Low Pressure Dosing (LPD) Systems:
Low Pressure Dosing systems are basically a modified conventional system. The treatment method and quality is the same, traditional septic tanks, which typically remove about 50% of the biological content of the effluent(wastewater) The remainder of the treatment takes place in the soil. The disposal portion of the system is what sets it apart from conventional systems. Instead of gravity flowing into the drain field, the effluent is pumped to the drain field, where each trench is separated from the others, and each has a valve to reduce the pressure of the water in that trench. Typically the pressure is reduced to 1 psi or less, the the Low Pressure. This change provides several significant benefits over conventional systems:
- The drain field no longer needs to be located down grade from the tanks and house.
- The effluent is applied in the top 18-24" of soil, where absorption, transpiration and evaporation are maximized.
- The effluent is applied in periodic doses instead of trickling out into the field when the water is used.
The Dosing component of LPD's is very powerful. Traditionally, when water was used in the home, the water slowly trickled out into the drain field over the next 30-45 minutes, and because of this tended to migrate to the same spot in the drain field. This in turn lead to that spot staying saturated and growing a bacterial slime known as Bio-Mat. Over the course of years, this Bio-Mat slowly spread through the entire drain field and ultimately lead to the drain field failing. By dosing the effluent, the entire drain field gets an even dose, and is given several hours to absorb that dose, and dry some. This dosing cycle has been scientifically proven to tremendously improve the long term reliability of the drain field. The main concern to keep in mind is that the system still depends on the soil to absorb the effluent, so weather and site conditions still impact the long term viability of the system, as well as usage. Any system will fail if the designed usage is exceeded.
Pros & Cons
- Low maintenance cost
- No surface application, thus no chance of coming in contact with the effluent
- Highest reliability of the subsurface systems
- Higher Installation Cost
- No long term guarantee of functioning, if usage or rainfall exceed design parameters