Dry spills

Dumping sewage when it’s dry?

Potentially illegal practices

Sewage overflows were designed and intended to be an ‘emergency release valve’ only to operate in ‘exceptional rainfall events’ to reduce pressure on the sewage system to avoid sewage backing up into our homes. The Urban Waste Water Treatment Regulations only permit sewage overflows to operate in ‘unusually heavy rainfall’. However, the government has admitted sewage overflows “are being used significantly beyond their original purpose”.²⁹

Water companies are prohibited from making ‘dry spills’ from sewage overflows when there has been no rainfall. However, with water companies now allowed to self-report and with little clarity on what is classed an ‘extreme rainfall event’ it’s unclear just how many ‘dry spills’ are happening and how much sewage is potentially being illegally discharged. So, we’ve been investigating where there have been discharges but no significant rainfall to indicate where sewage overflows are being used when they shouldn’t be. We’ve collated rainfall data provided by the Met Office from over 150 locations across England and Wales and linked the 455 locations on our Safer Seas & River Service (SSRS) to the nearest available data source to determine rainfall. We’ve then looked at the sewage discharge notifications issued for each of these locations and if there had been any rainfall in the [2] days preceding the discharge notification. Where we had seen a discharge notification but no rainfall in the preceding [2] days, we have assumed this to be a ‘dry spill’.

Take a look at the map below to investigate where we have found water companies to be making ‘dry spills’ over the last year – that’s raw sewage entering our waterways when there has been no rain.

What’s the damage?

Figure 9 shows ‘dry spills’ by month and water company. We can see Southern Water was the worst offender. They were responsible for an eye-watering 39 of the 58 ‘dry spills’ in October 2021 alone. This is just one month after the bathing season ended and at a time many people were still using the water.

Most bathers will consider avoiding the water after heavy rain, but our analysis shows that sewage is being discharged into our precious blue spaces even when there has been no rainfall, putting us and the environment at risk. What’s worse is that in dry conditions where there is less water, the pollution entering waterways is more concentrated, so the contamination risk from the infectious organisms present in these untreated discharges is even higher.

Limitations

It should be noted that we have only looked at rainfall in the 2 days before a sewage discharge notification. Each catchment is unique and therefore the lag time between a rainfall event and its impact on a sewage overflow could be longer. However, we consider [2] days to be a conservative time period. The SSRS also only provides sewage discharge notifications for designated bathing waters and popular swim spots rather than individual sewage overflows. So where one sewage overflow impacts multiple locations we will be overestimating the number of ‘dry spills’. On the other hand, where multiple sewage overflows impact one location, we will be underestimating the number of ‘dry spills’. Finally, we are unable to comprehensively consider more complex situations such as the effect of periods of drought – when there can be a large increase in surface water after a downpour due to the ground being too dry to absorb it.

Continue reading

Profiteering off pollution >