19 Designing a landfill
19.1 Bottom construction and Liners 19.2 Gas extraction
19.3 Biology of a landfill
19.4 Leachate production and collection 19.5 Covering
19.6 Redesigning a dumpsite into a sanitary landfill 19.7 Infrastructure around landfills
dump sanitary landfill
General
design a shape for the landfill that is acceptable to the
public (hide/keep distance)
“dry tomb”: limit impact by limiting transport of pollutants
(construct liners + cover waste)
think of future use after closure (recreational area)
be cost-effective (the higher the cheaper per ton)
capacity of at least 20 years General….
Component of landfill
Landfill gas
Leachate
Base liner Top cover
Ground water
19.1 Bottom Construction and Liners
a) function: to limit infiltration of leachate to subsoil b) materials must be chemically resistant to leachate c) subsoil settlements
d) stability of construction, subsoil and surrounding slopes e) distance to groundwater
f) availability of materials g) costs
h) experience in building
19.1 Bottom Construction and Liners
Guideline on base liner (NL, 1993)
1) waste must be 0.7 m above mean high groundwater level 2) settlements subsoil must be less then 0.25 m
3) construction depends on geohydrological situation and sensitivy of spreading of pollutants
Standard construction NL:
1) overall leakage <5 mm/yr with leakproof synthetic and mineral of <20 mm/yr
2) combination liner with a slope of 0.25%
3) 0.50 m drainage sand with drainage system
4) 2 mm HDPE (or equivalent) according to geomembrane guideline 5) 0.5 m sandbentonite mixture/ 0.5 m special clay/ 0.12 m trisoplast
19.1 Bottom Construction and Liners
Guideline on drainage and monitor systems (1993) 1) in drainage layer a leachate drain system is needed
2) HDPE-drains (min. diameter 110 mm, max. distance 15 m) 3) gravel around the drain
4) slope of 0.25%
gravel with leachate drain
Ground water monitoring seperating geotextile
19.1 Bottom Construction and Liners
19.1 Bottom Construction and Liners
19.2 Landfill gas management
functions: avoiding risk of explosions/fires/odour/leakage
• materials must be resistant to leachate
• collection of landfill gas by pipes (horizontal/vertical) • internal transport by pumping/pressure flow
• treatment depends on economy/environment
19.2 Landfill gas management
degradable
materials gas leachate
Aerobic organic CO2 low, but heavily polluted;
pH ~8
Hydrolytic large organic molecules small soluble molecules, like low fatty acids, sugars and amino acids
Acidogenic
(anaerobic)
low fatty acids, sugars and amino acids
CO2 and H2 high organic content, dominated by volatile fatty
acids, increased mobility of metals; low pH
Methanogenic
(anaerobic)
fatty acids CO2 and CH4 Organic content, low mobility of metals; pH ~7
19.3 Biology of a landfill; phases of degradation
19.3 Biology of a landfill
“a liquid that has passed through or emerged from solid waste and contains soluble, suspended, or miscible
materials removed from such waste”.
This implies that leachate is formed by any water that comes into contact with waste.
19.4 Leachate Production and Collection
LEACHATE
19.4 Leachate
The amount of leachate generated depends on: • climatic conditions
– precipitation
– ambient temperature • waste properties
– moisture content of waste
– unit weight, hydraulic conductivity, field capacity etc.
• operation practices – compaction effort • final cover design • age of landfill
Leachate Production
Prediction of leachate production
LPRE = P + S – E – SWASTE
LPOST = P – ET – R – SCOVER – SWASTE
• LPRE – pre-closure leachate volume
• LPOST – post-closure leachate volume
• P – precipitation
• S – pore squeeze liquid • E – evaporation
• ET – evapotranspiration • R– surface runoff
• ∆SCOVER – moisture storage in cover soil
S – moisture storage in waste
Leachate control measures
• Prevention of leachate formation
– accepting only limited amount of organic matter in waste – keeping working area of landfill limited
– diverting surface water – leachate recirculation
• Leachate collection and removal • Leachate treatment
Functions of Leachate Collection System: • To remove leachate out of the waste body
• Minimise the residence time of leachate being in contact with bottom liner
• Minimise the hydraulic head on the liner
1. Estimate amount of leachate
2. Estimate base grades and pipe spacing 3. Calculate drain layer hydraulic conductivity 4. Develop layout of leachate collection system 5. Select pipe material, size, thickness and
perforations
6. Size sumps, risers and transmission lines 7. Evaluate clogging potential and filtration
Design Process of Leachate Collection System
Failure of Leachate Collection System
• Clogging due to – type of waste – design failure
• Mechanical damage (crushing of pipes, change of slopes, damage of drainage layer) due to either
– careless operation practices – differential settling of subsoil
19.5 Landfill Covering
Functions: Control infiltration of rainfall into the waste
Control erosion of the surface
Provide durable surface drainage system
Control migration of gas and leachate
Support the planned after use
Maintain above while decomposition and
settlement continues
19.5 Landfill Covering
Covering Materials
Materials must be resistant to leachate waste settlements
Stability of construction (slopes) Availability of materials
Costs
Experience in building
Guideline on top cover (1991, NL)
1) vegetation layer (0.8 m to 1.0 m) 2) drainage layer (0.3 m)
3) combination liner (2 mm HDPE and 0.25 m sand-bentonite)
4) support layer (0.3 m) 5) slopes < 1:3 (H:V) 6) top with slopes > 3%
7) overall leakage <5 mm/yr with leakproof synthetic and mineral of <20 mm/yr
soil cover
Standard Design of Covering
19.6 Redesigning a Dumpsite into a Sanitary Landfill
19.6 Landfill redesigning
Dumpsites
EXISTING DISPOSAL SITES IN DELHI, INDIA
EXISTING DISPOSAL SITES IN DELHI, INDIA
What should we do?
Old Waste Dump + Cover
Waste Dump
Waste Dump
Old Waste Dump + Cover +Cut-off Wall
Old Waste In New Landfill
Waste Dump
Well designed landfill (vertical expansion)
Old waste New waste
Closure and Vertical Expansion
Redesigning a Dumpsite into a Sanitary Landfill
Keep out leachate-producing rainwater by shaping into convex heaps, with diversion drain uphill and catch-drain on lower slope.
Redesigning a Dumpsite into a Sanitary Landfill
SANITARY LAND FILL SITE CONVERTED
SANITARY LAND FILL SITE CONVERTED
INTO PARK (DELHI)
INTO PARK (DELHI)
• road connection to public road
• storm water drainage (including retention ponds) • weigh bridge ( allowing to charge a gate fee per
ton)
• fencing (to limit windblown litter and access) • wheel washing
• hot load area (for waste on fire in trucks) • office and parking for personnel
• landfill gas and leachate treatment area
19.7 Infrastructure Around a Landfill
19.7 Infrastructure around a landfill
