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Groundwater Contamination.ppt and solution of its effects

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The document discusses various sources and mechanisms of groundwater contamination. It describes how contaminants from sources like storage tanks, septic systems, hazardous waste sites, landfills, chemicals and road salts can seep into and migrate through the ground to contaminate groundwater supplies. It outlines key contaminant types and explains processes of advection, dispersion and retardation that transport contaminants through aquifers. Charts provide additional details on specific contaminants and groundwater contamination fundamentals.

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Ground Water Contamination
Groundwater contamination occurs when man-made products such as gasoline, oil, road salts and chemicals get into the groundwater and cause it to become unsafe and unfit for human use. Materials from the land's surface can move through the soil and end up in the groundwater.
Drinking contaminated groundwater can have serious health effects. Diseases such as hepatitis and dysentery may be caused by contamination from septic tank waste. Poisoning may be caused by toxins that have leached into well water supplies. Wildlife can also be harmed by contaminated groundwater. Other long term effects such as certain types of cancer may also result from exposure to polluted water.
Most contaminants are introduced to the subsurface by percolation through soils. The interactions between soil and a contaminant are important for assessing the fate and transport of the contaminant in the groundwater flow system. Contaminants that are highly soluble, such as salts (e.g. sodium chloride, NaCl) move readily from surface soils to saturated materials below the water table. This often occurs during and after rainfall events.
Those contaminants that are not highly soluble may have considerably longer residence times in the soil zone. Some contaminants adsorb readily onto soil particles and slowly dissolve during precipitation events, resulting in dissolve fraction concentrations of contaminants migrating to groundwater. This mode of transport is common for trichloroethylene.
Liquids spilled onto surface soils can migrate downward or can evaporate, which limits their potential for reaching the water table. Once below the water table, contaminants are also subject to dispersion (mechanical mixing with uncontaminated water) and diffusion (dilution by concentration gradients).
 Storage Tanks. May contain gasoline, oil, chemicals, or other types of liquids and they can either be above or below ground. There are estimated to be over 10 million storage tanks buried in the United States and over time the tanks can corrode, crack and develop leaks. If the contaminants leak out and get into the groundwater, serious contamination can occur.  Septic Systems. Onsite wastewater disposal systems used by homes, offices or other buildings that are not connected to a city sewer system. Septic systems are designed to slowly drain away human waste underground at a slow, harmless rate. An improperly designed, located, constructed, or maintained septic system can leak bacteria, viruses, household chemicals, and other contaminants into the groundwater causing serious problems.
 Uncontrolled Hazardous Waste. In the U.S. today, there are thought to be over 20,000 known abandoned and uncontrolled hazardous waste sites and the numbers grow every year. Hazardous waste sites can lead to groundwater contamination if there are barrels or other containers laying around that are full of hazardous materials. If there is a leak, these contaminants can eventually make their way down through the soil and into the groundwater.  Landfills. Landfills are the places that our garbage is taken to be buried. Landfills are supposed to have a protective bottom layer to prevent contaminants from getting into the water. However, if there is no layer or it is cracked, contaminants from the landfill (car battery acid, paint, household cleaners, etc.) can make their way down into the groundwater.
 Chemicals and Road Salts. The widespread use of chemicals and road salts is another source of potential groundwater contamination. Chemicals include products used on lawns and farm fields to kill weeds and insects and to fertilize plants, and other products used in homes and businesses. When it rains, these chemicals can seep into the ground and eventually into the water. Road salts are used in the wintertime to put melt ice on roads to keep cars from sliding around. When the ice melts, the salt gets washed off the roads and eventually ends up in the water.  Atmospheric Contaminants. Since groundwater is part of the hydrologic cycle, contaminants in other parts of the cycle, such as the atmosphere or bodies of surface water, can eventually be transferred into our groundwater supplies.
 Arsenic & Fluoride  Pathogens  Nitrate  Organic Compounds  Metals  Pharmaceuticals  Others
Generally three processes occur: i) Advection ii) Dispersion and iii) Retardation
 Contaminants that are dissolved in water are solutes and the water is the solvent and the combination is the solution. As the water flows, the contaminants are transported with the water a process known as advection.  As the water flows around the soil particles, it is mixed, a process known as mechanical dispersion. The result is dilution or reduction in the contaminant concentration.  A one time introduction of pollutants is termed a slug and opposed to a continuous source. If the pollutant is introduced at a discrete location, it is known as a point source as opposed to a non-point source
 The distribution and extent of contaminants migrating in the subsurface is known as the plume.  Contaminates, particularly the ionic and molecular constituents, will move from areas of high concentration to areas of low concentration and this process is termed diffusion.  In general, advective transport and associated mechanical dispersion dominate the contaminant transport in formations of medium to high hydraulic conductivity. In formations of low hydraulic conductivity, including clay liners, diffusive transport is frequently the controlling mechanism.

1. A pollutant has entered into groundwater and is traveling towards a well. When will the pollutant reach the well? The aquifer is a sandstone with a hydraulic conductivity of 5m/d and an effective porosity of 15%. 2. A chlorine spill has infiltrated through a well that crosses a confined level and reaches the piezometric level of a 20m thick sand and gravel aquifer immediately below the first one, with a hydraulic conductivity of 80m/d and effective porosity of 205. The piezometric level in this well is located at 400m, whereas the piezometric level in a well located 1km downgradient from the first one is 398. What is the groundwater and pollutant velocity? How long will it take for the pollutant to reach the second well?
Two ponds of water are 1000 ft. apart with the water surface in one pond being 150 ft. higher than in the other. Both ponds have a square shape, measuring 200 ft. on a side. A 2-ft thick sandy layer connects the ponds and the sand has a hydraulic conductivity (K) = 5 x 10-2 cm/sec with a porosity of 25%. • How long does it take for water to travel from the upper pond to the lower one? • How much water seeps from the upper pond into the lower one on a yearly basis? Assuming that K for the soil = 1 x 10-3 cm/sec and the gradient of the water table is 1%, how long does it take for water to travel 50 and 100 ft. through this soil? Assume a porosity of 15%

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Groundwater Contamination.ppt and solution of its effects

  • 2. Groundwater contamination occurs when man-made products such as gasoline, oil, road salts and chemicals get into the groundwater and cause it to become unsafe and unfit for human use. Materials from the land's surface can move through the soil and end up in the groundwater.
  • 3. Drinking contaminated groundwater can have serious health effects. Diseases such as hepatitis and dysentery may be caused by contamination from septic tank waste. Poisoning may be caused by toxins that have leached into well water supplies. Wildlife can also be harmed by contaminated groundwater. Other long term effects such as certain types of cancer may also result from exposure to polluted water.
  • 4. Most contaminants are introduced to the subsurface by percolation through soils. The interactions between soil and a contaminant are important for assessing the fate and transport of the contaminant in the groundwater flow system. Contaminants that are highly soluble, such as salts (e.g. sodium chloride, NaCl) move readily from surface soils to saturated materials below the water table. This often occurs during and after rainfall events.
  • 5. Those contaminants that are not highly soluble may have considerably longer residence times in the soil zone. Some contaminants adsorb readily onto soil particles and slowly dissolve during precipitation events, resulting in dissolve fraction concentrations of contaminants migrating to groundwater. This mode of transport is common for trichloroethylene.
  • 6. Liquids spilled onto surface soils can migrate downward or can evaporate, which limits their potential for reaching the water table. Once below the water table, contaminants are also subject to dispersion (mechanical mixing with uncontaminated water) and diffusion (dilution by concentration gradients).
  • 7.  Storage Tanks. May contain gasoline, oil, chemicals, or other types of liquids and they can either be above or below ground. There are estimated to be over 10 million storage tanks buried in the United States and over time the tanks can corrode, crack and develop leaks. If the contaminants leak out and get into the groundwater, serious contamination can occur.  Septic Systems. Onsite wastewater disposal systems used by homes, offices or other buildings that are not connected to a city sewer system. Septic systems are designed to slowly drain away human waste underground at a slow, harmless rate. An improperly designed, located, constructed, or maintained septic system can leak bacteria, viruses, household chemicals, and other contaminants into the groundwater causing serious problems.
  • 8.  Uncontrolled Hazardous Waste. In the U.S. today, there are thought to be over 20,000 known abandoned and uncontrolled hazardous waste sites and the numbers grow every year. Hazardous waste sites can lead to groundwater contamination if there are barrels or other containers laying around that are full of hazardous materials. If there is a leak, these contaminants can eventually make their way down through the soil and into the groundwater.  Landfills. Landfills are the places that our garbage is taken to be buried. Landfills are supposed to have a protective bottom layer to prevent contaminants from getting into the water. However, if there is no layer or it is cracked, contaminants from the landfill (car battery acid, paint, household cleaners, etc.) can make their way down into the groundwater.
  • 9.  Chemicals and Road Salts. The widespread use of chemicals and road salts is another source of potential groundwater contamination. Chemicals include products used on lawns and farm fields to kill weeds and insects and to fertilize plants, and other products used in homes and businesses. When it rains, these chemicals can seep into the ground and eventually into the water. Road salts are used in the wintertime to put melt ice on roads to keep cars from sliding around. When the ice melts, the salt gets washed off the roads and eventually ends up in the water.  Atmospheric Contaminants. Since groundwater is part of the hydrologic cycle, contaminants in other parts of the cycle, such as the atmosphere or bodies of surface water, can eventually be transferred into our groundwater supplies.
  • 10.  Arsenic & Fluoride  Pathogens  Nitrate  Organic Compounds  Metals  Pharmaceuticals  Others
  • 11. Generally three processes occur: i) Advection ii) Dispersion and iii) Retardation
  • 12.  Contaminants that are dissolved in water are solutes and the water is the solvent and the combination is the solution. As the water flows, the contaminants are transported with the water a process known as advection.  As the water flows around the soil particles, it is mixed, a process known as mechanical dispersion. The result is dilution or reduction in the contaminant concentration.  A one time introduction of pollutants is termed a slug and opposed to a continuous source. If the pollutant is introduced at a discrete location, it is known as a point source as opposed to a non-point source
  • 13.  The distribution and extent of contaminants migrating in the subsurface is known as the plume.  Contaminates, particularly the ionic and molecular constituents, will move from areas of high concentration to areas of low concentration and this process is termed diffusion.  In general, advective transport and associated mechanical dispersion dominate the contaminant transport in formations of medium to high hydraulic conductivity. In formations of low hydraulic conductivity, including clay liners, diffusive transport is frequently the controlling mechanism.
  • 15. 1. A pollutant has entered into groundwater and is traveling towards a well. When will the pollutant reach the well? The aquifer is a sandstone with a hydraulic conductivity of 5m/d and an effective porosity of 15%. 2. A chlorine spill has infiltrated through a well that crosses a confined level and reaches the piezometric level of a 20m thick sand and gravel aquifer immediately below the first one, with a hydraulic conductivity of 80m/d and effective porosity of 205. The piezometric level in this well is located at 400m, whereas the piezometric level in a well located 1km downgradient from the first one is 398. What is the groundwater and pollutant velocity? How long will it take for the pollutant to reach the second well?
  • 16. Two ponds of water are 1000 ft. apart with the water surface in one pond being 150 ft. higher than in the other. Both ponds have a square shape, measuring 200 ft. on a side. A 2-ft thick sandy layer connects the ponds and the sand has a hydraulic conductivity (K) = 5 x 10-2 cm/sec with a porosity of 25%. • How long does it take for water to travel from the upper pond to the lower one? • How much water seeps from the upper pond into the lower one on a yearly basis? Assuming that K for the soil = 1 x 10-3 cm/sec and the gradient of the water table is 1%, how long does it take for water to travel 50 and 100 ft. through this soil? Assume a porosity of 15%