Increasing size of sewage treatment plant?

[flanagaj]

Can anyone advise as to what the process is for increasing the size of the agreed sewage treatment plant to accommodate additional bedrooms?  The approved planning app was for two bedrooms and we want to add a third one in the roof space.  The architect has told us that this can be done as a minor amendment, but although 95% of the year the property will just be occupied by my wife and I, the other 5% might include our children and their partners.   As a result, the occupancy will be 6 and the Graf system that has been specified is a 1-5 person system, and I am concerned that when everyone is home it won't cope with the load.

 

The property sits in a nitrate mitigation area, and as part of the planning application they had to have a nitrate mitigation calculation done which calculated an average occupancy of 2.4 people.  So this equates to a couple and a third person staying 146 days of the year.

The nitrate mitigation credits have already been allocated, but if we increase the tank size will we have to get it agreed with planning and purchase additional credits?  

[JohnMo]

I think you need to speak with the architect, as the number of people allocated per room is never normally two, except for the main bedroom. He is likely going to have to include this sort of of detail on his application.

 

Not seeing any reason you would increase your treatment plant size.

 

Use open questions when you speak to the architect, don't go hunting for answers you don't really want to hear.

[joe90]

13 minutes ago, JohnMo said:

as the number of people allocated per room is never normally two,

It was with my application, 3 beds = 6 person treatment plant!  However I just found this…

Domestic Dwelling Calculation

A domestic dwelling is fairly straightforward to work out. This is usually the number of bedrooms in the property plus two.

For example, a three-bedroom house becomes five.

Edited March 23 by joe90

[nod]

To be fair If you added a nine pop treatment plant as apposed to a six 

Who would know or care Certainly not BC Once backfilled your left with a manhole cover and they all look the same 

[saveasteading]

For a single house with up to, and including, three bedrooms, a Minimum Population (P) of 5 people should be calculated. For each additional bedroom in a property thereafter, you should calculate for 1 additional person.

 

 

[saveasteading]

The next size up won't be much bigger or cost much more. Its mostly air.

I don't think that a bigger one works any less efficiently due to under-use, and the nitrate will be no greater. 

The manufacturer should be able to confirm this.

I'd probably just do it.

 

[crooksey]

Planning can't stipulate what treatment plant you use, this is down to building control, again you can only get it approved by them, they wont say use X plant.

 

Bigger plant means bigger dig, more energy usage etc. You can adjust the settings etc, personally I generally recommend a person tank, can then easily cope with "peak loads". As on most plants, if you put to much water through them, the internal overflow will discharge unclean effluent into the drainfield/ditch etc. The bigger the plant the more capacity you have between pump outs.

 

If you wanted to get technical, you could adjust the settings on a graf 5 person to pump out more frequently. (not recommended as the aeration cycle will be smaller then).

[saveasteading]

1 hour ago, crooksey said:

Bigger plant means  more energy usage

 

1 hour ago, crooksey said:

you put to much water through them, the internal overflow will discharge unclean effluent into the drainfield/ditch

 

1. The manufacturer can advise but I'd be surprised. It is an air bubble pump in most systems, like in  an aquarium and the power is light bulb level.

2. Again I'm surprised if any allow this. I like the principle of 3 chambers, as digestion continues if there is no power, and the arrangement prevents anything flowing through untreated.

 

Can you can advise which makes have these disadvantages?

[crooksey]

Graf plants are quoted to have energy usage per person, I presume the pump for the discharge runs for longer, I did state this can be adjusted, its the default settings though.

 

Thats fine for 3 chambers, one chamber plants can suffer from this, i'm talking you leaving the tap on for a long time, the outlet level of the plant will be nearly always lower than the last sink/toilet in the house and will cause a flood above the pumping levels. Even 3 chamber tanks can work on a settlement basis, they don't all use electronic pumps to move matter through the chambers.

[saveasteading]

3 hours ago, crooksey said:

they don't all use electronic pumps to move matter through the chambers.

The ones I know most about simply work by gravity and flow. In the first chamber the sewage enters by a high pipe but turned down into the bulk to avoid splatter, The outlet is similar so that solids float high and sink low but stay put and fester. Then the second chamber receives only very grey liquid, and gets the bubble treatment and  then  has an outlet  near the bottom and the third one's outlet is at at the top.

Thus one flush goes in and the equivalent comes out.

I have a single, ancient,  brick chamber , and it works only as the first chamber above , but what comes out is cleaner than you'd expect and goes off to a primitive soakaway......somewhere . I had it sucked out after 10 years of our use, but I think it will have had 30 years before. There was a maximum of 200mm at the bottom and a crust* of 100mm. I don't think annual cleaning is necessary if it is working properly.

* it was brown of course. I rested a brick on it for some reason, and it stayed put for a few minutes before needing rescuing. The stuff on the bottom was foul slimy grey stuff plus 'objects, various'.  Ohhh and  a lump of roof that had been chucked in by some previous cowboy.

[flanagaj]

Thanks all for the comments.  As we are going to be creating four bedrooms, then I am going to put in a 7 person tank instead of a 5 person one. 

On a side note, I see that drainage fields have to be 15 metres from the property.  The people we are purchasing the land from (was hoping to get exchanged next week) seem unable to confirm exactly where their drainage field is on their land.   As the plot formed the end of their garden, I am now concerned that it sits right over to our boundary and would put it at 4-5 metres from our house.   The solicitor is pushing for a map to be provided by the vendor so that we can be assured as to where it exactly sits.   All a bit of a pain, as you actually have no idea.   Wondering whether we should request a survey be provided.

 

 

[Russell griffiths]

Get a camera survey done. 

[saveasteading]

As hardly anyone appears to install a drainage field as required, I wouldn't assume it is even there. How would we know where one was, as it is all buried unless there are drawings?

3 hours ago, Russell griffiths said:

Get a camera survey done. 

I first typed 'a dirty video' then realised the water should be clean by there.