Storm overflow register · South West Water

Ipplepen sewage works: storm overflow spills 2025

Ipplepen sewage treatment works, run by South West Water, has 2 monitored storm overflows discharging to Halwell Stream. In 2025 they recorded 96 spills totalling 789 hours, against 147 spills and 1,185 hours in 2024. By hours spilling, it ranks 141 of 334 South West Water works, where 1 spilled longest.

Works size: 2,405 population equivalent (IPPLEPEN & TORBRYAN 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.

JanFebMarAprMayJunJulAugSepOctNovDecIpplepen Wastewater…4 spills, 103.5 h, 4 Jan to 9 Jan26 Jan 2025 11:19 GMT, 35.9 h30 Jan 2025 15:15 GMT, 9.1 h3 spills, 16 h, 20 Feb to 21 Feb7 spills, 59 h, 23 Feb to 26 Feb15 Apr 2025 23:37 GMT, 8 h18 Apr 2025 20:23 GMT, 16.7 h12 Jun 2025 10:26 GMT, 2.8 h29 Aug 2025 01:29 GMT, 94 min3 Sep 2025 01:43 GMT, 6.1 h11 Nov 2025 19:13 GMT, 26.1 h3 spills, 15.5 h, 13 Nov to 15 Nov2 spills, 31 h, 1 Dec to 2 Dec5 spills, 111.9 h, 5 Dec to 11 Dec4 spills, 106.6 h, 15 Dec to 21 DecIpplepen Wastewater…134 spills, 50.8 h, 4 Jan to 7 Jan42 spills, 9 h, 8 Jan to 9 Jan183 spills, 28.5 h, 26 Jan to 27 Jan23 spills, 2.7 h, 19 Feb to 21 Feb14 spills, 22.1 h, 23 Feb to 25 Feb26 Feb 2025 06:51 GMT, 80 min17 spills, 6 h, 15 Apr to 16 Apr102 spills, 10 h, 18 Apr to 19 Apr4 spills, 0.2 h, 22 Apr to 22 Apr25 spills, 0.9 h, 12 May to 12 May4 spills, 1.2 h, 7 Jun to 7 Jun6 spills, 3.3 h, 12 Jun to 12 Jun3 spills, 0.5 h, 27 Aug to 27 Aug3 spills, 1.7 h, 28 Aug to 29 Aug2 spills, 0.1 h, 31 Aug to 31 Aug11 spills, 2.4 h, 2 Sep to 3 Sep5 spills, 0.6 h, 9 Sep to 9 Sep10 spills, 0.5 h, 14 Sep to 14 Sep3 Oct 2025 22:19 GMT, 7 min20 Oct 2025 07:07 GMT, 23 min2 spills, 0.4 h, 22 Oct to 22 Oct1 Nov 2025 13:18 GMT, 11 min2 spills, 0.3 h, 6 Nov to 6 Nov7 Nov 2025 14:05 GMT, 18 min5 spills, 0.2 h, 9 Nov to 9 Nov3 spills, 0.2 h, 10 Nov to 10 Nov89 spills, 11.3 h, 11 Nov to 12 Nov25 spills, 3.4 h, 13 Nov to 14 Nov40 spills, 11.9 h, 1 Dec to 2 Dec44 spills, 9.9 h, 5 Dec to 6 Dec49 spills, 4 h, 7 Dec to 7 Dec70 spills, 20.3 h, 8 Dec to 10 Dec70 spills, 14.4 h, 15 Dec to 16 Dec111 spills, 25.9 h, 17 Dec to 19 Dec3 spills, 0.4 h, 22 Dec to 22 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.

010k20k30k40kJan 2025: 237 h spilling ≈ 9,754 m³ (range 3,885-24,488 m³)JanFeb 2025: 101 h spilling ≈ 4,166 m³ (range 1,659-10,459 m³)FebMar 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)MarApr 2025: 41 h spilling ≈ 1,681 m³ (range 670-4,221 m³)AprMay 2025: 0.9 h spilling ≈ 37 m³ (range 15-93 m³)MayJun 2025: 7.3 h spilling ≈ 301 m³ (range 120-755 m³)JunJul 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)JulAug 2025: 3.9 h spilling ≈ 161 m³ (range 64-403 m³)AugSep 2025: 9.5 h spilling ≈ 391 m³ (range 156-983 m³)SepOct 2025: 0.8 h spilling ≈ 33 m³ (range 13-83 m³)OctNov 2025: 57 h spilling ≈ 2,365 m³ (range 942-5,938 m³)NovDec 2025: 336 h spilling ≈ 13,858 m³ (range 5,520-34,792 m³)Dec
Cubic metres (m³), estimate. Hours are measured by the event duration monitor.

Longest single spills

Started (GMT)OverflowDurationEstimated volume
17 Dec 2025, 08:04Ipplepen Wastewater Treatment Works2.6 days1,025 - 6,462 m³
5 Jan 2025, 16:03Ipplepen Wastewater Treatment Works2.3 days918 - 5,783 m³
23 Feb 2025, 14:46Ipplepen Wastewater Treatment Works2.1 days808 - 5,093 m³
8 Dec 2025, 19:29Ipplepen Wastewater Treatment Works1.9 days729 - 4,595 m³
26 Jan 2025, 11:19Ipplepen Wastewater Treatment Works1.5 days590 - 3,717 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 estimate32,513 m³range 12,951 - 81,626 m³
In litres32.5 millionrange 13.0 million - 81.6 million L
Olympic swimming pools13at 2,500 m³ each
Organic load, as people's raw sewage48,770person-days of untreated BOD

Assumed spill rate while spilling: 4.6 - 28.7 L/s (central 11.4 L/s), from a dry-weather flow of 4.6 L/s.

Pollutant releasedLowCentralHighConcentration used (low / typical / high)
BOD₅ (organic load) 518 kg2,926 kg16,325 kg 40 / 90 / 200 mg/L
Low/high: Europe range, Ellis & Jenkins 2005; typical: UK, Ellis & Jenkins 2005 (both via botturi)
Suspended solids 1,360 kg13,818 kg58,852 kg 105 / 425 / 721 mg/L
Low/high: Europe range; typical: UK, Ellis & Jenkins 2005 (via botturi)
Ammonium-N 25 kg205 kg759 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 16 kg85 kg441 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 1.3 trillion organisms32.5 trillion organisms816.3 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.

Ipplepen Wastewater Treatment Works

Storm tank at sewage works · discharges to Halwell Stream

Spills 2025
41 (550 hours) · down 38% on 2024
Spills 2024
66 (822 hours)
Long-term average
48.7 spills a year (monitored since 2019)
Monitor uptime
95% of the year
High-spill reason (company)
Performance - SW Infiltration
Investigation
UWWTR investigation completed, Operational investigation completed
Improvement
No improvement action in reporting period
WFD catchment
Am Brook (GB108046005210)
Outlet location
SX82816676 (OS grid reference) · View on Apple Maps
EA ID / permit
SBB00615 · 203406 · company name: IPPLEPEN STW_SSO_IPPLEPEN

Ipplepen Wastewater Treatment Works

Inlet overflow at sewage works · discharges to Halwell Stream

Spills 2025
55 (239 hours) · down 32% on 2024
Spills 2024
81 (363 hours)
Long-term average
66.2 spills a year (monitored since 2019)
Monitor uptime
95% of the year
High-spill reason (company)
Performance - SW Infiltration
Investigation
UWWTR investigation ongoing, Operational investigation completed
Improvement
No improvement action in reporting period
WFD catchment
Am Brook (GB108046005210)
Outlet location
SX82816676 (OS grid reference) · View on Apple Maps
EA ID / permit
SBB00614 · 203406 · company name: IPPLEPEN STW_SO_IPPLEPEN

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.