Transcript Groundwater
What is Groundwater? LA’s Water Resources You may be familiar with Spring water… Aquifer: A water-bearing rock that readily transmits water to wells and springs Water Bearing Rock?? Let’s investigate! notes Slide 1: •Groundwater is water that is stored underground. •It is recharged when rain soaks into the ground. •We can access this water by drilling a well to pump it out. This is a renewable resource (as long as it is not pumped out much faster than it can be recharged). Slide2: Los Angeles actually gets 11% of it’s water from the ground, and the one of the city’s goals for the future is to use less imported water and more groundwater. Slide 3: •This is a picture of a spring. Springs are where water is comes out of the ground at the earth’s surface. Arrowhead water is an example of spring water (bring in bottle as ex.). Slide 4: •How is water stored underground? •A common misconception is that groundwater is stored in underground lakes. It is actually stored in layers of rock called aquifers. •Imagine that you took the sand that you found at the beach and put it under pressure for a long time. Eventually, you would end up with sandstone. Just like there is a tiny bit of space between individual grains of sand, there is a tiny bit of space between grains in sandstone. Water can be stored in and move through this space. Because underground rock layers can be very big, they can actually store a lot of water. Slide 5: •Here is what that would look like… •Now we are going to do an experiment to demonstrate this concept Additional slides & notes from the presentation I modified for this lesson www.elmhurst.edu/~richs/EC/102/Lectures/Groundwater.ppt Groundwater Depletion Groundwater Contamination Groundwater Groundwater is water, which originates from the infiltration of fluids through the soil profile and accumulates below the earth's surface in a porous layer. Porosity is the percentage of open void space in the subsurface material. It is expressed as a percent. Permeability is how readily a fluid can flow through a material. Often referred to as "connected pore space". Pieziometric surface is the surface in which water is pushed up to by the pressure below. Spring is where water flows out without the aid of pumping. It may be caused by hydrostatic pressure (pressure pushing upward), or the intersection of the pieziometric surface with the ground surface. Also referred to as an Artesian System. An aquifer is the porous unit or layer of rock that is able to store or hold water and transmit enough fluid to be of economic value. An aquitard is rock material that is low in porosity/permeability. Fluid flow is not good and the unit may often be termed a "cap rock", not allowing underlying water to flow upward. An aquiclude is a unit of rock or layer of rock, which is impermeable to fluids. It acts as a barrier to fluid flow. There probably are no true aquicludes. There are two (2) scenarios that may occur with aquifers: 1. Confined Aquifer -- when an aquifer is bounded by two (2) aquitards (one above and one below) 2. Unconfined Aquifer -- when an aquifer is not bounded on the surface side by an aquitard so that fluids may flow freely above the aquifer. The distribution of groundwater is present in several distinct layers or zones: a. Soil moisture zone -- usually top soil; much infiltration; much organic material b. Zone of aeration (Vadose Zone) -- mostly air but some interstitial water c. Capillary fringe -- transition between unsaturated and saturated zone; top of aquifer d. Zone of saturation (Phreatic Zone) -- pores completely saturated with water; main aquifer storage zone Where does water in the ground originate? Hydrologic Cycle explains the origin of groundwater. Depicts the occurrence and movement of water in the earth-atmosphere system. Water enters the GW system at recharge areas. Water leaves GW system at discharge areas. In areas in which soluble rock (i.e., limestone) is present in the layer near the groundwater, a situation often develops that is characterized by rock layer dissolving. This is referred to as karst topography. Indiana, Kentucky, and Georgia are areas in which karst topography may develop. The area is characterized by: • a. Soluble bedrock near the surface • b. Disappearing streams that feed downward with no end on the surface • c. Sinkholes • d. Patchy, pockmarked surface topography • e. Frequent fluctuations in water table • f. Caves • g. Submerged caves Caves are formed by the dissolving nature of the rock fed by groundwater. Large cavities develop as well as solid drops of rock that precipitate from the groundwater solution. Those overhead are called stalactites (stick tight to the ceiling) and those that build up from the ground floor are termed stalagmites (with a ''g''). There are several problems, which can develop, associated with the lowering of the groundwater surface due to overuse/over pumping: • 1. Cone of depression develops • 2. Lowering of the pieziometric surface, thus wells dry up • 3. Saltwater incursion/intrusion if near an ocean Groundwater Contamination Contamination results in a decline in water quality. Common contaminants: Types Nitrates Pesticides, herbicides Organic chemicals Metals Brines Sources Sewage, Fertilizers, Feedlots Agriculture, lawn care Industrial wastes, landfills, spills/leaks of fuels Industrial processes Oil production Protecting groundwater resources • Apply agricultural chemicals properly • Build better landfills • Regulate disposal of hazardous materials • Regulate underground storage tanks (USTs) • Limit contaminant levels in drinking water supplies.