A variety of volatile substances are used, manufactured, packaged, and sold by industry, and not infrequently, traces or higher concentrations are present in process waters which industries wish to discharge to the public sewer.
Under the Water Industry Act 1991 (section 94), sewerage undertakers have the following general duties (Crown Copyright, 1991; Ofwat and Defra, 2006):
- to provide, improve and extend a system of public sewers, and to cleanse and maintain them to ensure that the area is effectively drained; and
- to make provision for the emptying of those sewers and treatment of sewage.
Therefore, sewerage undertakers have a responsibility to protect their assets, the environment and, ultimately, people, as well as to control discharges that may impact on this responsibility. In order for water utility staff and contractors to work safely in sewers when carrying out operational duties such as cleaning, maintenance and/or refurbishment, water utilities need to determine the consent limits of volatile materials to minimise the occurrence of toxic atmospheres in sewers.
This report deals with the formation of toxic atmospheres in sewers, and outlines a scientific basis for predicting the vapour-phase concentration of toxic material in a sewer from the concentration of the material in sewage. This prediction can be used for setting consent limits to minimise the occurrence of toxic atmospheres in sewers.The information and procedures contained in this report are intended to be used by a competent person with sufficient knowledge and experience. The values obtained from the information and procedures contained in this report are estimates. Information and procedures contained in this report are given in good faith but WRc cannot accept responsibility for actions taken as a result.