Off Mains Drainage & Sewage Problems…
Most of us are on the mains and rarely ever think about it. When we use the lavatory or dishwasher, it just goes down the pipes to the mains, and we never think about it again. In the UK 96% of households are on the mains, that is to say, connected to a pipe in the road, which is pumped to or gravitates towards a municipal shared treatment plant, rather than an individual sewage treatment plant These are really big factories for cleaning the foul water, and sending the treated effluent into our river systems. Often when it rains heavily, storm water gets into the foul system.
The water companies are permitted to allow a degree of partially treated effluent to outfall into the river. Because of the heavy rain, the river has more water than normal and can tolerate a small amount of partially treated water, so the effect is negligible. However, this often occurs too many times, even when there is not enough water in the river for the right level of dilution. The consequence of this, apart from the fact that the water company is fined a hefty sum, there is water pollution. Fish die. Local natural ecosystems are affected.
Find out what happens when storm water enters your septic tank at home in our blog post: Warning High Rainfalls
How did we handle wastewater treatment in the past?
Towns next to the sea often lay a pipe hundreds of metres into the sea, but if it contains poor quality effluent, people bathing in the sea water are at risk of disease. The UK has more dirty beaches than many other countries in Europe, but individual house owners, up to large wastewater companies, continue to dispose of their water waste without a care. This state of affairs has been developing for the past 200 years. Gradually most villages are connected to a sewage treatment plant. All towns and cities, of course, are easily connected to the main sewage system. The smaller hamlets, isolated farms and cottages, have to fend for themselves, just as everybody did 200 years ago. This makes up the 4% of UK households on off-mains drainage. What was it like for them not having a drainage system to tap into? We used brick built septic tanks with an inlet, and an outlet pipe which was connected to a soakaway in the garden. When the soakaway becomes choked, a new drain might be added, and simply connected to the nearby ditch, so sewage water would end up in the river, and then into the sea.
You can learn more about soakaways and how they’re built in our blog post: How to Do a Percolation Test, aka the soakaway size calculator!
When I stayed in India, travelling by coach, we had a stop every 2-3 hours on a long distance run. People were bursting and the bus-stop toilet was occupied, so people went into the neighbouring fields, with 2 bricks to squat on. The ground was covered with excrement, and one had to be careful where you walked. This was on a major highway to Calcutter, in Malawi. I stayed in a simple bed and breakfast, but the next morning I came to see where all the waste from the house just formed a wet area in the neighbouring field. Closer to home in Lincolnshire, we have re-dug out an area of surface soakaways. The village sewage treatment plant was very overloaded. There were many more houses, and a far greater use of water (up from 70 litres per head a day to 200 litres a day). This system relied on sewage water evaporating while the part treated effluent was diverted to another part of the surface soakaway. The dried out effluent was taken away by a farmer as fertiliser to grow their cabbages on. Before the invention of primitive modern sewage techniques like this, people shouted before throwing their waste out of the windows into the street below. In France this was “gare de l’eau”, which means “beware of the water”. Later in Edinburgh this saying became “Gardyloo”.
Until 30 years ago septic tanks were emptied into a series of lagoons owned by the local council. When the first lagoon was filled the 2nd lagoon was used, then the 3rd. Eventually the liquid in the sewage had evaporated, and the muck that was left was loaded into farm trailers and used in the farmers field. The government passed a law in the 90s to the effect that septic tank water was to be taken to the water companies largest sewage works to be treated in the modern way. The local village sewage treatment plant was not capable of dealing with such septic material, and so the distance that the sludging wagon had to carry the effluent was considerably increased, making it much more expensive for septic tank emptying, and emptying cesspools. Gradually more and more people were connected to the mains, However this left about 2.5 million people who still have the problem wondering how to deal with sewage in their own gardens. The norm was to use brick septic tanks, but later in the latter part of the last century GRP septic tanks (Glass Reinforced Plastic, or Fiberglass) were more likely to be used. Being properly designed, they did a far better job than the small brick septic tanks. The GRP tanks were designed for modern water usage, not the meager amount that people used in the Victorian age. This difference in design is why It’s important to ask yourself, how old is my septic tank? They can have a lifespan of 15-40 years, depending on the type.
It’s important to know the details of your septic tank or sewage treatment plant, so you can be sure your system is in line with the General Binding Rules.
How Does Off Mains Drainage Work?
However good a septic tank is in design and volume, the partially treated effluent leaving the tank is a brownish liquid to be disposed of in the garden. The treated wastewater is pumped into Soakaways, or drainage fields. This is generally where drainage pipes are laid on a bed of gravel, a yard wide, and a foot deep, but often simply into a big hole filled with brick, rubble and other building materials. The problem is that without a pump system, the dirty brown liquid, still full of organic matter, was a metre deep in the ground, or often deeper. The soil at this depth is more impermeable than soil on the surface. Initially the water is still laden with fine organic matter and will soak away, providing the soakaway drains were long enough. Generally they were laid in a herringbone fashion, so the pipes were 2 metres apart, laid with a small gradient of 1 in 200 metres (nearly flat), but it still means a drain 1m deep was even deeper after 20m.
How long does a soakaway last? It can be up to 50 years, but once all the pores of the soil are blocked, water can back up into the septic tank. If conditions get worse, like after a heavy rain, then the water is likely to back up into the house drains, affecting the way the lavatory would flush, or the kitchen waste would overflow at the grid outside, spreading untreated effluent onto the paths outside. To remedy this people would add further soakaway drains, extending the soakaway into other parts of the garden, generally at a greater depth than before, getting deeper and deeper into the semi-impermeable subsoil, or getting close to the local water table, as in the Fens (either side of the River Witham). Septic Tank Problems could be caused by a blocked soakaway.
In limestone areas free drainage is the norm, but the environment agency insisted that we put a foot layer of sand below the soakaway. This was to stop treated effluent flowing into the limestone rock and eventually the aquifer, which is the source of our drinking water. This was after it was found water was often affecting the farmers own bore holes, and worse, the water companies bore holes. This contaminates the pure drinking water that the borehole was drilled for. This is how wastewater pollution occurs with off-mains sewage treatment systems too – if the incorrect system is used, or septic tank emptying isn’t employed as much as it should be, so the soakaway backs up. The General Binding Rules and manufacturing guidelines recommend emptying your tank at least once a year. In areas where the dirty water does permeate into the ground properly, and providing the septic tank was emptied of solids every year, the soakaway and septic tank can last a long time.
Modern Sewage Treatment Plants
The fact is, this happy state of affairs is not normally found. Septic tanks were backing up, and the homeowners would have to empty the septic tank not once a year, but twice a year, or even every 4 months or so. Each time costing over £100 or more. Gradually septic tanks were being phased out, and modern sewage treatment plants like the Diamond Sewage Treatment Plant are installed, but where does treated effluent go? Into the same ground as the septic tank water did. Some basic facts from raw sewage from the house has a value of around 300 ppm. The water leaving a properly maintained septic tank was at a value of 200 ppm, clearly still carrying organic matter. A modern sewage treatment plant is required to reduce effluent to less than 20 ppm. When properly emptied and maintained, this is the expected standard.
Learn more about the 5 ⭐ Sewage Servicing and Maintenance we provide!
The treated wastewater from the sewage treatment plant can be discharged easily into a ditch or river. The water looks like clear river water, though you can’t drink it, as some professionals used to claim, as it’s high in nitrates and phosphates. That’s perfect for the garden; it could carry some diseases, but plants with access to this water below the surface thrive on it. This is why another option, if a ditch or river to discharge to isn’t available, is to create a smaller soakaway – the cleaner wastewater means we can install a drainage field at a very shallow depth. The pipe could easily be laid 200-300 cm deep into the vegetable garden (about a foot). It still needs a gravel bed 600 mm by 250mm deep but at this depth the soil is more permeable, and plants will extract the water. On good days, the sun will dry the top soil and crack open the clay soil to depths of 2 metres. Even in a small garden, the percolation tests carried out at a depth of 300 mm is far far better than done at a depth of a meter, even when it’s over parts of the existing soakaway.
Options for off mains drainage
We can say to someone building a new house, the best option generally is to connect to the mains. This can either be by gravity, or connecting to a kind neighbor who is on the mains, or less effectively, by pumping through a standard 32mm pipe. Though the mains is an outdated system with its own problems, it means the responsibility for discarding of your household wastewater lies with the council, and not the homeowner. If this is not possible however, then a sewage treatment plant needs to be employed, which the household will be responsible for, generally with a external pump chamber or pump outlet, allowing for better percolation. Some septic tanks have worked well for many years, and at a very low annual cost (£100-£150) but generally septic tanks, even the well designed GRP tanks, will cause problems in the future. You can use the pump station to improve the effectiveness of older systems that lift the soakaway to a more effective shallow depth, allowing that dirty water to be taken out by evaporation and plant root systems.
We have created a list to summarise your options, starting from the best, to last resort.
Option 1
Using a sewage treatment plant with the water out falling into a ditch.
Option 2
Septic tank with a pump station and shallow soakaway system (drainage field)
Option 3
Sewage treatment plant with no pump, because the land falls away from the unit
Option 4
Septic tank in flat land in permeable sub-soil
Option 5
Septic tank in clay subsoil with a much larger soakaway (drainage field)
Option 6
Septic tank in clay or heavy soil with a small area soakaway
Often if you have a good sized brick or GRP Septic tank, you could install a Septic Tank Conversion like our own Allerton ConSept within the septic tank. This transforms it into a fully functioning sewage treatment plant, producing treated effluent at 20 ppm, instead of 200ppm. If there is a ditch, this is a very good option, similar to option 1. Apart from laying cables by hand, there is no excavation to tolerate or pay for, and the improved functioning saves you time and money on repairs and excessive emptying in the future.
Not sure where to start? Contact us – We’ll get you on the right track!