Waste Disposal/Contaminated Land

• Landfill Sites:

  • 85% Uk waste buried in over 4000 landfill sites; over 11oMt of waste buried each year + average waste per person 275kg
  • problems: noise, dust, odours, vermin, leachate, subsidence, methane gas and wind-blown litter
• • Inert Waste - construction and demolition materials.
  • Putrescible Waste - food, garden materials, paper and wood.
  • Special waste are items that are flammable, reactive, corrosive or toxic (+radioactive, medical and toxic industrial waste).
• Leachate (toxic liquid formed by rainwater percolating through landfill waste):

  • prior to 1980s, dealt with using 'dilute/disperse' technique where leachate allowed to escape into surrounding groundwater
  • contamination by leachates; many landfill sites are old/disused but built without impermeable liner at base + pollution is localised, eg. Drummond Moor Landfill, Scotland
  • landfills now designed so leachates contained in structure or collected for treatment and safe disposal (no contamination)
• • over 150 million tonnes of domestic/commercial/industrial waste goes into landfill each year (inert non-polluting and hazardous chemical wastes) + solid wastes are threat to groundwater quality from polluting leachates
• Landfill Sites:

  • Subsidence - buildings constructed on old landfills sites susceptible to subsidence + weight of building causes buried waste to subside/settle (first signs are cracks in exterior masonry).
  • Gas (CH4/CO2) - organic matter decomposed by anaerobic bacteria produces CH4/CO2; methane is flammable so needs to be vented out (may be burnt to generate heat/electricity).
• Leachate - solutions made by water percolating through landfill sites dissolving soluble chemicals (+carries bacteria from decay of food).

  • acidic leachates increase weathering of underlying rocks if they percolate + surrounding soils/groundwater at risk of contamination (forms lateral groundwater plume of pollution)
  • decomposition of vegetable matter produces CH4; if allowed to accumulate, danger of spontaneous combustion causing an explosion (pipes laid through material to collect methane)
• Choosing Landfill Sites:

  • Holes in ground - best to have impermeable rock (low porosity, fine-grained, well cemented, poorly sorted and angular) + few bedding planes/widely spaced joints + no faults/dip of beds.
  • Artificial holes in ground - manufactured by building retaining barriers around undulating site.
  • Improving geological conditions - impervious materials lining (clay/plastic) + grouting floors/sides (holes drills then filled in with cement; fills joints/pores) + cover tipped materials with inert material or impermeable layer (prevents downward percolation).
• • potential new landfill sites; abandoned quarries or sand, gravel, brick and clay pits + within short drive of urban area (<20km)
  • eg. Broadpath Landfill Site, Devon; close to A38 between Tiverton and Wellington + old sand/gravel workings
  • problems occur when underlying rocks are permeable (+ if joints, bedding planes, faults and water table close to surface)
• Landfill Site Construction:

  • Liners; impermeable base/liner needed to prevent toxic leachates leaving landfill; types are clay, composite, and Plastic High Density Polyethylene (HDPE).
  • Caps; when full, sealed with impermeable cap designed to keep rainwater out limiting leachate creation.
  • eg. modern landfill; synthetic membrane liner 2.5mm thick on layer of low permeability clay + leachate/methane removed through pipes + impermeable clay cap limits water/slows decay.
• Amelioration - the act of making something better (improvement).
• • 'Dilute and Disperse' Method: potentially hazardous waste dumped in permeable areas so it is gradually carried into the water table where they are continually diluted by groundwater; at surface, the pollution is dilute so deemed 'safe'.
  • 'Concentrate and Contain' Method: potentially hazardous waste placed in impermeable areas (or lined with impermeable clay/plastic membranes) where leakage to aquifers is limited + waste monitored and 'diluted' by less toxic waste + leachate removed for treatment.
• • old sandstone/limestone/igneous quarries suitable only for low risk waste due to high permeabilities (unless lined)
  • essential to monitor hydrogeology; abandoned quarries checked for rock permeability/groundwater flow to detect leakage
  • sites designed for different types of waste (low-high toxicity waste) then methods of confining waste/leakage determined
• Risk from Radioactive Waste Disposal:

  • small amounts of very low level radioactive waste have been disposed of in landfills + most low level waste deposited in concrete vaults/trenches in boulder clay
  • intermediate level waste disposed at depth of 1 km in underground repository within impermeable rock (using barriers of concrete/steel to contain waste)
• Types of Radioactive Waste:

  • Low Level - discarded clothing/wrapping materials + 90% of radioactive waste + small risk
  • Intermediate Level - metal fuel cladding, reactor components and chemical sludges + 10% of radioactive waste + long lifespan of radioactive decay + shielded in deep/underground repositories
  • High Level - reprocessing nuclear fuel + 0.1% of waste but 95% of radioactivity + stored at surface in vitrified form until temperature drops allowing safe disposal (473,000m$^3$ by 2100)
• • Disposal of Radioactive Waste; physical containment (concrete/steel boxes or immobilised in cement grout in steel drums) + chemical barriers (alkaline conditions limit solubility of radionuclides and backfill absorbs radionuclides).
• • Long Term Disposal Solutions; storage under ice sheets, bottom of ocean or top of subduction zone + deep drilling needed for underground storage; safe for thousands of years in areas tectonically stable, with no hazards/access to water.
  • Best Rock Structure for Storage; competent/impervious/low water content; eg. deep seated/crystalline igneous or metamorphic rocks + volcanic rocks, crystalline basement rocks or salt mines.
• Nuclear Waste Services - brings together nuclear waste management capabilities; Low Level Waste Repository, Radioactive Waste Management, and Nuclear Decommissioning Authority (these are working together to clean up nuclear waste, working towards more sustainable/efficient disposal practices).
• Geological Disposal Facility (GDF):

  • long-term solution; keeps radioactive waste safe permamently + will protect future generations (waste remains sealed away deep underground whilst radioactivity decays) + based on natural processes (GDF uses secure engineered barriers working together with natural rock barrier to stop radioactivity reaching surface) + rocks stand test of time (rocks for GDF deeply buried/stable) + sites assessed for suitability for GDF beforehand ensuring long term safety
• • Contaminated Land - land where there is a serious threat or risk to health, flora and/or fauna; generally areas where the pollutant or harmful substance is man-made or put there by people.
  • Brownfield Site - land/premises that have previously been used or developed (may be vacant, derelict or contaminated).
• • small amounts of heavy metals, organic compounds (herbicides, pesticides, solvents and paints) or petroleum products (oil/tar) can be classified as contamination (on or beneath surface)
  • where land is contaminated, the potential impact on health, environment or development depends on; contaminating substance, their ability to migrate and potential future land use
• • legislation/regulations place responsibility for assessing extent of contaminated land with local authorities; increasingly, landowners/developers/builders involved in remediation of contaminated land regardless of intentions to redevelop
  • need to use more brownfield sites in UK to limit development on greenbelt/greenfield sites
• • most UK contaminated land is historical; due to industrial activity, innopropriate management of waste disposal, or spillage of raw material/sewage onto land or drainage systems
  • industrial activities causing contamination; chemical production, gasworks, sewage treatment, armament manufacture, mining spoil heaps, dockside industries, steelworks and petrol stations
  • contaminants; heavy metals (zinc, copper, lead and cadmium), tars, cyanides, oil products, arsenic and organophosphates
• • geology interacts with contaminants to increase/decrease risk + groundwater vulnerable (dependant on hydraulic/chemical properties of underlying rock/soil) + poorly managed application of sewage sludge/slurry effluent can pollute rural environment
  • most problems from historic lack of care of industrial/waste management (inadequate planning for future use); land may be reused with appropriate remediation when inadequate records of contamination kept (contamination only revealed later)
• Remediation/Reclamation Methods:

  • bioremediation (uses micro-organisms); microbes (bacteria /yeast) part of natural decomposition cycle + some contaminants useful sources of nutrients to micro-organisms; can digest or remove some highly toxic man-made (organic) contaminants
  • phytoremediation (removal of contaminants by biological treatment on size by planting particular species); infrequently used/limited technical application + some plants able to take up contaminating metals from soil/concentrate them in leaves/stems
• Remediation/Reclamation Methods:

  • soil remediation by chemical treatment; addition of chemicals in situ/or at chemical plant + solidification/stabilisation by adding minerals to soil to 'fix' contaminants
  • groundwater remediation; pumping groundwater through specialist water treatment system then returing treated water into ground/putting it into drainage system