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UNM ENVS 101 - Water Under the Ground and in Society
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ENVS 101 1st Edition Lecture 12 Outline of Last Lecture I. Water on the GroundII. Water Under the GroundIII. Water and the Hydrologic CycleOutline of Current Lecture II. Water Under the GroundIII. Water in SocietyCurrent LectureGroundwater across the Earth in its entirety is 35 times larger than the volume of all the freshwater lakes and streams combined on Earth. Groundwater is also nearly a third as large as all the glaciers and sea ice water sources that are found on Earth. Thus, there is actually enough amounts of groundwater to cover the Earth's land surface in an even layer that would end up being 55 meters in depth, just shy of over 150 feet deep!More than 50% of groundwater is within 750 meters of depth of the Earth.Elements dissolved in groundwater include the following:Chlorides, sulfates, and bicarbonates of calcium, magnesium, sodium and potassium. The bicarbonates are materials which dissolve from common rock-forming minerals- From the ground surface of the Earth, reaching down beneath the water table, the regolith is filled with air: this is known as the aerated zone. - Another zone of regolith is filled with water, and this is known as the saturated zone, and the upper level surface of this is known as the water table. - The water table follows the shape of the ground surface, higher under hills, and lower under valleys.Groundwater typically flows from high water table areas to low water table areas in response to the effects of gravity on Earth. Thus, water that is on high mountain tops, will typically find its way down towards the bottom of the mountain, towards lower altitudes.Infiltration of precipitation is a means of “recharging” the groundwater sourcesIn general, water typically moves to areas of discharge, where it will end up meeting the surface, and water sources such as streams, lakes, ponds, or wetlands.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Groundwater flow depends on the porosity and permeability of the rock it moves through.Porosity: the percentage of the total volume of rock that consists of open pore spacesPermeability: a measure of how easily a solid allows fluids to pass thorough it.High porosity is found in materials such as gravel, and yields high permeability, which is about 30% water in the material when it comes into contact with water. Medium porosity is about 15% water inside of the material, and still yields a high permeability due to poorly sorted sediments. High porosity, but lower permeability is possible due to cements, such as those that are found in sedimentary rock. Clay has a high permeability but very low permeability because water does not flow well between the tiny pores. The porosity of clay, even at a molecular level, makes it difficult for water to even pass through.In granite, as well as basalt, groundwater actually flows in fractures only, not through pore spaces.Resource: a source or supply that can be used beneficially or for profit.Aquifer: a body of rock or regolith porous and permeable enough to be used as a resource.Confined aquifer: bounded above and below by impermeable rock layers called aquicludes. (Hasa potentiometric or piezometric surface rather than a water table where it would be confined bysomething impermeable).Artesian wells: where potentiometric surface is above the ground surface a well will flow freelyCone of depression: lowering of water table or potentiometric surface around a pumping well.Water level changes, and incredible effects like sinking of land in places can easily occur where water has been pumped excessively, ex. in the San Joaquin Valley, CA. Oftentimes, these changes in the environment tend to have greater impact where the demand will often exceed the supply.Water use in the USA, domestic use makes up just over 14% of water usage, industrial is the highest by far, at 48% due to the manufacturing processes needed to create a variety of products, from paper to blue jeans. Also, electricity that is used by turbines takes a fair bit of water away to generate energy. The other use is agricultural, with the vast majority of water being sourced to cultivate fields where crops are grown across the


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UNM ENVS 101 - Water Under the Ground and in Society

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