Storm overflow register · Northumbrian Water

Gunnerton sewage works: storm overflow spills 2025

Gunnerton sewage treatment works, run by Northumbrian Water, has 2 monitored storm overflows discharging to Gunnerton Burn. In 2025 they recorded 69 spills totalling 210 hours, against 72 spills and 223 hours in 2024. By hours spilling, it ranks 91 of 183 Northumbrian Water 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.

JanFebMarAprMayJunJulAugSepOctNovDecGunnerton STW2 spills, 0.8 h, 1 Jan to 1 Jan11 spills, 6 h, 6 Jan to 6 Jan13 Jan 2025 19:59 GMT, 15 min4 spills, 1.4 h, 22 Mar to 22 Mar2 spills, 0.5 h, 25 May to 25 May9 spills, 5.3 h, 29 May to 30 May3 spills, 1 h, 3 Jun to 3 Jun11 spills, 2.7 h, 4 Jun to 5 Jun3 spills, 0.9 h, 7 Jun to 7 Jun3 spills, 0.2 h, 9 Jun to 9 Jun2 spills, 0.6 h, 14 Jun to 14 Jun3 spills, 0.3 h, 22 Jun to 22 Jun3 spills, 0.4 h, 26 Jun to 26 Jun2 spills, 0.7 h, 28 Jun to 28 Jun5 spills, 4.1 h, 1 Jul to 2 Jul88 spills, 20 h, 7 Jul to 10 Jul8 spills, 4 h, 15 Jul to 16 Jul8 spills, 3.5 h, 19 Jul to 19 Jul2 spills, 0.6 h, 20 Jul to 20 Jul4 spills, 1.6 h, 11 Aug to 12 Aug60 spills, 7 h, 20 Aug to 22 Aug14 spills, 5.9 h, 2 Sep to 3 Sep12 Sep 2025 13:13 GMT, 32 min23 spills, 6.5 h, 14 Sep to 17 Sep30 spills, 16.7 h, 19 Sep to 20 Sep24 spills, 10.7 h, 2 Oct to 4 Oct5 spills, 1.8 h, 19 Oct to 20 Oct1 Nov 2025 02:35 GMT, 26 min2 spills, 1.7 h, 4 Nov to 4 Nov8 spills, 3.9 h, 5 Nov to 5 Nov8 spills, 1.9 h, 11 Nov to 11 Nov77 spills, 19.8 h, 13 Nov to 14 Nov19 spills, 4.4 h, 23 Nov to 24 Nov29 Nov 2025 14:27 GMT, 90 min29 spills, 22.2 h, 30 Nov to 2 Dec102 spills, 48.7 h, 7 Dec to 10 DecGunnerton STW22 Mar 2025 12:13 GMT, 2 min2 Jul 2025 12:25 GMT, 8 min14 Jul 2025 12:51 GMT, 4 min19 Jul 2025 11:46 GMT, 6 min11 Aug 2025 19:50 GMT, 8 min2 spills, 0.2 h, 3 Sep to 3 Sep2 Oct 2025 20:34 GMT, 18 min23 Nov 2025 07:26 GMT, 6 min7 Dec 2025 16:58 GMT, 12 min

Hours spilling by month, 2025

020406080Jan 2025: 7.0 hours spillingJanFeb 2025: 0.0 hours spillingFebMar 2025: 1.4 hours spillingMarApr 2025: 0.0 hours spillingAprMay 2025: 5.8 hours spillingMayJun 2025: 6.8 hours spillingJunJul 2025: 33 hours spillingJulAug 2025: 8.7 hours spillingAugSep 2025: 30 hours spillingSepOct 2025: 13 hours spillingOctNov 2025: 34 hours spillingNovDec 2025: 71 hours spillingDec
Hours, measured by the event duration monitor.

Longest single spills

Started (GMT)OverflowDuration
9 Dec 2025, 04:07Gunnerton STW19.3 h
7 Dec 2025, 13:53Gunnerton STW13.8 h
13 Nov 2025, 01:11Gunnerton STW10.0 h
1 Dec 2025, 03:31Gunnerton STW9.0 h
1 Dec 2025, 14:27Gunnerton STW8.9 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 estimate3,593 m³range 1,431 - 9,021 m³
In litres3.6 millionrange 1.4 million - 9.0 million L
Olympic swimming pools1.4at 2,500 m³ each
Organic load, as people's raw sewage5,390person-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) 57 kg323 kg1,804 kg 40 / 90 / 200 mg/L
Low/high: Europe range, Ellis & Jenkins 2005; typical: UK, Ellis & Jenkins 2005 (both via botturi)
Suspended solids 150 kg1,527 kg6,504 kg 105 / 425 / 721 mg/L
Low/high: Europe range; typical: UK, Ellis & Jenkins 2005 (via botturi)
Ammonium-N 2.7 kg23 kg84 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 1.7 kg9.3 kg49 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 143.1 billion organisms3.6 trillion organisms90.2 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.

Gunnerton STW

Inlet overflow at sewage works · discharges to Gunnerton Burn

Spills 2025
60 (208 hours) · down 13% on 2024
Spills 2024
69 (218 hours)
Long-term average
64.5 spills a year (monitored since 2024)
Monitor uptime
96% of the year
High-spill reason (company)
Not asset maintenance - Hydraulic capacity
Investigation
Operational investigation completed
Improvement
Operational improvement completed
WFD catchment
Gunnerton Burn from Source to N Tyne (GB103023074880)
Outlet location
NY9042074970 (OS grid reference) · View on Apple Maps
EA ID / permit
NWL00632 · 231/1078

Gunnerton STW

Inlet overflow at sewage works · discharges to Gunnerton Burn

Spills 2025
9 (1.2 hours) · up 200% on 2024
Spills 2024
3 (4.5 hours)
Long-term average
5.0 spills a year (monitored since 2021)
Monitor uptime
95% of the year
Investigation
No investigation activity in reporting period
Improvement
No improvement action in reporting period
WFD catchment
Gunnerton Burn from Source to N Tyne (GB103023074880)
Outlet location
NY9042074970 (OS grid reference) · View on Apple Maps
EA ID / permit
NWL00633 · 231/1078

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 Northumbrian 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.