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  • by Karma Loveday

Infrequent spilling overflows to be exempt from continuous water quality monitoring rules

Defra will exempt storm overflows that discharge fewer than ten times a year over a five-year average from the continuous water quality monitoring prescribed under the Environment Act.

Last week it published its response to feedback that was invited from specialists on its technical proposals to fulfil the two duties for sewerage undertakers set out under the Act:

  • to monitor sewerage assets and the impact they have on the local environment and publish the data (continuous water quality monitoring); and

  • to publish data from event duration monitors (EDMs) within an hour of operation (increasing public transparency).

Forty out of an invited 83 stakeholders responded. On the key question of exemptions on continuous monitoring, 47% of respondents called for low risk or low spillage to be excluded from the programme to save costs.

Defra responded by exempting overflows that spill fewer than ten times a year and descriptive only permitted treatment works. It reasoned: “Including the above changes to the programme will significantly reduce the cost of the programme to bill payers. It will also allow for greater deliverability of the programme, with water companies being able to focus efforts on a smaller number of assets in the initial rollout of the programme.”

It also made the following update to the technical guidance: “Water companies will be required to have completed rollout of 25% of all sites by 2030. This initial rollout should focus on high priority sites. We expect most water companies should be able to install monitors at 50% of high priority sites within the envelope of a 25% rollout of the total programme.”

Campaigners accused the government of watering down the rules and of continuing to allow water companies to mark their own homework.

The other main change in Defra’s response to feedback concerned clustering. Defra said it would update the clustering range rule in the technical guidance to the following: “Where there are two or more discharge outlets within up to 1km of one another in a single length of a watercourse, these can be considered a cluster and monitored by one pair of monitors. The downstream monitor for a cluster should be placed at the point of cumulative cross-sectional mixing for the last asset in the cluster. This will naturally mean that the first asset in a cluster will be further away from the downstream monitor. To assure quality of the data, the downstream monitor should be no more than 500m downstream from the point of cross-sectional mixing for the first asset in the cluster.”

It argued that by amending the clustering range, water companies would have greater flexibility when placing monitors without compromising on data quality. Defra stuck with the proposed cap of 10 on clustering. Elsewhere in its response, Defra confirmed the following: EDM There were no changes to EDM proposals. Sewerage undertakers will need to target 100% performance for monitoring and reporting (no allowance for equipment failure, despite 94% of respondents arguing there should be). They will also need to apply near time monitoring everywhere it is technically feasible, pushing for 100% coverage. Continuous water quality monitoring Most aspects remained unchanged from the original proposals. These included:

  • Focusing purely on sewage pollution rather than additional sources of pollution (such as from farming and mining), despite 85% of respondents seeking additional objectives.

  • Excluding nitrate monitoring, citing the additional costs this would bring. Using the maximum point of harm arising from ammonia, rather than dissolved oxygen.

  • Keeping the rule of monitoring “not more than 500m downstream from the point of cross-sectional mixing”. It said a standardised rule was desirable and that the distance could accommodate site-specific characteristics, though it will amend the guidance to say specifically that local and site-specific factors should be considered in final siting of downstream monitors.

  • Sewerage undertakers will be required to investigate the source of a breach to a particular asset.

  • Data should be displayed and contextualised in the form of an interactive national map.


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