Thanet Ground Water Quality     |     home Return to post and other links   |   Thanet Ground Water Quality   |   Thanet Ground Water Quality table   |   Manston map   |   Benzine   |   From the China Gateway environmental report   |   Xblocks   |   Phases   |   Source Protection Zones   |   EA   |   Environment Agency's Response   |   My response to the Environment Agency   |   My initial objection to the development   |   Executive Director of East Kent Opportunities LLP   |   Title 15   |   Title 16   |   CPRE Kent   |   CPREKent2   |   Title 19   |   Title 20   |   Title 21   |   Environment Agency being difficult     |   Information Request   |   Letter to Doug 5.7.8   |   Natural England's comments   |   complaint ref 1342   |   Title 33   |   power of the sea   |   BRIEFING DOCUMENT FOR THANET DISTRICT COUNCILLORS   |   More from the EA   |   Southern Water discharge consent letter.   |   INFRATIL LETTER   |   Recommendation to the planning committee to approve   |   Explosive   |   Developers clarification of points raised at the planning meeting   |   Doug Emails   |   CUMMINS POWER GENERATION LTD.   |   Title 47   |   voting   |   Sericol Investigations   |   Title 50   |   the history at Thor   |   EA letter to KIA 19.12.08   |   EA letter to KIA 18.12.08 Title 21 Prepared for: Commercial Group Properties plc Unit 7, Patricia Way Broadstairs Kent CT10 2LF Commercial Group Properties plc ‘China Gateway’ Manston Business Park Water and Sewage Strategy June 2008 D117016_01 rev4A – PRC Edited (13-06-2008) Commercial Group Properties plc China Gateway, Manston Business Park Scott Wilson Kanthack House Station Road Ashford Kent TN23 1PP Tel 01233 658 200 Fax 01233 658 299 www.scottwilson.com This document has been prepared in accordance with the scope of Scott Wilson's appointment with its client and is subject to the terms of that appointment. It is addressed to and for the sole and confidential use and reliance of Scott Wilson's client. Scott Wilson accepts no liability for any use of this document other than by its client and only for the purposes for which it was prepared and provided. No person other than the client may copy (in whole or in part) use or rely on the contents of this document, without the prior written permission of the Company Secretary of Scott Wilson Ltd. Any advice, opinions, or recommendations within this document should be read and relied upon only in the context of the document as a whole. The contents of this document do not provide legal or tax advice or opinion. ? Scott Wilson Ltd 2008 Revision Schedule Water and Sewage Strategy June 2008 Rev Date Details Prepared by Reviewed by Approved by 01 26.03.08 Preliminary Issue Melanie Sim Assistant Engineer Andy Pilbrow Associate Andy Pilbrow Associate 02 10.04.08 Update Melanie Sim Assistant Engineer Andy Pilbrow Associate Andy Pilbrow Associate 03 21.04.08 Update Melanie Sim Assistant Engineer Andy Pilbrow Associate Andy Pilbrow Associate 04 05 10.06.08 13.06.08 Revision 4 Revision 4A Melanie Sim Assistant Engineer PRC Group Andy Pilbrow Associate PRC Group Andy Pilbrow Associate PRC Group Commercial Group Properties plc China Gateway, Manston Business Park Table of Contents 1 Executive Summary .......................................................................... 1 2 Introduction ....................................................................................... 2 2.1 Commission .................................................................................................................... 2 2.2 Background..................................................................................................................... 2 2.3 Consultees ...................................................................................................................... 2 2.4 Aim & Objective .............................................................................................................. 3 3 Site Description ................................................................................. 4 3.1 Location .......................................................................................................................... 4 3.2 Environs .......................................................................................................................... 4 3.3 Water Bodies & Hydrology .............................................................................................. 4 3.4 Proposed Development .................................................................................................. 5 3.5 Southern Water - Sewers ................................................................................................ 5 4 Proposed Services ............................................................................ 7 4.1 The East Kent Spatial Development Company ............................................................... 7 4.2 Water Supply .................................................................................................................. 7 4.3 Surface Water Drainage Strategy ................................................................................... 8 4.4 Foul Drainage Scheme ................................................................................................. 11 5 Conclusion .......................................................................................15 Appendix 1 - Surface Drainage Strategy Drawing ....................................16 Appendix 2 - Foul Drainage Strategy Drawing .........................................17 Appendix 3 - Landscaping Masterplan .......................................................18 Appendix 4 - Source Protection Zones .....................................................19 Appendix 5 - Klargester / KEE Waste Treatment Plants .........................20 Appendix 6 - Asset Plan ...........................................................................21 Appendix 7 - Soakaway Tests ....................................................................22 Commercial Group Properties plc China Gateway, Manston Business Park Water and Sewage Strategy June 2008 1 1 Executive Summary With regard to surface water disposal there are no watercourses near to the site, nor are their any public sewers with adequate capacity to accept the surface water arising from the buildings drainage or hard landscaping. However, the site overlies permeable chalk strata. Therefore a sustainable drainage strategy is proposed to drain surface water into 3m deep soakaway trenches to be provided around the application site, outside the inner source protection zone in the north west of the Phase 1 site. Returning surface water to ground near the source complies with the principals of SuDs guidance in PPS25 and would be more economic than construction of a pump station and new drainage, laid possibly as far as Pegwell Bay where there may also be problems with crossing the SSSI. Recycling of rainwater collected from roof drainage in ‘grey water’ tanks will mitigate the amount of water to drain to soakaways. A drawing of the proposed surface drainage strategy is provided in Appendix 1. An alternative on site treatment strategy is proposed for the foul drainage which requires the provision of two treatment plants in Phase 1 and 3. The discharge from the treatment units is normally clean enough to discharge to watercourses. A drawing of the proposed foul drainage strategy is provided in Appendix 2. Commercial Group Properties plc China Gateway, Manston Business Park Water and Sewage Strategy June 2008 2 2 Introduction 2.1 Commission Scott Wilson was commissioned by Commercial Group Properties (CGP) in January 2008 to prepare a Water and Sewage Strategy to be submitted with a planning application for a proposed development at Manston, Kent. This report assess the impact of the Manston Business Park on existing water and sewage supply and sets out the intention for proceeding in these areas. A search was carried out initially to find what water and sewage capacity and services are in the area of the application site to assess what diversions or protection measures may be necessary. An assessment was carried out to determine the requirements of the development for water and sewage services, based on typical demand for a range of uses, predominantly mixed B1(c), B2 and B8 types. Enquiries were sent to the service providers with estimated loads to evaluate the additional capacity required to supply water to the development and to deal with the sewage treatment. Initial consultations with the East Kent Spatial Development Company determined that the existing public drainage operated by Southern Water had no capacity to accept drainage from the proposed development. Upgrading the capacity of the existing public drainage systems would be uneconomic; therefore a strategy for treatment and disposal of surface and foul drainage on the development was developed. 2.2 Background CGP wish to develop the Manston Business Park into a ‘mixed-use development’. The proposed masterplan is given in Appendix 3. The site is classified in the Thanet District Adopted Local Plan (TDC, 2006) as an ‘employment area’ and is identified for a development similar to the type proposed. The development site is split into 3 Phases with each seek planning permission. 2.3 Consultees Organisations consulted on the utility services and proposals for utility provisions for the development in addition to the service providers have included: • East Kent Spatial Development Company • Environment Agency • Owls Hall Environmental Ltd • KEE Process Ltd Commercial Group Properties plc China Gateway, Manston Business Park Water and Sewage Strategy June 2008 3 2.4 Aim & Objective The aim of this report is to provide the Council with an assessment of the impact that this development will have on existing water and sewage services. Commercial Group Properties plc China Gateway, Manston Business Park Water and Sewage Strategy June 2008 4 3 Site Description 3.1 Location The proposed development site comprises 71.6 hectares of open land and agricultural land located near Manston, Kent (E 631650, N166620). Currently, 31 hectares is a designated employment zone (coinciding with Phase 1 of the proposed development) with the remainder owned by Kent County Council. The western boundary of the site is defined by Columbus Avenue, an access road to a factory forms the eastern boundary of the site and the B2190 road forms the southern boundary of the site. No surface features define the northern boundary of the site. 3.2 Environs The site has a relatively even topography that slopes down gently from a level of 45m AOD in the east to 30m AOD in the north-west. The majority of the site is currently used for arable agriculture, but some ‘brownfield’ land is included in the Phase 1 section of the site on the west side. The site is surrounded generally by open land. Kent International Airport is immediately to the south of the site and there are residential developments to the east and west. Immediately to the west of the site are a few industrial buildings that are the initial phase of the Manston Business Park which was established in 1997. North of the site is open land intersected by the Manston Road. 3.3 Water Bodies & Hydrology There are no main water bodies in the immediate vicinity of the application site. The nearest surface watercourses are a network of tributaries across the Minster Marshes located 2.5km to the south. The English Channel is 2km distant from the site at its closest point at Pegwell Bay. There are two small attenuation ponds serving the properties on the business park west of the site. One of these ponds is located on the west boundary of the site and one pond is located near the two large (X-Type) units in the northwest of the site. The site is underlain by Upper Chalk, which constitutes a major aquifer used for public water supply. Hydrogeological information for the area (IGS, 1968) shows that the Upper and Middle Chalk beneath the site to be unconfined and the level of the groundwater table is 37 metres deep. Further details are included in Chapter 10 of the Environmental Statement. The whole site falls within the catchment of a Source Protection Zone for the Sparrows Castle public water supply. The inner protection zone (Zone 1) being in the north-west corner of the site and Zone 2 and 3 cover the remainder of the site. Commercial Group Properties plc China Gateway, Manston Business Park Water and Sewage Strategy June 2008 5 3.4 Proposed Development The Environmental Impact Assessment deals with the entire site area of 71.6 hectares, and will eventually comprise three separate phases for a total development of up to 325,158 sq metres (3.5 million sq ft) of predominately mixed B1(c), B2 or B8 uses. The Phase 1 application covers an area of 31.687 hectares accommodating 137,664 sq metres of floorspace. In addition to the industrial units, the Phase 1 development includes a prominent Gateway building, restaurant and amenity blocks. The detailed planning application (Phase 1) submitted with this Environmental Statement is wholly within the designated employment land and covers a large portion of the Manston Business Park, as it is currently known. This will make use of the existing brownfield land and undeveloped employment land. The remainder of the China Gateway Manston site outside of the designated employment area will be subject to a later detailed planning application(s) (Phase 2 and Phase 3) the total area of which is covered by this Environmental Statement The development comprises a mixture of single and two-storey sheds in 6 standard sizes with associated parking areas, access roads and soft landscaping, to be constructed in three phases. Phase 1 is adjacent to the existing factory on the western side of the development. It comprises 15 blocks over 31.6 hectares including two substantial single-storey sheds with a combined footprint of 131,568 m2. In addition a prominent Gateway Building, restaurant and a further amenity building are proposed. Phase 2 is a narrow strip in the middle of the development surrounding Alland Grange. This development will comprise 23 mixed industrial and business units, mostly smaller units, with a combined footprint of 44,255 m2. Phase 3 is on the eastern side near Cheeseman’s Farm. This development will comprise the construction of a further 32 mixed business and light industrial units with a combined footprint of 123,770 m2, all with associated vehicular parking and landscaping. 3.5 Southern Water - Sewers From initial discussions with the East Kent Spatial Development Company (EKSDC) we understand that there is no available capacity in the off site public sewers for discharge of surface or foul drainage from the proposed development. Subsequently EKSDC applied for a formal capacity check by Southern Water in April 2008. Southern Water advised (letter dated 18 April 08) that the existing pumped sewer main that serves the existing buildings at Kent International Business Park uses the Acol Pumping Station has a limited capacity of 12 litres per second. They advise that the proposed development would exceed the available capacity and therefore requires off site sewerage works to pump connect it to a point on the drainage network with sufficient capacity. Commercial Group Properties plc China Gateway, Manston Business Park Water and Sewage Strategy June 2008 6 The asset location plan of the site indicating the existing surface and foul drains has been requested from Southern Water and is included in Appendix 6. Essentially the plan indicates that surface drainage is absent from the area except for a small combined sewer to the south west of the site, which would not accept further surface drainage. There is a minor foul drainage system shown in the village of Acol to the north west of the site. Commercial Group Properties plc China Gateway, Manston Business Park Water and Sewage Strategy June 2008 7 4 Proposed Services 4.1 The East Kent Spatial Development Company Under current legislation, developers triggering demand for new water and sewage have to pay the full amount of installing the service even if they only intend to use a small amount of the connected capacity. They then have to try and claim some money back from subsequent users of the service. This has been a major hindrance to speculative development in areas needing regeneration or new development. The East Kent Spatial Development Company (EKSDC) was established by the following partners to direct public funding into the provision of strategic utilities to encourage business development sites specifically in central Thanet, including Manston Business Park. • South East England Development Agency (SEEDA) • Kent County Council • Thanet District Council • Dover District Council EKSDC secured funds from a variety of sources including the Government’s Single Regeneration Budget, managed by English Partnerships and SEEDA and the European Regional Development Fund, managed by Government Office for the South East Initially EKSDC provided funding for a massive improvement to the local electricity infrastructure in central Thanet, which will stimulate new investment in business developments. EKSDC signed a contract with EDF Energy for the construction of a new sub-station and distribution network to serve the area of central Thanet, including Manston Business Park. This work was completed in 2006. The intention is to recover these funds from EDF as developers pay to taking up the utility and the money will then be re-invested by EKSDC in further utility provision. The money will be ‘recycled’ and used again to fund the development of further utilities in the area. 4.2 Water Supply The daily water consumption for the proposed development has been estimated to be 280,000 litres. This is calculated on the basis of 1 person per 50m2 of floor space in the development and with water demand of 45 litres/day/person. An enquiry was sent to Southern Water on 19th March requesting budget costs for the distribution of water to the application site. Acad drawings files of the development masterplan were supplied on 17th April to draft their technical proposals. Response from Southern Water is outstanding on this cost estimate. The works comprise boosting the existing mains in Manston Road with a new pumped system from the Fleete Reservoir, which supplies water to most of the Isle of Thanet, Margate and Ramsgate. Commercial Group Properties plc China Gateway, Manston Business Park Water and Sewage Strategy June 2008 8 The new mains link will be over 3km long and connect to the existing mains at the junction of Manston Road and Alland Grange Lane. A further 0.5km extension of the existing water main system from the closest point at Manston Aerodrome will boost the existing mains (355mm dia. PE) in Columbus Avenue. This will enable supplies to the site to be connected to the mains in Columbus Avenue. 4.3 Surface Water Drainage Strategy 4.3.1 Drainage Principles & Policy A sustainable approach to surface drainage is proposed at the development site, fully in accordance with government policy guidance PPS25 Development and Flood Risk. Wherever possible, drainage strategies should incorporate sustainable drainage through the implementation of the ‘SuDS’ hierarchy, as presented in the Environment Agency’s publication ‘SuDS – A Practical Guide’ (2006). Traditionally, development drainage schemes have depleted the local ground water by diverting rainwater into piped systems that convey water rapidly to a local watercourse and contribute to flash flooding downstream. This development will use a combination of techniques to minimize long term impact on the local environment by eliminating off-site drainage and recycling rainwater. 4.3.2 Constraints Opportunities to discharge surface water off site are constrained by the inadequate capacity of existing public drains near the site (as advised by Southern Water) and the distance to suitable water bodies for a new pumped main. The nearest surface watercourses are the system of tributaries across the Minster Marches to the south west of the site. Alternatively the English Channel is 2km to the south, but there is a SSSI at the nearest point, Pegwell Bay. It was considered that balancing ponds would be unsuitable for this development due to the proximity of Kent International Airport; it was deemed that the ponds would attract wildfowl to the area and increase the risk of bird strike hazard to aircraft at Manston Airport. Therefore below ground storage is the only option. The site is located on chalk strata that is highly permeable and groundwater level is unconfined at 37 metres deep, which should be suitable for soakaway drainage. However, the site falls within the catchment of a Source Protection Zone as defined by the Environment Agency, for the Sparrows Castle public water supply. Therefore the quality of water that is drained to groundwater must be strictly controlled. The inner protection zone (Zone 1) being in the north-west corner of the site and Zones 2 and 3 cover the remainder of the site (see Appendix 6). Discharge of clean rainwater from the building roofs to shallow soakaways in Source Protection Zones 1 and 2 is acceptable to the Environment Agency in principle, unless the ground is currently or has previously been contaminated. Commercial Group Properties plc China Gateway, Manston Business Park Water and Sewage Strategy June 2008 9 Surface drainage runoff from car parks and roads is not acceptable to drain into Zone 1, but would be acceptable elsewhere if pollution prevention methods (trapped gullies etc) are employed to intercept hydrocarbon pollution. 4.3.3 Drainage Strategy Rainwater Recycling To mitigate the volume of drainage discharging to soakaways and to reduce demand for water supply by the development it is proposed that all clean rainwater drainage from building roofs is collected in local ‘grey water’ tanks for non potable uses, such as toilet flushing etc. With an annual rainfall of 590mm the total roof area (Ph1 - 92,100m2, Ph2 - 83,760 m2, Ph.3 – 116,359m2) could potentially collect 172,400,000 litres of water per year. In Section 5.5 the daily water consumption of the development was estimated to be 280,000 litres of water per working day, which is 40% of the total collectable. Infiltration Drainage The need for surface water drains and off-site sewers can be eliminated by encouraging rainwater to either permeate through the pavement into the ground, or be diverted into local infiltration trenches to soak away. Provision of temporary storage or attenuation will be necessary to hold storm water (100-year storms +20%) while it is being gradually absorbed by the ground. Storage capacity would be provided by a combination of buried tanks, oversized pipes and infiltration trenches filled with single sized filter stone. Further storage and absorption will be provided by a local network of irrigation pipes linking the infiltration trenches to nearby soft landscaping features and planting, especially tree pits, which should also significantly reduce regular water usage for landscape maintenance. The provision of separate oil interceptors (and maintenance thereof) for the car park and road runoff could be eliminated by using a more sustainable solution e.g. microbial treatment. 4.3.4 Treatment of Oils Any oil and hydrocarbon pollutants in the drainage from the parking areas would be removed by absorption, filtering and microbial decomposition by the filter stone, geotextile and surrounding soil. The texture of the specialist geotextile in particular has been developed to provide a habitat suitable for microbes that will digest hydrocarbons. Research at Coventry University on microbial growth has shown that geotextile ‘Inbitex’ (by Geosynthetics Ltd) is capable of degrading at least 70g of oil per m2 per annum. Trapped gullies and catchpits will be provided to pre-treat surface water entering the infiltration trenches and increase the longevity of the stone filter by intercepting excessive solids and trapping oil pollutants that can be removed during regular maintenance. Commercial Group Properties plc China Gateway, Manston Business Park Water and Sewage Strategy June 2008 10 4.3.5 Soakage Tests Preliminary soakage tests have been carried out at the development site and these are reported in detail in the Geo-Environmental report. These indicate that infiltration rates are sufficient for this to be feasible. Two soakage tests were carried out in trial pits on site and the infiltration rates were: SA1 1.25 – 2.26 x 10-4 m/s SA2 7.5 – 7.7 x 10-5 m/s The north-west part of the site is within a source protection zone therefore no soakaways can be located in this region. Drainage from here would be gravity fed to soakage trenches outside the source protection zone. 4.3.6 Drainage Methodology The drainage strategy has been developed using the industry standard software package MicroDrainage. It includes all the 3 Phases. The drainage strategy is presented in Appendix 1. Consideration of all the phases using MicroDrainage has enabled the development of a drainage strategy that will provide the necessary attenuation ensuring the proposed development discharges at rates that are no greater than rates prior to the proposed development. The drainage system has been designed such that rainstorms up to a 1% annual probability storm event including climate change (20%) are attenuated to discharge at a rate that will not exceed 7 l/s. The additional climate change allowance of 20% on rainfall intensities (for a 60 year development lifetime) was applied according to the recommendations set out in Table B.1 of PPS25. For the purpose of the drainage design a conservative estimate of 100% hardstanding was assumed for the development. The porosity value of 0.3 used in the MicroDrainage model for the infiltration trenches was derived from soakage testing undertaken by Geological Solutions Group in May 2007. 4.3.7 Attenuation Volumes The stormwater storage volumes estimated as necessary to attenuate peak flows in the different phases of the development are: Phase 1 805 m3 Phase 2 825 m3 Phase 3 2,190 m3 The underground storage tanks are proposed to be piped to infiltration trenches that have a cross sectional area of 9m2 (3 m wide and 3 m deep). The drainage infrastructure including the pipes will be designed in accordance with the design of the attenuation features (i.e. 1% annual probability storm event). Commercial Group Properties plc China Gateway, Manston Business Park Water and Sewage Strategy June 2008 11 4.4 Foul Drainage Scheme 4.4.1 Constraints Southern Water the drainage authority have advised that proposed development will exceed the current capacity of the adjacent wastewater pumped mains serving the existing Kent International Business Park. Therefore off site works will be required to construct a pump station to pump wastewater to a point on their drainage network with sufficient capacity. An alternative solution is to provide waste water treatment plants on site and to discharge the treated effluent to groundwater. Normally the treated effluent is of sufficient quality that the Environment Agency has approved discharges to surface water courses. However on this site the Source Protection Zone means that the standards of water to be discharged are much more sensitive to quality standards. In particular the Environment Agency are concerned about the existing high levels of nitrates in the groundwater from fertilizers used by farming. Therefore any discharge from a treatment plant will have to be strictly controlled in terms of overall quality and nitrate levels, possibly requiring tertiary treatment of the effluent discharge. An investigation with respect to Section 7 of the Groundwater Regulations 1998 would be necessary to demonstrate that the groundwater will not be adversely affected by the treated effluent. 4.4.2 Pumped Mains – Southern Water Proposal To discharge the foul drainage from the development Southern Water / Atkins have proposed (letter dated 20/11/07) that a new pump station is constructed and a rising main laid to Birchington some 2.5 km northwest of the site. The proposed route for the rising mains would be mostly in the existing roads, but there are potential ecological impacts at the southern and northern ends of the route including badger sets, snake habitats, protected trees and archaeological sensitive areas. Atkins have advised that the route of the rising mains also crosses and runs adjacent to old cast iron gas mains and cast iron water mains and there is a risk that these may need repair or replacement as a consequence of these works. Trial holes will be required to identify the exact location of these cast iron pipes, also electrical cables and sewers on the route. In addition there will be costs for traffic management because almost the entire route is constructed in the carriageway. EKSDC are to contact Southern Water to enquire whether their contingency allowance is adequate to cover these risks and the cost of further studies to determine the contingency costs more accurately. Despite being in the carriageway hand digging may be necessary where tree canopies overhang the road to avoid damage to the roots. At the northern and southern ends of the route the rising main also passes through a conservation area and woodland where a badger sett may be within 30m, also grasslands with potential as a reptile habitat. Commercial Group Properties plc China Gateway, Manston Business Park Water and Sewage Strategy June 2008 12 Scott Wilson have requested Southern Water to consider an alternative solution to pump waste water to the sewer network in Minster, which appears to be nearer to the site and possibly more economic. 4.4.3 On Site Treatment Works It is considered that an on-site treatment plant or system of local treatment plants is feasible and would provide a more cost effective and sustainable solution to disposal of foul drainage than the pumped main. The technology for local waste water treatment plants is already established and there are a range of sizes for this type of plant from a domestic to an industrial size with capacity for over 1,000 people. The effluent can be treated to reduce nitrates in the discharge to 0.2 mg/m3 , but further tertiary treatment will reduce this further to 0.15 mg/m3. Typically these plants are compact, self-contained, single piece treatment plants that utilise natural biological processes to effectively break down the pollutants in domestic and commercial waste water producing clean water that may be discharged into the surface drainage system. Periodic maintenance of the plant is necessary to remove settled out solids. The market leader in provision of these waste water treatment plants is Klargester and they were invited to provide a costed proposal for sewerage treatment at the development site. Typical details of the treatment plants supplied by Klargester (KEE) have been provided in Appendix 5 for information. Klargester have considered several options to provide a range of sizes for these plants that may be either centrally located in each phase or spread around in smaller units for each industrial unit or group of business units. Depending on the system proposed for management of Manston Business Park these treatment plants could be maintained centrally, or responsibility could be delegated to the leaseholders of the individual development units. 4.4.4 Individual Business Units The treatment plants that will be used for the individual units come in various sizes that suit different populations. The proposed product is KEE NuDisc Treatment System. This is a self contained, covered, single piece packaged treatment system that provides BOD removal, nitrification and nutrient removal. Information on the product can be found in Appendix 5 (Technical Brochure No 6, Drawings 881286, 881388, 881389 and 881391). The system consists of a Primary Settling Tank (PST) which is the first stage of the treatment process. The solids are settled out and removed periodically before moving into the biological stage of treatment. This consists of a Biological Rotating Contactor (RBC) which supports a biologically active film (biomass) of aerobic micro-organisms. As these rotate they are exposed alternately to wastewater (sewage) and air, and they oxidise the pollutants in the sewage. The RBC process removes the soluble, biodegradable and organic material from the sewage thereby achieving a high quality effluent. Commercial Group Properties plc China Gateway, Manston Business Park Water and Sewage Strategy June 2008 13 There are two stages of RBC, the first is the Anoxic RBC which is the initial biodegradation. Any solids return to the PST and the liquor is passed to the second stage of biodegradation the Aerobic RBC for further treatment. The liquor is then passed to the Final Clarifier where any remaining solids are settled out. The treated wastewater is then suitable for discharge into a watercourse with consent from the Environment Agency. This whole system is contained within a GRP (Glassfibre Reinforces Polyester) unit and this is installed in an excavation so only the low profile cover is exposed. A combination of these can be used around the site with a suitable size depending on the business unit they are attached to. They can then be managed by the leaseholders of the individual development units, or maintained centrally with a management company. 4.4.5 Central Plants A single modular treatment plant could be provided in each phase with capacity for a population equivalent of 2,364. This would consist of the following constituent parts. • Two stage primary settlement tank • Flow splitting chamber • Flow Disc Units • Settlement Tank • Sludge Return Pumping System Primary Settlement Tank A 80m3 (80,000 litre) two stage primary settlement tank will be the first stage in this modular process. Details of this product can be found in Appendix 5 Technical Brochure No 3 and Technical Drawing - DS0432. This is where the solids are settled out and retained as sludge, which is disposed of periodically. The partially clarified liquor then flows through to the next part of the system. Flow Splitting Chamber The Flow Splitting Chamber is a Y-Junction where the material from the Primary Settling Tank is split in half so go into the two Flow Disc Units arranged in parallel. Flow Disc Units The Flow Disc Units also known as DN17 RBC Modules form the biological treatment stage for the wastewater treatment plant. See Appendix 5 Technical Brochure No 1 and technical drawing 881787 for details. These use the Biological Rotating Contactor (RBC) technology as described in Section 5.7.1. The DN module range is optimized for carbonaceous BOD removal. The system will require 2 of these units arranged in parallel to treat the sewage. Final Settlement Tank The next part of the system is the Final Settlement Tank. This system will require 1 No ST8 the details of which can be found in Appendix 5, Technical Brochure No 2 and Technical Drawing No ST8. This is where the final settling takes place and the treated Commercial Group Properties plc China Gateway, Manston Business Park Water and Sewage Strategy June 2008 14 effluent can be discharges in a soakaway. This final clarifier is benched at the bottom to facilitate sludge consolidation. Any remaining sludge is sent through the Sludge Return Pumping System back to the Primary Settlement Tank. Sludge Return Pumping System Any sludge that still remains in the Final Settlement Tank is returned to the Primary Settlement Tank using a Sludge Return Pumping System. For this scheme a 900 diameter sludge recirculation chamber is recommended. Operation and Maintenance All parts of this system are designed to be delivered by an articulated lorry. The modular system is preferably arranged in a line. The area this will take is approximately 35m x 15m. The system will require emptying on a 3-6 month basis depending on the loading and size of the unit. If the unit is working to full capacity the maintenance will be more frequent than if there are fewer people than expected using it. Commercial Group Properties plc China Gateway, Manston Business Park Water and Sewage Strategy June 2008 15 5 Conclusion There are no watercourses near to the application site, nor are their any public sewers with capacity to accept the surface water arising from the buildings drainage or hard landscaping. However, the site overlies permeable chalk strata and therefore a sustainable drainage strategy is proposed to drain surface water into infiltration trenches to soakaway to groundwater within the application site. A drawing of the proposed surface drainage strategy is provided in Appendix 1. The public sewers near to the application site have insufficient capacity to accept foul drainage from the proposed development. Southern Water has proposed that a pump station is constructed with a rising main 2.5 miles to Birchington. A more cost effective and sustainable solution is proposed to provide on-site waste water treatment plants that discharge clean water to soakaway and irrigation of landscaping proposals. The quality of the water discharged from the waste water treatment plants is very high and commonly good enough to discharge to surface watercourses. However, on this site groundwater is protected by a Source Protection Zone and Environment Agency has requested an site specific investigation to demonstrate that groundwater will not be adversely affected by the treated waste water. CGP is currently proposing on-site treatment and is continuing discussions with the EA and Southern Water which has requested an condition in this respect. Southern Water has confirmed that there is sufficient water capacity, provided a new pump station is provided close to the existing reservoir and linked to the site. Again CGP is pursuing this route and the EA and Southern Water have requested a condition in this respect to any planning consent.