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Cleaning groundwater with nanoparticles
As for the concern of the condition of the environment, it has become more and more pressing. Now is the time that we must think of new ways to solve these monumental problems. One of the most promising answers is nanoparticlesW. This new technology is now being researched in order to discover all of its potential. Within the environment the benefits seem promising, especially dealing with groundwater clean up.
One major problem is that over the decades different contaminates have been released into the the groundwater. This occurs through improper disposal and storages of man-made products  , causing the groundwater to become unsafe for use. This is where the new technology of nanoparticlesW comes into play. These particles can be injected deep into the groundwater, where it would have been difficult to get to.
What is groundwater?
Groundwater is any snow, rain, sleet, hail, or lake overflow, which is absorbed through the many layers of rock, soil, and sands. It then settles in an area of gravel and sand only a few feet under the ground we stand on. A pump and well system is used to safely obtain the water, so it can be used for crops, drinking and industrial uses. This is where a majority of all are drinking water comes from. 
Due to the need to industrialize and some carelessness, a high number of groundwater reserves are contamination. The contamination can be caused by anything on the surface that is absorbed into the ground that is not what. In some areas it may just be the over use of pesticides or rock salt used on road. In other areas you have contamination due to acid rain caused by factories, landfill decompositions, oil leaks and nuclear and hazardous waste leaks. These things not only make the water unsafe to use, it also make the water deadly. Some of these harmful chemicals that can make it into the groundwater are carbon tetrachlorideW, hexavalent chromiumW, Technetium-7W, nitrates, and even some radioactive ones.
-Over time can start to destroy the nervous system
Used in dyes, paint, inks, plastics, primers, "hot work" wielding, protective coatings, and tanning.  Some on the Health affects this has is;
Types of remediations
Ferritin is protein found in humans that stores iron, and releases it later on when needed. In studies they have found that by using iron it can reduce many of the contaminates and make them safer. When this nanoparticle is introduced in a solution of Hexavalent chromium, for example, it has reduced it into Trivalent chromium. This chemical can be easily filtered out of the water, and is less toxic then the Hexavalent chromiumW. This has also been shown to reduce and precipitate Technetium-7, which is a growing problem around nuclear waste sites. This however does not completely solve the problem, it just make the groundwater safer to use with less risk of the health affects.
Palladium when used in conjuction with iron has shown some amazing results. This is currently being used to breakdown Trichloroethylene from the groundwater altogether. This process works by first injecting these particles down into an underground water pocket. From there the particles can freely move through the water, because of their hydrophilic outside layer. It can then draw in the trichloroethylene molecules and break them into harmless byproducts like non-toxic ethane, that are safe in the water.  This is also better to use then some iron nanoparticle, because when some react with the Trichloroethylene it actually makes a more toxic vinyl chloride.
How it works
The most common way to get the nanoparticles down to the groundwater is by an injection well. An injection well is just a pump set up to long pipes, drilled into the earths crust.(same concept used in oil and waste companies. When the well is set up there are two different ways the nanoparticles can be pumped. One way is in a porous medium in which several layers are placed on top of each other. These layers work as a filter and filter the contaminates as they pass through. The second way is nanoparticles are directly injected in to the groundwater. In this way the nanoparticles have more mobility to more through the the groundwater of their own accord. 
In this case as briefly mentioned before, certain nanoparticles can react more dangerously then others. This is a concern especially in areas that are contaminated with more then one contaminant. If you were to added the wrong nanoparticle or one that had the wrong coating, you could make the water even more lethal to drink or use. There is also the case that there isn't that much long term test on some of these reactions. Most are done in labs, but few are test in the actual ground. In many result they even say there is limited knowledge of what effects these particles could have with human, animals, or the environment over time. It has been shown to have amazing potential but it there a price?