Closure criteria

In addition to sections 33.1-20-04.1-05 and 33.1-20-04.1-09, at closure, an owner or operator shall cover an existing unit with a layer of compacted soil material having a thickness of eighteen inches [45.7 centimeters] or more, and a saturated hydraulic conductivity of 1 x 10-7 centimeters per second or less. A second layer of twelve inches [30.5 centimeters] or more of clay-rich soil material suitable for serving as a plant root zone must be placed over the compacted layer. At least six inches [15.2 centimeters] of suitable plant growth material must be placed over the covered landfill and the facility planted with adapted grasses. The total depth of final cover must be three feet [91.4 centimeters] or more. The requirements of this section may be modified by the department if the permit applicant demonstrates that an alternative design will appropriately limit percolation of liquid into the waste. The owners or operators of CCR landfills subject to chapter 33.1-20-08 are excluded from the provisions of this section. 1. If the permit applicant wishes to pursue an alternative cover design, one of the following methods shall be used to demonstrate that the alternative cover design will appropriately limit the amount of percolation that may enter the waste: a. Hydrologic modeling; b. Lysimetry or instrumentation using a field-scale test section; c. Comparison of the soil and climatic conditions of the site with the soil and climatic conditions at a site where the department has previously approved the same alternative cover design; or d. Other method approved by the department. 2. To demonstrate that an alternative cover design will appropriately limit percolation of liquid into the waste, the alternative cover design must be shown to limit the average rate of percolation of liquid into wastes to an equal or lower value than the final cover design described in this section or to an average long-term percolation rate less than 0.2 inches [5.0 millimeters] per year.