1 00:00:13,100 --> 00:00:14,633 - [Voiceover] Beneath the surface of Texas 2 00:00:14,633 --> 00:00:16,500 are extensive water bearing geologic 3 00:00:16,500 --> 00:00:18,767 formations that make up the state's vast 4 00:00:18,767 --> 00:00:21,700 and diverse system of aquifers. 5 00:00:21,700 --> 00:00:23,500 These aquifers provide more than half 6 00:00:23,500 --> 00:00:26,300 of the water Texans use each year. 7 00:00:26,300 --> 00:00:28,366 Aquifers are rarely underground lakes 8 00:00:28,366 --> 00:00:30,566 like you might see in a cave. 9 00:00:30,566 --> 00:00:33,833 They are typically rock formations that are mostly solid 10 00:00:33,833 --> 00:00:36,300 but like sponges they have interconnected fissures 11 00:00:36,300 --> 00:00:38,700 and pore spaces that hold water 12 00:00:38,700 --> 00:00:41,900 and allow it to move within the formation. 13 00:00:41,900 --> 00:00:43,766 An aquifer is best defined as a layer 14 00:00:43,766 --> 00:00:48,766 of saturated rock and the water in its pores. 15 00:00:49,100 --> 00:00:53,166 Aquifers were formed very slowly over vast periods of time. 16 00:00:53,166 --> 00:00:55,100 Water in aquifers comes originally 17 00:00:55,100 --> 00:00:57,366 from the surface of the Earth. 18 00:00:57,366 --> 00:01:00,033 When rain falls, some of the water infiltrates 19 00:01:00,033 --> 00:01:03,300 underground and collects in the pore spaces. 20 00:01:03,300 --> 00:01:05,166 Water in rivers and lakes can also 21 00:01:05,166 --> 00:01:07,966 seep into the subsurface pores. 22 00:01:07,966 --> 00:01:09,566 Eventually, some interconnected 23 00:01:09,566 --> 00:01:12,433 pore spaces become saturated with water. 24 00:01:12,433 --> 00:01:15,766 In other words, they become an aquifer. 25 00:01:15,766 --> 00:01:17,500 - [Voiceover] The ability of an aquifer 26 00:01:17,500 --> 00:01:19,966 to produce water depends on the properties 27 00:01:19,966 --> 00:01:23,033 of the aquifer's rock formation. 28 00:01:23,033 --> 00:01:24,900 The two most important properties 29 00:01:24,900 --> 00:01:27,833 are porosity and permeability. 30 00:01:27,833 --> 00:01:29,966 The porosity is a measure of the volume 31 00:01:29,966 --> 00:01:34,300 of empty space, or pore spaces, inside the rock. 32 00:01:34,300 --> 00:01:37,300 Pore spaces can be openings between grains, 33 00:01:37,300 --> 00:01:41,366 fractures in the rock, and even caverns. 34 00:01:41,366 --> 00:01:43,166 Porosity represents the volume 35 00:01:43,166 --> 00:01:46,633 of water a rock formation can hold. 36 00:01:46,633 --> 00:01:50,500 Porosity itself isn't enough to create an aquifer. 37 00:01:50,500 --> 00:01:53,966 The areas filled with water must connect with each other 38 00:01:53,966 --> 00:01:57,966 so the water can flow from one pore space to another. 39 00:01:57,966 --> 00:02:02,966 That connectivity between pores is known as permeability. 40 00:02:03,167 --> 00:02:05,966 Permeability is a measure of how readily 41 00:02:05,966 --> 00:02:09,366 water can flow within the rock. 42 00:02:09,366 --> 00:02:13,500 Rocks such as pumice and shale can have high porosity 43 00:02:13,500 --> 00:02:15,766 but do not form productive aquifers 44 00:02:15,766 --> 00:02:19,766 because the pores within the rock are not connected. 45 00:02:19,766 --> 00:02:23,566 The permeability of pumice and shale is low. 46 00:02:23,566 --> 00:02:26,433 On the other hand, gravel transmits water quickly 47 00:02:26,433 --> 00:02:29,567 because of large connected pore spaces. 48 00:02:29,567 --> 00:02:32,766 The permeability of gravel is high. 49 00:02:32,766 --> 00:02:34,033 - [Voiceover] Compared to water movement 50 00:02:34,033 --> 00:02:35,766 through rivers or lakes, 51 00:02:35,766 --> 00:02:38,766 the rate of movement through an aquifer is slow. 52 00:02:38,766 --> 00:02:41,233 Of the nine major aquifers in Texas, 53 00:02:41,233 --> 00:02:46,001 six of them, the Ogallala, Gulf Coast, 54 00:02:46,001 --> 00:02:50,500 Carrizo-Wilcox, Pecos Valley, Seymour, 55 00:02:50,500 --> 00:02:54,033 and Hueco-Mesilla Bolsons consist of sedimentary rock 56 00:02:54,033 --> 00:02:57,900 with relativity high porosity and permeability. 57 00:02:57,900 --> 00:02:59,300 Sedimentary rocks are composed 58 00:02:59,300 --> 00:03:03,833 of sand, gravel, silt, and clay. 59 00:03:03,833 --> 00:03:07,300 The three other major aquifers, the Edwards Aquifer, 60 00:03:07,300 --> 00:03:10,766 sometimes referred to as the Balcones Fault Zone, 61 00:03:10,766 --> 00:03:15,033 the Trinity Aquifer, and the Edwards-Trinity Plateau Aquifer 62 00:03:15,033 --> 00:03:19,100 consist either mainly or partly of limestone. 63 00:03:19,100 --> 00:03:21,967 Water in limestone aquifers is held in crevices 64 00:03:21,967 --> 00:03:24,233 and caverns left by the dissolution 65 00:03:24,233 --> 00:03:26,900 of the limestone by ground water. 66 00:03:26,900 --> 00:03:29,700 This subterranean landscape is known as Karst 67 00:03:29,700 --> 00:03:32,033 and it is highly permeable. 68 00:03:32,033 --> 00:03:34,566 Being on a fault zone, the Karst limestone 69 00:03:34,566 --> 00:03:38,233 of the Edwards Aquifer is highly fractured. 70 00:03:38,233 --> 00:03:39,567 Rainwater seeps very quickly 71 00:03:39,567 --> 00:03:42,633 into the Edwards Aquifer through the fault lines, 72 00:03:42,633 --> 00:03:45,300 even while a storm event is happening. 73 00:03:45,300 --> 00:03:49,566 Not all limestone aquifers in Texas recharge this quickly. 74 00:03:49,566 --> 00:03:51,633 - [Voiceover] In nature, aquifers are seldom 75 00:03:51,633 --> 00:03:55,100 separated neatly into geographic areas. 76 00:03:55,100 --> 00:03:57,869 Instead, like a stack of pancakes, 77 00:03:57,869 --> 00:04:02,633 aquifers overlay each other and dip at different angles. 78 00:04:02,633 --> 00:04:05,566 Some parts are exposed to the Earth's surface 79 00:04:05,566 --> 00:04:09,766 while other parts are buried under other aquifers. 80 00:04:09,766 --> 00:04:11,833 The part of an aquifer that is exposed 81 00:04:11,833 --> 00:04:16,100 at land surface is known as the outcrop. 82 00:04:16,100 --> 00:04:17,900 The part that is in the subsurface 83 00:04:17,900 --> 00:04:20,700 is known as the downdip extent. 84 00:04:20,700 --> 00:04:24,900 For example, the outcrop of the Carrizo-Wilcox Aquifer 85 00:04:24,900 --> 00:04:29,233 is a narrow band that lies parallel to the Gulf Coast. 86 00:04:29,233 --> 00:04:32,633 As we move toward the coast the aquifer slopes 87 00:04:32,633 --> 00:04:36,833 beneath the land's surface, forming the downdip. 88 00:04:36,833 --> 00:04:40,833 Aquifers are separated from each other by aquitards. 89 00:04:40,833 --> 00:04:43,566 Aquitards are impermeable layers 90 00:04:43,566 --> 00:04:45,766 that prevent water from easily flowing 91 00:04:45,766 --> 00:04:48,100 from one aquifer to another. 92 00:04:48,100 --> 00:04:50,566 An aquifer is confined when it is buried 93 00:04:50,566 --> 00:04:55,366 beneath other aquifers and/or aquitards. 94 00:04:55,366 --> 00:04:57,033 The combined weight of the rocks 95 00:04:57,033 --> 00:05:01,166 and water above pressurizes the ground water. 96 00:05:01,166 --> 00:05:05,233 This is sometimes referred to as Artesian pressure. 97 00:05:05,233 --> 00:05:08,233 When the aquitard above a confined aquifer 98 00:05:08,233 --> 00:05:10,433 is punctured by drilling a well 99 00:05:10,433 --> 00:05:14,900 Artesian pressure causes the water in the well to rise. 100 00:05:14,900 --> 00:05:17,766 Sometimes this water reaches land surface 101 00:05:17,766 --> 00:05:20,300 resulting in a flowing well. 102 00:05:20,300 --> 00:05:22,633 Springs are water flow into the surface 103 00:05:22,633 --> 00:05:24,433 through natural pathways caused 104 00:05:24,433 --> 00:05:29,433 by the faulting or dissolution of aquifer rocks. 105 00:05:29,700 --> 00:05:31,966 Pumping in a confined aquifer causes 106 00:05:31,966 --> 00:05:35,033 the pressure of the ground water to reduce. 107 00:05:35,033 --> 00:05:37,966 The reduction in pressure lowers water levels 108 00:05:37,966 --> 00:05:42,100 in Artesian wells and springs. 109 00:05:42,100 --> 00:05:45,700 Because confined aquifers are, by definition, 110 00:05:45,700 --> 00:05:47,766 not always well-connected to surface 111 00:05:47,766 --> 00:05:50,500 water sources like streams and lakes, 112 00:05:50,500 --> 00:05:55,314 recharge may be slow, if it happens at all. 113 00:05:56,391 --> 00:05:57,900 - [Voiceover] When an aquifer is exposed to the 114 00:05:57,900 --> 00:06:01,833 Earth's surface, such as at the outcrop, it is unconfined. 115 00:06:01,833 --> 00:06:04,366 The ground water is not pressurized. 116 00:06:04,366 --> 00:06:06,766 When we pump an unconfined aquifer 117 00:06:06,766 --> 00:06:10,100 it lowers water levels in the aquifer itself. 118 00:06:10,100 --> 00:06:13,233 In addition, because the water is not under pressure, 119 00:06:13,233 --> 00:06:16,900 it takes more energy to pump water out of the aquifer. 120 00:06:16,900 --> 00:06:19,633 Unconfined aquifers are usually replenished 121 00:06:19,633 --> 00:06:21,966 more easily than confined aquifers 122 00:06:21,966 --> 00:06:25,233 because rainfall and water from rivers and streams 123 00:06:25,233 --> 00:06:28,900 can flow into the exposed areas of the aquifer. 124 00:06:28,900 --> 00:06:32,633 In addition, the material above an unconfined aquifer is 125 00:06:32,633 --> 00:06:37,100 usually porous so surface water can seep into the aquifer. 126 00:06:37,100 --> 00:06:38,567 - [Voiceover] The better we understand 127 00:06:38,567 --> 00:06:40,833 the geologic properties of aquifers, 128 00:06:40,833 --> 00:06:43,033 the better we can understand their sensitivity 129 00:06:43,033 --> 00:06:45,433 and susceptibility to human use 130 00:06:45,433 --> 00:06:48,800 such as pumping and contamination.