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Groundwater Objectives I can describe that groundwater forms when water seeps into the ground, and can be stored in aquifers or come to the surface through springs. I can explain how porosity and permeability can affect the amount of groundwater in an area.
Groundwater Groundwater is the water found in layers of permeable rock or soil underground About 30% of Earth’s freshwater.
Getting Ground Water: • Pools of ground water build up when water from the surface seeps into the Earth. • It sinks lower until it hits a waterproof layer of rock. • To get this water—we dig wells and pump it up out of the ground.
Groundwater Zones The water table is the top of the water layer that fills in the pores of the soil or rock The layer of “dry” soil or rock above the water table is the unsaturated zone Everything below the water table and that is filled with water is the saturated zone Usually there is a layer of dry bedrock beneath the saturated zone.
Water Table Lab: Demonstration • Fill a beaker three-fourths full with the mixture of sand and gravel. • Pour water down the side of the beaker carefully until the water level is about halfway up the beaker. • Tie a piece of string around the beaker at the water table. Put the Water Table label on the string. • Put the Zone of Aeration and Saturation labels in the correct places on the side of the beaker. • Have the teacher check your beaker. Teacher initials: _______ • Draw the beaker, strings and labels and make observations.
Groundwater • The type of soil or rock in an area impacts the formation of groundwater. • Factors include: • Porosity • Permeability • Think about the difference between clay soil and sandy soil
Porosity and Permeability • Porosity- The ability of a substance to absorb liquid • If grains are tightly packed in a rock, it will have a low porosity • Permeable: substance that liquids can flow through easily (example=coffee filter or gravel) • Impermeable: a substance that liquids cannot flow easily through (example= glass, granite, or clay)
Permeable or Impermeable??? • Paper • Metal • Coffee Filter • Cotton Shirt • Bedrock (layer of solid rock) • Gravel • Clay
Question: How does permeability relate to the grain size of sediment? PERMEABILITY PREDICTION • Which sediment do you think will allow water to pass through most easily? • Which sediment do you think could hold the most water? • An aquifer is a rock layer that stores and allows the flow of groundwater. Compared to other types of rock layers, how permeable and porous would an aquifer be?
Question: How does permeability relate to the grain size of sediment? • Record the approximate amount of standing water you see just after you release 100 mL of water. Repeat the same procedure for the sand and silt. • Gravel: ___________ • Sand: ______________ • Silt: ______________ • Analyze: Based on your data, which is the most permeable sediment? _________________ • Draw conclusions: How is permeability related to the size of the grains that make up the sediment?
Question: How does porosity relate to the grain size of sediment? POROSITY PREDICTION • Which sediment do you think has can store the most water? __________________ • Explain your choice:
Calculating Porosity • Calculate: Find the amount of water that is stored within each sediment by subtracting the standing water volume from the original water volume (400 mL). Add this data to the table. • Calculate: To calculate the porosity percentage, divide the volume of water in the sediment by the sediment volume, and then multiply by 100. Add this data to the last row of the table.
Question: How does permeability relate to the grain size of sediment? • Analyze: Which is the most porous sediment? The least? • Draw conclusions: Compare the porosity number to the grain size of each sediment. • Does grain size determine the porosity of a sediment type? 3. Explain what you think controls a material’s porosity.