Storm overflow register · Yorkshire Water

Richmond sewage works: storm overflow spills 2025

Richmond sewage treatment works, run by Yorkshire Water, has 1 monitored storm overflow discharging to River Swale. In 2025 it recorded 52 spills totalling 364 hours, against 82 spills and 600 hours in 2024. By hours spilling, it ranks 120 of 283 Yorkshire Water works, where 1 spilled longest.

Works size: 9,161 population equivalent (RICHMOND 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.

JanFebMarAprMayJunJulAugSepOctNovDecRichmond Sewage…8 spills, 21.8 h, 1 Jan to 1 Jan26 spills, 45.3 h, 5 Jan to 7 Jan24 spills, 26.8 h, 13 Jan to 14 Jan3 spills, 4.8 h, 24 Jan to 24 Jan14 spills, 14.8 h, 26 Jan to 27 Jan2 spills, 1.5 h, 28 Jan to 28 Jan2 spills, 3.5 h, 20 Feb to 20 Feb5 spills, 5 h, 23 Feb to 24 Feb22 Mar 2025 17:30 GMT, 7.5 h29 May 2025 06:15 GMT, 90 min6 Jun 2025 08:00 GMT, 2 h6 Jul 2025 17:30 GMT, 30 min2 spills, 2.8 h, 15 Jul to 15 Jul3 spills, 4.5 h, 19 Jul to 19 Jul21 Jul 2025 15:30 GMT, 60 min2 spills, 2.5 h, 10 Sep to 10 Sep8 spills, 6.5 h, 14 Sep to 15 Sep4 spills, 3.3 h, 17 Sep to 17 Sep2 spills, 21.3 h, 20 Sep to 21 Sep2 spills, 2 h, 28 Sep to 28 Sep8 spills, 7.5 h, 2 Oct to 3 Oct19 Oct 2025 18:45 GMT, 7.3 h2 spills, 2.8 h, 5 Nov to 5 Nov2 spills, 6 h, 11 Nov to 12 Nov3 spills, 74.3 h, 12 Nov to 15 Nov19 Nov 2025 07:00 GMT, 7.8 h4 spills, 3.5 h, 24 Nov to 24 Nov3 spills, 5.3 h, 29 Nov to 29 Nov10 spills, 7.5 h, 1 Dec to 1 Dec4 spills, 6.8 h, 5 Dec to 6 Dec3 spills, 5 h, 7 Dec to 7 Dec26 spills, 29 h, 9 Dec to 10 Dec5 spills, 11.3 h, 15 Dec to 15 Dec6 spills, 8.8 h, 17 Dec to 18 Dec22 Dec 2025 01:15 GMT, 3.3 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.

020k40k60kJan 2025: 115 h spilling ≈ 18,020 m³ (range 7,178-45,240 m³)JanFeb 2025: 8.5 h spilling ≈ 1,334 m³ (range 531-3,350 m³)FebMar 2025: 7.5 h spilling ≈ 1,177 m³ (range 469-2,956 m³)MarApr 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)AprMay 2025: 1.5 h spilling ≈ 235 m³ (range 94-591 m³)MayJun 2025: 2.0 h spilling ≈ 314 m³ (range 125-788 m³)JunJul 2025: 8.8 h spilling ≈ 1,381 m³ (range 550-3,468 m³)JulAug 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)AugSep 2025: 36 h spilling ≈ 5,572 m³ (range 2,220-13,990 m³)SepOct 2025: 15 h spilling ≈ 2,323 m³ (range 925-5,832 m³)OctNov 2025: 100 h spilling ≈ 15,618 m³ (range 6,221-39,211 m³)NovDec 2025: 72 h spilling ≈ 11,223 m³ (range 4,470-28,176 m³)Dec
Cubic metres (m³), estimate. Hours are measured by the event duration monitor.

Longest single spills

Started (GMT)OverflowDurationEstimated volume
12 Nov 2025, 19:30Richmond Sewage Treatment Works2.0 days3,064 - 19,310 m³
5 Jan 2025, 18:15Richmond Sewage Treatment Works1.4 days2,032 - 12,807 m³
14 Nov 2025, 21:15Richmond Sewage Treatment Works1.0 days1,547 - 9,753 m³
13 Jan 2025, 15:15Richmond Sewage Treatment Works20.5 h1,282 - 8,079 m³
1 Jan 2025, 00:00Richmond Sewage Treatment Works19.5 h1,219 - 7,684 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 estimate57,168 m³range 22,771 - 143,522 m³
In litres57.2 millionrange 22.8 million - 143.5 million L
Olympic swimming pools23at 2,500 m³ each
Organic load, as people's raw sewage85,752person-days of untreated BOD

Assumed spill rate while spilling: 17.4 - 109.5 L/s (central 43.6 L/s), from a dry-weather flow of 17.4 L/s.

Pollutant releasedLowCentralHighConcentration used (low / typical / high)
BOD₅ (organic load) 911 kg5,145 kg28,704 kg 40 / 90 / 200 mg/L
Low/high: Europe range, Ellis & Jenkins 2005; typical: UK, Ellis & Jenkins 2005 (both via botturi)
Suspended solids 2,391 kg24,296 kg103,480 kg 105 / 425 / 721 mg/L
Low/high: Europe range; typical: UK, Ellis & Jenkins 2005 (via botturi)
Ammonium-N 43 kg360 kg1,335 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 27 kg149 kg775 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 2.3 trillion organisms57.2 trillion organisms1.4 × 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.

Richmond Sewage Treatment Works

Storm tank at sewage works · discharges to River Swale

Spills 2025
52 (364 hours) · down 37% on 2024
Spills 2024
82 (600 hours)
Long-term average
86.8 spills a year (monitored since 2020)
Monitor uptime
100% of the year
High-spill reason (company)
Not asset maintenance - hydraulic capacity
Investigation
UWWTR investigation ongoing, Operational investigation completed
Improvement
No improvement action in reporting period
WFD catchment
Swale from Clapgate Beck to Bedale Beck (GB104027069122)
Outlet location
SE1835099890 (OS grid reference) · View on Apple Maps
EA ID / permit
YWS00373 · 27/23/0279 · company name: RICHMOND/STW

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 Yorkshire 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.