Sewerage Capacity

Information on sewerage capacity in the district and how we are addressing it through the planning system

West Oxfordshire District Council is committed to ensuring that new housing developments are supported by the right infrastructure, particularly where the existing sewage network is already under pressure. 

Our concerns 

The Council is deeply concerned about the current state of the wastewater network in West Oxfordshire. Most of the district’s 20 sewage treatment works are already operating at or beyond capacity, and issues such as leaky pipes, overloaded pumping stations and surface water entering the system are contributing to the problem.  

Chronic underfunding of upgrades to our sewage network from Thames Water over many decades has left us in this difficult situation.  

As a result of the broken network, pollution is regularly pumped directly into our rivers and, in some cases, sewage spills in local areas.  

Our view is that action needs to be taken urgently by Thames Water to upgrade the network for existing homes and new ones. We have seen some improvements such as upgrades to the Witney sewage works but there is much more to be done. 

What are we doing and why? 

We are working closely with Thames Water and other relevant organisations such as the Environment Agency, to ensure that future planned growth is supported by the right investment in new and improved sewage infrastructure.  

At present, we have three main areas of focus:

• Setting out clear validation checklist requirements for planning applications.
• Applying planning conditions to planning permissions to ensure alignment with sewerage capacity upgrades.
• Prioritising the use of mains foul drainage in line with Government Planning Guidance and Environment Agency Advice.

Validation checklist requirements

To ensure that planning applications are supported by the right technical information, the Council publishes something called a ‘validation checklist’. Our current validation checklist requires the submission of a ‘Mains Sewage Capacity Assessment’ for all ‘major’ planning applications (i.e. residential schemes of 10 or more dwellings or commercial schemes of more than 1,000 sqm floorspace).

This assessment must include ‘confirmation from the relevant body, that the sewer network, including sewage pumping stations, linking the proposed development to the receiving sewage treatment works has adequate capacity for the increased volumes of sewage generated by the proposed development, and will not cause or increase local sewer flooding or unplanned discharges of untreated effluent’.

For more information on planning application validation requirements click here.

Use of planning conditions to align new development with sewerage capacity upgrades

In some instances, we may need to impose something called a ‘Grampian’ planning condition which effectively means that whilst a developer can build new homes, they can’t allow them to be occupied until the necessary improvements have been completed and made operational. Where a phased delivery plan has been agreed, the homes may only be occupied to the extent that the agreed plan has been completed and made operational.  

We are also currently considering whether in some instances, it would be reasonable to apply a condition that restricts above ground construction until a clear delivery plan is in place. 

In terms of process, the Council consults Thames Water on larger development proposals and if there is a concern regarding sewage capacity, will work with Thames Water to agree an appropriate planning condition depending on the specific circumstances of the case.  

In some instances, even where Thames Water have not provided a response to a planning application (e.g. smaller development proposals) the Council may still seek to impose a Grampian planning condition where there is clear evidence of insufficient sewerage capacity in the locality.

These measures are intended to make sure all new developments have the sewage infrastructure they need. By making sure we have the right infrastructure in place, we aim to benefit the residents moving into those homes, our existing communities, and the environment – all whom suffer as a result of ongoing sewage spills.  

Developments currently impacted by Grampian planning conditions 

The following developments in West Oxfordshire currently have Grampian planning conditions in place.

Locality	Site / development name	Planning application number	Number of homes affected
Brize Norton	Burford Road, Brize Norton	25/00487/OUT Outline	350
Carterton	Monahan Way, Carterton	22/03539/FUL  Full	99
Chipping Norton	Land South of Charlbury Road, Chipping Norton	24/00769/OUT Outline	104 Approved subject to S106
Chipping Norton	Land South of Hit and Miss Farm, Chipping Norton	23/00536/OUT  Outline	90
Freeland	East of Wroslyn Road, Freeland	25/00333/OUT Outline	60
North Leigh	New Yatt Road, North Leigh	23/00794/OUT  Outline	43
North Leigh	Witney Road, North Leigh	22/02498/OUT  Outline	55
Long Hanborough	Land North of Witney Road, Long Hanborough	22/01330/OUT  Outline	150
Woodstock	Banbury Road, Woodstock	21/00217/OUT  Outline	235
Woodstock	Hill Rise, Woodstock	21/00189/FUL  Full	180

We want to see new homes built, and people move into new homes, but ultimately, we need to make sure those homes have the required infrastructure.  

We therefore would advise anyone looking to buy these homes, or who are involved in the sale process that we will not be discharging the planning condition until we are satisfied that the necessary improvements have been secured.  

Prioritising the use of mains foul drainage

Because of the sewerage capacity concerns in some parts of the district, we are aware that developers are increasingly starting to consider the use of private, non-mains treatment facilities such as package sewage treatment plants as an alternative to mains foul drainage.

The Council’s position is that the first presumption in any development is to provide a system of foul drainage discharging into a public sewer to be treated at a public sewage treatment works and that the use of private non-mains treatment facilities will only be considered where it can be robustly demonstrated that it is not feasible or reasonable to discharge into a public sewer.  Issues with the public sewer being at capacity, or other operating problems with the public sewer, are not acceptable reasons to justify the use of non-mains drainage.

This position is in line with the Government’s Planning Practice Guidance ‘Water Supply, Wastewater and Water Quality’ which states that ‘Septic tanks or package sewage treatment plants may only be considered if it can be clearly demonstrated by the applicant that discharging into a public sewer is not feasible (taking into account cost and/or practicability and whether the package treatment plant poses a risk to a designated site) in accordance with Approved Document H of the Building Regulations 2010’.

What else are we doing to tackle the sewage problems in West Oxfordshire?

West Oxfordshire District Council has been actively working to address these issues and ensure that development in the district is supported by the right infrastructure. Steps we’ve already taken include: 

• Aligned planning with infrastructure delivery: Through our planning process and in line with the approach set out in our emerging Local Plan, we are committed to supporting the delivery of new homes alongside the essential infrastructure they need, including sewage systems. This helps avoid putting further pressure on an already stretched network and ensures development happens in a sustainable and responsible way. 

• Pushed for transparency and accountability: We have raised these concerns repeatedly with Thames Water and have called on national regulators, including Ofwat and the Environment Agency, to ensure the company meets its infrastructure obligations. 

• Supported affected communities and developers: We are in direct contact with affected developers and keeping local communities informed through updates like this page, as well as through ongoing conversations with partners. 

• Lobbied nationally for change: Alongside our local Witney MP, we have called for stronger national oversight of water companies and greater investment in essential infrastructure to meet the needs of growing communities. 

We will continue to advocate on behalf of residents and work to ensure the right infrastructure is in place for the homes and communities of West Oxfordshire.