Drainage contractors must beware of misconnections

Increased development density and greater stormwater run-off have raised the pressure on wastewater treatment plants. Split-sewage systems are increasingly being preferred. Instead of entering a single pipe, waste water goes to treatment systems while stormwater and clean run-off water are discharged directly into watercourses. 

That reduces sewage processing costs for water companies, but comes at a cost: any misconnections between sewage and stormwater pipes can overload the wastewater treatment plant or discharge raw, untreated sewage into local pools and watercourses. Pressure on sewage systems is such that in England and Wales alone there are almost 18,000 licensed emergency sewer outflows discharging raw sewage during extreme rainfall, and 1,902 ‘incidents’ were reported in 2016. During floods, water can back up into houses and other buildings. In dry periods surface pollutants become more concentrated in the run-off, with lower flow in the watercourses to flush it away. And in some countries with areas having low and intermittent rainfall, stormwater often needs to be reclaimed and reused. 

Drainage contractors should generally audit the drainage systems they're connecting up to. The audit and any corrective measures should follow a standard quality improvement process. You look first at the process outputs and the 'customers' of those outputs. For sewage pipes the output is polluted water and the customer is the water treatment plant. For stormwater pipes the output is acceptably clean water and the 'customers' are any local residents and wildlife around or downstream of the discharge outfalls. You trace the outputs back to the individual processes that produce them, and again back to the process inputs. 

Besides meeting all the relevant regulations, drainage systems may have to meet ISO 14001 implementation and documentation requirements. Our article tells you some of the things you should look out for. It discusses the drainage plan you should receive from your customer, what you'll need to check and update, and how to avoid misconnections in your own drain connections.