Compton & Marldon STW
The monitor is reporting and shows no discharge.
This looks like a fault, not a storm.
This overflow has discharged in dry weather 10 times since 2020 — spills with no rainfall to excuse them. Its treatment works is not itself over capacity, so a catchment-wide explanation does not hold. Applied to this record, the two-stage lawfulness test is hard to pass: a recurring dry-weather discharge is not an exceptional circumstance, and where the remedy is routine maintenance the disproportionate-cost exception is hard to run.
How this verdict is reached →Can its works cope?
Full capacity view →This overflow drains to Compton And Marldon STW, serving about 2,303 people.
The works has headroom — so spills here point to another problem, often on that branch of the network (a blockage, a failed pump or infiltration).
Its permit
What the environmental permit sets for this overflow — and where the public record is silent, which is itself the finding.
- Pass-forward flow
- Not published
- Spill frequency limit
- None set
- Monitoring tier
- Not published
- Assessment trigger
- Not crossed (threshold 10/year)
Is anyone acting on this?
- PR24 U_MON4 from U_INV2 investigation (U_MON4c)Monitoringdue 2026
- MCERTS certification of an AMP7 U_MON3 driver output overflow operation monitor (U_MON3a)Monitoringdue 2026
An investigation or monitoring measure is active — a step towards a fix, not a fix in itself. It must lead to an improvement before anything changes.
What you can do about this one
Ask for the data
Under the Environmental Information Regulations, Compton & Marldon STW's telemetry, the works' flow-to-full-treatment setting, and any spill investigations are emissions information — they cannot be withheld on commercial-confidentiality grounds. A written request is the fastest lever.
Get it into the next programme
Investigations that will shape the 2030–35 environment programme must complete by this date. Putting this overflow on the record now — to South West Water and the Environment Agency — is what gets it considered.
Put it in the drainage plan
South West Water's draft Drainage & Wastewater Management Plan goes to a twelve-week consultation. A named overflow with evidence behind it is far harder to leave out.
The record since 2020
10 dry spills and 0 pre-STW spills since 2020. Pick a year to see its events below.
2023: 45 spills · 45 discharge events
Counted spills — the EA's 12/24-hour block method, the basis of the 10-a-year cap. Published annual return where available, computed the same way for the current year. Two ways to count →
Dry spills, every year
10 dry spills since 2020 · showing up to 12
Spilled before its works
0 events since 2020 · started while Compton And Marldon STW stayed shut
This overflow has never been recorded spilling ahead of its treatment works.
Spills by month, 2023
Dry Wet weatherEvery spill in 2023, most recent first
Each event checked against the nearest rain gauge and against the treatment works’ own overflow. Open any row for its evidence dossier.
Excluded from the counts, classification and flags above — too short to weigh against rainfall, and often an operational blip rather than a genuine discharge. Listed here for completeness. How we know.