Why must a deep-well injection take place below groundwater level?

Is it necessary for an impermeable rock layer both above and below the site of a deep-well injection? Why or why not?

How might a deep well be used in conjunction with a solid-waste incinerator?

How do locations suitable for deep-well injection compare with those that contain freshwater aquifers?

Would a deep well injection be an appropriate method to use for getting rid of waste at a nuclear power plant? Explain.

Expert Answers

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Because we don't want to mix the particulates the contaminated water is carrying with the existing groundwater, as that would contaminate the local water supply.  Deep well injection is drilled beneath the location of groundwater, into a much lower elevation, usually between two impermeable rock layers.  This is a method used to allow the Earth to filter the treated waste water before it finally does reenter the groundwater supply at some point.  The idea is to allow the Earth to naturally filter the waste water between the two impermeable layers.  A deep well injection possibly could be used in conjuction with a solid waste incinerator, if you combined the combusted remains with water, then pumped it into the well.  Locations tend to vary, depending upon the specific strata of the Earth.  Some locations lend themselves more to this type of technology due to the structure of the underlying Earth layers.  Not every location has two layers of impermeable rock, for example.  And finally, the waste produced at a nuclear power plant might not be the type of waste we would want to redistribute into the Earth.  Many of the waste products of nuclear power plants have half-lives of thousands of years, which would require them to be centrally located in a controlled environment, as they under go nuclear decay into their more stable forms.

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