Virginia Law

A. A pad is an absorption area wider than three feet but not longer than 100 feet with a level infiltrative surface where the bottom of the pad meets the original soil. The minimum standoff to a limiting feature in accordance with 12VAC5-613-80 is to be met under the entire infiltrative surface.

B. The minimum effluent quality dispersed to a pad is TL-2 effluent and pad bottom loading rates shall not exceed the values for pads noted in Table 5.5 of 12VAC5-610-950.

C. The longest dimension of the basal area of the pad, its length, shall be oriented parallel to the natural surface topographic contours. Minor deviations from surface contours are acceptable as long as the bottom of the pad is level (the entire bottom surface of the pad is at the same elevation, not to exceed 10% of the depth of the pad from the ground surface or plus or minus two inches, whichever is less), and intersects a similar soil horizon across its surface.

D. Pads and trenches may be used together in a single system when the respective pad or trench subsystems follow the respective design criteria found in this chapter and are separated by a minimum of six feet between the sidewall of the pad and the trench. When multiple pads are used on a site, the pads must be separated by the width of the pad as measured perpendicular to the natural surface topographic contour.

E. Pads shall be limited to sites with slopes of 10% or less (less than or equal to 10 feet of rise for every 100 feet of run).

F. All pads must be dosed. Pad systems over 1,000 gallons per day must be pressure dosed. When pads are installed at less than 12 inches from the ground surface, timed dosing shall be used to disperse the effluent.

G. The minimum absorption area for single family residential dwellings shall be 400 square feet.

H. Pad construction.

1. Gravel pads shall have a minimum installation depth of 12 inches, unless in Texture Group I or II soils where the installation depth can be reduced to eight inches. On sloping sites, the minimum installation depth is measured on the downhill side of the pad infiltrative surface. The construction of the pad's gravity percolation line and gravel bedding shall follow 12VAC5-610-930 E with the exception that the bottom of the pad is level and not sloping. Piping shall have a maximum center to center spacing of nine feet.

2. Gravel pads utilizing low pressure distribution shall follow 12VAC5-610-940 for construction and dosing cycle (volume). Gravel pads using low pressure distribution shall have a minimum installation depth of 12 inches, unless in Texture Group I or II soils where the installation depth can be reduced to eight inches. On sloping sites, the minimum installation depth is measured on the downhill side of the pad infiltrative surface. Piping shall have a maximum center to center spacing of nine feet.

3. Pads utilizing gravelless material as found in 12VAC5-610-930 F shall follow 12VAC5-610-930 F and manufacturer instructions on minimum depth of installation, but in no case shall a pad be installed at less than eight inches from the original soil surface. Gravelless material shall have a maximum center to center spacing of nine feet. On sloping sites, the minimum installation depth is measured on the downhill side of the pad infiltrative surface.

4. Designs supported by a division approved manufacturer's design manual may deviate from the maximum slope, depth of installation, separation distance between pads, and timed dosing when the dispersal area is constructed in accordance with the approved manual.

I. The minimum soil cover, after settling, shall be six inches as measured from the finished ground surface to the uppermost limit of the dispersal media (or gravelless material) utilized in the absorption area. If the cover is mounded above grade, the finished sideslope cannot exceed 1:4 (rise:run). The soil cover, with amendments as needed, shall be of a quality, character, and fertility suitable to establish a vegetative cover that is uniform and sufficiently mature to survive and inhibit erosion.