Water plan

London Luton Airport has installed a ground breaking new water management system as part of its £110 million expansion and redevelopment programme

London Luton Airport is the first establishment in the UK to be equipped with ground breaking new stormwater treatment equipment, which is set to transform the way in which airports, and indeed all other major infrastructure projects, are able to manage surface water runoff.

SuDS best practice
Sustainable urban drainage systems, or SuDS, are now considered best practice to maximise the many benefits of surface water management, specifically the ways in which water quantity and quality, biodiversity and amenity can be managed together. Through recognising surface water as a valuable resource that can be harnessed, rather than solely as a problem that must be dealt with, SuDS provide real benefits to society and the environment, as well as helping to safeguard against flooding from storm events.

More recent legislative policy, including the 2015 Water Framework Directive (WFD), 2010 Water Management Act and River Basin Act, has placed increasing importance on the ability of SuDS to achieve prescribed Environmental Quality Standards (EQS) on water quality. Over the course of the next ten years, the UK Government has put in place milestones by which a series of stringent EQS requirements should be met. Latest SuDS guidance requires planners to incorporate the management of water quality into their designs, through specifying proprietary devices that enable proactive scheduled maintenance to be carried out.

To date, the primary response to these water quality demands has been to integrate into a ‘stormwater management system’ a series of mechanisms, which collectively fulfil a controlled sequence of water collection, treatment, storage and release practices. Above ground, water capture devices such as swales, ponds and wetlands, that provide both enhanced visual appeal and ecological benefits, are combined with underground devices that can further treat, store and control the flow and release of excess water volume to prevent flooding at the surface.

In its latest ‘SuDS Manual (C753)’, the Construction Industry Research and Information Association (CIRIA) recommends the use of such devices in their capacity to limit the amount of silts and attached pollutants from building up in the upper layers of the SuDS system and to mitigate against the ability of pollutant bioaccumulations to remobilise in the event of a surge of water, for example after a torrential downpour.

CIRIA has defined a risk assessment procedure whereby the designer of the water management system will assign risk levels of pollution, which are set according to key criteria such as the type of water-plan-131-bsite into which the system will be installed and the sensitivity of the receiving waters; similarly, each SuDS device will be assigned a mitigation factor. The sum total figure of pollution risks should then be measured against the sum total mitigation figure in order to define the series of devices required. This is the first time that guidance has stipulated the use of proprietary SuDS devices on their own to address and remedy water quality issues.

However, as standards for these devices have not yet been defined and published in the UK, the Environment Agency recommends that their performance is verified against standards which are already widely used in the United States, in the form of the New Jersey ‘CAT/DEP’ and European ‘DIBt’ protocols.

The New Jersey Corporation for Advanced Technology (NJCAT) and New Jersey Department of Environmental Protection (NJDEP) respectively provide a verification and certification process, based on particulate removal rates, for technologies used in the treatment of stormwater in order to meet the legislature and the regulatory requirements of the State of New Jersey, USA. DIBt (Deutsches Institut fuer Bautechnik) is the German Approval body that grants technical approvals for non-regulated construction products and types of construction.

Last year, SDS launched a range of water separation and filtration devices that have been tested and approved at both NJDEP and NJCAT levels. Most notably, these devices are largely of high strength HDPE plastic construction, thereby providing a lightweight and low cost alternative to the concrete devices, which until now have been the only option available. In the UK, therefore, SDS’s Aqua-Swirl Separator is unique in achieving NJDEP field certification, having been proven to achieve reliable and sustainable performance through both field and laboratory based testing programmes.

Luton Airport surface water drainage strategy
As part of its long term surface water drainage strategy defined in September 2014, London Luton Airport Operations Limited (LLAOL) commissioned Veolia Water Projects Ltd, supported by Mott MacDonald, to develop a surface water management strategy which would address the prerequisites to achieve planning consent for the airport’s further expansion.

LLAOL has subsequently embarked on a systematic programme of facilities and services development that ensures the Airport is able to comply with all current and anticipated future environmental regulations; this will prevent surface water and groundwater pollution in accordance with the objectives of the Luton Local Plan and the National Planning Policy Framework.

Data collected from water quality monitoring conducted at the Airport between 2005 and 2012 identified the main pollution risks from the Airport as oil spills and de-icing chemicals, for which oil interceptors and first flush drainage systems were considered the most appropriate pollution mitigation assets.

As well as providing storage and flow balancing to deal with contaminated surface water runoff, the Airport’s drainage scheme also includes methods to manage acute and chronic pollution events and techniques to continuously monitor the quality and quantity of surface water runoff from all points of discharge to either groundwater or surface waters.

The measures that have been adopted are based on sustainable mitigation, which balances environmental, social and economic factors. Hazardous substances are prevented from entering controlled waters, whilst non-hazardous substances may enter but should not cause pollution.

The water resource receptors, into which any contaminated surface water may flow, are identified as Luton Hoo Lake (via a Thames Water surface water sewer) and the River Lea, to which UK/EU Environmental Quality Standards have been applied, along with an underlying Principal Chalk aquifer which is monitored against UK Drinking Water Standards for Groundwater Luton Airport new SuDS system

Phase 1 of the Airport’s new development programme has included the resurfacing and expansion of car parking areas, extensions to buildings and the construction of a new dual carriageway.

In addition to a known flooding problem that already existed on Airport Way, which provides main access to and from the airport, the main impact of this first phase of development has been the increased risk of flooding caused by multiple new impermeable areas, due in the main to a new road layout and the construction of a second carriageway. The removal of pre-existing soakaways, installation of additional piping and the diversion of manholes required that a new SuDS system should not only prevent the increased risk of flooding but also protect habitat and amenity by improving water quality.

In late April 2016 SDS installed a new SuDS system to handle surface water runoff from Luton Airport’s extended medium term car park. Five SDS GEOlight attenuation tanks have the combined capacity to store up to 4277 cubic metres of water which has first been cleansed by each of two SDS Aqua-Swirl hydro dynamic vortex separators, designed to remove approximately 90 to 95 per cent of the total pollutants in the surface water runoff volume.

The system has been designed to series 500 of the specification for highways works and sewers for adoption and follows engineering consultancy Mott MacDonald’s flood risk design for a 1:100 year storm event including an allowance for an additional 20 per cent due to climate change. Surface water drainage is managed in accordance with the ‘Design Manual for Roads and Bridges’ (‘DMRB’), the ‘Manual of Contract Documents for Highways Works’ (‘MCHW’) and ‘Sewers for Adoption Seventh Edition’. Future publications of ‘DMRB’ will recommend SDS Aqua-Swirl as the first water treatment system of choice.

How does SDS Aqua-Swirl work?
water-plan-131-cSDS Aqua-Swirl separators use gravitational forces to separate out of suspension a diverse range of particulates that are typically found in surface water runoff, in the process removing attached pollutants such as free floating oil, poly-aromatic hydrocarbons and heavy metals. Inspection chambers provide direct access from the surface to the sediment and oils that accumulate in the reservoir enabling their simple and effective long-term maintenance.

Benefits of SDS Aqua-Swirl
As well as providing the site with essential control over water quality, of particular benefit to the infrastructure drainage contractor, Whitemountain, has been the robust build and light weight of the SDS Aqua-Swirl treatment device which could be lifted and manoeuvred easily into position by excavation plant that was already in use on site and without the need for heavy machinery. Site Engineer at Whitemountain, Brian Fegan, explains: “The installation of a system comprising a device of concrete construction, until now our only option, would have required the use of a 350 tonne crane and most likely, due to the massive inconvenience not just to us but to the airport and local road network, would not have been feasible at all. The Aqua-Swirl’s versatility meant that we could design the devices for the specific requirements of this site, without the need for any bends in piping, whilst their inherent strength allowed us to save on time and cost through not requiring a concrete surround. Their compact size and small footprint, together with the lifting supports and straps provided, meant installation was very quick and simple and final placement could be done manually; we needed only a single day in which to dig, position, connect up and back fill.”

Additional benefits of SuDS system
An additional benefit of the SuDS system has been the reduction, to a great extent, in the frequency and volume of the flooding that occurred in the neighbouring Airport Way underpass. Whilst the flooding hazard for both carriageways continues to remain categorised as ‘significant’ for a one in 100 year storm event, the severity of flooding across the access route in a 30 year event has been reduced to the category of ‘moderate’ for one carriageway whilst, for a one in ten year event, the second carriageway is deemed entirely clear. Furthermore, for all return periods the hazard remains in place for a maximum of only two hours, thereby significantly reducing the duration of restricted access, whilst the installation of a pump, which is able to transfer flows to the SDS GEOlight tanks, ensures that emergency access can still be gained at all times.

Future SuDS developments
Sufficient capacity exists within the underground storage facility landside to accommodate excess airside surface water runoff, the first flush of which will be highly contaminated with substances such as de-icing chemicals and will be diverted to the Thames Water foul system for treatment. Whilst airside and landside runoff have more typically been considered two entirely separate wastewater streams, LLAOL is developing plans to manage holistically all sources of surface water, including the control of their dispersal, in the most environmentally friendly/ecologically conscious way.

About SDS Widely acknowledged as the UK’s leading manufacturer and supplier of SuDS, SDS specialises in engineering innovative and cost-effective water management systems and equipment that enable the efficient control, treatment, storage and distribution of water within the storm-, waste- and industrial cooling- water industries.

The company’s expertise lies in delivering water management solutions that recognise both the value and the problems that water can bring, whilst ensuring compliance with legislation and accordance with policy.

For more information, please see www.sdslimited.com

About London Luton Airport London Luton Airport is the UK’s fifth largest airport carrying over 12 million passengers in 2015, an increase of almost 17 per cent on the previous year. £110 million has been invested over the next five years to improve access and passenger facilities both inside and outside the terminal, including rail shuttle bus connections and new and upgraded car parks. This expansion will create circa 10,500 new jobs over the next 15 years and see passenger volumes rise to 18 million. At its current rate of growth, the Airport, which already supports £1.3 billion of economic activity and 27,000 jobs, is anticipated to contribute £2.3 billion to the economy by 2030.

For more information, please see www.london-luton.co.uk