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Government has been urged to launch a public inquiry into the use of event duration monitors (EDMs) after the reliability of river water quality data was called into question.
It comes after an ongoing study found that Severn Trent may have “breached their permits thousands of times”.
Peter Hammond, retired professor and environmental campaigner, told the Environmental Audit Committee that low levels of accuracy with EDM data is “scandalous”.
Hammond said his ongoing research has found that more than half of EDM data is “unreliable”, adding that the technology should be replaced with volumetric measuring instead.
“My recent work is suggesting that EDMs are not very good,” Hammond said. “We’re pouring a lot of emphasis on them, too much in my opinion.”
As part of his work into sewage spills and treatment, Hammond has analysed data from 200 sewage treatment works operated by Severn Trent. He will now analyse data provided by two other sewerage companies, which he did not name.
He said that while volumetric sewage treatment data was “very reliable”, the EDM data series were not.
“Of the EDMs, 55% of the data series I have analysed so far are inconsistent with the treatment data. They’re unreliable,” Hammond said. “If you include the unreliable data in the analysis of compliance with permits you get that Severn Trent have breached their permits thousands of times, if you exclude that unreliable data, you get hundreds.”
This would mean Severn Trent’s classification as a four-star rated outstanding company by the Environment Agency was “based on very shaky data”, he added.
Hammond expressed his concern that too much emphasis is being put on EDMs and believes volumetric measurements of CSO spills should be used instead.
“If this is repeated across the other two water companies, which the Agency have given me data for, then it would be a scandal if the unreliability is at the rate of 50%.”
Philip Dunne, chair of the EAC iterated that the committee had recommended the use of volumetric measurements to government, which were not adopted.
The EAC hosted Hammond alongside academics and regulators to revisit work it had undertaken in 2021-23 to assess progress made on tackling water pollution and river health.
Water companies were instructed to install EDMs at all CSO points across England, which was completed by the end of 2023 to provide a data set across the country.
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