From another thread:
AIM, 1-1-19 g.)
g. GPS Approach Procedures
As the production of stand−alone GPS approaches has progressed, many of the original overlay approaches have been replaced with stand−alone procedures specifically designed for use by GPS systems. The title of the remaining GPS overlay procedures has been revised on the approach chart to “or GPS” (e.g., VOR or GPS RWY 24). Therefore, all the approaches that can be used by GPS now contain “GPS” in the title (e.g., “VOR or GPS RWY 24,” “GPS RWY 24,” or “RNAV (GPS) RWY 24”). During these GPS approaches, underlying ground− based NAVAIDs are not required to be operational and associated aircraft avionics need not be installed, operational, turned on or monitored (monitoring of the underlying approach is suggested when equip-ment is available and functional).
If the approach has NDB in the title only, then the navaid must be functioning and GPS cannot be used as substitute means of navigation. 90-94 was rescinded in 2009.
If your company has Op Spec C300, then you can use GPS as a substitute means, even if the underlying navaid is inop.
There is also a current notice regarding C300 removing the restriction to have WAAS if the approach is to be used as an alternate.