10.1.2 Groundwater

Direct Instruction Section 1 00:00:01 PROFESSOR: People have been digging wells to access groundwater for thousands of years. It's an especially important source of water because it's consistent, even in times of drought. So why is this water source so consistent? We're going to explore that in this section. Groundwater, Section One. In this section, we'll describe the location and 00:00:22 importance of the water table and assess the consequences of overuse and contamination of groundwater. And looking at the next section, we'll explain how human use of groundwater has changed over time. So what is groundwater? Well, simply stated, groundwater is underground water. It's pretty easy. 00:00:40 It's found in spaces in the ground, and it's stored and moved through aquifers. Aquifers are sometimes incorrectly explained as being large, underground lakes. Well, it kind of is like that, but you couldn't go and swim in it if there was a way you could get down there. It's very tiny spaces and pores in the rock that hold water, that are all connected. 00:01:03 But it's not one big, massive lake, one big volume of water. Very tiny spaces that fill up with water. So permeable layers of rock, soil, sand, and rock create these aquifers. The Floridian aquifer is a very large aquifer. In fact, it's one of the most productive aquifers in the world. And it covers more than just Florida. 00:01:24 South Carolina, Georgia, Alabama, and Mississippi are all included in this Floridian aquifer. So the water table is a term that you may have heard in the past. But before we learn about what, specifically, the water table is, let's talk about something called the saturation zone. The saturation zone is where water fills the aquifer. So it's this area that water fills up in the aquifer. 00:01:47 It's saturated with water. So the water table is then the top of the saturated zone. So we have this layer of rock that is filled up, or saturated, with water. All these little teeny, tiny pores that are filled up with water. Well at the top level of that water is the water table. So the depth of the water table can vary from one foot 00:02:12 to hundreds of feet, depending on where you are in the country or in the world. And it can rise and fall from seasons or from things like pumping. So if we take too much water out of an aquifer, that water level will go down. If we have a drought condition, the water level will go down. 00:02:30 If we have a certain time of year where we're receiving a lot of precipitation, that water level is going to come back up. So what is the importance of the water table? Well, it's a global fresh water supply. Groundwater supplies 30% of the world's fresh water. It's a natural storage, which can be long term, for water. So many of our water sources, such as little ponds, lakes, 00:02:59 rivers, are just temporary sources, and they can dry up, sometimes, in a very short period of time. But many times, groundwater is going to be there for an extended period of time. So it's going to be available for us even in times of drought. So it's very significant when surface water is lacking or when we're drought conditions. 00:03:18 It's naturally replenished by surface water. Things like precipitation, streams, and rivers all help to replenish that water when we take it out or when it's used. Groundwater replenishment or recharge. We talked about how it's recharged. Well, in certain areas of the world, groundwater is the only source of water. 00:03:39 So it's important to understand how this water source stays at a certain level. We mentioned that rivers, streams, things like that, can recharge this groundwater source. But also rain and snow melt are a very important recharging of this groundwater. So groundwater shortages usually occur when we're using the water faster than is being replaced by nature. 00:04:01 So if we're using up more water than we are receiving, that water table is going to go down. We also have groundwater shortages when we pollute our water. When we spray things on our land which leaches down into the soil, it's going to get into our water system, and then we can no longer use that groundwater. The layer of rock above aquifer is going to be 00:04:24 permeable, which means water can flow down through it. So it's also going to be permeable for things like chemicals. So these pollutants sink into the groundwater, as I mentioned. They can come from places like landfills, septic tanks that aren't working properly, fertilizer, and pesticide overuse in areas of agriculture. 00:04:43 The importance of groundwater. We use a lot of our groundwater for things like irrigation. In fact, that's probably what we use most of our groundwater for. We also use it for drinking water and just for everyday use. Over 50% of the people in the United States receive their 00:05:03 water from the ground. And almost everyone who lives in a rural area gets their water from groundwater sources. So this huge demand for water is causing groundwater overdraft. So we're using more water than is going into our groundwater systems. So this is lowering the water table, in some areas, at an alarming rate. 00:05:23 So it's going to cause a huge problem when this water table reaches below the level of our existing wells. We're going to have to dig deeper or drill deeper to get to that new lower water table. But it's not quite that easy because as we dig deeper and deeper into these aquifers, many times, you run into salt water. Not all groundwater is freshwater. 00:05:45 And many times, at the lower end of these aquifers, we have salty water or water with more saline concentration. We also have problems with subsidence, or the lowering of the ground. There have been instances in the desert Southwest, where a lot of groundwater is used, that huge areas of the desert simply collapse. Now if that happens in a place like a city, that can cause 00:06:07 huge problems. So we talked about wells at the beginning of this section, how people have been using them for thousands of years. They reach groundwater in the water table. So you dig down in order to reach that water table. In places where the water table is much lower, you're going to need a much deeper well. So they can very in depth, water quality, water volume. 00:06:32 And there are different types of wells also. We have dug wells, which people go and they dig them by hand until they reach the water table. But if the water table is extremely low, it's going to be really hard to dig a hole that deep by hand. So then we have driven wells, which are actually driven in. They're kind of like hammering a nail into a piece of wood. It's driven in. 00:06:53 There is this big spike that has pores in the bottom that allows water, when it reaches that water table, to get into that pipe so it can be pumped to the surface. Then we have drilled wells, which is just what it sounds like. We actually drill into the ground until you reach the water table. And then that water is pumped to the surface by some sort of 00:07:11 mechanical means. Thinking ahead to the next section, how has groundwater use changed over time?

Section 2 00:00:01 PROFESSOR: Wishing wells have been around for a long time. Where do you think we ever got the idea that throwing money into a well and making a wish would make it come true? In this section, we're going to talk about the many uses that people in the past had for groundwater, and we're also going to talk about where wishing wells came from. Groundwater, Section Two. We've already described the location and importance of the 00:00:25 water table and assessed the consequences of overuse and contamination of groundwater. Now we're going to explain how human use of groundwater has changed over time. So the Neolithic era-- or the New Stone Age-- was the earliest time that we see wells appear. It's the earliest evidence of wells that we've found. 00:00:46 In Israel, we've found some dated back to over 8,000 years ago. The Australian Aborigines used wells to survive in the Australian desert, and the hand-dug wells are called "soaks" or "soakages." A Karez well system is kind of a complex groundwater system. It's more than just a hole that's dug into the ground. It's an ancient water collection system that was 00:01:10 invented by the Persians 3,000 years ago. It's a series of wells and linked underground channels. So if you look at what they did, it's actually quite amazing. They understood that the water table wasn't always necessarily flat. And if they found some sort of land that was sloping, the water table was probably also sloping as well. 00:01:32 So they figured if they could go dig into the side of a mountain or hill, eventually they would reach the water table. Now, all this water up here that's above this channel that they just built is weight that's pushing down. So as soon as they open up this channel, this water is going to want to flow out their channel. So it's a series of wells and linked underground channels 00:01:58 that can collect water. And it collects and stores water and brings it to the surface. It also allowed them to transport the water from a distance using nothing more than the energy from gravity. The Industrial Revolution changed the way we use water. Before the Industrial Revolution, settlements were near rivers and surface waters. 00:02:18 People lived in small groups. We didn't need a lot of water. We could survive on the surface water of the planet. We had a very small-world population. But after the Industrial Revolution, things changed a little bit. We increased our ground use after Industrial Revolution. Because of things like urbanization and 00:02:36 industrialization, growing populations, there was an increasing demand on earth's resources. So we started settling away from surface water. So we had to find another way to get our water. We had an intense exploration and exploitation of groundwater. Now, in modern times, we use groundwater a lot. Today, groundwater use in the United States consists of crop 00:03:03 irrigation. In fact, our agriculture uses a large part of our groundwater. Public uses for water include things like delivery to homes and businesses. So all that water that comes into your house through your faucet, that is, a lot of times, groundwater. As we mentioned, 50% of people in the United States get their 00:03:22 water from groundwater sources. Mining and industries use a lot of water these days. Firefighting, public buildings, all the water that's supplied to them, a lot of times, is groundwater sources. And of course, places like community swimming pools are supplied with water that may have come from groundwater. So we talked about wishing wells. 00:03:43 Where you think we ever got the idea that throwing money into well is going to make our wish come true? Well, European folklore had a lot of stories about water. They believed that any spoken wish will be granted, and they would throw money into a well. Well, they believed that water was a gift from the gods, and it was a sacred gift, and it is a source of life. Water also had healing power, so it was seen as a very 00:04:09 magical thing. So they believed that the guardians or dwellers of the well would grant them their wish if they paid a price. So they'd throw money in there, say a wish, and it would come true. We've accomplished our mission when talking about groundwater. We talked about groundwater and the water table. 00:04:28 We talked about aquifers, saturated zones, and fluctuations in that water table, the importance of the water table. We talked about global freshwater, natural storage and replenishment of our water tables, groundwater supplies. We talked about pollution, the importance of groundwater, and how we're overdrafting from our groundwater supplies. We talked about how groundwater was used in 00:04:49 ancient times and the pre-Industrial Revolution and post-Industrial Revolution and how it's used in modern times.

According to the chart, California withdrew the most groundwater in 2000, with a total of 18%. The greatest use of groundwater is irrigation, with about 68% of groundwater used in 2000 being for irrigation. Surface freshwater is generally used more due to the fact that it is cheaper and easier to access surface water and it is more expensive and requires more work to extract the groundwater.

A) increased

A) surrounds the rock particles, leaving air between them

C) agriculture

B) use exceeding the rate of replenishment

C) It is the only source of freshwater

D) all of the above

D) all of the above

C) 30%

C) pollution