Storm overflow register · Anglian Water

Long Bennington sewage works: storm overflow spills 2025

Long Bennington sewage treatment works, run by Anglian Water, has 1 monitored storm overflow discharging to Trib River Witham. In 2025 it recorded 50 spills totalling 485 hours, against 88 spills and 1,251 hours in 2024. By hours spilling, it ranks 47 of 419 Anglian Water works, where 1 spilled longest.

Works size: 2,671 population equivalent (LONG BENNINGTON 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.

JanFebMarAprMayJunJulAugSepOctNovDecLong Bennington STW56 spills, 130.5 h, 5 Jan to 10 Jan2 spills, 0.1 h, 27 Jan to 27 Jan28 Jan 2025 14:42 GMT, 14 min10 spills, 3.8 h, 22 Mar to 22 Mar9 spills, 2.1 h, 24 May to 24 May33 spills, 11.1 h, 27 May to 28 May6 spills, 2.2 h, 3 Jun to 3 Jun3 spills, 0.2 h, 6 Jun to 6 Jun2 spills, 0.8 h, 11 Jun to 11 Jun23 Jun 2025 00:54 GMT, 20 min7 Jul 2025 09:22 GMT, 48 min3 spills, 0.2 h, 24 Jul to 24 Jul10 spills, 5 h, 17 Sep to 17 Sep6 spills, 3.9 h, 28 Sep to 28 Sep8 spills, 5.8 h, 23 Oct to 23 Oct115 spills, 82.3 h, 10 Nov to 17 Nov10 spills, 0.6 h, 18 Nov to 19 Nov24 spills, 15.8 h, 22 Nov to 24 Nov12 spills, 37.9 h, 29 Nov to 1 Dec32 spills, 65.9 h, 4 Dec to 7 Dec22 spills, 31.4 h, 9 Dec to 10 Dec32 spills, 83.7 h, 16 Dec to 20 Dec3 spills, 0.6 h, 22 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: 131 h spilling ≈ 5,986 m³ (range 2,384-15,029 m³)JanFeb 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)FebMar 2025: 3.8 h spilling ≈ 174 m³ (range 69-437 m³)MarApr 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)AprMay 2025: 13 h spilling ≈ 604 m³ (range 241-1,517 m³)MayJun 2025: 3.5 h spilling ≈ 160 m³ (range 64-402 m³)JunJul 2025: 1.0 h spilling ≈ 46 m³ (range 18-115 m³)JulAug 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)AugSep 2025: 8.9 h spilling ≈ 407 m³ (range 162-1,023 m³)SepOct 2025: 5.8 h spilling ≈ 265 m³ (range 106-666 m³)OctNov 2025: 137 h spilling ≈ 6,247 m³ (range 2,488-15,684 m³)NovDec 2025: 182 h spilling ≈ 8,316 m³ (range 3,312-20,877 m³)Dec
Cubic metres (m³), estimate. Hours are measured by the event duration monitor.

Longest single spills

Started (GMT)OverflowDurationEstimated volume
15 Nov 2025, 00:00Long Bennington STW1.0 days438 - 2,758 m³
8 Jan 2025, 00:00Long Bennington STW1.0 days438 - 2,758 m³
7 Jan 2025, 00:00Long Bennington STW1.0 days438 - 2,758 m³
6 Jan 2025, 00:00Long Bennington STW1.0 days438 - 2,758 m³
19 Dec 2025, 00:00Long Bennington STW20.0 h365 - 2,302 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 estimate22,206 m³range 8,845 - 55,748 m³
In litres22.2 millionrange 8.8 million - 55.7 million L
Olympic swimming pools8.9at 2,500 m³ each
Organic load, as people's raw sewage33,309person-days of untreated BOD

Assumed spill rate while spilling: 5.1 - 31.9 L/s (central 12.7 L/s), from a dry-weather flow of 5.1 L/s.

Pollutant releasedLowCentralHighConcentration used (low / typical / high)
BOD₅ (organic load) 354 kg1,999 kg11,150 kg 40 / 90 / 200 mg/L
Low/high: Europe range, Ellis & Jenkins 2005; typical: UK, Ellis & Jenkins 2005 (both via botturi)
Suspended solids 929 kg9,437 kg40,195 kg 105 / 425 / 721 mg/L
Low/high: Europe range; typical: UK, Ellis & Jenkins 2005 (via botturi)
Ammonium-N 17 kg140 kg518 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 11 kg58 kg301 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 884.5 billion organisms22.2 trillion organisms557.5 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.

Long Bennington STW

Storm tank at sewage works · discharges to Trib River Witham

Spills 2025
50 (485 hours) · down 43% on 2024
Spills 2024
88 (1,251 hours)
Long-term average
83.5 spills a year (monitored since 2022)
Monitor uptime
99% of the year
High-spill reason (company)
Not asset maintenance - Hydraulic capacity
Investigation
Env Act (SODRP) investigation ongoing, Operational investigation ongoing
Improvement
No improvement action in reporting period
WFD catchment
Witham - conf Cringle Bk to conf Brant (GB105030056780)
Outlet location
SK8392045310 (OS grid reference) · View on Apple Maps
EA ID / permit
AWS00764 · ANNNF13040 · company name: LONG BENNINGTON WRC

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 Anglian 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.