Nev. Admin. Code § 444.839 - Elevated mound system: Design criteria

1. An elevated mound system must not be constructed on a slope that is:

(a) Greater than 6 percent, if the soils comprising the slope have percolation rates that are slower than 60 minutes per inch; or

(b) Greater than 12 percent, if the soils comprising the slope have percolation rates that are equal to or faster than 60 minutes per inch.

2. At least 4 feet of unsaturated soil or fill material, or any combination thereof, must be maintained between the top of the seasonal high groundwater table or any impervious barrier such as bedrock. On sloping sites, the depth of unsaturated soil and fill material must be increased to maintain a level bed.

3. Percolation tests must be conducted at the depth anticipated by the engineer as being the point of interface of the native soil and sand fill, and at a depth of 20 inches below the surface of the native soil. The size of the required basal area of the elevated mound system must be based on the slowest percolation rate.

4. The fill material for the elevated mound system must meet the following criteria:

Sieve Size	Percent by Weight Passing Sieve
3/8 inch	100
No. 4	95-100
No. 8	80-100
No. 16	45-85
No. 30	15-60
No. 50	3-15
No. 100	0-4

5. Whenever practical, the bed for an elevated mound system must be a rectangular bed with a long axis that is parallel to the contour of the slope to minimize the possibility of seepage from the base of the elevated mound. The minimum area of the bed must be based on an estimated flow of 150 gallons per day per bedroom and a design application rate of 1.2 gallons per day per square foot. The bed must be filled with at least 9 inches of clean, graded aggregate that ranges in size from 3/4 to 2 1/2 inches.

6. The basal area of an elevated mound system must be sufficiently large enough to absorb the wastewater before it reaches the perimeter of the elevated mound to avoid the surfacing of the effluent. The minimum basal area must be based on the minimum capacity for a septic tank required by NAC 444.8306 and a design infiltration rate as follows:

Percolation Rate (minutes per inch)	Infiltration Rate (gallons per square foot)
0-30	1.2
31-45	.75
46-60	.50
61-120	.25

7. If the site on which an elevated mound system will be located is:

(a) Flat, the entire basal area, calculated as length multiplied by width, must be used to determine the area needed for the elevated mound system.

(b) Sloping, only the area below and down slope from the absorption bed, calculated as W x (A + I), must be used to determine the area needed for the elevated mound system, where:

(1) "W" equals the width of the absorption bed;

(2) "A" equals the length of the absorption bed; and

(3) "I" equals the required side slope of the elevated mound system as measured from the edge of the absorption bed to the perimeter of the mound in accordance with subsection 8.

8. The side slopes of the elevated mound system must extend in a horizontal to vertical ratio that is at least 3 to 1. The entire absorption bed must be covered with at least 1 foot of topsoil. The topsoil cap, which must be placed at the center of the mound, must maintain a minimum slope of 2 percent away from the crown. Untreated building paper, straw, geotextile fabric, or any similar covering approved by the health authority, must be placed over the aggregate in the absorption bed before the topsoil is placed.

9. At least one observation standpipe which extends down to the fill sand must be installed in the absorption bed.

10. The following is a diagram of an elevated mound:

Click here to view image.

Click here to view image.

Notes

Nev. Admin. Code § 444.839

Added to NAC by Bd. of Health by R129-98, eff. 3-25-99; A by R100-07, 10-31-2007

NRS 439.200, 444.650