Water resources

Context

Chapter 20 of Volume 2 of the PEIR presents a preliminary assessment of the effects of the Proposed Development on surface water and groundwater resources and the existing drainage network.

The Main Application Site spans two river valleys: the River Lea, which is located approximately 450m to the south west, and the River Mimram, approximately 3.5km to the east. The Proposed Development is also located within an area at low risk of flooding from rivers (within Environment Agency’s Flood Zone 1). However, the Environment Agency long-term flood risk map shows a number of areas of at risk of surface water flooding across the Main Application Site, likely to be associated with the impermeable surfaces of existing structures and hardstanding.

The Main Application Site is underlain by Chalk bedrock, which provides a high level of groundwater storage, and is therefore, classified as a Principal Aquifer. Northern and eastern parts of the Main Application Site are also within the total catchment area of a groundwater Source Protection Zone. However, groundwater quality in the vicinity of Luton has been known to be poor due to pollution related to the surrounding area’s industrial heritage.

The airport currently manages surface water via a combination of discharges to public sewers and by soaking into the ground. There are two Thames Water surface water drainage ponds located on Eaton Green Road adjacent to the site boundary. Foul water is currently discharged to the public foul water network owned and operated by Thames Water. This is collected via the airport’s own private foul water pipe network operated by Veolia Water. The public water supply assets are owned and operated by Affinity Water.

Mitigation measures

A range of mitigation measures are proposed to avoid and reduce the effects of the Proposed Development on water resources. Measures summarised in Soils and geology also mitigate the risk of contamination of water resources. Further mitigation includes:

Construction

• the Draft CoCP sets out proposed measures to be implemented by the construction contractors to protect surface water and groundwater resources. These include undertaking monitoring of groundwater and leachate from the former landfill, preparing a construction surface water management strategy, implementing good practice measures to minimise the risk of pollution, and preparing a pollution incident plan; and
• works within watercourses will be avoided.

Operation

• the drainage strategy for the Main Application Site has been designed to accommodate an increase in surface water flows during heavy rainfall events, including an allowance for increase in rainfall with climate change;
• the drainage strategy incorporates measures to prevent the pollution of water resources. Run-off from the Main Application Site would pass through hydrocarbon separators, located within the system at locations where there is a risk of hydrocarbons being present (airport aprons, taxi ways, runways and car parks). Permeable paving is being proposed for areas of car parking and bunding is proposed for the new fuel storage area. Real-time monitoring of contaminant concentrations is proposed with shut off valves to divert runoff to a storage tank, if trigger levels are exceeded, and from there into a treatment facility;
• a new Water Treatment Plant is proposed to treat sewage, from the new terminal and other facilities in the Proposed Development, including aircraft, and contaminated surface water runoff from the aprons, runways and taxiways. Sewage would be collected from within the Main Application Site via a new dedicated foul drainage system and combined with surface water runoff prior to treatment. Clean and treated effluent would be discharged into the ground under an Environmental Permit regulated by the Environment Agency;
• the new fire training ground would be served by an isolated drainage system, with contaminated run off tankered off-site;
• measures to maximise water reuse, such as greywater reuse and rainwater harvesting are also being considered; and
• the works at each Highway Intervention will be designed in line with accepted highway design standards to ensure no unacceptable increase in flood risk or potentially significant effect on local water quality occurs.

Likely significant effects

Construction

An assessment of potential effects on the identified surface water and groundwater resources and the existing drainage network during construction has been undertaken. With appropriate mitigation in place, as described above, no likely significant adverse effects have been identified. The excavation, processing and treatment of the former landfill material prior to reuse would remove potential sources of contaminants and is expected to result in a significant beneficial effect, as it improves the overall environmental conditions at the Main Application Site.

Operation

An assessment of potential effects on water resources during operation has been undertaken. With measures embedded within the design to attenuate and treat surface water runoff, as described above, no likely significant adverse effects were identified. The installation of a capping layer over the former landfill will minimise surface water infiltration into the underlying waste and prevent the generation of landfill leachate. This, together with the treatment of the controlled discharge of surface water, would result in a significant beneficial effect by reducing the risk of existing contamination polluting groundwater and the River Mimram, which is groundwater fed.

Completing the assessment

Further modelling and assessment of groundwater will be undertaken to inform the ES. In addition, a Water Cycle Strategy will be developed to accommodate the increase in passenger numbers as a result of the Proposed Development, and associated increase in water demand. The Water Cycle Strategy will propose options to minimise water use and maximise water reuse by employing techniques such as rainwater harvesting. All further work will be informed by ongoing engagement with the local lead flood authorities, Environment Agency, Affinity Water and Thames Water.

Documents

PEIR Chapter 20 : Click Here

Figures

20.1 Risk of flooding from River and Sea (EA dataset) : Click Here
20.2 Groundwater Features : Click Here
20.3 Risk of surface water flood risk (EA dataset) : Click Here
20.4 Water Framework Directive Water Bodies : Click Here
20.5 Risk of groundwater flooding susceptibility : Click Here

Appendices

20.1 Preliminary Flood Risk Assessment : Click Here
20.2 Preliminary Water Framework Directive Compliance Assessment : Click Here
20.3 Hydrogeological Characterisation Report : Click Here
20.4 Drainage Design Statement : Click Here