A bill regulating hydraulic fracturing, or fracking, is advancing in the Illinois legislature. The state Senate unanimously passed a bill yesterday addressing the decades-old but debated technology used to reach previously inaccessible natural gas reserves deep underground. The bill comes as energy companies are pushing to prospect possible drilling sites using fracking in southern Illinois. The legislation allows the state's Department of Natural Resources to regulate fracking. It also requires energy companies to publicly disclose the chemical composition of fluids used in the process and test the integrity of the cement and steel well casings meant to protect groundwater during drilling. Environmentalists are guarded about the technology because of possible pollution. The bill now awaits consideration from the state House.