Is there anything preventing one from putting a drainage field uphill from the dwelling/treatment plant that feeds it? I can't see anything in Approved Document H2 precluding it. I would've thought that pump(s, with one for redundancy) would be required.

 

Our proposed buildings are at the bottom of a valley and all about 15m from the boundaries, but we have 3 acres of land uphill that could be used instead.

cant see it being a problem, double chambers would be needed. A standard cheap pumped chamber at the house feeding the treatment plan wherever you put it.

 

The 63mm pipe they use is an absolute bastard to use be warned!

No, you would just need to pump it, no different to having a pumping station for raw sewage where you are lower than the main sewer. All I would say is have a failsafe pump, it will one day and there is an age old expression "Sh*t flows downhill".

 

With a site that large is there no watercourse there to discharge to? Depending on the length of the run needed to the drainfiled, there may be cheaper solutions.

You put the treatment plant at the bottom near the house so it drains by gravity.  Then the outflow from the treatment plant drains to a holding tank where that is pumped up to the drainage field.

 

FAR easier pumping grey water than foul water and only 50mm mdpe pipe needed.

 

We had this system at out last house.

 

Some treatment plants can be bought with the holding tank and pump built in.

The trouble with sewage  pumps is what happens in a failure, eg power cut. So usually you are required to provide a couple of days secure storage capacity. That gets to be a big tank, but a specialist pump supplier can advise.

With a good treatment plant, the outlet water should be very light grey, so perhaps the need for foul storage can be argued away. But still any overflow has to be dealt with.

When our pump failed we got a soggy lawn.  I learned early on to keep a (cheap) spare pump to swap over if the main (expensive) one failed.