UPDATE 3-US EPA looks at new rules for natgas 'fracking'
* EPA eyes new regulations for wastewater discharges
* EPA investigating use of diesel in fracking
* Republicans worried about overregulation
* EPA says greenhouse gas fracking leaks can be fixed (Adds details on study on greenhouse gases from fracking)
WASHINGTON, April 12 (Reuters) - The U.S. Environmental Protection Agency is looking at how best to address wastewater discharges produced by natural gas "fracking," and may revise regulations on wastewater from coal bed methane extraction, a top official said on Tuesday.