Sewage Treatment Plant self install

[MortarThePoint]

There are two reasons I am tempted to do this myself:

1. I'm a self builder and I like a challenge
2. Cost

 

Has anyone else here installed their own STP?

 

I've had quotes for installing just the STP tank and controls of £10-15k which feels like too much for what is involved (that's with me doing all the pipes to/from). At the bottom of this message is a rough costing I have done based on my understanding of what is involved. I expect the installation company to make a profit, but not £5k+. Have I forgotten some costs? I see it as a day of work on site. If I could find a digger driver that has done STPs before it would massively derisk the operation. I have a couple of IBCs that I would fill with water near the hole to then fill the tank during the concrete pour. A hose pipe alone couldn't cut it as I'd need to supply 4,800 - 6,500 litres in an hour. Need to check the concrete pump flow rate.

 

Costing (all ex VAT):

Assuming a 3.3m x 3m hole 2.5m deep and the tank 2/3 surrounded by concrete.

• 10 cubic yards of concrete: £1,000 + £90 = £1,090 [inc additional hour on site]
• Concrete pump up to 60m inc operator: £530
• 20tons of 10-20mm gravel: 20*£30 = £600
• Digger hire (1day): £323
• Experienced digger operator: £250 (guestimate)
• Dirty water pump: £55
• [Sparkie option to wire up: £400]

INSTALLATION TOTAL: £2,848 +£400 if Sparkie needed

TANK COST (INC CONTROL): £2,500

GRAND TOTAL: £5,348 +£400 if Sparkie needed

[Russell griffiths]

Digger hire far too low

operator for a day, you won’t get that work done in a day 

spoil from the hole, where’s that going

spoil, how are you moving it to where it’s going. 
digger and operator for second day to position gravel and lift in tank. 
concrete backfill should be a semi dry mix a wet mix can float the tank out. 
you can’t pump a dry mix. 
 

it’s a 3 day job, why do you want to fill the tank a bit at a time, position it in the hole and fill it up. 
you are underestimating this job massively. 

[Nick Laslett]

What kind of soil do you have?

 

My ground workers first install attempt failed, when the hole collapsed. 
 

They abandoned that hole and started in another location. 
 

We needed expensive shuttering and bracing to support the install. Special attachment on the digger, rams the shutters into the ground. 

 

 

[ProDave]

I did mine in 2 days myself.  One day digging the hole and putting the tank in, then the rest of day 1 mixing barrowing and pouring concrete.  Day 2 lots more mixing barrowing and pouring concrete.

 

I had my own digger and was reasonably competent driving it so no extra cost for that.  I had ordered a load of gravel and bags of cement and I had plenty of sand on site so I mixed my own concrete with my own mixer.

 

The trick was to dig the smallest hole the STP would fit into so there was not so much concrete to mix and pour

 

Disposal of spoil was not an issue.  This was a building site pre landscaping, so the contents of this excavation were spread around before the top soil was spread back on the site to finish it off.

 

 

 

[MortarThePoint]

40 minutes ago, Nick Laslett said:

What kind of soil do you have?

Clay, stiff below 1.25m. the ground workers didn't have any issues with shear sided trenches. As this is deeper, would be better to have angled edges.

[MortarThePoint]

50 minutes ago, Russell griffiths said:

Digger hire far too low

operator for a day, you won’t get that work done in a day 

spoil from the hole, where’s that going

spoil, how are you moving it to where it’s going. 
digger and operator for second day to position gravel and lift in tank. 
concrete backfill should be a semi dry mix a wet mix can float the tank out. 
you can’t pump a dry mix. 
 

it’s a 3 day job, why do you want to fill the tank a bit at a time, position it in the hole and fill it up. 
you are underestimating this job massively. 

 

That is the rate I can get a 6T digger for including transport and insurance. About double that for a week, which I'd go for as I have other jobs I need it for and will consume the spoil and would get a dumper for. That's efficiency I haven't factored into the costing though.

 

The dry mix is a concern, but I'd expect anyone would pump given the location. Ideas welcome how to address that.

 

I think the tank's installation manual sets out a maximum water fill height above backfill, but will check.

[MortarThePoint]

27 minutes ago, ProDave said:

I did mine in 2 days myself.  One day digging the hole and putting the tank in, then the rest of day 1 mixing barrowing and pouring concrete.  Day 2 lots more mixing barrowing and pouring concrete.

 

I wondered about mixing myself as takes the time pressure away and I can have a nice dry mix. The tank's installation manual says 500mm of backfill (i.e. concrete) all round so the volume becomes huge. Would be a lot to mix by hand, 10cube.

[ProDave]

I did the opposite, a wet mix so when poured it would flow down the small gap between the side of the tank and the edge of the hole.  Each tank is different but mine was concreted to just above the ring that can be seen around the cone at the bottom of the tank.

[Nick Laslett]

The main issue my ground workers had, was very high water table, and sandy/gravely soil. The site is a former gravel pit. 
 

We have the same STP as @ProDave. They were worried about the unit popping out of the ground. 
 

 

They took the concrete from the back of the mixer into the digger bucket. 
 

 

 

Edited yesterday at 09:21 by Nick Laslett

[nod]

I’ve installed one for our neighbor and the material came to £5700 including vat Labour £2000 

[MortarThePoint]

21 minutes ago, Nick Laslett said:

They took the concrete from the back of the mixer into the digger bucket

I wondered about a small dumper as that could cover the ground between tanker and hole. Hiring that would add about £200 I'd guess, but save the cost of the operated pump. I don't think the digger and dumper would need to be operated together so the same operator could do both(?). If each load was 500kg (half full) it would take about 20 trips and the round trip might be 5 minutes so within the realms. Could get a bigger dumper and use a ramp to help with the pour from the dumper.

[MortarThePoint]

1 minute ago, nod said:

I’ve installed one for our neighbor and the material came to £5700 including vat Labour £2000 

How big was the gang and for how long?

[Russell griffiths]

We all seam to answer with our opinions, but it’s never really answering the original question 

Dave said he did his in a couple of days, but his hole is tiny, the hole you are suggesting is huge and will have approx 

30 cubic m of clay coming out of it. 
 

dave said he mixed his concrete himself, again no problem but his hole is again tiny, yours is huge, your not hand mixing 10 cubic meters. 
 

you can use a wet mix if your hole is dry, if you have water in the hole you need a dry mix. 
 

I think this job is very different depending on ground conditions and tank used. 
 

@flanagaj has just done his maybe he could put up some more up to date and in context pictures. 

 

[nod]

8 minutes ago, MortarThePoint said:

How big was the gang and for how long?

Just a mate and me 3 days 9 pop

[MortarThePoint]

2 minutes ago, nod said:

Just a mate and me 3 days 9 pop

 

Nice to see the next generation showing an interest.

 

Did the 3days include digging and laying the pipework?

 

 

[nod]

23 minutes ago, MortarThePoint said:

 

Nice to see the next generation showing an interest.

 

Did the 3days include digging and laying the pipework?

 

 

Everything except putting some paving back and turf Which the neighbors did themselves 

[flanagaj]

2 hours ago, MortarThePoint said:

 

Nice to see the next generation showing an interest.

 

Did the 3days include digging and laying the pipework?

 

 

Agreed.  It's not rocket science and it just requires a lase level and understanding the necessary falls / inverts.  I reckon I saved over 10k doing it myself with one other chap.

[flanagaj]

4 hours ago, MortarThePoint said:

There are two reasons I am tempted to do this myself:

1. I'm a self builder and I like a challenge
2. Cost

 

Has anyone else here installed their own STP?

 

I've had quotes for installing just the STP tank and controls of £10-15k which feels like too much for what is involved (that's with me doing all the pipes to/from). At the bottom of this message is a rough costing I have done based on my understanding of what is involved. I expect the installation company to make a profit, but not £5k+. Have I forgotten some costs? I see it as a day of work on site. If I could find a digger driver that has done STPs before it would massively derisk the operation. I have a couple of IBCs that I would fill with water near the hole to then fill the tank during the concrete pour. A hose pipe alone couldn't cut it as I'd need to supply 4,800 - 6,500 litres in an hour. Need to check the concrete pump flow rate.

 

Costing (all ex VAT):

Assuming a 3.3m x 3m hole 2.5m deep and the tank 2/3 surrounded by concrete.

• 10 cubic yards of concrete: £1,000 + £90 = £1,090 [inc additional hour on site]
• Concrete pump up to 60m inc operator: £530
• 20tons of 10-20mm gravel: 20*£30 = £600
• Digger hire (1day): £323
• Experienced digger operator: £250 (guestimate)
• Dirty water pump: £55
• [Sparkie option to wire up: £400]

INSTALLATION TOTAL: £2,848 +£400 if Sparkie needed

TANK COST (INC CONTROL): £2,500

GRAND TOTAL: £5,348 +£400 if Sparkie needed

I had to excavate a 3m * 3m * 2.6m hole for our tank.  Digging the hole took a day with a 2.7T Kubota and then another day putting the tank in.  Filling the tank with water before back filling each section took a long time.  A bowser would have helped.

I would also hire the excavator for a week as it's nearly the same price.  Don't forget you'll need a dumper and have a lot of muck away too.

[MortarThePoint]

1 hour ago, flanagaj said:

I had to excavate a 3m * 3m * 2.6m hole for our tank.  Digging the hole took a day with a 2.7T Kubota and then another day putting the tank in.  Filling the tank with water before back filling each section took a long time.  A bowser would have helped.

I would also hire the excavator for a week as it's nearly the same price.  Don't forget you'll need a dumper and have a lot of muck away too.

 

Which system did you install? Did you have a concrete backfill?

[nod]

7 hours ago, MortarThePoint said:

There are two reasons I am tempted to do this myself:

1. I'm a self builder and I like a challenge
2. Cost

 

Has anyone else here installed their own STP?

 

I've had quotes for installing just the STP tank and controls of £10-15k which feels like too much for what is involved (that's with me doing all the pipes to/from). At the bottom of this message is a rough costing I have done based on my understanding of what is involved. I expect the installation company to make a profit, but not £5k+. Have I forgotten some costs? I see it as a day of work on site. If I could find a digger driver that has done STPs before it would massively derisk the operation. I have a couple of IBCs that I would fill with water near the hole to then fill the tank during the concrete pour. A hose pipe alone couldn't cut it as I'd need to supply 4,800 - 6,500 litres in an hour. Need to check the concrete pump flow rate.

 

Costing (all ex VAT):

Assuming a 3.3m x 3m hole 2.5m deep and the tank 2/3 surrounded by concrete.

• 10 cubic yards of concrete: £1,000 + £90 = £1,090 [inc additional hour on site]
• Concrete pump up to 60m inc operator: £530
• 20tons of 10-20mm gravel: 20*£30 = £600
• Digger hire (1day): £323
• Experienced digger operator: £250 (guestimate)
• Dirty water pump: £55
• [Sparkie option to wire up: £400]

INSTALLATION TOTAL: £2,848 +£400 if Sparkie needed

TANK COST (INC CONTROL): £2,500

GRAND TOTAL: £5,348 +£400 if Sparkie needed

You’ve forgotten spoil We had three grabs 250 plus vat 

and 20 tone of pipe bedding 700 

Diesels and extra days for digger hire 

Also you need to use a semi dry curb mix 

[MortarThePoint]

13 minutes ago, nod said:

You’ve forgotten spoil We had three grabs 250 plus vat 

and 20 tone of pipe bedding 700 

Diesels and extra days for digger hire 

Also you need to use a semi dry curb mix 

 

I can use the spoil landscaping so that's ok. I'm only considering the tank installation so included gravel for that not for pipe bedding. Hopefully diesel won't amount to much.

 

I think the dry mix means I need a dumper. But that means no pump so actually saves money. Extra digger hire wipes out that saving though plus an extra day of driver hire so about +£250 over my previous calculation.

[jfb]

I did mine with a capable digger driver friend.

Excavated the hole, put a dry mix, level concrete pad at the bottom.

tank in. Digger man did an excellent job of mixing up the dry mix in the dumper using the digger bucket. Hose speed was fine for the speed the concrete that went around the stp.

[Gone West]

7 hours ago, MortarThePoint said:

Has anyone else here installed their own STP?

We installed a conical shaped STP, which just sat on the top of a thick concrete paving slab. The sloping sided hole was dug out by the local farmer who placed the slab at the bottom of the hole. The STP was chained down to four angle irons which I banged into the side of the hole. It was easy to level the STP because it just sat on it's pointed base. The hole was back filled with type 1. The STP had a 450mm turret riser which was concreted in. The farmer charged £160 but this was fifteen years ago.

[Alan Ambrose]

We were working on this today. A properly anal approach, but I wanted to be able to get it out easily if there was a future problem. Very doable DIY - although it would be easier .... the next time 😁. Main issues were falls (courtesy of some earlier careless groundworkers) and, believe it or not, making the straps work sensibly. My digger skills are improving, although the original dig out was done by an experienced guy in one day. There was properly hard dried out clay that far down. The dry mix was done by hand on a piece of ply - we didn't even bother to get the cement mixer out.  The perforated twinwall in the last picture is for checking on GW level.

 

[nod]

7 hours ago, MortarThePoint said:

 

Nice to see the next generation showing an interest.

 

Did the 3days include digging and laying the pipework?

 

 

To be fair we had a full day sorting the drainage in the neighbors garden 

Bolder clay so the 3 tone digger I borrowed wasn’t man enough to dig right down So my maté reluctantly leant me his almost new 5 tonner