Low Pressure Pipe ​

The low pressure pipe system is series of pressurized pipes installed in trenches underground for delivering treated wastewater

Common Components Involved ​

Septic Tanks ​

The function of septic tanks in septic systems are to hold back the solid wastes and move on the wastewater. These are normally concrete tanks in the ground which may or may not contain separated compartments. Septic tanks are often crucial part in a septic design. Septic system designs often site septic tanks based first on the local concrete manufacturer. Often times, the capacity of the septic tank sited is dependent on which manufacturer is used. Some manufacturers have longer wait times to manufacturer specific septic tank capacities.

Here is a collapsed septic tank. Visible is the multi-compartments and large volume.

Septic Tank Materials ​

Some septic tanks are made of alternate materials other than concrete, including polyethylene or fiberglass. Some benefits to utilizing these alternate materials is that they are lightweight and can be carried easier with a chain and a small excavator machine. Some septic tanks are so lightweight they can be lifted with several people.

A polyethylene plastic septic tank. Lightweight but often more expensive than concreted.

The water from septic tanks is sometimes called septic effluent. The term septic itself means without oxygen and septic effluent is composed mostly of bacteria and human feces. It is a highly contaminated liquid and human contact is dangerous. Septic tank effluent contains particles of sewage of size 1/16 to 3/16 inch in diameter. The waste strength is measure in Biological Oxygen Demand or BOD.

Septic tank effluent is high in solid wastes and pathogens. It must be further treated.

Septic Tank Function ​

The function of septic tanks in septic systems are to hold back the solid wastes and move on the wastewater to further treatment. The solids can then be pumped at given intervals. The pumping frequency depends on the number of residents in the home and the capacity of the septic tank

Here is a septic tank pumping lookup charge based on residents and capacity.

Secondary Treatment ​

A treatment train is just a combination of technologies (active and passive) in a series that the water flows through. Secondary treatment is the use of aeration or filtration to further remove pollutants from the water as it moves through the treatment train.

Many advanced treatment systems are one tank with multiple chambers inside the tank. the secondary treatment compartment usually utilizes aeration, filtration, or a combination of both. the product of secondary treatment is usually a wastewater of significantly less polluted than primary wastewater.

How much of my yard will this take up? ​

I understand most concerns of homeowners is the impact this will have on their outdoor living space. The combination of tanks required to retain the solids and provide secondary treatment will be completely installed below ground. Unfortunately, it is required to provide access to the tank components through lids that extend at least 2 inches above the ground. The footprint of the tanks is generally 8 ft. wide x 20 ft. long and must be installed downslope of the house. The sewer main will be exiting the house below the final grade and fall at a general 1% slope towards the primary tanks.

Seen above are the typical green lids, generally 3 lids per treatment tank and one or two lids for the dosing tank. Also seen is a control panel which can alternatively be mounted on the house at a greater cost.

Above you can see the tanks without soil and grass cover. These tanks require electricity to power the aeration motors and control panels.

There are a two main different methods of secondary treatment and many, many proprietary products market and also non-proprietary approved proven construction methods for secondary treatment:

• Filtration

• Aeration

Maintenance required for secondary treatment units are typically recommended at 6 month by the manufacturer. The maintenance includes ensuring any aeration motor is functioning properly and free from obstruction and any filtration is cleaned.

Uniform Pressure Distribution ​

The series of trenches in low pressure pipe systems create a pipe network. This pipe contains small diameter holes drilled by the installation contractor. When the pump is turned on the pipe network becomes pressurized and the water distributes evenly over the entire area of the low pressure pipe trenches.

Pressure Distribution is not a new concept. It has been used in other states for decades to alleviate the problem of discharging wastewater into clayey soils. The main idea is to evenly distribute the wastewater load evenly over the entire designed soil absorption area. This is done by pumping the wastewater into a pressurized piping system with holes that literally squirt the water evenly into the designed media.

Pressurized septic treatment systems are often difficult to design. They provide a unique and difficult problem in selecting the properly sized and spaced holes in the pressure piping. Pressure piping are composed of sections of Force Main, Manifold, and one or more Laterals. Force main sections transmit the water from the dose tank to the manifold. The manifold splits the force main to the laterals. The laterals are sections of the pressure network that distribute the water to the soil.

Some problems with designing these systems are there are meeting the square footage per application hole rule and also meeting the requirement for less than ten percent flow loss, all while maintaining two ft. per second velocity.

Often times these systems require a valve system to ensure these rules are met for dosing every area uniformly. The low pressure pipe system is actually quite difficult to design because of the large amount holes and often have large flow rates. The high flow rates often lead to a large pump which often isn't easily attainable.

A distributing valve splits flow and alternates dosing different zones