Case studies

What is a Section 104 Adoption Agreement:

When a new development is planned, the Developer has the opportunity to construct the sewers using approved materials and to a standard which makes them suitable for adoption by the sewer provider when construction is complete. An adoption agreement can be entered into under Section 104 of the Water Industry Act 1991 prior to the sewers being built. This is the most desirable arrangement and if all new developments were covered by such adoption agreements, there would be few, if any, new private sewers on housing estates. However, there are many kilometres of existing private sewers that were built without an adoption agreement in place. Section 102 of the Water Industry Act 1991 provides for the adoption of such sewers to be considered.

It is important to draw a distinction between sewers, drains, lateral drains, and developments

Development Example 1: Fronting Existing Highway

Separate developments connected to the public sewer each with own adopted lateral drain

Development Example 2: Drains Not Adopted within Development boundary

Adopted lateral drain connecting development to sewer

Development Example 3: Drains Adopted within development boundary

Adopted lateral drain connecting last house. Adopted Sewer for connecting all other house

Thames Water (Section 104 adoption agreement)

Unfortunately TW do not differentiate between development examples.

The adoption process and fees for example 3 are applied to examples 1 & 2.

Drawnings: (example page 3)

Drawings to comply Thames Water local practice and in conjunction with the Design and Construction Guidance for foul and surface water sewers offered for adoption under the Code for adoption agreements for water and sewerage companies operating wholly or mainly in England (“the Code”)

Fees: (example page 4)

Same fees for 1 or 100 properties (only change in fees is the value of construction costs).

Time Scale: (process example page 5)

Approval acceptance period between 6 to 8 month.

Example drawing for section 50 licence pre May 2023

Example drawing for section 50 licence post May 2023

Thames Water Fees & Indicavative On-Costs

Thames Water S104 Adoption Proccess

About the project:

Working with both Marlborough and the London Borough of Haringey, we carried out a manhole construction and sewer connection for the ROJ Café Kiosk currently being developed within Ducketts’ Common Park.

Through the process of early engagement in the pre-construction period, we identified the most cost-effective and efficient method of construction and engaged Thames Water directly on behalf of the client.

During the Construction Period we delivered the project according to timescale, budget and QHSE standards.

As the site is within a public park, we also demonstrated high levels of communication and co-operation with stakeholders and site management in order to minimise disruption to the public.

Client Feedback:

We have received extremely positive feedback from the client and stakeholders, with Sean Rielly, Project Manager at Marlborough, praising us for, “A high quality project delivered in a timely and professional manner. We would have no hesitation in recommending PDS as a most Competent and Professional Contractor in these type of works.”

Dave Butcher, Resident Engineer at the London Borough of Haringey, also congratulated us for our, “Quality of work and attention to detail of the highest order, and an approach to Health and Safety that is exemplary. I would have no hesitation in engaging PDS for future works or recommending their work to other organizations.”

This connection into an existing 1140mm x 790mm Victorian main, at 2.5m depth, involved working within the confines of one lane of the highway, but thanks to our experience and rigorous process it was completed within the timescales given by the client – despite the very tight turnaround required between the order being placed and starting on site, which meant the relevant licences had to be obtained quickly.

The dig-and-push method that was used involved two levels of aluminium frames and hydraulic braces; we carefully core-drilled into the existing sewer and installed the new pre-formed saddle with sika sand and cement.

A single lane closure was agreed with the local authority, which was maintained at all times, plus we were able to suspend parking bays nearby which helped with the storage of materials and waste. Correct compaction and materials must be used within any highway at all times, so we used MOT Type 1 crush compacted in layers, with the correct number of petrol trench rammer to guarantee that the reinstatement will not fail when inspected at a later date.

“I would recommend Premier Drainage Solutions to anyone needing to complete a drainage project. We were impressed with the way the work was carried out, with little fuss and on time, considering there were complex logistical needs in terms of the local authority and Thames Water. We were shielded from these and the job was completed efficiently and effectively, on time.”

Suzanne Petrides, Architect / Director, Larkfield Investments

A timber heading is where a tunnel is manually excavated, and supported using timber sets, enabling the installation of sewer pipes where access is limited, and standard methods of sewer connection can’t be employed. This method of trenchless sewer connection dates back centuries, but it is very much still relevant today – it’s regularly used in London and in other large city centres, where space constraints, busy roads, and dense development makes laying sewers in trenches impossible.

Our client wanted to connect onto the public sewer within the highway in central London, but with the carriageway being a designated Red Route, a standard approach would have meant incurring a very high cost in lane closures and TFL rental scheme daily charges. With this in mind, we decided to propose a timber heading, which actually worked out cheaper than open-cut trenching when the extra costs of road closures were borne in mind. Using a timber heading, our work could be carried out from the site boundary, by tunnelling out to the main public sewer within the highway, keeping all traffic flowing as normal.

After taking level measurements from the existing upstream and downstream manholes within the highway, to give us our excavation depth for the shaft, the timber heading began as a shaft at the site boundary, excavated down to invert level. At the correct depth, the actual process of excavating towards the sewer does change depending on ground conditions, but does not change the way it is installed. Once we reached the existing sewer with the timber heading, we installed pre-formed clay saddle to complete the connection to the public sewer.

Sewer connection made, the back-fill process involved laying the pipe, and dry packing with concrete by hand, until the heading is filled back to the shaft. At this point we used the shaft to construct a new pre-cast concrete boundary manhole, leaving a stub pipe for our client to connect to.