Section 410IAC6-10.1-88. Elevated sand mound on-site sewage systems: design of basal area

   (a) The dimensions of the basal area shall be as long and narrow as the site allows, in compliance with the requirements of subsection (c).

  (b) Numerical dimensions provided in this section for basal area and elevated sand mound size are rounded up to the nearest whole number.

  (c) The size of the basal area shall be determined from the following:

(1) The minimum size of the basal area shall be calculated as:

Minimum basal area (ft2)(BA)	=	DDF (gpd)
		soil loading rate (SLR)

using the soil loading rates from Table VI in section 80(b)(7) of this rule. The soil loading rate used for this computation shall be the soil loading rate of the most restrictive horizon in the first twenty (20) inches below the ground surface.

(2) The minimum length for the basal area (BA_L) shall equal the length of the aggregate bed (AB_L).

(3) The minimum width of the basal area (BA_W) shall be calculated as the greater of:

	(A)	Minimum basal area width =	minimum basal area (ft.2) (BA)	; or
			length of aggregate bed (ft) (ABL)
	(B)	Slope	Minimum Basal Area Width (BAW)
		0% ≤ slope ≤ 1/2%	Aggregate bed width + 14 ft.
		1/2% < slope ≤ 6%	Aggregate bed width + 9 ft.
	(C) The dimensions determined from clause (A) or (B) for the INDOT Specification 23 sand shall maintain a minimum sideslope grade of three-to-one (3:1).

  (d) The location of the basal area within the elevated sand mound shall be:

(1) on sites with slopes of one-half percent (1/2%) or less, the area under the aggregate bed and extending an equal distance from each side along the length of the aggregate bed; and

(2) on sites with slopes greater than one-half percent (1/2%) and less than or equal to six percent (6%), the area under the aggregate bed and extending directly downslope from the aggregate bed.

  (e) The design of the basal area shall be for:

(1) sites with slopes one-half percent (1/2%) or less; or

(2) sites with slopes greater than one-half percent (1/2%) and less than or equal to six percent (6%).

  (f) The basal area shall be constructed on the tilled surface of the soil absorption system site in accordance with the provisions of section 94 of this rule.

  (g) The long axis of the basal area and elevated sand mound shall be constructed along the contour of the soil absorption system site.

  (h) The minimum depth of the INDOT Specification 23 sand under the aggregate bed shall be twelve (12) inches.

  (i) The INDOT Specification 23 sand shall have a minimum final grade on all sides of three-to-one (3:1).

  (j) The INDOT Specification 23 sand used in the elevated sand mound shall meet the following standard:

Table XVI - INDOT Specification 23 Sand*
Sieve Sizes	Percent (%) Passing Sieve (by Weight)
3/8 in (9.50 mm)	100
No. 4 (4.75 mm)	95 – 100
No. 8 (2.36 mm)	80 – 100
No. 16 (1.18 mm)	50 – 85
No. 30 (600 μm)	25 – 60
No. 50 (300 μm)	5 – 30
No. 100 (150 μm)	0 – 10
No. 200 (75 μm)	0 – 3
*The sand shall not have more than forty-five percent (45%) retained between any two (2) consecutive sieves.

  (k) Figure 1 in section 87(d) of this rule presents a visual depiction of the location of the basal area within the elevated sand mound. (Indiana State Department of Health; 410 IAC 6-10.1-88; filed Oct 19, 2012, 2:07 p.m.: 20121114-IR-410120157FRA)