6. Waste Options: Landfills Flashcards
Landfill definition
-waste management facility at which waste is disposed of by placing it on or in land
Land fills don’t include
- surface impound
- land treatment facility
- salt cavern
- disposal well
Dump
Place for the disposal of domestic waste
Sanitary Landfill
- Place for the disposal of refuse and other waste materials by burying it and covering it with soil
- engineer designed
- waste gets compacted
Alberta Landfill Regulatory bodies
- AEPEA
- WCR: States no hazardous waste will be disposed of in a landfill (except Class I can take hazardous solids)
Standards for Landfills in Alberta
-provide minimum requirements for the development, operation, monitoring, closure and post closure of landfills
Standards of Landfills applies to
- Disposal activities at new land fills
- New cell at existing landfills
- Lateral extensions at existing landfills
Purpose of Standards for Landfills
Provide assurance to the public regarding
- protection of ground water and surface water
- management of nuisances associated with landfills
Environmental Code of Practice for Landfills in Alberta
-Provides the minimum requirements for the construction, operation, and reclamation of landfills that accept < 10 000 tonnes of non-hazardous and inert waste per year
3 Types of Landfill Groups
- Municipal
- Industrial
- Oilfield
Municipal Landfill Classes
- Modified Sanitary Landfill
- Regional Sanitary Landfill
- Dry Waste Site
Modified Sanitary Landfill
- services <10,000 people
- municipal solid waste
Regional Sanitary Landfill
- services >10,000 people
- municipal solid waste
- generally in urban areas
Dry Waste site
- can’t be used for normal household waste
- takes demolition material
Industrial Landfill classes
Class I
Class II
Class III
Class I Industrial Landfill
-highest risk because accepts both solid and liquid hazardous waste except waste specifically excluded
-only landfill that accepts HW
=
Class II industrial landfills
- most common industrial landfill
- no HW
- high to medium risk
- can accept asbestos, paper mill waste, waste water treatment sludges, WH contaminated soils
- equivalent to municipal sanitary landfill
Class III Industrial Landfills
- inert
- low risk
- no HW
- no decomposable waste
- no liquids
- equivalent to municipal day landfill
Oilfield Landfill classes
- Class 1a
- Class 1b
- Class II
- Class III
Oilfield Class 1a
- accepts solid oil field waste (hazardous and non hazardous)
- have 2 liners of which at least 1 is a geosynthetic liner
- leak detection systems between the barriers
Oilfield Landfil class 1b
- accepts solid oil field waste (both hazardous and non hazardous)
- has 1 liner (either geosynthetic or compacted day liner)
- leachate detection system
Oilfield waste class II
- accepts only nonhazardous solid oil field waste
- has one liner
- has a leachate collection system
Oilfield Landfill class III
- accepts only nonhazardous, inert and non leachable solid oil field waste
- inert waste
3 major issues with Landfill siting
- Political/Social
- Economic
- Environmental/Technical
Political/Social issues with Landfill Siting
- NIMBY
- consider future use: golf course, parkland, recreational park
- must make process transparent and involve community from start
Economic issue with landfill siting
- Site Capacity (Volume)
- want 25+ years operational life
- Accessibility
- don’t want too long transport distances –> $
- don’t want in residential areas
Environmental/Technical concerns with landfill citing
- landfill shouldnt be in contact with surface or ground water
- must consider geology
- can’t put in a ravine, gully or coulee
- not located w/in 300m natural areas that permanently contain water
- not w/in 300m of manmade surface features that permanently contain water
- underlying soil and rock types (want to avoid high permeability areas
Potential Problems with landfills
- fires/explosions
- leachate
- odors
- windblown debris
- pests
Fire/Explosion risk of landfills
- biggest problem
- due to methane being produced from decomposition of the garbage
- daily cover to prevent too much CH4 mixing with the air
- spark from machinery operating at the landfill
- gas recovery systems (waste to energy initiative)
Leachate problems
- defined as a liquid which has been in contact with waste in the landfill cell and has undergone chemical and physical changes
- sources include precipitation, decomposition of garbage and compostable materials and from waste itself
Odor problem
-controlled with daily cover
Windblown debris problem
- use daily covers
- nets
- if waste leaves landfill, landfill is responsible for the cleanup
Pests problem
- use daily cover and waste compaction
- pests are disease vectors and include rats and sea gulls
- can’t build a landfill within 1.5 km of an airport owing to sea gulls
Migration routes for contaminants in a landfill
- solution into groundwater
- soil retention
- volatilization
- overland runoff
- plants
Ground water migration route for contaminants
-soluble materials readily dissolve into leachate which can then enter ground water
Soil retention migration route for contaminants
-mainly occurs with heavy metals such as Pb, Fe, Cr
Volatilization migration route for contaminants
- contamination of air
- eg. CH4, CO2, NH4, H2S
Overland Runoff migration route for contaminants
- flooding
- can enter surface bodies of H2O
Plants migration route for contaminants
- plants growing in landfill areas may take up heavy metals and other toxic materials
- if eaten by animals it goes up higher in food chain
Landfills clasified based on:
what type of area is being filled by the waste
- Area fill
- Trench fill
Area Fill
- AKA Depression fill
- fill a topographically low area with waste (not allowed in Alberta)
Trench Fill
- Used in topographically flat or rolling areas
- dig a trench, fill with waste
- cells are the basic building blocks of a trench fill
- average size 200m x 150m x 15m
5 basic design components of a sanitary landfill
- Liners
- Leachate Collection systems
- caps and covers
- Gas extraction systems
5, Groundwater monitoring wells
The Containment systems is designed to:
- Minimize the amount of leachate formed
- Prevent the migration of leachate offsite
- Remove landfill gases before they become a fire or explosion hazard
Purpose of a Liner in a landfill
- Prevent migration of leachate out of a landfill’s cells and into the surrounding soil which could result in surface and groundwater contamination
- Prevent groundwater from entering the cells
Location of a liner
is along the base and sides of the landfill
Materials in Liners
Clay
Synthetic
PVC
HDPE
Clay Liners
- can either be native clays to the site or brought in
- must be at least 1 m thick if its the only liner used
- must be compacted to have a hydraulic conductivity of less than 10 ^ -9 m/s
- most widely used liner for landfills
Problems with Clay Liners
- Cracking
- Desiccation during construction (liner must be kept moist)
- Different clays will swell or shrink to different degrees which can cause cracking if different clays are mixed together
Synthetic Liners and 2 types of them
- also called geomembranes, geotextiles, FMLs (flexible membrane liners)
- PVC- Polyvinyl chloride
- HDPE- high density polyethylene
Problems with synthetic liners
Can have/get holes
- while placed on site with heavy equipment
- Manufacturer defect
- seams not properly “glued”
- puncture by waste
Combination Liners
Geosynthetic clay liners
-made of a thin layer of bentonite (swelling clay found to or fixed between 2 geosynthetic sheets)
Double Composite Liner
- consists of 2 composite liners
- Class I Industrial landfills (ie ones that can accept hazardous waste)
- waste -> LCS -> Synthetic liner -> Clay liner -> LCS -> Synthetic liner -> clay liner
Leachate Collection System (LCS) design
- perforated pipes placed in gravels (high Hydraulic cond.)
- sump pit and pump station removes collected leachate
- pipe is angled down to direct leachate flow
Leachate Collection System location
- below the waste but above the liners
- between liners in double composite liner
4 options for final disposal of leachate
- send to municipal waste water treatment plant
- Land application
- leachate recirculation
- chemical and physical treatment of leachate
Land application
-limit the number of applications that can be made to a land area due to heavy metal concentration in leachate
Leachate recirculation
- land fill treats its own leachate
- landfill acts like a bioreactor as you recycle leachate through it
- try to create optimum conditions for microbes to “work”
- not an option in Vancouver due to high volume of leachate generated due to climate
Chemical and Physical Treatment of Leachate
- chemical oxidation
- chemical precipitation
- reverse osmosis
- ammonia stripping
Purpose of a cap (cover)
To control the migration of
- moisture (limit precipitation entering as it will increase leachate volumes)
- gas (prevent it from exiting the landfill as it can create explosive hazards or odors)
Cap design
Alberta, as specified in the Standards for Landfills in Alberta requires 3 layer landfill
Bottom layer of cover
- .6m of barrier with a hydraulic conductivity less than 10^-7 m/s
- can only be clay or clay and geosynthetic liner
- prevents gas leaving and water entering
Middle layer of cap
- 0.35-0.8 m subsoil
- thickness dependent on the end use of the site after closer
Top layer of Cap
-.2m topsoil
Additional things to a cap
- establish vegetation
- slope for the final cover
- 5-30 degrees
- allows runoff precipitation so it doesn’t pool over waste making more leachate
Purpose of Gas Extraction Systems
- remove landfill gases before they become a fire explosion hazard
- decrease odors
- minimize subsurface gas migration
- allow waste to energy management systems to be developed
2 types of Gas Extraction Systems
- Active systems- act like a vacuum by creating negative or positive pressure in the landfill pulling the gas out
- Passive Systems- gas removed based on the pressure it creates naturally in the landfill as it is generated
Passive systems include
- Perimeter Interceptor Trenches
- Flaring
- Slurry Walls
Active Systems include
- perimeter gas extraction trenches
- perimeter gas extraction wells
Perimeter Gas Extraction Trenches
- perforated pipe is laid in trenches around the perimeter of the landfill and backfilled with gravel
- gases migrate laterally through landfill and pulled out by the negative pressure created by a suction blower
Perimeter Gas Extraction Wells
- vertical wells are placed outside the landfill perimeter
- wells are connected by a common header pipe through which the blower pulls the methane from the area of include around each well
Perimeter Interceptor Trenches
- gravel packed trench containing perforated pipe surrounding the landfill
- gases migrate laterally and are removed
- similar to gravel packed extraction trench but without a pump
Flaring
- most common method
- drill wells into landfill
- helps decrease lateral methane migration by decreasing pressure with the landfill itself
Slurry Walls
- dig a trench outside perimeter
- fill with an impermeable material (eg bentonite, clay, slurries)
- gases can’t get beyond walls so migrate to surface
Groundwater monitoring wells
- must be placed both up gradient and down gradient of the landfill
- no more than 200m apart
- down gradient = detect contaminant plumes
- up gradient= monitors background levels
Minimum Landfill Monitoring Plan
- ground water monitoring plan
- surface water monitoring plan
- leachate monitoring plan (if has a leachate collection system)
- subsurface landfill gas monitoring plan (if accepts organic waste)
Daily Landfilling Procedures
- waste is dumped at the base of the work face
- moved into place and compacted to reduce volume
- end of each day a layer of soil approx. 6” thick to minimize pests, odors, windblown garbage, fire risk
Lift
Single layer of waste in a cell
Intermediate Cover
- Layer of soil between lifts in a landfill
- typically 2 lifts/cell
- once the cell is filled a final cover placed on top
3 stages of Waste Decomposition in a Landfill
- Aerobic Decomposition
- Fermentation
- Methanogenesis
Aerobic Decomposition
- mainly with organic matter
- approx. 1 month
- proceeds till all oxygen used up
- very exothermic –> high potential for fire at this stage
Fermentation
- Anaerobic and acetogenic bacteria ferment and hydrolyse organic components to simpler more soluble compounds
- takes several years
- begins once oxygen has been depleted
- Produces acidic leachate (pH 5-6), high BOD (>10, 000 mg/L), Ammonium (500-1000mg/L)
- releases CO2
- heavy metals released as a result of acidic leachate
Methanogenesis
- associated with slow growing methanogenic bacteria (killed by oxygen, don’t like acidic conditions)
- methane can be recovered and used as energy source (waste - energy)
- highly explosive if not vented
- years to decades
- main gases CH4 (55%) and CO2 (40%)
4 phases of a landfill life
- Active Phase
- Closure Phase
- Post-closure phase
- Eternity Phase
Phase I: Active Phase
-Operational phase when waste is being collected at the landfill
Phase II Closure Phase
- Final Closure plan enacted
- Reclamation of the site
- final cover
- erosion control system
- restore surface water drainage systems
- necessary changes to any monitoring systems (grd water, leachate, gas)
- decommissioning of old buildings and facilities
Phase III Post Closure Phase
- Maintain integrity of final cover
- remediate any areas affect by subsidence and differential settling
- maintain reclamation systems
- minimum 25 years OR until
- grd water standards are met
- gas [ ] limits below explosive levels
- leachate [ ] below control limits
- leachate not naturally occuring aren’t detected
- volume of leachate collected is qual to or less than the previous year for 5 consecutive years
Phase IV Eternity phase
- end use of the site
- had to be determined when the landfill was being done
