STANDORT HÖXTER FACHGEBIET ABFALLWIRTSCHAFT UND DEPONIETECHNIK

Appropriate Design and Operation of Sanitary Landfills

Hans-Günter Ramke, Höxter

Prepared for the

International Conference on Sustainable Economic Development and Sound Resource

Management in Central Asia

organised by the Tashkent State University, Tashkent, Uzbekistan and the Nottingham Trent University, United Kingdom

planned in Tashkent, Uzbekistan,

03-05 October 2001

Address of the Author

Professor Dr.-Ing. Hans-Günter Ramke

University of Applied Sciences Ostwestfalen-Lippe, Campus Hoexter An der Wilhelmshöhe 44, D-37671 Hoexter

Phone ++49/5271/687-130, e-mail hans-guenter.ramke@hs-owl.de

This publication can be cited as follows: RAMKE, H.-G., 2001: Appropriate Design and Operation of Sanitary Landfills in: Sustainable Economic Development and Sound Resource Management in Central Asia, Proceedings of an International Conference, planned October 2001 Tashkent State University, Tashkent, Uzbekistan and Nottingham Trent University, Nottingham, United Kingdom

APPROPRIATE DESIGN AND OPERATION OF SANITARY LANDFILLS

Hans-Günter Ramke University of Applied Sciences Hoexter, Germany

Abstract Landfills are an important element of waste management, but they can cause serious

environmental damages. Therefore an appropriate landfill design and operation is necessary. Starting with the general principles of landfilling, an overview of landfill

design is given, followed by a description of landfill operation, especially considering landfills for municipal solid waste. Finally some recommendations will be made for a

stepwise landfill improvement programme. Keywords: Sanitary Landfills, Landfill Technology, Landfill Design, Landfill Operation, Monitoring 1 Introduction In countries being in a period of economical and political transition with increasing incomes and increasing consumption waste management becomes an important task of urban development due to increasing waste generation. At the same time these countries receive the financial resources and the technology to improve waste management practice. This situation gives the opportunity to avoid some mistakes and to start “modern landfilling” on an appropriate level. Landfilling of wastes means the final and permanent disposal at a site without the intention to remove the waste in future. Landfills, often the main element of waste disposal, can cause serious environmental damages, especially groundwater pollution, and affect the surrounding communities. Therefore every landfill needs appropriate design and operation to reduce negative impacts on the environment. The following consideration do not recommend a simple transfer of design and operation standards used in the European Union to countries in Central Asia, but they intend to declare some general principles of landfilling. These principles might be helpful to develop the necessary standards in the different regions of Central Asia. Most of the topics mentioned in this paper are valid for each type of landfill, including landfills for hazardous waste, but standards of design and landfill operation described here are mainly focussed on landfills for municipal solid waste.

2 General Principles of Sanitary Landfilling 2.1 Waste Management and Sanitary Landfilling Landfilling is an important but not the only task in the scope of activities of waste management. Municipal waste management includes the tasks

- waste collection and transportation - recycling of organic waste and recyclable materials - pre-treatment of waste - disposal (landfilling)

Table 1 shows an example of a fully integrated waste management concept, typical for many medium sized towns in Western Europe. This scheme follows the line

- to avoid waste wherever it is possible - to establish effective recycling systems - to treat waste before disposal - to ensure a long-term non-environmental polluting waste disposal

Table 1: Scheme of Municipal Waste Management

Table 1 furthermore shows that successful waste management has to consider the different types of waste. Each “waste stream” requires special collection, treatment and marketing or disposal systems. Apart from such an advanced system waste management has to cover two main tasks in each municipality all over the world:

- waste collection (to keep the streets tidy) - and waste disposal

In countries with limited financial and technological resources landfilling is the appropriate method of waste disposal. Especially countries with a low population density and plenty of land available can use landfill technology for many years as the base of their management strategy. Building on this base, a complete waste management concept, adapted to the regional conditions, can be established. Considering this important role of landfilling in the field of urban development the requirements on landfill technology shall be discussed

2.2 Environmental Risks of Landfills An operating landfill causes polluting emissions or other negative effects such as

- leachate - landfill gas - surface runoff - noise - wind-blown litter and dust - birds, vermin and insects

Many negative effects such as noise, wind-blown litter and dust or accumulations of birds, vermin and insects can be minimised by appropriate landfill operation, especially the runoff of contaminated surface water can be totally avoided. The most important emissions of a (well operated) landfill are leachate and landfill gas, and even a closed (and recultivated) landfill will cause leachate and landfill gas for a period of time. Leachate and landfill gas generation cannot be avoided, but the environment can be protected against pollution by liner systems, collection and treatment.

Figure 1: Developments in Gas and Leachate Composition in a Landfill (from [1])

Leachate and gas composition of landfills for municipal solid waste are a consequence of anaerobic microbiological degradation of organic substances. Figure 1 describes the idealised development of leachate and gas composition for a homogenous volume of waste. Five phases of degradation process can be distinguished (see [1]):

- Phase I This is a short aerobic phase immediately after landfilling the waste, where easily degradable

organic matter is aerobically decomposed during carbon dioxide generation. - Phase II A first intermediate anaerobic phase develops immediately after the aerobic phase. The activity

of the fermentative and also the acetogenic bacteria results in a rapid generation of volatile fatty acids, carbon dioxide and some hydrogen.

The acidic leachate may contain high concentrations of fatty acids, calcium, iron, heavy metals

and ammonia. The latter due to hydrolysis and fermentation of proteineous compounds in particular. The content of nitrogen in the gas is reduced due to the generation of carbon dioxide and hydrogen. The initial high content of sulphate may slowly be reduced as the redox potential drops. The generated sulphide may precipitate iron, manganese and heavy metals that were dissolved in the initial part of this phase.

- Phase III A second intermediate anaerobic phase will start with slow growth of methanogenic bacteria.

The methane concentration in the gas increases, while hydrogen, carbon dioxide and volatile fatty acid concentrations decrease. Also, the sulphate concentration decreases due to continued sulphate reduction. The conversion of the fatty acids results in a pH and alkalinity increase which results in a decreasing solubility of calcium, iron, manganese and heavy metals. The latter are supposedly precipitated as sulphides. Ammonia is still being released and is not converted in the anaerobic environment.

- Phase IV The methane phase is characterised by a fairly stable methane production rate resulting in a

methane concentration in the gas of 50-65% by volume. The high rate of methane formation maintains the low concentrations of volatile fatty acids and hydrogen.

- Phase V Where only the more refractory organic carbon remains in the landfilled waste, the methane

production rate will be so low that nitrogen will start appearing in the landfill gas again due to diffusion from the atmosphere. Aerobic zones and zones with redox potentials too high for methane formation will appear in the upper layers of the landfill.

The absolute concentration of leachate constituents and the quantity of landfill gas production depend on the composition of waste, waste pre-treatment and the type of landfill operation. Non pre-treated municipal waste with 30 % of organic waste disposed of on a landfill with rapid growth of height might lead to maximum COD-concentrations of about 20,000 mg/l and a specific gas generation of 200 m3/t waste (dry solid matter). This rough outline of degradation processes in a landfill demonstrates the necessity of technical and operational measures to prevent pollution of groundwater and atmosphere and to protect people from risk of explosion caused by landfill gas.

2.3 Multi-Barrier Concept The multi-barrier concept, developed in the eighties [2], illustrates the main principles of modern landfill technology and management. The following elements are considered to perform the role of barriers against pollution of the environment (see figure 2):

- the site (the geological barrier) - the bottom liner system - the landfill body (waste) - the surface liner system - the landfill operation - the controlled post-closure use of the landfill area - the long-term monitoring

Figure 2: Multi-Barrier Concept

Each of the barriers should fulfil its purpose independently from the others. The geological barrier – the site – is the main barrier against pollution of the environment – especially of groundwater and surface water – in the long-term. The technical barriers – bottom liner system and surface liner system – might have a limited life span, but they can be constructed in a way that emissions during the critical phases of landfill development can be prevented. The behaviour of landfill body can be influenced by pre-treatment of waste before dumping and by landfill operation. The objective should be to realise a landfill body with minimised degradation processes and a low potential of emissions. Landfill operation, controlled post-closure use and long-term monitoring are “non-hardware” barriers, but the importance of “landfill management” cannot be underestimated. Only embedding the technical measures into proper management systems can guarantee system’s long-term efficiency.

2.4 Overview of Standards of Landfilling in the European Union Directives and Guidelines existing in the European Union can only be transferred to other countries with adaptation to the climatic, geological, technical and financial conditions in the respective region. The existing guidelines might be helpful to set standards of landfilling under different conditions. Therefore some legislative and technical standards as well as some good sources of information concerning landfilling will be mentioned here. The European Union has passed a Directive on the Landfill of Waste [3], which will come into force in every member state of the European Union. According to this directive three categories of landfills could be distinguished:

Category 1: Landfill for inert waste (such as soil and debris) Category 2: Landfill for non-hazardous waste (such as municipal waste) Category 3: Landfill for hazardous waste

This principle of definition of different landfill categories is used by many states. The following wastes are not to be accepted in any kind of landfill:

- liquid waste - wastes which, under the conditions of the landfill, are explosive, oxidising or highly flammable - hospital or other clinical wastes which are infectious

The Directive defines general standards for landfilling (permit system, management, monitoring) and specific technical standards for each landfill category. In Germany there are two national guidelines (directives) dealing with requirements on landfills and on waste management principles:

- Technical Guidance for Hazardous Waste Management (TA Abfall) [4] - Technical Guidance for Municipal Solid Waste Management (TA Siedlungsabfall) [5]

Geotechnical aspects of landfilling are covered by the German Geotechnical Society:

- Technical Recommendations on Geotechnics of Landfill Design and Remedial Works [6] In detail the recommendations deal with the geotechnical aspects of on-site measurements, landfill design, construction and quality assurance. Finally two books can be recommended for more information about sanitary landfilling:

- Guidelines for an Appropriate Management of Sanitary Landfill Sites [7] - Sanitary Landfilling: Process, Technology and Environmental Impact [8]

The first provides many practical recommendations for countries at the beginning of modern waste management, the second helps to get an overview of the scientific background of landfill technology.

3 Design 3.1 Site Selection The most important task in the design phase of a landfill is the selection of the site of the landfill. Adequate site selection minimises risks of groundwater pollution and the negative effects on the surrounding areas. Site selection is a step by step process which can be subdivided into four main phases:

Phase 1: Exclusion of non suitable areas (negative mapping) Phase 2: Identification of suitable areas (positive mapping) Phase 3: Site investigation Phase 4: Final decision

At the beginning the whole area is investigated by means of a desk study. During the next phases increasing information decreases the number of sites to be evaluated. Criteria to eliminate sites absolutely unsuitable for landfilling, should be the following:

- existing or planned drinking water protection-areas and catchment-areas, flood areas - karst and areas with soil conditions allowing a fast permeation of water to the next aquifer - areas with an extreme morphology (steep slopes, danger of landslides, avalanches etc.) - areas with unstable ground such as swamps, moors or marshes - areas closer than 300 m to residential areas (500 m should be kept) - historical, religious or other important cultural or heritage sites - protection zones for legally protected natural objects or zones worth to be protected (such as national parks, areas with a large number of precious fauna and flora)

Criteria for the identification of potential suitable sites can be

- hydrogeological and geological conditions - geotechnical aspects - meteorological aspects - land-use and availability of land - distance to roads, sewage systems, electricity

After Identification of sites which generally fulfil the requirements an investigation of each potential site becomes necessary:

- investigation of hydrogeological and geological conditions - environmental impact assessment study - cost/benefit analysis

The final decision is founded on these investigations as well as on the economic and ecological comparison of the alternatives. This process, described in detail by [7], assures to identify the site with the most advantages and the fewest disadvantages in the project area.

3.2 General Landfill Design Landfill design has to consider site specific conditions, but many design elements of landfills (such as entrance area, temporary storage area, dumping area, internal roads) are identical. The entrance area consists of

- access road and main entrance - fence (wire fence or a “living fence”, an hedgerow) - scale bridge (for big landfills) - office and workshop/garage

It is recommended to define separate areas for temporary storage of special types of waste. The following wastes should be stored separately:

- green waste, biowaste (and perhaps an area for composting) - recyclable materials (container should be provided for paper, glass etc.), - special types of bulky waste (such as refrigerators or iron materials for separate recycling) - tires (for industrial recycling) - debris or construction waste (for maintenance of roads, dams, surface covering)

The dumping area, sealed by a bottom liner system, must have a minimum slope of 3 % to guarantee free drainage of leachate collected at the bottom. Details of the drainage system are described below. The dumping area is surrounded by an internal road for monitoring and maintenance purposes. Where it is necessary a surrounding ditch has to be excavated to discharge external surface water thus preventing it from flooding the disposal site. Finally leachate and landfill gas treatment plants are necessary, too. A cross section of a well operated landfill is given in figure 3. Main constructive elements to be considered during the operation are

- waste layers with a height of about 2 m - daily cover of the waste layers with non-cohesive soil (in case of low compaction) - surrounding dams at each top of the actual waste layer in operation - temporary cover of the embankment with a soil layer (for temporary recultivation) - cultivation of bushes and woods at the foot, as well as grass in the middle and at the top

Details of landfill construction are discussed in the chapter below.

Figure 3: Cross Section of a Well Operated Landfill

3.3 Bottom Liner Systems The bottom liner system has – together with the geological barrier – to protect soil, groundwater and surface water against pollution. The geological barrier – the landfill base – should consist of a natural mineral layer with low permeability (measured in k, the hydraulic conductivity) and sufficient thickness. The EC-Directive on the Landfill of Waste [3] defines the following requirements on the geological barrier:

- landfill for hazardous waste: k ≤ 1,0 · 10-9 m/s, thickness > 5m - landfill for non-hazardous waste: k ≤ 1,0 · 10-9 m/s, thickness > 1m - landfill for inert waste: k ≤ 1,0 · 10-7 m/s, thickness > 1m

The groundwater depth should be more than 1 m under the bottom of the landfill. In addition to the geological barrier a bottom liner system has to be installed. Figure 4 shows different bottom liner systems, partly following the requirements defined by German Technical Guidelines [4,5].

Figure 4: Bottom Liner Systems (Cross Sections)

The lining elements could be

- a mineral layer - a geomembrane - a composite liner - an asphalt liner

In many countries in Central Asia it might be economically difficult at present to meet the sophisticated Western European standards (especially composite liners), but in any case a bottom liner is a must for every landfill. An interesting alternative can be an asphalt liner, if experience in road construction with asphalt exists.

If the natural conditions (deposits of clay) are positive, the following recommendations for a low cost system (given by [7]) might be helpful:

- The first element is the geological barrier. (subsoil with a low permeability, k ≤ 10-7 m/s and a thickness of at least 3 – 5 m) - The second element is a two-layer mineral bottom liner. (each layer about 30 cm thick) - Local clayey material for the construction of the mineral liner should be used, if possible.

Therefore firstly the material for the top-layer of the mineral liner should be excavated and stored for future use.

- Secondly the natural soil at the surface has to be excavated (app. 30 cm deep, without roots) by

means of a grader to get a homogenous material. This material may be mixed with 2 – 3 % of bentonite for further reduction of its permeability , if necessary. The foundation liner material has to be compacted in-situ (Proctor-density DPR ≥ 95 %).

- Upon this “bottom layer” , now with homogenous density, a second mineral liner (“top layer”)

has to be constructed in the same way as the one below, using the stored material. - Each of the layers should have a thickness of 30 cm after compaction.

Figure 4 shows a cross section of such an adapted mineral liner system. More geotechnical advice is given by [6]. The recommendations describe in detail all the aspects of mineral liners. 3.4 Leachate Collection and Treatment Lining of landfill bottom requires a leachate collection system

- to collect leachate - to discharge it at defined points out of the dumping area - to avoid an accumulation of leachate at the bottom of the landfill

A leachate collection system basically consists of a drainage layer of inert material with a high permeability and of drain pipes which have to collect the leachate and to discharge it out of the dumping area. Some general design criteria shall be compiled here:

- drainage material: coarse material, without limestone, grain size ≥ 16 - 32 mm - drainage layer: height 30 cm - drain pipes: diameter 250 mm, made of PEHD - manholes: diameter 1,0 m

Mineral liners and geomembranes have to be protected against the coarse drainage material using geotextiles or sand layers. If geotextiles are too expensive local materials such as bamboo-mats or jute-mats are recommended. The (sandy) material for the protective layer over the geomembrane can be manually spread with baskets in case of missing earth construction machinery. The whole system of drain pipes, manholes and collection pipes have to be sealed to avoid intrusion of air into the system and emissions of gas. The pipe system must allow inspection and maintenance (e.g. flushing) at each point. Figure 5 demonstrates two different examples of design of leachate collection systems. Type 1 shows the standard system in flat areas, where the drainage layer, consisting of coarse material for long-term permeability, is placed on the roof-shaped landfill bottom with drain pipes at the deep points. The following design parameters are typical:

- cross slope: ≥ 3 % - longitudinal slope: ≥ 1 % - drain pipes spacing: ≤ 30 m

Figure 5: Leachate Collection Systems – Cross Sections

Figure 6: Leachate Collection Systems with Trenches of Split Gravel

If there is no coarse drainage material available in a region, type 2 might be an alternative. In this case a combination of a drainage layer, consisting of coarse sand/fine gravel, and split gravel trenches, placed at 15 to 20 m intervals, can improve the life span of the leachate collection system (see fig. 6). A more detailed overview of design and maintenance of leachate collection systems is given by [9], geotechnical details are described by [6]. The leachate collected at the bottom needs to be treated before discharging to the next surface water. The effluent quality depends on legislative standards, available technology and last but not least the special requirements of various surface waters. If a landfill is sited close to a municipal sewage treatment plant, a co-treatment of leachate and sewage might be possible. In case of using municipal sewage pipes leachate pre-treatment may be necessary to avoid smell caused by the high content of organics (especially volatile fatty acid) in the leachate. An appropriate method of minimum treatment is aerated lagooning, described for the purpose of simple leachate treatment by [7]:

- at the lower end of the landfill three ponds with a sealed bottom should be constructed - the first pond will serve as a settling pond - the second pond could get an artificial aeration (if possible) - the third pond would serve as a final settling pond with natural aeration

A first overview of leachate treatment is given in [8], including design parameters of aerated lagooning, a detailed description of biological and physicochemical treatment methods can be found e.g. in [10]. 3.5 Gas Collection and Treatment Large landfills and landfills with high landfill gas generation need an active gas collection system with gas wells/gas drains, gas ventilators and flares for gas collection and treatment. An adapted system - presenting minimum measures for gas collection - should consist of “gravel filled chimneys” (distance about 50 m), with a steel pipe at the top (length about 3 m, diameter 1 m). Landfill gas flows to these “gas wells” and can be collected by a collection pipe system at the top of the chimneys. The pipes will be torn and filled with gravel, when an actual working level is completed. The pipes should stay in the waste at a minimum depth of 1 m. Landfill gas collected can be utilised by combustion engines (production of electricity and heat), but must be flared in any case Apart from such a gas collection and treatment system some simple constructive measures can be recommended and should be considered if gas generation is not very high. Only an area of about 2 500 m2 should be used for disposal, while the rest is covered with a thin layer of soil. It should be avoided that landfills gas (and odouring substances) can emit into the atmosphere from the whole landfill. Where spots are discovered with intensive odour or gas migration it is recommended to cover these areas with a so called degassing window, working as a biofilter (passive system). In the covering soil a space of about 2.50 m length to 2.50 m width is excavated and filled with:

- coarse gravel/debris layer: 0.30 m - green waste, tree cut: 0.50 m - covered with ripe compost: 0.30 m

Degassing is concentrated to these spots and odour is reduced by the biofilter. Independently from the system selected the risk of explosions and human health or environmental damages has to be checked by measuring the methane and oxygen concentration.

3.6 Collection of Surface Water Collection of surface water can be subdivided into two different tasks:

- collection of surface water coming from outside the landfill (to prevent a flow into the dumping area) - collection of surface runoff from the dumping area

The intrusion of non-contaminated surface water (esp. surface runoff of rain water) can be prevented by means of surrounding dams and collecting ditches or intercepting drains. The non-contaminated surface water has to be discharged into the next receiving ditch. The collecting ditches must have a sufficient cross section, recommended is a depth at least 0.50 m, a bottom width of 0.50 m, and a width at top of 1.50 m. The ditches should be sealed with loamy or clayey soil. The inclination should not be less than 0.5 %. The system has to be maintained at least once a year. It is also recommended, to control the water quality once a year (chemical analysis). If there are no surrounding dams contaminated surface runoff from the landfill has to be collected in ditches and in intercepting drains. It is necessary to collect the contaminated runoff from the disposal areas in a special pond or tank for later treatment in a sewage treatment plant. 4 Landfill Operation 4.1 Introduction An adequately organised landfill site is necessary to ensure a long-term technical safety of waste disposal and to avoid relevant impacts on or damages to the environment. The organisation of a landfill has to cover the following topics:

- definition of waste admitted to disposal - entrance control on landfills for municipal solid waste - handling of special types of waste - biological pre-treatment of municipal solid waste - techniques of waste disposal - general improvement of landfill conditions - documentation and recording of landfill activities

All site specific regulations have to be compiled with in a "Basic Operation Manual". 4.2 Definition of Waste Admitted to Disposal For each landfill a list of wastes has to be defined giving information about the types of waste admitted to disposal. This list has to enclose

- the key number of the waste according to a unique waste classification system - a short description - characteristic parameters

In general on landfills for municipal solid waste household waste (delivered by waste management companies as well as by private persons), commercial waste (similar to household waste) and the non-hazardous waste, which is accepted by the local administration and the landfill operator, can be disposed of. The non-municipal waste, which is admitted to disposal, has to be defined and listed. In addition a list of industrial and hazardous wastes should exist, which names the waste not admitted to disposal on the municipal landfill site. The types of waste listed there should be in accordance with national or international waste classification waste systems.

4.3 Entrance Control The type of waste delivered has to correspond with the list of waste admitted to disposal. This list must be available on the landfill site and must be part of the operation manual. Delivered waste which is doubtful due to the yardmen should be unloaded on a paved small place near the entrance area for further check (sampling etc.). The waste should be checked at the entrance as well as at the dumping place (to detect hidden components). The landfill workers are to carry mirrors with long sticks and ladders (to check the open vans and containers), and walky-talkies for the communication between the entrance and the dumping place. If household waste is delivered by an approved waste management transportation company an entrance control is not normally necessary. At the entrance the waste is to register and to record. According to the EC-Directive on the Landfill of Waste the following reception procedures are to be respected by the operator:

- checking of the transport papers (company, vehicle, licence) in case of municipal waste and in

addition checking of the waste documentation in case of non-municipal waste - determination of weight or volume of the waste - check of the waste by its properties (odour, colour, consistency, components etc.) at the

entrance and at the point of deposit to verify the conformity with the description provided in the documentation of the waste generator

- keeping a register of the quantities and characteristics of waste deposited

4.4 Handling of Special Types of Waste The following recommendations are given for the handling of special types of waste on smaller landfills for municipal solid waste:

- Recyclable Materials Recyclable materials should be rejected from disposal, if there are any possibilities for their

recycling in the respective region. A separate area for temporary storage of recyclable materials and containers should be provided at the entrance area. The term “recyclable waste” includes separately delivered paper/plastic as well as green waste/biowaste, but also tires etc.

- Bulky Waste The disposal of specific types of bulky wastes (such as refrigerators or iron materials) should be

organised in a way that dumping on landfills is not necessary. - Debris or Construction Waste The disposal of debris or construction waste on municipal landfills should be reduced to a

minimum. Debris should only be accepted for maintenance of operation roads or for covering of dumping areas. If debris cannot be used as recycling material, special landfills for inert materials are to be established.

- Sludge The disposal of sewage sludge may cause problems. Often the contamination of the sludge has

as a consequence that the acceptance criteria are not fulfilled. In addition layers of spreaded sludge can cause problems for the stability of the landfill (risk of sliding etc.). A practical rule is that sludge should not exceed 10 % of the total weight of waste disposed of.

- Industrial Waste and other Non-Hazardous Waste of Non-Municipal Origin Industrial waste and non-hazardous waste of non-municipal origin (mining waste, slag etc.)

have to be rejected from disposal on municipal landfills. There is just one exception for the generator who has the allowance from the local administration and from the operator, which have to consider waste properties and landfill capacities.

- Hazardous Waste According to the definitions of the EC-Directive on the Landfill of Waste the disposal of

hazardous wastes is not to be allowed on municipal landfills (landfill category 2). 4.5 Biological Pre-Treatment of Municipal Solid Waste 4.5.1 Objectives of Pre-Treatment The main objectives of biological pre-treatment of municipal waste are

- increasing of compaction density - decreasing of emissions of the landfill (landfill gas, leachate)

On small landfills mainly used for the disposal of municipal waste, rotting of waste in windrows during a period of 6 to 9 month is to recommend. The compaction density will be increased after rotting while using the same compaction energy due to the destroying of the bearing structures during the rotting process. Landfill volume is more intensively used, and landfill operation becomes more economical because investment costs can be depreciated longer. During the process of biodegradation of waste in windrows under aerobic conditions (“composting phase”) most of the easily degradable organic substances are decomposed. After dumping and com-paction of pre-treated waste landfill gas production decreases. In many cases – especially for small landfills – a passive degassing is acceptable and no expensive gas collection systems are required. A further effect is the reduction of total leachate quantity. Higher density of compacted waste reduces the total area of a landfill or of the landfills in the respective region, and therefore leachate generation caused by precipitation is reduced. In addition leachate quality will be extremely improved by biological pre-treatment. The reason is that the methane phase of anaerobic decomposition (with low pollution of leachate) is much faster to achieve when the easily degradable substances are decomposed before dumping. 4.5.2 Description of Rotting-Procedure Figure 7 shows a cross section of a waste composting windrow. The household waste is piled up to windrows of 2 m height, which might be placed on the dumping area (on the waste compacted). The width of its base normally is about 30 to 60 m, the length depends on the area available. Before setting up the windrow (using a caterpillar loader) bulky waste and unsuitable fractions of the municipal waste have to be sorted out. At the base of the windrow (along width), perforated drain pipes are embedded horizontally (from both sides) and are connected to a vertical pipe reaching to the top in the centre of the windrow. This ventilation – working like a chimney – is recommended every 3 m. The system aerates the windrow because of the difference between the warm air temperature inside the windrow and the cooler air temperature outside. The circulation of air produces aerobic conditions and accelerates the aerobic decomposition of the organic fraction of household waste (including parts of paper etc.)

Figure 7: Pre-Treatment of Waste with Composting Windrows – Cross Section

During the rotting process the windrow must not become dry. In arid areas or during dry summer periods irrigation is recommended. For this purpose sewage and leachate can be used. After 6 to 9 month of “composting” the windrow is spread into 20 cm high layers and has to be well compacted. 4.6 Techniques of Waste Disposal 4.6.1 Theoretical Background Waste delivered to the landfill has to be disposed of in the dumping area and should be strongly compacted. Waste compaction has different objectives:

- saving of landfill volume by increasing the density of waste - reduction of the risk of fire by minimising the intrusion of air - less vermin spreading and less blowing of waste

Apart from these operational advantages waste compaction increases the economical benefits due to the longer life span of the landfill and the larger mass of waste dumped on the same area. The density which can be achieved depends on many different factors such as

- waste (material size, organic components, inert materials, sludge) - technique of disposal (thin layer operation, tipping edge operation, number of passes) - compaction engine (compactor or bulldozer, operating weight, wheel concept) - shape of the site (pit site or dump site, height of site) - weather conditions (precipitation, temperature)

Three different types of densities shall be defined:

- Compaction Density Density of the waste immediately after waste disposal and compaction, only influenced by the

kind of waste and the disposal technique

- Disposal Density Average density of waste in all depths of the landfill during landfill operation, influenced by

biochemical degradation, settlement, caused by static pressures and consolidation effects - Post Operation Density Final density of waste after operation, most of decomposition and consolidation

processes are nearly finished

Four different types of waste disposal techniques can be distinguished (see figure 8):

- thin layer operation - operation with extended tipping edge (downwards) - operation with extended tipping edge (upwards) - tipping edge operation only

The best disposal technique is the thin layer operation because of the highest possible compaction densities which can be achieved by this method. The unloaded waste is distributed by the compactor, crushed, compressed and then compacted by several passes. The compaction layers are varying between 30 and 50 cm in depth.

Figure 8: Techniques of Waste Disposal

The tipping edge operation leads to quite low compaction densities, because the influence of the compactor stresses sharply decreases after some decimetres. This kind of operation should only be used when bulky waste or sludge must be disposed of. Practical experiments showed that even when no compactor can be used, thin layer operation using a bulldozer is much more efficient than tipping edge operation. The compaction density which can be achieved with a compactor is furthermore a direct function of the number of passes, but also clearly influenced by the type of operation. A really satisfying compaction density is only to achieve with the thin layer operation. The advantage of high compaction densities is demonstrated by the following example: When the compaction density increases by about 0.2 t/m3 – relating to an initial value of 0.8 t/m3 - the necessary volume decreases by about 20 %. That means that the landfill can be used 20 % longer, considering equal delivery of waste during all the time. This demonstrates the necessity of good landfill practice including adequate procedures of waste compaction. According to these theoretical principles the following parameters have to be varied to optimise landfill operation:

- height of waste layers - number of passes - pre-separation of waste

In all cases thin layer operation should be used. 4.6.2 Practical Recommendations Compaction tests have been performed by the author in Poland on a landfill near Katowice [11], and these experiences might be transferable to the situation on many landfills in Central Asia. The following recommendations can be made:

- It is possible to increase the density of the dumped waste by compaction with a modern compactor from 0.70 t/m3 (without compaction) to about 1.20 t/m3(after compaction). The compaction density after compaction can be 70 % higher than the spreading density without compaction.

- Before compaction the waste has to be must to be spreaded in layers with heights of 30 cm or

50 cm and has to be compacted by at least 6 roller passes.

- The compaction density of 1.20 t/m3 can be achieved by a layer with a height of 30 cm and 6 to 10 roller passes.

- Spreading the waste with a height of 50 cm and compacting it by 6 to 10 roller passes will result

in a compaction density of about 1.00 t/m3.

- At present it is recommended to use a waste layer of 30 cm during the spreading, and to compact it by 6 roller passes at minimum and to try to make 10 roller passes.

- A rough economic calculation has proved that - even taking into consideration a very low level

of specific costs of landfill volume - the benefits by saving landfill volume are significant. - In addition the positive effects to the environment are evident. Beginning with the extended

period of landfill operation (about 50 - 70 %), going on with the improvement of landfill operation (smaller open dumping areas, better handling of bulky waste) up to minimisation of dust, litter and the risk of fire.

Furthermore the compaction tests clearly showed that on a small landfill the capacity of a modern compactor (with a weight of 28 t) cannot be used completely. The following recommendations can be made for a better use of a compactor:

- The capacity of a modern compactor is estimated to at least 350 t waste/day. If the amount of waste daily delivered is just about 30 t/day to 40 t/day, the compaction engine is used not much more than 10 %.

- A modern compactor has to be used on a couple of smaller landfills. The waste has to be stored

temporarily and than spread and compacted by the compactor. An adequate cycle depends on the operational demands and the transport capacities, but in general a shorter cycle is to prefer.

It is recommended to use a dumping area of about only 2 500 m2, while the other areas of the landfill are to be covered with a thin layer of soil. Depending on the amount of waste the dumping area can be moved every one or two weeks. Special types of waste should be treated on the landfill in the following ways:

- Bulky waste must be compacted very carefully to crush it intensively. Large pieces of metals must be removed before compaction.

- Tires, refrigerators and other large or non-compactable pieces must be removed before

compaction. - Very wet zones (water saturated) have to be avoided. They should be drained and stabilised

with debris before compaction. - When sludge is delivered, it must be spread horizontally in thin layers for dewatering purposes,

and than this layer has to be covered with a layer of household waste. Measures against odour are necessary (mixing with calcium or covering with soil).

It is recommended to record daily the location, height level and volume/type of waste, which actually is disposed of. A determination of these data is possible by using a measuring grid for example. When recording is performed properly, it is later possible to identify the place of waste dump when required (i.e. investigating potential contaminants). But beside that, recording is helpful in controlling and managing the landfill. 4.7 General Measures on Landfills The landfill operator has to take care for a proper appearance and image of the plant. With some simple measures the general condition of smaller landfills can be improved:

- Fencing off the landfill Each landfill should be enclosed by a fence to avoid non allowed access and illegal dumping of

waste. - Temporary pavement of internal access landfill roads The internal access landfill roads (construction roads) should be paved with debris, to improve

the access to the dumping areas. - Surrounding dams Surrounding dams are necessary for a proper definition of dumping areas and for a better (and

safe) operation of the compactor. Dams are helpful to minimise litter and pollution of the surrounding areas. They must be raised with the development of height of the dumped waste.

The following items have to be regarded within the daily landfill operation in order to ensure that the whole area is in an acceptable visual condition:

- measures are required to reduce the litter problem (i.e. by adequate fencing, collecting of paper in the surrounding areas). - adequate measures are required to reduce nuisance by birds and vermin (e.g. by fast compaction/daily cover of waste with non cohesive soil) - cleaning of paved roads and areas - maintenance of the surrounding dams, internal access roads and others - fast realisation of recultivation measures

These simple measures can help to increase peoples' acceptance of the landfill. 4.8 Recording and Documentation Recording and documentation are necessary to check:

- that waste has been accepted for disposal in accordance with the criteria defined - that the processes within the landfill proceed as desired - that the environmental protection systems are in working order - that the permit conditions for the landfill are fulfilled

A detailed recording is necessary as an evidence of compliance towards the controlling administration and to inform the people, living in the region. In a case of environmental impact it is possible to prove whether the impact is caused (or not caused) by emissions or by insufficient operation of the landfill site (according to the polluter pays principle). Recording starts with the documentation of the permanent conditions of landfill operation:

- documentation of the installed technical protection measures (fence, collection and treatment of surface water, measuring equipment) - documentation of the constructional measures during operation (covering of dumping areas,

surrounding dams, surface capping activities, recultivation) - responsible operator and controlling administration - situation of staff, working schedule - operating instructions (landfill and equipment) - updated emergency plans (fire protection, hospital etc.) - maintenance of equipment - laboratory, equipment and activities

Daily recording is necessary due to

- mass and cost balance - control of landfill operation - documentation of unexpected events.

The daily recording must enclose all activities (staff, machinery, expenses for fuel, maintenance of equipment, maintenance of landfill structure, other activities such as construction works etc.). All measurements concerning control of potential environmental emissions have to be recorded and documented as well. All records have to be kept until the landfill is closed and the phase of aftercare is finished. The data of the records are to evaluate, i.e. by diagrams, tables and maps.

5 Monitoring of Landfills 5.1 Objectives and Responsibilities Landfill monitoring has to cover the source of emissions (landfill body) and the environment as well. In order to assess the influence of a landfill on its environment monitoring activities should comprise

- meteorological data (if water balances shall be prepared) - leachate emissions (quality and quantity) - landfill gas emissions (quality) - groundwater and surface water monitoring. - data on landfill body (type of waste, height, volume etc.)

A clear definition of the responsibility for landfill monitoring is recommended. In many countries responsibilities for monitoring are divided between local, regional and national level:

- Local Level The self-monitoring principle should be installed for landfills, too. Especially in case of new

landfills the operators should be obliged to run a permanent monitoring programme, which should be supervised and amended by monitoring activities of the regional authorities.

- Regional Level The quality of the ambient environment of landfills should be monitored by the authorities at the

regional level. In addition the regional authorities should take the responsibility for monitoring of abandoned or smaller, old landfills operated by smaller municipalities. The regional authorities can take samples of groundwater and surface water (and perhaps

measure emissions of landfill gas), and analyse these samples in the environmental laboratories.

- National Level The main task at the national level is the establishment of conditions for landfill monitoring. If

national directives on landfill monitoring do not exist at present, the following improvement programme might be helpful (see [12]):

- definition of the responsibility for landfill monitoring - elaboration of monitoring guidelines - selection criteria for landfills which need to be observed - organisation of the reporting system - improvement of the hardware at the regional level (portable gas detectors, groundwater pumps, pH-meter etc.)

These proposals consider the personnel and financial capacities at the different levels of administration and can be implemented step by step. 5.2 Monitoring Practice During landfill operation the following parameters have to be measured:

- Meteorological Data The main objective of measuring meteorological data is the preparation of water balances of the

landfill. The necessary parameters, which have to be measured daily, are precipitation, average daily temperature and evapotranspiration. In general evapotranspiration has to be calculated by data such as humidity, solar radiation and temperature.

- Leachate Emissions Leachate is the main emission of the landfill. If a leachate collection system exists, periodical

measurements of leachate quality and quantity are necessary for design and operation of treatment plants. In addition leachate quality clearly shows the phase of degradation of a landfill.

Important parameters for quality control are pH-value, electrical conductivity, BOD (biological

oxygen demand), COD (chemical oxygen demand), TOC (total organic carbon) and the content of cations (e.g. Na, K, Ca, Fe and NH4

+) and anions (esp. Cl- and SO4--)

- Landfill Gas Emission (composition) Measurement of landfill gas is recommended to avoid explosions (dangerous range: 5 – 15 %

of methane in normal air), to design landfill gas collection systems and to calculate potential benefits of gas utilisation. The measurement must be representative for each section of the landfill.

Monitoring of landfill gas production inside the landfill can be done with probes, combined with

methane, carbon dioxide and oxygen detectors. If a landfill gas collection system exists, gas samples can be extracted from the system.

Landfill gas emission at the surface is measured with a FID (flame ionisation detector), which

can detect methane (hydrocarbons) down to a range of 1 ppm.

Figure 9: Impacts of Landfills on Groundwater (acc. to [8])

- Groundwater and Surface Water Monitoring. The measurement of groundwater must provide information on groundwater likely to be affected

by disposal of waste, with at least one measuring point in the groundwater inflow region and two measuring points in the outflow region. Figure 9 gives an example for the impact of a landfill on groundwater. Apart from groundwater sampling and analysing the hydrogeological situation has to be described, the direction of groundwater flow must be determined and the transport of contaminants in groundwater (if there are any) is to be assessed.

Monitoring of surface water (if present) shall be carried out at not less than two points in the

river, one upstream from the landfill and one downstream. Monitoring parameters are the same as in the case of leachate analyses. Some “target”

parameters can be used to identify the influence of waste disposals on groundwater (boron, NH4, SO4, chlorinated hydrocarbons).

- Data on Landfill Body (type of waste, height, volume etc.) Data on landfill body have to be collected by the entrance control (type and mass of waste

delivered) and by the landfill staff during operation. Table 2 shows recommendations on the frequency of sampling, given by the Annex III of the EC-Directive on the Landfill of Waste [3]. The Directive contains more details about frequency of sampling and gives additional advice on the parameters to be measured and the substances to be analysed.

Table 2: Landfill Monitoring – Frequency of Sampling (acc. to [3])

6 Strategies for Stepwise Improvement of Landfill Practice 6.1 General Strategy Improvement of landfilling starts on the national level with clear definitions of responsibilities and requirements on landfills and with activities for institutional strengthening:

- definition of responsibilities (for municipal waste management and for landfill construction and operation - elaboration of national directives on landfill of waste (design criteria and operation requirements) - training of experts on national, regional and local level (for construction, operation and monitoring) - financial support of landfill operators (buying of special equipment such as compactors)

The EU-Directive on the Landfill of Waste shows the topics, which should be covered by a national directive:

- definition of classes of landfills - definition of waste to be accepted in the different classes of landfill - installation of a permit system for landfill construction and operation - design of barrier-systems for the different landfill categories - landfill operation including waste acceptance procedures - landfill monitoring - closure and aftercare-procedures

This national directive is the base for the stepwise improvement of landfill practice. Starting at a low level, the directive may include time schedules for the realisation of various improvement measures. Landfills with low ecological risks which are important in a local or regional waste disposal concept should be improved, even when these landfills do not have a sufficient bottom liner system, but only when financial resources will not allow a closure of the old disposal sites and construction of new landfills. Landfills with high ecological risks or depleted volume have to be closed and recultivated. 6.2 Risk Assessment of Existing Landfills The environmental impact assessment of an existing landfill can be described as "Risk Assessment Study". At each step of a risk assessment study the questions on the existence of risks, necessary emergency actions and a sufficient level of information for the design of reclamation measures have to be answered. The standard phases of a risk assessment are:

- Phase 0: Registration - Phase 1: Historical Exploration - Phase 2: Screening Investigation - Phase 3: Detailed Investigation - Phase 4: Remediation Concept

The identification of environmental impacts starts with the registration of existing landfills and dump sites, a review of existing reports, information and topographical/geological maps (if available) as well as with a summary of the present knowledge about the site, landfill operation and environmental impacts, before on-site investigations are performed (if necessary).

The components of risk assessment must follow a multi-media approach and focus on human health, groundwater, surface water, soil and air. Necessary information needed for the assessment of the environmental impact is the affecting pollutants (mass, risk of emission, transport mechanisms and observed pollution) and the importance as well as the use of the affected media (esp. in the case of groundwater and surface water). The environmental risks should be assessed with site related criteria (such as distance to human settlements, agricultural land use) and applied to environmental standards (such as quality criteria for groundwater or air). The most important task is to assess the influence on the people, living in the surrounding areas. Furthermore the evaluation of the influence of the landfill on groundwater and surface water has to be given top priority. Following the results of such a regional risk assessment study, existing landfills can be divided into different categories to decide which landfills can operate in future, perhaps with improvement of operation and technical installations, and which landfills have to be closed to avoid further environmental damages. 6.3 Improvement of Existing Landfills In general landfill operation can be improved by a couple of easy implementable steps:

- Improvement of landfill operation and management The improvement of landfill operation begins with a clear definition of dumping areas and the

preparation of an entrance area. Furthermore a minimum control of waste delivery and recording of waste disposal is required. Landfill operation must be described by a site operation manual.

- Improvement of the techniques of waste disposal On larger landfills the use of a compactor is recommended to minimise dumping volume and to

avoid other problems caused by insufficient compaction such as litter and dust emissions. Smaller landfills can co-operate to use a compactor together, or can use a bulldozer for compaction. Thin layer operation is recommended in general.

- Aerobic pre-treatment of waste (composting) Due to the high content of organic waste a biological pre-treatment could help to minimise the

emissions of a landfill. Aerobic pre-treatment of waste using composting windrows is a low-cost solution, quite easily to perform, and will strongly reduce the emissions of a landfill (better leachate quality, reduction of landfill gas production).

- Installation of a gas collection system If landfill gas generation is at an significant level, a gas collection system should be installed.

On smaller landfills with low gas generation a compost filter should be enough, on larger landfills or on landfills with a high gas generation rate gas treatment with a flare is necessary. An on-site gas-utilisation (e.g. for the production of thermal or electrical energy) can be economic on large landfills in the vicinity of large cities.

Following this rough outline even the environmental effects of “ugly, smelly, risky” landfills can be reduced, and surrounding areas will be prevented from the worst effects of landfills.

6.4 Recultivation Measures and Surface Liner Systems When a landfill is to be closed it has to be embedded into the landscape. The tasks necessary to reduce future risks depend on the situation of the respective landfill. In case of a worse operated landfill with a high content of organic material, sited in an area with high precipitation, the following measures are to be taken:

- concentration of the solid waste and shaping of the landfill body - recultivation of the landfill by a surface cover with soil (incl. vegetation) - installation of a gas extraction system (with a flare) - installation of a surface runoff collection system

A surface cover with soil is the minimum standard of surface covering. A surface cover has to

- isolate the wastes from surface environment - provide long-term minimisation of leachate production - control venting of landfill gas

A complete surface liner system consists of the following elements (see figure 10)

- bearing layer (~ 30 cm thick, sandy material, suitable for gas drainage) - liner (different materials can be suitable) - drainage layer (≥ 20 cm thick, high permeability) - recultivation layer (≥ 75 cm thick, cohesive material) - vegetation (grass and bushes, depending on the region)

Figure 10: Surface Liner Systems (Cross Section)

The bearing layer is to compensate the inhomogeneity and unevenness of waste surface. In addition the bearing layer can be used for gas collection under the surface capping. The selection of liner materials depends on the availability of the necessary materials. If clay is available, a mineral liner system is recommended, in spite the fact that clay tends to get cracks caused by drying. The design of the mineral liner system has to consider the climatic conditions and the risk of drying. Under arid conditions the use of geomembranes can be useful. In case of hazardous waste landfills a composite liner system can be recommended. Figure 10 gives some examples of surface liner systems with different liner materials. The drainage layer has to collect the infiltrating precipitation. The layer material should be coarse sand or fine gravel. The slope should not be less than 5 % to minimise the hydraulic pressure on the liner. The recultivation layer is very important for long-term efficiency of the surface liner system. This top soil layer has the following functions:

- location for the vegetation - water storage for increasing of evapotranspiration - protection of the liners against roots and frost

The recultivation layer should be constructed of non-compacted cohesive soil with a high usable field capacity such as silt, sandy loam or loamy sand. The thickness of the recultivation layer depends on the climatic conditions, the requirements defined for the respective landfills and the vegetation. In general, under climatic conditions similar to Western Europe, a minimum thickness of 1.0 m is recommended. In case of a mineral liner the recultivation layer should have a thickness of 1.5 m. The vegetation is to increase the evapotranspiration, but plants with very deep roots (like trees) should not be used for recultivation. Otherwise, the roots might damage the liners. If the climatic conditions and the available soils are appropriate, the final vegetation should be a good stand of grass, completed by rows of bushes. More information on landfill recultivation are given by [6], [7] and [13]. 7 Conclusion Sanitary landfilling of waste is an important measure of waste disposal, and often the only one. Appropriate landfill design and operation has to consider the multi-barrier principle with different independent barriers of design and operation. Landfill design starts with the selection of a landfill site with suitable geological and hydrogeological conditions. The bottom liner system as well as the surface liner system are to isolate the waste from the environment. The lining systems integrate lining elements and drainage layers. In addition to the lining systems leachate and landfill gas collection as well as treatment is necessary. Landfill operation includes organisational and technical measures. Good landfill organisation starts with the definition of waste admitted to disposal, followed by an entrance control. Very important is an intensive waste compaction, which minimises environmental risks and saves landfill volume. Biological pre-treatment of waste reduces leachate pollution and landfill gas generation. Monitoring of landfill sites will allow to detect environmental damages early. In a period of transition from “waste dumping” to “modern landfill technology” the national authorities can support the regional and local authorities by elaboration of guidelines considering the regional conditions, as well as by training and hardware supply. Old dump sites should be closed step by step, following a risk assessment procedure to identify the most dangerous landfills. Closed landfills have to be recultivated. The surface of the landfill should finally be covered with soil, whereas a real surface liner system is the better solution. The “landfill experience” of the countries of the European Union might be helpful for Central Asia to develop regional standards for appropriate design and operation of sanitary landfills.

References [1]: Christensen, Th. H.; Kjeldsen, P., 1989: Basic Biochemical Processes in Landfills in: Christensen et al. (ed.), 1989: Sanitary Landfilling: Process, Technology and Environmental Impact, Academic Press, London [2]: Stief, K., 1989: Multi-Barrier Concept in West Germany in: Christensen et al. (ed.), 1989: Sanitary Landfilling: Process, Technology and Environmental Impact, Academic Press, London [3]: Council of the European Union, 1999: Council Directive on the Landfill of Waste Council Directive 1999/31/EC of 26 April 1999, Official Journal of the European Union, L 182 [4]: Federal Ministry for the Environment, Germany, 1991: Technical Guidance for Hazardous Waste Management (TA Abfall) [5]: Federal Ministry for the Environment, Germany, 1993: Technical Guidance for Municipal Solid Waste Management (TA Siedlungsabfall) [6]: German Geotechnical Society (ed.), 1993: Geotechnics of Landfill Design and Remedial Works Technical Recommendations GLR, edited for the International Society of Soil Mechanics and Foundation Engineering, Ernst & Sohn, Berlin [7]: Oeltzschner, H.; Mutz, D., 1996: Guidelines for an Appropriate Management of Sanitary Landfill Sites, Division Water, Waste Management and Protection of Natural Resources Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ), Eschborn [8]: Christensen, Th. H.; Cossu, R.; Stegmann, R. (ed.), 1989: Sanitary Landfilling: Process, Technology and Environmental Impact, Academic Press, London [9]: Ramke, H.-G., 1989: Leachate Collection Systems in: Christensen et al. (ed.), 1989: Sanitary Landfilling: Process, Technology and Environmental Impact, Academic Press, London [10]: Merten, M.; Meul, Ch.; Kollbach, J. St., 1998: Ist die Nachsorgephase vor dem Hintergrund der Sickerwasserreinigung und Deponiegasverwertung ein wirtschaftlich kalkulierbares Risiko? Enviro Consult, Aachen [11]: Ramke, H.-G.; Wewetzer, D., 1997: Final Report Task H: Landfill Improvement Pilot Project for Municipal Waste Management in the City of Katowice (EC/EPP/91/2.1.2) Association CES (Consulting Engineers Salzgitter, Germany) and OBREM (Poland) National Fund for Environmental Protection and Water Management, Republic of Poland [12]: Ramke, H.-G., Vosu, A.; Lehtla, R., 1996: Final Team Report: Sector Waste and Contaminated Sites, Master Plan for Pollution Monitoring and Enforcement in Estonia (EC-Phare Program) Association VKI (Denmark), SGS Ecocare (Belgium), CES (Germany) Ministry of the Environment, Tallinn, Estonia [13]: Ramke, H.-G.; Berger, K.; Stief, K. (ed.), 2000: Wasserhaushalt der Oberflächenabdichtungs- systeme von Deponien und Altlasten – Anwendung des HELP-Modells und Gestaltung der Rekultivierungsschicht, Fachtagung, Hamburg, Hamburger Bodenkundliche Arbeiten, Band 47 Institut für Bodenkunde, Universität Hamburg