MSWLF extracts or recovers at least sixty percent (60%) of the total volume of landfill gas produced or generated by the MSWLF.

(Solid Waste Management Division; 329 IAC 10-22-6; filed Mar 14, 1996, 5:00 p.m.: 19 IR 1883; filed Aug 2, 1999, 11:50 a.m.: 22 IR 3861; filed Feb 9, 2004, 4:51 p.m.: 27 IR 1856, eff Apr 1, 2004)