Storm overflow register · Northumbrian Water

Consett sewage works: storm overflow spills 2025

Consett sewage treatment works, run by Northumbrian Water, has 1 monitored storm overflow discharging to River Derwent. In 2025 it recorded 46 spills totalling 305 hours, against 67 spills and 728 hours in 2024. By hours spilling, it ranks 68 of 183 Northumbrian Water works, where 1 spilled longest.

Works size: 40,849 population equivalent (CONSETT 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.

JanFebMarAprMayJunJulAugSepOctNovDecConsett STW16 spills, 7.3 h, 1 Jan to 1 Jan3 spills, 31 h, 5 Jan to 7 Jan20 spills, 23.8 h, 13 Jan to 14 Jan7 spills, 6.3 h, 24 Jan to 24 Jan7 spills, 12 h, 26 Jan to 27 Jan3 spills, 19.5 h, 10 Feb to 11 Feb2 spills, 0.5 h, 12 Mar to 12 Mar15 spills, 1.2 h, 5 Jun to 5 Jun12 spills, 1.6 h, 2 Jul to 3 Jul4 spills, 1.2 h, 7 Jul to 8 Jul35 spills, 10.5 h, 19 Jul to 21 Jul10 spills, 5.4 h, 14 Sep to 15 Sep26 spills, 21.7 h, 20 Sep to 21 Sep14 spills, 4 h, 1 Oct to 1 Oct9 spills, 5.1 h, 3 Oct to 3 Oct5 spills, 3.2 h, 19 Oct to 20 Oct18 spills, 52 h, 12 Nov to 15 Nov95 spills, 30.5 h, 23 Nov to 25 Nov26 spills, 6 h, 28 Nov to 28 Nov6 spills, 7.4 h, 29 Nov to 30 Nov26 spills, 16.4 h, 1 Dec to 2 Dec11 spills, 6.8 h, 5 Dec to 6 Dec6 spills, 8.4 h, 7 Dec to 8 Dec37 spills, 20.5 h, 9 Dec to 10 Dec9 spills, 2.8 h, 17 Dec to 18 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.

050k100k150k200kJan 2025: 80 h spilling ≈ 56,134 m³ (range 22,359-140,926 m³)JanFeb 2025: 20 h spilling ≈ 13,649 m³ (range 5,436-34,265 m³)FebMar 2025: 0.5 h spilling ≈ 350 m³ (range 139-879 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: 1.2 h spilling ≈ 840 m³ (range 335-2,109 m³)JunJul 2025: 13 h spilling ≈ 9,239 m³ (range 3,680-23,195 m³)JulAug 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)AugSep 2025: 27 h spilling ≈ 18,968 m³ (range 7,555-47,620 m³)SepOct 2025: 12 h spilling ≈ 8,609 m³ (range 3,429-21,613 m³)OctNov 2025: 96 h spilling ≈ 67,193 m³ (range 26,764-168,690 m³)NovDec 2025: 55 h spilling ≈ 38,426 m³ (range 15,306-96,470 m³)Dec
Cubic metres (m³), estimate. Hours are measured by the event duration monitor.

Longest single spills

Started (GMT)OverflowDurationEstimated volume
12 Nov 2025, 23:11Consett STW1.8 days11,812 - 74,446 m³
5 Jan 2025, 20:14Consett STW1.3 days8,503 - 53,594 m³
20 Sep 2025, 12:05Consett STW16.7 h4,656 - 29,345 m³
13 Jan 2025, 08:29Consett STW14.0 h3,903 - 24,601 m³
10 Feb 2025, 23:44Consett STW11.8 h3,276 - 20,647 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 estimate213,407 m³range 85,004 - 535,767 m³
In litres213.4 millionrange 85.0 million - 535.8 million L
Olympic swimming pools85at 2,500 m³ each
Organic load, as people's raw sewage320,110person-days of untreated BOD

Assumed spill rate while spilling: 77.4 - 488.1 L/s (central 194.4 L/s), from a dry-weather flow of 77.4 L/s.

Pollutant releasedLowCentralHighConcentration used (low / typical / high)
BOD₅ (organic load) 3,400 kg19,207 kg107,153 kg 40 / 90 / 200 mg/L
Low/high: Europe range, Ellis & Jenkins 2005; typical: UK, Ellis & Jenkins 2005 (both via botturi)
Suspended solids 8,925 kg90,698 kg386,288 kg 105 / 425 / 721 mg/L
Low/high: Europe range; typical: UK, Ellis & Jenkins 2005 (via botturi)
Ammonium-N 162 kg1,344 kg4,983 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 102 kg555 kg2,893 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 8.5 trillion organisms213.4 trillion organisms5.4 × 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.

Consett STW

Storm tank at sewage works · discharges to River Derwent

Spills 2025
46 (305 hours) · down 31% on 2024
Spills 2024
67 (728 hours)
Long-term average
100.2 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
Derwent from Burnhope Burn to River Tyne (GB103023074790)
Outlet location
NZ0940255072 (OS grid reference) · View on Apple Maps
EA ID / permit
NWL00320 · 234/1061

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.