Urban diffuse pollution has, for good reason, been sitting in the government’s ‘too difficult’ pile for close to a decade. It includes many kinds of pollution from diverse sources - road run-off, sewage from misconnected drains, oil spills and silt from construction works - which can combine to impact on streams, rivers and groundwater.
Diffuse pollution is now the biggest threat to water quality, the Environment Agency says, with one in eight urban rivers in England and Wales of poor or bad chemical and biological quality. One in five domestic properties has foul drains illegally connected to surface water drains, it estimates, channelling untreated sewage directly into watercourses.
Diffuse pollution is harder to address than point sources - although the Environment Department (DEFRA) is encouraging farmers to curb agricultural pollution through agri-environment schemes and linking subsidies to environmental performance.
But with urban pollution there is no such group of potential polluters to address. Householders, small businesses, road users and builders may all from time to time be sources of diffuse pollution.
Faced with the water framework Directive’s requirement to achieve good ecological status - or, for heavily modified waters, good ecological potential - by 2015, DEFRA has dusted off the file and set about building a platform for action.
Its first move was to hold stakeholder workshops on urban diffuse pollution in 2004 and establish a steering group - comprising key people in the environment agencies, national and regional government and Water UK.
Phil Chatfield, the Agency’s soil manager and a member of the steering group, explained the difficulties: "With most problems there is one approach which will address, say, 80% of the problem. Here there is no single thing that will solve even 10%. And there is no single group of people to whom you can turn to achieve improvement."
The workshops and steering group have responded to DEFRA’s consultation, launched in February, on ‘non-agricultural diffuse water pollution’ or NADWP in England and Wales.1 The term covers urban diffuse sources, but also includes forestry and abandoned mines in an effort to bring together all remaining sources (ENDS Report 386, pp 49-51 ).
The consultation suggests that pollution problems should be divided into five classes - industry, transport, abandoned mines, sewage and sediment. However, it is clear that many areas overlap, and problems could fall under several headings (see box, p 37 ).
London’s dirtiest river
The case study of the lower Lea, or Lee, catchment illustrates the problems of urban watercourses better than most. The river, which flows through Hertfordshire, Essex and east London before entering the Thames below Stratford, is attracting attention because it will form the backdrop to the Olympic Park for the 2012 games.
It is London’s dirtiest river, achieving only a "poor" class E chemical classification downstream of Tottenham, where inputs from urban streams deliver regular batches of pollution. The river at this point is a complex web of culverts, streams and flood relief channels, with the main river canalised for navigation.
Centuries-old modifications to facilitate barge and boat traffic have raised the level of the river. Tributaries must now follow the main channel until it descends to a suitable level to allow them to join the main flow.
These tributaries drain the suburbs of Tottenham, Enfield, Edmonton, Chingford and Walthamstow, which were built up in the 19th and early 20th centuries. What were once rural ditches and streams were culverted and diverted and now receive inputs from surface water drains, unlike outside inner London’s combined system, where all foul and surface water drains end up at sewage works.
One watercourse, the Moselle brook, was described by a local historian as "sparkling… with a plentiful supply of fresh water, with an abundance of fish" as it meandered through fields and marshes around Tottenham.
Now it is nearly invisible. Culverted for most of its length, it suffers pollution from long-standing sewer misconnections and other unidentified sources. Although areas of marshland still adjoin the river, much of the original valley is taken up with water supply reservoirs. Further changes were made in the 1960s following flooding in north London - bequeathing a network of hard-engineered channels and culverts, often in inaccessible places.
Agency catchment officer Pete Rudd is one of few people familiar with the river’s highly modified and rarely visible tributaries.
"Many rivers are lost forever because they are now part of the sewerage system," Mr Rudd reflects. "Many others can be saved, but you can’t appreciate rivers if you can’t see them or sense them."
He is a facilitator of efforts to improve the Lea, and works alongside local authorities and the sewerage undertaker, Thames Water.
The London Borough of Haringey is aiming to uncover part of the Moselle that runs through a recreation ground west of Tottenham. But before this can happen, pollution sources must be addressed.
Haringey and Thames are working together to identify and correct sewer misconnections. The first stage, says Mr Rudd, is identifying the most contaminated catchments, inserting wire netting cages into surface water drains and leaving them for several weeks to see how much sewage debris accumulates. The worst areas can then be targeted in a house-to-house, business-by-business survey.
The local authority, rather than the sewerage undertaker, has powers to require misconnections to be rectified. But it is often a painstakingly slow job to secure residents’ help and identify freeholders who are ultimately responsible. DEFRA is considering whether more extensive powers are needed.
Haringey is also addressing the pollution of two other tributaries, the Old Moselle and Stonebridge brook, which run under and adjacent to another park. In addition to sewer misconnections, there is also a problem with an inadequate sewer overflow which will need to be funded under Thames Water’s current asset management plan.
Such tributaries also suffer periodic inundation with polluting run-off from roofs and roads during heavy rainfall. The first pulse of water contains the stagnant water and sediment accumulated in gulley pots, with metals rendered soluble by anaerobic conditions.
Phil Chatfield describes the experience of field workers caught by storm flows: "There can be a sudden flush - a six-foot wall of black water carrying a load of pollutants moving swiftly along watercourses which are little more than concrete channels."
These brief pollution episodes are rarely documented by routine water quality monitoring - but their effect on the main river is marked. Although water quality may appear reasonably good, the impact of these pollution events is evident in the impoverished fish and insect life.
Accumulated sediment in the main river downstream of Tottenham, Mr Rudd explains, has a high oxygen demand which sometimes results in fish kills. British Waterways, which manages the navigation, is not responsible for removing sediment just to improve water quality. The treatment and disposal costs are likely to be high and there is no obvious funding mechanism for a clean-up.
In an effort to understand the fluctuations in water quality, the Agency has set up a 24-hour monitoring network. Samples are taken by automated samplers across the catchment to characterise changes in water quality.
One of the variable factors is Thames Water’s Deephams sewage works, which discharges to the Pymmes brook. The treated effluent constitutes a large part of the flow during dry weather, and although the works complies with its consent, Agency staff are discussing with the company how effluent quality might be improved.
Mr Rudd expresses guarded optimism: "My personal view is that it will take two generations to effect a real change in urban water quality. There is a need to improve visibility. Taking streams out of culverts will not only raise public awareness, but will make sources of pollution more easy to identify."
Nevertheless, his expectations are tempered by realism. "We’re working with partner organisations to improve water quality in the lower Lea," he said: "There is no quick fix, but only small steps in the direction of bringing London’s rivers back to life."
Phil Chatfield complains that public knowledge of what drains are and where they go is pitifully low. Few appreciate the difference between surface water drains, intended for relatively clean run-off and leading straight to watercourses, and foul sewers which end up at the sewage works.
To date, there have been few efforts to change this - but exceptions include the oil care campaign, and the less well-known yellow fish campaign.
The oil care campaign seeks to reduce oil pollution incidents by informing householders of the disposal routes available for waste oils, particularly sump oils from home oil changes. It also highlights the environmental threat posed by such materials when tipped into drains.
Potentially wider ranging is the yellow fish campaign, which gets children - and through them wider local communities - involved in marking drain covers with yellow fish symbols. The aim is to foster awareness about what might lie at the end of the drain and the dangers to wildlife.
The Environment Agency and its Scottish counterpart have had some experience of using the yellow fish campaign, which originated in Canada, to some effect. The Bourne Stream Partnership is an example of how the campaign can be part of a community focus for improving an urban watercourse.2 However, the potential of this idea has yet to be exploited fully.
The aim of the NADWP consultation, says DEFRA’s Catherine Pike, is to establish a framework and reach consensus on the priority areas to be tackled.
Although it is still too early to talk in detail about mechanisms to tackle urban diffuse pollution, the consultation puts forward ideas which are almost certain to be part of the solutions.
General binding rules (GBRs), for instance, could be introduced by new regulations. They are already embedded in integrated pollution prevention and control (IPPC) and Scottish water legislation. They are suggested in the water framework Directive as a means to counter diffuse pollution and are likely to be used as a way of making current best practice statutory.
Their advantages are their simplicity of enforcement - they would attract low-level penalties - and the low cost of compliance. GBRs for commercial or industrial sites, for example, could be lifted from pollution prevention guidance and might include measures such as marking drain covers to distinguish surface and foul sewer connections, possession of a site drainage plan and the reporting of pollution incidents.
The rules would go a long way towards reducing the number of incidents where poorly trained staff dispose of wastes or flush spills into surface water drains.
In many cases, GBRs would reinforce and focus existing best practice. For construction sites, for example, GBRs might require a site surface water management plan and include waste management rules for dealing with the washing of buckets and equipment by trades such as plastering, painting and bricklaying.
Silt inputs, which often originate from construction sites, can be a significant problem for urban watercourses, leading to smothering of the river bed.
The lesson from existing legislative pollution prevention mechanisms is that they are often only as good as their enforcement. The 2001 oil storage regulations, for example, introduced minimum standards for industrial oil storage facilities in England. The Environment Agency considers that they have succeeded in bringing about a 30% decrease in serious oil pollution incidents.
Given this success, it is surprising that the government has not found time to ensure regulations are extended to the rest of the UK.
Building regulations, however, which introduced similar controls on domestic properties in 2000, have been relatively unsuccessful. The number of pollution incidents from domestic sources are reported to be increasing due, the consultation suggests, to a lack of resources in local authorities to inspect installations and enforce the legislation.
Lack of resources is also blamed for the failure of local councils to check all new drainage connections made during building works. The growing number of misconnections is a major contributor to the poor quality of some urban rivers.
A review of powers to tackle misconnections may be on the cards following the consultation. Currently only local authorities, not sewerage undertakers or the environment agencies, have legislative powers to inspect and require their correction.
DEFRA is also reviewing the right to connect to sewer contained in section 106 of the Water Industry Act 1991. The Act allows the connection and discharge of sewage by any property owner or occupier, subject only to certain restrictions regarding the treatability and safety of the sewer contents.
A review might allow stipulations regarding how surface water drainage might be treated and surface water drains protected from pollution, the consultation suggests. There might also be a requirement for the use of sustainable urban drainage systems (SUDS) for certain applications. At its simplest, this might mean porous paving for car parks and hard standing to reduce run-off.
A more advanced requirement might be for rainwater harvesting. Holding ponds or swales - sloping grass banks to filter and abate run-off - might be required for larger new developments.
Few dispute that SUDS have an important part to play in the future management of urban watercourses. Stemming the rapid flush of polluted water entering urban rivers will reduce pollution loads, and increasing groundwater recharge will restore natural water purification through infiltration and biodegradation of contaminants. SUDS therefore have the potential to increase water resources and alleviate flooding - both high priorities for dealing with the potential impacts of climate change.
Planning policy statement 25, issued in December, advocates the use of SUDS to mimic natural water flows, manage run-off and help prevent flooding. Planning authorities are charged with encouraging developers to use them.
But SUDS have yet to take off, particularly in England and Wales. One barrier to their uptake is a lack of funding and incentives to install them.
Pete Rudd points out that developers are generally not keen to incorporate them because of the land required. He says they are only a possibility with large new retail or housing developments.
Only where SUDS offer apparent amenity benefits - such as green space or wildlife refuges - are developers likely to consider fitting them or local communities feel strongly enough to lobby for them.
Another possibility is that sewerage charges might be varied to promote SUDS by, for example, penalising organisations with large areas of hard standing or roofing whose impact on the drainage system is not ameliorated.
But if SUDS are really to improve the problems of urban rivers, they must be retrofitted to existing development whenever possible. Certain technologies such as green roofs, porous paving and rainwater harvesting particularly lend themselves to retrofit.
Green roofs may be as simple to install as planting a layer of stonecrop or other drought-tolerant succulents on an existing surface. The vegetation traps deposited silt, and holds and filters rainfall. It provides a green outlook for residents and constitutes an additional layer of insulation for the building.
Phil Chatfield cites the London Borough of Lambeth’s Ethelred estate, where residents requested existing council blocks be fitted with green roofs. The result, Mr Chatfield says, is the largest area of green roofing in Europe.
Concrete blocks or porous asphalt can replace concrete or tarmac with its drains and gullies that carry away surface water. These surfaces allow infiltration to the ground without puddling, provided soil conditions are suitable. The number of drains and entry points for litter, spills and other polluting matter to enter watercourses can be greatly reduced.
‘Home zone’ traffic-calming schemes, where roads, gutters and drains are removed and replaced by porous paving, are an example of where SUDS may be a by-product of efforts to create a safer and more attractive streetscape. The Dings and Southville suburbs of Bristol are two areas which have benefited from this approach.
Another barrier is the issue of maintenance. Here Scotland is ahead of the rest of the UK, already having a framework for the adoption and maintenance of SUDS. A consultation launched by the Scottish Executive in April proposes that public systems, if designed and constructed to specified standards, should be vested in Scottish Water (ENDS Report 387, p 50 ).
In England and Wales, with a variety of sewerage undertakers, the same model may not be appropriate. However, the issue is not raised in the current consultation document and will presumably be addressed in DEFRA’s second phase, due later this year.
Detailed proposals for control mechanisms are still being worked up and will be subject to a preliminary cost effectiveness analysis and a regulatory impact assessment before the second consultation, DEFRA says.
Summing up SUDS’ potential, Phil Chatfield concludes: "If you are prepared to think on a 50-60 year timescale, then probably you will see improvement in water quality. But there is a danger of building hard engineering solutions to problems where a softer approach is more desirable. In the final analysis it is about changing public attitudes and behaviours."
Addressing the multiple sources of urban water pollution requires the kind of shift in public perceptions that has occurred in the past 20 years over waste recycling. The water framework Directive’s 18-year programme for bringing waters up to good ecological status or potential could provide the focus needed to bring about such a change.