Paul Conroy of WRc looks at minimising sewage pollution incidents
Sewerage undertakers are under pressure to avoid incidents that have the potential to result in pollution and, when an incident occurs, to minimise any resulting pollution. Serious failures can cause disruption, health risks, a loss of service, a poor image to customers and unnecessary expense to operators.It is in the interests of undertakers to provide an efficient response to problems. This reduces the adverse effect of an incident, raises public confidence in the sewerage undertaker and often minimises expenditure. Achieving this requires the undertaker’s staff to have access to reliable, detailed knowledge of the local infrastructure and to be able to work effectively.
A review of current operational practice examined a wide range of pollution related incidents.
There were a number of findings that suggested operational efficiency may become over stretched. Most important was the observation that sewer system operators use a variety of different systems and procedures. This is particularly so with regard to:
- handling/routing of external telephone calls reporting pollution/incidents,
- responding to telemetry alarms,
- information management or database systems and the identification of repeat occurrences
From a public perspective, the most serious pollution incidents are those resulting in sewage pollution of watercourses and the flooding of property/gardens. Yet, when it came to a review of clean-up procedures, specifically in the case of gardens, feedback suggested there is a lack of advice available to offer people affected by sewage flooding. For example, ‘how long should people/pets be kept off the flooded areas?’ and ‘how long before the children can play on the lawn?’ are questions not easily answered. It is astonishing this has only recently become an issue and that suitable information is only now becoming available.
Various performance data relating to pollution control is available from reports published by Ofwat and the EA. Companies appear to be performing well. The total number of watercourse pollution incidents from all sources has been gradually reducing during recent years. Typically, over 90% of all incidents were classified as the least significant category three. More significant category two incidents accounted for less than 10% overall and the very serious category one incidents accounted for less than 1%.
This type of statistic would appear to vindicate current policy, though the reality of lost knowledge and confusing data may start to outweigh the benefits created by more proactive management policy.
An effective incident management procedure should be an essential element of a sewerage undertaker’s strategy for dealing with operational emergencies. Included in this should be systems for avoiding, or at worst, minimising pollution during emergencies. Incident management procedures should enable operators to respond to incidents in a timely and cost effective manner. In this respect procedures should:
- be comprehensive, yet short and easy to read,
- be simple, with a minimum of bureaucracy.
- communications – both between the organisation and customer, and internally,
- management systems – including systems that give an early warning of problems, pollution management and clean-up procedures, and follow-up reviews,
- information – including contingency plans and access to reliable and appropriate information/databases etc,
- training – the above elements are all worthless unless the people concerned know how to use them.
1: An effective communication system – this will need to address the problem of communications in larger centralised systems being more complex and remote than in local operating systems. An effective system will include:
- call management procedures to ensure calls relating to a pollution incident, or potential incident, are immediately identified and actioned,
- call routing systems within a sewerage undertaker’s organisation to ensure problems and all other information are passed to the relevant sections/individuals as rapidly as possible.
- easily understood contingency plans,
- accessible information management systems,
- techniques that give an early warning of problems, for example through the use of telemetry, may be justified in certain situations.
4 Follow-up systems, to review why the failure occurred and to ensure there is no repeat. In addition, it will be necessary to demonstrate best practice procedures are followed in the event of a challenge from a regulator or other body.
A review of recent prosecutions showed sewerage undertakers may have avoided/controlled the failures in 22% of pumping station incidents and 10% of sewer blockage related incidents if reliable contingency plans had been available and used. Furthermore, by demonstrating the use of a reliable contingency plan, a sewerage undertaker may prove their commitment to minimising pollution in incidents and avoid a subsequent prosecution.
Contingency plans are an essential part of an incident management procedure and should cover all foreseeable operational failures where customers and/or the environment may be affected. They should:
- provide direction and guidance to those involved in responding to incidents,
- identify the actions which are required to rectify the failure, contain the sewage or, if a sewage escape has already occurred, clean-up and minimise its effects on the environment,
- enable incidents to be dealt with in an efficient and effective manner.
The most effective way for a sewerage undertaker to avoid the expense and inconvenience of cleaning up after an incident, and a possible prosecution, is to ensure the incident does not occur in the first place, or at worst, is contained as a minor incident. Traditionally this has been achieved by visiting high-risk assets on a regular basis. However, the need to reduce operational expenditure often results in the frequency of visits being reduced.
An alternative way of identifying problems is to telemeter the important functions of an asset and react whenever the operation goes outside normal operating limits. This approach is already used at the majority of pumping stations. However, data is rarely comprehensive enough to enable a failure to be diagnosed and remedial measures actioned without visiting the site first. This can waste valuable time when there is a problem and unnecessarily utilise resources when there is a false alarm.
There have been considerable advances in electronic monitoring and communication technology since pumping station telemetry was first introduced. Many of these advances are becoming commercially available so it is practical and affordable to monitor more functions and at more locations than has previously been the case. Furthermore, modern filtering techniques enable increased monitoring to be undertaken without an increase in the number of alarms/demands on system operators. Therefore, opportunity exists for sewerage undertakers to use technology to monitor assets far more efficiently, to help give better warning and remote diagnosis of potential problems.
The Way forward
The review of current sewerage operational practice showed the vast majority of activities relating to pollution prevention control are undertaken efficiently and effectively. However, there are areas with the potential for improvement:
- incident management procedures, in particular, replacing local management systems with more cost-effective company-wide/regional structures,
- communication systems, with effective call-handling and problem-routing procedures,
- availability of reliable information, through the use of information management systems and contingency plans,
- monitoring systems, to give an early warning of operational failures