WASTE DISPOSAL Types of Waste Inert wastes - no chemical or biological hazards Special (hazardous) wastes e.g. –ignitable, corrosive, reactive –Carcinogenic.

WASTE DISPOSAL

Types of Waste

Waste disposal routesLandfill Incineration Recycled Composted

UK 88 11 1 <1USA 70 30 <1Denmark 31 50 18 1

• Inert wastes - no chemical or biological hazards

• Special (hazardous) wastes e.g.– ignitable, corrosive, reactive – Carcinogenic or mutagenic (PCBs, medical waste,

radioactive waste, asbestos)– heavy metals, azides, acids/alkalis

Landfill Sites

Many old landfills are poorly designed and major environmental hazard. They are not designed for 50, 100 or 1000 years into the future

There are 4000 operational and 4000 closed landfill sites in the UK

Two types of landfill in the UK are • leach and disperse (old sites)• containment and treatment (new sites)

What Happens in a Landfill Site?

Rain water dissolves & reacts chemically & biologically with waste

Leachate

Landfill Gas

Leachate

• toxins kill aquatic life• eutrophication in rivers

• precipitates iron

• kills vegetation

• pathogens/bacteria

• non-hazardous materials can decompose into hazardous products

• serious groundwater pollution

Landfill Gas

methane

Landfill Gas

Loscoe, Derbyshire - 1986

Landfill Gas

Loscoe, Derbyshire - 1986

Possible Routes by Which Landfill Gas Can Migrate from a Site

Caves & natural cavities

Highly permeable strata

Fissured & fractured strata

Mine shafts

Gas vents Tree roots

Highly permeable strata

Underground services e.g. sewer pipes

Desiccation cracks in soil

Landfill Site Selection

Geology of Area• Porosity & permeability of rock

• Resistance to weathering

• Joints & fracture systems in rock

• Dip of rock strata (no dip or synform)

Hydrogeology of Area

• Rate of groundwater flow

• Gradient of groundwater flow

• Depth to water table

• Fluctuations of groundwater

Impermeable to contain leachate & landfill gas

Reduce groundwater contamination from leachate

Topography of Area

• Existing hole or steep sided quarry

• Free from disturbance (tectonic/subsidence)

A site capable of retaining waste

Groundwater

Hydraulic Gradient

Groundwater

• Pore spaces

• Joints/fractures

Water Table

Recharge

Saturated zone

Aquifers

Impermeable rock

Groundwater

Pore spaces unsaturated

Pore spaces saturated

What rocks in the UK make good aquifers?

Sandstone40% porosity

30% specific yield

High permeability

Clay

45% porosity

3% specific yield

Low permeability

Impacts of pumping water from aquifers

Impacts of pumping water from aquifers

Drawdown

Hydraulic Gradient

Cone of Depression

Impacts of pumping water from aquifers

Saline wedge

Control – reduce/stop abstraction, change pattern of abstraction ( winter not summer) or move borehole

Monitoring – chemical testing (boreholes/salinity testing)

two feet of compacted clay

strong, flexible, very thick plastic, called high density polythene (HDPE) known as a geomembrane.

one-foot layer of gravel with pipes running through it. The leachate collects in these pipes and is pumped out of the landfill and filtered.

very tough fabric, called a geotextile fabric, to protect the pipes.

top layer is about one foot of compacted soil to protect the entire liner system from the waste.

Each evening, large trucks roll over the landfill to crush the day's rubbish and then cover it with 15cm of soil so the waste doesn't smell or attract flies and rats.

When an area of the landfill is completely full, it is capped with clay and soil. This final landfill cover helps keep rainwater out of the waste and reduces the amount of leachate that forms.

Site Preparation

Modern Landfill Site

Site Management & Monitoring

• monitoring groundwater for chloride & ammonia in plumes

• monitoring unsaturated zone for gases

• venting of methane gas by boreholes• porous pipes to transfer leachate into sumps for collection & removal

Site Restoration

Uses

• Parkland

• Recreation

• Open spaces

• Greenbelt

• Low level industrial development

• Housing

Site Restoration

Trumps Farm is a former sand pit which was used by Surrey County Council for the disposal of household waste from the early 1980s until its closure in 1998.

The overall objective of the works is to reinstate the landfill to pasture and meadow, to a landscape typical of the area and create a variety of wildlife habitats.

Site Restoration

Problems

• Methane gas hazard – leakage through permeable rocks

• Ground instability on completion - subsidence

• Groundwater pollution

• Landfill site needs to remain accessible for over 25 years to manage & monitor

Agriculture

• Nitrates

• Pesticides

Industry

• Chemical leaks

• Chemical spills

• Contamination from chemical storage

Waste Disposal

• Leachates from landfill sites

• Radioactive waste

Contamination of aquifers

Contamination of aquifers

Chloride content (milligrams per litre) of leachate

Monitoring

• chemical testing of water from boreholes, springs, extraction wells• ground penetrating radar (remote sensing methods)

• electrical resistivity analysis (oil pollutants = high resistivity)

• soil gas chemical monitoring (organic pollutants give off a vapour such as methane)

borehole

Most expensive

Cheapest

Contamination of aquifers

1. Control

• clay liner

• synthetic liner

• leachate collection

total containment

Contamination of aquifers

2. Control

• build barriers to plume

• trenches filled with concrete

• hammered piles injected with cement grout

Barrier to predicted depth of pollution

Pollution localised

10 – 20m max

Contamination of aquifers

3. Control

• pump pollutant to surface for treatment/disposal

Contamination of aquifers

4. Control

• direct polluted groundwater into to bioreactive barrier

• bioreactive barrier use naturally occurring bacteria to breakdown the pollutant

• oxygen & nitrates injected into barrier to encourage decay processes

factory

pollutant

Impermeable wall to direct groundwater

Bioreactive filter

Non-hazardous

Waste Disposal

Landfill Sites

Factors Affecting Site

Selection

Site Management &

Monitoring

Site Preparation

What happens in a landfill site

PollutantsProblems of

LeachateProblems of Landfill Gas

Problems after site is restored

Hazardous Waste

What are hazardous waste materials?

What specific problems do they cause?

What factors need to be taken in to account with hazardous waste disposal?

What are the options for their disposal? (examples)

Possible Routes by Which Landfill Gas Can Migrate from a Site