If the track addition requires no extra right of way, it's usually exempt from CEQA, NEPA, and similar requirements. Obviously, permits would still be needed for things like building or widening bridges or lengthening culverts - water quality laws, not environmental documents - but those programs usually have some time limit to act and working on, probably, an existing bridge has fewer requirements than building a new one.

Examples I've seen:

San Diego has done a lot of double-tracking by connecting sidings in areas between bridges. Under the guise of "lengthening sidings" they essentially did 2MT under Categorical Exemptions/Exclusions, then came back with the environmental big guns for the bridges. Del Mar, of course, will be different, as would some radical refiguring of the Miramar hill.

3rd Main Track on BNSF over Cajon did require a CEQA EIR, but not for the railroad itself. There were a couple of spots where they needed extra right of way for cut & fill, and they had to relocate part of a county road. That's what triggered it. For NEPA, they had to deal with some minor details regarding permits in the National Forest, but those weren't significant problems.

Bottom line: as long as UP is doing the work in their own existing r/w, there probably are few or no permits or other environmental complications. $envirogroup has no standing.

Other thoughts: I kind of agree about the siding lengths. Why go for 15K' when the trains are trending toward 20K? The sidings obviously need to be longer. At what point does a siding become 2MT?