I decided to rip out the previous owner's DIY finished basement and discovered two 2x12s, sistered, that support the floor joists, but someone removed the double 2x4s that were supporting one end of this beam. It's free floating for about 24". A 4" PVC waste line was then run right where the double 2x4s were. Can I put a steel support column right up against the waste pipe to support the beam or do I need to put the support column flush against the wall again and reroute the waste line?
Altering or damaging the structural integrity of a house is, unfortunately, an all-too-common mistake made during many DIY home remodels. The consequences of incorrectly removing a crucial framing member or cutting into a loaded support post can be serious, which is why you should always consult a structural engineer or experienced carpenter before tackling any significant remodeling projects.
In your case, it sounds as though someone thought it would be okay to remove the end stud from the basement wall that supports the main girder in your home's floor system. But it isn't okay. Keep in mind that a girder beam holds up all of the floor joists, which in turn bear the weight of the walls, the roof, and everything else inside a home. The seriousness of your problem depends on how many vertical support studs remain holding up the girder and how far the last one is from the end of the beam. You should check to see if the beam has dropped or is sagging, either of which would be an indication that the problem is very serious.
Your best solution would probably be to replace the missing support and redirect the plumbing waste line that sits flush to the wall. If moving the plumbing line is out of the question then your next best solution would be to install a new vertical support as close to the end of the beam as possible. If you go this route, you should have an engineer decide what size the new support post should be and confirm the distance that the beam can be safely cantilevered over the new post. Another option might be to install a new support post as close as possible to the plumbing line and then lag bolt a support block to the concrete wall directly below the end of the beam.
For your own piece of mind, you should probably have an experienced carpenter inspect your home's basement and look for any other home "improvements" completed by the previous owners. If this one obvious mistake was made, there's a chance that there may be other unseen issues.