Sewer connection, Waddesdon

Projects

Sewer connection, Waddesdon, case study

We were approached by Fitzgerald Building Services to connect one new property to the public sewer, on the main road running through the picturesque town of Waddesdon in Buckinghamshire.

Location
Waddesdon, Buckinghamshire
Client
Fitzgerald Building Services
Value
Circa £14k
Transport-Truck-02

Objective

Our objective was to make a new connection onto the public sewer in the main road running through the town. And then to lay pipework back to the boundary where our customer had terminated his pipework and built a demarcation manhole.

About the project

On this occasion our customer already had the Section 106 approval from Thames Water which was really handy, and enabled us to go straight to Highways and apply for the Section 50 application, which we always take care of on behalf of our customer. (You cannot apply for a Section 50 before you have the Section 106)

This required us filling out the Section 50 Application Forms, supplying our accreditations, insurance documents, a traffic management plan, utilities drawings for all other services (Highways have a duty of care to ensure we know where all other utilities are before we start excavating) and various other documents. For the traffic management, we opted for 2-way traffic lights, as this was quite a busy main road.

Our S50 application was rejected initially, as the road was a HS2 diversion route at the time, and traffic lights and road closures are prohibited on HS2 diversion routes. This created a huge problem for our customer as the house was pretty much finished, and waiting for HS2 to complete in the area would have meant a delay of over a year, before he could finish the project and sell the property.

If you need a sewer connection doing, please contact us as early as possible, there are many reasons why the lead-time for a sewer connection can be up to a year or more. For more information click here.

We appealed to Highways and they eventually agreed on ‘give & take’ traffic management for this job, if we were able to keep our excavation far enough over, that we could leave 7m of road remaining outside of the works, for two lanes of traffic to be maintained. We took measurements on site, and this was indeed possible.

The Section 106 approval letter from Thames water detailed connection to the public sewer by way of Junction Insertion, which is the most common method of connection for a single house. This is simply putting a Y-Junction onto the sewer – but of course it’s not that simple with it being a live sewer! It requires us to stop the flow upstream in order that our exaction is not flooded with sewerage whilst the connection is being made. We had all manner of other utilities in our excavation where the connection was made, which is usual, including a gas main and a water main.

We knew where these were in advance as we had the utilities drawings for existing utilities, but there are always services in the Highway that are not on any drawings!

The pipework was laid from the connection point and back to the site. The majority of the pipework, for about 8 metres, was in a wide parking layby. With the connection having been made at approximately 1.4m deep, it made the pipework back to the site a bit over a metre throughout, and of course becoming shallower as we worked back to the site. The carriageway and the layby had to be backfilled and made safe before we could extend our excavation into the footpath – the road was too busy for us to ask pedestrians to cross the road and use the other footpath. In advance of reinstating the carriageway and the layby, we used a ‘footpath board’ to enable pedestrians to cross our back-filled excavation in the layby, whilst we excavated in the footpath.

As usual, we found plenty of smaller utilities in the footpath, including electric cables, BT cables and ducts, and a water service pipe, all of which we had to hand-dig underneath.

The pipework was laid up to the boundary with the private property. A demarcation manhole is always required within 1 metre of the boundary with the Highway, but this was not within our remit, and the customer had already fitted this, and left a plastic 110mm spur from the demarcation manhole to the boundary, onto which we connected our clay pipework. With all pipework complete and tested, we prepared for tarmac reinstatement. We collected base course tarmac and 10mm tarmac ourselves on our own 4-wheel grab lorry and the reinstatement was completed just over a week after we started on site.   

Timeline

Time to quote for the works: Less than a week

Time taken to obtain Section 106 Licence from AW: (Our customer already had this)

Time taken to obtain Section 50 Licence from Highways: 5 weeks – included talks between us and Highways regards traffic management

Leadtime to use S50 Licence: 5 weeks 

Time taken to do the work: Just over a week

Total time:  12 weeks

Do you need a sewer connection needs doing? Click here to enquire.

Don’t leave it too late for a sewer connection, most people do! Read our article here: How long does it take to do a sewer connection?

Click here to see more of our case studies.

House Extension, Towcester

Projects

Conservatory demolition and groundwork for house extension, case study

We were approached by a long term customer of ours, a builder and developer, to do the groundwork for a reasonable sized house extension in Towcester.

Location
Towcester, Northants
Client
Private customer
Value
circa £20k

Objective

Our objective was to demolish the existing conservatory. Then to dig and pour footings for the new extension and do the masonry up to underside of block & beam. Then some foul and rainwater drainage, followed by installation of block & beam.

About the project

We started by removing the conservatory from site, and we removed this to a skip in our own yard, due to limited space on site. We we’re only able to get a 1.5 tonne digger in to this back garden through a narrow gap between the existing house and the standalone garage. There were a few steps here as well, so we put some plastic down on the steps and then laid type 1 MOT to form a ramp for the digger and to enable easier access for wheelbarrows back and forth. With the digger in the back garden, we started breaking out the floor of the conservatory. This came out easily enough, as it was only about 150mm thick, and not reinforced.

The footings were a bit more difficult to remove. At about a metre deep, which is a bit unusual for a conservatory, we had to break with the breaker attachment on the machine, then put the bucket on the machine and dig out what we’d broken. Then we had to put the breaker back on, then the bucket back on, and so on. We got the footing broken out in a bit over a day, and then we were ready to set out for the new footings.

The drawings asked for a 1-metre deep footing, but this is standard, and final depths were subject to the Building Inspector’s decision. There were a few small trees within 10 metres, and ordinarily any trees within 15 metres will have an effect on the footing depth, subject also to ground conditions of course. The Inspector asked for slightly deeper footings on two sides, to a depth of 1.4 metres, and then stepped back up to 1 metre on the final stretch.

We poured the footings to a depth that would enable 300mm of masonry to be laid to the underside of the beams (block & beam floor on this one). There was 8 cubic metres of concrete required in the footing, so we used a ‘line’ pump to get the concrete round the back of the house. We dug the oversite off to the required depth the next day, so that we had 250mm clearance underneath the block and beam floor.

With the masonry done, we filled the cavity to the required level, with Gen 1 concrete. Due to the available access, we had no choice but to carry the concrete beams round, one by one. These were laid within 2 days nonetheless, and the infill blocks and splits done thereafter. The floor was sealed with cement slurry, to complete the block and beam. 

There was some drainage to complete for the project including foul and also rainwater from the new roof. The extension was generally for a new kitchen, so we laid new drainage from the proposed drainage points, to the existing foul manhole within the patio. We dug out for and laid underground rainwater pipes from the new downpipe positions. We had planned to dig out for and form a soakaway, but we discovered there was a dedicated surface water sewer in the Highway, and the existing rainwater pipes were connected to this system. We spoke to the Building Inspector, and he was fine for the new rainwater pipes to connect into this existing system, within the confines of the property.   

With all of this work complete, we handed over to our customer, who continued with the build. It was good to carry out a small domestic job, and locally as well. A lot of our work is far from home and often on much bigger sites. Please contact us should you have a similar project you’d like help with.  

Culvert/Bridge Install, Stanwick

Projects

Culvert/Bridge install, Stanwick, Case Study

We had already been asked to do the groundwork for a new build on this site, but the existing bridge was not suitable for bringing multiple lorries across, to remove hundreds of tonnes of spoil from site and bring all the materials in etc. Therefore a new bridge in the form of a culvert was proposed and designed, and we were instructed to install this.

Location
Stanwick, Northants
Client
Private customer
Value
£xx,xxx
commercial contracts

Objective

Our objective was to demolish the existing concrete bridge with its steel supports, install the culvert sections and then form a road on top including kerbs and tarmac etc.

About the project

We decided to carry out these works in the middle of the summer, as the flow of the stream would be at its lowest, as opposed to the wetter months, when the stream was significantly faster-flowing. We started by demolishing the existing bridge, taking care not to pollute the stream with debris from the old structure. The culvert sections could have been laid on consolidated type 1 MOT, but due to the stream being live, and the volume of water being considerable even during the drier months, we decided to lay a concrete slab instead.

By laying a concrete slab, we could envelop the shuttering in plastic and divert the stream around. However we were struggling with room, as the concrete culvert sections took up more than the width of the stream, there was not much room to divert the stream around. Therefore we installed a small catchpit ‘upstream’, and from here we ‘over-pumped’ the work area to reduce the flow of the stream.

With the flow significantly reduced, we were able to excavate for and form shuttering for a concrete pad, for the culvert sections to sit on. We put a double-layer of thick dpm plastic within the shuttering, and formed a concrete slab 200mm thick, with 2 layers of reinforcing mesh to the middle. The concrete was allowed to cure for two weeks before the concrete culverts sections were scheduled to be delivered.

We looked into different ways of lifting the concrete culvert sections into place. We originally planned to have a 13-tonne ‘track machine’ on site, this would lift the sections off the lorry and onto the concrete pad. But due to trees on either side of the site entrance, some of which had protection orders on, we had to look at bringing a crane onto site. The size of crane required meant that it would have to sit in the road, and this in turn would close half of the road off for many hours. This also had implications for pedestrians as they would be passing on the pavement underneath the crane and through a live site, in effect. We spoke to Northants Highways and it was decided that we would use 2-way traffic lights to control the traffic. And that the pedestrians would be diverted into a temporary pedestrian walkway around the crane as it sat in the road.

We instructed A-Lift Crane Hire from Northampton to assist us with these works. (A few other local crane companies told us this job couldn’t be done!) We had to co-ordinate the crane hire, the delivery of the culvert sections, and the traffic lights, and all other deliveries, all to happen on the same day. The crane lift was particularly difficult due a combination of various overhead BT cables and also the many trees that surrounded the front of the site, it was very tight as the 7-tonne culvert sections were lowered down amongst all these overhead obstacles! We decided on a strong sand and cement mix to bed the culvert sections onto, on top of the pre-formed concrete. There were only 3 culvert sections to go onto the concrete base, but at 7 tonnes each, we didn’t want to be lifting them on and off our screed too many times, so we spent a lot of time getting the screed exactly right, on top of the concrete slab.

The culvert sections interlocked where they met, and we had to seal them at this point as well, with bitumen and with thick flexible bitumen strips as well. 

Looking down the culvert sections either side, we laid a double sand-bag wall 450mm thick, to retain the fill between the long edges of the culvert sections. We used 6F2 for the fill, which we compacted in layers with a heavy duty trench wacker, as the road above was to go on top of all this construction.

Before we could form the road on top of the new culvert, we had to lay services across to the proposed new build. These included electric, BT & Water. With these in, we brought type 1 in to form the sub-base of the new road. We laid kerbs either side to retain the tarmac and then laid 150mm of 20mm base course tarmac, to enable heavy traffic across the culvert/bridge for the duration of the build.  The tarmac will be topped later on at the very end of the build, with a 6mm top coat. 

Our last job was to lay oak sleepers at each end of the culvert, purely for cosmetic reasons. We finished these works just in time, as the wetter weather set in towards the end of September and the flow increased significantly. It was a pleasure to carry out this very exciting and challenging job for our customer, and from here we were ready to make a start on the groundwork for the new build. Case study coming soon for this.

Sewer connection and associated utilities works, Creaton

Projects

Sewer connection and associated utilities works, Creaton, case study

We were approached by David, a friend of his recommended he contact us regarding his project whereby he required a sewer connection and various other utilities laying from his barn conversion, all the way down to the Highway, 250 metres away.

Location
Creaton, Northants
Client
Private customer
Value
circa £40k
Transport-Truck-02

Objective

Our objective was to connect to the sewer in the Highway and lay pipework to the boundary with the property. And then to lay drainage including pipework & manholes, from the boundary with the Highway, all the way to the location of the barn conversion, over 200 metres away. We also laid other services in the same trench.

About the project

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As is usual, we took care of both the Section 106 to Anglian Water, and also the Section 50 to Highways. Our customer already had drawings for the proposed drainage in the site, but we asked for amendments to be made to include the work in the Highway. These included for the pipework to be laid across the road to the connection point in the footpath. A ‘drainage drawing’ submitted to the Water Authority for a Section 106 has to include the pipework, detailing the pipe material & size, it has to detail the size of the existing sewer we are to connect onto, and the method of connection. In this case the method of connection was ‘Junction Insertion’.

With the drainage drawing amended, we facilitated the Section 106 application to Anglian Water. This was passed within a couple of weeks, and with the Section 106 Approval Letter in hand we made the application to Highways for the Section 50 – you cannot legally apply for a Section 50 to ‘dig up the road’ before you have the Section 106 from the water authority. Highways have a duty of care to ensure we have permission to connect onto the target apparatus, in this case the public sewer. As part of our Section 50 application to Highways, we nominated ‘give and take’ traffic management, as the road was a quiet ‘dead-end’ road without much traffic. The Section 50 was approved within 3 weeks, as is usual for a simple S50 application – but beware, the application can often take much, much longer. Click here to find out more.

We had to give 3 weeks’ notice to Highways that we wished to use our Section 50 Licence. We started on the ‘other’ side of the road to the site, in the footpath, where we believed the public sewer to be. We found the pipe at 1.6m deep, and under various other services. We made the connection onto the public sewer on day 1, and this was inspected and passed by Anglian Water on day 2. With the connection made and approved, we worked our way across the road, laying 100mm clay pipes in the direction of the site. We completed the work in the road in two halves, reinstating the first half with tarmac before continuing with the second half. The work in the Highway was complete in 6 days, including all reinstatement.

We arranged with our customer to carry out the works in private property straight after the work in the Highway. The work in private property included laying 110mm plastic pipework for the foul drainage, and various manholes along the way, and also other services relating to the barn conversion. These included 125mm electric duct, 90mm BT duct, 32mm water pipe and also a spare 63mm electric duct for future use, i.e. electric gates or similar.  

We dug various trial holes and CAT-scanned the site for electric, and luckily found there to be no services in the first half of the route. There was some electric in the second half nearest the barn conversion, we marked these and also dug exploratory holes to ascertain depth of cables etc.

The electric ducts were supplied by National Grid, as is usual, and we collected them from their local depot. We dug our trench about 1.2m deep. The foul and the water pipe were laid towards the bottom, the foul in gravel surround and the water in sand surround, with warning tape to cover. The two electric ducts were laid above and also the BT, and laid in sand surround and with more warning tape to finish.

The services were all laid to one side of the farm track leading to the barn conversion, but we had two tarmac roads to cross further up, which we reinstated with tarmac afterwards. We pulled draw cords through the ducts to enable cables to be pulled through later. With the total distance of pipework being in excess of 200 metres, and with four separate rolls of 32mm water pipe being laid and joined together, we decided to fusion-weld the water pipes together so we could be sure that the joints were 100% watertight under pressure later on when the connection was done in the Highway by Anglian Water. The most common way to join water pipes together is by way of ‘compression joints’, but it is harder to know for sure that the connections are good, in advance of the pipes being live, and we wanted to have confidence that we could backfill in advance of this. 

All trenches were compacted in layers and reinstated, whether it be with grass or topsoil, or tarmac where we crossed roads further up. The ground at the top was particularly wet, and some of the foul pipe runs were in excess of 1.8m deep here. We found various land drains running through our trenches at this point as well, which made our job harder, with water pouring into our trenches as we were excavating and laying various pipes and ducts. With all of the trenchwork complete, we went back to the bottom of the track and tidied the site from start to finish, scraping the farm track as we went, and hosing and sweeping where required

Timeline

Time taken to quote for the works: Less than 1 week

Time taken to obtain Section 106 Licence from AW: 2 weeks

Time taken to obtain Section 50 Licence from Highways: 3 weeks

Leadtime to use S50 Licence: 3 weeks

Time taken to do the work: 3 weeks

 

Total time:  12 weeks

Do you need a sewer connection needs doing? Click here to enquire.

Don’t leave it too late for a sewer connection, most people do! Read our article here: How long does it take to do a sewer connection?

Click here to see more of our case studies.

Vehicle crossover, Knuston

Projects

Vehicle crossover and tarmac drive, Knuston

We were approached by a regular customer of ours, who had been redeveloping a large property in the village of Knuston in Northamptonshire. The driveway had already been block-paved in the main. The entranceway was being made bigger with new walls and electric gates, and the customer wanted tarmac for this part. There was an existing crossover, in tarmac, but it was very tired and falling to bits, so it was decided to resurface this at the same time.

Location
Knuston, Northants
Client
Private customer
Value
£x,xxx
Sewer Connections - Building-Site-Scene - JW Clark

Objective

Our objective was to lay tarmac in within the new entranceway and between the new stone walls, but also to excavate the existing crossover and to relay with tarmac, all at the same time.  

About the project

Whilst our customer was having completing the remainder of the block paving within the site, and building the walls either side of the new crossover, we approached Highways regards resurfacing the existing crossover. We were told this would need a Section 171, as opposed to a Section 184, which is to create a new crossover from scratch. In deciding method of traffic management we had to consider that the footpath would be out of action for 2 days. As there was no footpath on the other side of the road, we didn’t have the option to simply close the footpath and send the pedestrians over to a footpath on the other side of the road. The pedestrians would have to go in the road, via a dedicated ‘pedestrian walkway’, and for this to be possible we would need 2-way traffic lights to close the lane nearest. This would also enable us to park works vehicles adjacent to the site.  

We set up the traffic lights at 8am on day 1. We proceeded to excavate the existing crossover to the required depth for type 1 MOT and for the crossover construction which in Northamptonshire is 100mm of 20mm-size base course, and 20mm of 6mm ‘top-coat’. The area to be laid in tarmac extended beyond the crossover at the front, between the new walls that had been build to the front of the property, and all the way to where the block paving had been laid in the site. The type 1 that had been laid and compacted by the customer was checked for levels and didn’t require any further work.

The spoil was removed from site by the end of day 1 and preparations made to tarmac the following day. On day 2 we arranged for base course to be delivered at 8am, and it arrived shortly after. The tarmac was delivered on a lorry with chutes to the rear, which we used to fill wheelbarrows. The base course was in and laid before 11am. The 6mm ‘top-coat’ was delivered around 1pm and this was in and compacted within an hour and a half.

The new crossover and tarmac laid to the rear of the crossover was cool to walk on within a couple of hours. The traffic lights were taken down ready for the heavier teatime traffic, but we kept traffic off the crossover until the following morning, when it was open and for the customer to use.

Timeline

Time taken to quote for the works: Less than 1 week

Time taken to obtain Section 171 Licence: 1 week

Leadtime to use S171 Licence: 4 weeks

Time taken to do the work: 2 days

Total time: Just over 6 weeks

Do you need a vehicle crossover doing? Click here to get a quote. Click here to see more Vehicle Crossover case studies. 

Treatment Plant Installation, Preston Deanery

Projects

Treatment Plant, Finedon, Case Study

Location
Finedon, Northants
Client
Private customer
Value
Circa £12k

 

We were approached by a domestic customer in Preston Deanery, Northants, They had an old septic tank, and this was preventing them from selling their house, as septic tanks are no longer compliant in most cases.

Sewer Connections - Building-Site-Scene - JW Clark

Objective

Our objective was to install a new septic tank, including electrical connection. Then to lay pipework to a live watercourse, and to switch the old foul system over to the new Treatment Plant.

We did a site survey first, to ascertain levels, including levels of the existing foul system and septic tank, and how it would work with the inlet level on a new Treatment Plant. We also had to factor in the level of the watercourse (the stream) relative to the outlet on a new Treatment Plant. The house had 6 bedrooms, so would ordinarily need an ‘8-person’ Treatment Plant. However, the property had he potential to add more rooms and bedrooms, and was soon to be sold, so we opted for a 10-person plant to allow for extra future capacity. The levels didn’t work very well with the stream – the outlet level on the plant was about the same height as the level of the stream in summertime. With the level of the stream likely to be much higher during wetter months, this would put the outlet of the plant below the level of the stream, which would have the effect of flooding the plant. A one-way non-return valve would be solution to prevent the plant from being flooded, but still, the effluent from the plant would not be able to discharge for many months of the year.

We therefore opted for a ‘pumped outlet’ whereby the effluent is pumped uphill and then discharges into the stream at the very top, and away from the level of the stream down below.

We started the work in September, but the weather wasn’t great, so we brought track mats to site, to move the plant about the garden without causing too much damage to the grass. We excavated for the Treatment Plant first, and installed it on a concrete slab, with full concrete surround. The plant was installed in order that the inlet was low enough for the existing foul drainage system to be able to discharge into it. This put the plant about 250mm below the existing grass, so we needed a riser fitting to the plant, which was supplied to us by the manufacturer, Marsh Industries. We’ve been working with Marsh for nearly 20 years and always install their Treatment Plants, which are made to order.

With the plant installed, we excavated for and lay the outlet pipe, this was a black 32mm MDPE pipe. This was laid to within 3m of the stream, and then put into a 110mm underground drainage pipe. The pipe was surrounded with ‘fill’ sand, and warning tape laid above, and then the trench backfilled and the grass reinstated.

We then excavated for the electric feed to the plant, this was laid in a black 63mm duct. The electric feed was taken from one of the outhouses, with an isolator fitted, as per Building Regs. We instructed an electrician, who connected up by the ‘blower’ which blows oxygen into the plant, and also the pump which pumps the effluent out to the stream, when the effluent in the plant gets to a certain level.

We then excavated for and made the switchover from the old system to the new system, which included fitting a new manhole where the old pipework met our new pipework. All systems were tested, and the remainder of the garden and gravel driveway reinstated.

The work took a bit more than a week, and as with an install of any Treatment Plant, it’s good to see a satisfied customer, and no longer with the worry of a non-compliant septic tank. 

 

Our customer was kind enough to leave us a 5-star review on Google afterwards.  Click here to see our Google reviews

Timeline

Time taken to quote for the works: Less than 1 week

Our leadtime to carry out the works: 6 weeks

Time taken for Treatment Plant to be manufactured: 6 days

Time taken to do the work: 6 days

Unfortunately it took over two weeks for the customer to obtain the full Building Control approval certificate. Whilst this is usual, it did hold up the sale of the property.

If you need a Treatment Plant installling and the project is part of selling a property, be sure  to contact us with as much notice as possible. 

Gabion retaining wall, Irthlingborough

Projects

Gabion stone Retaining wall, Irthlingborough, Case Study

Longstanding customer of ours, Whitworths, asked us to construct a gabion stone retaining wall to enable extension of existing parking area at their site in Irthlingborough.

Location
Irthlingborough, Northants
Client
Whitworths
Value
£xx,xxx
Sewer Connections - Building-Site-Scene - JW Clark

Objective

We were tasked with creating a gabion stone retaining wall 1.8m high and 200m long, to enable our customer to extend their existing hardstanding area, in preparation for future expansion. 

About the project

A gabion stone wall had been started many years ago adjacent to the boundary with surrounding fields. This had been done with granite stone. Our customer asked us to extend this to bring it up to a height in order that the existing hardstanding area could be extended closer to the site boundary.

The design included a foundation for the baskets, made with 6F2 recycled concrete. This was already on site and had been processed on site recently, as part of a demolition project. We compacted the 6F2 in layers to bring it up to the required level. The gabion stone baskets were installed with a slight fall to the site, to help with the pressure of the ground that would be put up against the wall later. We used good quality gabion baskets for this, there are varying qualities of gabion baskets on the market, but from previous experience some of the cheaper options available tend to ‘bulge’ in time with the weight. We’ve also learnt to install the internal straps that are available and that go inside the baskets prior to filling them with stone, this also helps to reduce bulging.

The original gabion stone wall that had been done many years ago had been done with granite stone, however we used ironstone on this occasion, this with cost in mind and also local availability. With the baskets in place, we started to fill them with stone. The stone can, generally, be put into the baskets with a machine. But there is some sorting required, which had to be done by hand, particularly with the face of the wall and on top, where the stone will be seen. 

The wall was 1.8m high in places and stepped back from the watercourse at 45 degrees. With all of the gabion wall constructed, we put some of the excess 6F2 that was on site, up against the wall. The work to bring the site up to the required level is a long term project, but is ready to be completed at a later date.

It was a pleasure to carry out this work for a longstanding customer of ours, and on our doorstep too, in Irthlingborough. A lot of our employees actually live in the town. We look forward to continuing our working relationship with Whitworths in the future.

Do you have a similar project you would like a price for?  Please visit our website and fill out our contact form. We undertake all types of groundwork projects, both commercial and domestic, see here for our full list of services www.jwc.co.uk 

Treatment Plant Installation, Silsoe, Bedfordshire

Projects

Treatment plant installation, Silsoe, Case Study

We were approached by our domestic customer in Silsoe, Bedfordshire, who had an old septic tank with various problems and which was not compliant. They wanted a new Treatment Plant fitting in its place.

Location
Silsoe, Bedfordshire
Client
Private customer
Value
£13k
commercial contracts

Objective

Our objective was to install a new treatment plant and re-route the existing drainage to this, from the old septic tank. The septic tank was not particularly old, but was not compliant to discharge effluent into the ground under new EA and Building Regs guidance, and the land drainage or soakaway was not coping well in discharging the effluent, this is one of the most common reasons for septic tanks failing. 

About the project

Prior to ordering the new treatment plant, we had to take some levels to site to ascertain the invert level of the existing drainage, this level is critical in determining the length of the ‘neck’ on the new plant, which are all made to order. We use Marsh Industries for all our Treatment Plants and Pump Stations, and have been doing so for over 15 years now. We gave our customer the choice of either an 8-person plant or a 10-person, and they chose to go with the 8-person.

We started by excavating for and installing the new treatment plant, leaving all of the existing drainage running into the old septic tank whilst the bulk of the work was being carried out on site. The plant was laid on concrete and completely surrounded in concrete. The plant has to be filled with water whilst the concrete is being packed around the outside, with the level of the concrete never coming higher than the level of the water inside. On the following day, with the concrete having ‘cured’, the water can then be pumped out. The strength of the plant is dependent on the concrete surround, they are not designed to take the weight and the pressure of the ground around the outside without the concrete.

The effluent from the new Treatment Plant was to disperse into a watercourse on the boundary of the property, which is by far the best way to legally discharge of the effluent, and it’s also the cheapest way, much cheaper than excavating for and laying land drainage. The levels worked for the effluent to discharge to the stream by gravity, which was great. This pipework was installed after the plant install, and the grass reinstated on top.

The plant was conveniently located adjacent to a double garage, with full electrics. This was ideal for connecting the plant up to. We excavated for and laid a 63mm black electric duct to the outside of the garage. The duct was surrounded in sand with electric warning tape to cover, the trench backfilled and the grass reinstated. Our customer appointed their own electrician, but we liaised with him as to what was required. As per building regs, a treatment plant needs its own isolator, which the electrician sited on the inside of the garage. Quite often they are sited outside, but either is acceptable.

We then had to divert the existing drainage from the old septic tank, to the new treatment plant. We excavated for all the pipework first before making the switchover. With everything dug out ready for the final piece of pipework, we ‘bunged’ the pipework from the house and switched the pipework over. This way, our customer was able to continue to flush their toilets and carry on using the system throughout.

The existing septic tank was quite extensive and the customer asked that we fill this huge void underneath their driveway, with some of the spoil that had been generated from the excavation for the new treatment plant. To enable us to do this, we asked the customer to have the septic tank emptied one last time after the switchover had been done. This enabled us to fill it with the excavated material. We compacted it best we could on top, and reinstated with grass, getting rid of all the old manhole covers on the top of the septic tank.

With the electrical connection done by the customer’s electrician we checked the new system over and everything was working great. We reinstated some tarmac on the edge of the driveway, but most of the reinstatement was in grass. We managed to salvage most of the turf that we had taken up and put this back, which just left a few gaps here and there, which we filled with fine-grade topsoil and grass seed.  

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How deep are public sewers?

How deep are public sewers in the UK?

For the purposes of this article, when we talk about ‘public sewers’ we are talking about sewers owned and/or adopted by the local Water Authority, such as Thames Water, Anglian Water etc. These sewers will ordinarily be in the Highway, i.e. the road, the pavement or the verge. In around 90% of cases we find them to be in the road. And a public sewer can either be ‘foul’, by which we mean that common sewerage is discharged into them, ‘surface water’, by which we mean that rainwater and other ‘run-off’ water is discharged into them, or ‘combined’ which of course means a combination of the two.

Just because a sewer is owned by a Water Authority, it doesn’t mean that it is in the Highway, it can actually be in private property. So you could have a public sewer running through your back garden, and on a lot of old properties they actually do run across the backs of people’s houses, this is most common in council properties (including ex-council properties) and also many old terraced streets dating back to Victorian times, but also up until 1950s and beyond. We have even known instances of new-build estates nowadays having public sewers running through people’s back gardens. To find the location of most public sewers, click here. 

Back to “How deep are public sewers”, we have been doing sewer connections all over the country for 20 years now, and so this article is based on our experience, not from any official statistics from any water authority.

To date, we have never known a foul  public sewer to be less than 1 metre deep. This will normally be at the ‘start of the run’, which basically means where the public sewer picks up the first house. From this shallowest point of course the sewer will get deeper and deeper, but sometimes if the road is falling in the opposite direction, then the sewer will get shallower relative to the level of the road. In the event that a sewer started at 1m deep, but the level of the road was falling towards the ‘start of the run’, then relative to the road the sewer will become shallower.

Conversely, if the road is falling more than the sewer needs to fall (makes sense…?!) then the sewer is going to get very deep, very quickly.

By the way – all sewers have to be in excess of 750mm deep to prevent freezing during the winter months in the UK, but we have never found them this shallow.

But how deep do they get? Well, from our experience we tend to find them to be between about 1.5m deep and 3m deep. But they can be much much deeper. In Northampton Town Centre they tend to be 5-6m deep. This is because the ground is relatively flat, but with such a dense population and sheer number of properties packed in together, and all in need of a connection to the sewer, the main foul sewers have to fall as they collect more sewerage from each property, resulting in such deep depths. A lot of large towns and cities are the same.

The deepest sewer we have ever known is 7m deep, this was only 6 metres from the River Thames in Richmond. A quick Google search tells us that the River Thames is only 4.5m deep at this point, so the sewer is a lot deeper than the Thames! If you see on the picture it looks to have been about 6m deep when built, but with another 1 m of brickwork added later on.

A lot of these sewers date back to Victorian times, and of course they would have been dug “by hand”, with no machinery such as excavators available back then. When you stop and think about that, it’s not just a nice historical detail — it’s outrageous. We are talking about gangs of men in the 1800s standing in a trench, lowering themselves down with shovels, picks and buckets, and physically cutting their way through clay, gravel and whatever else was in the ground. There were no 13‑tonne diggers, no breakers, no trench boxes, no piling rigs. Just muscle, time and a lot more risk.

Just imagine a 7m deep trench having been dug by hand. Seven metres is basically a two-storey house turned upside down. Today, at anything over about 1.2–1.5m and we already have to start thinking about shoring, collapse risk and safe access. By 3m, you’re into proper engineered temporary works, method statements, permits, edge protection etc. At 5m and deeper, you’re talking about serious planning and cost just to keep people safe in the hole before you even start installing the pipe. Picture the Victorian version of that: narrow timber supports at best, candles or oil lamps for light, people standing at the bottom in stale air, passing spoil up in buckets and lowering bricks, mortar and pipes back down the same way.

 

That level of effort explains two things we still see today: first, why so many of the old sewers were built to last, often in brick or salt-glazed clay, and why they’re still in use more than 100 years later; and second, why they’re often so deep. Once you’ve dug a main run down the street to that depth, you don’t want to come back and move it or lower it. It just stays there, and everybody up the line has to work with it. That’s why we still come across foul sewers at 5m, 6m, sometimes 7m plus in older towns and city centres. The route and depth were set in Victorian times by men with shovels, and we’re all still dealing with those decisions every time we apply for permission to connect to a public sewer all these years later.

When a customer asks why a connection can’t just be done “next week” or “for a couple of grand”, this is the background. We’re not just tapping into a pipe. We’re tying into a piece of Victorian civil engineering that sits ridiculously deep in the ground, and every metre of that depth multiplies the planning, the paperwork, the temporary works and the risk. The Victorians did the hard digging. And now we are the ones who now have to dig back down to it safely and legally, and of course to today’s standards.

If you Google “deepest sewer in the UK”, you’ll come across the Lee Tunnel, a ‘combined’ sewer, which means it carries both foul and surface water mixed. It runs from Abbey Mills pumping station to Beckton Sewage Treatment Works in East London, and was completed in 2016. This tunnel is just over 4 miles long and in some sections it runs more than 70 metres below ground level, which is an insane depth when you think about it — that’s far deeper than any basement, foundation or standard utility run.

A job like that can’t be done with normal ‘open excavation’. Instead of the traditional cut-and-cover method (which basically means digging a huge trench from the surface, laying the pipe, and backfilling), the Lee Tunnel was constructed using TBMs — Tunnel Boring Machines. A TBM is essentially a giant underground drilling and lining machine that bores its way forward through the ground, supports the face, and builds the tunnel as it goes. You don’t see most of the work from the surface; it’s all happening deep below your feet.

The scale of that project shows what’s possible with modern engineering, but it also highlights how extreme some of the UK’s foul drainage infrastructure really is. We’re not just dealing with pipes a metre or two down under the pavement. In some areas the public sewer network is on a completely different level — literally tens of metres down — and that depth drives complexity, cost and lead time any time you want to connect into it or work anywhere near it.

We’ve generally covered ‘foul’ sewers above, and most of that applies to surface water sewers as well. However, surface water sewers by their very nature do not need to fall as much as foul. As they only generally carry water and no solids, the fall on these pipes can be hardly anything at all. For this reason, albeit they start off around the 1m mark, although they get deeper and deeper, they do so at a lesser extent. In any location where there is a foul and surface water sewer running side by side, the surface water sewer is likely to be the shallower of the two, This is good news in the event that you need a connection doing to the surface water sewer, as of course it will be cheaper, the shallow it is.

As and when a new connection is required onto an existing sewer – which we specialise in at JW Clark Ltd – the pipework has to be laid to the ‘invert’ of the existing sewer. So if the sewer is 4m deep for example, and plenty of them are, then the connection we undertake will be 4m deep. It is not possible to make a connection near to the top of a 4m deep manhole and for the sewage to ‘plop’ into the bottom of the manhole, as this causes blockages to the network and the water authorities don’t allow that under any circumstances. And so the deeper the existing sewer, the more costly the sewer connection. A 1.5m deep sewer connection will require that our excavation is made safe whilst the work is being carried, using trench sheets or a ‘trench box’ for example. But to make a 4m or a 6m excavation safe, is a completely different ball game. We can spend literally days, just sheeting an excavation and making it safe throughout. All of this makes a deep sewer connection particularly expensive. 

If you need a sewer connection completing for a new build, or for an existing property where there is no mains sewerage connection, please be sure to contact us as soon as possible. A lot of developers build a house and then make contact with us, when they should ideally be contacting us prior to starting a project. We even have regular customers of ours who consult us prior to buying a plot of land. If a sewer connection is going to be particularly deep, or if the sewer is a long way from the site, then sometimes this makes it cost-prohibitive to build a new property.

See our fact sheet here which details why you should give us as much notice as possible when you need a sewer connection completing. 

Use our Contact Us form here for a new sewer connection. 

See here for an explanation of how to find the location and depths of existing sewers.

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Guide to downloading Wastewater Asset Plans for Anglian Water & Severn Trent

(For Thames Water Asset Plans please Click Here), and start by clicking the green ‘Register Now’ button on the right hand side of the first page you come to. (Top tip – it’s generally £60 for their standard 5-day service and £120 for their express 1-day service – but we find that if you choose ‘standard service’ it still tends to come within 24 hours!)

For Anglian Water & Severn Trent asset plans, go to www.utilities.digdat.co.uk. At the top of the page, on the far right-hand side click ‘login’. Or ‘Register’ if you
haven’t done so before – it only takes 2 minutes! Click ‘Maps’ at the top right hand side 

Enter the site address, or if this is a new site then
enter the nearest address to your site. Click search and click on the relevant address that comes up below, to continue.

On the map that comes up, make sure your site is within the area displayed. You will now have 3 or 4 options to buy different products, depending on location. Click ‘Buy’ in the green box next to the ‘Wastewater’ option.

In the first field named ‘Title’, enter the name of the plot – this is just for your own reference. Further down next to ‘Manhole Report’, make sure this box is ticked! (Please note that some customers may wish to also purchase the Clean Water drawing – although we will never need this ourselves to quote for your sewer connection)
Click ‘confirm’ at the bottom to continue

Click ‘Proceed to Checkout’

Click the little box at the bottom to agree to Ts & Cs, and then click ‘Next’ at the bottom right

Enter payment details on the final page and you’re done! The drawing should be delivered to
the email address you entered when you first registered. Page 1 will normally be a drawing
showing the various assets in that area, foul water and surface water. On page 2 you may or
may not have some helpful information showing the depths of manholes etc. In any case, this
is the drawing we need! Please email us this drawing for us to be able to quote for your sewer connection.

If you struggle with any of the above, please let us know and we’ll help you as
best we can.

NEW: JW Clark now provide a service whereby we download a drawing on your behalf. Of course it’s cheaper to do this yourself, but for £80+VAT we can do this for you, and this includes paying the required fee. Click here to use this service.

Beware….! In some instances the asset plan that you download will not show any sewers at all. But the Digdat system will still allow you to purchase and download a drawing for that particular area. And to confuse things even more, the fact that there are no sewers indicated on a drawing, does not necessarily mean that there aren’t any, it just means that the Water Authority don’t have a record of them. The main reason for this is that over time, the government has forced Water Authorities to take on and adopt more of the sewer network as their own, with pipes that were once private and unadopted (including those in the Highway) later on becoming the property of the Water Authority. However, when it comes to public sewers in the Highway, we estimate that about 90% of drawings you download, will show an accurate record. If you need any help interpreting a Water Authority Asset Drawing, then please don’t hesitate to talk to us.

Click here for a quote for a sewer connection

Click here to read more about Section 106 applications to a water authority

Click here to read about Section 50 applications to Highways

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