Pollution from fracking comes from faulty cement or metal "sleeves" where the pipeline gets close to ground level and encounters the water table. Such pollution obviously occurs - it must, given the number of fracking sites - but as is true in any analysis of the cost and benefit, we need to know how much pollution is occurring, at what cost to fix, and compare that to the benefits of fracking in bringing highly-efficient and cost-effective gas to the market.
Such pollution may be more likely due to simple spills involving trucks moving the fracking chemicals, and dumping those chemicals onto the surface, where they migrate into the groundwater. Again, I don't doubt that some pollution occurs with fracking, but the concept of significant groundwater pollution due to fracking is just not supported by the evidence. One New York Times article (linked below) noted, "In one study of 200 private water wells in the fracking regions of Pennsylvania, water quality was the same before and soon after drilling in all wells except one. The only surprise from that study was that many of the wells failed drinking water regulations before drilling started."
Fracking would not be occurring if it were unnecessary. Fracking is taking place because the process recovers a lot of natural gas, a very good energy supply, at very reasonable prices. The decline in natural gas prices over the past 8 years is due in significant part to the gas reaching the market due to fracking.
This is the excellent article on fracking I noted earlier that covers the costs, including pollution and accidents, and benefits of fracking:
http://www.nytimes.com/2013/03/14/opinion/global/the-facts-on-fracking.html?_r=0