Monthly Archives: September 2018

How septic tank works and what goes wrong?

When you live outside of a town area in Western Australia, then your house will need a Septic tank or similar sewerage treatment system. This simple yet effective system is designed to take in all the sewerage from a domestic house or commercial property. There are a few things that can go wrong with a Septic sewerage system to can cause it to fail. Some are fixed simply, while other things need the assistance of a licensed plumber.

What is a Septic System?

A septic sewerage system is made up of a number of components. This includes:

  1. The sewer main. From your house, a PVC mainline is installed by a plumber for the sewerage to flow out. This mainline is laid on a constant slope, usually 1m for every 60m of travel if it’s 100mm sized, which is the most common. This line will also have inspection points that come up to the surface, so if there is a blockage a plumber can access the sewer without digging it up.
  2. The solids tank (or septic tank). The first tank in a septic sewerage system is called the settling or solids tank. The sewerage enters this tank through a submerged right angle inlet. The solids tank fills up to the level of the inlet and outlet and it forms a scum layer on the liquid surface. There is a right angle pipe on the inlet and outlet and this means all fresh sewerage falls into the tank under the scum and the heavy solids sink to the sludge layer at the bottom. In the sludge some of the heavy solids are broken down slowly over time, but this sludge will need to be pumped out and disposed occasionally. As the outlet also has a submerged fitting on it, this means the scum all stays in the solids tank and only semi clean effluent falls into the next tank.
  3. The liquid tank. The liquid tank is designed to received clarified and semi broken down effluent. The remaining light solids will further decompose and fall out of suspension here. They will still form a light sludge in the bottom but this should break down fairly constantly and so the sludge level should never build up like the solids tank. From the liquids tank, the clear effluent either gravity feeds out into the leach drain or is pumped with a small sump pump if the leach drains have to be installed above the septic tanks.
  4. Leach drain. The water comes out of the liquids tank with a low level of solids but still a lot of nutrients ( particularly nitrogen and phosphates) and a high loading of bacteria. The leach drains are a buried long pit with a lot of air space inside it and an easy draining gravel media surrounding the pit to allow effluent to drain away.


What is a leach drain?

A Leach drain also has a number of important parts too. The principle of the leach drain is to catch all the effluent from the liquids tank, spread it evenly across the leach drain field and then let it soak into the surrounding soil. Usually a domestic house has 2 leach drain beds anywhere from 9-15m long depending on the house size. A diverter valve is used on the inlet pipe so the effluent can be directed into on bank at a time. This allows the leach drains to dry out and break down the built up nutrients and recover, to increase their service life. Sometimes when the groundwater level is very shallow or the soil has really low percolating rates, then the local government will request that the leach drain is inverted or semi-inverted. This means that instead of being buried, the leach drain is installed on the surface or slightly dug in. Then a large amount of fast draining sandy soil is used to surround the leach drain and this light well drained soil helps evaporation and nutrient absorption. The parts of a leach drain are:

The drain.

The drain is the main structure of the leach drain. It’s usually made of concrete sections 800mm deep 1m to 1.5m long and has an open bottom. Sometimes the leach drain is also constructed from mesh boxes made from reinforced plastic usually polyethylene, these can blocked easier than concrete but can be useful if the leach area is an unusual shape or is difficult to access. If there is a heavy non absorbing soil or a ground water level that is shallow, then there are wide and flat leach drain modules made from polyethylene that can be used too. Usually in modern times, the modules are covered by a geofabric which is a fluffy white synthetic matting. This matting is designed to let water leach out but it stops roots and sand from covering the holes on the sides and top and blocking the system.









The aggregate.

Surrounding the leach drain modules is a vertical layer of bluemetal or similar large rock aggregate. This layer is usually 300mm to 600mm wide. It’s purpose is to hold the soil back from the outlets of the leach drains and let’s the effluent evenly percolate out across the leach bed so the nutrient loading is not concentrated anywhere.

The surrounding soil.

One of the most important parts of the leach drain is the free part. The leach drain works by spreading the effluent over a large volume of soil. The native microbe population in the soil then set to work on the residual nutrients in the effluent and break them down and absorb them into the structure so the water can evaporate or leach away without causing pollution of the groundwater or your yard.


What are the main problems that go wrong with a Septic System ?

There is sewerage flowing down my driveway…

The most common problem that happens in a septic system is a blockage. Blockages can be in the following parts:

  1. The sewer. If properly built, a sewer should drain properly and self clean any solids. But sometimes something catches on a sharp edge or there is a build up of hard or fibrous material. This is the reason why you shouldn’t flush wet wipes, even the “flushable” wipes don’t work well and can cause a bad stringy mess.
  2. The solids tank. The tank basically gets blocked on the inlet, or the outlet . Occasionally the sludge level in the tank builds up to the point where water can’t move through the system any more.
  3. The liquids tank doesn’t usually get blocked. The only problem could be when sludge falls into the tank and blocks the tank up. If the leach drain is inverted, the main problem that happens is when the sump pump fails. When this happens, the tank and sometimes the solids tank will overflow and cause a real mess which is also a health hazard.
  4. The leach drain. The main blockage in a leach drain is either at the inlet when something solid blocks the inlet pipe so the water can’t fall into the drain. The other problem is when roots or a crust form over the outlet holes and the leach drain can’t percolate effluent out into the soil. This usually shows up with the area around the tanks getting smelly, waterlogged and flooded.

It smells bad…

The other main problem that happens with a sewer is that it stops breaking down sewerage properly and starts to smell. This is usually due to a number of things:

  1. The flow rate in is too much. This may be is the system is too small for the number of people living in the house and can happen sometimes if a lot of people are staying at your house. This usually coincides with an important event like a 21st birthday party or a big family Christmas gathering, and is a classic occurrence of Murphy’s law.
  2. There is too much water and not enough solids going into the septic. This happens if there is a leaking tap or rainwater is draining into the sewer somehow. The bacteria in the septic don’t have enough “food” and go into stress mode, which causes them to start to smell.
  3. Chemicals or too much fat and oil. If you use chlorine or bleach and some other strong cleaning chemicals, then this also causes the bacteria to stress and eventually die. An overload of fats and oils also contributes.

The solution to this is to change the inflow to suit the septic, by sorting the leak or changing the chemicals used to more friendly options. The other thing to do is to add some septic enzymes (a brand we use is Bio-Pak) and then some nutrient. There are a few options for nutrients but the common ones are a tin or canned dog food or some sheep or cow manure. This releases nitrogen and amino acids into the tank and also puts a new population of good bacteria in which help digest all the bad things and get everything back in balance.

There is a big hole in my backyard suddenly..

The other main thing that happens is that either one of the tanks or the leach drain can collapse. This can happen from old age, being made from poor quality materials or usually if someone drives a heavy vehicle or machine over it. While not really a breakdown of the septic, this can be very dangerous and needs to be repaired immediately so people (particularly children) aren’t hurt from falling in the hole or exposure to raw sewerage.

How do you fix the problems?

In the sewer main.

Any sewerage pipework in your house and out to the septic is plumbing work. Its has to be installed or repaired by a licensed plumber as it needs to be constructed properly to comply with the Plumbing standards. If there is a blockage in the sewer, a licensed plumber will also have the tools to either rod out or jet out the blockage and get the sewer clean and flowing again. Sometimes there might be root intrusion or actual damage to the pipework and so a section needs to be excavated up and repaired to make it work again.

In the solids tank.

In the solids tank, unless something is broken then the main thing to fix is removing the sludge build up. This needs to be done by a contractor with a suck truck and a controlled waste license to cart the sludge away. They have a special pump on their truck that can suck up sludge and they clean the tank completely out so that the sludge build up can begin again.

In the liquid tank.

The liquid tank might sometimes get a build up of sludge in it that also needs to be sucked out when the solids tank is cleaned out, this is also good as it gives everything a clean start and gets the system to start working again properly. If the leach drains are inverted in any way or above the level of the liquids tank, then occasionally the sump pump will also fail. If this fails then the pump needs to be pulled out, disconnected by a licensed technician and then replaced with a new one. Small sump pumps are not worth fixing as they are only $300-$500 (for a good one) and you should get 5-10 years out of one. Its more inconvenient to get the pump in and out that for the sake of $100-200, you just replace it with a new one.

In the leach drain.

In the leach drain, most of the components are buried. So to repair the leach drain you need someone with a decent sized excavator and the skill to use it without destroying things too much. Usually the thing that goes wrong is a plug of roots and other debris on the outlets. To fix this, the soil and aggregate on the outsides of the leach drain need to be excavated and then all the blockages and roots cleaned away with a shovel or a pressure cleaner. Then new geofabric and aggregate can be reinstalled and the surrounding soil repacked around the leach drain. Depending on how saturated the soil is with effluent, sometimes this soil will need to be disposed of by a controlled waste license holder as this is classed as septage, or solid sewerage waste.

What if my property is not suited to a septic tank?

There are a number of properties in WA, particularly on the coastal plain that have a high groundwater level. There are also a lot of properties that have heavy clay soil and suffer from waterlogging in winter. These properties would generally be classified as unsuitable for a conventional septic system. Sometimes you can get away with an “inverted” leach drain, where the system is built into a mount of good soil sitting on the surface of the ground level. Gradually these days though Shire Councils are classifying properties as “ATU only” or “alternative systems only” and making the choice over the sewerage system needed much smaller.

In addition to normal septic systems, Oasis Plumbing and Southern’s Water technology have been installing Fujiclean ATU (Aerobic Treatment Unit) systems for around 3 years. These Japanese designed and Australian made systems allow you to build on a property where the soil or groundwater won’t allow you to treat sewerage with a septic system. While a bit more expensive than a normal septic system, they save you money in the long run and also don’t limit your house site selection to suit soil conditions.

I hope we have answered any questions you have. With any problems with Septic Systems, all repairs and excavation for them and the conversion or installation of an ATU system, then send us an email or give us a call on 0407 996 065.