PRESSURE DISTRIBUTION SYSTEMS
The household plumbing collects the wastewater and sends it to the septic tank where it is separated into the three layers : sludge, scum and wastewater. In a Pressure Distribution System, the effluent from the tank's 2nd chamber (effluent dosing chamber) is delivered to the treatment field using a pump and small diameter pvc lines with small orifices drilled into each line. It acts much like an underground sprinkler system for your effluent.
The advantage of a Pressure Distribution System is that it helps to ensure that the entire treatment field receives relatively equal distribution of effluent, eliminating over-saturation of just one area that can happen with a Gravity System. Treatment fields receiving effluent via Pressure distribution have a smaller design footprint. A disadvantage of a Pressure Distribution System is the small orifices in the pipes (usually 1/8") can become clogged from mineral build-up over time and need to be flushed and cleaned occasionally.
Examples of Pressure Distribution Systems with different field types are below.
Sand (Raised) Mound Field (Pressure Distribution System required)
-Sand, rock and pipe
-Sand, rock, pipe and chambers
-Sand, pipe and chambers
At-grade Field (Pressure Distribution System required)
-Pipe and chambers
Buried Field (Gravity or Pressure Distribution System)
-Sand/rock and pipe
-Sand/rock, pipe and chambers
Open Discharge (Pressure Distribution Only)
SAND MOUND TREATMENT
Uses Pressure distribution only. A pump in the effluent dosing chamber delivers the effluent to the mound system. Pressure distribution pipes are placed in a bed of aggregates or chambers with a 12” layer of sand below. The wastewater is pumped into the pressure distribution system and sprays into the sand layer, where aerobic bacteria cleans the water.
A sand mound receiving primary treated effluent (Type 1) must be above ground and must have a separation of three feet (AB, SK & MB) or two feet (BC) between the bottom of the sand layer and a restrictive layer or water table. Sand mounds receiving secondary treated effluent (Type 2) may have a reduced sand layer depending upon the regulatory requirements in the jurisdiction in which it is installed. Mounds must be landscaped with grass and be regularly maintained in order to have improved efficiency.
AT-GRADE TREATMENT FIELD
Uses Pressure distribution only. Similar to a raised mound field or a buried field, except the distribution lines are not buried. The lines are placed on the ground, and covered with chambers, which are then covered with mulch to prevent freezing and damage.
At-grade fields are an excellent option for areas with trees. The lines can be woven through the trees in a snake-like pattern, eliminating the need to cut down trees on the property. Because the lines are not buried, it is relatively easy to troubleshoot and maintain access if there is a problem.
Disadvantages of this type of system is that you must have an Advanced Treatment System (upgrade from just a normal septic tank) (see Eco-Options section) which raises the cost of the overall system. However, these costs can be balanced against having to remove trees or requiring major excavation.
A typical At-Grade will perform at a rate 4.3 times better than any subsoil absorption method. Within 2 – 6 years, the entire area of the At-Grade will become infiltrated by local flora and fauna, blending it in with the surrounding terrain. The efficiency of the At-Grade is expected to improve as time passes, decomposition and growth in the area aid in the absorption/distribution of water. Research indicates that At-Grades out perform all other methods of final treatment in high water table areas and tight clay soils. At-Grades perform best in treed areas where protection from wind and vehicles is greatest. The vegetation in the forest provides the best infiltration available. Areas with sloping terrain are preferred, but level areas are also acceptable.
BURIED TREATMENT FIELD
Uses Pressure OR Gravity distribution. For Pressure Distribution, a pump in the effluent dosing chamber delivers the effluent to the distribution lines buried in a trench. Pressure distribution lines are placed in a bed of aggregates or chambers not more than 24" below the surface. The wastewater sprays into the gravel layer (or into the chambers) and is distributed into the in-situ soil for treatment. Pictures to the right are examples of a different buried fields using Pressure Distribution.
Uses Pressure distribution only. Open Discharge systems are sometimes used on farms or acreages. In this system waste enters the septic tank and the wastewater is discharged through a pipe system onto the open property. There are strict provincial guidelines on size of property required to run a direct or open discharge as the discharge must occur a certain distance from the property line and any water source on the property or within a certain radius of the discharge. Refer to the regulations for the jurisdiction the system is located in to obtain information on the requirements and restrictions regarding open discharge systems.