The absorption area receives the liquid from the septic tanks and distributes it over a specific area. This liquid is filtered through the soil under pipes and is treated by the components of the soil.

The size of the absorption area is based on the size of the home and the percolation rate of the soil. Pennsylvania state law requires that there be at least 4 feet of usable soil for the liquid to distribute through before it reaches the water table.

In-ground absorption areas

The in-ground absorption area may consist of a seepage bed or trenches.

A seepage bed is one large excavation. The bottom is covered with 12 inches of aggregate (stone) and multiple pipes are laid on top, 3 to 5 feet apart. These pipes are covered with aggregate, then geotextile fabric, and finally dirt.

A trench absorption system consists of two or more excavated trenches in which perforated pipes (laterals) are laid on top of aggregate.

Equal distribution of the liquid is very important to ensure the proper functioning of the system. Uneven distribution could result in one of the areas being overloaded, leading to the failure of a system. In all trench systems and some seepage beds, a distribution box is used to split the flow equally to all individual pipes. It is important that the box remain level so that the liquid flows equally from each pipe.

Pressure dosed systems

Some systems require pressure distribution because of permeability characteristics of the soil. With this type of system, the liquid from the septic tanks flow by gravity into a pump (dosing) tank. From the pump tank, the liquid is forced into the pipes in the absorption area. Because the flow into the absorption area is controlled, the pipes discharge the liquid at the same rate throughout.

The pump located in the pump (dosing) tank is equipped with an alarm that will sound if a pump malfunction occurs. It is very important that the necessary repairs are made as soon as the problem is found. Failure to make these repairs could damage the absorption area and result in very costly repairs.

Elevated Sand Mounds

The elevated sand mound is used in areas with low permeability, shallow soils, and poor drainage characteristics. These soils require the addition of sand above the ground to provide for enough filtration of the sewage before it reaches the water table. This absorption area is constructed similarly to a seepage bed or trench, except that the system requires pressure distribution and a layer of sand must be placed between the crushed stone and the soil cover. A soil berm is placed around the mound to protect it and provide for grass cover.

The sand mound is served by a septic tank followed by a pump (dosing) tank that must be equipped with an alarm. This alarm will sound when a pump failure occurs, alerting the homeowner to the problem. It is very important that the necessary repairs are made as soon as the problem is found. Failure to make these repairs could damage the sand mound system and result is very costly repairs.