This page sets out the agreed Wealden and Southern Water framework for foul drainage in constrained catchments. It explains when the approach applies, the four step method we expect you to follow, and exactly what to submit.
We use Old Orchard, Horam which connects to Horebeech Lane Pumping Station and Vines Cross Wastewater Treatment Works as a teaching example. Where figures are quoted on this page they are drawn from that case so applicants can see how the method works in practice. Your site will have its own evidence and the numbers will differ.
The framework has been used on live cases. It will be applied consistently in consultation responses and in decisions on discharge of condition.
Use this framework where a site connects to a foul network with known capacity or performance constraints, and permission includes a Grampian style condition that controls occupation until a satisfactory foul drainage scheme is approved. It can also inform primary applications where constraints are known at the outset.
Occupancy
- Use the approved mix and standard design occupancy to derive a design population.
- One bed 2 persons. Two bed 3 persons. Three bed 4 persons. Four bed 5 persons.
- If you want to use different figures, agree that in writing with Southern Water.
Storage hours from flow rates
- Test three per capita flow rates and show all three.
- 110 litres per person per day. 125 litres per person per day. 137.5 litres per person per day which is 125 plus 10 percent for infiltration and inflow as a precaution.
EDM evidence for the local assets
- Use the most recent Event Duration Monitoring for the receiving pumping station and works.
- Summarise event count and duration bands, and call out any outliers.
Resilience and operating logic
- Show how the system behaves safely during surcharge and during power loss.
- This includes telemetry gated release, alarms, triggers, maintenance access, and adoption or private management.
This example is provided to show the method. Open the case Old Orchard, Horam WD/2025/1563/CD to view the associated reports:
- Southern Water consultation 07 10 2025 and
- Monson Report Rev C
Context
Connection to Horebeech Lane Pumping Station, onward to Vines Cross Wastewater Treatment Works. Known constraints. Upgrades planned in AMP 9.
Design population and flows
Design population from standard occupancy = 148 persons.
Test rates and daily flows
- 110 lpd → 16.28 m³ per day
- 125 lpd → 18.50 m³ per day
- 137.5 lpd → 20.35 m³ per day
Storage
Usable storage volume = 40.6 m³. Hours of cover:
- About 60 hours at 110 lpd
- About 53 hours at 125 lpd
- About 48 hours at 137.5 lpd
Lower assumed usage gives more hours of cover.
EDM picture 2023 to 2024 for Horebeech Lane
- 79 recorded events
- 72 ended within 48 hours
- 6 were around 50 to 52 hours
- 1 was an extreme fault event of several hundred hours
The storage cover of 48 to 60 hours aligns with the great majority of events in this catchment. Your catchment will have its own pattern.
Adoption
Southern Water indicated willingness to adopt at Old Orchard subject to technical acceptance, build to standard and fees. Adoption is encouraged for new cases.
Use the relationship
- required volume = daily flow × hours ÷ 24
- daily flow = design population × per capita flow
Worked example with a design population of 148 and a tank of 40.6 m³
- 148 × 110 lpd = 16.28 m³ per day → hours ≈ 40.6 ÷ 16.28 × 24 ≈ 60
- 148 × 125 lpd = 18.50 m³ per day → hours ≈ 53
- 148 × 137.5 lpd = 20.35 m³ per day → hours ≈ 48
Occupancy uses standard design practice for sewer and pumping station sizing and is the basis Southern Water expect.
Flow rates are drawn from common design assumptions for new housing and from water efficiency standards. The top rate includes a 10 percent allowance for infiltration and inflow as a conservative case. If you propose other rates, justify them and agree in writing with Southern Water.
Event Duration Monitoring records when and for how long storm overflows operate.
It is time based rather than volume based. It is the recognised national dataset for frequency and duration. Use the latest season for the relevant pumping station and treatment works. Present event count and duration bands. Explain how your storage hours correlate with the pattern in that catchment.
Where we cite figures on this page they come from the Horam example so users can see the method in action.
Your design must turn a tank into a system.
Controls and telemetry
- Controls, level sensors and telemetry remain live during a power cut using uninterruptible power on controls and communications. Pumps do not run on the battery.
Power for pumping
- Option A standby generation. Fixed or mobile with safe changeover and routine test schedule.
- Option B storage based resilience with safeguards. Hours of storage ride through outages, plus uninterruptible power for controls and telemetry, outage assumptions matched to local restoration times, a pre wired generator connection point, a tanker plan with response times, and automatic restart proven at commissioning.
Telemetry gated release
- The site does not release while the public system is in alarm. The controller reads downstream level and alarms. When the public system returns to normal and a short verification period has elapsed, the valve opens and discharge is limited and ramped. If a downstream alarm returns the valve closes. Log events and valve movements.
Sealed foul system
- There is no consented overflow from the new on site system to any ditch or watercourse. Any legacy route to a ditch must be removed or isolated. Any discharge to a watercourse would require a permit. None is proposed.
Alarms, triggers, tanker plan
- Define high and critical high set points. Define call out and response times. Prove tanker access. Commissioning includes witnessed alarm and restart tests.
Southern Water have indicated they will adopt where the asset is built to standard and fees are paid. We strongly encourage adoption and ask promoters to enter the adoption process early.
Where a private route is proposed, the approval will secure a management and maintenance plan, telemetry and data sharing, a twelve month post occupation review, and defined triggers with defined actions. We do not assume failure and we will size any security only if a clear and proportionate case arises from evidence.
Equalisation storage for a foul pumping arrangement can comply with Approved Document H when it is clearly designed and explained.
Building Control will expect capacity calculations, ventilation and odour control, safe access for maintenance, protection from surcharge, and a resilience plan.
Reference the relevant British Standards for pumping systems. These are sealed foul systems connected to the public foul sewer
Please include all of the following.
- Site description and point of connection
- Approved housing mix and standard occupancy basis
- The three test flow rates and one line sources for each
- Design population and daily flows for each rate
- Storage volume and hours of cover for each rate
- Latest EDM evidence for the receiving assets and a short analysis of duration bands and outliers
- Full resilience package including telemetry gated release logic
- Adoption route or private management route with named contacts and response times
- Commissioning test plan to be witnessed
- Monitoring plan including a twelve month post occupation review with defined triggers and defined responses
- Drawings showing location, access, kiosk, control philosophy, tanker route and any crane or lifting access if relevant
Q: What does “power resilience” mean in this context?
A: Power resilience does not always mean a fixed generator. Option B relies on storage hours with controls and telemetry kept alive, a generator connection point, a tanker plan, and automatic restart.
Q: How are odour and amenity impacts managed?
A: These are sealed systems. Provide a vent path and carbon filtration and avoid dead zones. Include a maintenance clean at sensible intervals.
Q: How does the layout impact the design?
A: You can place tanks below carriageway or within open space. Plan access, tanker route, kiosk location and geotechnical uplift early.
Q: Why can’t developers make a payment to upgrade the wider network?
A: Planning obligations must be necessary, directly related and fairly related in scale and kind. We cannot use planning to fund general network upgrades. The lawful route is site mitigation and directly related off site works if needed.
Q: What happens during unusually long incidents (long events)?
A: In unusually prolonged incidents the tank may fill. Fresh inflow will then go back to sewer at a controlled rate. This is why the Southern Water investment programme still matters. The design remains sealed to the environment.
The occupation control is clear.
Where a condition prevents occupation until a foul drainage scheme is approved and occupation has already occurred, submitting details after the event does not make that lawful.
Section 73 will not usually be available to rewrite the trigger. The proper route is a retrospective application that regularises the position with a complete and deliverable scheme.
We will contact known sites once to offer an expedited route to compliance. Where harm is shown or where the scheme cannot be made acceptable, we will enforce.
We welcome early discussion. Please email planning@wealden.gov.uk with the site address, approved mix, proposed storage volume, and a one page flow table.
If you want to pursue adoption, contact Southern Water Developer Services at the same time and include your reference in your submission.
Wealden District Council co-ordinates the Southern Water Local Authority Stakeholder Group which includes representatives from more than 20 councils across the south east, spanning from Folkestone & Hythe to the New Forest. Its main objective is to act as a platform for local authorities to come together across political party lines, to hold Southern Water (and their regulators) to account for the poor quality of our waterways and coastline.
Visit the Southern Water Stakeholder Group page for more information.