by Martin Lambley, Product Manager - Foul, Utilities & Water Management – Wavin Limited

Drainage contractors: avoid misconnections in your customer's sewage systems

When connecting new pipes to customers' drainage systems, contractors must avoid misconnections between stormwater pipes and sewage pipes. Often, that's not easy. Even if you connect to the right pipes, there's no guarantee that stormwater and sewage will then be kept separate. Previous contractors may well have just connected pipes to the nearest available drain, so existing systems can already suffer from misconnections. Any extra discharges may tip the scales, with the pollution being attributed to your work. 

As a drainage expert, you should be alerting your customers to any actual or potential problems. Unless responsibilities are clearly written into the contract, you'll need to do some form of audit of existing systems, and that will need to be included in your work estimates. At the least you'll have to study the branch(es) of the system that you're connecting to. 

The audit

Stormwater drains must carry the rainwater from roofs and any clean ground run-off to prevent overwhelming sewage treatment plants. Waste water must go to treatment plants to prevent subjecting residents and wildlife around outfalls to a polluting mix of sewage and chemicals. Central and local governments and water authorities set their regulations to prevent such spills, so you'll need to know the relevant regulations. Pollution incidents are being tolerated less and less, so laws and regulations are becoming stricter and fines are increasing. 

In Europe, the best first place to start is the EU's Water Framework Directive, which gives an excellent introduction. This feeds into individual country's laws, and also any local water company regulations. 

Wastewater producing sectors like food and drink, pharmaceutical, paper, chemicals and agriculture can produce huge waste flows. These companies, and any ISO 14001 certified organizations need strict procedures to prevent pollution. ISO 14001 requires that an organization "considers all environmental issues relevant to its operations, such as air pollution, water and sewage issues, waste management, soil contamination, Climate Change mitigation and adaptation, and resource use and efficiency."

The drainage plan

Check the documentation you have been given, and that all pipe runs are correctly identified.   An example of domestic site plan requirements  to UK Government recommendations is at Figure 1. Industrial and commercial site plans may be much more complex. 

The plan should show the layout of buildings and roads on the site, and above-ground gradients that show where surface water will flow and enter the drains. It should identify the path and direction of stormwater and wastewater drains, and which substances and chemicals go into which drain. It should show the location of any:

  • rainwater pipes, gullies, drainage channels
  • drain covers and manholes (new manholes suggest recent alterations to the system) 
  • bunded and other areas where chemicals (particularly hazardous chemicals) are stored, and what's stored there
  • soakaways, oil separators, sumps, stormwater attenuation and water recycling systems, retention and balancing tanks, and fire-water storage ponds 
  • shut-off and sprinkler control valves, mains stopcocks and fire hydrants
  • discharge points for surface water and trade effluent
  • nearby waterways, boreholes or wells and if any drains discharge into them
  • any natural springs, spring lines or issues, whether currently active or not. 

An audit should be based on standard quality-improvement procedures. Waste streams from processes are just as much process outputs as what the processes were actually set up to produce. Outputs with significant impacts to the receiving environment will need detailed assessments, and your customers may need additional permits to discharge. The UK's Environment agency for example gives advice on assessing impacts from surface water discharges. 

Is all as it should be?

You'll need to physically check that pipe runs are correctly identified and located on maps (particularly old ones), and that there have been no extra connections since the map was drawn. Contaminated water must go to foul-water drains, and chemicals must not contaminate groundwater. 

Many companies keep a check on water consumption by monitoring water readings, with analytical techniques allowing for actual usage to show up leaks in incoming water pipes. Wet patches in the ground can also indicate pipe leaks. 

Leaks from drains may be intermittent and can be harder to identify. A full audit would check that pipes, connections between pipes, and any chambers are watertight to prevent pollution of groundwater and infiltration to neighbouring pipes (see our White Paper "Watertightness of stormwater and foulwater systems").  This may require a specialist auditing company since it can need dedicated equipment. Drainage test techniques include non-toxic dyes, smoke blowers, manhole  inspections, CCTV cameras, pipe tracers, thermal imaging, flow monitors, temperature loggers (temperature changes in discharges can show misconnections), Diffusion Gradients in Thin Films (DGT) devices, optical brighteners and faecal indicator organisms (FIOs). 

Connecting up the new systems

Stormwater can sometimes be contained on site, and the effects of Climate Change on rainfall levels and frequencies have encouraged many companies to consider long term solutions for water attenuation and infiltration into the soil. Attenuation tanks  can for example help manage rainfall peaks, with some installations having above 2000 modular tanks. 

New drainage systems must meet regulations like the UK's Approved Document H Drainage and Waste Disposal document. 

It's not just the connection you're making that you'll need to look at. Once again you may be blamed if the processes you've connected up to are themselves leaky. You'll need to know the outputs of the various processes and where they should be directed. You may also need to check that any polluting materials and wastes are stored safely and securely in suitable containers away from open drains, permeable surfaces, soakaways and watercourses. Hazardous wastes should be stored separately, and signs should warn of hazardous materials and activities. 

Waste should be minimized by reducing it at source, then re-using, recovering and recycling resources where possible and only then disposing of them. This makes financial sense: raw materials are expensive, as is their disposal and there can be many opportunities for contractors to save their customers money. 

Vehicle cleaning areas will need oil separators. Processes discharging toxic chemicals like ammonia and chlorine, and any excess nutrients, pathogens and invasive species must similarly not be discharged into stormwater pipes. In the UK, important resources include the Government's Pollution prevention for businesses and a pollution incident response plan

Your own work should clearly identify which pipes go where. Foul and storm sewers should be clearly marked on the construction drawings at the design stage. Unfortunately, this is not the case when it comes to installation where there is no requirement (in either Sewers for Adoption 7 or Part H Building regulations) for the installer to identify what the pipe is carrying. Installers should ensure they do this, though. Stenciling an arrow on the manhole can show the direction of flow (and on the ground so that the cover is correctly replaced after removal). And the drainage plan should be updated. 

If waste water includes that from toilets, customers should educate their staff and visitors not to flush away products like single-use wet wipes. These can block sewers, pumps and wastewater engineering works inlets, causing flooding and pollution incidents and expensive emergency callouts. Food waste, fats, oils and greases should similarly not go down kitchen sinks since they can solidify and block the pipes. 

Larger-scale projects

Larger projects may need detailed flood risk assessments to comply with the EU's Floods Directive. Cities particularly must be resilient to the increasingly frequent and intense rainstorm events that are accompanying Climate Change. Civil engineering projects should demonstrate good urban stormwater management to avoid increasing flow unacceptably and making areas susceptible to intense rainfall, Wavin has developed an urban stormwater resilience tool kit to raise awareness of the issues. 

Civil engineering projects should look at cradle-to-cradle sustainable drainage systems, which model nature's own processes for reducing floods. 

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