Alternative Septic Systems

Alternative Septic Systems are commonly mistaken to be inferior septic systems. Calling a system alternative just means that the system uses technology that is an alternative to a Conventional Septic System.

There are several types of Alternative Septic Systems, but the most common are: (click any system name to jump to that section)

North Carolina Low Pressure Pipe System (LPP)

North Carolina Modified Low Pressure Pipe System (MLPP)

Typically, an alternative septic system will perform better than a conventional system. This is due to the fact that alternative technology tends to do a better job of distributing the wastewater once it leaves the septic tank.

The common fallacy with the Conventional Septic System is being an "on-demand" system (something comes in, something must go out). This does not allow the septic tank, or the disposal trenches, ample opportunity to "work and rest". Most Alternative Septic Systems (not all) have a big advantage over conventional systems, in that they have the additional tank with a pump inside that sends wastewater to the disposal trenches.

The advantages of a tank and a pump are two-fold. One, wastewater can be stored in the second tank until enough has accumulated to "dose" the disposal trenches. Two, all of the trenches can receive part of the wastewater during each dosing cycle. Meaning, instead of all of the wastewater going into one trench, it can be "spread-out" over 2, 3, or more trenches. This will help to reduce over saturation that is commonly experienced with conventional gravity septic systems.

Systems with a pump (pressurized systems) achieve the more preferred work and rest type of system. The system receives a dose (work), and then has time for the trenches to dry-out (rest).

North Carolina Low Pressure Pipe System (LPP)

North Carolina is credited with creating the Low Pressure Pipe system (LPP). The LPP is typically a two-tank system, with a mechanism (pump, siphon, etc.) to allow pressurized dosing of the system trenches, commonly called laterals. Take a look at the simplified drawing below to note the typical location of the components.

Typical LPP Septic System Layout: Click the image to enlarge

The biggest advantage of the LPP system is the uniform distribution of the wastewater in the disposal trenches. By using pressure, ALL of the trenches get a smaller amount of wastewater. And, since the system can store wastewater, the trenches are allowed to rest during doses. This type of uniform dosing and resting makes it more difficult for a Biomat to form. Thereby giving the system a far greater chance of having a longer life.

The disadvantage to this type of system is the initial cost. Many states require that LPP systems be designed by a registered Professional Engineer. Depending on the requirements of the state, or county within the state, the price can range from $300.00 to upwards of $2500.00 per design. Additionally, some states will not allow LPP systems to be designed from a "perc test". Although I personally would not want a perc test done for a home where I was considering a septic system, they are cheaper to have done. The alternative is to have a soil map done by a soil scientist.

Another additional cost over a conventional gravity septic system, is the second tank (pump tank), plus the pump and electronic controls. Still, I would prefer the LPP to a conventional gravity septic system.


North Carolina Modified Low Pressure Pipe System (MLPP)

The Modified LPP system is the same as the LPP system, with the exception of Modifying the area of soil where the trenches will be installed. This is done in areas where the soils for a systems are suitable, but the depth of the soil is just shy of being adequate. Soil is added on top of the ground to artificially raise the bottom of the disposal trench. Meaning, if a trench were normally to be dug to a depth of 18 inches into the original soil, adding 6" of topsoil would mean the trench is now only 12 inches into the original soil. See below.

Click the image to enlarge

Conventional Septic System - What is a Conventional Septic System?

This is the most common type of septic system that people are familiar with (hence, Conventional). Conventional Septic Systems are identified by names like: Conventional, Overflow, and Leach Field System.

Here is a typical Septic System Layout:

These names all refer to the same type of system. Don't get confused by the different names. The term Overflow is actually the most accurate way to describe the operation of your septic system. Wastewater from your plumbing (sinks, showers, commodes, etc.) flows by gravity to the inlet of your septic tank. This is the beginning of the process of treatment and disposal.

The inlet of the tank should be equipped with either a baffle, or a pipe fitting that diverts the wastewater downward as it enters the tank. The reason that the wastewater is diverted downward is to attempt to increase the amount of time that the wastewater "spends" in the septic tank. This time is referred to as "Detention Time". Over time, materials in the wastewater stream that are heavier, and lighter, than water will separate (sink and float) within the septic tank.

It is very common for a homeowner to notice that their drains are running slow, and look inside their tank to see that the inlet baffle is clogged. Many will simply remove the baffle. Without this baffle, wastewater now has the potential to "short-circuit" the detention time by flowing over the top of the "floatable" layer in the septic tank. This will likely begin the ultimate failure of the septic system.

Here is a typical Septic System Break-Out: Neighbors will love you if this is in your backyard!! This WILL smell!

So, if the baffle is working properly, wastewater will flow through the septic tank, and eventually "Overflow" the outlet of the tank. The septic system must now have a place to make the overflow go away. This is where the trenches in the yard come into play.

The trenches receive the overflow from the septic tank by gravity. Once the septic tank is full (usually within 5 to 10 days after moving into the home), the system becomes an "on-demand" system. Meaning, what-goes-in, must-go-out. There is NO storage in the septic tank. So, the treated wastewater begins to fill the disposal trenches.

As the water enters the trenches, it begins to percolate (hence, the term "perc test") into the soil below the trenches. The trenches are all connected together with the same "overflow" technology as the rest of the septic system (gravity is very cheap!). If you have multiple trenches, the first trench will likely be the only trench receiving wastewater. This trench will eventually become saturated (stay wet all the time), and because of lack of oxygen, will form a "Biomat" in the bottom of the trench. This Biomat will act like a liner in the bottom of the trench, and will prevent the wastewater from percolating into the soil below. Now, the wastewater "overflows" to the next trench.

Here is another view of the same Septic System Break-Out:

Eventually, all the trenches will form a Biomat, and the wastewater will have to find a new place to go. There is usually no place left to go, but up. Wastewater will now begin to "break-out" onto the surface of the property. Surfacing of wastewater is always a sign of a problem.

As the owner, you will now be required to install the back-up disposal system. If there is no area reserved for a back-up system, then a connection to public sewer may be required. If there is no public sewer available, then you will have to find a very expensive solution, or vacate the home.

Please Contact Me before this happens to you.

Basic Understanding Of Septic Systems

Septic Systems fall into a few basic categories:

Conventional
Alternative
Experimental

Conventional Septic Systems
This is the most common type system that people are familiar with (hence, Conventional). They are identified by names like: Conventional, Overflow, and Leach Field System.

These names all refer to the same type of system. Don't get confused by the different names. For a more in-depth description see my entry Conventional Septic System - What is a Conventional Septic System?

Alternative Septic Systems
These systems are typically a little more high-tech, and are used when limitations would not allow the use of a conventional septic system. Limitations could include:
- Shallow soils
- Marginal Soils
- Limited amount of suitable soils

Continuing to call them Alternative systems suggests that they may have a reduced ability to perform. Conversely, these systems usually have a higher success rate than Conventional Systems. For a more in-depth description see my entry Alternative Septic Systems

Experimental Septic Systems
These systems are very rare, and usually only exist in states that have an experimental program. These systems will typically require a Restrictive Covenant be placed on the property deed, as well. Property with this type system is usually very difficult to re-sell, and should only be considered in if the owner never intends to sell the land.