What is hydraulic fracturing or "fracking?"
Natural gas
is an important fuel to help us transition from the dirty fuels of the 20th century
to the cleaner fuels of the 21st century. It is cleaner than burning
coal and we have a domestic supply of it as opposed to oil, which we have to
import. There is a technique called hydraulic fracturing, or "fracking" that enables us to produce natural gas from deep
within the earth. What happens is we send down a drill vertically, then drill horizontally and after that push through a
combination of drilling fluid made of toxic chemicals like benzene, sand, and
water that helps break up the shale and free the natural gas from the pores of
the shale. That gas is collected, pumped to the top and then it's set for commercial
or industrial use. 
What are the environmental concerns
about it?
Hydraulic
fracturing poses a number of threats to the environment. First, the chemicals
used to force the gas out of the shale rock include toxic components, including
cancer-causing chemicals like benzene. Second, there is concern that in pushing
the chemicals down or bringing the gas up that you can contaminate groundwater
which is often used for drinking water. In addition, there is lots of excess
water or produce water that is produced from hydraulic fracking
to produce shale gas. This water contains toxic chemicals, lots of salt, and
what's called naturally occurring radioactive materials. Often this water is
sent to sewage treatment plants that are not designed to remove these contaminants.
Then lastly, the production of shale gas could release fugitive methane, which
is a global warming pollutant. 
How can we address these concerns?
The
technologies exist to prevent contamination of our air, water, and atmosphere
from hydraulic fracking. Some natural gas producers
use them, but many do not. What we need to do is require companies to protect
groundwater and surface water from contamination, report on the toxic chemicals
they use in the fracking fluid, and, finally, capture
the methane that would otherwise escape in the atmosphere and cause global
warming. In fact companies that capture this methane actually use it for energy
generation and make a profit on it.