Storm overflow register · Wessex Water

Pucklechurch sewage works: storm overflow spills 2025

Pucklechurch sewage treatment works, run by Wessex Water, has 1 monitored storm overflow discharging to Feltham Brook. In 2025 it recorded 63 spills totalling 657 hours, against 96 spills and 1,119 hours in 2024. By hours spilling, it ranks 58 of 242 Wessex Water works, where 1 spilled longest.

Works size: 2,687 population equivalent (PUCKLECHURCH STW, UWWTD 2018). Used for the spill volume estimate.

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.

JanFebMarAprMayJunJulAugSepOctNovDecPucklechurch WwTW5 spills, 4.4 h, 1 Jan to 1 Jan50 spills, 65.3 h, 5 Jan to 7 Jan11 spills, 4.9 h, 24 Jan to 24 Jan65 spills, 71.1 h, 26 Jan to 29 Jan29 spills, 3.3 h, 31 Jan to 31 Jan20 spills, 3.3 h, 10 Feb to 10 Feb13 spills, 24.3 h, 23 Feb to 25 Feb9 spills, 17 h, 26 Feb to 27 Feb4 spills, 2.6 h, 27 May to 27 May3 spills, 1.3 h, 5 Jun to 5 Jun2 spills, 4.8 h, 31 Jul to 31 Jul7 spills, 4.2 h, 27 Aug to 27 Aug14 spills, 0.7 h, 3 Sep to 3 Sep6 spills, 2.1 h, 4 Sep to 4 Sep3 spills, 9 h, 7 Sep to 7 Sep5 spills, 7.7 h, 12 Sep to 12 Sep13 spills, 21.9 h, 14 Sep to 15 Sep7 spills, 0.7 h, 17 Sep to 17 Sep3 Oct 2025 22:59 GMT, 7.6 h2 spills, 8.7 h, 20 Oct to 20 Oct3 spills, 1.7 h, 21 Oct to 21 Oct2 spills, 2 h, 23 Oct to 23 Oct26 spills, 18 h, 24 Oct to 25 Oct7 spills, 10.7 h, 10 Nov to 10 Nov98 spills, 92.3 h, 11 Nov to 16 Nov25 spills, 17.5 h, 22 Nov to 24 Nov3 spills, 6.7 h, 29 Nov to 29 Nov15 spills, 41.1 h, 1 Dec to 3 Dec116 spills, 85.2 h, 4 Dec to 10 Dec5 spills, 1.1 h, 12 Dec to 12 Dec81 spills, 112 h, 15 Dec to 20 Dec25 spills, 4.2 h, 21 Dec to 22 Dec

Estimated spill volume by month, 2025

Hours spilling each month × the estimated spill rate for a works of this size. The bars are central estimates and the whiskers show the low-high range. Method.

010k20k30kJan 2025: 149 h spilling ≈ 6,860 m³ (range 2,732-17,222 m³)JanFeb 2025: 45 h spilling ≈ 2,049 m³ (range 816-5,144 m³)FebMar 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)MarApr 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)AprMay 2025: 2.6 h spilling ≈ 120 m³ (range 48-301 m³)MayJun 2025: 1.3 h spilling ≈ 60 m³ (range 24-150 m³)JunJul 2025: 4.8 h spilling ≈ 221 m³ (range 88-555 m³)JulAug 2025: 4.2 h spilling ≈ 193 m³ (range 77-485 m³)AugSep 2025: 42 h spilling ≈ 1,938 m³ (range 772-4,866 m³)SepOct 2025: 38 h spilling ≈ 1,745 m³ (range 695-4,381 m³)OctNov 2025: 127 h spilling ≈ 5,856 m³ (range 2,333-14,703 m³)NovDec 2025: 244 h spilling ≈ 11,211 m³ (range 4,465-28,145 m³)Dec
Cubic metres (m³), estimate. Hours are measured by the event duration monitor.

Longest single spills

Started (GMT)OverflowDurationEstimated volume
26 Jan 2025, 11:25Pucklechurch WwTW2.7 days1,176 - 7,415 m³
13 Nov 2025, 20:37Pucklechurch WwTW2.3 days1,009 - 6,361 m³
15 Dec 2025, 11:17Pucklechurch WwTW2.2 days966 - 6,091 m³
17 Dec 2025, 23:03Pucklechurch WwTW2.1 days931 - 5,870 m³
5 Jan 2025, 01:37Pucklechurch WwTW2.0 days890 - 5,612 m³

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.

Volume, central estimate30,248 m³range 12,049 - 75,940 m³
In litres30.2 millionrange 12.0 million - 75.9 million L
Olympic swimming pools12at 2,500 m³ each
Organic load, as people's raw sewage45,373person-days of untreated BOD

Assumed spill rate while spilling: 5.1 - 32.1 L/s (central 12.8 L/s), from a dry-weather flow of 5.1 L/s.

Pollutant releasedLowCentralHighConcentration used (low / typical / high)
BOD₅ (organic load) 482 kg2,722 kg15,188 kg 40 / 90 / 200 mg/L
Low/high: Europe range, Ellis & Jenkins 2005; typical: UK, Ellis & Jenkins 2005 (both via botturi)
Suspended solids 1,265 kg12,856 kg54,753 kg 105 / 425 / 721 mg/L
Low/high: Europe range; typical: UK, Ellis & Jenkins 2005 (via botturi)
Ammonium-N 23 kg191 kg706 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 14 kg79 kg410 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 1.2 trillion organisms30.2 trillion organisms759.4 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.

Pucklechurch WwTW

Storm tank at sewage works · discharges to Feltham Brook

Spills 2025
63 (657 hours) · down 34% on 2024
Spills 2024
96 (1,119 hours)
Long-term average
71.9 spills a year (monitored since 2018)
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
Boyd - source to conf R Avon (Brist) (GB109053027510)
Outlet location
ST7118075713 (OS grid reference) · View on Apple Maps
EA ID / permit
WXW00894 · 010071 · company name: PUCKLECHURCH STORM TANK

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.