The NYT is reporting on a recent study by U.S. EPA regarding complaints of water contamination in Pavillion, Wyoming: "Chemicals used to hydraulically fracture rocks in drilling for natural gas in a remote valley in central Wyoming are the likely cause of contaminated local water supplies, federal regulators said Thursday." For more, including a copy of the EPA report, see here.
A note of caution, however: U.S. EPA's record on these issues isn't good so far. See also here.
[Update: For Encana's response to the report, see here (E.g., "Several of the man-made chemicals detected in the EPA deep wells have never been detected in any of the other wells sampled. They were, however, detected in many of the quality control (blank) samples - which are ultra purified water samples commonly used in testing to ensure no contamination from field sampling procedures." Hmmm ...). (Bumped.)]