R 299.4304 Type III landfill final cover design.

Rule 304. (1) The owner and operator of a type III landfill unit shall install a final cover system which is designed to minimize erosion and infiltration to the extent necessary to protect the public health and the environment. (2) If methane or other decomposition gases will be generated within a type III landfill, the owner and operator shall design and employ a means of ensuring that gases cannot travel laterally from the site or accumulate in structures. (3) The owner and operator of a type III landfill shall grade portions of the landfill that have received final cover so as to prevent storm water runoff from entering the active portion. (4) The owner and operator of a type III landfill shall design and operate the landfill so as to bring the active portion up to final grade as soon as possible. (5) To prevent the ponding of water on completed fill surfaces, the grading contours shall tend to forestall development of local depressions due to post-construction settlement. Slopes of the final cover shall not exceed 1 vertical on 4 horizontal or as necessary to permit the establishment of vegetative cover. The final slope for a type III landfill that is a new disposal area shall not be less than 2%, unless the director approves a final cover that is not designed to minimize infiltration, as provided in subrule (7) of this rule, or otherwise approves a variance under R 299.4108. (6) Except as provided in subrule (7) of this rule, final cover for type III landfills shall be comprised of an erosion layer underlain by an infiltration layer, as follows: (a) The infiltration layer shall be comprised of 1 of the following: (i) A minimum of 2 feet of compacted soil that is in compliance with R 299.4913. For new disposal areas, the compacted soil shall also be protected by at least 2 feet of additional soil. (ii) A flexible membrane liner that is in compliance with R 299.4915.when properly sloped and protected by at least 2 feet of soil. (iii) An approved alternative material, when properly sloped and protected, if equivalent protection is provided. (b) The erosion layer shall consist of a minimum of 6 inches of earthen material that is capable of supporting native plant growth. (7) The owner and operator of a type III landfill may install a final cover that is not designed to minimize infiltration if the landfill unit meets the design criteria of R 299.4307(3)(b) and the owner and operator demonstrate that infiltration through the final cover will not violate the performance standards of R 299.4306 throughout the postclosure period.