Increasing encroachment of housing on older sewage treatment works and a tendency to pump sewage from one catchment to another for treatment have made odour nuisance from sewage works an increasing problem.
There have been several high-profile cases of residents mounting long-standing campaigns to get odour problems remedied at sites like South West Water’s Cattedown works in Plymouth and Thames Water’s Mogden works in Twickenham. However, the problem is widespread, with scores of works receiving regular complaints.
The consultation document reveals some startling facts: 26% of local authorities in England and Wales have experienced problems with odour at sewage treatment works in the past five years. These problems affect around 230 treatment works - representing one-third of the industry’s larger sites. Local authorities receive some 2,400 odour complaints about sewage works a year, comprising 10% of all odour complaints.
The regulation of sewage works has gone from A to B and back again in recent years (ENDS Report 357, pp 26-29 ). Traditional controls under the statutory nuisance provisions of the Environmental Protection Act 1990 were thrown into confusion in 2000 when the courts decided that sewage works were not premises in the meaning of the Act.
A consultation ensued in which water companies and the Environment Agency were pitched against industry regulator Ofwat and DEFRA. Firms and the Agency sought a tough statutory approach which would provide a firm basis for funding, while Ofwat and DEFRA preferred a voluntary code of practice - as is now being discussed.
The courts then changed their view in June 2003 when the Court of Appeal ruled that sewage works were indeed premises under the Act. The ruling confirmed the pre-2000 status quo, leaving the general public and water firms without the levers to tackle foul sewage odours.
Thames’ Mogden works continues to be a focus of complaint underlining the unsatisfactory nature of current odour regulation (ENDS Report 359, pp 12-13 ). Water companies are free to continue endless appeals against abatement notices handed out by the courts, there are no effective sanctions against companies which fail to meet the notices and Ofwat is not obliged to provide funding for improvements to abate odour. There is no direct regulation of sewage works processes, allowing companies to cut corners and adopt practices which might exacerbate odour.
The consultation offers few answers to these difficulties. It aims to set standards for odour management at sewage works and to improve regulation. DEFRA-funded research, it reveals, found a "lack of uniformity and consistency of approach in dealing with odour problems". Also, water companies’ solutions are often ineffective. "In many cases," the document reveals, "the sewage treatment works had installed odour abatement plant and this alone did not remedy the problem."
DEFRA’s draft code of practice is similar to the Scottish Executive’s code issued last year. The consultation also includes a guide for local environmental health officers.
The code covers the legal framework for odour control, the nature of sewage odours and when odour complaints constitute a statutory nuisance.
The statutory nuisance provisions of the 1990 Act require a decision as to whether reported odours are "prejudicial to health or a nuisance". Factors to be considered include the nature of the smell, its intensity, frequency and duration, the nature of the locality affected, the number of people involved and whether best practicable means have been used to minimise odour. Some consideration is also given to the Agency’s treatment of odours under IPPC and the parallels with noise nuisance.
Methods of measuring offensiveness of odour include qualitative measures like the number, spread and frequency of complaints and odour diaries kept by local residents. Semi-quantitative estimates can be made using sniff testing, and an Agency protocol is a suggested reference point for use by local authority officers.
Fully quantitative measures are only possible via odour modelling or by monitoring of component gases like hydrogen sulphide. Depending on the odour, this may or may not give useful results. Olfactometry - the measurement of smells by the response of individuals to air samples - cannot be used to assess the exposure of receptors because it is generally not sufficiently sensitive.
Sewage works operators are required to use best practicable means to limit odours, which includes not only the general management of the works but also its design, operation and maintenance. Engineering solutions such as containment, venting and abatement are "often expensive and would not normally be adopted unless a cost-benefit case has been made first", the draft guidance comments.
Where odour control is needed, the draft guidance warns that there is "no simple one-size fits all solution" and the choice needs to be based on the balance of costs and benefits. There is no arbitrary definition of what constitutes best practicable means suitable under all circumstances. Often a combination of measures may be needed ranging from simple and inexpensive to complex and costly.
Where water companies face competing demands for investment in odour measures, the guidance requires them to follow "a documented prioritisation process to ensure those sites with the greatest odour problems are targeted first". The number and severity of complaints should be taken into account, but that "does not mean that sites further down a priority list are exempt," the guidance warns.
Operators are also required to implement measures "as quickly as is reasonably practicable", but they are given the get-out that prioritisation and funding restrictions can be taken into account.
The draft guidance includes advice on good housekeeping at sewage treatment works and outlines the "good practice approach" to resolving odour complaints. This is a nine-step procedure starting with the assessment of complaints, deciding whether a statutory nuisance exists, investigation of the source, the options for controlling the odour and deciding whether BPM is in place. Where it is not, further odour control measures will be needed and checks performed to ensure that this is effective.
The guide also explains sewage treatment processes and the likely causes of odour. Where abatement is necessary it covers the hierarchy of controls, beginning with good housekeeping measures through progressively more complex and expensive methods such as process control or modification, containment, enclosure and venting, or enclosure and abatement through treatment of odorous air.
There is also a chapter on the management and maintenance of odour abatement systems. Past experience suggests that once installed, these do not always function satisfactorily due to poor operational practices.
To check whether operators’ solutions remain effective, environmental health officers may conduct surveys of local residents’ opinion or use monitoring equipment. These may be hydrogen sulphide or ammonia sensors used either at the site boundary or close to housing or other sensitive receptors.
A regulatory impact assessment responds to comments made during the Government’s 2002 consultation, and asks whether respondents consider that the code will mean extra costs, even though it is merely reinforcing the status quo. But it is possible that the code and guide will raise public expectations and increase costs for both operators and local authority regulators.