What can you tell me about the environmental and safety ramifications of hydraulic fracturing?

"I know this has been a controversial question at times within the industry. With all the benefits that come from unconventional gas harvesting have also come questions about the environmental effects of hydraulic fracturing. From what I've read, I believe that Exxon takes very seriously its responsibility to ensure environmental care during the entire life cycle process - from exploration to decommissioning - in order to protect human safety, groundwater and the surrounding landscape."