Updated at 8:46 a.m. EST.

House Democrats have joined in a congressional chorus of criticism aimed at U.S. EPA's plan to delay an investigation into groundwater contamination near hydraulic fracturing sites in Wyoming.

Illinois Rep. Jan Schakowsky and 19 co-signers sent a letter today to EPA Administrator Lisa Jackson, urging her to speed up the agency's probe of water contamination from oil fields around Pavillion, Wyo.

After releasing hotly contested draft conclusions in late 2011, EPA has extended the public comment period a number of times, most recently announcing that a final report would not be released until September (E&ENews PM, Jan. 10).

"The people of Pavillion -- whose water is riddled with unsafe chemicals -- deserve faster action," the lawmakers wrote.

The Democrats' letter comes a day after a similar one from Republican Sens. David Vitter of Louisiana and James Inhofe of Oklahoma, who also railed on EPA's eight-month delay, accusing the agency of prioritizing politics over science in its investigation (EnergyWire, Jan. 17).

EPA's initial results in 2011 showed that fracking fluid was present in deep groundwater but not in shallower drinking water -- still giving environmentalists the high-profile case they needed to back up claims of fracking's harmful effects. But those results were questioned when the U.S. Geological Survey tried to do further testing from EPA's two monitoring wells and found that one of them was not up to USGS's testing standards.

Industry has charged EPA with conducting sloppy research to raise public concern over fracking, a well stimulation technique that pushes chemical-laced water and sand deep underground to loosen up oil and gas. The agency is in the middle of a nationwide study into fracking's safety.

"We are very disappointed in this delay, which we believe must be the last," the Democrats wrote in today's letter. "As we await your findings, we ask that your agency continue to work collaboratively with state, tribal, and local agencies, as well as impacted residents, to protect public health and the environment."

Co-signers to the letter are Reps. Earl Blumenauer (Ore.), Matt Cartwright (Pa.), Steve Cohen (Tenn.), John Conyers (Mich.), Pete DeFazio (Ore.), Sam Farr (Calif.), Raúl Grijalva (Ariz.), Mike Honda (Calif.), Rush Holt (N.J.), Jared Huffman (Calif.), Barbara Lee (Calif.), Jim McDermott (Wash.), Jerrold Nadler (N.Y.), Jared Polis (Colo.), Mike Quigley (Ill.), Charlie Rangel (N.Y.), Carol Shea-Porter (N.H.), Niki Tsongas (Mass.) and Maxine Waters (Calif.).