Storm overflow register · Yorkshire Water

Crofton sewage works: storm overflow spills 2025

Crofton sewage treatment works, run by Yorkshire Water, has 2 monitored storm overflows discharging to Oakenshaw Beck. In 2025 they recorded 60 spills totalling 310 hours, against 29 spills and 166 hours in 2024. By hours spilling, it ranks 135 of 283 Yorkshire Water works, where 1 spilled longest.

Works size: 9,321 population equivalent (CROFTON 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.

JanFebMarAprMayJunJulAugSepOctNovDecCrofton STW2 spills, 3.5 h, 1 Jan to 1 Jan5 Jan 2025 19:15 GMT, 20.5 h27 Jan 2025 02:45 GMT, 30 min22 Mar 2025 16:30 GMT, 45 min4 spills, 1.5 h, 15 Jul to 15 Jul19 Jul 2025 15:15 GMT, 15 min2 spills, 2.3 h, 20 Jul to 20 Jul3 spills, 0.8 h, 27 Aug to 27 Aug28 Aug 2025 14:00 GMT, 15 min2 spills, 0.5 h, 4 Sep to 4 Sep3 spills, 1.3 h, 11 Sep to 11 Sep3 spills, 5 h, 17 Sep to 17 Sep4 spills, 14.3 h, 20 Sep to 21 Sep3 spills, 4 h, 27 Sep to 28 Sep8 spills, 7.3 h, 2 Oct to 4 Oct3 spills, 2.8 h, 19 Oct to 20 Oct3 spills, 1.3 h, 31 Oct to 31 Oct4 spills, 1.3 h, 4 Nov to 4 Nov8 spills, 11.5 h, 10 Nov to 12 Nov5 spills, 42 h, 14 Nov to 16 Nov5 spills, 2.8 h, 18 Nov to 19 Nov22 Nov 2025 06:15 GMT, 15 min5 spills, 3.3 h, 23 Nov to 23 Nov8 spills, 22.5 h, 28 Nov to 30 Nov3 spills, 1.8 h, 1 Dec to 1 Dec6 spills, 11.3 h, 4 Dec to 6 Dec3 spills, 17.3 h, 9 Dec to 10 Dec6 spills, 13 h, 15 Dec to 16 Dec7 spills, 19.3 h, 17 Dec to 20 Dec4 spills, 7 h, 21 Dec to 22 DecCrofton STW6 spills, 15.8 h, 1 Jan to 1 Jan15 spills, 34.8 h, 5 Jan to 7 Jan6 spills, 2.8 h, 27 Jan to 27 Jan3 spills, 6 h, 20 Sep to 21 Sep2 spills, 20.5 h, 14 Nov to 15 Nov4 spills, 10.8 h, 18 Dec to 19 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.

020k40k60kJan 2025: 78 h spilling ≈ 12,409 m³ (range 4,943-31,154 m³)JanFeb 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)FebMar 2025: 0.8 h spilling ≈ 128 m³ (range 51-321 m³)MarApr 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)AprMay 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)MayJun 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)JunJul 2025: 4.0 h spilling ≈ 639 m³ (range 254-1,604 m³)JulAug 2025: 1.0 h spilling ≈ 160 m³ (range 64-401 m³)AugSep 2025: 31 h spilling ≈ 4,951 m³ (range 1,972-12,430 m³)SepOct 2025: 11 h spilling ≈ 1,789 m³ (range 712-4,491 m³)OctNov 2025: 104 h spilling ≈ 16,610 m³ (range 6,616-41,700 m³)NovDec 2025: 80 h spilling ≈ 12,825 m³ (range 5,108-32,197 m³)Dec
Cubic metres (m³), estimate. Hours are measured by the event duration monitor.

Longest single spills

Started (GMT)OverflowDurationEstimated volume
14 Nov 2025, 08:30Crofton STW1.7 days2,545 - 16,038 m³
5 Jan 2025, 19:45Crofton STW1.1 days1,670 - 10,525 m³
5 Jan 2025, 19:15Crofton STW20.5 h1,304 - 8,220 m³
14 Nov 2025, 18:15Crofton STW20.3 h1,288 - 8,119 m³
9 Dec 2025, 04:00Crofton STW16.8 h1,066 - 6,716 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 estimate49,510 m³range 19,721 - 124,297 m³
In litres49.5 millionrange 19.7 million - 124.3 million L
Olympic swimming pools20at 2,500 m³ each
Organic load, as people's raw sewage74,265person-days of untreated BOD

Assumed spill rate while spilling: 17.7 - 111.4 L/s (central 44.4 L/s), from a dry-weather flow of 17.7 L/s.

Pollutant releasedLowCentralHighConcentration used (low / typical / high)
BOD₅ (organic load) 789 kg4,456 kg24,859 kg 40 / 90 / 200 mg/L
Low/high: Europe range, Ellis & Jenkins 2005; typical: UK, Ellis & Jenkins 2005 (both via botturi)
Suspended solids 2,071 kg21,042 kg89,618 kg 105 / 425 / 721 mg/L
Low/high: Europe range; typical: UK, Ellis & Jenkins 2005 (via botturi)
Ammonium-N 37 kg312 kg1,156 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 24 kg129 kg671 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 2.0 trillion organisms49.5 trillion organisms1.2 × 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.

Crofton STW

Inlet overflow at sewage works · discharges to Oakenshaw Beck

Spills 2025
50 (220 hours) · up 285% on 2024
Spills 2024
13 (22 hours)
Long-term average
17.2 spills a year (monitored since 2020)
Monitor uptime
100% of the year
High-spill reason (company)
Not asset maintenance - hydraulic capacity
Investigation
Env Act (SODRP) investigation ongoing, Operational investigation completed
Improvement
No improvement action in reporting period
WFD catchment
Oakenshaw Beck from Source to River Calder (GB104027062560)
Outlet location
SE3629018470 (OS grid reference) · View on Apple Maps
EA ID / permit
YWS00094 · 2207 · company name: CROFTON/STW

Crofton STW

Storm tank at sewage works · discharges to Oakenshaw Beck

Spills 2025
10 (91 hours) · down 38% on 2024
Spills 2024
16 (144 hours)
Long-term average
38.5 spills a year (monitored since 2020)
Monitor uptime
100% of the year
Investigation
Env Act (SODRP) investigation completed, UWWTR investigation completed, Operational investigation completed
Improvement
No improvement action in reporting period
WFD catchment
Oakenshaw Beck from Source to River Calder (GB104027062560)
Outlet location
SE3629018470 (OS grid reference) · View on Apple Maps
EA ID / permit
YWS00093 · 2207 · company name: CROFTON/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.