Replacement of a Septic Tank

[Dave and Helen]

Hi, 

 

We're currently waiting for planning to come through the conversion of an old Severn Trent pump house and tank, but whilst we're waiting, we're starting to plan some of the required ground work. 

One of the issues we need to address relates to an old septic tank. 

 

The tank is currently used solely by our neighbours, who's house use to be where the waterworks engineer use to live back in the day. Now the pump house and tank are a separate plot, sold off by Severn Trent, we have the pleasure of housing the tank which our neighbours use and have access to in our front yard.  

 

In developing the house, we will need to utilise the same septic tank as there is no mains drainage. We've previously had the tank emptied and inspected, together with a camera inspection of the pipework. The tank is a circular brick construction, with a flat bottom that we believe holds 3,500 litres, this is how much the form had written on it the last time it was emptied and it was full. The tank doesn't empty into a ditch, but we believe drains into a septic field of some type. Unfortunately we have no information on this. 

 

The company that emptied the tank for us, County Drains in Coalville, recommended that we continue to use the same tank where possible as it appeared to be working perfectly OK despite it's age, rather than look at installing a modern 'plastic' alternative, as in the engineer's opinion the old ones are much better. Our concern now is whether the tank is big enough to accommodate the requirements of two houses. Our neighbours house has six bedrooms and we're looking to build a property with four bedrooms. I understand you can calculate the required tank volume from this, but I guess I was more interested in knowing:

 

1. can two houses share the same tank and if so, are there any restrictions around this? I guess as our neighbours have a right of access to the plot for the purpose of emptying the tank, we need to continue to support their needs. 

2. could we make the existing tank bigger, i.e go down or is this simply a non starter? ( not a job I'd be volunteering for )

3. if we were to replace it, I'm assuming it would be less hassle to retain a single tank for both properties rather than ask them to get there own... think there would also be some legal implications as well and bad feeling if we took this route. 

4. should we look at a more modern water treatment option rather than just a replacement septic tank and if so, which options are available to us.
 

Would anyone have any contacts in the local area, Melbourne in Derbyshire, that they would recommend we speak to in order to get some advice and pricing? 

 

Many thanks

 

Dave C

[ProDave]

2 properties can share the same tank.  I know of 5 houses sharing one large tank not far from here.

 

The issue you are going to have is getting this approved by building control.  There is a set forula to work out how many people (PE) you house has to be designed for based on the number of bedrooms.  The tank must be capable of processing the PE of both houses combined.  That is the easy bit.  BC may accept the tank as is for that, or may demand a new one with a known rating.

 

There is then another formula for determining the area of the infiltration field, that again depends upon the PE but also the percolation rate of the ground.  That bit will almost certainly be unknown unless there are any old plans that state the area of the infiltration field.  This I expect will cause more issues with building control.

 

Worst case is you need a new tank and you need to dig up and re lay the infiltration field to a known size.  This will not be a pleasant task as the ground will by now be heavily contaminated.

 

Is there enough land to fit a new tank and infiltration field just for your new house and leave the old tank for the neighbours and remaining their responsibility?

 

If fitting a new tank, make it a treatment plant, not just a septic tank.

[Ferdinand]

You need to look at this carefully. so good question. Arrangements may be different between 

England and Scotland, so check all the detail wrt to @ProDave‘s post from that viewpoint.

 

This page on the gov site may help, if you have not already found it, as it is all in midstream of fundamental change.

 

https://www.gov.uk/guidance/general-binding-rules-small-sewage-discharge-to-a-surface-water#rules-for-existing-and-new-treatment-systems

 

It looks complex, and your circs .. including a proposed new connection to an existing tank and uncertainty about where it all goes ... make it more so.

 

Given that Severn Trent sold it to you and may own some of the pipes, or not if the rules did not apply to private systems, under the adoption rules from a few years ago, I would start with them and an open conversation.

 

 I have always found the, quite willing to discuss things over the phone.

 

They will hopefully tell you what has to be done, or direct you somewhere.

 

I rather suspect that if it was not an auction, you would have had this explained in more detail. Was there anything in the legal pack?

 

Ferdinand

 

 

Edited June 17, 2019 by Ferdinand

[Dave and Helen]

4 hours ago, ProDave said:

Worst case is you need a new tank and you need to dig up and re lay the infiltration field to a known size.  This will not be a pleasant task as the ground will by now be heavily contaminated.

 

Is there enough land to fit a new tank and infiltration field just for your new house and leave the old tank for the neighbours and remaining their responsibility?

 

If fitting a new tank, make it a treatment plant, not just a septic tank.

 

We've already raised this issue with Building Control (independent, not local council) and they have suggested it be replaced, although I've yet to have a meaningful conversation with them about it. I'm OK with changing out the tank, but not to happy about the though of digging up the existing infiltration field (if that's what it's called). I've no idea how far this extends and it would have predated Severn Trent's ownership of the property. It's been hard enough trying to get information from them about the pipework on site, that related to the old workings, so I'm pretty sure they'd have no clue about the septic tank. 

 

If we were to install a bang up to date treatment plant, could we not continue to use the existing infiltration field? I'd assume even the most up to date system would still need one? 

 

We wouldn't have enough land to install a new system and leave the old to the sole use of our neighbours, so it would need to cater for both. My other concern is that our neighbours would expect us to pay for it all, after all, the system that's currently in place is working just fine for them. Some negotiation needed I feel. I'm wondering if I could spin a yarn around the need to replace it due to the change in policy, but it looks like this only applies to septic tanks that discharge into water courses. 

 

Dave C

[ToughButterCup]

You need to read the General Binding Rules. And also realise that discussion amongst neighbours about the soft and smelly stuff is never going to be easy. 

 

We had to solve exactly the same problem at the start of our build. Because people understand the basic rule: no foul drain no house - in our case it brought out the very worst in one or two of our neighbours. But the very best in another. We were very lucky indeed. 

 

I wish you similar luck. 

 

Beware also of the number of pure charlatans operating as drainage 'engineers'. 

Your only defence is detailed, in depth knowledge of the rules and regulations. And a clear understanding of proper drainage design. 

 

Reading this Aesop's tale might be useful

[PeterW]

@Dave and Helen give MBC Services a call - they are not far from you and they are very good at this sort of stuff from design to servicing. 

[Dave and Helen]

Thanks for the advice guys, I'll be sure to do my homework. 

 

Dave C

[Dave and Helen]

8 hours ago, PeterW said:

@Dave and Helen give MBC Services a call - they are not far from you and they are very good at this sort of stuff from design to servicing. 

Thanks for the suggestion. I've searched for MBC Services and drainage etc, but couldn't find an obvious web site. Do you have a web site for them or a number? 

Have you personal experience of using them? Can anyone recommend a couple more... always like to speak and obtain a quote from a few. 

 

Thanks again... Dave C

[PeterW]

Sorry ..!!

 

MPC Services ..!! And yes, personal experience the they are superb. MPC

[Dave and Helen]

Thanks Peter, i’ll give them a call.

[Dave and Helen]

Just following up on my last post.

 

I met with Dean from MPC Services, nice guy and he's going to provide me with a quote for a new water treatment system.

We've always said that we were going to obtain at least three quotes for all the major work we're looking to undertake on our build, so would anyone be able to offer any suggestions of other local companies, ideally ones they've had personal experience with? 

 

Dave C