Width depth ratio >12 Pool-7 Riffle-8 Length of pool Over 50% of river 2421 (m)

Length of riffle 30-40% of river 1587 (m)

Table 9 Design summary for the Mole

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Feature Existing Suggestions from Design literature Channel length 2611 2721 (m) Valley length (m) 2500 2628 Average channel 0.0010 0.0004 bed slope (m/m) Valley slope 0.0010 <0.02 0.0005 (m/m) Start elevation 57.59 57.5 (m) End elevation (m) 55.06 56.3 Discharge – (m3/s) Bankfull- 8.5 to 2.2 11.1 1:2 year-2.2 Feature Existing Suggestions from Design literature Sinuosity (P) 1.04 >1.4 1.03 Meander 1569-170m 56-88m 58-88 wavelength (Lm) 609m average (m) Meander 41-83m 13-30 13-30 amplitude (Am) 60m average (m) Feature Existing Suggestions from Design literature Bankfull width 3-18.1m 5.23 Pool-6.8 (m) 10.3m average Riffle-7.9 Bankfull depth 1.1-4.1m 0.43 Pool-0.9 (m) 3m average Riffle-0.7 Bedwidth (m) 1.1 -6.4m 5.23 Pool-2.3 3.1m average Riffle-3.7 Passing area (m2) 3.98 Pool-4.1 Riffle-4.06

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Width depth ratio >12 Pool-8 Riffle-11 Length of pool Over 50% of river 1572 (m)

Length of riffle 30-40% of river 1149 (m)

Table 10 Design summary for the Crawters Brook

D.2 Outline design considerations D.2.1 Sediment transport It is important that the channel diversions do not have a negative impact on sediment transfer within the catchments as this can result in excessive erosion or deposition and damage to the diversion and potentially the channel up and downstream. No assessment of existing sediment transport, or the implication of the diversion design on future sediment transport has been undertaken as part of this design as the data is not currently available. Given the low stream powers estimated as part of these works further analysis will be needed to make an assessment on sediment transport and the potential impacts this may have on the diversion. It should be noted that this assessment may result in a change to planform and cross section design.

D.2.2 Bed substrate The addition of coarse sediment to the designed channel bed will be beneficial in habitat creation by providing flow and form variability. However, if not undertaken with care, seeding the channel with sediment may cause local accumulations that choking the channel, and finer sediments may be eroded during flood flows if they are poorly armoured. Further analysis of the suitable size of sediment for the diversion channel is required. Sizing of bed material is not the only consideration and placement and packing properties also influence sediment behaviour. Based on this understanding, the design for sediment seeding should consider: • Coarser, tightly packed materials should tend to overlie finer materials, giving a degree of armouring and compaction to the infill; • Avoid the placement of over-large keystones, as these tend to create small weirs that adversely affect flow (Brookes & Sear, 1996); • The material should be from local surface sources, to ensure appropriate rock type and shape characteristics that influence water chemistry and habitat; • Material should not protrude above the water at bankfull depth (Brookes & Sear, 1996);

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• The infill layer should be partially tied into the bed to regulate downstream transmission. A number of individual particles could be incorporated into the channel liner bed during construction.

The longitudinal distribution of sediments cannot be easily specified. Instead, it is recommended that a near-continuous bed infill of locally varying depths be provided and that a period of redistribution during higher discharge flows is permitted. Such an approach would require post-project appraisal to assess the effectiveness of this strategy. The result of this appraisal may involve sediment management, including mechanical redistribution and/or additional of additional sediment.

D.2.3 Ecological design The ecological design of the new channel should be informed by survey of the streams to be lost, and upstream and downstream reference reaches. Surveys of the existing rivers should include extended Phase I Habitat survey, River Habitats Survey, River Corridor survey and detailed species surveys (including desk studies). Habitats of ecological value that are to be lost should be recreated and enhanced to compensate for losses. The new channel is also an opportunity to link high value habitats upstream and downstream from the airport and create new habitats that will contribute to local biodiversity targets.

Options for habitat creation within the channel and floodplain will be dependent on the habitat management policy of the airport and requires guidance from Gatwick on which habitats are permitted in which areas/proximity to the new and existing runways. The following options would be suitable for the river type and local context of the River Mole and Crawters Brook.

D.2.3.1 Channel bed habitats. Many of these channel bed habitats have been included in the present design of the channel, and others should be considered during later stages of the design works; • Pools. Deep water areas between riffles and on outside of meander bends (asymmetrical bed). These provide refuge areas for fish species.

• Riffles. Shallow fast flowing water over gravel substrate. Riffles provide aerated shallow water habitat that provides spawning sites for fish and habitat for invertebrates.

• Gravel bars (side and point bars). Gravel bars are important habitats for aquatic and terrestrial invertebrates providing refuges that are periodically submerged.

• Mid-channel bars and islands. Mid channel bars and islands provide habitats with some protection from terrestrial predation and disturbance.

• Submerged, emergent and floating vegetation. A range of vegetation types provides greater diversity of habitat and food sources within the channel and therefore greater diversity of

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invertebrate and fish species. Vegetation provides breeding sites, food and shelter (particularly for juvenile fish) and can also create natural detention of flows and raise water levels. Vegetation can contribute to aeration of water although management may be required to reduce de-oxygenation of water caused by decomposing vegetation at times of low flow.

D.2.3.2 Bankside habitats Bankside habitats will be considered during further design stages to include;

• Variety of bank profiles to include vertical cliffs (e.g. on outside of meanders), shallow slopes (e.g. on inside of meanders) and compound profile slopes (along straighter sections). Steep or vertical slopes provide ideal locations for burrowing species e.g. and kingfisher. Shallow slopes provide gradations of vegetation and a range of frequency of inundation.

• Bankside trees provide shaded habitats and reduce heating of water (of benefit to salmonids). In addition bankside roots create shelter for species such as otter, and underwater roots can shelter fish. Bankside trees also provide inputs of detritus and woody debris into the system, which is a valuable habitat in its own right.

D.2.3.3 Floodplain habitats Floodplain habitats will be considered during further design stages to include;

• Ponds, oxbow lakes and backwaters. These features add diversity to the flow, oxygenation and nutrient conditions available to aquatic species. They also provide habitat connectivity between the channel and the floodplain. A range of these features should be included within the design wherever there is sufficient capacity and suitable ground conditions in the floodplain.

• Ditches are important habitats by providing a high ratio of potentially species-rich marginal habitat to open water, which may be desirable to deter use by wetland birds while optimising biodiversity. Ditches can also be located to intercept potential diffuse pollution and provide a buffer to the watercourse.

• Broadleaved woodland and wet woodland. Broadleaved woodlands are a feature of the River Mole valley downstream from the airport and therefore a continuation of this habitat through the new river corridor may be a preferred option for habitat creation. Wet woodland is a Priority Habitat in England and could be created where ground conditions allow on the floodplain. Wet woodland is habitat for many plant species, invertebrates and provides shelter for species such as otter. Woodland habitats can be used to screen the watercourse from wetland bird species and the proximity of trees can deter wetland birds from gathering in the floodplain.

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D.2.3.4 Other habitats Other Habitats should be included within the design in order to provide diversity. In addition it is likely that woodland habitat will not be suitable at some locations due to safety reasons and therefore other habitats that can be netted to deter birds (airport hazards) will be more suitable. These include:

• Wet grassland. This habitat requires management by hay cutting or grazing and high (but sub- surface) water tables and/or seasonal inundation. Wet grassland should be created using species- rich seed mixes of local provenance.

• Reedbeds. This habitat will require periodic management to prevent drying over time due to build- up of dead vegetation. Reedbeds can be created where the water table is at the surface or higher year-round. Reedbeds are generally of most benefit to bird species therefore location of reedbeds would require careful consideration in proximity to the airport.

• Tall ruderal/swamp habitats. These habitats are more variable in structure and species composition than reedbeds and therefore support a wide range of animal and plant species. Habitats can be left to develop naturally and if required can be enhanced by seeding with species of local provenance. Swamps and drier stands of tall ruderals require minimal management.

D.2.3.5 Ecological survey An ecological appraisal of the route of the new channel should be undertaken preferably at least one year prior to construction (allowing enough time to undertake further surveys and mitigation if necessary). This should comprise an extended Phase 1 Habitat Survey (Optimum timing April to October) and desk study. Further surveys that may be required are:

• Protected species surveys as recommended within the Ecological Appraisal (optimum timing depends on species).

• Non-native invasive species surveys as recommended within the Ecological Appraisal (optimum timing May-October).

Mitigation actions and program will depend on findings.

D.2.4 Topographic Survey A topographic survey of the valley should be undertaken prior to detail design work. The survey will provide improved ground level data and allow greater accuracy of the valley land footprint. If ground levels are significantly higher than shown in the outline design drawings the footprint may extend outside of the current boundary line, based on 1 in 3 valley slopes. If this is the case steeper valley slopes, a reduced valley width, additional land purchase or structural retaining solutions will be required.

The survey will also pick up additional channels and outfalls that will be to be diverted in to the new channels which currently haven not been picked up in the outline design phase.

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D.2.5 Geotechnical design of valley and channel A full geotechnical site investigation to BS EN 1997 (Eurocode 7) along the route of the channel should be undertaken. The results of the investigation will provide an understanding of the geology, highlighting excavation risks and ground properties to undertake slope stability design of the permanent works. It will also provide an understanding into the suitability to reuse excavated material as on site fill, including any contamination risks.

It is anticipated that the valley will be formed using 1 in 3 graded slopes, a full slope stability analysis should be undertaken, and if the proposed ground profile is found to be unstable an increase land footprint or structural retaining solutions in some areas would be required. The analysis will also need to consider the position of the channel at the base of the slope, including destabilisation risks due to excavation of the embankment toe and to potential erosion as a result of the diverted river.

D.2.6 Weir design The current weir design is based on initial hydraulic modelling and is an economical solution incorporating environmental solutions, including provisions for fish and eel passage. A study could be undertaken to asses if further environmental enhancements are practical. A beneficial solution would be to remove the need for any impoundment. This could be achieved by grading the upstream channel to fall with an average bed slope of 1 in 100 and include a series of features, including small head losses and pools. This may allow a greater range of fish species to utilise the channel over a greater flow range. The channel alterations would affect the upstream reach for over 250m, depending on the existing bed slope, and will require an increased land footprint to incorporate new features.

The chosen option will require the following design steps to complete detailed design:

• Undertake a full hydraulic design to ensure any alterations are able to pass the 100year flood event and does not pose a flood risk to upstream properties. • Design of fish and eel passes and the completion of a fish pass approval form, allowing the Environment Agency to comment on the scheme. • Completion of structural calculations including stability design to BE EN 1997 (Eurocode 7) and reinforced concrete design to BS EN 1992 (Eurocode 2). • River bank reinforcement, required around hydraulic structures, unnatural changes in channel direction and where there is a risk of increased water velocities.

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D.2.6 Additional channel diversions A number of additional channels join Crawters Brook and the River Mole, many can be identified on OS mapping and it is anticipate more unmapped outfalls are likely to exist.

Identified channels include,

• Channel to the south east of the site, • Drains close to the west boundary that may be affected by the construction of the valley, • Westfield Stream to the north west.

Each channel may need to be diverted into the new Crawters Brook or River Mole channels, this could involve alterations to their bed profiles and alignments. The channels will need to be assessed for environmental impacts and any enhancements will need to be incorporated into the design process.

D.2.7 Footpath It is important that the footpath is not placed on top of the river bank and design allows for a wide space between the top of the bank and the edge of the footpath. This is important for a number of reasons, the first being to enable the establishment and functioning of a natural river corridor which includes bankside habitats and buffer zones. Additionally, the river channel in this new diversion will require space to settle and change over time.

D.3 Assumed construction sequence The following construction sequence has been assumed for the diversion of Craters Brook and the River Mole, this assumes all topographic surveys, ground investigation surveys and a full detailed design has been completed.

• Take ownership of complete land footprint for the proposed diversion and proposed airport site. • All diversion works to be completed prior to any runway expansion works. • Excavate valleys and channels for Crawters Brook and River Mole diversions, except for the locations of existing channels which will continue to flow on their existing routes. • Construct all in river features such as pool and riffles as excavation works progress. • Stock pile excavated material in designated area within site boundary, if required remediated and then use as fill to build up airport ground profiles as required, or send to landfill if not needed. If material is of suitable quality it may be possible to spread direct onto airport site and avoid double handling. • Make downstream connection of diverted River Mole channel to existing live River Mole channel. • From downstream location work upstream connecting any drainage outfalls and brooks as required (locations may not yet be known)

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• Continue process until the upstream River Mole connection is reached. The new weir structure can be constructed offline. Once the structure is complete make the downstream connection to the new River Mole channel. The existing river Mole channel can now be diverted over the weir. • Back fill the original River Mole channel. • Work upstream along Crawters Brook connecting any drainage outfalls and brooks as required (locations may not yet be known). • Connect existing Crawters Brook to the new channel at the upstream extent of the diversion. • Back fill the original Crawters Brook. • Make good and complete finishing works such as grass seeding.

D.4 Post project appraisal It is recommended that a river diversion scheme of this scale would be accompanied by an ecological and geomorphological post project monitoring scheme.

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Appendix E – Surface water drainage technical methodology

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Appendix E – Surface water drainage technical methodology

E.1 Conceptual design For the concept design stage a “Business as Usual” and “Exemplar” design have been developed. The Business as Usual option has been developed to ensure the current regulatory requirements are meet and is based on current best practice guidance. This is described in the main report as the option with embedded mitigation.

The Exemplar option tries to foresee changes to the regulatory environment and what will likely be best practice business as usual in the future. This is described in the main report as the option with additional mitigation.

The design of both options has been developed based on the assumption that the site development will be as that outlined in drawing number: LGW_MP_Opt03_NoEAT_001, Issue 1.1, provided by ARUP in March 2014.

The design has also been based on the proposed site contours presented in drawing CE_LGW_Layout_Southern_Runway_Option3_64.0_Rev02. However, it should be noted that these are a work in progress and any significant change to these will affect the feasibility and effectiveness of the proposed drainage design.

Due to the diversion of the River Mole, the existing Culvert that runs underneath the existing Gatwick runway is likely to be available to be utilised for storage and conveyance. This is proposed within the options.

E.1.1 Drainage Design – Business as Usual Although this option is outlined as Business as Usual, it includes both common and best practice mitigation options as outlined in section 5.2.2 & 5.2.3. It should also be noted that the approach is flexible and will be fully developed during the design stage.

The plan and cross sectional views of this drainage proposal are presented as drawings in Appendix A.

The proposal for the site drainage is to install approved slot drainage across paved areas that require runoff to be quickly drained from the surface. This includes installing slot drains along the edges of taxiways and runway shoulders.

Combined filter drain with a grass or swale top are proposed around the edges of the taxiways and side of the runway where there is a transition between paved and grassed areas. These are proposed to provide attenuation of runoff by allowing runoff to drain slowly into the drainage system; help provide a route for exceedence flow paths; and act as additional storage within the system when required.

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The grass top helps ensures that the drainage feature is suitable at the ground surface for maintenance and provides safety against risks associated with exposed gravel.

To provide attenuation and storage within the system, flow controls are proposed at strategic locations within the drainage network. This is in the aim to reduce the land take and pumping required (which has associated carbon emissions) to provide a surface water attenuation pond which is proposed to be positioned downstream of the culvert that runs underneath the runway 1.

At this concept stage the type of control features have not been decided, but could be in the form of orifice plates, hydrobrakes, penstocks, or other suitable control. These could also either be static and controlled via hydraulic principles, or controlled via real time control if monitoring devices where installed within the system. This should be considered further at the preliminary design stage.

Underneath the grassed area between the existing runway and new taxiways it is proposed that underground storage is provided. It is recommended that this is provided in the form of a series of pipes in align to allow variation in the volume of storage to be provided without significant depth to install the storage feature, but this should be considered further at the preliminary design stage.

At the downstream end of the existing culvert it is proposed that a new channel be installed within the channel of the existing River Mole, and that this be used as the feed to a pumping station located to pump flows into the pond. This pumping station is required due to the levels of the surrounding ground.

In order to separate heavily polluted flow from cleaner flow which is considered acceptable to discharge to the environment, two ponds are proposed.

The first is the “clean” pond and this should be designed as a detention basin. This has been sized assuming that it will be used when the concentration of biological oxygen demand (BOD) is measured to be less than 14mg/l as it leaves the culvert.

The second is a “dirty” pond and is proposed to be aerated to provide some form of treatment whilst being stored. This has been sized assuming that it will be utilise when the concentration of biological oxygen demand (BOD) is measured to be greater than 14mg/l.

The discharge rate at which both the clean and dirty ponds can discharge at is yet to be confirmed.

The discharge from the clean pond would normally be designed to ensure it was in align with its green field rate as discussed above. However, based on this site it is thought unlikely that this will be considered acceptable by the Environment Agency, with the greenfield rate calculated to be almost 9m3/s for a 1 in 30 year event. As such the pond has been sized assuming a much reduced 1m3/s discharge rate significantly better than the greenfield runoff rate. This is significantly lower and will mean that more storage will be required to attenuate flows, but it will ensure that a much greater level of flood protection is provided downstream.

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Based on this flow rate the volume of storage to be provided in the clean pond has been calculated to be approximately 80,000m3. This has been sized based on a 100 year design storm event of critical duration, but an allowance for attenuation in the dirty pond has been assumed and this is discussed below.

The final destination of treatment has not been determined at this stage, but we have tested two options, 100l/s and 400l/s. 100l/s our forecast maximum discharge to Crawley STW, and our consultation with them indicate discharge of this additional flow into their system does not cause significant engineering difficulties. 400l/s is the maximum flow rate that would be sustainable to be treated by an on-site moving bed bioreactor treatment works, given the type of pollutant load.

We have used data from the worst case winter from three years of modelling data we have available to assess the size of the pollution control storage. When we come to design we will test the system against a range of worst case scenarios to ensure that the system is resilient to predictable shocks. The programme hasn’t allowed us to do that for this assessment, but sufficient land should be retained within the masterplan for different configurations of drainage design, storage and treatment to allow a flexible and resilient solution.

This period has used as this was a particularly cold winter and therefore considered to be appropriate to ensure the system is suitably designed, and in order for the water quality model to work accurately it was not considered appropriate that a typical design rainfall event was used to size this element.

Table 11 provides calculated volumes based on each assumed discharge rate.

Discharge rate Dirty Pond (l/s) Volume (m3)

100 92,021

200 75,884

300 71,768

400 68,793

Table 11 - Calculated dirty pond volumes based on variable discharge rates

The design specification and schedules for this option are presented in Annex B.

E.1.2 Drainage Design – Exemplar At this stage it is envisaged that the exemplar option would provide a better standard of protection within the drainage system would be incorporated to protect runway from flooding.

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Extensive use of swales and filter drains for source control and embedded attenuation, and additional storage in geocellular unit would look to be provided.

All runoff flows would be pumped up to balancing tank in new runway southern runway strip and treated via an active wetland treatment system. It is anticipated that this wetland treatment system will treat 95% of all flows to <5mg/l. Refer to the Water and People section for design details of this system.

Flows would then be diverted back into the culvert and pumped into attenuated storage in the North West zone.

It is estimated this attenuated storage would need to be designed for a total volume of 200,000m3.

If stored runoff was considered to be clean (<5mg/l), it would be pumped into 150,000m3 the clean side, and up to 75,000m3 of this would be stored for reuse (refer to the Water and People section for further details), with the rest discharged to the River Mole at better than greenfield rates.

If it was considered to be still polluted (>5mg/l) then it would be stored in the 50,000m3 side of the pond designed to attenuate this “dirty” effluent. This would either be discharged into existing pollution control system, or recycled back around the wetland treatment system.

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Appendix F – Water and people supporting technical information

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Appendix F – Water and people supporting technical information

F.1 Sewage and wastewater treatment forecasting model Our projected sewage flow and load to Crawley STW and Horley STW for the baseline scenario to 2019, based on most recent projections are as below:

Year/PE current 2019 Increase

Horley 8,774 9,661 887

Crawley 16,588 18,449 1,861

Total 25,362 28,110 2,748

F.1.1 Waste streams analysis Airport passengers and staff

The requirements for sewage treatment are people-driven and will be also be dependent on the ‘dwell- time’ within the airport. Whilst water-saving devices will affect the volume of sewage that will be generated, they will not affect the biological load that the sewage represents, just that it will be less dilute.

Our sewage forecasts and population equivalent forecasts have assumed that the ‘dwell time’ for staff is a working day (8 hours) and one eighth of a day for a passenger (3 hours).

Airport Operations

There are three airport operations activities that create wastewater that requires treatment: de-icing, aircraft cleaning and aircraft servicing and these are expanded on separately below:

De-icing

During freezing weather conditions de-icing compounds are used for two purposes – ensuring the runway, taxi-ways and stands are free of ice and to ensure that any ice build-up on aircraft is removed and the control surfaces are able to operate satisfactorily. A range of compounds are used but they fall into two basic categories – glycols and acetates. Both these compounds have high biological oxygen demands and can have a significant impact on the water environment if they are discharged into a river. Current operations de-ice the aircraft on their aprons and some of the de-icer that is used on site is recovered for recycling but the majority finds its way into the surface water system.

There are a variety of options for reducing the de-icer load for wastewater treatment – these include:

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• Drainage segregation systems that localise high concentration contamination for possible recycling.

• Scavenging vacuum sweeper that can lift excess de-icer from aprons, taxi-ways, etc. for recycling.

• Advanced de-icer application systems using techniques such as robotic arms, ice imaging, etc.

• Centralised de-icer stands.

Aircraft cleaning

Routine aircraft cleaning practice varies from operator to operator – some operators clean their aircraft regularly in an effort to limit the build-up of dirt and thus reducing friction and fuel consumption, whereas others only clean before maintenance. Whilst the cleaning agents may have a treatment requirement this will be relatively minor, sufficient to assume that it is contained within the rather general approach for passengers; however there is a specific need to pre-treat the water before disposal to remove cadmium which is widely used in the aircraft industry as a plating material for fixings because of its galvanic compatibility with aluminium. This is currently done on-site and will need to continue for the foreseeable future; although cadmium’s environmental toxicity is causing it to be superseded as a plating material.

Aircraft servicing

Inbound flights will have their foul tanks that receive the waste from the on-board toilets emptied as part of the routine servicing during the aircraft turn-around. At the present time most of this is directed into the North Terminal sewer system including the aircraft that use South Terminal aprons. In a similar manner to that adopted for passengers in the terminals it has been assumed that load in PE terms will be proportional to the ‘dwell time’ in the aircraft and in the absence of more definitive data a value of 5 hours has been assumed for this.

General comments

The treatment requirements for wastewater is usually expressed in terms of its oxygen demand, usually its biological oxygen demand (BOD). As mentioned previously the major source of wastewater for treatment is surface water run-off that has been contaminated by de-icer that has been used to keep the runways and aircraft operating during freezing conditions. There are two broad types of de-icer in current use glycol-based and acetate-based and these can be in liquid or solid form and the selection and method of application is dictated by the requirements to ensure safe operation of the airport and aircraft.

The BOD requirements of glycol-based de-icers is about 0.8kg per litre and that of acetate-based de-icers is about 0.3kg per litre or kg.

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Records of de-icer used in the winter of 2012/2013 have been assessed and 1,765,383 litres of glycol- based de-icer were used and 109,036 litres and 23,255 kg of acetate-based de-icer were used. This amount of de-icer would have a total treatment requirement of approximately 24,200 tonnes of BOD. To put this figure into context the sewage produced in a day by an individual member of a population is reckoned to have a treatment requirement of about 60g BOD or 0.06kg BOD. The treatment requirement of the de-icer used in 2012/2013 is therefore equivalent to an additional 85 million passengers using the airport.

The winter of 2012/2013 was relatively harsh and therefore it has been used as what the high-end requirement for wastewater treatment might be.

Current wastewater treatment system

There are four drainage catchments that may be contaminated by de-icer which discharge to a series of treatment ponds. Each treatment pond has the aim to attenuate runoff from the airport site and provide treatment through aeration and settlement. Their arrangement is shown in Figure 11 below.

Effluent from Pond A can either pass forward to the next pond when further treatment is necessary to meet water quality requirements, or discharge to the River Mole when effluent meets the required standards or in emergency conditions.

Pond M is split into two sides; ‘clean’ and ‘dirty’. If biological oxygen demand (BOD) of flow from the upstream catchment, which includes effluent from Pond A, is less than 10mg/l then it will be pumped to the ‘clean’ side. If it is greater than this it will be transferred to the ‘dirty’ side.

If the volume in the ‘dirty’ side is exceeded, and both Pond D Lower and a treatment lagoon adjacent to Crawley treatment works are full, then flow can migrate to the clean pond via a weir. If there is capacity at Pond D Lower then flow will be transferred on for further treatment.

The ‘clean’ Dog Kennel Pond attenuates and treats runoff from a car park area located to the north of the airport. Effluent from this pond discharges out to the River Mole.

If runoff from the Dog Kennel catchment becomes polluted, flows can transfer to the ‘dirty’ Dog Kennel Pond. Flows from this pond continue to the drainage catchment for Pond D Lower.

Effluent from Pond D Lower can either pass forward to Pond D Upper before discharging to the River Mole, or be directed to a further pollution lagoon and onto Crawley STW if water quality does not meet the standard required.

The existing pollution lagoon has a working storage capacity of 205,000m3 and an additional lagoon with a working capacity of 100,00m3 is currently under construction.

There are restrictions placed on the flow which can be transferred to Crawley STW under its trade effluent consent. These restrictions are that the volume of flow to be treated in a 24-hour period must

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not exceed 4,320m3 and that it should not be passed at a rate above 50l/s. The total suspended solids received at Crawley STW must not exceed 1100kg per day and chemical oxygen demand (COD) must be less than 1400kg per day.

Figure 11 Schematic showing the concept of the Gatwick pollution control system

F.2 Wastewater and sewage design with embedded mitigation F.2.1 Mitigation 1: Managing demand for water We have concluded that there is significant scope for further reductions in water use. The areas that have been observed to date that support this assessment are set out below. A more detailed technical review of Demand management measures is set out in Appendix B.

Some use of low water use appliances has been made on site but there is significant scope for a Gatwick wide standard specification of low water use fittings. The existing assets at Gatwick Airport are aging and to manage the risk of leakage, Gatwick have been undertaking water balance assessments and sounding. In order to most effectively manage lost water through leakage, a swift response is essential. Our business as usual scenario specifies leak detection monitoring with a daily water meter logger download. These data should be regularly monitored and acted upon as quickly as possible where major leaks are detected.

Water recycling

Roof-based rainwater harvesting will be built into the new buildings and used for toilet flushing and other non-potable requirements within the building. This would be based on capturing the run-off from the roof areas of the new terminal building and storage local to the terminal. The surface area for the

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proposed terminal buildings measure 13.49 hectares and assuming an annual rainfall of 750mm and a capture rate of 70% the new terminal buildings have the potential to yield 70,849m3 per annum. A rainfall capture rate of 70% has been assumed ahead of any detailed design of this system to allow for wetting/evaporation losses but probably most significantly overflow losses when the storage is full. The ultimate requirement for toilet flushing in the new terminal is estimated to be 266,043m3 per annum so rainwater harvesting based on roof run-off will only provide less than a third of the potential toilet flushing requirement so there will need to be a back-up supply of potable water from SESW. Standard design practice would be to install storage equivalent to 18 days usage to cover periods of low rainfall which would indicate a storage volume of 13,176m3 which seems high at over two months of average rainfall on the new terminal roof area. A tank of this size would improve rainfall capture percentage but at the expense of creating storage volume that would not be utilised for most of the year. The storage would need to be installed mainly at low level within or adjacent to the building but some of this storage could be dispersed through the new building in the form of day tanks.

Other water savings

A 1% year on year reduction in water use for the whole of the site has been assumed. This will eventually reduce the per capita consumption to what is currently considered best in class. This will be the outcome of a range of activities and actions including specification of low water use appliances for the new terminal and for replacements in the existing terminals, better pipe material performance for the new terminal construction, improved leakage detection and replacement of life-expired pipework.

S&ESW strategy to meet demand and provide supply resilience

SESW have made allowance for increased demand from the Gatwick Airport operations, and from the associated economic development associated with an expanded airport in their Water Resources Management Plan. The scale of the requirement identified can be absorbed within their current plans for supply improvements.

By 2015 there may be some need to extend the supply system to feed the new terminal and it is possible, depending on the option selected, that there might be a need to reinforce the local supply network between Outwood Reservoir and the Airport. However, the local supply system appears to be robust and therefore the scale of this requirement is likely to be limited and at some time in the future as local demand in general increases.

Gatwick Airport will benefit from the additional level of assurance for their water supply provided by the enhancements at Bough Beech works and SESW’s plan to extend this to the whole of their supply system, the balance of which tends to rely on borehole sources.

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The net effect of this is that a lot of headroom has been and will continue to be created and this means that the expansion plans at Gatwick can be absorbed with no impact on the local community or environment.

F.2.2 Mitigation 2: Sewage and Wastewater treatment and discharge There are two options proposed for sewage and wastewater treatment and discharge for the Business as Usual scenario. • Option 1 proposes meeting demand at Crawley and Horley STWs for sewage and wastewater treatment • Option 2 proposes treating the wastewater element locally on site Option selection is dependent on ongoing liaison with EA and TW.

Figure 12 below provides a conceptual diagram of the wastewater and deicer management system

Figure 12 Scheme with embedded mitigation

Option 1 – meeting demand at Crawley and Horley STWs

We have agreed with Thames Water that that the sewage from the new terminal would be sent to Crawley STW (as Option 1 – section 4.3.1). There will be a requirement to re-route the current sewage transfer from North Terminal to Crawley STW because the present configuration clashes with the new runway and terminal. There is likely to be an intermediate requirement to transfer some of the sewage from South Terminal to Crawley STW because of capacity restrictions to and at Horley STW which serves South Terminal at present.

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Our projected flow and load to Crawley STW and Horley STW, based on most recent projections are as below and assume that all the sewage loads for the new terminal are sent to Crawley STW:

Year/PE current 2021 2026 2029 2031 2035 2040 2045 2050 Horley 8,774 10,016 13,154 14,877 9515 9391 9273 9255 9257 Crawley 16,588 21,065 23,699 25,276 32,193 38,273 47,157 49,676 53,222 Total 25,362 31,081 36,853 40,153 41,708 47,664 56,430 58,931 62,479

It should be noted that the current load to Horley STW is predicted to be just under 9000PE and the long-term load is predicted to just over 9000 (reducing slightly from 2031 because, while passenger numbers through South Terminal are forecast to remain constant for this period, staff numbers are predicted to fall). Of concern is the predicted increase in passenger numbers through South Terminal to 2030 whilst the new runway starts to be utilised but before the new terminal comes on-line. There appears to be space within the site at Horley STW for expansion of the facilities within the current site boundary but the site is hemmed in on three sides by residential developments, some of which appear to be recent and relatively up-market. Expansion of the existing facilities at Horley are therefore likely to be resisted by nearby residents and consequently a problem for Thames Water. It may therefore be necessary to transfer some of the growth in load at South Terminal to Crawley STW as a temporary measure until the new mid-runway terminal comes on-line. It should be possible to design this infrastructure so that it can in part be re-used for flows from the new mid-runway terminal. It is also possible that TW might prefer that long-term all the flow from South Terminal is transferred to Crawley STW so that greater headroom is created at Horley STW.

Crawley STW is close to South Terminal as the crow flies and the new mid-runway terminal will be even closer but they are separated by the London to Brighton railway line which will intersect the route for any apparatus that is required to connect the airport development to Crawley STW. At present the sewers that serve North Terminal discharge to the Thames Water network to the south and west of the railway station and the Thames Water sewer then passes under the railway line and the Gatwick Stream flood attenuation area. Surcharging of the sewers in the Gatwick Flood Attenuation area is reported, indicating that the existing assets that might transmit the additional flows to Crawley STW do not have any spare capacity. New sewerage to connect the new development to Crawley STW will have to negotiate several route challenges. A new pumping station located so that it can handle the diverted flows from North Terminal and transfer flows from south Terminal and be convenient for flows from the new mid-runway terminal is proposed. It is also proposed that twin 450 rising mains are utilised between the pumping station and Crawley STW because the rising main route will not facilitate future access if maintenance is required and the twin configuration would allow some flow to be maintained if one of the pipes needs to be de-commissioned for maintenance using no-dig techniques.

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Crawley STW is well-developed and appears to have expanded to the limits of its current site. GAL have identified land that it owns to the south and east of the current works where the works can expand into.

There is a large pond to the north-east of Crawley STW that stores de-icer contaminated surface water prior to it being fed into the treatment stream for processing. The pond is aerated to prevent septic conditions developing and to provide an element of pre-treatment.

Thames Water are subject to a 1mgl-1 phosphorus limit for its discharges and it is likely that any similar discharges in this area would be subject to a similar limit.

There is an anaerobic digestion (AD) plant on site at Crawley STW that also digests sludge imported from treatment works in the area that do not have this facility. The plant generates gas that is used to create electricity. It is understood that the plant is due to be uprated by the addition of a hydrolysis plant to increase the efficiency of gas production (and reduce the production of sludge). Given the size of the works, this is likely to be enzymic hydrolysis rather than thermal hydrolysis. The plant will have excess water heat which is probably being discharged to atmosphere.

TW also treat the de-icer contaminated run-off from the airport at Crawley STW as a trade waste with some pre-treatment in an aerated holding lagoon before the wastewater is combined with flow through the treatment. There is a large pond to the north-east of Crawley STW that stores de-icer contaminated surface water prior to it being fed into the treatment stream for processing. The pond is aerated to prevent septic conditions developing and to provide an element of pre-treatment. One proposal to treat the de-icer contaminated run-off from the new development is to create a new 90,000m3 dirty water storage pond adjacent to the new surface water attenuation pond and to transfer the wastewater at a rate of 100litres per second to Crawley STW for treatment. This will require a new pumping station adjacent to the dirty water pond and a 350 diameter rising main to connect the pumping station to Crawley STW. This option will also require additional storage and treatment facilities at Crawley STW.

Balancing flows between Horley and Crawley

TW also advise that there may be capacity issues with the gravity sewer system to Horley and there is only limited headroom to absorb increases in load at Horley. There was currently about 10,000PE headroom following upgrading at Crawley however this headroom also had to cope with any increases in the wider catchment and may also be required to pick up some of the load that might otherwise go to Horley. This imbalance in available capacity will be exacerbated by the intermediate growth plans which forecast a levelling of the passenger numbers at North Terminal while the passenger numbers at South Terminal will continue to increase until falling back to a steady level when the new mid-runway terminal is opened. We have developed options for balancing flows between Horley and Crawley treatment works that will ensure that that there is no increase in discharge to Horley STW beyond a specified

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threshold. This threshold is subject to agreement with Thames Water, and we are continuing to work with them to agree what this threshold is.

Option 2: Alternative Wastewater Treatment Option - a new local treatment plant

As indicated in section 4.3.1, two sub-options are proposed for the treatment of wastewater as part of the Business as Usual option. One option is to continue to send the contaminated surface water to Crawley STW for treatment in similar manner to that employed at present, i.e. a pre-treatment lagoon and feed to co-treatment in the STW process lanes and an alternative option is to install a local treatment plant to allow the contaminated run-off to be treated on site.

A more detailed technical appraisal of treatment processes is set out in Appendix B however it is considered that the best current technology to employ for a small footprint plant would be based around a Moving Bed Biofilm Reactor (MBBR).

A plant to treat 100l/s could be sited in less than 1 hectare and the main element would be a 55m by 25m by 4m deep MBBR reaction tank that would be subdivided into cells containing plastic media that would be aerated and mobilised by air from diffusers laid out on the bottom of the tank. Downstream of the reaction tank the flow would pass through a 22.5 metre diameter 4m, deep humus tank where organic matter that would be created by the microbiology in the MBBR reaction tank could settle out. The treated and clarified flow could then be sent to the surface water attenuation pond for discharge to the River Mole. Sludge from the humus tank would need to be regularly drawn off from the humus tank by sludge pumps that would transfer the sludge to a 5m diameter by 5m high sludge holding tanks where the sludge could further settle and consolidate before being taken off-site for disposal (Crawley STW would be ideal for this purpose because the sludge could be fed into TW’s Anaerobic Digestion (AD) plant at that site).

The plant would require an inlet pumping station to lift flows into the reaction tank when levels in the dirty water pond were low and blowers would be required to provide the air for the reaction tank. It is proposed that all the pumps and blowers for the site are controlled from a single Motor Control Centre (MCC) building. It is probable that the inlet pumps will need to be variable speed with

Two 50m3 (4m diameter by 4m high) nutrient storage tanks are proposed to provide nutrient/microbiology sources to start up the plant in anticipation of treatment loads from the airport and to sustain the plant through mild winter periods when de-icer contaminated surface water for treatment is not available. When starting up the plant one of these tanks could contain surplus activated sludge from Crawley STW which would provide a microbiology source as well and some nutrients and the other could be used for de-icer (possibly scavenged) to condition the reaction tank to treating de-icer.

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Measures to reduce de-icer use and to capture de-icer waste at source should be developed as far as practicable but it is recognised that there are practical constraints that prevent eliminating the problem of de-icer contamination at source.

F.3 Wastewater and sewage design with additional mitigation

F.3.1 Additional Mitigation 1: Managing demand Rainwater / surface water harvesting and recycling

Gatwick Airport starts from a favourable position because it already has some surface water management that manages the run-off from the site for a variety of purposes:

• It diverts run-off that has been heavily contaminated by de-icer during freezing conditions to storage for later treatment

• It attenuates flow to the River Mole

• It stores some run-off to supply the site fire main system

The last application offers an opportunity to create a site-wide network for rainwater re-use similar to the fire systems found in many military installations where they have dual-purpose fire mains that also supply potable water. In many cases the base incoming water supply is insufficient to meet the requirements of the Crown Fire Standards so there is a reservoir of water with a small jockey pump to meet day to day supply requirements and significantly larger fire pumps that will cut on if a large demand that would signify use for fire-fighting is encountered.

Thus, rather than a roof-based rainwater harvesting (BAU), a site-wide surface water harvest system is proposed utilising a reserved volume of 80,000m3 in the pond that is used for attenuating surface water run-off into the River Mole. This volume would be replenished by any clean run-off from the development or similar contaminated flows that have been through the proposed enhanced wetland treatment and is now clean. This volume and the larger catchment area should mean that that the toilet flushing (266,043m3 per annum) and other non-potable requirements within the new building should be fully met by this source although a back-up supply from the SESW potable water network should be installed to ensure resilience (please note that this will need to incorporate some form of siphon break to prevent the possibility of contaminating the potable water supply). This recycled water could be transmitted to the new terminal using a combined fire main and recycled water system which would make the recycled water more readily available if other opportunities to exploit it arose.

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The surface water storage would need to be sufficient to meet the site’s non-potable water requirements and retain sufficient in reserve for any fire-fighting requirements. The usual advice is that 18 days non-potable water use is stored to weather out any dry spells, but it would be advisable, given the changing weather patterns that the UK has been experiencing recently, to store a greater provision. We have used climate change estimates to consider how the rainfall pattern in the south east might change, and this analysis indicates that 2 to 3 months of storage is more appropriate. Our 80,000m3 of long-term storage is based on 3 months of storage.

Additional mitigation 2: Sewage and Wastewater treatment and discharge Infrastructure at Crawley and Horley STWs

There will be a requirement to re-route the current sewage transfer from North Terminal to Crawley STW because the present configuration clashes with the new runway and terminal. There is likely to be an intermediate requirement to transfer some of the sewage from South Terminal to Crawley STW because of capacity restrictions to and at Horley STW which serves South Terminal at present. There is some scope for collaborative working with Thames Water notably there is probably an opportunity to integrate the waste heat that will be available at the Anaerobic Digestion plant at Crawley into new terminal facilities for space heating/cooling.

Sewage Treatment:

We have considered options for treating the sewage produced from the new terminal and associated buildings on site at the proposed wastewater treatment works or the wetland treatment system. Whilst there are benefits in considering this arrangement, the risks and costs outweigh the benefits. The technical justification for this decision is presented in Annex F

It has therefore been assumed that the sewage from the new terminal would be sent to Crawley STW. If more complex solutions are desired, then there ought to be scope to develop these collaboratively with Thames Water.

A conceptual image of the additional mitigation deicer and wastewater system for is shown in Figure 12 below.

Wastewater Treatment (Wetland option):

Source control within drainage system: There are effective methods of de-icer separation and recovery as previously discussed. We have not, however, included the benefits of a system like this within our pollution control design at this stage because their feasibility in our climate is uncertain.

Our assessment therefore assumes that the following elements will be adopted for the new runway and terminal development based on a worst case assessment of de-icer load:

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• A 70,000m3 balancing tank upstream of wetland treatment system with integral pumps capable of passing up to 2,000 litres per second to the wetland for treatment but capable of a range of flows.

• A 150,000m2 active wetland treatment system, designed to meet a discharge standard for BOD and DO consistent with good ecological status for 95% of the time.

• New gravity sewer or gravity drain to convey treated effluent from the wetland to storage

• Storage of treated water in north-west zone. 150,000m3 of clean storage. 80,000m3 of this retained for long term storage and effluent reuse, 70,000m3 for surface water attenuation, providing 100yr plus climate change protection, when combined with balancing tank

• A further 70,000m3 of storage downstream of the wetland that can be used for hold dirty water when the quality is not good enough to discharge to river. This will be equipped with pumps capable of recirculating flow to the head of the wetland at the rate of 100l/s for a further pass (or passes) of the wetland until the water quality is acceptable or sent into the existing pollution control system for onward discharge to Crawley STW

• Air blowers to aerate the wetland

• 2no. 50m3 nutrient storage tanks

The proposed wetland area would be 15 hectares in extent with the wetland aerated by blowers that force air into the base of wetland media so it could percolate up through the media while the flow being treated passed through it. This is a biological treatment which relies upon microbiological populations within the treatment system, which use the contaminant load as a food source. Upstream of the wetlands would be about 70,000m3 of storage to moderate flows through the wetland and contribute to the overall attenuation of surface flows for the site. The upstream 70,000m3 of storage could allow the rate through the wetland to be adjusted to minimise the impact of shock loading and the air rate could also be adjusted with the load on the wetland.

Downstream of the wetland would be a further 70,000m3 of storage for flows that require to be recycled through the wetland before they achieve the discharge consent requirements. The facility to send treated flow to Crawley STW for treatment should be retained as a contingency measure but this should only be required in extreme circumstances and the BOD load would be considerably reduced and, as a consequence, the additional flow should be easier to treat.

The wetland treatment system will need to be fed with a nutrient source (e.g. screened and settled sewage from the terminal buildings and offices). This is particularly important in the summer months, when de-icer will not be fed to the treatment system. Settled sewage could be an option but is likely to

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run into consent problems because a phosphorus limit is likely to be stipulated in the discharge consent that is likely to require additional treatment to achieve compliance.

Due to the absence of deicer loading through the summer the microbiology needs to be “warmed up” by artificial addition of nutrients in advance of the de-icing season. Two 50m3 nutrient storage tanks are included in the design to facilitate this ‘warm-up’ process and possibly supply some maintenance dosing during the summer months. Scavenged de-icer ought to provide a cost- and process-effective nutrient source.

Measures to reduce de-icer use and to capture de-icer waste at source should be developed as far as practicable but it is recognised that there are practical constraints that prevent eliminated the problem of de-icer contamination at source. Our proposed design may change in the future as we continue to actively explore the feasibility of implementing more innovative methods of de-icer separation.

Figure 13 Conceptual diagram of deicer management system for additional mitigation scheme

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Appendix G – Consultation

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Appendix G – Consultation

G.1 Environment Agency and GAL agreed design schedule[MA1]

G.1.1 Meeting summary and design schedule

Table 12 Meeting summary

Date(s) Consultee and Issues Raised How would this be addressed 22 January Environment Agency (Environmental For both rivers sustainable channels, 2014, Regulator) riparian zone and floodplain would be provided. 12th The classified of the River Mole under February the EU Water Framework Directive The gradient of the diverted river 2014, (WFD) currently achieves Moderate has been chosen to ensure sediment Ecological Status and this would need to can be transported downstream 14th March maintained or improved in the long without the need to locally lower the 2014, term. river.

26th March The impact of surface water needs to be However, where required this would 2014. mitigated against downstream of the be carefully managed to ensure site. upstream fish passage and downstream sediment transfer are Any loss of floodplain needs to be not disturbed. understood and mitigated against. Cross sections have been designed to encourage natural flow processes in order to support ecological diversity.

Based on the above good ecological status could be achieved along the

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Date(s) Consultee and Issues Raised How would this be addressed river Mole. Loss of floodplain due to the R2 and associated developments has been calculated.

Short term and long term volume storage required to mitigate up to the 1 in 100 year probability + climate change rainfall event would prevent any increase to downstream flooding.

Appendix G provides full details of policy and design agreements reached.

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Table 13 Agreed design schedule

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G.1.2 Formal consultation response from Environment Agency

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G.2 Water company consultation G.2.1 Thames Water, Sewage and wastewater treatment

Table 14 Meeting summary

13th March Thames Water Utilities Limited (Sewerage Growth in sewage loads by terminal 2014 Utility) forecast

Current planning based on Gatwick Airport Transfer of South Terminal load to passenger increasing to 40million by 2025. Crawley STW

Headroom at Crawley STW currently being Proposed inter-connection to Crawley increased to 10,000PE (population STW equivalent) for general growth to De-icer recycling 2010. Horley STW has limited headroom. De-icer contamination pre-treatment Horley STW serves South Terminal and Crawley STW serves North Terminal and most aircraft loads.

Network connecting to STWs may have capacity limitations.

Additional sewerage and sewage treatment facilities would be built into their growth plans once they were known.

Additional de-icer contaminated surface water, if anticipated would require additional facilities

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The following questions and responses are based on Thursday 13th March 2014, subsequent ongoing consultation discussions and an email from Victor Alonso, Thames Water, to CH2M HILL on 23 April 2014.

Projected flow and load to Crawley STW and Horley STW are as below. These are based on annual average passenger numbers of 87million. The information presented in Appendix F and the Water and People chapter of the main report are based on an amended, slightly higher maximum passenger throughput of 95mppa. The implications of the increase to 95mppa is discussed in the table below, alongside Thames Water consultation response.

year current 2021 2026 2029 2031 2035 2040 2045 2050 Horley 8,774 10,016 13,154 14,877 9515 9391 9273 9255 9257 Crawley 16,588 21,065 22,919 23,717 29,854 35,155 43,259 44,999 47,765

Table 15 Thames Water consultation response

Number Gatwick consultation question Thames Water response Impact of increase from 87mppa to 95mppa 1 We understand that you have accounted Our calculations show that Crawley STW has We will provide the updated passenger forecasts for some additional load and flow from capacity to 2021 but not to 2026. In order to refine to Thames Water as part of our ongoing Gatwick Airport at both Horley and our assessment we request up to date passenger consultation. Crawley STWs, alongside wider number splits (by terminal/month). development in both towns. Horley STW has some spare capacity but some Based on the forecast flow and load, do upgrades are anticipated, subject to the necessary you have capacity, either already funding being approved. We will investigate

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Number Gatwick consultation question Thames Water response Impact of increase from 87mppa to 95mppa delivered, or planned, for forecast rationalising the flows to Crawley and Horley as passenger and airport growth: part of future capacity considerations. - To 2021? - To 2026?

2 We understand that you do not have It is anticipated that Crawley STW will not meet the This conclusion remains valid capacity for the forecasts to 2030. Is this demand forecasted to 2030. Upgrades of our assets correct? will be required. It may be necessary to extend the site boundary to complete the upgrades.

It is anticipated that Horley STW will have capacity to 2030 but some upgrades will be necessary to This conclusion remains valid achieve this, subject to the necessary funding approval.

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Number Gatwick consultation question Thames Water response Impact of increase from 87mppa to 95mppa 3 Sewage: We are exploring various options Working in close partnership we do not see any Sewage capacity is based on peak loads, ,not for sewage and wastewater treatment and reason currently why the necessary sewage annual average, which remin unchanged. disposal. At its simplest, one option is for upgrades could not be provided during AMP7 Therefore this conclusion does not change. all of the additional sewage and (2020-2025), subject to the necessary funding being wastewater load across the campus to be approved. discharged to Crawley STW. This would be achieved by a series of pumping stations and transfers to ensure that there was no increased flow or load to Horley WwTW. If we continue to work with you on passenger and wastewater forecasts, and can confirm forecast numbers by 2016, are there any reasons why you would not be able to provide the necessary infrastructure for sewage: 4 De-icer contaminated wastewater: As long as the way forward for the de-icer loads / This conclusion remains valid As a secondary option, we are considering terminal loads is clearly laid out, we see no reason the development of a wetland treatment subject to the necessary funding approvals why the system to manage the entire additional necessary infrastructure upgrades could not be in load from the second runway and terminal place to support these proposals. development.

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Number Gatwick consultation question Thames Water response Impact of increase from 87mppa to 95mppa Would this affect the viability of your infrastructure plans for Crawley or Horley STW? 5 Are there any other points you would Other points we would like to raise: like to raise with us? Network (sewers crossing the proposed site): There are public sewers crossing or close to your development proposal. In order to protect public sewers and to ensure that Thames Water can gain access for future repair and maintenance, details of your proposals will need to be approved.

Where sewers or rising mains are to become redundant or have to be diverted the full cost of administering and undertaking the works shall be financed by the GAL.

Network (Capacity): Can you please provide some clarification of when the decision to extend at Gatwick will be made? We also request details and timing of the provision of industrial development to the east of the airport.

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Number Gatwick consultation question Thames Water response Impact of increase from 87mppa to 95mppa

Due to the current uncertainty of this proposal, detailed design has not being undertaken. We can if instructed carry out investigations to identify upgrade requirements ahead of decision but there will be a fee for undertaking this work.

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G.2.2 Water resource and supply: Sutton and East Surrey Water

Table 16 Meeting summary

6th March Sutton and East Surrey Water (Water Supply On-going water savings 2014 Utility) Water recycling Gatwick Airport water consumption now

about 2Mld (previously 3Mld).

Water saving activity in recent years has had a noticeable impact.

Production capacity at Bough Beeches has been increased recently as part of resilience improvement programme. Further increases at Bough Beeches scheduled as programme rolls out.

Resilience programme to include Gatwick Airport by end of 2015.

Potential increases at Gatwick Airport are well within SESW future production plans.

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The following questions and responses are based on 6th March 2014, subsequent ongoing consultation discussions and an email from Jeremy Downer, Customer Services Manager Sutton and East Surrey Water to CH2M HILL on 24 April 2014.

The forecast water consumption numbers for worst case (historic practice), scheme with embedded mitigation, and scheme with additional mitigation in assessment years 2030, 2040 and 2050 follows. These are based on annual average passenger numbers of 87million. The information presented in Appendix F and the Water and People chapter of the main report are based on an amended, slightly higher average passenger throughput of 95mppa. The implications of the increase to 95mppa is discussed in the table below, alongside Sutton and East Surrey Water’s consultation response.

Worst case (historic practice) Current practice Exemplar practice

Total (Terminal Terminal buildings Terminal buildings buildings + Terminal buildings Terminal buildings + associated Terminal buildings + associated associated commerce commerce commerce) Average daily use 3269 4370 2283 3220 2283 3220 2030 m3/d Peak daily use 5048 5344 3562 4664 3562 4664 m3/d

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Worst case (historic practice) Current practice Exemplar practice

Total (Terminal Terminal buildings Terminal buildings buildings + Terminal buildings Terminal buildings + associated Terminal buildings + associated associated commerce commerce commerce) Peak hourly use m3/hour 436 598 354 491 354 491

Average daily use 4329 5912 2768 3913 2083 3228 2040 m3/d Peak daily use 6560 8422 4104 5451 3119 4466 m3/d

Peak 512 745 459 627 366 534 hourly

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Worst case (historic practice) Current practice Exemplar practice

Total (Terminal Terminal buildings Terminal buildings buildings + Terminal buildings Terminal buildings + associated Terminal buildings + associated associated commerce commerce commerce) use m3/hour

Average daily use 4467 6200 2320 3478 1635 2794 2050 m3/d Peak daily use 6738 8777 3500 4863 2467 3830 m3/d Peak hourly 481 735 418 588 358 528 use m3/hour

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Table 17 Sutton and East Surrey Water consultation response

Number Gatwick consultation question Sutton & East Surrey Response Impact of increase from 87mppa to 95mppa 1 We understand that your water Our draft Water Resources Management Plan No change resources management plan indicates (WRMP) identifies the investment we will need to that you have water resource capacity make in order to meet demand in the period up to to meet your forecasts of demand up to 2040. The investments necessary will be 2040, subject to approval of the plan, incorporated into our Capital Programme and will and subject to your financial regulator be subject to Ofwat’s Price Review process approving any necessary currently carried out at 5 year intervals. The investment. Is this interpretation investments include demand side measures such as correct? water efficiency, leakage reduction and metering as well as supply side measures such as developing additional resource. The WRMP is designed to ensure that we continue to meet our duty of supply to domestic customers included within our licence conditions, and also to provide sufficient water to serve our non-household customers.

Progress against our WRMP is reported annually and the plan itself will be updated and revised in 2019.

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Number Gatwick consultation question Sutton & East Surrey Response Impact of increase from 87mppa to 95mppa 2 What confidence can you give us that We have received no requests from the Secretary No change your water resources management of State for additional information and are plan will be approved? confident that we will be given permission to publish our final WRMP shortly. The timescale for approval by the Secretary of State has been delayed because of the recent flooding but we understand that decisions will be taken in May 2014. 3 Is the forecast future demand identified below consistent with the demand you have forecast in your water resources management plan:

3a a. For the demand The forecasts are not entirely consistent with the This conclusion remains valid forecast from the figures included in our WRMP. However, any terminal buildings differences are not significant and would fall well within the allowance we have made for uncertainty

(headroom). 3b b. For the total demand including business and commercial expansion

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Number Gatwick consultation question Sutton & East Surrey Response Impact of increase from 87mppa to 95mppa forecast

4 If not, do you consider the difference between our forecasts and your water resources management plan significant? 5 How resilient is your water network Each of our Water Treatment Works has been No change serving Gatwick to external shocks, assessed for resilience as part of our requirements such as asset flooding, terrorist attacks under the Security and Emergency Measures and power outage? Direction 2000. These take into account a number of scenarios including deliberate acts of damage.

A separate study carried out in 2009 assessed all of our operational sites for flood risk. Flood defence schemes to mitigate the highest risks identified either have now been, or are now being, implemented.

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Number Gatwick consultation question Sutton & East Surrey Response Impact of increase from 87mppa to 95mppa

The principal Works which supplies Gatwick is Bough Beech. This source is supplied from Bough Beech Reservoir which has a volume of 10,000 Ml. It is topped up each year between the months of November and April in accordance with the licence condition.

All our Water Treatment Work sites have standby power facilities and storage tanks to hold fuel supplies for typically more than 1 week. Given that we have treated water storage at each site, our ongoing maintenance programme and the relatively short lead time to switch to standby power, a power outage at a site will not have any impact on our ability to continue supply.

The resilience of the mains network supplying

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Number Gatwick consultation question Sutton & East Surrey Response Impact of increase from 87mppa to 95mppa Gatwick is being significantly enhanced with the installation of our new 800mm Trunk Main due for completion later this year. This will enable Gatwick and the surrounding areas to receive a supply from an alternative WTW if there should be a failure of the single trunk main currently transferring the treated water supply from Bough Beech to our Service Reservoir in Outwood. 6 How resilient is your water resources The WRMP planning process considers climate No change management planning to climate change scenarios as part of the modelling and change forecasts? analysis we carry out. 7 Do your forecasts take changing yield Yes No change due to climate change into account? 8 Your water resources management We are legally obliged to produce a WRMP every No change plan is a 25 year plan, but you are only five years. We are confident that future plans will funded to deliver infrastructure on a receive regulatory approval. five year basis. What confidence do you have that your infrastructure plans from 2020 – 2040 will secure regulatory approval?

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Number Gatwick consultation question Sutton & East Surrey Response Impact of increase from 87mppa to 95mppa 9 Can our plans impact on the water Neither Gatwick nor its surrounding areas are No change quality status of Drinking Water within Drinking Water Protected Areas and we Protected Areas (DrWPA)? have no water sources in either of these locations.

We understand that the drainage catchment for Gatwick is linked to the River Mole. Whilst we do have ground water sources further downstream on the River Mole they are not within a DrWPA.

Based on the above we do not believe that the Gatwick plans referred to here have any impact on the water quality status of DrWPA. 10 The 2050 forecasts are outside your Our WRMP includes a number of feasible options No change forecast horizon. Are you able to that are not implemented by 2040. We are comment at a strategic level on the confident that we will have, or can make, sufficient availability of water to meet our needs water available to meet demand from customers, in 2050? including Gatwick up until 2050. 11 Is there any other relevant information No you feel we should be aware of or taking into account at this time?

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Appendix H – sustainability assessment

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Appendix H – sustainability assessment

Resource Water environment resource assessment Sustainability assessment

Flood risk

With embedded WFD groudnwater hydromorhpology, WFD water quality biology fishery and

WFD water resource Assessment criteria Current quality USD quality Scale Rarity Substitutability mitigation With additional mitigation

· Does the proposal affect 'protected areas' as defined Good NA Regional/national Rare None under the Water Framework

 Directive? +/- +/-

· Does the proposal avoid Moderate / deterioration of Good Local Common None poor    existing water body status? ++ ++

· Does the proposal result in a decrease in length of Moderate / Good Local Common None waterbody that meets a good poor

   standard? ++ ++ - Does the proposal result in an Moderate / overall decrease in length of Good Local Common None poor    water body? ++ ++

· Does the proposal Moderate / contribute towards achieving Good Local Common None poor    good status in water bodies? + ++

· Does the proposal seek to minimise and manage the Moderate / Moderate Local Common None effects on water quality poor

 during construction + ++

· Does the proposal affect a significant groundwater NA NA Regional NA NA

 aquifer? +/- +/-

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· Does the scheme reduce water consumption and conserve and manage water High High Regional Scarce None efficiently during

   construction? + ++

· Does the scheme reduce water consumption and High High Regional Scarce None conserve and manage water

   efficiently during operation? + ++

· Does the scheme minimise increases in flood risk on the local area and protect against NA NA Regional NA NA flood risk, including in light of

 likely climate change? + ++

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Appendix I

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Appendix I - Airport Masterplan option 3 – No end around taxiway

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Appendix J – Scheme assessment with EATS

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Appendix J – Scheme assessment with End Around Taxiways (EATs).

Gatwick's Masterplan submission also identifies a possible alternative solution which includes taxiways around the ends of the existing runway, which would reduce or eliminate the need for aircraft to cross the existing runway. This Appendix summarises how the alternative option with end around taxiways would affect the results of the appraisal.

The scheme with EATs would increase the landtake area on the north-western side of the airport to accommodate the EAT and a noise bund. This would move the landtake boundary slightly closer to Charlwood (See Figure 14).

Figure 14 Scheme with EATs boundary

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J.1 Assessment of operational and construction effects (with embedded mitigation)

Water and flood risk The potential effects of the scheme with EATS on flood risk to upstream and downstream communities would be unchanged from that described for the scheme without EATs. Whilst the proposed route of the River Mole diversion would need to be further west as per Figure 15, the proposals for a wide river valley with embedded floodplain mitigation remain unchanged. The conclusion that detailed design of this channel and floodplain could bring a reduction in floodrisk to downstream communities also remains unchanged.

Figure 15 Scheme with EATs river diversion route

The surface water drainage system and the deicer management system philosophy remain the same, although the small increase in impermeable area may require a small increase in the planned volume of surface water attenuation to prevent any increase in flood risk.

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There are no differences to the construction specification or mitigations to those described for the scheme with EATS.

Water and the environment The potential effects of the scheme with EATS on biodiversity and water quality would be unchanged from that described for the scheme without EATs. Whilst the proposed route of the River Mole diversion would need to be further west as per Figure 15, the proposals for a wide river valley designed to meet the Water Framework Directive’s “Good Hydromorphological status” remain unchanged.

The surface water drainage system and the deicer management system philosophy remain the same. Although the small increase in impermeable area may require a small increase in the volume of deicer used, the system design would ensure that only water of a good physiochemical quality would be discharged to the River Mole.

There are no differences to the construction specification or mitigations to those described for the scheme with EATS.

Water and people The potential effects of the scheme with EATS on water supply, wastewater and sewage would be unchanged from that described for the scheme without EATs. There would be no increase in demand for water and no increase in the volume of sewage produced.

General remarks on construction There are no differences to the construction specification or mitigations to those described for the scheme with EATS.

J.2 Conclusions and Overview The assessment of effects of the scheme with EATs upon water and flood risk, water and the environment and water and people would be unchanged from that of the scheme without EATs.

The appraisal identifies that there are no adverse impacts attributable to the scheme with EATs, and that there are a number of areas where our design is supportive or strongly supportive of sustainability.

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