Managing storm overflows in AMP 7

Date: 10/07/19 | In: wastewater management

Maintaining a good reputation is key for any business and none more so than companies that operate in the UK water industry. In such a highly regulated sector, Water & Sewage Companies (WaSCs) understand only too well the damaging reputational issues that can potentially occur at every stage of the process involved in handling, managing and treating water and wastewater.

One such issue that has threatened WaSCs for many years is the discharge from storm overflow. Many factors, including population growth, infiltration, urban creep and dramatic changes in rainfall patterns, have combined to further add to the headache of storm overflows and how to address the environmental problems they can create.

So, is it actually possible to mitigate the pollution risks associated with large sewers by better managing storm overflows? Here at Detectronic, the answer is a definitive yes!

Regulations, regulations, regulations

The Urban Waste Water Treatment Regulations (England and Wales) 1994 state that sewer networks that are handling the waste of a population equating to 2,000 people or more must be ‘designed, constructed and maintained according to best technical knowledge not entailing excessive costs (BTKNEEC)’. Included in these regulations is the need for WaSCs to understand the volume and characteristics of their wastewater, prevent leaks and limit the pollution of receiving waters as a result of a storm water overflow.

And then, back in 2013 the Government set out requirements for Water & Sewage Companies (WaSCs) to monitor the performance of storm overflows.

Using a risk-based approach with the priorities being environmental factors, public visibility and spill frequency, storm overflows were to be categorised according to discharge significance. Based on the criteria of amenity, spill frequency and delivery of information, the majority of storm overflows have since been identified as high or medium significance and have required event duration monitoring (EDM).

The implementation of the Storm Overflow Assessment Framework (SOAF)

In order to support all of these regulations and help the water industry to address the problems associated with storm overflow discharges operating at too high a frequency, the Environment Agency (EA) established the Storm Overflow Assessment Framework (SOAF).

One of the main elements of the SOAF is to ensure that WaSCs are proactively monitoring and managing the performance of overflows as the contributing factors continue to pile on the pressure. At present, the SOAF only applies to discharges into receiving rivers but it is expected that the assessment will soon be extended to address storm overflows to lakes, estuaries and coastal waters.

What’s your capacity and storage potential?

To better manage your storm overflows you must first fully understand your network and get to know your capacity. After all, CSOs are there for when the sewage system is under pressure so if you can predict, through robust monitoring and data analysis, when there might be an issue you can do something to prevent or moderate it!

In order to effectively measure capacity, you must monitor the flow and not just the level of your wastewater. At the same time, if you’re monitoring flow and level it makes perfect sense to measure water quality too in order to inform effectively dilution properties in relation to any receiving river or rivers. Understanding the dilution potential can be achieved by using simple mass balance techniques that will assist in identifying the environmental impact from what is termed ‘first flush’.

Promoting self-reporting

Better comprehension of storm overflows (and your overall network!) also facilitates improved self-reporting of pollutions and spills. More monitoring means much more awareness, something that the EA is particularly focused on. Last July, in its ‘water and sewerage companies’ performance summary for 2017’ the EA reported that more than three-quarters of incidents (76%) were self-reported by the respective water company to the agency. This indicates an improved awareness of events at treatment works and in sewerage networks, however, the agency is also quick to highlight that much more needs to be done to reduce serious pollution incidents.

Our solution

At Detectronic we work with several WaSCs to deliver specific flow, level and water quality monitoring using our MSFM MCERTS multi-sensor flow meter. A battery powered insertion monitor, the MSFM MCERTS can be used in part-filled pipes and open-channels and is very versatile since it is not reliant on a flume or weir to deliver accurate flow measurement. The MSFM MCERTS will deliver guaranteed levels of accuracy and data-quality and enable you to further improve self-reporting.

Utilising storage potential in a network brings its own risk, but with careful planning and monitoring, in-network storage acts as an efficient means of stormwater attenuation.