Chapter 10 Section 2&3 Groundwater Weathering and Supply PDF

11/18/2024 Chapter 9 Section 2 & 3 How do caves form? 1  11/18/2024 What are the major problems that threaten groundwate...

11/18/2024 Chapter 9 Section 2 & 3 How do caves form? 1  11/18/2024 What are the major problems that threaten groundwater supplies? Carbonic Acid Most groundwater is slightly acidic due to carbonic acid. Carbonic acid forms when carbon dioxide gas dissolves in water and combines with water molecules. Copyright © McGraw-Hill Education Groundwater Weathering and Deposition 2  11/18/2024 Dissolution by Groundwater The process by which carbonic acid forms and dissolves calcite can be described by three simple chemical reactions. Copyright © McGraw-Hill Education Groundwater Weathering and Deposition Dissolution by Groundwater In the first reaction, carbon dioxide (CO2) and water (H2O) combine to form carbonic acid (H2CO3 ). In the second reaction, carbonic acid splits into hydrogen ions (H+) and bicarbonate ions (HCO3–). CO2 + H2O → H2CO3 H2CO3 → H+ + HCO3– Copyright © McGraw-Hill Education Groundwater Weathering and Deposition 3  11/18/2024 Dissolution by Groundwater In the third reaction, the hydrogen ions (H+) react with calcite (CaCO3) and form calcium ions (Ca2+) and bicarbonate ions (HCO3–). CaCO3 + H+ → Ca2+ + HCO3– Copyright © McGraw-Hill Education Groundwater Weathering and Deposition Dissolution by Groundwater The processes of dissolving, called dissolution, and precipitation of calcite both play a major role in the formation of limestone caves. Copyright © McGraw-Hill Education Groundwater Weathering and Deposition 4  11/18/2024 Dissolution by Groundwater Caves A natural underground opening with a connection to Earth’s surface is called a cave or cavern. As groundwater infiltrates the cracks and joints of limestone formations, it gradually dissolves the adjacent rock and enlarges these passages to form an interconnected network of openings. Copyright © McGraw-Hill Education Groundwater Weathering and Deposition Dissolution by Groundwater Karst topography Limestone regions that have sinkholes and disappearing streams are said to have karst topography. Copyright © McGraw-Hill Education Groundwater Weathering and Deposition 5  11/18/2024 Dissolution by Groundwater Karst topography A sinkhole is a depression in the ground caused by the collapse of a cave or by the direct dissolution of limestone by acidic water. Copyright © McGraw-Hill Education Groundwater Weathering and Deposition Dissolution by Groundwater Dripstones Dripstones are rock formations that are built over time as water drips through caves. Each drop of water hanging on the ceiling of a cave loses some carbon dioxide and precipitates some calcite. Copyright © McGraw-Hill Education Groundwater Weathering and Deposition 6  11/18/2024 Dissolution by Groundwater Dripstones A form of dripstone, called a stalactite, hangs from the cave’s ceiling like icicles and forms gradually. Copyright © McGraw-Hill Education Groundwater Weathering and Deposition Dissolution by Groundwater Dripstones As the water drips to the floor of the cave, it may also slowly build mound- shaped dripstones called stalagmites. Copyright © McGraw-Hill Education Groundwater Weathering and Deposition 7  11/18/2024 Wells Ordinary wells The simplest wells are those that are dug or drilled below the water table, into what is called a water-table aquifer. Overpumping from one well or multiple wells can result in a cone of depression and a general lowering of the water table. Copyright © McGraw-Hill Education Groundwater Supply 8  11/18/2024 Wells Artesian wells An artesian aquifer contains water under pressure. Copyright © McGraw-Hill Education Groundwater Supply Threats to Our Water Supply Freshwater is Earth’s most precious natural resource. Changes to groundwater supplies can lead to environmental issues. Copyright © McGraw-Hill Education Groundwater Supply 9  11/18/2024 Threats to Our Water Supply Overuse If groundwater is pumped out at a rate greater than the recharge rate, the groundwater supply will decrease and the water table will drop. Copyright © McGraw-Hill Education Groundwater Supply 10  11/18/2024 Threats to Our Water Supply Subsidence Another problem caused by the excessive withdrawal of groundwater is ground subsidence—the sinking of land. Copyright © McGraw-Hill Education Groundwater Supply 11  11/18/2024 Threats to Our Water Supply Pollution in groundwater The most easily polluted groundwater reservoirs are water-table aquifers, which lack a confining layer above them. When the recharge areas of confined aquifers are polluted, those aquifers can also become contaminated. Copyright © McGraw-Hill Education Groundwater Supply Threats to Our Water Supply Pollution in groundwater Sources of groundwater pollution include sewage from faulty septic tanks and farms, landfills, and other waste disposal sites. Pollutants can spread rapidly through a highly permeable aquifer. Note how the polluted well has drawn the pollution toward it as it has withdrawn water from the water table. Copyright © McGraw-Hill Education Groundwater Supply 12  11/18/2024 Threats to Our Water Supply Pollution in groundwater Once chemical contaminants have entered groundwater, they cannot be easily removed. Over time, an entire aquifer can become contaminated and toxic to humans. Copyright © McGraw-Hill Education Groundwater Supply Threats to Our Water Supply Pollution in groundwater Once chemical contaminants have entered groundwater, they cannot be easily removed. Over time, an entire aquifer can become contaminated and toxic to humans. Copyright © McGraw-Hill Education Groundwater Supply 13  11/18/2024 Salt Water Contamination Salt pollution is one of the major threats to groundwater supplies, especially in coastal areas, where the intrusion of salt water into groundwater is a major problem. Copyright © McGraw-Hill Education Groundwater Supply Threats to Our Water Supply Pollution in groundwater Another source of natural groundwater pollution is radon gas, which is one of the leading causes of lung cancer in the United States. Copyright © McGraw-Hill Education Groundwater Supply 14  11/18/2024 Protecting Our Water Supply Humans must be aware of how their activities impact the groundwater system so that they can protect the water supply. Copyright © McGraw-Hill Education Groundwater Supply 15