Soil based Treatment Facilities
Again there are many different ways to design a soil based septic system within the bounds of the 2009 Standard of Practice. Also just because they are allowed by the Standard of Practice does not mean they are the best solution for your acreage.
The one single design factor that will increase the life of your investment is to make sure the complete treatment area is flooded with effluent each time the tank discharges. In this way the whole area required by the design will do a little bit of the treatment and no single area will get saturated.
So designs, such as chambers and stone trenches that are syphon fed from one end are doomed to failure from the start. They rely on the bio mat sealing up the first portion of the trench before using the next portion. In a short time the whole trench is covered with bio mat and the system fails.
Standard tile and stone
This is the treatment field or leech field that most people are familiar with. 12” of screened drainage stone with 3 or 4 inch perforated plastic pipe running the length of the trenches.Simple and good. Life doesn’t have to be complicated so if possible stay with the tried and true. Can be syphoned or pumped from the tank. Pumped is better as the effluent is forced to flow down the full length of the trench pipe. With syphon systems the effluent usually only runs the first ten or twenty feet of the trench and does not use the whole treatment bed to its best advantage. As the first section of the trenches (laterals) get clogged up with bio mat the effluent is force to flow farther toward the ends of the runs. Eventually the effluent reaches the ends of the runs because the
rest of the run is clogged. As the effluent continues to run over the bio mat, there is no chance for recovery (breaking down of the bio mat) so the whole system goes into saturation and anaerobic conditions which can no longer treat the effluent and the system fails.If this is the soil based treatment facility that is to be used for your acreage, it is best to introduce the pumped effluent into the middle of the trench runs through a control mechanism rather then using a distribution box or a header system. Both make it hard to get equal distribution to the different lines, need to stay exactly level and use less of the trench with each discharge.
Pressure tile and stone
This is one step up from the traditional tile and stone. The effluent is distributed by pump pressure to emitters place evenly along the pipe in each trench. This allows for equal distribution of the effluent to each square inch of infiltration area. In sandy soils, the Standard of Practice requires that all effluent is delivered under pressure. If this is not done, all the effluent will simple drain through the first ten feet or so of the trench and will form a plume of untreated effluent the may reach the water table.
Chamber and chamber and pressure
Chambers are designed to create a void for the effluent to flow into. In this they are similair to drainage stone. They are often dosed by letting the effluent simply run into the end of the chamber. This is a very poor way of distributing effluent and the system will fail.Chambers are also sometimes used with pressure distribution. Again this is similar to pressure distribution in a tile and stone system. This can be a good system when drainage stone is not available or very expensive, however it is not on par with pressure distributed stone systems.
Raised treatment mounds
Raised treatment mounds are used when the ground water or seasonally saturated soil are to close to the surface. The 2009 Standard of practice calls for five feet of separation between the infiltration zone (bottom of the stone or chamber) and the first occurrence of standing water or evidence of seasonal saturation. This distance may be reduced to three feet if secondary treated effluent is applied. In the case of the raised mound, the
treatment system is raised with wash sand, which provides secondary treatment therefore the three-foot rule would apply. The mound itself consists of 12 inches on sand on top of the existing soils with either stone or chambers containing a pressure distribution system. If the saturation zone is higher then three feet below the surface more sand must be added to reach the three-foot separation. Can be used in conjunction with time-dosed effluent to reduce mound foot print They can be the answer for small lots or difficult soils