GROUNDWATER

Groundwater• What happens to precipitation once it

reaches the ground– infiltration– percolation

• Water filling pore space, cracks & crevices in rocks- Porosity

• Aquifer- Geologic unit that can store, transmit and yield appreciable amounts of water

Porosity and Permeability• Porosity

– % of rock or sediment that is open (void spaces)

– ability to hold water

• Permeability- ability to transmit water

Movement of ground water • Moves in response to differences in water

pressure & elevation

• Velocity influenced by– Slope of water table– Permeability

Aquifers• Geologic unit that can store, transmit

and yield appreciable amounts of water• Highly permeable & saturated with water

– Good aquifers

• Aquitards- impermeable• Unconfined aquifer

– open to atmosphere

• Confined aquifer– under pressure– artesian- flows w/o being pumped

Groundwater Movement• Darcy’s Law

– Q= KA (h1-h2)/(l)

– Where Q is discharge; A= BxW– K is hydraulic conductivity

– (h1-h2)/(l) is hydraulic gradient

Wells• Penetrate aquifer within the saturated

zone

• Water table rises and falls during seasons– Recharge

• Cone of depression– Drawdown

• Artesian well- no need to pump– Artesian aquifer

Cone of Depression

After pumping in a well stops, the water level slowly recovers its previous level and the cone of depression disappears

Springs and Streams

• Spring– Water table intersecting hillside

• Gaining stream= Effluent Stream

• Losing stream= Influent Stream

Springs and Streams

• Spring– Water table intersecting hillside

• Gaining stream= Effluent Stream

• Losing stream= Influent Stream

WTWT

Pollution of Ground Water• Pollutants

– Chemicals• Gasoline• Pesticides & herbicides• Fertilizers• Heavy metals

– Bacteria, viruses, parasites- Sewage– Acid mine drainage– Radioactive waste– Natural pollution

Balancing Withdrawal & Discharge

• Overpumping results in:– Falling water table– Ground subsidence

• Artificial recharge

Subsidence of landcaused by extraction of groundwater in theSan Juaquin Valley, CAThe land sank 9m or30 ft in 52 years

Effects of Groundwater Action

• Karst topography-Caves– Rock usually limestone– Dissolves by weakly acidic water

– rainwater pH 5.5 and carbonic acid from humus

– Dripstone- Speleothem• stalagtite • stalagmite

– Flowstone

– Sinkholes

GUILIN DISTRICT, CHINA

Hot Water Underground• Hot springs

– Near magma or cooling igneous rocks– Deep-circulating groundwater or

• Geyser• Precipitation of dissolved ions

– Travertine- calcite– Sinter- silica

• Mudpot

• Geothermal Energy

Hot Water Underground• Hot springs

– Near magma or cooling igneous rocks– Deep-circulating groundwater or

• Geyser• Precipitation of dissolved ions

– Travertine- calcite– Sinter- silica

• Mudpot

• Geothermal Energy