crooksey

The key to remember here is all to do with the winter water table level. If your tank is deep, there is a chance your drainage field could be below the level of the winter water table (therefore useless). If you have a pumped outlet, you can have the field 300mm below the finished ground level and remove any doubts about winter water table level. Or go gravity, and have an NRV on the drain-field and have an overflow tank, so that in the event your drainage field is under-water, the outlet of the PTP goes into an ancillary tank, that can then be pumped out whenever back to the drain-field when the water table drops. I have been on sites where one winter the water table was -3m, the next winter it was minus 200mm. Sandy soils are worse for high water table as there is no resistance to it (although offer low vp).

At the risk of being marked as "contaminated land" in the future. You are best getting it emptied and jetted, once this is done, if there are no connections to it, fill with soil/hardcore whatever.

Get a pumped outlet, have a very shallow drainage field, it will be fine (as long as the water table is not stupidly high). Or if there is a ditch on/bordering the property, discharge to this. Septic tanks are known for not being horrendous in high water table areas and rely on gravity, so the drainage fields are often set far to low.

He is correct.

Your logic is correct, but flawed in execution. A correctly designed drainage field that matches the percolation rate of the ground (during the winter) and sized accordingly to building regs will have no issues dealing with an output from the graf style outlets (twice a day volumes).

Graf one2clean works with the control module controlling the blower and the pump, if an error code comes about it can throw the cycle off and you will have had no aeration. Once its all running again, if it doesn't go away after 5 days, just get it emptied, it won't go away. Always good to keep a spare pump and diaphragm rebuild kit for any sewage plant owners.

nothing in the tunnel, 70mm+ rocks on the bottom if you follow the spec correctly. Its basically just a huge void, water just hits the rocks and drains away, basically a hollow soak-away with an air vent.

You can use infiltration tunnels with BCO and EA approval, its very quick to get it approved. Graf make the infiltration tunnels so BCO usually state they want a Graf plant to go with it.

40m isn't that long. It will be far easier to install a package treatment plant and discharge to the ditch, If it eventually goes into the sewer fair enough. But will save you huge time and headache, and the ditch will also drain naturally for a lot of its run (i imagine).

Personally I would stick with Graf. Nothing in the tank to fail, spares readily available and top class support from Graf.

Thorfun, your cabinet is an additional cost (that most go for). Cabinet placement is something that can make or break an installation. They can be moved (within reason) limited by distance from the tank etc.

No membrane, mix of pea gravel with some coarser stones for bedding/around pipe. Make sure every inspection chamber has a catch pit of at-least 100mm., regularly clean out the silt. It would also be advisable to have the runs jetted every 5 years.

Underground pipes that are not adopted are very rarely queried by building control. You have made provisions for rodding which is good, they will probably just want a pressure test once finished, especially considering the presence of groundwater after such a long dry spell.

I use Ecover everywhere, safe with the kids and no harm to my septic system or drain field. Buy the large 5LT drums online and if I am ever caught short its also in most shops.

Ross, just get the Graf and get the dosing system. You can even fit remote monitors to alert you of any failures. I have the 9PE personally and it is a great system. You can even control the discharge time, to suit. It has loads of capacity in there, for instance, I can empty two full baths, shower, washing machine etc and it leaves me loads of capacity.

Tanks come with a guarantee, if its lost its shape, its on them to prove its through no manufacturing fault. This is why building control exists, they would have had to guarantee and oversee the installation of a new tank is done correctly. I would suggest speaking to the small local builder and his building controller as a first point of call.

Agree with the above, Graf can supply a "dosing" system and you can also set "holiday mode" which reduces energy consumption. If the plant will be used in holiday mode, I strongly recommend a gravity outlet over a pumped (if possible) and adding a dual flap NRV between the water course and the pump. If you are not there in the event of extreme weather or a higher than usual water course, this will protect the plant.

As long as your proven percolation tests come back correctly, take photos and it will be fine. Only thing is, you will need to know the depth of the TP relative to the fall of the rest of the drainage runs. If you really wanted to get it in, sit the tank a bit deeper, get a pumped outlet and then put the drainage field in nice and high. Such a small job in the scheme of things, and hiring a 5t digger seems a bit of a waste when you probably have a bigger machine in when you start the build.

In theory a diaphragm should be replaced every 2-3 years. If your plant was under a service plan, this is the interval it would be changed at. I order the repair kits from ALI express and keep two in stock. £30 every 2 years isn't a huge expense.

You are over complicating this, when you dig the tank in, you will need a control box somewhere (usually hidden) for the compressor etc, so put the vent direct from the tank there.

Quite common for IC and pipes to fill with crud during the build phase, avoidable but common. Usually always cleaned out, they have used concrete risers and caps, so imagine pipes been installed with a laser level. Jetting and vac out of drains isn't as expensive as you would think.

You only need to replace a septic tank if you discharge to a watercourse (or anything other than a drainage filed). Trouble is many solicitors scare buyers as they (and the buyers) aren't really too clued up on non-mains drainage. You can still install new septic tanks today. If you are selling, I would recommend saying to your solicitor you will get the tank emptied and jetted before the sale completes and provide evidence. If its been in and working since 1983, you have no issues (unless you discharge to a watercourse etc). Also I would state how often tank is emptied and provide evidence of it, compared to waste water costs these days, its actually cheaper to have a tank/treatment plant on a monthly basis than it is to have a mains connection.

Isn't this just a normally/open closed solenoid coil?

because if you add the NRV in that manhole in the house, it would only work up to the "back" edge of the inspection chamber, water that entered the mahole next to the road would still back fill into the IC in your kitchen. If you fitted the NRV i posted into the IC in the kitchen it would be the wrong way round, and effectively block that IC from passing effluent into the manhole in the road. If you are not confident doing it, I am sure a local drainage company would be able to assist. It cold also be that the manhole in the driveway needs replacing with an "air tight" one, this will ensure no flood water enters it. It may be worth getting a CCTV survey just to check there is nothing un-toward. I see you are in Surrey, I am not affiliated with them, but I use "Totally Blocked" for all my CCTV surveys and any patch repairs that need doing. https://www.totallyblockeddrains.co.uk/.

It won't work on the IC in the kitchen, probably flows from there to the one on the drive (easy to test). It would need to be on the last IC before the property, so it does't allow backflow.