4 LANDFILL
4.4 BOTTOM LINING CONSTRUCTION
4.4.1 Introduction
The selection of the appropriate type of liners is based on:
The type of waste to be disposed (municipal solid waste)
The availability of materials in the area
The hydrogeological conditions of the site.
The liners were selected upon the following requirements:
to keep the cells sealed from precipitation and surface water
to be resistant to temperature of at least 70oC
to seal the produced gas and leachate
to be resistant to any sedimentations and erosions
to be resistant to the effect of the microorganisms
to be easy to install
to be easy to check during both the construction and the operation
to be easy to mend
not to be of high expenditure
The lining system of the new landfill includes (from the bottom to the top):
Compacted Clay liner
Geomembrane
Geotextile
Sand layer
Drainage layer (or equivalent) 4.4.2 Compacted Clay liner
According to the legislation, the landfill base and the sideslopes will consist of a mineral layer, which satisfies permeability and thickness requirements with a combined effect in terms of protection of groundwater and surface water at least equivalent with k ≤ 1.0 x 10-9 m/s, thickness ≥ 1.0 m.
28| P a g e In case that the above conditions are not fulfilled in the natural situation, an artificial soil barrier shall be constructed. This barrier consists of clay-sized soil and shall have a thickness of at least 0.5 m thickness and a minimum coefficient of permeability of 10-9m/sec, as required by Kosovar regulation for non-hazardous waste landfilling. In any case the bottom of the barrier system should also have a minimum distance of 1m to the ground water table position if such water table found.
The permeability and thickness requirements are checked through the following equation:
s
where ΗCC = thickness of compacted clay liner (m) kCC = permeability of compacted clay liner (m/sec)
ΗNC = thickness of the natural clayey barrier up to groundwater surface (m) και kNC = permeability of the natural clayey barrier (m/sec).
If these conditions are not fulfilled in the natural situation, an artificial hydrogeological barrier shall be constructed. This barrier can consist of clay or another material with equivalent properties and shall have a thickness of at least 0,5 m thickness as required by Kosovar regulation.
The clay liner will be constructed as a compacted layer. To function as a liner, the clay must be kept moist. However, the following possible problems should be taken into consideration:
Clay liners are difficult to compact properly on a soft foundation (i.e. waste).
Compacted clay will tend to desiccate from above and/or below and crack unless protected adequately.
Differential settlement of underlying compressible waste will cause cracking in the compacted clay if tensile strains in the clay become excessive.
Compacted clay liners are difficult to repair if they are damaged.
Technical Specifications
A geological barrier constructed as a built-in compacted clay layer consists of minimum 0.50 m thick compacted clay layer with a permeability coefficient of less than k = 1.0 x 10-9 m/s.
The barrier may be constructed of clay or clayey soils excavated on the site or of suitable soils imported to the site from a borrow area not containing stones or rock fragments larger than 0.03 m.
No new layer may be installed over an installed clay layer before the latter has been checked and approved by the supervising authority.
29| P a g e All surfaces will be finalized at designed level for the base of the polymer membrane. The compaction shall be concluded using a smooth vibratory roller or equivalent plant, which ensures a smooth surface of the clay layer.
The filling works shall be performed in such a manner, that the base-materials is not unacceptably hydrated from rain or surface water or dehydrated from evaporation. In any areas where clay-materials are unacceptably hydrated or dehydrated or otherwise do not comply with requirements, the materials shall be replaced with suitable materials.
Visible stones or other particles larger than 0.10 m shall be removed from the surfaces during the works - if necessary manually.
Immediately upon inspection, check and acceptance of the finished surface the surface shall be covered by the polymer-membrane.
The minimum values f physical properties of clay material in order to achieve the permeability requirements, after the standard Proctor compaction are summarized in the following table:
Table 4-3: Clay liner specifications
Property Value
Liquid limit, LL (%) 20 - 40, preferred 25 - 30
Plasticity Index, PI (%) 10 - 25
Clay content (particle diameter < 0,074 mm) (%) > 30, preferred 40 - 50 Clay content (particle diameter < 2 μm ) (%) ≥20, preferred 20 - 25 Content of swelling clays (i.e. smectite, illite) (%) >10
Sand content (%) < 40
Organic content (% κ.β.) < 5
Carbonate content (% κ.β.) < 10
Max diameter of gravel or cluster (mm) 25 - 32
Prior to the clay liner construction, laboratory tests will be conducted to the clay material compacted at different moisture contents in order to define an acceptable zone of moisture and dry density complied to the permeability requirements, according to the following table.
Table 4-4: Clay liner material testing
Test Specification Frequency
Sieve analysis A.A.S.H. TO T-11 ASTM D 1140-71
ASTM D 422
1 out of 800 m3
Atterberg limits A.A.S.H. TO 89/60 A.A.S.H. TO 90/61
ASTM D 4318
1 out of 1,600 m3
Natural Water content 1 out of 800 m3
Organic content 1 in each borrow area
Compaction A.A.S.H. TO T 180
ASTM D 1557 1 out of 4,000 m3 or 1 in each borrow area Permeability ASTM D 5084 1 out of 4,000 m3 or 1 in
each borrow area
Triaxial test CUPP ASTM 2850-82
ASTM 4767-88 1 in each borrow area
30| P a g e In the case of the use of GCL, this is a mechanical and thermal welding geosynthetic consisting of a layer of natural sodium bentonite powder of 5,000g/m2 weight containing about 70% of montmorillonite. Bentonite is placed between two geotextiles:
Carrier layer: PP woven, weight of 200g/m2.
Cover layer: PP non-woven, weight of 300g/m2.
The total material weight is 5,500g/m2 and the tensile strength is 20KN/m (MD) and 11KN/m (CMD). The thickness of the material is 7mm in dry condition.
However, after hydration and depending on the salinity of the MSW leachate, the thickness increases giving a coefficient of permeability of 2x10-11 m/s.
GCL is anchored in the trenches covering one side of the trench.
The successive layers of GCL during placement are overlapped over a length of 150mm. For the sealing in the areas of overlapping, powder bentonite is used.
The liner material shall be delivered at the site with a quality certification from the producer.
Further the delivery shall be accompanied by a protocol with the results of the producers quality check for the specific batch delivered to the site.
4.4.3 Geosynthetic liner – polymer membrane
The polymer membrane type selected is HDPE, because it has a higher chemical resistance compared to the most of other types of polymer membranes. In addition, HDPE has physical properties that can generally withstand most pressures related to landfill. The thickness of the polymer membrane will be at least 2,5 mm. In general, the only disadvantage of polymer membranes is that they are subject to defects and pinholes during the construction stage, improper seaming and long-term durability concerns, especially in cases where polymer membrane is used as a single barrier. In our case, this disadvantage is minimized, because of the selection of a composite liner (clay liner and polymer membrane), instead of a single liner (either a clay liner or a membrane liner).
The material for the polymer liner shall be High Density Poly Ethylene (HDPE) with the technical specifications according to the EU standards and the relevant Romanian requirements.
Technical Specifications
The proposed HDPE membrane should be textured on both sides. The liner material shall be delivered at the site with a quality certification from the producer. Further the delivery shall be accompanied by a protocol with the results of the producers quality check for the specific batch delivered to the site.
The supplier shall deliver a testing certificate for all welding-seams performed before delivery on site. The membrane shall be protected against physical damages during transport to the site and during storage at the site.
31| P a g e Installation
General
The installer shall submit an installation plan showing the position of the individual rolls of material and deliver the plan to the Supervising Authority for approval before installation works commence.
Installation may only be done by technical staff approved by the producer of the liner material and with equipment approved by the same.
Welding
All welding-seams shall be double-seam welds with the possibility of testing with pressurized air, or extrusion welds with a spark-leader welded into the seam, enabling full testing of the tightness of the seams with high-voltage spark methods.
At the beginning and end of each day of installation, a welding test shall be performed by each combination of welding equipment and welder in work to ensure the correct adjustments of welding temperature, pressure and speed according to the prevailing weather conditions. The welding shall be tested for seam strength (peel and shear) and the results are reported to the Supervising Authority.
The welding test shall be repeated after any interruption of the installation works during the day, caused by e g. changes in weather conditions or equivalent.
Before welding, each lane of material shall be laid out without wrinkles, but with sufficient material and overlapping to ensure, that no significant problems arise during the welding due to temperature variations.
All edges of the liner material shall be protected against folding until the time of welding. The Contractor decides the method for protection and submits the description to the Supervising Authority for approval.
Overlapping shall be done with overlaps in the direction of the slope of the liner, i.e. roof-tile like.
The seam between the membrane at any near-horizontal areas and the membrane at a slope shall be positioned at the near-horizontal plane and no closer to the toe of the slope than 1.0 m.
No machinery of any kind is allowed to operate directly on top of the installed liner. At all times sufficient protection of the liner shall be ensured before any machinery is allowed to enter.
Sufficient protection can be e.g. min. 1.0 m of soil not containing stones larger than 0.1 m.
Covering
Until the membrane has been checked and approved, the liner material shall be anchored using sandbags or any other equivalent system ensuring, that the installed liner material is not moved by wind or down slope by gravity.
32| P a g e The Contractor shall cover the installed liner with geotextile immediately upon check and approval by the Supervising Authority. At slopes the drainage or cover material shall be installed starting from the toe of the slope taking any slack in the liner material to the top of the slope. At the top of the slope the liner shall be anchored in an anchoring trench after the drainage material / cover at the slopes has been installed.
Connections to future stages of the landfill
Where the polymer liner in the future shall be connected to coming stages of the landfill, the polymer liner shall be finalized with a loop of min. 1.0 m. i.e. the liner shall be folded back and welded in order to preserve a 1.0 m wide lane along the edge from damages and weathering. A soil cover of min 0.5 m shall protect the fold.
Check of liner material and installation
The check of the installation works shall be based on a check plan set up by the Contractor and approved by the Supervising Authority. The check plan shall describe who has the responsibility for performing each check, the extent of the check and when the check shall be performed. Further the plan shall indicate whether the works may proceed or shall wait pending the results of the tests and checks.
Table 4-5: Checks of lining material Stage Item Subject to
check Method Extent Acceptance
Delivery Liner material Datasheet Quality check 1 nos. per
roll Delivered
Reception Liner material Appearance Visual 1 nos. per
1,000 m2 No flaws or defects
Thickness Measurement 1 nos. per 1.000 m2
33| P a g e Stage Item Subject to
check Method Extent Acceptance
Prefabricated
(cut sample) Shear and peel cut sample min.
36 cm x 60 During cm
installation Liner material Appearance Visual 100% No flaws or
defects
seam, spark-testing 100% No leaks
Mechanical Stress and strain at break
(cut sample) Stress and strain at yield
4.4.4 Geotextile
Geotextiles are used for protection of the polymer liner against tear and wear during the installation works and against damages from particles in the drainage layer. The geotextile shall be a non-woven geotextile of UV-stable polypropylene, polyethylene or polyester capable of resisting exposure to the sun for minimum two years. The weight of the geotextile shall be ≥ 1,000 gr/m2. Installation
Simple overlapping with a width of min. 0.5 m shall connect lanes of installed geotextile.
Alternatively sewn connections may be used. Sewn connections shall have tensile strength equal to the tensile strength of the geotextile.
The geotextile shall be delivered at the site with a quality certification from the producer certifying the characteristics of the material according to the above specifications. Further the delivery shall
34| P a g e be accompanied by a protocol with the results of the producers quality check for the specific batch delivered to the site.
The geotextile shall be protected against physical damages during transport to the site and during storage at the site.
4.4.5 Sand layer
Sand layer is used, in addition to geotextile, for the protection of the polymer liner against tear and wear during the installation works and against damages from particles in the drainage layer.
The sand layer will consist of particles smaller than 0.08 m. The layer’s thickness will be at least 0.10m.
4.4.6 Drainage layer
The gravel layer will serve the purposes of a drainage layer. The thickness of the drainage layer will be 50 cm. Materials used for drainage layer shall be free-draining graded gravel without any content of clay- or silt. The content of organic material (CaCO3) shall be less than 20%. Crushed rock or stones shall not be used. The coefficient of permeability of the drainage material shall be larger than 10-3 m/s. The grain size distribution will be from 16 to 32 mm while maximum grain size is 32 mm.
In the case of use of geosynthetic drainage net, this is a prefabricated approximately 12mm thick drainage mat consisting of an extruded wave-shaped monofilament fixed to a layer of geotextile or installed between two layers of geotextile.
The geosynthetic drainage mat has a high capacity for transporting water in its own plane and the geotextile ensure a filtering function towards the surrounding materials (soil / waste).
The geosynthetic drainage mat shall have a transmissivity in its own plane at an overburden pressure of 200 kN/m2 corresponding to a 0.5 m gravel layer of permeability coefficient of k > 10-3 m/s.
Execution of the works
Before any installation of drainage materials on top of the polymer liner is commenced the Contractor shall set up a plan for the execution of the works to be approved by the Supervision Authority. The plan shall describe which plant and methodology the Contractor intends to utilize, ensuring that no damage is done to the liner system.
No equipment is allowed to enter on top of the polymer liner without adequate protection of the liner against mechanical damage. Protection can be ensured by:
permitting the trucks bringing drainage material in to the cells at all times drive on a "dike"
with a thickness no less than 1,0m between the wheels and the liner, or at protective plates of concrete or steel.
35| P a g e
permitting only vehicles and other machinery with belt-drive or low wheel pressure enter onto the installed drainage layer.
During installation works, it is not allowed to push the drainage using bulldozers or equivalent machinery that may cause tension in the polymer membrane. Drainage material shall be "rolled" or
"laid" out using e.g. excavation machinery on belts or equivalent.
When the drainage material has been installed excavations for e.g. installation of drainage pipes and filter material around the pipes may only be done manually, and all excavated trenches shall be visually inspected and approved by the Engineer before drain pipes are installed.
The installation of filter material around drain pipes shall ensure the designed dimensions of the filter material.
36| P a g e
4.5 LEACHATE MANAGEMENT
4.5.1 Leachate generation - composition
Leachate is produced in landfills, as water enters the waste volume, due to humidity, precipitation and/or rising groundwater level.
Leachate contains suspended solids, soluble waste components, soluble decomposition products and microbes. The most of leachate components have the potential to be toxic and could cause the death of river life, directly (through toxins and BOD5) or indirectly (via eutrophication). They can also contaminate drinking water. Therefore, under no circumstances should the leachate be discharged to surface and underground water. Besides, the legislation is very strict concerning this matter. The composition of the leachate produced in a landfill, depends on the type, composition and age of waste, the degree of compression in landfills, etc. A typical composition of the leachates produced from domestic waste landfills are given in the table below.
Table 4-6: Composition of produced leachates Parameter Concentration limits
Total Suspended Solids 200 – 1.000 500
Organic nitrogen 10 – 600 200
Ammonia nitrogen 10 – 800 200
Nitrates 5 – 40 25
Total phosphorus 1 – 70 30
Orthophosphoric 1 – 50 20
Alkalinity (CaCO3) 1.000 – 10.000 3.000
pH 5,3 – 8,5 6
Totalhardness(CaCO3) 300 – 10.000 3.500
Calcium 200 – 3.000 1.000 leachate, can ultimately cause more harm than good. Therefore, a collection and drainage system is essential, and is one of the most important stages in the construction of a landfill, as the lifetime of the isolation is largely dependent on this.
The principles of leachate collection system that rule the proposed design are:
The input amount of rainwater should be reduced as much as possible. Leachate collection system is designed in accordance with the surface water management, as the correlation
37| P a g e between them is strong. Trenches parallel with the footprint of the landfill will be developed in order to prohibit the runoff into the landfill’s body.
The collection and drainage system should ensure long-term collection of the total quantity of leachate and exclude any admixture with rainwater.
The system for leachate management should be chosen upon the following requirements:
not to cause damage, deformities or shifts in the isolation system during its placement
the pipes should be hydraulically efficient and should withstand chemical, industrial and physical burdens, not only during the phase of operation, but at the phase of the landfill aftercare, as well (50 years, 40oC, waste density: 1,5 Mg/m3)
free flow of leachate towards its collection tank should be enabled and leachate should be treated in a rather easy way
the hydraulic height of leachate should not exceed 50 cm above the geomembrane.
The selection of the most appropriate scheme should be based on the expected quantities of the produced leachate, which must be collected, removed and finally treated according to the suggested technique.
For the determination of the volume, the rate of production and the qualitative composition of leachate, the following information were required:
the climatic conditions of the region (height and distribution of precipitation. temperature)
the qualitative composition of waste
the way of the sanitary landfill operation
the age of layers
4.5.2 Leachate production
In this study, the quantity of leachate has been estimated for the following operation phases:
Cell A in operation (10 years operation)
Cell A filled
To estimate the leachate production, initially the evapotranspiration had to be determined. The evapotranspiration (ET) presents the sum of the real water losses through the evaporation of soil and mold and the transpiration of the flora. Dynamic (potential) evapotranspiration (ETP) presents the evapotranspiration that could have occurred, if there was an excess of moisture on the relevant surfaces. For the calculation of the hydrological balance, the dynamic evapotranspiration is used.
38| P a g e In this study, the determination of the potential evapotranspiration has been conducted using the
38| P a g e In this study, the determination of the potential evapotranspiration has been conducted using the