Storm overflow register · United Utilities

Grange Over Sands sewage works: storm overflow spills 2025

Grange Over Sands sewage treatment works, run by United Utilities, has 1 monitored storm overflow discharging to Kent Estuary (Morecambe Bay Estuary). In 2025 it recorded 52 spills totalling 58 hours, against 57 spills and 44 hours in 2024. By hours spilling, it ranks 243 of 289 United Utilities works, where 1 spilled longest.

Works size: 9,229 population equivalent (GRANGE-OVER-SANDS 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.

JanFebMarAprMayJunJulAugSepOctNovDecGrange Over Sands WwTW105 spills, 3.4 h, 1 Jan to 2 Jan22 spills, 0.7 h, 5 Jan to 6 Jan26 spills, 0.8 h, 14 Jan to 15 Jan3 spills, 0.1 h, 25 Jan to 26 Jan3 spills, 3.8 h, 26 Feb to 26 Feb34 spills, 1.3 h, 14 Jun to 15 Jun3 spills, 1.5 h, 21 Jun to 21 Jun20 spills, 0.7 h, 15 Jul to 16 Jul4 Aug 2025 15:09 GMT, 3 min4 spills, 0.7 h, 11 Sep to 11 Sep17 spills, 0.7 h, 13 Sep to 13 Sep16 Sep 2025 01:52 GMT, 3 min62 spills, 2.5 h, 17 Sep to 18 Sep141 spills, 5.8 h, 20 Sep to 22 Sep129 spills, 4.4 h, 3 Oct to 5 Oct256 spills, 13.3 h, 3 Nov to 7 Nov16 spills, 0.4 h, 13 Nov to 13 Nov2 spills, 0.1 h, 18 Nov to 18 Nov13 spills, 0.3 h, 27 Nov to 28 Nov132 spills, 3.9 h, 1 Dec to 3 Dec2 spills, 0.1 h, 4 Dec to 4 Dec315 spills, 13.3 h, 6 Dec to 10 Dec54 spills, 1.2 h, 14 Dec to 16 Dec63 spills, 1.5 h, 17 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.

02,0004,0006,0008,000Jan 2025: 5.1 h spilling ≈ 806 m³ (range 321-2,025 m³)JanFeb 2025: 3.8 h spilling ≈ 601 m³ (range 239-1,509 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: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)MayJun 2025: 2.8 h spilling ≈ 443 m³ (range 176-1,112 m³)JunJul 2025: 0.7 h spilling ≈ 111 m³ (range 44-278 m³)JulAug 2025: 0.1 h spilling ≈ 16 m³ (range 6.3-40 m³)AugSep 2025: 9.8 h spilling ≈ 1,550 m³ (range 617-3,891 m³)SepOct 2025: 4.4 h spilling ≈ 696 m³ (range 277-1,747 m³)OctNov 2025: 14 h spilling ≈ 2,214 m³ (range 882-5,558 m³)NovDec 2025: 20 h spilling ≈ 3,147 m³ (range 1,253-7,900 m³)Dec
Cubic metres (m³), estimate. Hours are measured by the event duration monitor.

Longest single spills

Started (GMT)OverflowDurationEstimated volume
26 Feb 2025, 09:24Grange Over Sands WwTW2.1 h131 - 827 m³
7 Dec 2025, 15:25Grange Over Sands WwTW1.8 h114 - 721 m³
4 Nov 2025, 05:44Grange Over Sands WwTW1.6 h100 - 629 m³
26 Feb 2025, 11:29Grange Over Sands WwTW1.4 h88 - 556 m³
21 Jun 2025, 12:58Grange Over Sands WwTW1.2 h78 - 490 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 estimate9,156 m³range 3,647 - 22,986 m³
In litres9.2 millionrange 3.6 million - 23.0 million L
Olympic swimming pools3.7at 2,500 m³ each
Organic load, as people's raw sewage13,734person-days of untreated BOD

Assumed spill rate while spilling: 17.5 - 110.3 L/s (central 43.9 L/s), from a dry-weather flow of 17.5 L/s.

Pollutant releasedLowCentralHighConcentration used (low / typical / high)
BOD₅ (organic load) 146 kg824 kg4,597 kg 40 / 90 / 200 mg/L
Low/high: Europe range, Ellis & Jenkins 2005; typical: UK, Ellis & Jenkins 2005 (both via botturi)
Suspended solids 383 kg3,891 kg16,573 kg 105 / 425 / 721 mg/L
Low/high: Europe range; typical: UK, Ellis & Jenkins 2005 (via botturi)
Ammonium-N 6.9 kg58 kg214 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 4.4 kg24 kg124 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 364.7 billion organisms9.2 trillion organisms229.9 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.

Grange Over Sands WwTW

Inlet overflow at sewage works · discharges to Kent Estuary (Morecambe Bay Estuary)

Spills 2025
52 (58 hours) · down 9% on 2024
Spills 2024
57 (44 hours)
Long-term average
53.8 spills a year (monitored since 2017)
Monitor uptime
100% of the year
High-spill reason (company)
Not asset maintenance - Hydraulic capacity
Investigation
No investigation activity in reporting period
Improvement
Env Act (SODRP) improvement ongoing
Bathing water
Morecambe North; Morecambe South
WFD catchment
KENT - transitional (GB531207312000)
Outlet location
SD3926075060 (OS grid reference) · View on Apple Maps
EA ID / permit
UUP00826 · 017370128 · company name: GRANGE-OVER-SANDS WwTW

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 United Utilities 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.