Technical Guidelines for the Identification of Mixing Zones General Introduction John Batty – DEFRA UK

Background During the latter stages of formal negotiations for 2008/105/EC (EQS Directive) it became clear that, for Mixing Zones to form part of the proposal, a technical guidance document would have to be developed The EQS approach is largely based upon a mechanism used in UK for many years where mixing zones form a key part of the management platform Without mixing zones EQS values would effectively become Emission Limit Values The drafting group was drawn from a range of backgrounds to ensure that the Technical Guidelines for the identification of mixing zones under Article 4(4) of the EQS Directive would provide a robust approach

Philosophy EU27 encompasses a very wide range of water bodies, our task was to develop a flexible mechanism that could be used in the majority of circumstances A clear view was evident from the outset that the approach adopted should focus on real problems and not waste resources regulating trivial discharges This provided the basis for the “Tiered Approach” that forms the core of the document -A tailored approach that provides an appropriate level of scrutiny and detail

Purpose The purpose of these guidelines is: to assist Competent Authorities to first establish where a mixing zone is required and to then determine its size and acceptability using a tiered approach designed to apply an appropriate level of detail and scrutiny

Remember ! These Guidelines may be new to you... but the theory and associated mathematics has been in use across the world for many years with several books written on the subject! Our intention in compiling these Guidelines was to provide a succinct document to assist all practitioners in their task with links to other information sources

Working Definition The Directive sets out options but does not provide a specific definition. The drafting group therefore agreed the following working definition: "A mixing zone is designated by the Competent Authority as the part of a body of surface water which is adjacent to the point of discharge and within which the concentrations of one or more contaminants of concern may exceed the relevant EQS, provided that compliance of the rest of the surface water body with the EQS is not affected."

The tiered approach

“Tiered Approach” Tier 0 Contaminant of Concern present? Tier 1 Initial Screening Tier 2 Simple approximation Tier 3 Detailed assessment Tier 4 Investigative Study/Validation of models

“Tiered Approach 2” The guidelines provide solutions that are: Efficient - Resources are only used when necessary and are commensurate with the environmental concern Robust – Leading to sound reproducible decisions that contribute to sustainable use of the aquatic environment Flexible – To meet the needs of Europe’s aquatic environment

Tier 0

Tier 1

Tier 2

Tier 3

Tier 4

Any Questions? Thanks for your attention