In an Oct. 1 letter to EPA Administrator Whitman, Rep. Waxman asked why technical data submitted to Congress was changed to minimize the risk that hydraulic fracturing, an oil and gas extraction technique promoted by Halliburton, would contaminate underground sources of drinking water. In a follow-up letter to Administrator Whitman, Rep. Waxman details contradictions in EPA statements on whether EPA changed its data on hydraulic fracturing in a way that benefits Halliburton.