Storm overflow register · United Utilities

Dent sewage works: storm overflow spills 2025

Dent sewage treatment works, run by United Utilities, has 1 monitored storm overflow discharging to Trib River Dee. In 2025 it recorded 126 spills totalling 319 hours, against 87 spills and 232 hours in 2024. By hours spilling, it ranks 148 of 289 United Utilities works, where 1 spilled longest.

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.

JanFebMarAprMayJunJulAugSepOctNovDecDent WwTW2 spills, 4 h, 1 Jan to 1 Jan6 spills, 3.8 h, 5 Jan to 6 Jan5 spills, 6 h, 13 Jan to 14 Jan2 spills, 1 h, 21 Jan to 21 Jan6 spills, 5.8 h, 23 Jan to 24 Jan25 Jan 2025 23:45 GMT, 45 min3 spills, 6 h, 27 Jan to 27 Jan2 spills, 1.5 h, 4 Feb to 4 Feb3 spills, 2.8 h, 19 Feb to 20 Feb4 spills, 2.8 h, 23 Feb to 24 Feb26 Feb 2025 07:00 GMT, 45 min6 Mar 2025 22:00 GMT, 45 min3 spills, 2 h, 27 Mar to 28 Mar29 Mar 2025 17:00 GMT, 2.5 h2 spills, 2 h, 16 Apr to 16 Apr15 May 2025 06:12 GMT, 4 min6 spills, 4.9 h, 23 May to 25 May8 spills, 6.7 h, 26 May to 27 May22 spills, 11.8 h, 29 May to 30 May3 spills, 2 h, 1 Jun to 1 Jun7 spills, 4.3 h, 3 Jun to 4 Jun11 spills, 7.2 h, 5 Jun to 7 Jun2 spills, 6.4 h, 9 Jun to 10 Jun4 spills, 2.4 h, 13 Jun to 14 Jun4 spills, 0.9 h, 17 Jun to 17 Jun2 spills, 0.2 h, 19 Jun to 19 Jun2 spills, 0.3 h, 22 Jun to 22 Jun3 spills, 1.1 h, 24 Jun to 24 Jun26 Jun 2025 05:18 GMT, 26 min7 spills, 5.3 h, 27 Jun to 28 Jun9 spills, 12 h, 3 Jul to 6 Jul12 spills, 7 h, 14 Jul to 15 Jul17 Jul 2025 06:10 GMT, 8 min3 spills, 0.8 h, 19 Jul to 19 Jul4 spills, 1.9 h, 20 Jul to 20 Jul2 spills, 0.3 h, 31 Jul to 31 Jul3 Aug 2025 07:00 GMT, 22 min9 spills, 4.2 h, 4 Aug to 4 Aug5 Aug 2025 14:10 GMT, 6 min2 spills, 1 h, 7 Aug to 7 Aug6 spills, 1.6 h, 27 Aug to 28 Aug3 spills, 1.3 h, 30 Aug to 30 Aug31 Aug 2025 14:44 GMT, 12 min8 spills, 2.7 h, 1 Sep to 2 Sep3 Sep 2025 00:22 GMT, 40 min4 Sep 2025 20:58 GMT, 6 min7 spills, 2.1 h, 7 Sep to 8 Sep22 spills, 8.2 h, 10 Sep to 13 Sep33 spills, 16.2 h, 14 Sep to 17 Sep18 Sep 2025 15:26 GMT, 56 min17 spills, 14.7 h, 19 Sep to 21 Sep4 spills, 1.6 h, 27 Sep to 28 Sep10 spills, 12.7 h, 2 Oct to 4 Oct4 spills, 1.6 h, 19 Oct to 19 Oct2 spills, 0.7 h, 21 Oct to 21 Oct5 spills, 1.1 h, 26 Oct to 26 Oct2 spills, 0.8 h, 27 Oct to 27 Oct4 spills, 1.7 h, 28 Oct to 29 Oct12 spills, 8 h, 31 Oct to 2 Nov11 spills, 30.9 h, 3 Nov to 5 Nov8 spills, 3.7 h, 9 Nov to 10 Nov10 spills, 4.6 h, 10 Nov to 12 Nov8 spills, 6.4 h, 12 Nov to 13 Nov3 spills, 2.2 h, 18 Nov to 19 Nov2 spills, 0.4 h, 22 Nov to 22 Nov8 spills, 4.6 h, 23 Nov to 24 Nov6 spills, 8.6 h, 26 Nov to 28 Nov8 spills, 15.3 h, 30 Nov to 2 Dec4 Dec 2025 14:40 GMT, 20 min30 spills, 26.7 h, 5 Dec to 10 Dec7 spills, 5 h, 14 Dec to 15 Dec12 spills, 9.2 h, 17 Dec to 19 Dec

Hours spilling by month, 2025

020406080Jan 2025: 27 hours spillingJanFeb 2025: 7.8 hours spillingFebMar 2025: 5.2 hours spillingMarApr 2025: 2.0 hours spillingAprMay 2025: 24 hours spillingMayJun 2025: 31 hours spillingJunJul 2025: 22 hours spillingJulAug 2025: 8.8 hours spillingAugSep 2025: 47 hours spillingSepOct 2025: 19 hours spillingOctNov 2025: 70 hours spillingNovDec 2025: 55 hours spillingDec
Hours, measured by the event duration monitor.

Longest single spills

Started (GMT)OverflowDuration
3 Nov 2025, 01:28Dent WwTW9.0 h
1 Dec 2025, 04:22Dent WwTW8.6 h
9 Dec 2025, 03:22Dent WwTW5.6 h
9 Jun 2025, 20:04Dent WwTW5.6 h
4 Jul 2025, 14:50Dent WwTW5.2 h

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.

This works serves fewer than 2,000 people, or was not matched to a UWWTD report, so its size is not published. The population equivalent above is a placeholder of 1,000. Enter the population served if you know it.

Volume, central estimate5,464 m³range 2,176 - 13,718 m³
In litres5.5 millionrange 2.2 million - 13.7 million L
Olympic swimming pools2.2at 2,500 m³ each
Organic load, as people's raw sewage8,196person-days of untreated BOD

Assumed spill rate while spilling: 1.9 - 11.9 L/s (central 4.8 L/s), from a dry-weather flow of 1.9 L/s.

Pollutant releasedLowCentralHighConcentration used (low / typical / high)
BOD₅ (organic load) 87 kg492 kg2,744 kg 40 / 90 / 200 mg/L
Low/high: Europe range, Ellis & Jenkins 2005; typical: UK, Ellis & Jenkins 2005 (both via botturi)
Suspended solids 229 kg2,322 kg9,891 kg 105 / 425 / 721 mg/L
Low/high: Europe range; typical: UK, Ellis & Jenkins 2005 (via botturi)
Ammonium-N 4.1 kg34 kg128 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 2.6 kg14 kg74 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 217.6 billion organisms5.5 trillion organisms137.2 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.

Dent WwTW

Inlet overflow at sewage works · discharges to Trib River Dee

Spills 2025
126 (319 hours) · up 45% on 2024
Spills 2024
87 (232 hours)
Long-term average
111.8 spills a year (monitored since 2021)
Monitor uptime
99% of the year
High-spill reason (company)
Not asset maintenance - Hydraulic capacity
Investigation
No investigation activity in reporting period
Improvement
No improvement action in reporting period
WFD catchment
Dee - conf Deepdale Bk to conf Rawthey (GB112072071680)
Outlet location
SD7021087350 (OS grid reference) · View on Apple Maps
EA ID / permit
UUP00630 · 017270015 · company name: DENT 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.