How to put a stop to contaminated water
The UK’s crumbling drainage network is struggling to cope with changing weather patterns. More must be done to prevent hazardous backflow flooding in homes and commercial properties, says Chris Ricketts.
The once-in-a-generation floods that we have seen in recent years in areas such as Cumbria, Herefordshire and Cornwall have been life-changing events for the individuals caught up in the devastation, with appalling damage to property and livelihoods.
At the heart of the issue lies our crumbling drainage network that is struggling to cope with the effects of climate change and its altering of our rainfall patterns, which are now, more often than not, short, sharp intensive bursts as opposed to a steadier fall of rain.
However, television coverage of burst river banks only tells half the story. The often untold story of many of these floods is the flow of greywater and even blackwater sewage back into commercial properties and residential homes.
This phenomenon, known as backflow flooding, is resulting in a significant increase in enquiries and orders for prevention devices at our specialist BSS Drainage centres across the UK.
The Environment Agency (EA) currently estimates that 80% of UK buildings, both commercial and residential, are at risk from backflow flooding at times of heavy rainfall.
What is more, the number of properties that are vulnerable to damaging sewer backflows is increasing. This is due to multiple factors, including the greater use of hard landscaping that prevents rainwater attenuation, the increased use of flood plains for development and the popularity of installing equipment which requires connection to the drainage system, such as WCs and showers, in basement areas.
In cases of severe flash flooding, such as those seen recently in Cumbria, a storm sewer has the potential to surcharge. In this situation, the water level in the manhole rises above the top of the pipe and hydraulic pressure causes the drains below the rising water level to back-up.
When this happens, contaminated floodwater can flow back though foul sewers causing flooding inside buildings. This is a particular issue with commercial buildings, where parking facilities and plant rooms are often sited below ground level.
The backflow level is the highest level to which rainwater can rise in a drainage installation and is usually defined by local authorities. In the absence of any specific definition, the backflow level is usually taken as the level of the road above the sewer connections.
All drainage installations below this level are at risk of backflow flooding and therefore need protecting with appropriate prevention measures. One of the most serious implications of backflow flooding is on an individual’s health with, on average, more than 10,000 reported cases of backflow contamination each year. It is scientifically acknowledged that pathogens present in water can cause infection with micro-organisms entering through the oral route via ingestion, or by eyes, ears, nose or through an open wound.
Pathogens associated with sewage contaminated water include bacillary dysentery, pneumonia, botulism, hepatitis A, meningitis and septicaemia. Furthermore, many of these pathogens linger once the flooding has subsided. For example, hepatitis A can survive for up to 100 days.
Backflow flooding is best controlled via prevention with the fitting of a non-return valve within the private sewer of a property upstream of the public sewerage system. There are a number of specialist backflow prevention products now available in the UK market from BSS Drainage and manufactured by companies like ACO Building Drainage, Kessel and OSMA.
These products vary greatly and have different specifications and uses, including motorised versions which include acoustic alarms and pneumatic sensors to alert when the potential for backflow is signalled.
The key to specifying this type of product is for building contractors, groundworkers, and drainage contractors to ascertain what the area of backflow risk is to be used for.
For example, if a backflow risk area, such as a basement only contains a washing machine or hand basin, then greywater compatible non-return backflow valves could be fitted.
However, if the area of potential risk contains toilet facilities then blackwater compatible non-return valves must be fitted.
Secondly, it is important that any product specified conforms to BS EN 13564-1:2002 Anti-flooding devices for buildings. This will ensure that any product is fit for purpose.
Finally, it must be remembered that anti-flooding devices require very careful installation and must be regularly maintained. Maintenance depends on the type of device fitted,
but is normally required every six months.
Flash flooding is an increasing problem in the UK, but backflow remains in many respects a lesser known element in its potential for damage. The technology now exists to prevent this type of flooding, but building contractors, groundworkers and drainage specialists should seek expert help when specifying a backflow solution.
Chris Ricketts is a specialist in drainage at BSS Industrial.
T: 0116 262 3232.
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