I wouldn't trust any analysis that SpaceX submits itself given Musk's long history of lying, including right now on this very subject. Others have pointed out problems in the way the water is being sampled (surface water vs ground water) but I'm not an expert. It is certainly possible that no serious contamination has already occurred.

But the way it works is not that you dump stuff out of your factory and then, after getting caught, try to run some tests to show it's okay. It's almost impossible to remove contaminants out of the water after the fact so the way it works is that you go through a process with the government where you show that you are not going to dump contaminants into the ground, then they issue a permit, then you can discharge the water. Otherwise you would have people doing what Musk is doing now, which is to dump the water first and if there is any irreversible contamination say "oops, my bad".