5 3SITE DEVELOPMENT 3.SITE DEVELOPMENT 3.1 SITE LAYOUT material available and that required.If there is a material deficit it will be necessary to import The landfill design should enable a practicable material to achieve the balance.An appropriate off- operation of the facility.The site layout plan should site source of the material required should be show clearly the location of the area to be landfilled. identified.If there is a material excess the disposal of such material should be planned for. The production of a digital ground model(DGM) also referred to as digital terrain model (DTM),or The investigation stage of the design process should topographical map should be undertaken during the include a detailed geotechnical assessment.Such an investigations stage.Typical scales used are 1:500 or assessment should include trial pits;boreholes;in 1:2500 for larger sites (greater than 60 hectares). situ tests;sampling;laboratory testing and Contour intervals vary depending on ground compaction trials.This would assist the designer in: elevation.Sites with little topographical relief (almost level)may have contour intervals at 0.25m, .determining the suitability of in situ materials while sites with high topographical relief may have (type and quantity)for use in the construction, contours at intervals of 0.5m or 1.0m. operation and restoration of the landfill facility:and A diagrammatic landfill layout is presented in Figure 3.1. carrying out a materials balance on a phase by phase basis. 3.2 SITE PREPARATION The extent of preparatory works is site specific and Materials are required during landfill development should be determined during the investigation stage. for: The preparatory works will include the stripping/filling of soil to formation level for the: ·basal mineral liner; lining system for cell/phase construction: ·cap barrier layer; leachate and gas management facilities; leachate drainage blanket; groundwater,surface water and leachate systems; other drainage layers e.g.capping layer and groundwater/surface water: landscaping and screening;and gas collection and venting system; all other site infrastructure ·roads: Existing services located within the proposed area of waste disposal must be relocated. Borehole cover (daily,intermediate); installations within this area should be grouted up to prevent a direct conduit to the groundwater. 。embankments, 3.3 MATERIALS REQUIREMENT AND internal and external bunds:and BALANCE restoration layers(subsoil and topsoil). Materials (soils,etc.)are required at all stages of landfill development (construction,operation and Materials required for the above operations may restoration).It is important that the designer need to be stored on site for a period of time.The estimate the quantities of material required.the material should be stored in a manner that maximises quantities arising from site development,the its reuse potential. quantities of suitable usable material available on site and,if necessary,the deficit between suitable
3.1 SITE LAYOUT The landfill design should enable a practicable operation of the facility. The site layout plan should show clearly the location of the area to be landfilled. The production of a digital ground model (DGM), also referred to as digital terrain model (DTM), or topographical map should be undertaken during the investigations stage. Typical scales used are 1:500 or 1:2500 for larger sites (greater than 60 hectares). Contour intervals vary depending on ground elevation. Sites with little topographical relief (almost level) may have contour intervals at 0.25m, while sites with high topographical relief may have contours at intervals of 0.5m or 1.0m. A diagrammatic landfill layout is presented in Figure 3.1. 3.2 SITE PREPARATION The extent of preparatory works is site specific and should be determined during the investigation stage. The preparatory works will include the stripping/filling of soil to formation level for the: • lining system for cell/phase construction; • leachate and gas management facilities; • groundwater, surface water and leachate systems; • landscaping and screening; and • all other site infrastructure. Existing services located within the proposed area of waste disposal must be relocated. Borehole installations within this area should be grouted up to prevent a direct conduit to the groundwater. 3.3 MATERIALS REQUIREMENT AND BALANCE Materials (soils, etc.) are required at all stages of landfill development (construction, operation and restoration). It is important that the designer estimate the quantities of material required, the quantities arising from site development, the quantities of suitable usable material available on site and, if necessary, the deficit between suitable material available and that required. If there is a material deficit it will be necessary to import material to achieve the balance. An appropriate offsite source of the material required should be identified. If there is a material excess the disposal of such material should be planned for. The investigation stage of the design process should include a detailed geotechnical assessment. Such an assessment should include trial pits; boreholes; in situ tests; sampling; laboratory testing and compaction trials. This would assist the designer in: • determining the suitability of in situ materials (type and quantity) for use in the construction, operation and restoration of the landfill facility; and • carrying out a materials balance on a phase by phase basis. Materials are required during landfill development for: • basal mineral liner; • cap barrier layer; • leachate drainage blanket; • other drainage layers e.g. capping layer and groundwater/surface water; • gas collection and venting system; • roads; • cover (daily, intermediate); • embankments; • internal and external bunds; and • restoration layers (subsoil and topsoil). Materials required for the above operations may need to be stored on site for a period of time. The material should be stored in a manner that maximises its reuse potential. 5 3 SITE DEVELOPMENT 3. SITE DEVELOPMENT
6 LANDFILL MANUALS FIGURE 3.1:DIAGRAMMATIC LAYOUT OF A LANDFILL Site Boundary Operational Area with secure fencing Disposal Area PHASEI PHASE II Leachate Treatment Plant Weather TA Station PHASEⅢ PHASE IV Service Road Equipment PHASE VI PHASE V Compound Wheelwash Gas Compound Waste Inspection Service Road Area Civic Amenity- Administration Car Weighbridge Park Reception
FIGURE 3.1: DIAGRAMMATIC LAYOUT OF A LANDFILL 6 LANDFILL MANUALS
7 3SITE DEVELOPMENT 3.4 PHASING 3.6 BUNDING The landfill should be developed in a series of Bunds are generally used in landfill development for: phases.Phasing should allow progressive use of the landfill area so that construction,operation(filling) perimeter screening; and restoration can occur simultaneously in different parts of the site.To avoid frequent(and disruptive) temporary screening:and preparatory works it is recommended that the design lifespan of a phase be a minimum of 12 months. boundary bunds-intercell bunds and phase boundaries Factors that need to be considered in determining the phasing are;waste intake which will determine the Perimeter bunds are used for screening and to assist size and lifespan of the phase and the sequence of in the restriction of unauthorised access to the site. operation which must take into account the Their design should be consistent with existing following: topography.The height of the perimeter screen can vary from 2m to a height that screens the proposed progressive construction,filling and restoration; development.Embankment slopes should be stable. forward planning to,in so far as possible ensure Temporary bunds can be used around the operational that subsequent phases are developed in the area for further screening and to assist in control of appropriate season; nuisances such as litter and noise.As the landfill development progresses the temporary bunding maximise use of on site materials and minimise arrangement is moved along concurrently. double handling of material, Temporary bunds are generally around 2m height with side slopes of 1:2.5.These bunds may also act installation of leachate and gas controls: as a storage area for final/intermediate cover material. management of the leachate collection system; and Boundary bunds may be divisions between cells, within a phase,or separators between phases. management of surface water run off. Consideration needs to be given to the relationship between the bund.base liner and leachate collection A recommended phasing sequence is illustrated in system.Generally a bund of approximately 2m Figure 3.2. height located on the base of the facility will be used. It is normal practice for the primary liner to continue 3.5 CELLS under the intercell bunding.Where a flexible membrane liner is used,a sacrificial layer can be Cells are sub-divisions of phases.The number of placed over the bunds and then connected to the cells in a phase and cell size should be based on underlying liner.This provides a barrier between water balance calculations (Section 7.2.1). cells and prevents seepage of leachate into adjoining Consideration should be given to a combination of cells thus preventing contamination of surface water the factors discussed under phasing'and from collected in cells prior to waste emplacement. constraints on vehicular maneuvering.Cells within Alternatively it may be possible to form the bund a phase are separated by intercell bunds which are using the mineral sub-base and to lay the flexible discussed in section 3.6.Minimising the cell size membrane liner over same. facilitates the landfilling operation through reducing leachate generation,minimising the area of exposed waste thereby reducing cover requirements,and assisting in the control of windblown litter.For each cell the designer should indicate estimated void space volume,active lifespan,and development sequence
3.4 PHASING The landfill should be developed in a series of phases. Phasing should allow progressive use of the landfill area so that construction, operation (filling) and restoration can occur simultaneously in different parts of the site. To avoid frequent (and disruptive) preparatory works it is recommended that the design lifespan of a phase be a minimum of 12 months. Factors that need to be considered in determining the phasing are; waste intake which will determine the size and lifespan of the phase and the sequence of operation which must take into account the following: • progressive construction, filling and restoration; • forward planning to, in so far as possible ensure that subsequent phases are developed in the appropriate season; • maximise use of on site materials and minimise double handling of material; • installation of leachate and gas controls; • management of the leachate collection system; and • management of surface water run off. A recommended phasing sequence is illustrated in Figure 3.2. 3.5 CELLS Cells are sub-divisions of phases. The number of cells in a phase and cell size should be based on water balance calculations (Section 7.2.1). Consideration should be given to a combination of the factors discussed under ‘phasing’ and from constraints on vehicular maneuvering. Cells within a phase are separated by intercell bunds which are discussed in section 3.6. Minimising the cell size facilitates the landfilling operation through reducing leachate generation, minimising the area of exposed waste thereby reducing cover requirements, and assisting in the control of windblown litter. For each cell the designer should indicate estimated void space volume, active lifespan, and development sequence. 3.6 BUNDING Bunds are generally used in landfill development for: • perimeter screening; • temporary screening; and • boundary bunds - intercell bunds and phase boundaries. Perimeter bunds are used for screening and to assist in the restriction of unauthorised access to the site. Their design should be consistent with existing topography. The height of the perimeter screen can vary from 2m to a height that screens the proposed development. Embankment slopes should be stable. Temporary bunds can be used around the operational area for further screening and to assist in control of nuisances such as litter and noise. As the landfill development progresses the temporary bunding arrangement is moved along concurrently. Temporary bunds are generally around 2m height with side slopes of 1:2.5. These bunds may also act as a storage area for final/intermediate cover material. Boundary bunds may be divisions between cells, within a phase, or separators between phases. Consideration needs to be given to the relationship between the bund, base liner and leachate collection system. Generally a bund of approximately 2m height located on the base of the facility will be used. It is normal practice for the primary liner to continue under the intercell bunding. Where a flexible membrane liner is used, a sacrificial layer can be placed over the bunds and then connected to the underlying liner. This provides a barrier between cells and prevents seepage of leachate into adjoining cells thus preventing contamination of surface water collected in cells prior to waste emplacement. Alternatively it may be possible to form the bund using the mineral sub-base and to lay the flexible membrane liner over same. 7 3 SITE DEVELOPMENT
8 LANDFILL MANUALS FIGURE 3.2:PHASING OF A LANDFILL DEVELOPMENT Filled Area Filled Area Working Cell Working Cell i IV Haul Road Lining works Lining works under way VI VI under way Phase I in operation Phase II in operation Phases I,II,III &IV restored Soil Storage Phases I&Ⅱ restored Phase V subject to temporary capping Working Cell Phase III subject to temporary capping Lining works under way Phase IV in operation Phase VI in operation
FIGURE 3.2: PHASING OF A LANDFILL DEVELOPMENT 8 LANDFILL MANUALS
9 3SITE DEVELOPMENT 3.7 COVER MATERIAL 3.8 LANDSCAPING Cover material is an essential element of landfilling The landfill should present a clean and well managed operations.In this section only that material for appearance to the public.Provision of a buffer zone daily or intermediate cover is discussed.The with landscaped berms and other tree planting may capping system is discussed in Chapter 10.The lessen the environmental impact.The development daily/intermediate cover material assists in control of sequence should allow for early screening of the nuisances such as windblown litter,odour,vermin, landfill and this may warrant construction and flies and birds. planting of screening bunds around the landfill perimeter at the beginning of the project. Daily cover (about 150mm if soil cover used)is the term used to describe material spread over deposited The designer should take into account the proposed waste at the end of every working day.Daily cover end use of the site after completion as this to some should ideally be permeable to allow water to pass degree will dictate the final landform.This final through thereby preventing ponding/perched water landform should fit in with the surrounding buildup.Intermediate cover refers to placement of environment. material(minimum 300mm if soil used)for a period of time prior to restoration or prior to further Further guidance on site closure and restoration is disposal of waste.Intermediate cover should provided in the Agency's manual on 'Landfill significantly reduce rainfall infiltration. Restoration and Aftercare' Details of cover material requirements should be provided under the heading of 'materials requirement and balance'as outlined in Section 3.3. The availability of on site material should be determined from investigations.The designer should identify borrow pit sources and stockpiling arrangement for cover material on site if required. The designer should consider the use of alternative biodegradable materials for daily cover.These include: heavy duty reusable and biodegradable sheets; non reusable plastic films; geotextiles; 。foams and sprays; shredded wood/green grass;and compost. Advantages of using alternative daily cover over traditional methods may include: preservation of void space; preservation of soil material: ·biodegradable,:and permeable to water and gas
3.7 COVER MATERIAL Cover material is an essential element of landfilling operations. In this section only that material for daily or intermediate cover is discussed. The capping system is discussed in Chapter 10. The daily/intermediate cover material assists in control of nuisances such as windblown litter, odour, vermin, flies and birds. Daily cover (about 150mm if soil cover used) is the term used to describe material spread over deposited waste at the end of every working day. Daily cover should ideally be permeable to allow water to pass through thereby preventing ponding/perched water buildup. Intermediate cover refers to placement of material (minimum 300mm if soil used) for a period of time prior to restoration or prior to further disposal of waste. Intermediate cover should significantly reduce rainfall infiltration. Details of cover material requirements should be provided under the heading of ‘materials requirement and balance’ as outlined in Section 3.3. The availability of on site material should be determined from investigations. The designer should identify borrow pit sources and stockpiling arrangement for cover material on site if required. The designer should consider the use of alternative biodegradable materials for daily cover. These include: • heavy duty reusable and biodegradable sheets; • non reusable plastic films; • geotextiles; • foams and sprays; • shredded wood/green grass; and • compost. Advantages of using alternative daily cover over traditional methods may include: • preservation of void space; • preservation of soil material; • biodegradable; and • permeable to water and gas. 3.8 LANDSCAPING The landfill should present a clean and well managed appearance to the public. Provision of a buffer zone with landscaped berms and other tree planting may lessen the environmental impact. The development sequence should allow for early screening of the landfill and this may warrant construction and planting of screening bunds around the landfill perimeter at the beginning of the project. The designer should take into account the proposed end use of the site after completion as this to some degree will dictate the final landform. This final landform should fit in with the surrounding environment. Further guidance on site closure and restoration is provided in the Agency’s manual on ‘Landfill Restoration and Aftercare’. 9 3 SITE DEVELOPMENT