Federal agencies have little data on the costs and benefits of environmental reviews required by the National Environmental Policy Act, even though thousands of projects requiring the reviews are high-profile and expensive, according to a new report by the Government Accountability Office. NEPA requires reviews for any project that will have an environmental impact, such as roads, docks and drilling projects.
Some reviews are routine and need only a "categorical exclusion" or "environmental assessment;" others require costly and time-consuming Environmental Impact Statements, which often take years to complete and cost the government and private companies millions of tax dollars. "According to [Department of Energy] data, the average payment to a contractor to prepare an EIS from calendar year 2003 through calendar year 2012 was $6.6 million, with the range being a low of $60,000 and a high of $85 million," the report said.
These expensive reviews are also used in lawsuits filed against a proposed project, meaning agencies have an incentive to create a "litigation-proof" EIS, GAO noted. There are about 100 NEPA lawsuits each year, and the government prevails in most cases, according to GAO......To Read More.....
My Take - In short they're guessing, or making it up according to their own personal ideological environmental vision. It's time to repeal the NEPA and start over.