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Groundwater Contamination and Monitoring Techniques

This article discusses the characteristics of aquifers in the UK, impacts of pumping water from aquifers, and different methods of monitoring and controlling groundwater contamination. It also highlights various techniques such as ground penetrating radar, electrical resistivity analysis, and soil-gas monitoring.

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Groundwater Contamination and Monitoring Techniques

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  1. Groundwater Water Table Recharge Saturated zone Groundwater Hydraulic Gradient • Pore spaces • Joints/fractures

  2. Aquifers Pore spaces unsaturated Groundwater Impermeable rock Pore spaces saturated

  3. What rocks in the UK make good aquifers? Sandstone 40% porosity 30% specific yield High permeability Clay 45% porosity 3% specific yield Low permeability

  4. Impacts of pumping water from aquifers

  5. Impacts of pumping water from aquifers Cone of Depression Drawdown Hydraulic Gradient

  6. 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)

  7. Contamination of aquifers • Industry • Chemical leaks • Chemical spills • Contamination from chemical storage • Waste Disposal • Leachates from landfill sites • Radioactive waste • Agriculture • Nitrates • Pesticides

  8. Contamination of aquifers borehole Chloride content (milligrams per litre) of leachate Monitoring Most expensive • 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) Cheapest

  9. Contamination of aquifers 1. Control • clay liner • synthetic liner • leachate collection total containment

  10. Contamination of aquifers Barrier to predicted depth of pollution 10 – 20m max 2. Control Pollution localised • build barriers to plume • trenches filled with concrete • hammered piles injected with cement grout

  11. Contamination of aquifers 3. Control • pump pollutant to surface for treatment/disposal

  12. Contamination of aquifers factory pollutant Bioreactive filter Impermeable wall to direct groundwater 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

  13. Key Terminology: Aquifer Confined aquifer Groundwater Water table Porosity Permeability Specific yield Hydraulic gradient Recharge Cone of depression Drawdown Contamination plume Ground penetrating radar Electrical resistivity Soil-gas monitoring Bioreactive barrier

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