Storm overflow register · South West Water

Kilmington sewage works: storm overflow spills 2025

Kilmington sewage treatment works, run by South West Water, has 1 monitored storm overflow discharging to River Axe. In 2025 it recorded 110 spills totalling 995 hours, against 158 spills and 1,181 hours in 2024. By hours spilling, it ranks 114 of 334 South West Water works, where 1 spilled longest.

Works size: 9,034 population equivalent (AXMINSTER 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.

JanFebMarAprMayJunJulAugSepOctNovDecKilmington WwTW2 spills, 0.7 h, 1 Jan to 1 Jan39 spills, 60 h, 4 Jan to 7 Jan14 spills, 6.7 h, 8 Jan to 10 Jan9 spills, 4 h, 20 Jan to 20 Jan6 spills, 37.8 h, 23 Jan to 25 Jan24 spills, 72 h, 26 Jan to 29 Jan5 spills, 1.3 h, 31 Jan to 31 Jan4 Feb 2025 15:50 GMT, 2 min3 spills, 0.2 h, 15 Feb to 15 Feb6 spills, 49.6 h, 19 Feb to 22 Feb4 spills, 77.9 h, 23 Feb to 27 Feb2 spills, 0.1 h, 28 Feb to 28 Feb3 spills, 1.4 h, 21 Mar to 21 Mar4 spills, 3.4 h, 15 Apr to 16 Apr4 spills, 37 h, 18 Apr to 19 Apr4 spills, 4.9 h, 22 Apr to 23 Apr24 Apr 2025 07:30 GMT, 1 min21 May 2025 08:23 GMT, 46 min7 Jun 2025 13:06 GMT, 2.8 h12 Jun 2025 08:10 GMT, 4.2 h19 Jul 2025 23:07 GMT, 116 min2 spills, 1.8 h, 23 Jul to 23 Jul3 spills, 1.5 h, 27 Jul to 27 Jul3 spills, 3.2 h, 27 Aug to 27 Aug3 spills, 5.5 h, 29 Aug to 29 Aug2 spills, 6.8 h, 30 Aug to 30 Aug8 spills, 14 h, 2 Sep to 3 Sep4 Sep 2025 06:50 GMT, 43 min5 spills, 4.7 h, 7 Sep to 7 Sep9 spills, 31.9 h, 9 Sep to 13 Sep14 Sep 2025 13:18 GMT, 114 min2 spills, 1.9 h, 17 Sep to 17 Sep28 Sep 2025 03:09 GMT, 3 min2 spills, 0.1 h, 29 Sep to 29 Sep4 spills, 2.1 h, 3 Oct to 4 Oct15 spills, 19.5 h, 19 Oct to 21 Oct13 spills, 5.7 h, 22 Oct to 23 Oct18 spills, 5.3 h, 30 Oct to 1 Nov10 spills, 14.9 h, 4 Nov to 5 Nov3 spills, 7.9 h, 7 Nov to 7 Nov3 spills, 30.8 h, 9 Nov to 10 Nov11 spills, 68.8 h, 11 Nov to 15 Nov13 spills, 40 h, 22 Nov to 25 Nov26 Nov 2025 13:31 GMT, 2 min5 spills, 4.1 h, 29 Nov to 29 Nov91 spills, 218.6 h, 30 Nov to 12 Dec21 spills, 96.8 h, 15 Dec to 20 Dec56 spills, 40.1 h, 20 Dec to 23 Dec2 spills, 0.1 h, 24 Dec to 24 Dec30 Dec 2025 13:17 GMT, 1 min2 spills, 0.1 h, 31 Dec to 31 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.

050k100k150kJan 2025: 182 h spilling ≈ 28,234 m³ (range 11,246-70,883 m³)JanFeb 2025: 128 h spilling ≈ 19,767 m³ (range 7,874-49,626 m³)FebMar 2025: 1.4 h spilling ≈ 217 m³ (range 86-544 m³)MarApr 2025: 45 h spilling ≈ 6,997 m³ (range 2,787-17,565 m³)AprMay 2025: 0.8 h spilling ≈ 124 m³ (range 49-311 m³)MayJun 2025: 7.0 h spilling ≈ 1,084 m³ (range 432-2,720 m³)JunJul 2025: 5.2 h spilling ≈ 805 m³ (range 321-2,021 m³)JulAug 2025: 16 h spilling ≈ 2,399 m³ (range 956-6,023 m³)AugSep 2025: 55 h spilling ≈ 8,545 m³ (range 3,403-21,451 m³)SepOct 2025: 29 h spilling ≈ 4,458 m³ (range 1,776-11,192 m³)OctNov 2025: 171 h spilling ≈ 26,439 m³ (range 10,531-66,375 m³)NovDec 2025: 355 h spilling ≈ 55,013 m³ (range 21,913-138,113 m³)Dec
Cubic metres (m³), estimate. Hours are measured by the event duration monitor.

Longest single spills

Started (GMT)OverflowDurationEstimated volume
23 Feb 2025, 14:09Kilmington WwTW2.4 days3,582 - 22,578 m³
17 Dec 2025, 15:42Kilmington WwTW2.2 days3,311 - 20,868 m³
4 Jan 2025, 18:42Kilmington WwTW2.2 days3,246 - 20,460 m³
8 Dec 2025, 11:05Kilmington WwTW2.2 days3,217 - 20,279 m³
19 Feb 2025, 21:12Kilmington WwTW2.0 days3,014 - 18,997 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 estimate154,065 m³range 61,367 - 386,786 m³
In litres154.1 millionrange 61.4 million - 386.8 million L
Olympic swimming pools62at 2,500 m³ each
Organic load, as people's raw sewage231,097person-days of untreated BOD

Assumed spill rate while spilling: 17.1 - 107.9 L/s (central 43.0 L/s), from a dry-weather flow of 17.1 L/s.

Pollutant releasedLowCentralHighConcentration used (low / typical / high)
BOD₅ (organic load) 2,455 kg13,866 kg77,357 kg 40 / 90 / 200 mg/L
Low/high: Europe range, Ellis & Jenkins 2005; typical: UK, Ellis & Jenkins 2005 (both via botturi)
Suspended solids 6,444 kg65,478 kg278,873 kg 105 / 425 / 721 mg/L
Low/high: Europe range; typical: UK, Ellis & Jenkins 2005 (via botturi)
Ammonium-N 117 kg971 kg3,597 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 74 kg401 kg2,089 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 6.1 trillion organisms154.1 trillion organisms3.9 × 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.

Kilmington WwTW

Storm tank at sewage works · discharges to River Axe

Spills 2025
110 (995 hours) · down 30% on 2024
Spills 2024
158 (1,181 hours)
Long-term average
163.0 spills a year (monitored since 2019)
Monitor uptime
100% of the year
High-spill reason (company)
Not asset maintenance - hydraulic capacity
Investigation
Env Act (SODRP) investigation ongoing, Operational investigation completed
Improvement
Env Act (SODRP) improvement ongoing
WFD catchment
Lower Axe (GB108045008870)
Outlet location
SY27869759 (OS grid reference) · View on Apple Maps
EA ID / permit
SBB00631 · DRA 1559 · company name: KILMINGTON STW_SSO_AXMINSTER

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 South West 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.