Case Study | How much does it cost to put right?

Friday, 7 May, 2021 | Gerry Rowe

A sewage pipe renewal and connection to foul drains.

We’ve all done it – grabbed that opportunity for someone to do something on the side. We know it’s taking a risk, but the temptation to save some money is all too damning when the result is less than adequate OR even very damaging. The final costs that we incur to ‘put right’ what has been poorly done far outweigh what it would have cost in the first place to do it properly.

The following case study will hopefully convince you that – It is better to do it properly from the start, and you get what you pay for. We know we are not the cheapest in our field, but we use the best materials and equipment for the job. We want you to have an all-round good experience of our services - so we don’t install your private sewage systems and drainage badly ‘on the cheap’.

Observations & Findings

Grid gully designed to catch all surface water.

Further to your request, we attended to excavate and check the soakaway. Upon excavation and inspection, we found the soakaway full of sewage water, sewerage, grease, and fat.

We carried out a brief inspection of the drains and discovered a vast amount of surface water from the downpipes and aqua drains is entering the foul system, which has caused problems with the separation. When water enters in a surge, such as during heavy rainfall, or a storm, the incoming water stir’s up the first tank, destroying any separation in the primary settlement chamber.

The sewage, paper and unwelcome fat in suspension pushed through into the soakaway, coating the absorbent surface and gradually diminishing the soakaway's ability to disperse water until it finally ceased to work altogether.

In addition to the above, we also found the inspection chamber installed (by the builder's) before the septic tank has a back fall and is causing blockages. We recommend this chamber is completely removed and replaced.

In the first instance, we proposed the following:

To carry out a CCTV drainage survey of all drains around the property to check for any structural breaches and establish if any further surface/groundwater is entering the foul system.
To report back our findings with an estimate for any essential repairs required along with an estimate to install a surface water soakaway.

The proposed CCTV drain survey revealed:

The builders have completely re-laid the sewage drainage pipe around the house as per the schematic diagram below. In doing so, they connected the surface water gully and roof water downpipes into the sewage drain.

An investigatory survey and schematic diagram of a properties drainage prior to ASL carrying out a sewage pipe renewal and connection to main drain.

Advisement

To rectify this error, here are my recommendations:

STAGE ONE

Surface Water Area 1

To excavate and install 3 x new uPVC gullies and pipework.
To connect the new gullies to the inspection chamber located to the right-hand side of the chimney using new uPVC pipework.
To excavate and construct a new soakaway using Aquacell crates on a base of flintstone.
To protect the crates with a geotextile membrane.
To lift patio slabs and install 14 linear meters 100mm pipe up to and into the new soakaway.
To surround new pipe in the shingle.
To backfill the excavation and leave the garden and lawn area flat.
To relay paving slabs.

Our charge to carry out the above works is £5,500.00 plus VAT inclusive of labour, plant, and materials. Price is subject to a percolation test to a depth of 2m.

Examples of ill kept surface water drainage pipes allowing surface water into the sewage system. — Examples of ill-kept surface water drainage pipes allowing surface water into the sewage system.

STAGE TWO

Surface Water Area 2

To excavate and install 1 x new uPVC gully at the base of the rainwater downpipe located to the right of the front door.
To excavate and install 14 linear meters and connect to the existing 100mm pipe leading to the existing soakaway. We can install an inspection chamber as an optional extra.
To shorten all surface water downpipes by 50mm.
To surround all new pipe in shingle.
To backfill the excavation and make good to existing levels.
To supply and install a new gully surround required at an additional cost of £40.00 plus VAT per surround.

Our charge to carry out the above works is £900.00 plus VAT inclusive of labour, plant, and materials. Please arrange to temporarily remove the small trees and shrubbery to carry out the above work.

Surface Water Area 3

Side of the property, soakaway next to the road

To remove and store 20mm stone in front of the green building whilst works are being carried out.
To excavate and construct a new concrete ring soakaway chamber in the driveway on a bed of flintstone.
To surround the new soakaway with eight tones of flintstone.
To disconnect the surface water channel grating pipe from the foul drainage system.
To excavate and install new 100mm pipe from the channel grating to the new soakaway.
To connect 4 x downpipes to the new soakaway.
To surround all new pipe in shingle.
To backfill excavations and make good to existing levels.

Our charge to carry out the above works is £8,500.00 plus VAT inclusive of labour, plant, and materials. Price is subject to a percolation test to a depth of 2m.

Please note: Subsidence is the downward movement of the ground below a pipe, where the soil beneath the pipe has become unstable. When repairing a pipe that has already subsided, we will pay special attention to consolidating the bottom of the trench before installing the new pipe.

STAGE THREE

Foul Water - Preparation

To carry out High-Pressure Water Jetting to clean all the foul drains, before and after repair works.

Our charge to carry out the above works is £100.00 plus VAT per hour (or part of) inclusive of labour and plant.

Foul Water Area 1 - Front of property

To excavate down and remove the subsided pipe.
To compact the base of the trench and install new uPVC pipework.
To surround new pipe in shingle.
To backfill and make good to existing levels and finishes.
To re-survey pipe.

Our charge to carry out the above works is @ £200.00 plus VAT per linear meter (approximately 3m) inclusive of labour, plant, and material. Price excludes making good the tarmac drive.

Foul Water Area 2 – Side of property

To excavate and remove the round inspection chamber.
To supply and install a new 450mm x 600mm inspection chamber constructed with concrete sections and a gentle 90° sweeping bend channel.
To supply and install a new 450mm 600mm cover and frame to suit.

Our charge to carry out the above works is £850.00 plus VAT inclusive of labour, plant, and material.

To excavate down and remove the subsided pipe.
To compact the base of the trench and install new uPVC pipework.
To surround new pipe in shingle.
To backfill and make good to existing levels and finishes.
To re-survey pipe.

Our charge to carry out the above works is @ £200.00 plus VAT per linear meter (approximately 3m) inclusive of labour, plant, and material. Price excludes making good.

Foul Water Area 3 – Rear of property

To carry out High-Pressure Water Jetting to clear ponding kitchen waste and to methodically clean the pipe.
To remove patio slabs from an area measuring approximately four m².
To excavate down and remove the subsided pipe.
To compact the base of the trench and install new uPVC pipework.
To surround new pipe in shingle.
To backfill and make good to existing levels and finishes.
To relay patio slabs.
To re-survey pipe.

Our charge to carry out the above works is @ £300.00 plus VAT per linear meter (approximately 3m) inclusive of labour, plant, and material. Price excludes making good the patio.

Example of pollution in the ground forced through by surface water that should not have been connected.

Foul Water Area 4 – inspection chamber Before Tank

To carry out High-Pressure Water Jetting to clear ponding waste and to methodically clean the pipe.
To excavate down and remove the deep inspection chamber located before the septic tank.
To compact the ground and lay a concrete base.
To supply and install a new inspection chamber constructed with concrete. Sections and torq strip joints.
To supply and install a new cover and frame to suit.
To backfill and make good to existing levels and finishes.

Our charge to carry out the above works is £850.00 plus VAT inclusive of labour, plant, and materials.

Please find our estimate to install a new soakaway for the septic tank to discharge as follows:

ESTIMATE – New Soakaway

To carry out a test hole to check if the ground conditions are suitable for the new installation. If the ground conditions are unfavourable, we will revise our estimate accordingly.

If the test hole proves successful, we will continue with the following:-
- To construct a new trench type soakaway and infill with 12 ton of flint material
- To cover the soakaways with a geotextile membrane
- To supply and install new uPVC pipework from the septic tank up to the new soakaways
- To backfill excavations and make good to existing levels
- To spread excess spoil in the area of the soakaway
- To leave the site in a tidy state

Our charge to carry out the above works is £3,800.00 plus VAT inclusive of labour plant and materials. Price is subject to a survey and test holes.

SPOIL REMOVAL (if required)

Any excess spoil to be removed from the site will be charged additionally as per the following rates:-

1-2 ton load = £120.00 plus VAT

2-10 ton load = £250.00 plus VAT

10-15 ton load = £350.00 plus VAT

Conclusion

As you see, the cost to put this right could cost over £22,000.00! Certainly worth doing things right from the start, and a simple survey to have been carried out in the planning stage of the installation could have saved all this upheaval and expense.

Please see our web page entitled ' private systems' if you would like to know about treatment plant installations from ASL Limited .

Other information that may be helpful to you:

CHEMICALS

We often get asked about the use of cleaning chemicals and agents with a treatment system, and although not recommended, it doesn’t seem to have a significant impact if used in small quantities.

To keep the population of microorganisms working well, we advise that any cleaning agents such as bleach and dilute proprietary products very well before disposing of them down the drains. We also advise against the use of anti-bacterial cleaning products, as these can harm the microorganisms working away in your new drains.

FATS & GREASE

The small number of unwelcome fats and grease deposits will get trapped in the holding tank, which then gets emptied down during maintenance.

Fats and grease do not decompose in a private system, i.e. septic tanks, treatment plants, upgraded clinker beds, etc. Therefore it is a good idea to minimise the number of fats and grease entering the system to reduce the risk of possible pollution or damage. To this end, we suggest that any excess fats and grease from cooking, once sufficiently cool, should be poured into the waste food bin and disposed of with the general refuse collection and not poured down the drains.

WASTE DISPOSAL UNITS

Waste disposal units can cause problems when used in conjunction with septic tanks and domestic sewage treatment plants. Waste disposal units grind up the vegetable matter, can discharge it into the sewage system. Because the vegetable matter is very fine, it takes a longer time to separate and float to the bottom. Therefore, it can float in suspension through to the secondary chamber and possibly into the soakaways as it does not settle to the bottom. Another factor is that the enzymes which digest the sewage do not tackle cellulose. Cellulose is the chief constituent of vegetable matter, and it accumulates rather than breaking down, so – in time, it degrades the quality of treatment.

Kindly note that any estimate given is subject to ground conditions and adverse weather conditions. Suppose a job has been priced using a mechanical excavator or mole. We encounter various services, root ingress, or poor ground that prevents using a mechanical excavator or mole for all or part of the works. In that case, there will be a revised estimate to excavate by hand, which will be charged per meter and is dependant on depth, surface type, etc. Similarly, should we encounter a high water table causing water infiltration during our excavation, we will revise the price to allow for shoring and de-watering to make the excavation safe.