EA to step up enforcement of flow regulations

As part of its wider duty to protect the environment, the EA requires

dischargers to measure and record their effluent flows. This requirement is

included in most discharge consents granted by the EA.

Under a new policy, the EA will soon start to implement a new programme

designed to ensure compliance with European directives, under the Water

Resources Act (1991) and the Environment Act (1995).

Where consents already include flow measurement conditions, these will be

enforced ­ where they do not, appropriate conditions will now be added.

98% of STWs in the UK have open channel flows, and for many it is also the

preferred type of channel for discharge.

As one of the first steps in its programme to ensure compliance, in January

the EA published Technical Report P150: Flow Monitoring of Discharges; An

Audit Manual.

The report summarises the essential relevant information from the European

directives, and from the British Standard BS 3680. Methods of measurement of

liquid flow in open channels are described, beginning with the design and

use of primary flow structures, such as flumes and weirs.

Based on existing documentation and experimental data, the EA report has

identified a maximum tolerance of 8% for discharge flow monitoring.

Work by Mobrey¹s flow audit team indicates that about 90% of all open

channel flow structures in the UK do not meet this level of accuracy.

According to the EA, many sites are inadvertently sub-standard, and

operators may not even be aware that there is a problem. Typical problems

include design inaccuracies, build-up of deposits over time, inappropriate

up or down-stream flow conditions and incorrectly calibrated secondary

instrumentation.

Technical report P150, which will now be used by EA personnel surveying

sites, sets out guidelines for the flow audit procedure. It is also

available for companies which carry out their own flow audits.

The EA will require that dischargers install flow monitoring to the required

specification and have the installation certified by an external body. A

number of installations will be audited by the EA each year.

There is no doubt that technical report P150 is a useful, and much needed

document; the widespread use of which is to be encouraged throughout the

industry. However, there do appear to be a number of discrepancies between

it and other standards which need to be resolved, if confusion is to be

avoided. These include:

• In section 2.2.2.7 (Construction of the Primary Device), P150 quotes the

  BS3680 tolerance for flume construction. In fact, these tolerances are

  almost universally unachievable in practice and most flow engineers tend to

  employ more practical guidelines to ensure accuracy of the flume.

  Meggitt understands that implementation is currently being discussed within

  the EA, but it seems likely that, as long as the overall accuracy of the

  installation can be shown to be within 8%, the BS tolerance details will

  probably not be enforced.

• In section 2.2.3 (Installation Effects), the technical report quotes

  BS3680, saying that the distance that should be allowed upstream of a weir

  is Œ10 times the maximum width of the nappe, plus five times the maximum

  head.

The report omits to say that this distance is only required by the BSI if

the approach velocity is negligible. If there is no disturbance to the

water, then the upstream distances are not necessary for accurate

measurement.

To comply with the legislation on effluent discharge, water companies must

complete a full flow audit, correct any errors and implement a maintenance

programme to ensure that accuracy is maintained.

Notably, they must document all these procedures in a manner suitable for

inspection by the EA, in order to prove compliance.

Mobrey offers flow auditing and consultancy for compliance with these new

regulations. A certificate of compliance for inspection by the EA is issued

when work has been completed to the required standard.

However, as the EA does not operate an accreditation scheme for bodies

carrying out this work, there is still a serious risk of inexperienced

operators offering sub-standard compliance audits, despite publication of

the P150 report.

Meggitt would welcome an accreditation scheme for companies offering

consultancy and contract civil work, such as the Œcompetent body’ scheme,

which authorises test laboratories to certify electromagnetic products used

in the electronics industry.

Such a scheme would set minimum levels of quality and give the industry a

practical means of ensuring compliance with the EA’s regulations.