Introduction/Overview

All aqueous effluents on site therefore need to be identified. thoroughly investigated and measured. This includes:

• point source discharges to surface waters and sewers
• indirect source discharges that may arise from accidental spillages and leaks, runoff (for example oil on car parks).

It is particularly important to remember that the discharges to groundwater are difficult to quantify and remedial actions, in turn, are complex to undertake

• A thorough drainage survey: a thorough investigation of all drains on site, including all branches (especially on old factory sites) is essential. This will enable to pin point those areas on site that give rise to the greatest pollution load. It will also assist a company in drawing up environmental improvement programme, lead to a better understanding of effluent flows themselves and to devise emergency spill procedures. The outfall is only usually sampled although it may also be wise to monitor other areas of the system itself.

A general water monitoring programme should be designed to measure:

• Those substances that are specified in discharge consents.
• Legal compliance with any discharge consents.
• Substances that are not covered by a discharge consent, although may enter drains through leaks and spills.

Taking flow measurements at each outfall on site is useful in that this enables the conversion of concentration values of substances into mass discharge rates. Flow meters are usually fixed within the drain itself, although mobile devices may be used for smaller flows for less frequent monitoring.

It is possible to link analysers that monitor continuously to detect any spillages to a control room and in turn, to an alarm system. This is most relevant at larger sites. Other items that it is worthwhile considering are the undertaking of a risk assessment to assess the likelihood of breaching a discharge consent and also the consideration of the environmental sensitivity of the receptor ie the receiving waters.

The type and frequency of aqueous monitoring on site is dependent upon the conditions set down by the discharge consent and upon the information required such as continuous, snap or time-averaged.

Should a company discharge effluent containing red, black or grey list substances should be aware of the relevant environmental quality standards that they must comply with at the edge of the mixing zone in the receiving water. Here, the company must undertake sampling at agreed monitoring points to test whether environmental quality standards are being breached or nearly exceeded. Here, the Environment Agency (EA) will look to minimise the concentration of the consented substance in the discharge. They will most likely require an authorisation from the Environment Agency, which will detail the means by which monitoring and measuring is to be undertaken.