Storm overflow register · Wessex Water

Edford sewage works: storm overflow spills 2025

Edford sewage treatment works, run by Wessex Water, has 2 monitored storm overflows discharging to Mells River (S). In 2025 they recorded 92 spills totalling 585 hours, against 129 spills and 1,043 hours in 2024. By hours spilling, it ranks 68 of 242 Wessex Water works, where 1 spilled longest.

Every spill in 2025

Each blue mark is one spill, placed by when it started and sized by how long it lasted. Hover over a mark for the date and duration.

JanFebMarAprMayJunJulAugSepOctNovDecEdford Wastewater…82 spills, 39.6 h, 5 Jan to 7 Jan2 spills, 0.5 h, 24 Jan to 24 Jan54 spills, 68.5 h, 26 Jan to 29 Jan4 spills, 3.5 h, 31 Jan to 31 Jan3 spills, 0.1 h, 10 Feb to 10 Feb23 Feb 2025 20:22 GMT, 4.3 h35 spills, 15.1 h, 25 Feb to 27 Feb2 spills, 0.2 h, 23 Apr to 23 Apr7 Sep 2025 11:24 GMT, 61 min4 spills, 3 h, 16 Sep to 16 Sep10 spills, 1.3 h, 20 Oct to 20 Oct2 spills, 0.1 h, 10 Nov to 10 Nov9 spills, 9.7 h, 11 Nov to 12 Nov57 spills, 39 h, 13 Nov to 15 Nov70 spills, 16.8 h, 22 Nov to 24 Nov9 spills, 4.6 h, 29 Nov to 29 Nov61 spills, 38 h, 1 Dec to 3 Dec85 spills, 22.3 h, 4 Dec to 7 Dec11 spills, 35.1 h, 8 Dec to 10 Dec72 spills, 52 h, 16 Dec to 20 Dec26 spills, 11.7 h, 21 Dec to 22 DecEdford Wastewater…55 spills, 34.2 h, 4 Jan to 6 Jan2 spills, 7.3 h, 23 Jan to 24 Jan26 Jan 2025 04:12 GMT, 63 min19 spills, 27.2 h, 27 Jan to 28 Jan3 spills, 1.4 h, 31 Jan to 31 Jan8 spills, 20.7 h, 23 Feb to 24 Feb9 spills, 8.3 h, 26 Feb to 26 Feb4 spills, 1.5 h, 23 Apr to 23 Apr21 May 2025 17:26 GMT, 5 min2 spills, 0.5 h, 12 Jun to 12 Jun4 spills, 0.2 h, 27 Aug to 27 Aug2 Sep 2025 15:51 GMT, 10 min2 spills, 0.1 h, 4 Sep to 4 Sep7 Sep 2025 10:16 GMT, 2 h3 spills, 0.8 h, 15 Sep to 16 Sep5 spills, 0.8 h, 3 Oct to 3 Oct6 spills, 0.3 h, 19 Oct to 19 Oct3 spills, 0.3 h, 31 Oct to 31 Oct3 spills, 0.2 h, 10 Nov to 10 Nov2 spills, 1.4 h, 12 Nov to 12 Nov27 spills, 25.1 h, 13 Nov to 15 Nov8 spills, 2 h, 22 Nov to 23 Nov7 spills, 4.9 h, 24 Nov to 24 Nov5 spills, 5.2 h, 29 Nov to 29 Nov22 spills, 31.3 h, 1 Dec to 2 Dec4 spills, 2.2 h, 4 Dec to 4 Dec3 spills, 0.8 h, 5 Dec to 5 Dec5 spills, 1.2 h, 7 Dec to 7 Dec12 spills, 17.3 h, 8 Dec to 9 Dec9 spills, 1.4 h, 16 Dec to 16 Dec15 spills, 17.9 h, 18 Dec to 19 Dec2 spills, 1.1 h, 21 Dec to 21 Dec

Hours spilling by month, 2025

0100200300Jan 2025: 183 hours spillingJanFeb 2025: 49 hours spillingFebMar 2025: 0.0 hours spillingMarApr 2025: 1.7 hours spillingAprMay 2025: 0.1 hours spillingMayJun 2025: 0.5 hours spillingJunJul 2025: 0.0 hours spillingJulAug 2025: 0.2 hours spillingAugSep 2025: 7.1 hours spillingSepOct 2025: 2.7 hours spillingOctNov 2025: 109 hours spillingNovDec 2025: 232 hours spillingDec
Hours, measured by the event duration monitor.

Longest single spills

Started (GMT)OverflowDuration
5 Jan 2025, 04:55Edford Wastewater Treatment Works1.2 days
1 Dec 2025, 02:51Edford Wastewater Treatment Works1.1 days
27 Jan 2025, 14:24Edford Wastewater Treatment Works1.1 days
26 Jan 2025, 10:03Edford Wastewater Treatment Works1.0 days
27 Jan 2025, 14:50Edford Wastewater Treatment Works23.4 h

Estimated 2025 spill volume and pollution

Estimate, not a measurement. Monitors record how long an overflow spills, not how much. This calculator back-calculates a spill rate from the size of the works, using the Environment Agency's permit formulae, and multiplies it by published storm-sewage concentrations. How it works.

This works serves fewer than 2,000 people, or was not matched to a UWWTD report, so its size is not published. The population equivalent above is a placeholder of 1,000. Enter the population served if you know it.

Volume, central estimate10,022 m³range 3,992 - 25,160 m³
In litres10.0 millionrange 4.0 million - 25.2 million L
Olympic swimming pools4.0at 2,500 m³ each
Organic load, as people's raw sewage15,033person-days of untreated BOD

Assumed spill rate while spilling: 1.9 - 11.9 L/s (central 4.8 L/s), from a dry-weather flow of 1.9 L/s.

Pollutant releasedLowCentralHighConcentration used (low / typical / high)
BOD₅ (organic load) 160 kg902 kg5,032 kg 40 / 90 / 200 mg/L
Low/high: Europe range, Ellis & Jenkins 2005; typical: UK, Ellis & Jenkins 2005 (both via botturi)
Suspended solids 419 kg4,259 kg18,141 kg 105 / 425 / 721 mg/L
Low/high: Europe range; typical: UK, Ellis & Jenkins 2005 (via botturi)
Ammonium-N 7.6 kg63 kg234 kg 1.9 / 6.3 / 9.3 mg/L
Low: Germany, Brombach 2005; typical/high: Paris range 3.3-9.3 midpoint and top, Gasperi 2012 (via botturi); no UK value found
Total phosphorus 4.8 kg26 kg136 kg 1.2 / 2.6 / 5.4 mg/L
Low/high: Paris, Gasperi 2012; typical: Slovakia (via botturi). UK figure of 10 mg/L treated as an outlier
E. coli 399.2 billion organisms10.0 trillion organisms251.6 trillion organisms 10,000 / 100,000 / 1.0 million per 100 mL
Median range at CSO and retention-tank outlets, Stott et al. 2018 (via botturi); typical = log midpoint

Low combines the low spill rate with low concentrations, and high combines high with high, so the true figure is very likely inside the range. Long spills become more diluted as they go on, so the central figure tends to overstate the load of long events. The calculator does not estimate the effect on the receiving water, which depends on river flow or tide at the time of the spill.

Edford Wastewater Treatment Works

Storm tank at sewage works · discharges to Mells River (S)

Spills 2025
46 (366 hours) · down 25% on 2024
Spills 2024
61 (657 hours)
Long-term average
68.0 spills a year (monitored since 2023)
Monitor uptime
100% of the year
High-spill reason (company)
Not Applicable - Ongoing investigation
Investigation
No investigation activity in reporting period
Improvement
No improvement action in reporting period
WFD catchment
Mells source to conf with Somerset Frome (GB109053022020)
Outlet location
ST6718448659 (OS grid reference) · View on Apple Maps
EA ID / permit
WXW00402 · 010034 · company name: EDFORD STORM TANK

Edford Wastewater Treatment Works

Inlet overflow at sewage works · discharges to Mells River (S)

Spills 2025
46 (219 hours) · down 32% on 2024
Spills 2024
68 (385 hours)
Long-term average
63.7 spills a year (monitored since 2023)
Monitor uptime
100% of the year
High-spill reason (company)
Not Applicable - Ongoing investigation
Investigation
No investigation activity in reporting period
Improvement
No improvement action in reporting period
WFD catchment
Mells source to conf with Somerset Frome (GB109053022020)
Outlet location
ST6718448659 (OS grid reference) · View on Apple Maps
EA ID / permit
WXW00401 · 010034 · company name: EDFORD INLET

How the estimate works

  1. Dry-weather flow (DWF) = population × water use per person × (1 + infiltration). Water use is 136.5 L per person per day, England's per-capita consumption for 2024-25 [EA]. Infiltration of groundwater into sewers is taken as 0-40% of that flow [Escritt, via HBF]. The Environment Agency defines DWF as PG + I + E [EA].
  2. Population. The size of each works comes from the load entering it as reported under the Urban Waste Water Treatment Directive, in population equivalents (1 p.e. = 60 g of BOD a day) [UWWTD]. We treat population equivalent as population. That overstates flow where trade effluent adds load, and no official source links the two. Works serving fewer than 2,000 p.e. are not reported, so their size has to be entered by hand.
  3. Low spill rate = DWF. This is the method used by Giakoumis & Voulvoulis (2026), which they note likely underestimates storm loads [G&V].
  4. High spill rate = Formula A − flow to full treatment = (DWF + 1360P) − 3DWF. This is the largest flow the permit expects the storm tanks to handle before it passes on to treatment or overflows [EA]. The central rate is the geometric mean of the low and high rates.
  5. Volume = spill rate × hours spilling, with hours taken from the event duration monitor.
  6. Pollution = volume × published storm-sewage concentrations [Botturi et al.] [US EPA]. Organic load is also shown as person-days of untreated sewage at 60 g of BOD per person per day [UWWTD].

What this cannot tell you. It gives no real flow for any single spill, and no effect on the river or sea, which depends on the flow, tide and the other pressures on the water at the time. It gives no figure for spills from overflows on the sewer network, which serve catchments of unknown size. It is a way to put hours into rough physical terms, not a substitute for flow monitoring.

Sources

  1. EA: Water companies - environmental permits for storm overflows and emergency overflows
  2. EA: Water resources 2024 to 2025 - per capita consumption
  3. HBF: Foul sewer design - historic conventions (citing Escritt 1984 on infiltration)
  4. Giakoumis & Voulvoulis (2026), Environ. Sci.: Water Res. Technol., doi:10.1039/D5EW00860C
  5. Botturi et al. (2021), Crit. Rev. Environ. Sci. Technol. 51:1585 - CSO quality review, Table 2
  6. US EPA (2004) Report to Congress on CSOs and SSOs, chapter 4
  7. Urban Waste Water Treatment Directive, Article 2(6): 1 p.e. = 60 g BOD5/day
  8. Olympic-size swimming pool: 2,500 m³ at the nominal 2 m depth

← All Wessex Water works · Contains Environment Agency data licensed under the Open Government Licence v3.0. Spill start and stop times: © Environment Agency copyright and/or database right 2026. All rights reserved. They are water-company data and have not been verified by the Environment Agency. Works size: EEA Waterbase UWWTD. How to read the data.