What is the emerging legislation or other threat that lies behind the proposal?

DEFRA and the regulators are reviewing the way in which sector share of pollution is derived. The review is to complete in the Autumn. The sector share allocation approach (whether revised or as for PR19) needs to be embedded in SAGIS for catchment work.

Regulators, encouraged by Government (DEFRA in England) are increasingly managing the water environment at catchment scale. In England and Wales catchments mean operational catchments. These have been identified by the regulators and are reasonably homogenous, thereby making it easier to identify the non-water industry sector impacts. (There are over 300 such catchments in England).

The SAGIS-SIMCAT system was first used in PR14 and more extensively in PR19, where several billion pounds of investment were based on calculations provided by it. Indirect benefits include a consistent approach across the water Industry for environmental planning and closer, cooperative working with the regulators.

The purpose of this proposal is to develop the facilities for catchment scale calculations, analysis and reporting, in preparation for PR24.

Why is the Industry concerned about this issue?

Water Industry environmental obligations for PR24 will be contingent on sector share allocation, at catchment scale.

The absence of the means to compute this Water Industry share could result on undue obligations and hence costs being placed on the Industry.

This will support the development of PR24 measures, and allow us to better explore catchment solution options.

The specific problem is:

• To have catchment scale information in a reliable and accessible form to support the PR24 process.

We note that:

• SAGIS-SIMCAT already provides some of the tools needed for catchment scale work. These include the Decision Support Tool and the Environment Agency optimiser.  

The missing parts, to be provided by this project, are:

• Specification of operational catchments within SAGIS and SIMCAT
• Summary statistics for catchments
• Sector share of EQS

Summary statistics are the usual mean, standard deviation and percentile concentrations. These are to be provided on a sector by sector basis, thereby providing a clear picture of each sector’s contributions. These statistics will also allow better inter-catchment comparisons. Sector share is derived from these summary statistics. (The details of the sector share derivation will need to be consistent with PR24 guidance, following the DEFRA review.)

1. There is continuing pressure to reduce CSO spills and unless additional action is taken to separate sewers and/or limit infiltration, then this results in a larger flow of more dilute sewage arriving at the STW for treatment. Conventionally, full treatment is only given the a notional three times the dwf before making a storm discharge. But with similar pressure on storm tank discharges, this imposes expectations on full treatment (whilst recognising that some smaller 'village' plants may be 'treat all flow' sites). What are the 'technical' limits on the overall envelope of flows that can be treated and how might this be enhanced? Where there are expectations of applying advanced treatment for CEC, how will this interact and what scope of flows can be successfully treated by advanced options?
2. As an adjunct: What technologies exist (membranes?) that could separate the 'clean' water on arrival at the works (or better still, at some location in the catchment) so that an acceptable discharge quality could be achieved, whilst retaining the majority of the polluting load, but much less flow, for onward passage to the STW? At what cost, both financial and carbon?

Diffuse pollution is a well-established polluting load. Whilst a proportion may be discharged via Highway drainage, much will either be direct from WASC assets (surface water sewers) or indirect via combined sewers - CSOs and STWs. With recent concerns of microplastics and 'chemicals of emerging concern' more widely, we need to understand sources and possible interventions. Equally, we see increasing interest in sludge quality and assumed impacts on soil - but how much of the PAHs, PFAS or microplastics have simply arrived by deposition?