Storm overflow register · Northumbrian Water

East Tanfield sewage works: storm overflow spills 2025

East Tanfield sewage treatment works, run by Northumbrian Water, has 2 monitored storm overflows discharging to Causey Burn. In 2025 they recorded 129 spills totalling 818 hours, against 174 spills and 1,438 hours in 2024. By hours spilling, it ranks 15 of 183 Northumbrian Water works, where 1 spilled longest.

Works size: 20,160 population equivalent (TANFIELD 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.

JanFebMarAprMayJunJulAugSepOctNovDecEast Tanfield STW1 Jan 2025 05:53 GMT, 88 min2 spills, 52.9 h, 5 Jan to 7 Jan4 spills, 29.2 h, 13 Jan to 14 Jan2 spills, 1.4 h, 24 Jan to 24 Jan8 spills, 18.1 h, 26 Jan to 28 Jan13 spills, 19.5 h, 10 Feb to 12 Feb29 May 2025 07:34 GMT, 48 min19 Jul 2025 16:59 GMT, 5.8 h10 Sep 2025 21:56 GMT, 15 min15 Sep 2025 13:03 GMT, 35 min3 spills, 26.7 h, 20 Sep to 21 Sep3 Oct 2025 16:22 GMT, 4.2 h19 Oct 2025 23:23 GMT, 4 h42 spills, 58.7 h, 13 Nov to 16 Nov6 spills, 16.1 h, 19 Nov to 20 Nov6 spills, 63.3 h, 22 Nov to 25 Nov3 spills, 7.6 h, 26 Nov to 27 Nov10 spills, 86.4 h, 28 Nov to 2 Dec6 spills, 29.6 h, 4 Dec to 6 Dec6 spills, 41.8 h, 7 Dec to 10 Dec12 Dec 2025 08:21 GMT, 109 min15 Dec 2025 13:20 GMT, 8.7 h3 spills, 13.3 h, 17 Dec to 18 Dec22 Dec 2025 03:03 GMT, 4.8 hEast Tanfield STW5 spills, 1.2 h, 1 Jan to 1 Jan64 spills, 38.5 h, 5 Jan to 7 Jan60 spills, 18.2 h, 13 Jan to 14 Jan7 spills, 4.4 h, 24 Jan to 24 Jan45 spills, 12.3 h, 26 Jan to 28 Jan89 spills, 9.9 h, 10 Feb to 11 Feb3 spills, 0.6 h, 20 Feb to 20 Feb6 spills, 0.8 h, 26 Feb to 26 Feb5 spills, 0.6 h, 7 Mar to 7 Mar4 spills, 0.1 h, 12 Mar to 12 Mar21 spills, 2.3 h, 22 Mar to 22 Mar11 spills, 2.5 h, 24 May to 24 May8 spills, 0.8 h, 27 May to 27 May19 spills, 3 h, 29 May to 29 May9 spills, 3 h, 5 Jun to 5 Jun5 spills, 1.1 h, 7 Jun to 7 Jun9 spills, 0.4 h, 9 Jun to 9 Jun3 spills, 1 h, 14 Jun to 14 Jun3 spills, 0.9 h, 21 Jun to 21 Jun37 spills, 4 h, 1 Jul to 2 Jul4 spills, 2.5 h, 6 Jul to 6 Jul12 spills, 1.5 h, 7 Jul to 7 Jul6 spills, 1.6 h, 14 Jul to 14 Jul5 spills, 0.8 h, 15 Jul to 15 Jul14 spills, 6.8 h, 19 Jul to 20 Jul11 spills, 0.3 h, 4 Aug to 4 Aug4 spills, 1.3 h, 11 Aug to 11 Aug11 spills, 0.7 h, 31 Aug to 31 Aug8 spills, 0.9 h, 3 Sep to 3 Sep8 spills, 4.5 h, 10 Sep to 11 Sep9 spills, 0.2 h, 12 Sep to 12 Sep19 spills, 2.4 h, 14 Sep to 15 Sep8 spills, 0.8 h, 17 Sep to 17 Sep23 spills, 17.6 h, 19 Sep to 21 Sep12 spills, 2 h, 1 Oct to 1 Oct22 spills, 6.7 h, 2 Oct to 3 Oct16 spills, 5.2 h, 19 Oct to 20 Oct8 spills, 0.2 h, 28 Oct to 28 Oct6 spills, 0.2 h, 5 Nov to 5 Nov5 spills, 2.1 h, 11 Nov to 11 Nov37 spills, 44.2 h, 12 Nov to 15 Nov51 spills, 7.8 h, 18 Nov to 19 Nov20 spills, 3.1 h, 22 Nov to 22 Nov3 spills, 25.2 h, 23 Nov to 25 Nov2 spills, 3.8 h, 26 Nov to 26 Nov6 spills, 5.2 h, 28 Nov to 28 Nov2 spills, 10.2 h, 29 Nov to 30 Nov4 spills, 17.1 h, 1 Dec to 2 Dec9 spills, 7.6 h, 5 Dec to 6 Dec4 spills, 7.4 h, 7 Dec to 7 Dec23 spills, 10.1 h, 9 Dec to 9 Dec3 spills, 1.1 h, 12 Dec to 12 Dec26 spills, 5.3 h, 15 Dec to 15 Dec10 spills, 6.3 h, 17 Dec to 18 Dec22 Dec 2025 00:59 GMT, 4.5 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.

0100k200k300kJan 2025: 178 h spilling ≈ 61,348 m³ (range 24,436-154,018 m³)JanFeb 2025: 31 h spilling ≈ 10,639 m³ (range 4,238-26,710 m³)FebMar 2025: 3.0 h spilling ≈ 1,036 m³ (range 413-2,602 m³)MarApr 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)AprMay 2025: 7.1 h spilling ≈ 2,453 m³ (range 977-6,157 m³)MayJun 2025: 6.3 h spilling ≈ 2,176 m³ (range 867-5,463 m³)JunJul 2025: 23 h spilling ≈ 7,979 m³ (range 3,178-20,033 m³)JulAug 2025: 2.3 h spilling ≈ 794 m³ (range 316-1,995 m³)AugSep 2025: 54 h spilling ≈ 18,653 m³ (range 7,430-46,830 m³)SepOct 2025: 22 h spilling ≈ 7,703 m³ (range 3,068-19,339 m³)OctNov 2025: 291 h spilling ≈ 100,555 m³ (range 40,053-252,447 m³)NovDec 2025: 202 h spilling ≈ 69,777 m³ (range 27,794-175,178 m³)Dec
Cubic metres (m³), estimate. Hours are measured by the event duration monitor.

Longest single spills

Started (GMT)OverflowDurationEstimated volume
5 Jan 2025, 17:36East Tanfield STW2.2 days7,269 - 45,818 m³
13 Nov 2025, 01:11East Tanfield STW1.9 days6,336 - 39,935 m³
13 Nov 2025, 01:25East Tanfield STW1.5 days5,086 - 32,058 m³
5 Jan 2025, 14:24East Tanfield STW1.5 days4,878 - 30,743 m³
24 Nov 2025, 04:04East Tanfield STW1.4 days4,690 - 29,558 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 estimate282,665 m³range 112,592 - 709,643 m³
In litres282.7 millionrange 112.6 million - 709.6 million L
Olympic swimming pools113at 2,500 m³ each
Organic load, as people's raw sewage423,998person-days of untreated BOD

Assumed spill rate while spilling: 38.2 - 240.9 L/s (central 96.0 L/s), from a dry-weather flow of 38.2 L/s.

Pollutant releasedLowCentralHighConcentration used (low / typical / high)
BOD₅ (organic load) 4,504 kg25,440 kg141,929 kg 40 / 90 / 200 mg/L
Low/high: Europe range, Ellis & Jenkins 2005; typical: UK, Ellis & Jenkins 2005 (both via botturi)
Suspended solids 11,822 kg120,133 kg511,652 kg 105 / 425 / 721 mg/L
Low/high: Europe range; typical: UK, Ellis & Jenkins 2005 (via botturi)
Ammonium-N 214 kg1,781 kg6,600 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 135 kg735 kg3,832 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 11.3 trillion organisms282.7 trillion organisms7.1 × 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.

East Tanfield STW

Storm tank at sewage works · discharges to Causey Burn

Spills 2025
51 (497 hours) · down 41% on 2024
Spills 2024
86 (856 hours)
Long-term average
82.7 spills a year (monitored since 2020)
Monitor uptime
100% of the year
High-spill reason (company)
Performance - SW Infiltration
Investigation
Env Act (SODRP) investigation ongoing, Operational investigation ongoing
Improvement
Operational improvement ongoing
WFD catchment
Team from Source to Tyne (GB103023075670)
Outlet location
NZ1973655324 (OS grid reference) · View on Apple Maps
EA ID / permit
NWL00488 · 235/1871

East Tanfield STW

Inlet overflow at sewage works · discharges to Causey Burn

Spills 2025
78 (321 hours) · down 11% on 2024
Spills 2024
88 (583 hours)
Long-term average
93.6 spills a year (monitored since 2021)
Monitor uptime
100% of the year
High-spill reason (company)
Performance - SW Infiltration
Investigation
Env Act (SODRP) investigation ongoing, Operational investigation ongoing
Improvement
Operational improvement ongoing
WFD catchment
Team from Source to Tyne (GB103023075670)
Outlet location
NZ1946054891 (OS grid reference) · View on Apple Maps
EA ID / permit
NWL00487 · 235/1871

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.