Laterals and orifices can not be more than 30 inches apart and the lateral or orifice closest to the edge can be no further than 15 inches from the edge. The minimum contained surface area needed for a sand filter for a single-family residence of four bedrooms or less is 360 square feet. Most shapes that total 360 square feet are acceptable if the even distribution requirement can be met. Each orifice is protected with an orifice shield. The container itself can either be 2X4 foot enforced inch plywood or oriented strand board both supported by an earthen berm, or a reinforced concrete box designed and inspected by a certified physical engineer.
Setbacks are the same as listed for all sewage disposal areas with one exception.
A bottomless sand filter may be 50 feet from public surface water. The earthen berm is not considered part of the disposal area, but often the berm creates conflicts in siting near property lines and structures. On a surface mounted sand filter, the berm following the required 3 to 1 slope will extend out 12 feet on flat ground. On a downhill slope the berm will extend further. When placing a berm near a house, be aware of the building code which requires a slope away from houses for drainage.