Aerobic treatment units are built of concrete, fiberglass, or plastic. All materials are not equally durable, and we don’t recommend plastic tanks. Our experiences have not been good and other installers we know agree. Norweco is the exception.
Concrete tanks are massive and require more substantial equipment to carry them when on the job site. This can delay installation during wet periods. Some concrete systems incorporate the trash tank, aeration chamber, clarifier, and pump tank into a single structure. Others include the trash tank, aeration chamber, and clarifier in one structure. These are called an “all-in-one system.”
There are multiple advantages to having the components in one structure. The first is that the system can be delivered pre-built. The installer also only needs to dig one hole with a level bottom in which to set the tank. This reduces installation time. Finally, there is no chance of pipe separation between the tanks so for less experienced installers there is no chance for error.
Drawbacks to this type of system are if something breaks in the system they are not all easily accessible to repair. It could maybe call for the whole top being removed. That will take a backhoe or crane to accomplish and is not cheap to do. There are many manufacturers of all in one system, as they are the most cost-effective way to make a system. Also, most are not new designs; just copies of the original JET system with a different aeration pump like a Hiblow, or Gast rotary vane pump.
Fiberglass tanks are light enough to be carried to the installation site by a small track hoe or backhoe. Often, even just manpower will do the job. They have an aeration chamber and clarifier in one structure. They are built very robust and thick and last a very long time. A separate concrete trash tank and pump tank accompany the aeration chamber and clarifier.
Fiberglass is becoming less prevalent in some areas due to cost. An all-in-one type system cost $440-500 in concrete and less than 50 dollars in rebar for a manufacturer to pour and can be done in hours for a whole system. With fiberglass, you only get one tank for about the same cost.
Both tank types can meet your wastewater management needs. The systems must be installed according to manufacturer specifications and must be watertight to prevent groundwater from entering the system and overloading the treatment unit and land application area.
Plastic or Poly Septic Tanks
Plastic septic tanks or poly tanks are also an option. However, we advise you to avoid this option. They implode, collapse, and/or float. The problem with a poly tank is that it is not as strong as concrete or fiberglass. A lot of installers like them because they save weight and are easy to move around but at the cost of long-term dependability. Infiltrator, Snyder, Norwesco, Nuconsept are some examples of poly tank manufacturers. Poly tanks also float very easily if not secured properly with ground anchors.
The tanks, like we said above, have significant issues with ground pressure collapsing them. Because of their inherently weak structure, backhoe operators can’t properly consolidate the earth around the systems. As the earth settles around the tanks, more and more pressure is put on them, causing multiple things to happen to the tanks and pipes going into the system.
One more thing that can happen is the pipes entering the system or leaving the system will not stay level due to the earth around the tank sinking proper term is settling. This elevates the pipe in the septic tank, holds the water in the pipeline, and things that are transported in the pipe like toilet paper get stuck. All of these things cause backups in the house and expensive repairs down the road.
Another thing that is common with plastic tanks is that they just don’t hold up. Like we said above, they tend to collapse after a while. The sides and top are obviously where this happens, and it makes servicing them very difficult. It’s also not uncommon for the walls to crack and open up either from this letting dirt inside. When this happens, the tank is ruined and needs replacing. We definitely recommend going with a concrete or fiberglass tank. It’s more of an initial investment, but you save a lot of money on repairs and replacements down the road.