Dangerous Substances in Discharges: Setting Consent Conditions and Assessing Compliance

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Applying Maximum Limits (MLs) to Dangerous Substances (DSs) in Wastewater Treatment Works (WwTWs) effluents poses problems. This report describes work for UKWIR and the Environment Agency to quantify effluent variability and propose consenting alternatives.

A three-element alternative is proposed: a 95%ile for routine control, a 99.5%ile to address the skewness of DS distributions, and an absolute maximum for legal reasons. The performance of each element is investigated.

The Project Steering Group recommends the following approach, the practical implications of which are described in the report:

Limits on each DS at a WwTW:

  • A Lower-Tier 95%ile, assessed every calendar year by Look-up Table (LUT).
  • A Middle-Tier 99.5%ile, assessed annually on a 5-calendar-year basis by LUT.
  • An Upper-Tier absolute maximum (an agreed multiple of the Middle-Tier limit).

Applied to pooled DSs at a WwTW:

  • Compliance with all Middle-Tier limits, assessed on an annual 5-calendar-year basis by LUT.


UKWIR Reference :- 07/WW/21/9Published Date :- 15/01/2007
Retail Price (£) :- 24ISBN :- 1 84057 429 1