The federal government spent at least $43 million defending the Environmental Protection Agency against lawsuits filed by environmental groups, businesses and others over the past 15 years, according to a report released this week by the Government Accountability Office.

The study, done at the request of Sen. James Inhofe (R-Okla.) and Sen. David Vitter (R-La.), didn’t find any consistent pattern for when lawsuits were filed against the EPA. Some 2,500 have been filed in the past 15 years, with about 60 percent of them filed in connection with the Clean Air Act and 20 percent tied to the Clean Water Act.