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Chapter 12: Groundwater and Wetlands

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1 Chapter 12: Groundwater and Wetlands
1. 2. 3. 4. Meet Your Drinking Water Holes in Earth Materials Groundwater Systems A Case Study: The High Plains Aquifer Groundwater Quality Introduction to Wetlands 5. 6. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2 Meet Your Drinking Water Self Reflection Survey
Answer the following questions as a means of uncovering what you already know about groundwater and wetlands: Which of the following have you experienced or observed? An underground cave A spring A wetland (or marsh or swamp) The Good Earth/Chapter 12: Groundwater and Wetlands

3 Meet Your Drinking Water Self Reflection Survey
Answer the following questions as a means of uncovering what you already know about groundwater and wetlands: 2. How often do you drink bottled water? When at home, are you more likely to drink bottled water or water from the tap? Why do you make that choice? The Good Earth/Chapter 12: Groundwater and Wetlands

4 Meet Your Drinking Water Self Reflection Survey
Answer the following questions as a means of uncovering what you already know about groundwater and wetlands: 3. List all the things you use water for in and around your home. In addition, what other ways is water used in your community? The Good Earth/Chapter 12: Groundwater and Wetlands

5 Meet Your Drinking Water
Which is better to drink? Whether it is from a bottle or the tap, our drinking water comes from the same place and undergoes similar processing and monitoring to make it safe. The Good Earth/Chapter 12: Groundwater and Wetlands

6 Meet Your Drinking Water
The consumption of bottled water in the U.S. is growing fast, faster than any other beverage. Tap water is just as good, and costs 1,000 times less than bottled water. About ¼ of all bottled water is simply bottled tap water. Purified water = tap water that has undergone additional treatment prior to bottling Where does our drinking water come from? Streams and lakes (on the Earth’s surface) Groundwater (water in rocks or unconsolidated materials below the Earth’s surface) The Good Earth/Chapter 12: Groundwater and Wetlands

7 Meet Your Drinking Water
Water supplies are most likely to be contaminated by human actions e.g. chemical leaks from storage tanks 53,000 community water systems in the U.S. Few become polluted, but this pollution can cause health risks Cleanups can be tricky, especially for underground sources The Good Earth/Chapter 12: Groundwater and Wetlands

8 Meet Your Drinking Water
Woburn, Mass – a case of groundwater pollution with extreme consequences Several potential sources of pollution Children diagnosed with leukemia after their mothers drank water from two polluted wells while they were pregnant dry cleaning chemicals trucking plastics tannery The Good Earth/Chapter 12: Groundwater and Wetlands

9 Meet Your Drinking Water
The families accused companies of illegally dumping chemicals Geologists studied the interactions between the local rock and water system in Woburn to try to determine how these factors influenced the flow of chemicals to the wells: • distance of each company from the wells • properties of the chemicals themselves and how they influenced flow • influence of local geology on flow Jury found that chemicals from W.R. Grace could have contaminated the wells. They settled for $8 million dollars Surrounding landowners coughed up ~$70 million for clean up National Priorities List – over 1500 sites in the U.S. where contamination is likely by companies that are out of business or unknown About ¼ of the U.S. population lives within 4 miles of an NPL site The Good Earth/Chapter 12: Groundwater and Wetlands

10 Go back to the Table of Contents
Go to the next section: Holes in Earth Materials The Good Earth/Chapter 12: Groundwater and Wetlands

11 Holes in Earth Materials
There’s more water underground than in lakes and streams on Earth’s surface (about 70% more!) Most groundwater is in billions of tiny spaces between mineral grains or in narrow cracks. The amount of groundwater at any location depends on the porosity and permeability of materials beneath the surface. Porosity = the proportion of a material that is made up of spaces. (e.g. if ½ the total volume of a rock is pore space, the porosity is 50%) Depends on size and arrangement of the grains (better sorted – higher porosity). The Good Earth/Chapter 12: Groundwater and Wetlands

12 Holes in Earth Materials
As material grains compacted or cemented, porosity decreases. The Good Earth/Chapter 12: Groundwater and Wetlands

13 Holes in Earth Materials
Do you think porosity is higher in unconsolidated material or in its rock equivalent? Porosity is greater in unconsolidated materials: Sand, gravel are more porous than sandstone, conglomerate Specific yield – the groundwater that can drain from a rock or sediment Specific yield = porosity – specific retention Specific retention = water on the surface of grains that will not flow through the material (i.e. stuck on grain surfaces) The specific yield of fine-grained materials is low, even though their porosity can be high The Good Earth/Chapter 12: Groundwater and Wetlands

14 Holes in Earth Materials
Permeability = the capacity of water to flow through earth materials. Water can flow readily through materials with well connected pore space or many fractures. Connections between pore spaces are wider in coarse-grained material (gravels) than fine-grained material (sand). High permeability does not always go hand in hand with high porosity. Q: Why do you think groundwater flows more slowly than water on the Earth’s surface? A: More opportunities for friction to slow it down as it pushes through spaces between millions of tiny grains. The Good Earth/Chapter 12: Groundwater and Wetlands

15 Holes in Earth Materials Checkpoint 12.2
Imagine that you have three identical containers (A,B,C). A is filled with flour, B is filled with uncooked rice, and C is filled with coffee beans. Predict what would happen if you were to pour water into each container. How would they rank in terms of permeability (from highest to lowest)? A) B) C) The Good Earth/Chapter 12: Groundwater and Wetlands

16 Checkpoint 12.3 A large volume of liquid waste was dumped on the ground at Otis Air Base, Massachusetts. Both the base and the city are located over the same deposit of sand and gravel. Examine the following diagram and predict the approximate length of time before the waste would begin to show up in the drinking water wells of the city of Falmouth assuming a flow rate of 0.5 meters per day. 10 months 8 years 16 years 40 years The Good Earth/Chapter 12: Groundwater and Wetlands

17 Go back to the Table of Contents
Go to the next section: Groundwater Systems The Good Earth/Chapter 12: Groundwater and Wetlands

18 Groundwater Systems Groundwater is stored in bodies of rock and/or sediment called aquifers, which are composed of sufficient saturated permeable material to yield significant quantities of water. The Good Earth/Chapter 12: Groundwater and Wetlands

19 Aquifers can form in a variety of geologic settings
Aquifers can be composed of sands, gravels, sandstone with good porosity and permeability, and fractured rocks. The Good Earth/Chapter 12: Groundwater and Wetlands

20 Groundwater Systems Aquifer Quality High porosity and permeability
Most productive aquifers are found in unconsolidated earth materials (80% of all groundwater withdrawn in U.S. comes from sand and gravel aquifers) Aquitards – low-permeability materials such as clay, shale, or unfractured igneous or metamorphic rock, that act as a barrier to water flow Open water Aquifer. The Good Earth/Chapter 12: Groundwater Wetlands

21 In general, the water table follows the shape of the land surface
Groundwater Systems In general, the water table follows the shape of the land surface The top of the saturated zone is the water table, and it is highest under hills and lowest in valleys. Water flows down the slope of the water table (hydraulic gradient). When the water table intersects the land surface a stream, lake, or spring will occur. The Good Earth/Chapter 12: Groundwater and Wetlands

22 Groundwater Systems Confined (Artesian) Aquifer – enclosed above and below by impermeable materials. Water can only enter the well through the exposed rock layer (recharge zone). The Good Earth/Chapter 12: Groundwater and Wetlands

23 Groundwater Systems Checkpoint 12.5
The following cross section simplifies the groundwater sources in a county in a midwestern state. Which location would have the potential for the best groundwater production? Location A Location B Location C Location D The Good Earth/Chapter 12: Groundwater and Wetlands

24 Groundwater Systems Checkpoint 12.5
Liquid hazardous waste is disposed of by pumping it down injection wells. On the following diagram, which well location would be most suitable for use as an injection well? Well A Well B Well C The Good Earth/Chapter 12: Groundwater and Wetlands

25 Inflow (recharge) vs. Outflow (discharge)
Groundwater Systems Inflow (recharge) vs. Outflow (discharge) Especially important issue is southwestern states Recharge can occur through infiltration of rainwater or streams Losing streams – flow over ground in dry areas and lose water into the groundwater supply Recharge can also occur from stored groundwater, present from a wetter time in the past (e.g. water that precipitated into the ground when the last ice sheets melted; this is non-renewable water) Gaining streams – gain water from an area with a high water table (this is a form of discharge, not recharge, of groundwater) The Good Earth/Chapter 12: Groundwater and Wetlands

26 Groundwater Systems Confined Aquifers
Recharge occurs through eroded rocks at higher elevation than where water is withdrawn. Water is under pressure. Water can flow without pumping until water table equals elevation where water is withdrawn. The Good Earth/Chapter 12: Groundwater and Wetlands

27 Groundwater Systems Groundwater can reach the surface at springs and wetlands. Springs form where (a) fractures or (b) cave systems intersect the land surface. (c) Wetlands may form where several small springs distribute water over a region underlain by a low-permeability material such as clay or shale. The Good Earth/Chapter 12: Groundwater and Wetlands

28 Groundwater Systems Look at these graphs – which one do you think is a gaining stream? Why? The Good Earth/Chapter 12: Groundwater and Wetlands

29 How does groundwater interact with oceans?
Groundwater Systems How does groundwater interact with oceans? In coastal regions, fresh water is found floating above a denser layer of saltwater. Saltwater infiltrates the ground just like fresh water. Where the freshwater layer meets the coast it flows into the ocean. In coastal cities, freshwater can be extracted from the freshwater layer, but if it is extracted faster than it is replenished, saltwater can flow into wells. The Good Earth/Chapter 12: Groundwater and Wetlands

30 Consequences of Human Actions
Groundwater Systems Consequences of Human Actions • Rapid population growth = greater need for groundwater Goundwater overdraft - the supply cannot replenish as fast as we extract it for human use • Decline in water table The water table surrounding a well can decline if water is pumped out too fast. The surface of the depleted water table forms a cone of depression around the well. Trying to pump groundwater is like sucking up a spilled drink from a table. No matter how big a straw you use, most of the drink stays on the table top. The Good Earth/Chapter 12: Groundwater and Wetlands

31 Groundwater Systems Checkpoint 12.9
Two wells (A and B) are drilled in rocks that have the same porosity, but the rocks around well A have a higher permeability than those around well B. Suppose both wells are pumped at the same rate. Which statement is true? Well A will have a larger cone of depression. Well B will have a larger cone of depression. The cone of depression will be the same for both wells. The Good Earth/Chapter 12: Groundwater and Wetlands

32 Consequences of Human Actions
Groundwater Systems Consequences of Human Actions • When groundwater is rapidly removed from unconsolidated material, the grains may compact as the empty pore spaces close Subsidence – A drop in the ground surface in response to a decrease in volume of the underlying sediment Subsidence due to groundwater withdrawal has occurred in some of the world’s largest cities. It is responsible for the lean in the leaning tower of Pisa. The Good Earth/Chapter 12: Groundwater and Wetlands

33 Go back to the Table of Contents
Go to the next section: A Case Study: The High Plains Aquifer The Good Earth/Chapter 12: Groundwater and Wetlands

34 A Case Study: The High Plains Aquifer
About 2/3 of all fresh U.S. groundwater pumped from aquifers is used for irrigation, much of which occurs in the Great Plains (Texas, Oklahoma, Kansas, Nebraska, and their neighbors). Was originally dubbed “The Great American Desert” – unfit for cultivation. Irrigation for the Great plains is mainly taken from the High Plains aquifer Sand and gravel with some underlying sandstone Open aquifer – partially recharged by rain and snowmelt Water table is typically less than 100 meters below the surface Today, the High Plains aquifer produces more water than any other groundwater source in the nation! The Good Earth/Chapter 12: Groundwater and Wetlands

35 A Case Study: The High Plains Aquifer
More than 170,000 wells draw water from the aquifer. The largest area of irrigation-sustained cropland in the world! There is no contemporary source for water the recharge the whole aquifer. Most of the water in the aquifer entered it during the last glacial maximum (wetter climate). “Fossil” water being used up faster than it is recharged Water table is dropping over much of the aquifer The Good Earth/Chapter 12: Groundwater and Wetlands

36 A Case Study: The High Plains Aquifer
The groundwater overdraft has caused a drop in the water table of up to 70 meters. Left panel shows thickness of saturated zone, center panel shows rises/drops in water table, and right panel shows variations in annual precipitation. Approximately 11% of the total groundwater supply has been extracted. The Good Earth/Chapter 12: Groundwater and Wetlands

37 A Case Study: The High Plains Aquifer Checkpoint 12.13
Which is the best explanation for the changes in water level in the High Plains aquifer? Explain why you chose your answer. The distribution of present-day rainfall on land above the aquifer Differences in thickness of the rocks that make up the aquifer The number of water wells that have been drilled into the aquifer The type of crops supplied by irrigation from the aquifer The Good Earth/Chapter 12: Groundwater and Wetlands

38 A Case Study: The High Plains Aquifer Checkpoint 12.14
Sketch your prediction of the approximate shape of the High Plains aquifer below some of the Great Plains states. Use the templates here and what you know about the character of the aquifer. Indicate the depth below the surface along the side of each diagram. The Good Earth/Chapter 12: Groundwater and Wetlands

39 A Case Study: The High Plains Aquifer Checkpoint 12.16
Much of the agriculture in the middle United States relies on water from the High Plains aquifer. What are the long-term implications if we continue to use large volumes of groundwater for irrigation faster than it can be replenished? The Good Earth/Chapter 12: Groundwater and Wetlands

40 Go back to the Table of Contents
Go to the next section: Groundwater Quality The Good Earth/Chapter 12: Groundwater and Wetlands

41 Groundwater Quality Although natural groundwater is not pure, in the U.S. it typically contains few chemicals in sufficient quantities to cause harm. Under certain conditions harmful elements (arsenic, mercury) can contaminate drinking water. In Bangladesh – widespread groundwater contamination by arsenic – may end up being the worst mass poisoning in history. Most densely populated nation in the world One of the poorest nations in the world People used to drink surface water contaminated with pollutants until wells were drilled in late 1970’s The Good Earth/Chapter 12: Groundwater and Wetlands

42 Groundwater Quality High concentrations of arsenic in the water – discovered after wells were already in use. On map – darkest greens are highest proportion of wells contaminated by arsenic. Worst affected wells are south of the confluence of the Ganges and Brahmaputra rivers. These two rivers are sourced from the Himalayan foothills – the rocks there contain unusually high natural concentrations of arsenic. ~Half the population of Bangladesh (60 million people) may be exposed to arsenic levels above the WHO standard. The Good Earth/Chapter 12: Groundwater and Wetlands

43 Groundwater Quality In the U.S. the standard for arsenic in drinking water is 10 ppb (parts per billion, or 0.05 milligrams per liter, as set by WHO). In Bangladesh, the standard is 50 ppb. Some wells in Bangladesh have levels as high as 2,000 ppb. Arsenic levels tend to be higher in western states that have more igneous and metamorphic rocks. The Good Earth/Chapter 12: Groundwater and Wetlands

44 Groundwater Quality Nature can cause contamination of groundwater, but mostly it is due to human activities. Sources of human and natural contamination can be from point sources and nonpoint sources. A point source can be specifically identified and located – e.g. a leaking gasoline storage tank. A point source, once identified, can be shut down. Nonpoint sources occur over a wide area. Examples of human contaminants in groundwater: Benzene, nitrates, pesticides, fertilizers, microbes from untreated human and animal waste. The Good Earth/Chapter 12: Groundwater and Wetlands

45 Groundwater Quality Potential sources of groundwater pollution in the U.S. The Good Earth/Chapter 12: Groundwater and Wetlands

46 Groundwater Quality Checkpoint 12.17
Did the natural arsenic contamination of groundwater in Bangladesh originate from a point source or nonpoint source? Explain the reasoning behind your answer. a. Point source b. Nonpoint source The Good Earth/Chapter 12: Groundwater and Wetlands

47 Groundwater Quality Checkpoint 12.19
1. Can occur anywhere there are people 2. Can occur anywhere 3. May not be obvious to those using the system 4. Affected by local geology 5. Occurred in relatively recent past 6. May have been occurring for millions of years 7. If contaminated, may cause illness or death 8. Typically associated with a point source 9. Typically associated with a non-point source 10. Can be mitigated by using clean water 11. Once identified, pollution source often can be cleaned up 12. Once identified, pollution source often cannot be cleaned up Use the Venn diagram provided here to compare and contrast groundwater pollution from human actions (e.g., Woburn) and natural sources (e.g., Bangladesh). Place features unique to either group in the larger areas of the left and right circles. Note features that they share in the overlap area in the center of the image. The Good Earth/Chapter 12: Groundwater and Wetlands

48 Go back to the Table of Contents
Go to the next section: Introduction to Wetlands The Good Earth/Chapter 12: Groundwater and Wetlands

49 Introduction to Wetlands
Ramsar Convention: A treaty intended to preserve and protect more than 321 acres of wetlands around the world (12 sites in the U.S.) To be a wetland an area must be saturated with water and have poorly drained soils and specific types of plants. Two types: coastal and freshwater The Good Earth/Chapter 12: Groundwater and Wetlands

50 Introduction to Wetlands
Wetlands must meet the following criteria: Hydrologic conditions – water present on land surface, or soils in root zone must be saturated during growing season or longer. Hydrophytic vegetation – specific plants that are water-tolerant and grow under wet conditions (e.g. cattails, wild rice, willows, sawgrass) must be present Hydric soils – poorly drained soils that exhibit anaerobic conditions during growing season The Good Earth/Chapter 12: Groundwater and Wetlands

51 Introduction to Wetlands
In lower 48, largest wetland areas are in Texas, Florida, Minnesota. Outside of Alaska, wetlands have declined by ~55% since 1600’s in the U.S. ~10% or less of original wetlands remain in California, Ohio, and Iowa. Losses are due to draining to support agriculture, or draining and infilling for urbanization and development. Why should we care? Wetlands perform many positive functions in the environment such as improving water quality in rivers by filtering out sediments and contaminants, providing breeding grounds for fish and shellfish which supports commercial fishing, providing ecological habitats for migrating birds, modifying the effects of flooding by slowing runoff, and providing recreation for humans. The Good Earth/Chapter 12: Groundwater and Wetlands

52 Introduction to Wetlands
The Florida Everglades (the “river of grass”) experienced a loss of wetlands due to population growth and urbanization. Development in the early 1900’s had four goals – “dike it, dam it, divert it, drain it.” Lost 50% of original wetlands destroying fish and wildlife habitats. Wetlands were replaced by agricultural sugarcane, and expansion of coastal cities further stressed the ecosystem. The Good Earth/Chapter 12: Groundwater and Wetlands

53 Introduction to Wetlands Checkpoint 12.22
After a series of summer thunderstorms, Cathy’s lawn is covered with a shallow pond of water up to 15 centimeters (6 inches) deep in places. The water remains for nearly 10 days. Does the water in Cathy’s backyard make it a wetland? Explain your answer. The Good Earth/Chapter 12: Groundwater and Wetlands

54 Introduction to Wetlands Checkpoint 12.23
1. Source for drinking water 2. Used for recreation 3. Part of hydrologic cycle 4. Involve the slow flow of water 5. Contain vegetation 6. Contain poorly drained soils 7. May be freshwater or saltwater 8. Below ground 9. Above ground 10. Affected by agricultural practices 11. May be polluted due to human actions 12. May reduce the effects of flooding 13. Less today than in the past due to human actions 14. Example: Florida Everglades 15. Example: High Plains aquifer Use the Venn diagram below to compare and contrast wetlands and groundwater systems. Write features unique to either groups in the list and put their corresponding numbers in the large areas of the circles. Write features found in both in the list and put those numbers in the intersection of the circles. The Good Earth/Chapter 12: Groundwater and Wetlands

55 Groundwater and Wetlands Concept Map
Complete the concept map to evaluate your understanding of the interactions between the earth system, groundwater and wetlands. Label as many interactions as you can using information from this chapter. The Good Earth/Chapter 12: Groundwater and Wetlands

56 Go back to the Table of Contents
The End Go back to the Table of Contents The Good Earth/Chapter 12: Groundwater and Wetlands


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