groundwater hydraulic gradient groundwater pore spaces joints/fractures water table recharge...

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)

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

Key Terminology:

1.Aquifer2.Confined aquifer3.Groundwater4.Water table5.Porosity6.Permeability7.Specific yield8.Hydraulic gradient9.Recharge10.Cone of depression11.Drawdown12.Contamination plume13.Ground penetrating radar14.Electrical resistivity15.Soil-gas monitoring16.Bioreactive barrier