§258.62. Approval of site-specific flexibility requests in Indian country.

(2) Additional cover soil which, prior to placement, shall be wetted to optimal moisture and thoroughly mixed to near uniform condition, and the material shall then be placed in lifts with an uncompacted thickness of six to eight inches, spread evenly and compacted to 90 percent of the maximum dry density, and shall:

(i) Exhibit a grain size distribution that excludes particles in excess of three inches in diameter;

(ii) Have a minimum fines content (percent by weight passing U.S. No. 200 Sieve) of seven percent for an individual test and eight percent for the average of ten consecutive tests;

(iii) Have a grain size distribution with a minimum of five percent smaller than five microns for an individual test and six percent for the average of ten consecutive tests; and

(iv) Exhibit a maximum saturated hydraulic conductivity on the order of 1.0E-03 cm/sec.; and

(3) A minimum six-inch surface erosion layer comprised of a rock/soil admixture. The surface erosion layer admixture and gradations for 3% slopes and 3:1 slopes are detailed below:

(i) 3% slopes: For the 3% slopes the surface admixture shall be composed of pea gravel ( 3/8-inch to 1/2-inch diameter) mixed with cover soil at the ratio of 25% rock to soil by volume with a minimum six-inch erosion layer.

(ii) For the 3:1 side slopes the surface admixture shall be composed of either: gravel/rock ( 3/4-inch to one-inch diameter) mixed with additional cover soil as described in paragraph (b)(2)(iii)(A)(2) of this section at the ratio of 50% rock to soil by volume and result in a minimum six-inch erosion layer, or gravel/rock ( 3/4-inch to two-inch diameter) mixed with additional cover soil as described in paragraph (b)(2)(iii)(A)(2) of this section at the ratio of 50% rock to soil by volume and result in a minimum 12-inch erosion layer.

(iii) The owner and operator shall place documentation demonstrating compliance with the provisions of this section in the operating record.

(iv) All other applicable provisions of this part remain in effect.

(2) Additional cover soil from on-site sources, which, prior to placement, shall be wetted to optimal moisture and thoroughly mixed to near uniform condition, and the material shall then be placed in lifts with an uncompacted thickness of six to eight inches, spread evenly and compacted to 90 percent of the maximum dry density, and shall:

(i) Exhibit a grain size distribution that excludes particles in excess of three inches in diameter;

(ii) Have a minimum fines content (percent by weight passing U.S. No. 200 Sieve) of 12 percent for the average of ten consecutive tests; and

(iii) Have a grain size distribution with a minimum of six percent finer than five microns for the average of ten consecutive tests; and

(1) Top deck slope surface erosion layer requirements: The top deck slope surface erosion layer shall be a minimum six-inch surface erosion layer comprised of a rock/soil admixture. The top deck surface erosion layer shall achieve the following gradation specification:

(i) Exclude particles in excess of three inches in diameter;

(ii) 40% to 75% passing No. 4 sieve

(iii) 10% to 50% passing No. 40 sieve

(iv) Less than or equal to 15% passing No. 200 sieve

(2) Side slope surface erosion layer: The side slope surfaces erosion layer shall consist of a 4-inch thick rock armor underlain by an 8 ounce per square yard (oz/sy) non-woven geotextile filter fabric. The side slope surface erosion rock armor layer shall achieve the following gradation specification:

(i) Exclude particles in excess of three inches in diameter;

(ii) 10% to 40% passing No. 4 sieve

(iii) 0% to 10% passing No. 40 sieve