Storm overflow register · Yorkshire Water

Swinton sewage works: storm overflow spills 2025

Swinton sewage treatment works, run by Yorkshire Water, has 1 monitored storm overflow discharging to River Don. In 2025 it recorded 106 spills totalling 801 hours, against 119 spills and 1,109 hours in 2024. By hours spilling, it ranks 54 of 283 Yorkshire Water works, where 1 spilled longest.

Works size: 18,046 population equivalent (SWINTON SEWAGE TREATMENT WORKS, 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.

JanFebMarAprMayJunJulAugSepOctNovDecSwinton Sewage…91 spills, 293.8 h, 1 Jan to 17 Jan134 spills, 144 h, 19 Jan to 7 Feb4 spills, 2 h, 8 Feb to 9 Feb2 spills, 2.3 h, 10 Feb to 10 Feb2 spills, 0.8 h, 16 Feb to 16 Feb20 Feb 2025 09:15 GMT, 15 min7 spills, 3 h, 24 Feb to 25 Feb7 spills, 5.5 h, 26 Feb to 27 Feb2 spills, 0.5 h, 3 Mar to 4 Mar9 spills, 4.3 h, 8 Mar to 9 Mar4 spills, 1.8 h, 22 Apr to 23 Apr4 spills, 2 h, 27 Apr to 27 Apr2 spills, 1 h, 24 May to 24 May4 spills, 3.5 h, 5 Jun to 6 Jun5 spills, 6.8 h, 6 Jul to 7 Jul10 spills, 7.8 h, 20 Jul to 21 Jul2 spills, 4.8 h, 17 Sep to 17 Sep3 spills, 24.3 h, 20 Sep to 21 Sep28 Sep 2025 01:45 GMT, 3.3 h1 Oct 2025 09:00 GMT, 30 min3 spills, 6.5 h, 3 Oct to 3 Oct2 spills, 3 h, 19 Oct to 20 Oct3 spills, 7.8 h, 23 Oct to 23 Oct29 Oct 2025 10:30 GMT, 15 min6 spills, 8 h, 31 Oct to 1 Nov2 Nov 2025 18:30 GMT, 30 min4 Nov 2025 19:45 GMT, 3.5 h6 Nov 2025 10:30 GMT, 15 min7 Nov 2025 16:30 GMT, 15 min2 spills, 4.8 h, 10 Nov to 10 Nov11 Nov 2025 18:30 GMT, 15 min12 Nov 2025 19:00 GMT, 15 min4 spills, 74 h, 14 Nov to 17 Nov3 spills, 6.3 h, 18 Nov to 19 Nov5 spills, 10.3 h, 23 Nov to 23 Nov16 spills, 63.5 h, 29 Nov to 3 Dec6 spills, 30.8 h, 4 Dec to 6 Dec7 Dec 2025 19:00 GMT, 2.3 h25 spills, 19.8 h, 8 Dec to 10 Dec2 spills, 0.8 h, 13 Dec to 13 Dec8 spills, 17.8 h, 14 Dec to 16 Dec4 spills, 17 h, 17 Dec to 19 Dec21 Dec 2025 22:15 GMT, 11.3 h

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.

0100k200k300k400kJan 2025: 418 h spilling ≈ 129,249 m³ (range 51,483-324,485 m³)JanFeb 2025: 34 h spilling ≈ 10,358 m³ (range 4,126-26,005 m³)FebMar 2025: 4.8 h spilling ≈ 1,484 m³ (range 591-3,726 m³)MarApr 2025: 3.8 h spilling ≈ 1,175 m³ (range 468-2,950 m³)AprMay 2025: 1.0 h spilling ≈ 309 m³ (range 123-776 m³)MayJun 2025: 3.5 h spilling ≈ 1,082 m³ (range 431-2,717 m³)JunJul 2025: 15 h spilling ≈ 4,484 m³ (range 1,786-11,256 m³)JulAug 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)AugSep 2025: 32 h spilling ≈ 9,956 m³ (range 3,966-24,996 m³)SepOct 2025: 24 h spilling ≈ 7,266 m³ (range 2,894-18,243 m³)OctNov 2025: 145 h spilling ≈ 44,681 m³ (range 17,797-112,172 m³)NovDec 2025: 121 h spilling ≈ 37,476 m³ (range 14,927-94,085 m³)Dec
Cubic metres (m³), estimate. Hours are measured by the event duration monitor.

Longest single spills

Started (GMT)OverflowDurationEstimated volume
5 Jan 2025, 09:30Swinton Sewage Treatment Works4.7 days13,825 - 87,137 m³
14 Nov 2025, 06:15Swinton Sewage Treatment Works2.8 days8,221 - 51,817 m³
29 Nov 2025, 04:15Swinton Sewage Treatment Works1.5 days4,526 - 28,528 m³
1 Jan 2025, 00:00Swinton Sewage Treatment Works1.2 days3,418 - 21,542 m³
20 Sep 2025, 13:00Swinton Sewage Treatment Works23.8 h2,925 - 18,437 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 estimate247,521 m³range 98,593 - 621,411 m³
In litres247.5 millionrange 98.6 million - 621.4 million L
Olympic swimming pools99at 2,500 m³ each
Organic load, as people's raw sewage371,281person-days of untreated BOD

Assumed spill rate while spilling: 34.2 - 215.6 L/s (central 85.9 L/s), from a dry-weather flow of 34.2 L/s.

Pollutant releasedLowCentralHighConcentration used (low / typical / high)
BOD₅ (organic load) 3,944 kg22,277 kg124,282 kg 40 / 90 / 200 mg/L
Low/high: Europe range, Ellis & Jenkins 2005; typical: UK, Ellis & Jenkins 2005 (both via botturi)
Suspended solids 10,352 kg105,196 kg448,037 kg 105 / 425 / 721 mg/L
Low/high: Europe range; typical: UK, Ellis & Jenkins 2005 (via botturi)
Ammonium-N 187 kg1,559 kg5,779 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 118 kg644 kg3,356 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 9.9 trillion organisms247.5 trillion organisms6.2 × 10¹⁵ 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.

Swinton Sewage Treatment Works

Storm tank at sewage works · discharges to River Don

Spills 2025
106 (801 hours) · down 11% on 2024
Spills 2024
119 (1,109 hours)
Long-term average
107.0 spills a year (monitored since 2020)
Monitor uptime
86% of the year · Comms failure / issue
High-spill reason (company)
Performance - SW Infiltration
Investigation
Env Act (SODRP) investigation completed, UWWTR investigation completed, Operational investigation ongoing
Improvement
No improvement action in reporting period
WFD catchment
Don from Greasborough Dyke to River Dearne (GB104027057452)
Outlet location
SK4694099190 (OS grid reference) · View on Apple Maps
EA ID / permit
YWS00088 · 2160 · company name: MEXBORO SWINTON/STW

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 Yorkshire 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.