Storm overflow register · Northumbrian Water

Sacriston sewage works: storm overflow spills 2025

Sacriston sewage treatment works, run by Northumbrian Water, has 1 monitored storm overflow discharging to South Burn. In 2025 it recorded 27 spills totalling 268 hours, against 49 spills and 464 hours in 2024. By hours spilling, it ranks 78 of 183 Northumbrian Water works, where 1 spilled longest.

Works size: 5,341 population equivalent (SACRISTON 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.

JanFebMarAprMayJunJulAugSepOctNovDecSacriston Sewage…5 Jan 2025 16:28 GMT, 54.7 h5 spills, 40 h, 26 Jan to 28 Jan4 spills, 18.1 h, 10 Feb to 11 Feb2 spills, 5.8 h, 19 Jul to 19 Jul3 spills, 14.9 h, 20 Sep to 21 Sep3 spills, 6.1 h, 3 Oct to 3 Oct18 spills, 40.4 h, 13 Nov to 15 Nov5 spills, 12 h, 19 Nov to 19 Nov2 spills, 14.8 h, 24 Nov to 24 Nov2 spills, 12.2 h, 29 Nov to 30 Nov7 spills, 18.8 h, 1 Dec to 2 Dec5 spills, 9.1 h, 7 Dec to 8 Dec5 spills, 16.6 h, 9 Dec to 9 Dec4 spills, 2.2 h, 15 Dec to 15 Dec2 spills, 1.8 h, 18 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.

010k20k30kJan 2025: 95 h spilling ≈ 8,666 m³ (range 3,452-21,758 m³)JanFeb 2025: 18 h spilling ≈ 1,656 m³ (range 660-4,159 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: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)JunJul 2025: 5.8 h spilling ≈ 531 m³ (range 211-1,333 m³)JulAug 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)AugSep 2025: 15 h spilling ≈ 1,364 m³ (range 543-3,423 m³)SepOct 2025: 6.1 h spilling ≈ 558 m³ (range 222-1,401 m³)OctNov 2025: 80 h spilling ≈ 7,275 m³ (range 2,898-18,265 m³)NovDec 2025: 49 h spilling ≈ 4,438 m³ (range 1,768-11,143 m³)Dec
Cubic metres (m³), estimate. Hours are measured by the event duration monitor.

Longest single spills

Started (GMT)OverflowDurationEstimated volume
5 Jan 2025, 16:28Sacriston Sewage Treatment Works2.3 days1,993 - 12,560 m³
13 Nov 2025, 12:03Sacriston Sewage Treatment Works1.1 days939 - 5,920 m³
27 Jan 2025, 02:56Sacriston Sewage Treatment Works20.6 h750 - 4,729 m³
9 Dec 2025, 06:50Sacriston Sewage Treatment Works16.3 h593 - 3,737 m³
20 Sep 2025, 15:25Sacriston Sewage Treatment Works14.8 h539 - 3,397 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 estimate24,489 m³range 9,755 - 61,482 m³
In litres24.5 millionrange 9.8 million - 61.5 million L
Olympic swimming pools9.8at 2,500 m³ each
Organic load, as people's raw sewage36,734person-days of untreated BOD

Assumed spill rate while spilling: 10.1 - 63.8 L/s (central 25.4 L/s), from a dry-weather flow of 10.1 L/s.

Pollutant releasedLowCentralHighConcentration used (low / typical / high)
BOD₅ (organic load) 390 kg2,204 kg12,296 kg 40 / 90 / 200 mg/L
Low/high: Europe range, Ellis & Jenkins 2005; typical: UK, Ellis & Jenkins 2005 (both via botturi)
Suspended solids 1,024 kg10,408 kg44,328 kg 105 / 425 / 721 mg/L
Low/high: Europe range; typical: UK, Ellis & Jenkins 2005 (via botturi)
Ammonium-N 19 kg154 kg572 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 12 kg64 kg332 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 975.5 billion organisms24.5 trillion organisms614.8 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.

Sacriston Sewage Treatment Works

Storm tank at sewage works · discharges to South Burn

Spills 2025
27 (268 hours) · down 45% on 2024
Spills 2024
49 (464 hours)
Long-term average
55.2 spills a year (monitored since 2020)
Monitor uptime
99% of the year
Investigation
Env Act (SODRP) investigation ongoing, Operational investigation completed
Improvement
Operational improvement completed
WFD catchment
South Burn to confluence with Wear (GB103024077623)
Outlet location
NZ2454047830 (OS grid reference) · View on Apple Maps
EA ID / permit
NWL01135 · 245/1254

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.